"uuid","repository link","title","author","contributor","publication year","abstract","subject topic","language","publication type","publisher","isbn","issn","patent","patent status","bibliographic note","access restriction","embargo date","faculty","department","research group","programme","project","coordinates"
"uuid:6e75cf19-6c11-4c37-b1f9-ebcd240c9451","http://resolver.tudelft.nl/uuid:6e75cf19-6c11-4c37-b1f9-ebcd240c9451","Ducted wind turbines in yawed flow: a numerical study","Dighe, V.V. (TU Delft Wind Energy); Suri, Dhruv (Manipal Academy of Higher Education (MAHE)); Avallone, F. (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2021","Ducted wind turbines (DWTs) can be used for energy harvesting in urban areas where non-uniform flows are caused by the presence of buildings or other surface discontinuities. For this reason, the aerodynamic performance of DWTs in yawed-flow conditions must be characterized depending upon their geometric parameters and operating conditions. A numerical study to investigate the characteristics of flow around two DWT configurations using a simplified duct-actuator disc (AD) model is carried out. The analysis shows that the aerodynamic performance of a DWT in yawed flow is dependent on the mutual interactions between the duct and the AD, an interaction that changes with duct geometry. For the two configurations studied, the highly cambered variant of duct configuration returns a gain in performance by approximately 11 % up to a specific yaw angle (α= 17.5∘) when compared to the non-yawed case; thereafter any further increase in yaw angle results in a performance drop. In contrast, performance of less cambered variant duct configuration drops for α>0∘. The gain in the aerodynamic performance is attributed to the additional camber of the duct that acts as a flow-conditioning device and delays duct wall flow separation inside of the duct for a broad range of yaw angles.","","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:ccd0d1f5-99f9-40eb-b283-da2794aef402","http://resolver.tudelft.nl/uuid:ccd0d1f5-99f9-40eb-b283-da2794aef402","Performance Characteristics of a Micro Wind Turbine Integrated on a Noise Barrier","Chrysochoidis-Antsos, N. (TU Delft Energy Technology); van Bussel, G.J.W. (TU Delft Wind Energy); Bozelie, Jan (Qirion Alliander); Mertens, Sander M. (De Haagse Hogeschool); van Wijk, A.J.M. (TU Delft Energy Technology)","","2021","Micro wind turbines can be structurally integrated on top of the solid base of noise barriers near highways. A number of performance factors were assessed with holistic experiments in wind tunnel and in the field. The wind turbines underperformed when exposed in yawed flow conditions. The theoretical cosθ theories for yaw misalignment did not always predict power correctly. Inverter losses turned out to be crucial especially in standby mode. Combination of standby losses with yawed flow losses and low wind speed regime may even result in a net power consuming turbine. The micro wind turbine control system for maintaining optimal power production underperformed in the field when comparing tip speed ratios and performance coefficients with the values recorded in the wind tunnel. The turbine was idling between 20%–30% of time as it was assessed for sites with annual average wind speeds of three to five meters per second without any power production. Finally, the field test analysis showed that inadequate yaw response could potentially lead to 18% of the losses, the inverter related losses to 8%, and control related losses to 33%. The totalized loss led to a 48% efficiency drop when compared with the ideal power production measured before the inverter. Micro wind turbine’s performance has room for optimization for application in turbulent wind conditions on top of noise barriers","micro wind turbines; performance; experiment; field test","en","journal article","","","","","","","","","","","Energy Technology","","",""
"uuid:21430682-ec9c-4852-bbc7-a0245e90be41","http://resolver.tudelft.nl/uuid:21430682-ec9c-4852-bbc7-a0245e90be41","Wind resource characteristics and energy yield for micro wind turbines integrated on noise barriers: An experimental study","Chrysochoidis-Antsos, N. (TU Delft Energy Technology); Amoros, Andrea Vilarasau (Student TU Delft); van Bussel, G.J.W. (TU Delft Wind Energy); Mertens, Sander M. (The Hague University of Applied Sciences); van Wijk, A.J.M. (TU Delft Energy Technology)","","2020","This paper assesses wind resource characteristics and energy yield for micro wind turbines integrated on noise barriers. An experimental set-up with sonic anemometers placed on top of the barrier in reference positions is realized. The effect on wind speed magnitude, inflow angle and turbulence intensity is analysed. The annual energy yield of a micro wind turbine is estimated and compared using data from a micro-wind turbine wind tunnel experiment and field data. Electrical energy costs are discussed as well as structural integration cost reduction and the potential energy yield could decrease costs. It was found that instantaneous wind direction towards the barrier and the height of observation play an influential role for the results. Wind speed increases in perpendicular flows while decreases in parallel flow, by +35% down to −20% from the reference. The azimuth of the noise barrier expressed in wind field rotation angles was found to be influential resulted in 50%–130% changes with respect to annual energy yield. A micro wind turbine (0.375 kW) would produce between 100 and 600 kWh annually. Finally, cost analysis with cost reductions due to integration and the energy yield changes due to the barrier, show a LCOE reduction at 60%–90% of the reference value.","Field experiment; LCOE; Micro wind turbines; Noise barrier; Urban energy","en","journal article","","","","","","","","","","","Energy Technology","","",""
"uuid:588b99a3-e219-4567-993f-510abf763fa8","http://resolver.tudelft.nl/uuid:588b99a3-e219-4567-993f-510abf763fa8","Effects of yawed inflow on the aerodynamic and aeroacoustic performance of ducted wind turbines","Dighe, V.V. (TU Delft Wind Energy); Avallone, F. (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2020","Ducted Wind Turbines (DWTs) can be used for energy harvesting in urban areas where non-uniform inflows might be the cause of aerodynamic and acoustic performance degradation. For this reason, an aerodynamic and aeroacoustic analysis of DWTs in yawed inflow condition is performed for two duct geometries: a baseline commercial DWT model, DonQi®, and one with a duct having a higher cross-section camber with respect to the baseline, named DonQi D5. The latter has been obtained from a previous optimization study. A numerical investigation using Lattice-Boltzmann Very-Large-Eddy Simulations is presented. Data confirm that the aerodynamic performance improvement, i.e. increase of the power coefficient, is proportional to the increase of the duct thrust force coefficient. It is found that, placing the DWT at a yaw angle of 7.5°, the aerodynamic performances of the DonQi D5 DWT model are less affected by the yaw angle. On the other hand, this configuration shows an increase of broadband noise with respect to the baseline DonQi® one, both in non-yawed and yawed inflow conditions. This is associated to turbulent boundary layer trailing edge noise due to the turbulent flow structures developing along the surface of the duct.","Aeroacoustics; Aerodynamics; CFD; Ducted wind turbine","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:c31ce4b2-c55e-46bf-a2d6-c3ec1baae233","http://resolver.tudelft.nl/uuid:c31ce4b2-c55e-46bf-a2d6-c3ec1baae233","Fatigue design load calculations of the offshore NREL 5 MW benchmark turbine using quadrature rule techniques","van den Bos, L.M.M. (TU Delft Wind Energy; Centrum Wiskunde & Informatica (CWI)); Bierbooms, W.A.A.M. (TU Delft Wind Energy); Alexandre, Armando (Det Norske Veritas); Sanderse, Benjamin (Centrum Wiskunde & Informatica (CWI)); van Bussel, G.J.W. (TU Delft Wind Energy)","","2020","A novel approach is proposed to reduce, compared with the conventional binning approach, the large number of aeroelastic code evaluations that are necessary to obtain equivalent loads acting on wind turbines. These loads describe the effect of long-term environmental variability on the fatigue loads of a horizontal-axis wind turbine. In particular, Design Load Case 1.2, as standardized by IEC, is considered. The approach is based on numerical integration techniques and, more specifically, quadrature rules. The quadrature rule used in this work is a recently proposed “implicit” quadrature rule, which has the main advantage that it can be constructed directly using measurements of the environment. It is demonstrated that the proposed approach yields accurate estimations of the equivalent loads using a significantly reduced number of aeroelastic model evaluations (compared with binning). Moreover, the error introduced by the seeds (introduced by averaging over random wind fields and sea states) is incorporated in the quadrature framework, yielding an even further reduction in the number of aeroelastic code evaluations. The reduction in computational time is demonstrated by assessing the fatigue loads on the NREL 5 MW reference offshore wind turbine in conjunction with measurement data obtained at the North Sea, for both a simplified and a full load case.","aeroelasticity; binning; fatigue loads; quadrature rules; seed balancing","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:7e2428a3-69ea-478d-ba63-48daf87a4095","http://resolver.tudelft.nl/uuid:7e2428a3-69ea-478d-ba63-48daf87a4095","An immersed boundary method based on domain decomposition","Krishnan, Navaneetha (TU Delft Wind Energy); Viré, A.C. (TU Delft Wind Energy); Schmehl, R. (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2020","A novel immersed boundary method based on a domain decomposition approach is proposed in the context of a finite element discretisation method. It is applicable to incompressible flows past rigid, deforming, or moving bodies. In this method, unlike most immersed boundary methods, strong boundary conditions are imposed in the regions of the computational domain that are occupied by the structure. In order to achieve this, the proposed formulation decomposes the computational domain by splitting the finite element test functions into solid and fluid parts. In the continuous Galerkin formulation, this produces a smeared representation of the fluid-structure interface. The absence of an immersed boundary forcing term implies that the method itself has no influence on the CFL stability criterion. Furthermore, the stiffness matrix in the momentum equation is sparser than compared with other forcing immersed boundary methods, and symmetry and positive-definiteness of the Laplacian operator in the pressure equation is preserved. As shown in this paper, stability and accurate imposition of boundary conditions make the method promising for high Reynolds number flows. The method is applied to the simulations of two-dimensional laminar flow over stationary and moving cylinders, as well as a moderately high Reynolds number flow past an aerofoil. Good results are obtained when compared with those from previous experimental and numerical studies.","Finite element method; Fluid-structure interactions; Immersed boundary method","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2020-10-01","","","Wind Energy","","",""
"uuid:45252b15-b9f4-4209-a0fc-70225171b136","http://resolver.tudelft.nl/uuid:45252b15-b9f4-4209-a0fc-70225171b136","How does yawed inflow affect the performance of ducted wind turbines?","Dighe, V.V. (TU Delft Wind Energy); Suri, Dhruv (Manipal Academy of Higher Education (MAHE)); Avallone, F. (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2020","Ducted Wind Turbines (DWTs) are used for energy harvesting in urban areas where the flow is non-uniform in comparison to the free-field because of the presence of buildings or other surface discontinuities. For this reason, the aerodynamic performance and far-field noise of DWTs in yawed inflow conditions must be characterized. Both the aerodynamic and the acoustic fields are dependent on the geometry of the duct. In this study, the effect of the duct geometry is analysed with high fidelity numerical simulations carried out with the lattice-Boltzmann method.","","en","conference paper","American Institute of Aeronautics and Astronautics Inc. (AIAA)","","","","","","","","","","Wind Energy","","",""
"uuid:30f0cb41-cdc9-4c09-a57d-7c1589b9a4e8","http://resolver.tudelft.nl/uuid:30f0cb41-cdc9-4c09-a57d-7c1589b9a4e8","A comparative analysis of Lagrange multiplier and penalty approaches for modelling fluid-structure interaction","Brandsen, J.D. (TU Delft Wind Energy); Viré, A.C. (TU Delft Wind Energy); Turteltaub, S.R. (TU Delft Aerospace Structures & Computational Mechanics); van Bussel, G.J.W. (TU Delft Wind Energy)","","2020","Purpose: When simulating fluid-structure interaction (FSI), it is often essential that the no-slip condition is accurately enforced at the wetted boundary of the structure. This paper aims to evaluate the relative strengths and limitations of the penalty and Lagrange multiplier methods, within the context of modelling FSI, through a comparative analysis. Design/methodology/approach: In the immersed boundary method, the no-slip condition is typically imposed by augmenting the governing equations of the fluid with an artificial body force. The relative accuracy and computational time of the penalty and Lagrange multiplier formulations of this body force are evaluated by using each to solve three test problems, namely, flow through a channel, the harmonic motion of a cylinder through a stationary fluid and the vortex-induced vibration (VIV) of a cylinder. Findings: The Lagrange multiplier formulation provided an accurate solution, especially when enforcing the no-slip condition, and was robust as it did not require “tuning” of problem specific parameters. However, these benefits came at a higher computational cost relative to the penalty formulation. The penalty formulation achieved similar levels of accuracy to the Lagrange multiplier formulation, but only if the appropriate penalty factor was selected, which was difficult to determine a priori. Originality/value: Both the Lagrange multiplier and penalty formulations of the immersed boundary method are prominent in the literature. A systematic quantitative comparison of these two methods is presented within the same computational environment. A novel application of the Lagrange multiplier method to the modelling of VIV is also provided.","Finite element; Fluid-structure interaction; Immersed boundary; Lagrange multiplier; Penalty","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2021-03-05","","","Wind Energy","","",""
"uuid:39e01955-8bec-429e-9c4a-d717a113e773","http://resolver.tudelft.nl/uuid:39e01955-8bec-429e-9c4a-d717a113e773","Generating nested quadrature rules with positive weights based on arbitrary sample sets","van den Bos, L.M.M. (TU Delft Wind Energy; Centrum Wiskunde & Informatica (CWI)); Sanderse, Benjamin (Centrum Wiskunde & Informatica (CWI)); Bierbooms, W.A.A.M. (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2020","For the purpose of uncertainty propagation a new quadrature rule technique is proposed that has positive weights, has high degree, and is constructed using only samples that describe the probability distribution of the uncertain parameters. Moreover, nodes can be added to the quadrature rule, resulting in a sequence of nested rules. The rule is constructed by iterating over the samples of the distribution and exploiting the null space of the Vandermonde system that describes the nodes and weights, in order to select which samples will be used as nodes in the quadrature rule. The main novelty of the quadrature rule is that it can be constructed using any number of dimensions, using any basis, in any space, and using any distribution. It is demonstrated both theoretically and numerically that the rule always has positive weights and therefore has high convergence rates for sufficiently smooth functions. The convergence properties are demonstrated by approximating the integral of the Genz test functions. The applicability of the quadrature rule to complex uncertainty propagation cases is demonstrated by determining the statistics of the flow over an airfoil governed by the Euler equations, including the case of dependent uncertain input parameters. The new quadrature rule significantly outperforms classical sparse grid methods.","Numerical integration; Quadrature formulas; Uncertainty propagation","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:ac8a0a1d-6f41-43e3-a0dd-a10dedf545a8","http://resolver.tudelft.nl/uuid:ac8a0a1d-6f41-43e3-a0dd-a10dedf545a8","Immersed boundary methods and their applicability in wind energy","Krishnan, Navaneetha (TU Delft Wind Energy); Viré, A.C. (TU Delft Wind Energy); Schmehl, R. (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2020","Airborne wind energy systems often use kites made of thin membranes to save material costs and increase mobility. However, this design choice increases the complexity of the aeroelastic behaviour of the system and demands high-fidelity tools. On the aerodynamic side of the multi-physics problem, it is quite challenging to create a high quality body conforming grid due to the complexity of the geometry and the degree of deformation it undergoes. Immersed boundary methods (IBMs) are quite popular in fluid-structure interaction (FSI) problems that involve arbitrarily deforming bodies with complex geometries and are more tolerant to deformations compared to mesh deforming methods like ALE. This paper will look at some of the popular IBMs, outline criteria to evaluate their applicability, and discuss the limitations they have in fulfilling those in problems involving thin membranes.","","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:1b0a6714-bf62-4d51-9980-2f1d31c8a62d","http://resolver.tudelft.nl/uuid:1b0a6714-bf62-4d51-9980-2f1d31c8a62d","Bayesian model calibration with interpolating polynomials based on adaptively weighted leja nodes","van den Bos, L.M.M. (TU Delft Wind Energy; Centrum Wiskunde & Informatica (CWI)); Sanderse, Benjamin (Centrum Wiskunde & Informatica (CWI)); Bierbooms, W.A.A.M. (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2020","An efficient algorithm is proposed for Bayesian model calibration, which is commonly used to estimate the model parameters of non-linear, computationally expensive models using measurement data. The approach is based on Bayesian statistics: using a prior distribution and a likelihood, the posterior distribution is obtained through application of Bayes' law. Our novel algorithm to accurately determine this posterior requires significantly fewer discrete model evaluations than traditional Monte Carlo methods. The key idea is to replace the expensive model by an interpolating surrogate model and to construct the interpolating nodal set maximizing the accuracy of the posterior. To determine such a nodal set an extension to weighted Leja nodes is introduced, based on a new weighting function. We prove that the convergence of the posterior has the same rate as the convergence of the model. If the convergence of the posterior is measured in the Kullback-Leibler divergence, the rate doubles. The algorithm and its theoretical properties are verified in three different test cases: analytical cases that confirm the correctness of the theoretical findings, Burgers' equation to show its applicability in implicit problems, and finally the calibration of the closure parameters of a turbulence model to show the effectiveness for computationally expensive problems.","Bayesian model calibration; Interpolation; Leja nodes; Surrogate modeling; interpolation; surrogate modeling","en","journal article","","","","","","accepted author manuscript","","","","","Wind Energy","","",""
"uuid:4ac3a112-a678-4a10-b05b-d35f2dabce21","http://resolver.tudelft.nl/uuid:4ac3a112-a678-4a10-b05b-d35f2dabce21","A modified free wake vortex ring method for horizontal-axiswind turbines","Dong, J. (TU Delft Wind Energy); Viré, A.C. (TU Delft Wind Energy); Ferreira, Carlos (TU Delft Wind Energy); Li, Zhangrui (Rijksuniversiteit Groningen); van Bussel, G.J.W. (TU Delft Wind Energy)","","2019","A modified free-wake vortex ring model is proposed to compute the dynamics of a floating horizontal-axis wind turbine, which is divided into two parts. The near wake model uses a blade bound vortex model and trailed vortex model, which is developed based on vortex filament method with straight lifting lines assumption. By contrast, the far wake model is based on the vortex ring method. The proposed model is a good compromise between accuracy and computational cost, for example when compared with more complex vortex methods. The present model is used to assess the influence of floating platform motions on the performance of a horizontal-axis wind turbine rotor. The results are validated on the 5 MW NREL rotor and compared with other aerodynamic models for the same rotor subjected to different platform motions. The results show that the proposed method is reliable. In addition, the proposed method is less time consuming and has similar accuracy when comparing with more advanced vortex based methods.","Aerodynamics; Floating wind energy; Free wake vortex method; Horizontal-axis wind turbine","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:4bdfef19-d0c2-48d9-bf6a-402d3833ce35","http://resolver.tudelft.nl/uuid:4bdfef19-d0c2-48d9-bf6a-402d3833ce35","Multi-element ducts for ducted wind turbines: A numerical study","Dighe, V.V. (TU Delft Wind Energy); Avallone, F. (TU Delft Wind Energy); Igra, Ozer (Ben-Gurion University of the Negev); van Bussel, G.J.W. (TU Delft Wind Energy)","","2019","Multi-element ducts are used to improve the aerodynamic performance of ducted wind turbines (DWTs). Steady-state, two-dimensional computational fluid dynamics (CFD) simulations are performed for a multi-element duct geometry consisting of a duct and a flap; the goal is to evaluate the effects on the aerodynamic performance of the radial gap length and the deflection angle of the flap. Solutions from inviscid and viscous flow calculations are compared. It is found that increasing the radial gap length results in an augmentation of the total thrust generated by the DWT, whereas a larger deflection angle has an opposite effect. Reasonable to good agreement is seen between the inviscid and viscous flow calculations, except for multi-element duct configurations characterized by large flap deflection angles. The viscous effects become stronger at large flap deflection angles, and the inviscid calculations are incapable of taking this phenomenon into account.","","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:8487075a-5070-4a0d-b655-8ead0951eb07","http://resolver.tudelft.nl/uuid:8487075a-5070-4a0d-b655-8ead0951eb07","Airfoil optimisation for vertical-axis wind turbines with variable pitch","De Tavernier, D. (TU Delft Wind Energy); Ferreira, Carlos (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2019","To advance the design of a multimegawatt vertical-axis wind turbine (VAWT), application-specific airfoils need to be developed. In this research, airfoils are tailored for a VAWT with variable pitch. A genetic algorithm is used to optimise the airfoil shape considering a balance between the aerodynamic and structural performance of airfoils. At rotor scale, the aerodynamic objective aims to create the required optimal loading while minimising losses. The structural objective focusses on maximising the bending stiffness. Three airfoils from the Pareto front are selected and analysed using the actuator cylinder model and a prescribed-wake vortex code. The optimal pitch schedule is determined, and the loadings and power performance are studied for different tip-speed ratios and solidities. The comparison of the optimised airfoils with similar airfoils from the first generation shows a significant improvement in performance, and this proves the necessity to properly select the airfoil shape.","airfoil optimisation; optimal loading; variable pitch; vertical-axis wind turbine (VAWT)","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:177d0c46-05ef-4905-8868-8031ec7aeb95","http://resolver.tudelft.nl/uuid:177d0c46-05ef-4905-8868-8031ec7aeb95","A Modified Free Wake Vortex Ring Method for Horizontal-Axis Wind Turbines","Dong, J. (TU Delft Wind Energy); Viré, A.C. (TU Delft Wind Energy); Ferreira, Carlos (TU Delft Wind Energy); Li, Zhangrui (Shanghai Electric Group Company); van Bussel, G.J.W. (TU Delft Wind Energy)","","2019","A modified free-wake vortex ring model is proposed to compute the dynamics of a floating horizontal-axis wind turbine, which is divided into two parts. The near wake model uses a blade bound vortex model and trailed vortex model, which is developed based on vortex filament method with straight lifting lines assumption. By contrast, the far wake model is based on the vortex ring method. The proposed model is a good compromise between accuracy and computational cost, for example when compared with more complex vortex methods. The present model is used to assess the influence of floating platform motions on the performance of a horizontal-axis wind turbine rotor. The results are validated on the 5 MW NREL rotor and compared with other aerodynamic models for the same rotor subjected to different platform motions. The results show that the proposed method is reliable. In addition, the proposed method is less time consuming and has similar accuracy when comparing with more advanced vortex based methods.","free wake vortex method; horizontal-axis wind turbine; floating wind energy; aerodynamics","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:441e1c01-5762-49e6-b9bf-05c1985fe545","http://resolver.tudelft.nl/uuid:441e1c01-5762-49e6-b9bf-05c1985fe545","Characterization of aerodynamic performance of ducted wind turbines: A numerical study","Dighe, V.V. (TU Delft Wind Energy); De Oliveira Andrade, G.L. (TU Delft Wind Energy); Avallone, F. (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2019","The complex aerodynamic interactions between the rotor and the duct has to be accounted for the design of ducted wind turbines (DWTs). A numerical study to investigate the characteristics of flow around the DWT using a simplified duct–actuator disc (AD) model is carried out. Inviscid and viscous flow calculations are performed to understand the effects of the duct shape and variable AD loadings on the aerodynamic performance coefficients. The analysis shows that the overall aerodynamic performance of the DWT can be increased by increasing the duct cross-sectional camber. Finally, flow fields using viscous calculations are examined to interpret the effects of inner duct wall flow separation on the overall DWT performance.","CFD; ducted wind turbines; optimization; panel method; RANS","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:1e2d747c-63d4-470d-b748-0c826de847f1","http://resolver.tudelft.nl/uuid:1e2d747c-63d4-470d-b748-0c826de847f1","Experimental investigation on the effect of the duct geometrical parameters on the performance of a ducted wind turbine","Tang, J. (TU Delft Wind Energy); Avallone, F. (TU Delft Wind Energy); Bontempo, R. (Università degli Studi di Napoli Federico II); van Bussel, G.J.W. (TU Delft Wind Energy); Manna, M. (Università degli Studi di Napoli Federico II)","","2018","This paper reports an experimental investigation on the effect of the duct geometry on the aerodynamic performance of an aerofoil shaped ducted wind turbine (DWT). The tested two-dimensional model is composed of an aerofoil equipped with pressure taps and a uniform porous screen. The experimental setup is based on the assumption that the duct flow is axisymmetric and the rotor can be simulated as an actuator disc. Firstly, different tip clearances between the screen and the aerofoil are tested to point out the influence of this parameter on the DWT performance in terms of aerofoil pressure distribution, aerofoil lift and flow field features at the duct exit area. Then, the combined effect of tip clearance, of the angle of attack and of the screen position along the aerofoil chord is evaluated through a Design of Experiments (DoE) based approach. The analysis shows that, among the analysed range of design factor variation, increasing angle of attack and the tip clearance leads to a beneficial effect on the lift and back-pressure coefficients, while they show a poor dependence upon the screen axial position. Finally, the configuration characterized by the maximum value of all three main factors (15 degree of angle of attack, 5% of tip clearance and 30% backward to the nozzle plane), has the best values of lift coefficient and back-pressure coefficient.","","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:e772f5f7-3f08-4800-8908-dd9045c689d4","http://resolver.tudelft.nl/uuid:e772f5f7-3f08-4800-8908-dd9045c689d4","Efficient ultimate load estimation for offshore wind turbines using interpolating surrogate models","van den Bos, L.M.M. (TU Delft Wind Energy; Centrum Wiskunde & Informatica (CWI)); Sanderse, B. (Centrum Wiskunde & Informatica (CWI)); Blonk, L. (DNV GL); Bierbooms, W.A.A.M. (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2018","During the design phase of an offshore wind turbine, it is required to assess the impact of loads on the turbine life time. Due to the varying environmental conditions, the effect of various uncertain parameters has to be studied to provide meaningful conclusions. Incorporating such uncertain parameters in this regard is often done by applying binning, where the probability density function under consideration is binned and in each bin random simulations are run to estimate the loads. A different methodology for quantifying uncertainties proposed in this work is polynomial interpolation, a more efficient technique that allows to more accurately predict the loads on the turbine for specific load cases. This efficiency is demonstrated by applying the technique to a power production test problem and to IEC Design Load Case 1.1, where the ultimate loads are determined using BLADED. The results show that the interpolating polynomial is capable of representing the load model. Our proposed surrogate modeling approach therefore has the potential to significantly speed up the design and analysis of offshore wind turbines by reducing the time required for load case assessment.","","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:d9b51a8d-d323-4e63-9e66-33dc90e8ae86","http://resolver.tudelft.nl/uuid:d9b51a8d-d323-4e63-9e66-33dc90e8ae86","Correlation between Lidar measured wind speeds and aerodynamic loading","Giyanani, A.H. (TU Delft Wind Energy); Savenije, F.J. (ECN Solar Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2018","The IEC standards prescribe an inflow wind field based on models with empirical assumptions to perform load calculations. The use of preview wind speed measurements using nacelle-mounted Lidars allows mitigation of structural loads by suggesting appropriate control action. This relationship is affected by uncertainty in site conditions and the dynamic control of wind turbine in different operation regimes. Although efforts have been put to derive the relation between the aerodynamic loading and the wind speed, there is scope to explore this relation using measurements. Deriving the load statistics based on the inflow wind field is therefore necessary to establish the correct control strategies. This study focuses on two aspects: firstly, the effect of variability in the inflow conditions due to wind speed fluctuations, turbulence and wind evolution on loading statistics and secondly, the effect of different wind turbine operation modes and Lidar measurement ranges on loading statistics. By understanding the effect of these two aspects on aerodynamic loading, a suitable control strategy can be designed by establishing correlation and coherence based look-up tables with inflow-loading relationship for each operation regime. The study defines a correlation between the Lidar measured wind speed and aerodynamic loading for three Lidar measurement ranges at below and above rated operation modes. Strong correlations are observed at above-rated operation, while uneven correlations at below-rated operation are observed. Strong correlations are observed for turbulence intensities higher than 12%. The preview distances of 50 m and 110 m provide the high correlation estimates The study of coherence between these two signals provides useful insights on the evolution of wind, the length scales present and the frequencies. The coherence remains high for wavelengths upto 200m for above-rated and below-rated operations, the time scale was found to be around 2-2.5 s and the decay parameter ranges from 2 to 7.","","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:87b375b0-ef95-4074-b7b2-9bff4bd51dff","http://resolver.tudelft.nl/uuid:87b375b0-ef95-4074-b7b2-9bff4bd51dff","Towards improving the aerodynamic performance of a ducted wind turbine: A numerical study","Dighe, V.V. (TU Delft Wind Energy); De Oliveira Andrade, G.L. (TU Delft Wind Energy); Avallone, F. (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2018","This paper aims to study the aerodynamic performance of ducted wind turbines (DWT) using inviscid and viscous flow calculations by accounting for the mutual interaction between the duct and the rotor. Two generalized duct cross section geometries are considered while the rotor is modelled as an actuator disc with constant thrust coefficient. The analysis shows the opportunity to significantly increase the overall aerodynamic performance of the DWT by a correct choice of the optimal rotor loading for a given duct geometry. Present results clearly indicate that the increased duct cross section camber leads to an improved performance for a DWT. Finally, some insights on the changes occurring to the performance coefficients are obtained through a detailed flow analysis.","","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:de9988cc-c814-4006-a14a-a775ca203010","http://resolver.tudelft.nl/uuid:de9988cc-c814-4006-a14a-a775ca203010","Experimental parameter study for passive vortex generators on a 30% thick airfoil","Baldacchino, D. (TU Delft Wind Energy); Ferreira, Carlos (TU Delft Wind Energy); De Tavernier, D. (TU Delft Wind Energy); Timmer, W.A. (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2018","Passive vane-type vortex generators (VGs) are commonly used on wind turbine blades to mitigate the effects of flow separation. However, significant uncertainty surrounds VG design guidelines. Understanding the influence of VG parameters on airfoil performance requires a systematic approach targeting wind energy-specific airfoils. Thus, the 30%-thick DU97-W-300 airfoil was equipped with numerous VG designs, and its performance was evaluated in the Delft University Low Turbulence Wind Tunnel at a chord-based Reynolds number of 2×106. Oil-flow visualizations confirmed the suppression of separation as a result of the vortex-induced mixing. Further investigation of the oil streaks demonstrated a method to determine the vortex strength. The airfoil performance sensitivity to 41 different VG designs was explored by analysing model and wake pressures. The chordwise positioning, array configuration, and vane height were of prime importance. The sensitivity to vane length, inclination angle, vane shape, and array packing density proved secondary. The VGs were also able to delay stall with simulated airfoil surface roughness. The use of the VG mounting strip was detrimental to the airfoil's performance, highlighting the aerodynamic cost of the commonly used mounting technique. Time-averaged pressure distributions and the lift standard deviation revealed that the presence of VGs increases load fluctuations in the stalling regime, compared with the uncontrolled case.","DU97W300; Parametric study; Passive flow control; Separation delay; Vane type; Vortex generators","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:4a8fddb9-cee4-446c-9761-fc46b47fd2aa","http://resolver.tudelft.nl/uuid:4a8fddb9-cee4-446c-9761-fc46b47fd2aa","A Review of Urban Wind Energy Research: Aerodynamics and Other Challenges","Micaleff, Daniel (University of Malta); van Bussel, G.J.W. (TU Delft Wind Energy)","","2018","Urban wind energy research is crucial for the success or failure of wind turbines installed in the built environment. Research in this field is fragmented into various research groups working on different topics in isolation with seemingly few efforts of integrating the various fields. This review aims at highlighting the synergies between the various advances, particularly in aerodynamics, but also in other areas. Past and current work has been focused on establishing reliable wind statistics at the site of interest. Advances in building aerodynamics have provided new insight on the local flow occurring at the rotor location. An outlook toward future research and the need to treat the different flow scales in a holistic manner is emphasized given also the recent advances in rotor aerodynamics related to the effect of flow skewness and turbulence. This will shed light on the critical issues that need to be addressed by scientists in order to make urban wind energy viable for decentralized generation. Various other present challenges are discussed briefly including structural aspects, noise emissions, economics and visual impact. Research in this field should be the guidepost for more targeted certification standards, in an effort to regularize the small wind energy market.","urban wind energy; wind resource; small-scale wind turbine; Vertical Axis Wind Turbine (VAWT); Horizontal Axis Wind Turbine (HAWT); building integrated wind energy; OA-Fund TU Delft","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:e4d19fdf-0eda-4d8b-8c52-90795a702444","http://resolver.tudelft.nl/uuid:e4d19fdf-0eda-4d8b-8c52-90795a702444","The MEXICO rotor aerodynamic loads prediction: ZigZag tape effects and laminar-turbulent transition modeling in CFD","Zhang, Y. (TU Delft Wind Energy); van Zuijlen, A.H. (TU Delft Aerodynamics); van Bussel, G.J.W. (TU Delft Wind Energy)","","2017","This paper aims to provide an explanation for the overprediction of aerodynamic loads by CFD compared to experiments for the MEXICO wind turbine rotor and improve the CFD prediction by considering laminar-turbulent transition modeling. Large deviations between CFD results and experimental measurements are observed in terms of sectional normal and tangential forces at the blade tip (r/R=0.82 and 0.92) of the MEXICO rotor operating in axial condition at the design tip speed ratio λ=6.7. The first part of this study identifies the effects of ZigZag tape, which is used in the experiment to trigger boundary layer transition, by analyzing the available experimental data of a single, non-rotating MEXICO rotor blade. The analysis indicates that ZigZag tape has a significant impact on sectional aerodynamic tip loads: it alters the boundary layer thickness and additionally reduces the effective airfoil camber besides the expected tripping. These additional effects most likely also occur in the rotating MEXICO experiment, reducing the sectional loads and hence lead to an overprediction by CFD. To eliminate the ZigZag tape interference, experimental data with an untripped blade is preferred to be used as validation case. In the second part of this study, a transitional flow simulation for the MEXICO rotor is performed by using RANS-based transition model k−kL−ω within OpenFOAM-2.1.1. The numerical results are compared against experimental data obtained from the untripped, new MEXICO experiments. The comparison gives that transitional simulation present a very good tip loads prediction for the untripped blade. The measured data also confirms that the ZigZag tape indeed has a significant influence on the blade tip loads in rotating conditions. The transition onset over 3D MEXICO blade is visualized and transition locations are identified. The results shown in the present study can explain the causes of the large differences between CFD and experiment observed in the MEXICO blind comparisons.","Laminar-turbulent transition; OpenFOAM; Tip loads overprediction; Wind turbine rotor simulation; ZigZag tape effects","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:85edde26-e9d9-4074-8b60-567d1c72fffa","http://resolver.tudelft.nl/uuid:85edde26-e9d9-4074-8b60-567d1c72fffa","On the kidney shape of the wake of a HAWT in yaw","Berdowski, T.J. (TU Delft Wind Energy); Ferreira, Carlos (TU Delft Wind Energy); van Zuijlen, A.H. (TU Delft Aerodynamics); van Bussel, G.J.W. (TU Delft Wind Energy)","","2017","A PhD project is being carried out on the topic of far-wake aerodynamics of Horizontal Axis Wind Turbines (HAWTs) in yawed conditions, which has a large relevance for wind farm design and optimization. Characteristic for a turbine in yaw are the inherent unsteady and non-uniform rotor loading, and the typical wake deflection and strong three-dimensional deformation effects under influence of self-induction (see figure 1). Investigation of HAWTs in yaw is important, as the larce-scale eddies of the turbulent atmosphere dictate that a wind turbine is in practise always operating in unsteady yaw, while the resulting wake effects are already significant for small yaw angles. Despite this relevance, research into the far-wake of yawed wind turbines has been very limited and the symmetry assumptions on which common wake engineering models are based conflict with the physics of the skewed wake of a yawed turbine. Nevertheless, there is an increasing interest into this topic, as it is recognized that the effect of wake deflection can be exploited as a way to optimize the overall wind farm power production through active yaw control. For this purpose, simple two-dimensional models are applied for approximating the wake deflection, but which are unable to capture the typical three-dimensional deformation effects. In summary, there is a large gap of fundamental knowledge on wake physics in yawed conditions, and what the relevance of these phenomena is on the development and issues like the re-energization process of the far-wake. To bridge this gap, the PhD project aims at improving our understanding of the wake physics of HAWTs in yaw and to draft guidelines for reduced-order models that can be applied for wind farm design and optimization. In support of this aim, the objective is to analyze the different physical “modes” that play a role in the yawed wake, through a numerial and experimental investigation of the skewed wakes aft of HAWTs and actuator discs. The results from these investigations are collected (along with results from third parties) into a high-fidelity benchmark database for model validation purposes and to be able to derive the reduced-order models. For the current conference, results will be presented of both two- and three-dimensional free-wake vortex simulations of an actuator disc in yaw. The focus is put on the crescent or kidney shaped convective wake deformation (figure 1), which is naturally not present in a two-dimensional simulation. The magnitude of this phenomenon is investigated as function of the yaw angle and thrust coefficient, and the effect on global wake parameters is assessed such as the wake deflection and velocity profile. The outcomes of this investigation are relevant for assessing the validity of two-dimensional assumptions made in current yaw models regarding the wake deflection, definition of the wake center and width, and the wake profile.","","en","abstract","","","","","","","","","","","Wind Energy","","",""
"uuid:8f17912c-580f-4c95-b33b-b12c56f460e3","http://resolver.tudelft.nl/uuid:8f17912c-580f-4c95-b33b-b12c56f460e3","Passive and active flow augmentation: From diffusers to multi-rotor machines","De Oliveira Andrade, G.L. (TU Delft Wind Energy); Balbino dos Santos Pereira, R. (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy); Avallone, F. (TU Delft Wind Energy); Ragni, D. (TU Delft Wind Energy)","","2017","Flow augmentation consists in modifying mass flow across the actuation plane of a rotor to enhance energy extraction or propulsive efficiency. The talk sketches the distinction between passive and active rotor augmentation strategies. Power coefficient trends are compared analytically while numerical results illustrate differences in flow topology. Rotors are stylized as actuator disks that exert homogeneous normal forces on the steady flow of inviscid fluids to highlight the distinctive features of each augmentation principle. Passive augmentation principles have been well documented because they guide the design of ducted, shrouded and diffuser-augmented wind turbines1-6. These axisymmetric bodies decrease average static pressures on the rotor plane to increase mass flux and power coefficient. Rotor-body interactions are dominated by conservative forces5,7: the bodies don’t exchange energy with the fluid but act as augmenting devices and affect global energy balance by changing rotor state. Virtual work arguments show that bodies exert streamwise forces4,6 that can be related with the power coefficient through the law of de Vries1,6. Active flow augmentation is a rather recent theoretical concept8. Its simplest energy extraction embodiment consists of an upstream actuator that accelerates flow onto a downstream actuator. This augmentation strategy is coined as active because the upstream actuator injects (spends) energy into the flow for the downstream actuator to extract (produce) energy from a greater mass flux than if it were alone. The interaction mechanism depends on the action of non-conservative forces and actuators interact exclusively through changes in total flow enthalpy when they are sufficiently far apart. No pressure interactions occur in this asymptotic case and a closed solution exists together with an analytical power coefficient law. Parallels can be drawn with wake ingestion propeller setups9 but no practical energy extraction realizations have been attempted yet. Passive and active flow augmentation concepts are different but we hope that parallels between them shed further light on the physics of energy extraction from ideal fluid flows. The communication concludes with a few reflections meant to trigger an open discussion about the implications and applicability of the discussed theories.","","en","abstract","","","","","","","","","","","Wind Energy","","",""
"uuid:26f67e56-3566-4275-9109-6f3e6f0fa10a","http://resolver.tudelft.nl/uuid:26f67e56-3566-4275-9109-6f3e6f0fa10a","Ducted wind turbine optimization: A numerical approach","Dighe, V.V. (TU Delft Wind Energy); De Oliveira Andrade, G.L. (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2017","The practice of ducting wind turbines has shown a beneficial effect on the overall performance, when compared to an open turbine of the same rotor diameter1. However, an optimization study specifically for ducted wind turbines (DWT’s) is missing or incomplete. This work focuses on a numerical optimization of the duct orientation and the ideal loading coefficient for the rotor. A 2D planar geometry was employed to model the DWT and the rotor is modelled as an uniformly loaded actuator disc (AD). The flow-field around the DWT is obtained through numerical solutions of Reynolds-averaged-Navier-Stokes (RANS) equations2 and a steady state Lagrangian approach based on vortex ring method3 . The study determines the optimal angle of attack for the duct corresponding to the AD loading, in order to achieve the optimal performance for a given DWT configuration.","","en","abstract","","","","","","","","","","","Wind Energy","","",""
"uuid:b1454bf3-0d82-4da2-90d8-37f5d1723632","http://resolver.tudelft.nl/uuid:b1454bf3-0d82-4da2-90d8-37f5d1723632","High-Lift Low Reynolds Number Aerofoils With Specified Pressure Drop for Ducted Wind Turbine","Tang, J. (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2017","A new high-lift aerofoil modification for the duct has been developed and will be experimentally tested in a small wind tunnel. Aerofoils for such wind tunnel ducts typically operate in the low Reynolds number range from 2 × 105 to 6 × 105. The effect of a duct and of rotor on power and pressure drop were considered separately in previous studies. This paper focuses on the optimization of aerofoil geometry for a Reynolds number of 3 × 105 taking into account of the presence of a screen, having a pressure drop similar to a real rotor. In particular, the current work concentrates on obtaining high lift, instead of high lift-to-drag ratio. Since high lift is the only desirable feature when modifying an aerofoil for ducts, the factors most related to enhanced high-lift low Reynolds numbers aerofoil performance are investigated. Previous experimental data of a three-dimension aerofoil-shaped duct model are used. Combining these data, and applying the Liebeck type high-lift design philosophy, which is to make use of an optimal pressure recovery with aft loading, variations in thickness, camber, and the shape of leading and trailing edges are analysed through the fully inversed method. The XFOIL 6.99 code was adopted as the analyse tool in this study. With the specified velocity distribution, it is found that an increase of both camber and thickness of the duct leads to an increase in lift coefficient with the presence of the pressure drop. In particular, the thickness increment for the aft part of the aerofoil generates higher lift coefficient. The installation of screen divides the duct into two parts, the duct fore part starts from the leading edge until the screen plane, while the duct aft part includes the screen plane to trailing edge. It is observed from previous experimental data that, with the screen presence, the front stagnation point moves towards the inner part of the duct. Consequently, the pressure coefficient reduces in the front part of the suction side, although the pressure differences, between the upper surface and the lower surface, of the duct fore part enlarges. Decreasing the leading edge radius, in essence, accelerates the airflow around it so that a negative area was created. Building on these results, the modified aerofoil model is fabricated and will be tested in a wind tunnel experiment. The test two-dimension model, with the assumption of symmetrical flow, is composed of an aerofoil and a uniform porous screen to simulate half part of the rotor from centreline. The aerofoil has a chord length of 20 mm and the screen has a length of 130 mm in vertical direction. To find the highest lift coefficient of this 2-dimension model, measurements will be conducted with the varying angle of attack and wind speed. Moreover, to investigate the effect of screen loading onto the configuration, there will be two different screens tested. Since the experiment will be carried out in April 2017 the comparison with the XFOIL 6.99 predictions cannot be provided at present, but will be shown during the symposium.","","en","abstract","","","","","","","","","","","Wind Energy","","",""
"uuid:8440676a-3afd-4239-95ba-61f2ef72e849","http://resolver.tudelft.nl/uuid:8440676a-3afd-4239-95ba-61f2ef72e849","Experimental and numerical investigations of aerodynamic loads and 3D flow over non-rotating MEXICO blades","Zhang, Y. (TU Delft Wind Energy); Gillebaart, T. (TU Delft Aerodynamics); van Zuijlen, A.H. (TU Delft Aerodynamics); van Bussel, G.J.W. (TU Delft Wind Energy); Bijl, H. (TU Delft Aerodynamics)","","2017","This paper presents the experimental and numerical study on MEXICO wind turbine blades. Previous work by other researchers shows that large deviations exist in the loads comparison between numerical predictions and experimental data for the rotating MEXICO wind turbine. To reduce complexities and uncertainties, a non-rotating experimental campaign has been carried out on MEXICO blades Delft University of Technology. In this new measurement, quasi-2D aerodynamic characteristics of MEXICO blades on three spanwise sections are measured at different inflow velocities and angles of attack. Additionally, RANS simulations are performed with OpenFOAM-2.1.1 to compare numerical results against measured data. The comparison and analysis of aerodynamic loads on the blade, where three different airfoil families and geometrical transition regions are used, show that for attached flow condition, RANS computation predicts excellent pressure distribution on the NACA airfoil section (r=R D 0.92) and good agreement is observed on the DU (r=R D 0.35) and RISØ (r=R D 0.60) airfoil sections. Unexpected aerodynamic characteristics are observed at the intermediate transition regions connecting the RISØ and DU airfoils, where sudden lift force drop is found at the radial position r=R D 0.55. Through numerical flow visualization, large-scale vortical structures are observed on the suction side of the blade near the mid-span. Moreover, counter-rotating vortices are generated behind the blade at locations where unexpected loads occurs. Consequently, the RISØ airfoil could not give expected 2D aerodynamic characteristics because of upwash/downwash effects induced by these counter-rotating vortices, which make 3D effects play an important role in numerical modeling when calculating the aerodynamic loads for MEXICO rotor.","3D effects; aerodynamic loads; non-rotating blades; MEXICO wind turbine; OpenFOAM","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:b7d791b8-9127-49f2-9407-0625f5c54875","http://resolver.tudelft.nl/uuid:b7d791b8-9127-49f2-9407-0625f5c54875","Experimental comparison of a wind-turbine and of an actuator-disc near wake","Lignarolo, L.; Ragni, D.; Simao Ferreira, C.J.; Van Bussel, G.J.W.","","2016","The actuator disc (AD) model is commonly used to simplify the simulation of horizontal-axis wind-turbine aerodynamics. The limitations of this approach in reproducing the wake losses in wind farm simulations have been proven by a previous research. The present study is aimed at providing an experimental analysis of the near-wake turbulent flow of a wind turbine (WT) and a porous disc, emulating the actuator disc numerical model. The general purpose is to highlight the similarities and to quantify the differences of the two models in the near-wake region, characterised by the largest discrepancies. The velocity fields in the wake of a wind turbine model and a porous disc (emulation of the actuator disc numerical model) have been measured in a wind tunnel using stereo particle image velocimetry. The study has been conducted at low turbulence intensity in order to separate the problems of the flow mixing caused by the external turbulence and the one caused by the turbulence induced directly by the AD or the WT presence. The analysis, as such, showed the intrinsic differences and similarities between the flows in the two wakes, solely due to the wake-induced flow, with no influence of external flow fluctuations. The data analysis provided the time-average three-component velocity and turbulence intensity fields, pressure fields, rotor and disc loading, vorticity fields, stagnation enthalpy distribution, and mean-flow kinetic-energy fluxes in the shear layer at the border of the wake. The properties have been compared in the wakes of the two models. Even in the absence of turbulence, the results show a good match in the thrust and energy coefficient, velocity, pressure, and enthalpy fields between wind turbine and actuator disc. However, the results show a different turbulence intensity and turbulent mixing. The results suggest the possibility to extend the use of the actuator disc model in numerical simulation until the very near wake, provided that the turbulent mixing is correctly represented.","","en","journal article","American Institute of Physics","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:b7d549f2-ddd4-482b-96c2-ed41ada15736","http://resolver.tudelft.nl/uuid:b7d549f2-ddd4-482b-96c2-ed41ada15736","Long-term research challenges in wind energy – a research agenda by the European Academy of Wind Energy","van Kuik, G.A.M. (TU Delft Wind Energy); Peinke, Joachim (Carl von Ossietzky Universitat Oldenburg); Nijssen, Rogier (Knowledge Centre WMC); Lekou, Denja (Centre for Renewable Energy Sources); Mann, Jakob (Technical University of Denmark); Sørensen, Jens Nørkær (Technical University of Denmark); Ferreira, Carlos (TU Delft Wind Energy); van Wingerden, J.W. (TU Delft Team Raf Van de Plas); Schlipf, David (University of Stuttgart); Gebraad, P.M.O. (National Renewable Energy Laboratory); Polinder, H. (TU Delft DC systems, Energy conversion & Storage); Abrahamsen, Asger Bech (Technical University of Denmark); van Bussel, G.J.W. (TU Delft Wind Energy); Sørensen, John Dalsgaard (Aalborg University); Tavner, Peter (Durham University); Botasso, Carlo (Technische Universität München); Muskulus, Michael (Norwegian University of Science and Technology (NTNU)); Matha, Denis (University of Stuttgart); Lindeboom, Han (Wageningen University & Research); Degraer, Steven (Royal Belgian Institute of Natural Sciences); Kramer, Oliver (Carl von Ossietzky Universitat Oldenburg); Lehnhoff, Sebastian (Carl von Ossietzky Universitat Oldenburg); Sonnenschein, Michael (Carl von Ossietzky Universitat Oldenburg); Sørensen, Poul Ejnar (Technical University of Denmark); Kunneke, R.W. (TU Delft Economics of Technology and Innovation); Morthorst, Poul Erik (Technical University of Denmark); Skytte, Klaus (Technical University of Denmark)","","2016","The European Academy of Wind Energy (eawe), representing universities and institutes with a significant wind energy programme in 14 countries, has discussed the long-term research challenges in wind energy. In contrast to research agendas addressing short- to medium-term research activities, this eawe document takes a longer-term perspective, addressing the scientific knowledge base that is required to develop wind energy beyond the applications of today and tomorrow. In other words, this long-term research agenda is driven by problems and curiosity, addressing basic research and fundamental knowledge in 11 research areas, ranging from physics and design to environmental and societal aspects. Because of the very nature of this initiative, this document does not intend to be permanent or complete. It shows the vision of the experts of the eawe, but other views may be possible. We sincerely hope that it will spur an even more intensive discussion worldwide within the wind energy community.","","en","review","","","","","","","","","","","Wind Energy","","",""
"uuid:84f8d77a-4fda-462c-9aa0-03d7fd12f608","http://resolver.tudelft.nl/uuid:84f8d77a-4fda-462c-9aa0-03d7fd12f608","How does the presence of a body affect the performance of an actuator disk?","De Oliveira Andrade, G.L. (TU Delft Wind Energy); Balbino dos Santos Pereira, R. (TU Delft Wind Energy); Ragni, D. (TU Delft Wind Energy); Avallone, F. (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2016","The article seeks to unify the treatment of conservative force interactions between axi-symmetric bodies and actuators in inviscid ow. Applications include the study of hub interference, di_user augmented wind turbines and boundary layer ingestion propeller con_gurations. The conservation equations are integrated over in_nitesimal streamtubes to obtain an exact momentum model contemplating the interaction between an actuator and a nearby body. No assumptions on the shape or topology of the body are made besides (axi)symmetry. Laws are derived for the thrust coe_cient, power coe_cient and propulsive e_ciency. The proposed methodology is articulated with previous e_orts and validated against the numerical predictions of a planar vorticity equation solver. Very good agreement is obtained between the analytical and numerical methods","","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:e78146c1-af2f-4a0a-b94a-f63cf5663a25","http://resolver.tudelft.nl/uuid:e78146c1-af2f-4a0a-b94a-f63cf5663a25","Experimental Study Of Flow Field Of An Aerofoil Shaped Diffuser With A Porous Screen Simulating The Rotor","Tang, J. (TU Delft Wind Energy); Avallone, F. (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2016","This study presents an experimental investigation on a diffuser augmented wind turbine (DAWT). A screen mesh is used to simulate the energy extraction mechanisms of a wind turbine in experiment. Different screen porosities corresponding to different turbine loading coefficients are tested. Measurements of the axial force and of the velocity distribution in radial direction are reported. The general purpose is to highlight the dependency between the diffuser and the screen, and to compare the radial velocity distributions in the diffuser between unloaded and loaded conditions. It is shown that the thrust on an unshrouded screen is lower than on a shrouded screen, under the same inflow condition. Moreover, the thrust on the diffuser largely depends on the screen loading. For the present configuration, the thrust on the screen with high loading coefficient contributes for more than 70% of the total thrust on the DAWT. Smoke visualizations and radial velocity profiles reveal that the high loading screen induces flow separation on the outer surface of the diffuser, justifying the results of the thrust measurements. It is also inferred that the flow separation leads to loss of thrust and has a great effect on the total pressure drag. It should be emphasized that the experimental results indicate that the flow field around the diffuser is strongly affected by the choice of screen porosity, that is, turbine loading. And that, the thrust coefficient of the diffuser does not show a linear dependence on the thrust coefficient of the screen. The axial momentum theory, therefore, is not a solid predictor for DAWT performance with high loaded screens.","actuator disc; axial momentum theory; diffuser; ducted wind turbine","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:3bdf0f3f-dd49-4cdb-8995-596bb53bba70","http://resolver.tudelft.nl/uuid:3bdf0f3f-dd49-4cdb-8995-596bb53bba70","Gazing at clouds to understand turbulence on wind turbine airfoils","De Oliveira Andrade, G.L. (TU Delft Wind Energy); Balbino dos Santos Pereira, R. (TU Delft Wind Energy); Timmer, W.A. (TU Delft Wind Energy); Ragni, D. (TU Delft Wind Energy); Lau, F. (University of Lisbon); van Bussel, G.J.W. (TU Delft Wind Energy)","","2016","There are many ways to learn from data. Our first experiment consisted in reproducing the way aerodynamicists work [2] with a genetic optimizer. The data pool was too narrow and asymptotic tendencies were unreliable. Our 2nd Experiment, a simple version of [4], had a virtually unlimited data pool and used neural networks. Results were better, but computationally expensive. Data assimilation approaches used in EO [ 7] could yield better results..","","en","poster","","","","","","","","","","","Wind Energy","","",""
"uuid:e77091a0-b076-4e9d-99d9-fb0ea86372b7","http://resolver.tudelft.nl/uuid:e77091a0-b076-4e9d-99d9-fb0ea86372b7","Computational Study Of Diffuser Augmented Wind Turbine Using Actuator Disc Force Method","Dighe, V.V. (TU Delft Wind Energy); Avallone, F. (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2016","In this paper, a computational approach, based on the solution of Reynolds-averaged-Navier–Stokes (RANS) equations, to describe the flow within and around a diffuser augmented wind turbine (DAWT) is reported. In order to reduce the computational cost, the turbine is modeled as an actuator disc (AD) that imposes a resistance to the passage of the flow. The effect of the AD is modeled applying two body forces, upstream and downstream of the AD, such that they impose a desired pressure jump. Comparison with experiments carried out in similar conditions shows a good agreement suggesting that the adopted methodology is able to carefully reproduce real flow features.","actuator disc simulation; CFD; diffuser augmented wind turbine","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:b99f4660-77e7-44dc-b355-15f769687439","http://resolver.tudelft.nl/uuid:b99f4660-77e7-44dc-b355-15f769687439","Point vortex modelling of the wake dynamics behind asymmetric vortex generator arrays","Baldacchino, D. (TU Delft Wind Energy); Ferreira, Carlos (TU Delft Wind Energy); Ragni, D. (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2016","In this work, we present a simple inviscid point vortex model to study the dynamics of asymmetric vortex rows, as might appear behind misaligned vortex generator vanes. Starting from the existing solution of the in_nite vortex cascade, a numerical model of four base-vortices is chosen to represent two primary counter-rotating vortex pairs and their mirror plane images, introducing the vortex strength ratio as a free parameter. The resulting system of equations is also de_ned in terms of the vortex row separation and the qualitative features of the ensuing motion are mapped. A translating and orbiting regime are identi_ed for di_erent cascade separations. The latter occurs for all unequal strength vortex pairs. Thus, the motion is further classi_ed by studying the cyclic behaviour of the orbiting regime and it is shown that for small mismatches in vortex strength, the orbiting length and time scales are su_ciently large as to appear, in the near wake, as translational (non-orbiting). However, for larger mismatches in vortex strength, the orbiting motion approaches the order of the starting height of the vortex. Comparisons between experimental data and the potential ow model show qualitative agreement whilst viscous e_ects account for the major discrepancies. Despite this, the model captures the orbital mode observed in the measurements and provides an impetus for considering the impact of these complex interactions on vortex generator designs.","","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:240700bd-8359-4810-b913-ce795d26bf0f","http://resolver.tudelft.nl/uuid:240700bd-8359-4810-b913-ce795d26bf0f","Estimation of rotor effective wind speeds using autoregressive models on Lidar data","Giyanani, A.H. (TU Delft Wind Energy); Bierbooms, W.A.A.M. (TU Delft Wind Energy); van Bussel, G.J.W. (TU Delft Wind Energy)","","2016","Lidars have become increasingly useful for providing accurate wind speed measurements in front of the wind turbine. The wind field measured at distant meteorological masts changes its structure or was too distorted before it reaches the turbine. Thus, one cannot simply apply Taylor's frozen turbulence for representing this distant flow field at the rotor. Wind turbine controllers can optimize the energy output and reduce the loads significantly, if the wind speed estimates were known in advance with high accuracy and low uncertainty. The current method to derive wind speed estimations from aerodynamic torque, pitch angle and tip speed ratio after the wind field flows past the turbine and have their limitations, e.g. in predicting gusts. Therefore, an estimation model coupled with the measuring capability of nacelle based Lidars was necessary for detecting extreme events and for estimating accurate wind speeds at the rotor disc. Nacelle-mounted Lidars measure the oncoming wind field from utpo 400m(5D) in front of the turbine and appropriate models could be used for deriving the rotor effective wind speed from these measurements. This article proposes an auto-regressive model combined with a method to include the blockage factor in order to estimate the wind speeds accurately using Lidar measurements. An Armax model was used to determine the transfer function that models the physical evolution of wind towards the wind turbine, incorporating the effect of surface roughness, wind shear and wind variability at the site. The model could incorporate local as well as global effects and was able to predict the rotor effective wind speeds with adequate accuracy for wind turbine control actions. A high correlation of 0.86 was achieved as the Armax modelled signal was compared to a reference signal. The model could also be extended to estimate the damage potential during high wind speeds, gusts or abrupt change in wind directions, allowing the controller to act appropriately under extreme conditions.","","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:7b6b95d2-076e-4f38-b167-879253805263","http://resolver.tudelft.nl/uuid:7b6b95d2-076e-4f38-b167-879253805263","Wind turbine and actuator disc wake: Two experimental campaigns","Lignarolo, L.; Ragni, D.; Simao Ferreira, C.J.; van Bussel, G.J.W.","","2015","The present paper is the summary of 3 years of research on the wake aerodynamics of horizontal axis wind turbine at Delft University of Technology, the Netherlands. In particular, the main results and the conclusions of two experimental campaigns are collected. The underlying research question is: how do the near-wake turbulent flow structures affect the re-energising of the far wake and to what extend is the actuator disc assumption valid for the representation of the near wake dynamics? In the first experiments, stereo particle image velocimetry is used for analysing the turbulent velocity field in the near and transition wake of a small two-bladed wind turbine model. The results showed the important role of the tip-vortex helix instability (leapfrogging) in the mixing process and in the re-energising of the wake. The tip-vortex instability and breakdown, in fact, give rise to a more efficient turbulent mixing. In the second campaign, the same measurement technique is used for acquiring data in the near wake of the wind turbine model and in the near wake of a porous disc, emulating the numerical actuator disc. The results show a good match velocity fields between wind turbine and actuator disc, but show a different turbulence intensity and turbulent mixing. The analysis suggest the possibility to extend the use of the actuator disc model in numerical simulation until the very near wake, provided that the turbulent mixing is correctly represented.","Tip-Vortex Instability; Wind Turbine Wake; PIV Experiments; Wake Turbulence; Actuator Disc","en","conference paper","UFRGS","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:a1de399f-fd5d-44f8-932e-805fee00bd4a","http://resolver.tudelft.nl/uuid:a1de399f-fd5d-44f8-932e-805fee00bd4a","Lidar uncertainty and beam averaging correction","Giyanani, A.H.; Bierbooms, W.A.A.M.; Van Bussel, G.J.W.","","2015","Remote sensing of the atmospheric variables with the use of Lidar is a relatively new technology field for wind resource assessment in wind energy. A review of the draft version of an international guideline (CD IEC 61400-12-1 Ed.2) used for wind energy purposes is performed and some extra atmospheric variables are taken into account for proper representation of the site. A measurement campaign with two Leosphere vertical scanning WindCube Lidars and metmast measurements is used for comparison of the uncertainty in wind speed measurements using the CD IEC 61400-12-1 Ed.2. The comparison revealed higher but realistic uncertainties. A simple model for Lidar beam averaging correction is demonstrated for understanding deviation in the measurements. It can be further applied for beam averaging uncertainty calculations in flat and complex terrain.","OA-Fund TU Delft","en","journal article","Copernicus Publications","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:14430c56-26d9-438d-89aa-55fd2648e2fc","http://resolver.tudelft.nl/uuid:14430c56-26d9-438d-89aa-55fd2648e2fc","Capturing the journey of wind from the wind turbines (poster)","Giyanani, A.H.; Bierbooms, W.A.A.M.; Van Bussel, G.J.W.","","2015","Wind turbine design, control strategies often assume Taylor’s frozen turbulence where the fluctuating part of the wind is assumed to be constant. In practise, the wind turbine faces higher turbulence in case of gusts and lower turbulence in some cases. With Lidar technology, the frozen turbulence assumption could be avoided and the evolution of wind towards the wind turbine could be studied. This studey therefore bridges the gap between measurements and controls of the turbine. In this poster, the autoregressive methods for prediction of the wind speeds evolving from farwind to nearwind are analysed and an empirical state space model is developed. The results are therefore useful in developing the transfer function for efficient wind turbine control thereby, reducing fatigue and extreme loads in the wind turbine.","","en","conference paper","","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:0ec9edf7-5eac-4191-b63d-9a6c7e3619af","http://resolver.tudelft.nl/uuid:0ec9edf7-5eac-4191-b63d-9a6c7e3619af","Evolution of wind towards wind turbine","Giyanani, A.H.; Bierbooms, W.A.A.M.; Van Bussel, G.J.W.","","2015","Remote sensing of the atmospheric variables with the use of LiDAR is a relatively new technology field for wind resource assessment in wind energy. The validation of LiDAR measurements and comparisons is of high importance for further applications of the data.","wind evolution; remote sensing; lidar data; wind field modelling","en","conference paper","EAWE","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:1364e60c-0f1e-47b9-b7ca-2b7c476b7dfb","http://resolver.tudelft.nl/uuid:1364e60c-0f1e-47b9-b7ca-2b7c476b7dfb","An integral boundary layer method for modelling the effects of vortex generators","Baldacchino, D.; Ragni, D.; Simao Ferreira, C.J.; Van Bussel, G.J.W.","","2015","In this work, the measured modulated integral boundary layer (IBL) characteristics of low-profile vortex generators (VGs) are used to validate new developments in a viscousinviscid interaction code which is modified to incorporate the effect of the passive mixing devices. The motivations are laid out and sample validation data is presented within this abstract.","passive flow control; vortex generator; integral boundary layer; flat plate; RFOIL; PIV","en","conference paper","EAWE","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:18d88d33-d4e2-46f0-8319-703c58b8a346","http://resolver.tudelft.nl/uuid:18d88d33-d4e2-46f0-8319-703c58b8a346","Importance sampling of severe wind gusts","Bos, R.; Bierbooms, W.A.A.M.; Van Bussel, G.J.W.","","2015","An important problem that arises during the design of wind turbines is estimating extreme loads with sufficient accuracy. This is especially difficult during iterative design phases when computational resources are scarce. Over the years, many methods have been proposed to extrapolate extreme load distributions from relatively short time series with “mean turbulence”. In this work, however, we focus on finding the response to extreme gusts based on the ability to generate conditional turbulent wind fields. Load distributions can then be constructed on the basis of a Monte Carlo method with importance sampling.","extreme loads; wind gusts; Monte Carlo method; importance sampling","en","conference paper","","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:1df6a732-0863-43f8-b5ed-ca09aa287f47","http://resolver.tudelft.nl/uuid:1df6a732-0863-43f8-b5ed-ca09aa287f47","FSI of Inflatable Kite Wings (poster)","Rajan, N.K.; Vire, A.; Schmehl, R.; Van Bussel, G.J.W.","","2015","A novel fluid-structure interaction (FSI) simulation framework is being developed at the KitePower group of TU Delft. Developing an FSI simulator suitable for the kite problem has to take into account the following factors.","","en","conference paper","","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:0eeb06e2-20bb-48a5-98e1-daf9a7df6baa","http://resolver.tudelft.nl/uuid:0eeb06e2-20bb-48a5-98e1-daf9a7df6baa","Fluid-Structure Interaction of an Inflatable Kite Wing","Rajan, N.K.; Viré, A.; Schmehl, R.; Van Bussel, G.J.W.","","2015","","","en","conference paper","","","","","","","","","","","","","",""
"uuid:ae654160-7984-4667-aeba-29ec46b4d181","http://resolver.tudelft.nl/uuid:ae654160-7984-4667-aeba-29ec46b4d181","Estimating atmospheric stability from observations and correcting wind shear models accordingly","Holtslag, M.C.; Bierbooms, W.A.A.M.; Van Bussel, G.J.W.","","2014","Atmospheric stability strongly influences wind shear and thus has to be considered when performing load calculations for wind turbine design. Numerous methods exist however for obtaining stability in terms of the Obukhov length L as well as for correcting the logarithmic wind profile. It is therefore questioned to what extend the choice of adopted methods influences results when performing load analyses. Four methods found in literature for obtaining L, and five methods to correct the logarithmic wind profile for stability are included in the analyses (two for unstable, three for stable conditions). The four methods used to estimate stability from observations result in different PDF's of L, which in turn results in differences in estimated lifetime fatigue loads up to 81%. For unstable conditions hardly any differences are found when using either of the proposed stability correction functions, neither in wind shear nor in fatigue loads. For stable conditions however the proposed stability correction functions differ significantly, and the standard correction for stable conditions might strongly overestimate fatigue loads caused by wind shear (up to 15% differences). Due to the large differences found, it is recommended to carefully choose how to obtain stability and correct wind shear models accordingly.","","en","journal article","IOP Publishing","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:7aec19ec-fcbd-4268-a5c7-5a40320a7869","http://resolver.tudelft.nl/uuid:7aec19ec-fcbd-4268-a5c7-5a40320a7869","Effects of geometry and tip speed ratio on the HAWT blade's root flow","Akay, B.; Micallef, D.; Simao Ferreira, C.J.; Van Bussel, G.J.W.","","2014","In this study, the effect of the parameters playing a role in the root flow behavior of HAWT are only partly understood. To better reveal the root flow properties, this study presents the progression of HAWT blade root flow at two different blade geometries and at two different tip speed ratios. The effects of the geometry and the tip speed ratio on the root flow behavior and on the evolution of the root flow features are investigated. This study aims to answer the following questions: (i) What are the effects of the blade geometry and tip speed ratio on the root flow behavior? (ii) How are the blade wake and the root vortex evolution affected by the change of these parameters? The analysis of the velocity fields shows that the radial flow behavior changes with different blade geometries but a remarkable difference in the radial flow behavior is not observed with the change of tip speed ratio. The formation of the wake is different at three test cases because of different loading that the blades are encountered. From the circulation distribution along the blades, while a strong root vortex can be observed in Blade 1, the bound vorticity along Blade 2 builds up gradually when moving outboard, and do not show a trace of a strong root vortex.","","en","journal article","IOP Publishing","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:f38bc7db-6a35-4214-b455-6832b0835861","http://resolver.tudelft.nl/uuid:f38bc7db-6a35-4214-b455-6832b0835861","Active stall control for large offshore horizontal axis wind turbines: A conceptual study considering different actuation methods","Pereira, R.; Van Bussel, G.J.W.; Timmer, W.A.","","2014","The increasing size of Horizontal Axis Wind Turbines and the trend to install wind farms further offshore demand more robust design options. If the pitch system could be eliminated, the availability of Horizontal Axis Wind Turbines should increase. This research investigates the use of active stall control to regulate power production in replacement of the pitch system. A feasibility study is conducted using a blade element momentum code and taking the National Renewable Energy Laboratory 5 MW turbine as baseline case. Considering half of the blade span is equipped with actuators, the required change in the lift coefficient to regulate power was estimated in Cl = 0:7. Three actuation technologies are investigated, namely Boundary Layer Transpiration, Trailing Edge Jets and Dielectric Barrier Discharge actuators. Results indicate the authority of the actuators considered is not sufficient to regulate power, since the change in the lift coefficient is not large enough. Active stall control of Horizontal Axis Wind Turbines appears feasible only if the rotor is re-designed from the start to incorporate active-stall devices.","","en","journal article","IOP Publishing","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:22278c14-5611-41c6-affd-64ba0d8f2a14","http://resolver.tudelft.nl/uuid:22278c14-5611-41c6-affd-64ba0d8f2a14","Coupling of a free wake vortex ring near-wake model with the Jensen and Larsen far-wake deficit models","Van Heemst, J.W.; Baldacchino, D.; Mehta, D.; Van Bussel, G.J.W.","","2014","","","en","journal article","IOP Publishing","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:c948d7c3-1cb8-41a2-a658-709815786195","http://resolver.tudelft.nl/uuid:c948d7c3-1cb8-41a2-a658-709815786195","Wind turbine wake stability investigations using a vortex ring modelling approach","Baldacchino, D.; Van Bussel, G.J.W.","","2014","In the present study, a simple inviscid vortex ring (VR) modelling approach is used to represent the developing rotor wake. This allows a straightforward investigation and comparison of the impact of uniform, yawed and sheared flow conditions on the development of the rotor wake, with the additional possibility of including ground effect. The effect of instabilities on the development of the wake is manually introduced in the form of perturbations of strength, ring position and size. The phenomenon of vortex filament interaction or leapfrogging, could play a role in the observation of unsteady phenomena and is therefore also addressed. Such a study is hence performed in light of recent conflicting views on the causes of wake meandering: is the observed dynamic wake behaviour a result of large scale turbulent forcing or do more subtle and intrinsic wake instabilities play a role? This study concludes that the presence of the ground and external perturbations, most notably changes in the wake pitch and the rotor thrust coefficient, can significantly affect the steady development of the wake. The mutual vortex pairing instability, whilst displaying interesting periodic behaviour, does not correlate with periodic wake behaviour reported by Medici et al. [1]. However, in the absence of unsteady inflow, it is shown that the wake of a Horizontal Axis Wind Turbine (HAWT) is certainly prone to displaying unstable, dynamic behaviour caused by these additional factors.","","en","journal article","IOP Publishing","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:e77ab570-e7be-4851-8a90-d6ddce1cb0b9","http://resolver.tudelft.nl/uuid:e77ab570-e7be-4851-8a90-d6ddce1cb0b9","The origins of a wind turbine tip vortex","Micallef, D.; Akay, B.; Simao Ferreira, C.J.; Sant, T.; Van Bussel, G.J.W.","","2014","The tip vortex of a wind turbine rotor blade originates as a result of a complex distribution of vorticity along the blade tip thickness. While the tip vortex evolution was extensively studied previously in other work, the mechanism of the initiation of the tip vorticity in a 3D rotating environment is still somewhat obscured due to lack of detailed experimental evidence. This paper therefore aims at providing an understanding of how tip vorticity is formed at the wind turbine blade tip and what happens just behind the tip trailing edge. Stereo Particle Image Velocimetry (SPIV) is used to measure the flow field at the tip of a 2m diameter, two- bladed rotor at the TU Delft Open Jet Facility (OJF). The rotor has a rectangular blade tip. Spanwise measurements were performed for both axial and yawed flow conditions with a very small azimuthal increment. A 3D, unsteady, potential flow panel method is also used for the purpose of better understanding the tip bound vorticity. A validation study is carried out with positive results. This paper is focused on axial flow results. A complex distribution of vorticity is found along the blade tip thickness. Just after release, the tip vortex becomes almost immediately round and well defined. Observations from the MEXICO rotor are confirmed again by a slight inboard convection of the tip vortex. This is explained by means of the effect of chordwise vorticity at the tip from the numerical solutions. The results presented in this work suggest that a more physical interpretation of the tip loss effect is required. Currently, inclusion of tip effects are based primarily on either wake induced effects or on an empirical 3D correction for airfoil data. This research should stimulate a more rigorous approach, where the effects of the blade tip chordwise vorticity are implemented in tip correction models.","","en","journal article","IOP Publishing","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:005162c6-e131-4f6b-ba20-1615c77502fd","http://resolver.tudelft.nl/uuid:005162c6-e131-4f6b-ba20-1615c77502fd","Analysis of inflow parameters using LiDARs","Giyanani, A.H.; Bierbooms, W.A.A.M.; Van Bussel, G.J.W.","","2014","Remote sensing of the atmospheric variables with the use of LiDAR is a relatively new technique for wind resource assessment and oncoming wind prediction in wind energy. The validation of LiDAR measurements and comparisons with other sensing elements thus, is of high importance for further applications of the data. A measurement campaign with two vertical scanning pulsed LiDARs and met mast measurements was used here for comparison of inflow wind variables from LiDAR, sonic and cup anemometers. A comparison of the wind directions, wind speed and wind shear was performed to determine the validity of LiDAR measurements in wind energy applications. The LiDAR measurements correlated well with met mast measurements and a major cause for wind direction bias was found.","","en","conference paper","EAWE European Academy of Wind Energy","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:634a3ec3-98b8-4863-b987-31447cf99d8f","http://resolver.tudelft.nl/uuid:634a3ec3-98b8-4863-b987-31447cf99d8f","LiDAR for accurate wind resource assessment (poster)","Giyanani, A.H.; Bierbooms, W.A.A.M.; Van Bussel, G.J.W.","","2014","","","en","conference paper","","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:f34844c4-213d-4e63-81a1-ae631bdb8b63","http://resolver.tudelft.nl/uuid:f34844c4-213d-4e63-81a1-ae631bdb8b63","Towards integral boundary layer modelling of passive vortex generators (poster)","Baldacchino, D.; Simao Ferreira, C.J.; Van Bussel, G.J.W.","","2014","","","en","conference paper","","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:90a04b22-6618-4a67-b340-d0a5ef279260","http://resolver.tudelft.nl/uuid:90a04b22-6618-4a67-b340-d0a5ef279260","Definition of the equivalent atmospheric stability for wind turbine fatigue load assessment","Holtslag, M.C.; Bierbooms, W.A.A.M.; Van Bussel, G.J.W.","","2014","In this paper the dependence of wind turbine fatigue loads on atmospheric stability is assessed. It is shown that fatigue loads depend strongly on stability, and highest loads occur for very unstable conditions. For a given hub height wind speed one can dene an equivalent atmospheric stability that corresponds to the same cumulative loads as if one performs an infinite amount of simulations for all stability conditions that may occur. It is shown that stability, conditionalised to hub height wind speed, is approximately normally distributed and the equivalent stability corresponds well to the mean stability for a given hub height wind speed. If one follows the IEC guidelines for offshore sites, neglecting atmospheric stability, one will compute higher cumulative lifetime fatigue loads (~ 10%). This overestimation is caused by conservatism in both wind shear and turbulence levels, which is explicitly shown for the turbulence levels analyzed in this paper","","en","journal article","IOP Publishing","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:8ae3eea4-fcf9-45f3-8cd9-e8f0adbef1b3","http://resolver.tudelft.nl/uuid:8ae3eea4-fcf9-45f3-8cd9-e8f0adbef1b3","Influence of Nonlinear Irregular Waves on the Fatigue Loads of an Offshore Wind Turbine","Van der Meulen, M.B.; Ashuri, T.; Van Bussel, G.J.W.; Molenaar, D.P.","","2012","In order to make offshore wind power a cost effective solution that can compete with the traditional fossil energy sources, cost reductions on the expensive offshore support structures are required. One way to achieve this, is to reduce the uncertainty in wave load calculations by using a more advanced model for wave kinematics. As offshore wind turbines are generally sited in shallow water, nonlinear effects which results in steeper waves with higher velocities and accelerations are common. Whereas extreme waves are modeled with higher-order nonlinear regular wave models, fatigue loads are calculated from kinematics obtained by a low-fidelity linear irregular wave model. In this paper, a second-order wave model that is employed to simulate the dynamic response due to nonlinear irregular waves on a full set of IEC-standard load cases. This method is computationally efficient, which is particularly useful for design optimization studies. It is shown that by using this method for a 25 m deep site in the German Bight, equivalent fatigue loads increase by 7.5 % compared to the traditional linear wave model. The effect of nonlinear waves on fatigue is most prevalent in the foundation and tower parts near the sea surface. Furthermore, it is found that the increase in fatigue damage accumulation is most prevalent in wind-wave misaligned load cases, in which aerodynamic damping is absent.","","en","conference paper","","","","","","","","","Aerospace Engineering","Aerodynamics and Wind Energy","","","",""
"uuid:10c08a16-ebe8-4926-b090-31262628923e","http://resolver.tudelft.nl/uuid:10c08a16-ebe8-4926-b090-31262628923e","Experimental and Numerical Quantification of Radial Flow in the Root Region of a HAWT","Akay, B.; Ferreira, C.S.; Van Bussel, G.J.W.; Herraez, I.","","2012","This paper explores the evolution of radial flow in a Horizontal Axis Wind Turbine (HAWT) blade root region. The radial flow is analyzed in the potential flow and viscous flow regions. An experiment carried out by means of stereo Particle Image Velocimetry to measure the velocity field produced by a HAWT blade. While the radial flow in the potential flow region was obtained from the measurements, the radial flow in the boundary layer was derived from CFD. By the direct observations obtained from the experiment, an insight is gained about the nature of the radial flow in the suction side of the blade as well as in the near wake. An outboard radial flow motion is observed in the root region. This tendency of the flow changes dramatically when it reaches the maximum chord position of the blade, where the radial flow moves inboard. The trace of the viscous region due to merging of the boundary layers and trailing vorticity are observed clearly in the radial velocity and vorticity distributions at 135º azimuth angle of the blade. In the viscous flow region the radial flow is more pronounced than in the potential flow region. The performed CFD simulations are able to predict the vortex formation in the maximum chord region and its interaction with the nacelle.","","en","conference paper","American Institute of Aeronautics and Astronautics (AIAA)","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:e5fa41d8-f83f-4f86-a5cc-aad5ab2cdeb4","http://resolver.tudelft.nl/uuid:e5fa41d8-f83f-4f86-a5cc-aad5ab2cdeb4","Stereo PIV Experiments on Horizontal Axis Wind Turbine Rotor Model","Akay, B.; Micallef, D.; Ferreira, C.S.; Van Bussel, G.J.W.","","2011","This paper sets out to describe the measurements and computations to construct three components of velocity field around the blade. The primary aim of the measurements was to gain insight into the physics of the flow field produced by a horizontal axis wind turbine-HAWT blade. Stereo Particle Image Velocimetry experiments were performed on a two-bladed HAWT rotor in the open jet facility. Three components of velocity on 2D planar measurement planes were obtained from the defined field of views. The three components of velocity at the different radial positions are analysed in the present paper by comparing the experimental results with the panel code results. Besides having an insight about the flow field around the blade section, this comparison enables to improve and validate the panel code. The measurements show very well agreement with the computations except at the tip trailing edge region which is expected. The key observation of this work is inboard motion of the tip vortex. Also, clear outward motion of the radial flow on the suction side of the inboard sections of the blade is observed in the measurements and computations.","","en","conference paper","","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:70195ec0-ef1f-4225-8f0d-bf0c56b58458","http://resolver.tudelft.nl/uuid:70195ec0-ef1f-4225-8f0d-bf0c56b58458","Experimental and numerical study of radial flow and its contribution to wake development of a HAWT","Micallef, D.; Akay, B.; Sant, T.; Simao Ferreira, C.J.; Van Bussel, G.J.W.","","2011","The scope of this work was to investigate radial flow component for a Horizontal Axis Wind Turbine in axial flow conditions and to assess its impact on the turbine operation. This was done by means of Particle Image Velocimetry and numerical simulation with a 3D unsteady potential-flow panel model. A direct comparison between the numerical and experimental radial velocity results show differences in the tip and root regions. These differences have important implications on the wake development just at the moment of release of the tip vortex. Moreover, the impact of the radial velocities on the blade loading has been studied using the numerical results. The contribution of the radial velocity to the normal load on the blade is only slightly appreciable in the tip and root regions of the blade. However, as the numerical model does not account for viscous effects, further analysis of impact on boundary layer development is necessary.","horizontal axis wind-turbine; radial flow; wake expansion","en","conference paper","","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:921eba0a-7a07-42d6-a3c5-66548db09009","http://resolver.tudelft.nl/uuid:921eba0a-7a07-42d6-a3c5-66548db09009","A Non-Linear Upscaling Approach for Wind Turbines Blades Based on Stresses","Castillo Capponi, P.; Van Bussel, G.J.W.; Ashuri, T.; Kallesoe, B.","","2011","The linear scaling laws for upscaling wind turbine blades show a linear increase of stresses due to the weight. However, the stresses should remain the same for a suitable design. Application of linear scaling laws may lead to an upscaled blade that may not be any more a feasible design. In this paper a non-linear upscaling approach is presented with the aim of keeping the stresses in the upscaled blade the same as the reference blade. The stresses due to the weight, aerodynamics and centrifugal forces are taken into account and the blade is modeled as a beam with equivalent structural properties. This new methodology is used to upscale the 5 MW NREL wind turbine blade to a 20 MW wind turbine blade. As a result, a 20 MW wind turbine blade is obtained in which the stresses are the same as the 5 MW blade. This provides initial blade design solution for optimization studies that is feasible and enables the designer to explore other interesting aspects of larger scale wind turbines.","wind turbines blade design; non-linear scaling law; Blades aeroelasticity; upscaling","en","conference paper","","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:58d76fff-a25e-4254-b642-36257ad1b8bd","http://resolver.tudelft.nl/uuid:58d76fff-a25e-4254-b642-36257ad1b8bd","Artificial Neural Networks for SCADA Data based Load Reconstruction (poster)","Hofemann, C.; Van Bussel, G.J.W.; Veldkamp, H.","","2011","If at least one reference wind turbine is available, which provides sufficient information about the wind turbine loads, the loads acting on the neighbouring wind turbines can be predicted via an artificial neural network (ANN). This research explores the possibilities to apply such a network not only within a wind park but on turbines located at different sites. Following the idea to develop a tool to forecast the particular loads of any wind turbine in the field without the need to install additional measuring systems, a model has been developed needing only signals contained in the Supervisory Control and Data Acquisition (SCADA) data as input signals.","","en","conference paper","","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:7b821f51-8fd7-43ee-aedf-1bbd3a3e6b54","http://resolver.tudelft.nl/uuid:7b821f51-8fd7-43ee-aedf-1bbd3a3e6b54","An Analytical Model of Wake Deflection Due to Shear Flow","Micallef, D.; Simao Ferreira, C.J.; Sant, T.; Van Bussel, G.J.W.","","2010","The main motivation behind this work is to create a purely analytical engineering model for wind turbine wake upward deflection due to shear flow, by developing a closed form solution of the velocity field due to an oblique vortex ring. The effectiveness of the model is evaluated by comparing the results with those of a free-wake model. The solution of the velocity field due to an oblique vortex ring is obtained by using the result of an upright ring along with an equivalent point method. The wake model is derived using oblique ring elements with a number of suitable assumptions. Results of wake vertical deflection are compared with a free-wake solution. A linear trend between wake deflection and shear flow exponent is found with both models. The oblique ring model shows some discrepancies from the free-wake result in terms of the dependence of the deflection on the reference tip speed ratio. The oblique ring model needs further refinements and validation with experimental work and is only currently suited for the determination of general wake kinematics. It however provides immediate results for a given input and can be useful in generating databases with wake geometry information.","horizontal axis wind turbines; atmospheric shear flow; vortex rings","en","conference paper","European Wind Energy Association","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:e7148dbf-c609-415d-90a6-7e481d9795f8","http://resolver.tudelft.nl/uuid:e7148dbf-c609-415d-90a6-7e481d9795f8","Controller Design Automation for Aeroservoelastic Design Optimization of Wind Turbines","Ashuri, T.; Van Bussel, G.J.W.; Zaayer, M.B.; Van Kuik, G.A.M.","","2010","The purpose of this paper is to integrate the controller design of wind turbines with structure and aerodynamic analysis and use the final product in the design optimization process (DOP) of wind turbines. To do that, the controller design is automated and integrated with an aeroelastic simulation tool. This integrated tool is linked with an optimization engine. The automated controller has two built-in control algorithms; a generator-torque controller and an above rated pitch-controller. This new tool is used in the DOP of the 5MW NREL research wind turbine. To show how this method works some parameters of both the generatortorque controller and the pitch-controller are introduced as design variables in the DOP. As the result of changing controller related design variables within each optimization iteration, the values of the objective function and the design constraint also change. This shows that by introducing the controller’s parameters as design variables in the DOP a more realistic assessment of the objective function and constraints is possible that helps the optimizer to search for better solutions.","controller design; wind turbine; design optimization; aeroservoelasticity","en","conference paper","European Wind Energy Association","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:7a1d441f-1128-4874-af40-d50089c99e89","http://resolver.tudelft.nl/uuid:7a1d441f-1128-4874-af40-d50089c99e89","Experimental and Numerical Investigation of the Effect of Rotor Blockage on Wake Expansion","Akay, B.; Simao Ferreira, C.J.; Van Bussel, G.J.W.; Tescione, G.","","2010","A detailed quantitative description of the aerodynamics of a horizontal axis wind turbine (HAWT) is difficult due to complexity of the flow field. Several methods from experimental to analytical are used to investigate the aerodynamics of a HAWT. In the present study, a wind tunnel experiment and computational fluid dynamics (CFD) simulations are used to explore the expansion of the wake. 2D actuator disc (AD) simulations are compared with the wind tunnel experiments. To understand the aerodynamic behavior of a model wind turbine blade, a detail flow field measurements in chordwise-spanwise directions and in the wake have been done. The measurements are performed on a 2 bladed rotor by means of Stereo Particle Image Velocimetry (Stereo PIV) in an open jet wind tunnel. In this paper, the velocity measurements performed in the wake region of the blade is presented. Actuator disc simulations are performed by applying a constant pressure jump on a permeable disc of zero thickness. Actuator disc simulations are carried out by using FLUENT 6.3.26 with the incompressible version of the Reynolds Averaged Navier-Stokes (RANS) equations. By validating the simulations with the experimental results, one may conclude that the unsteady CFD modeling works correctly and the wake expansion of the prescribed model is affected by the geometry of the Open Jet Facility (OJF).","","en","conference paper","European Wind Energy Association","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:a7c93ec4-7000-4bba-867b-b58e34de563e","http://resolver.tudelft.nl/uuid:a7c93ec4-7000-4bba-867b-b58e34de563e","An Analytical Model to Extract Wind Turbine Blade Structural Properties for Optimization and Up-scaling Studies","Ashuri, T.; Van Bussel, G.J.W.; Zaayer, M.B.; Van Kuik, G.A.M.","","2010","A wind turbine blade has a complex shape and consists of different elements with dissimilar material properties. To do any aeroelastic simulation, the structural properties of the blade such as stiffnesses and mass per unit length should be known in advance, and extracting these properties is a difficult task. This paper presents an analytical model to extract these structural properties in a simple way. It starts with calculating an equivalent material property of the cross section using weighting method. Then the centroid of each section is obtained. Next the second moment of inertia of each element relevant to its local coordinates system is calculated and transferred to the centroid of the section using parallel axis theorem. A coordinate transformation is employed to rotate these second moment of inertias around any arbitrary axis. Finally, flapwise and edgewise stiffnesses are found by multiplying the equivalent modulus of elasticity to the second area moment of inertia in each section. Mass per unit length is calculated by multiplying the equivalent density to the real area of each section. The method is verified with the structural properties of a commercial 660 kW wind turbine blade. Despite the simplicity of the method the results show a good agreement.","wind turbine blade; structural properties; analytical model","en","conference paper","European Wind Energy Association","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:7f9ca562-07c1-48ce-a361-3b01e95213d0","http://resolver.tudelft.nl/uuid:7f9ca562-07c1-48ce-a361-3b01e95213d0","Dynamic modeling of a spar-type floating offshore wind turbine","Savenije, L.B.; Ashuri, T.; Van Bussel, G.J.W.; Staerdahl, J.W.","","2010","The installation of floating wind farms in deeper water is encouraged by the stronger and steadier wind, the lower visibility and noise impact, the absence of road restrictions, but also the absence or shortage of shallow water. In the summer of 2009, the first large-scale floating wind turbine ”Hywind” was installed. Hywind is a spar-buoy concept with three catenary mooring lines. The experience with modeling floating turbines is still limited. Furthermore, existing models for the design of offshore wind turbines are highly complex as they focus - by definition - mostly on the forces of the wind on the turbine. The correctness and applicability of existing simulation models for the design of floating wind turbines can therefore not be assumed a-priori and need to be researched. This requires that the driving physical processes governing the behaviour of floating wind turbines are investigated first. For this purpose, a new basic model A.T.FLOW has been developed. The requirement of A.T.FLOW is that it incorporates the most significant physical processes so as to be able to provide insight into the dominant physical behaviour of spar-type floating wind turbines. Assumptions have been made that illustrate the limitations of A.T.FLOW. Various verification methods show that the model simulates load cases as expected and is a useful tool for assessing the physical behaviour of spar-type floating wind turbines. The coming two years the body forces and behaviour of the operating full-scale Hywind demo project is monitored. This data should be used to further test and validate A.T.FLOW and to guide further development of the model.","wind; offshore; floating; modeling; hywind; spar","en","conference paper","","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:40cc44d5-fa76-4a9b-b209-123a7e1a549e","http://resolver.tudelft.nl/uuid:40cc44d5-fa76-4a9b-b209-123a7e1a549e","Validating BEM, Direct and Inverse Free Wake Models with the MEXICO Experiment","Micallef, D.; Kloosterman, M.; Ferreira, C.S.; Sant, T.; Van Bussel, G.J.W.","","2010","The primary objective of the MEXICO (Model Experiments in Controlled Conditions) project was to generate experimental data for validation of models for wind turbines. Kulite©pressure sensors were used for pressure measurements while Particle Image Velocimetry was used with the aim of tracking the tip vortex trajectory. The pressure measurements were carried out for both axial and yawed flow conditions with yaw angles of 15º; 30º and 45º. For the Particle Image Velocimetry measurements data was gathered for axial flow and for the ±30º yaw cases at a single tip speed ratio. In this work, an inverse free wake lifting line model, a direct free wake model and a BEM model are validated with the MEXICO data. Particular emphasis is placed on the study of yawed flow conditions. The inverse free-wake model makes use of the experimental loads as input in order to find the distribution of inductions and angle of attack. The predictive capability of BEM may therefore be assessed based on this. Validation of the inverse free-wake model was performed by investigating the stagnation pressureprediction as well as the vortex trajectory prediction. This was done by means of the PIV data gathered from the MEXICO experiment. This PIV data was also used for validation purposes of the direct free-wake model. The differences in the angle of attack distributions in yawed flow with these models was studied in order to assess the difference in results between the use of 2D and 3D airfoil data.","","en","conference paper","American Institute of Aeronautics and Astronautics (AIAA)","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:00f65e8e-b32e-4478-95bd-69afc2eff95f","http://resolver.tudelft.nl/uuid:00f65e8e-b32e-4478-95bd-69afc2eff95f","Experimental Investigation of the Wind Turbine Blade Root Flow","Akay, B.; Ferreira, C.S.; Van Bussel, G.J.W.","","2010","Several methods from experimental to analytical are used to investigate the aerodynamics of a horizontal axis wind turbine. To understand 3D and rotational effects at the root region of a wind turbine blade, correct modeling of the flow field is essential. Aerodynamic models need to be validated by accurate experimental data. In this paper, the experimental results of the aerodynamic behavior of a model wind turbine blade, by focusing on the blade root flow, are presented. The measurements are performed on a 2 bladed rotor having 1 m radius by means of Stereo Particle Image Velocimetry in a wind tunnel. The spanwise velocity distribution on the suction side of the blade is determined in detail. It shows a complex flow pattern in the root region and positive spanwise flow component apparent at radial stations beyond r/R=0.4 at the leading edge (z/c=0.25).","","en","conference paper","American Institute of Aeronautics and Astronautics (AIAA)","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:9c8890f9-f52f-49b4-b63a-a1da87343871","http://resolver.tudelft.nl/uuid:9c8890f9-f52f-49b4-b63a-a1da87343871","3D wake dynamics of the VAWT: Experimental and numerical investigation","Ferreira, C.; Hofemann, C.; Dixon, K.; Van Kuik, G.A.M.; Van Bussel, G.J.W.","","2010","The Vertical Axis Wind Turbine, in its 2D form, is characterized by a complex unsteady aerodynamic flow, including dynamic stall and blade vortex interaction. Adding to this complexity, the 3D flow causes spanwise effects and the presence of trailing vorticity and tip vortices. The objective of the current paper is to bring insight into the 3D development of the near wake of a H-VAWT, understanding: The spanwise blade load distribution in the upwind and the downwind blade passages. The trajectory of tip vortices, including the inboard movement and the radial expansion of the shed and the trailing vorticity. The impact of the 3D flow phenomena on the efficiency of the VAWT. The blade vortex interaction of the upwind tip vortex with the downwind blade passage. The induction due to trailing vorticity. The investigation is composed of experimental wind tunnel research with Stereo-PIV and modeling of the rotor and wake with a 3D unsteady panel method. A two bladed H-Darrieus VAWT model is tested in the low speed/low turbulence wind tunnel at Delft University of Technology. Stereo-PIV measurements are used to visualize the flow in the near wake focusing on the flow field around four tip geometries. The measurement planes cover several sections of the rotor volume, allowing for the reconstruction of the evolution of the tip vortex. The formation, the convection and the dissipation for each tip vortex are quantified. The experimental PIV data is used to validate the 3D, unsteady, multi-body, free-wake panel method. The combination of the results of the panel model validated by experiments, in particular the Stereo PIV results, allows to understand the impact of the near wake development on the upwind blade passage, as well as the energy conversion process during the downwind blade passage.","","en","conference paper","American Institute of Aeronautics and Astronautics (AIAA)","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:af7544a9-0e4d-41e3-8b14-e5474675863a","http://resolver.tudelft.nl/uuid:af7544a9-0e4d-41e3-8b14-e5474675863a","Aerodynamic Analysis of a Vertical Axis Wind Turbine in a Diffuser","Geurts, B.M.; Simao Ferreira, C.; Van Bussel, G.J.W.","","2010","Wind energy in the urban environment faces complex and often unfavorable wind conditions. High turbulence, lower average wind velocities and rapid changes in the wind direction are common phenomena in the complex built environments. A possible way to improve the cost-efficiency of urban wind turbines is the application of flowenhancing structures on or near the turbines. For horizontal axis wind turbines (HAWTs), applying a diffuser has shown to have a beneficial impact on the power production, but it is still under development. For a vertical axis wind turbine (VAWT) it is expected that flow augmentation will also strongly increase the performance of the turbine, but very little research has been done in this field. The purpose of this research is to investigate the effects of a diffuser on the airflow through a VAWT. In order to investigate these effects, the turbine (with and without diffuser) is simulated using a 2-D unsteady free-wake potential-flow panel model. The local flow field, local angles of attack, shed vorticity, the shape and strength of the wake, and the rotor torque are investigated for both the case with and without the diffuser. The diffuser used in this research consists of two mirrored airfoil cross-sections. The size of the duct-opening in which the turbine operates is varied. This work shows that unlike for a 1-D actuator disc analysis, the area ratio B of the diffuser exit with respect to the diffuser nozzle area is not the only driving factor in the augmentation of the rotor torque of the VAWT. More important are the effect of the directional change of the rotor inflow and the faster downstream transport of the shed vorticity.","","en","conference paper","European Wind Energy Association","","","","","","","","Aerospace Engineering","Aerodynamics, Wind Energy & Propulsion","","","",""
"uuid:33950a07-dbaf-492b-bfec-8833984afd2f","http://resolver.tudelft.nl/uuid:33950a07-dbaf-492b-bfec-8833984afd2f","Comparison and validation of BEM and free wake unsteady panel model with the Mexico rotor experiment","Micallef, D.; Kloosterman, M.; Simao Ferreira, C.J.; Sant, A.; Van Bussel, G.J.W.","","2009","","MEXICO experiment; BEM; Free Wake Code","en","conference paper","European Mechanics Society","","","","","","","","Aerospace Engineering","Aerospace Design, Integration and Operations","","","",""
"uuid:e3e9d472-d48f-48ac-aef2-76f24517d8e4","http://resolver.tudelft.nl/uuid:e3e9d472-d48f-48ac-aef2-76f24517d8e4","The VAWT in skew: Stereo-PIV and vortex modeling","Simao Ferreira, C.J.; Dixon, K.R.; Hofemann, C.; Van Kuik, G.A.M.; Van Bussel, G.J.W.","","2009","One of the results of the development of wind energy conversion solutions for the built environment is the reappearance of Vertical Axis Wind Turbines (VAWTs). The application of wind turbines in urban environments presents design challenges driven by the complex wind fields experienced in the urban boundary layer. Urban Wind Turbines operate near, on and in the wake of bluff bodies larger than the rotor scale. These flow conditions might result in skewed flow operation. The objective of the current paper is to bring insight into the development of the near wake of a H-VAWT in skewed flow, namely understanding: Blade loading asymmetry in spanwise direction. Trajectory of the tip vortices, including inboard movement and radial expansion of the shed and trailing vorticity. Asymmetry of the wake in spanwise direction. Blade vortex interaction of upwind tip vortex with downwind blade passage. Load distribution in downwind blade passage. Effect of skew in the expansion of the mid-wake. The investigation is composed of experimental wind tunnel research of a two bladed H-Darrieus VAWT model with Particle Image Velocimetry, and modeling of the rotor and wake with a 3D unsteady panel method. Simulations of the rotor in skewed flow are validated with the experimental PIV data and with the torque measurements of 1 and 2 . The results of the panel model, validated by experiments, show the impact of skew angle on the near wake’s development, both for the upwind blade passage as well as the downwind blade passage.","","en","conference paper","American Institute of Aeronautics and Astronautics, AIAA","","","","","","","","Aerospace Engineering","Aerospace Design, Integration and Operations","","","",""
"uuid:7a500ed8-586c-40da-af62-3cd65d5e3bfe","http://resolver.tudelft.nl/uuid:7a500ed8-586c-40da-af62-3cd65d5e3bfe","3D Stereo PIV study of tip vortex evolution on a vawt","Hofemann, C.; Simao Ferreira, C.J.; Van Bussel, G.J.W.; Van Kuik, G.A.M.; Scarano, F.; Dixon, K.R.","","2008","","vertical axis wind turbine; PIV; tip vortex; wake; Darrieus","en","conference paper","European Wind Energy Association EWEA","","","","","","","","","","","","",""
"uuid:5ca656bb-f98a-4f2f-b73b-56b8a0b84dc6","http://resolver.tudelft.nl/uuid:5ca656bb-f98a-4f2f-b73b-56b8a0b84dc6","Estimating the angle of attack from blade pressure measurements on the national renewable energy laboratory phase VI rotor using a free wake vortex model: Yawed conditions","Sant, A.; Van Kuik, G.A.M.; Van Bussel, G.J.W.","","2008","","wind turbine; yawed conditions; blade element momentum theory; National Renewable Energy Laboratory phase VI experiments; free wake vortex model; wake vorticity; aerofoil data; dynamic stall","en","journal article","Wiley","","","","","","","","Aerospace Engineering","","","","",""
"uuid:614025fe-e543-496c-a92d-cfe41110e4ba","http://resolver.tudelft.nl/uuid:614025fe-e543-496c-a92d-cfe41110e4ba","Visualization by PIV of dynamic stall on vertical axis wind turbine","Simao Ferreira, C.J.; van Kuik, G.A.M.; van Bussel, G.J.W.; Scarano, F.","","2008","","","en","journal article","Springer","","","","","","","","Aerospace Engineering","","","","",""
"uuid:83dd41be-78c7-41c9-88de-d6422d968317","http://resolver.tudelft.nl/uuid:83dd41be-78c7-41c9-88de-d6422d968317","A 3d unsteady panel method for vertical axis wind turbines","Dixon, K.; Simao Ferreira, C.J.; Hofemann, C.; Van Bussel, G.J.W.; Van Kuik, G.A.M.","","2008","","VAWT; panel method; near wake structure","en","conference paper","European Wind Energy Association EWEA","","","","","","","","Aerospace Engineering","","","","",""
"uuid:733e4dbf-18c0-4084-84c3-47ef54259002","http://resolver.tudelft.nl/uuid:733e4dbf-18c0-4084-84c3-47ef54259002","PIV visualization of dynamic stall VAWT and blade load determination","Simao Ferreira, C.J.; Van Bussel, G.J.W.; Scarano, F.; Van Kuik, G.A.M.","","2008","","","en","conference paper","American Institute of Aeronautics and Astronautics AIAA","","","","","","","","Aerospace Engineering","","","","",""
"uuid:18975345-7e9d-4566-a193-89faca7215ac","http://resolver.tudelft.nl/uuid:18975345-7e9d-4566-a193-89faca7215ac","Suppression of classical flutter using a 'smart blade'","Politakis, G.; Haans, W.; Van Bussel, G.J.W.","","2008","","","en","conference paper","American Institute of Aeronautics and Astronautics AIAA","","","","","","","","Aerospace Engineering","","","","",""
"uuid:92e8ad42-c4e6-4a12-9bfa-aa96d5483532","http://resolver.tudelft.nl/uuid:92e8ad42-c4e6-4a12-9bfa-aa96d5483532","IEA wind annex XX: HAWT aerodynamic and models from wind tunnel measurements - final report","Masson, C.; Johansen, J.; Sorensen, N.N.; Zahle, F.; Bak, C.; Madsen, H.A.; Politis, E.; Schepers, G.; Lindenburg, K.; Snel, H.; Van Rooij, R.P.J.O.M.; Arens, E.A.; Van Bussel, G.J.W.; Van Kuik, G.A.M.; Meng, F.Z.; Sant, T.; Knauer, A.; Moe, G.; Munduate, X.; Gonzalez, A.; Ferrer, E.; Gomez, S.; Barakos, G.; Ivanell, S.; Schreck, S.","","2008","","","en","report","National Renewable Energy Laboratory","","","","","","","","Aerospace Engineering","","","","",""
"uuid:e86c19db-3e6f-4a78-a0f6-351a9a8e78b2","http://resolver.tudelft.nl/uuid:e86c19db-3e6f-4a78-a0f6-351a9a8e78b2","Fault Diagnosis approach based on a model-based reasoner and a functional designer for a wind turbine. An approach towards self-maintenance","Echavarria, E.; Tomiyama, T.; Van Bussel, G.J.W.","","2007","","","en","journal article","IOP","","","","","","","","Mechanical, Maritime and Materials Engineering","","","","",""
"uuid:51e5d68e-83e1-404e-9527-1e9b9fcfea0f","http://resolver.tudelft.nl/uuid:51e5d68e-83e1-404e-9527-1e9b9fcfea0f","Aerodynamic force on a vawt in dynamic stall by integration of the velocity field from 3C particle image velocimetry","Simao Ferreira, C.J.; Scarano, F.; Van Kuik, G.A.M.; Van Bussel, G.J.W.","","2007","","","en","conference paper","European Academy for Wind Energy EAWE","","","","","","","","Aerospace Engineering","","","","",""
"uuid:2f19000e-f2b5-468e-8d10-5e338e1be888","http://resolver.tudelft.nl/uuid:2f19000e-f2b5-468e-8d10-5e338e1be888","The science of making more torque from wind: Diffuser experiments and theory revisited","Van Bussel, G.J.W.","","2007","","","en","journal article","IOP","","","","","","","","Aerospace Engineering","","","","",""
"uuid:602dec1f-0861-4268-83bb-4ab85baeac1f","http://resolver.tudelft.nl/uuid:602dec1f-0861-4268-83bb-4ab85baeac1f","Reliability, availability and maintenance aspects of large-scale offshore wind farms, a concepts study","Van Bussel, G.J.W.; Zaayer, M.B.","","2001","The DOWEC projects aims at implementation of large wind turbines in large scale wind farms. part of the DOWEC project a concepts study was performed regarding the achievable reliability and availability levels. A reduction with a factor of 2 with regard to the present state of the art seems fairly easy achievable. This is however not sufficient for application at more exposed sites. Availability levels are lower than targeted, but moreover the O&M cost turn out to be substantially higher than initially anticipated. The main cause for the high O&M costs is the rather frequent need for an expensive external crane vessel. A second design round is necessary to reconsider the reliability levels adopted for almost all concepts. Furthermore a more ""farm like design approach"" is needed to reduce major maintenance cost and increase availability.","","en","conference paper","Institute of marine engineers","","","","","","","","Civil Engineering and Geosciences","","","","",""
"uuid:3e7c9c17-d050-405e-89f3-f07d7fbcb51b","http://resolver.tudelft.nl/uuid:3e7c9c17-d050-405e-89f3-f07d7fbcb51b","The aerodynamics of horizontal axis wind turbine rotors explored with asymptotic expansion methods","Van Bussel, G.J.W.","Dragt, J.B. (promotor); Hermans, A.J. (promotor)","1995","","aerodynamics; wind turbines","en","doctoral thesis","","","","","","","","","Electrical Engineering, Mathematics and Computer Science","","","","",""
"uuid:22fab232-0caf-4a73-af4e-923e9e97067d","http://resolver.tudelft.nl/uuid:22fab232-0caf-4a73-af4e-923e9e97067d","Aerodynamic research on tipvane windturbines","van Bussel, G.J.W.; van Holten, Th.; van Kuik, G.A.M.","","1982","","","en","report","Delft University of Technology","","","","","","","","Aerospace Engineering","","","","",""
"uuid:ed85fc66-7298-433e-b8f0-b4c066d6829e","http://resolver.tudelft.nl/uuid:ed85fc66-7298-433e-b8f0-b4c066d6829e","Aerodynamic and aeroelastic research on tipvane turbines","van Bussel, G.J.W.; Hensing, P.C.; van Kuik, G.A.M.","","1980","","","en","report","Delft University of Technology","","","","","","","","Aerospace Engineering","","","","",""