"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:d04ea880-208f-44ca-8440-7080fb509683","http://resolver.tudelft.nl/uuid:d04ea880-208f-44ca-8440-7080fb509683","Effect of Surface Roughness Geometry on Boundary-Layer Transition and Far-Field Noise","Ye, Q. (TU Delft Wind Energy); Avallone, F. (TU Delft Wind Energy); Ragni, D. (TU Delft Wind Energy); Choudhari, Meelan (NASA Langley Research Center); Casalino, D. (TU Delft Wind Energy)","","2021","Surface roughness elements are often used to force laminar to turbulent transition in aerodynamic and aeroacoustic wind-tunnel experiments. The statistical features and spectral content of the pressure fluctuations in the resulting turbulent boundary layer at the trailing edge can affect far-field noise. To elucidate this dependence, boundary-layer transition induced by randomly distributed roughness elements and a zigzag strip of the same height over a NACA 0012 airfoil is investigated experimentally. The effects of roughness geometry on the near-field flow topology, transition location, and far-field noise are addressed in the common experimental setting for the first time. For a fixed roughness height, distributed roughness elements are less effective in forcing transition than the zigzag strip at low freestream velocity (u∞<20 m/s). As u∞ increases, the transition front for the distributed roughness elements moves closer to the roughness location, reaching the same or even further upstream locations compared to the transition onset in the presence of the zigzag strip. The far-field noise depends on the transition location. For u∞≤20 m/s, a higher noise level is measured for the distributed roughness elements with respect to the zigzag strip. In contrast, for u∞>20 m/s, the earlier onset of transition with the distributed surface roughness leads to a lower noise level than that with the zigzag strip. The data confirm that an adequate characterization of the boundary-layer transition is necessary when measuring the far-field noise during wind-tunnel experiments.","","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.","","2021-09-22","","","Wind Energy","","",""
"uuid:63ccb5db-d5b2-4676-a4f6-17a4cce003b9","http://resolver.tudelft.nl/uuid:63ccb5db-d5b2-4676-a4f6-17a4cce003b9","Effect of Vortex Generators on NREL Wind Turbine: Aerodynamic Performance and Far-Field Noise","Ye, Q. (School of Aeronautics and Astronautics, Zhejiang University); Avallone, F. (TU Delft Wind Energy); Van Der Velden, Wouter (Dassault Systèmes); Casalino, D. (TU Delft Wind Energy)","","2020","Passive flow separation control with vortex generators (VG) is actively used over the wind turbine blade. In this paper, the effect of vortex generators is simulated on a full-scale 2-blade wind-turbine tested at the National Renewable Energy Laboratory. The simulation is performed using Very-Large-Eddy/Lattice-Boltzmann method (VLES/LBM). The analysis focuses on the effect of vortex generators on the aerodynamic performance and far-field noise. The simulation results without vortex generators are compared with the experimental results, reaching good agreement. The vortex generators produce counter-rotating vortices in the wake which effectively delay flow separation, leading to better aerodynamic performance. The acoustic analysis indicates that the dominant noise sources are the tonal noise produced by the flow separation and the turbulent-boundary-layer trailing-edge noise. Similar noise levels are obtained for the configurations with and without vortex generators.","","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:860d69e2-d4d5-4b97-9bb4-00332c7d08ff","http://resolver.tudelft.nl/uuid:860d69e2-d4d5-4b97-9bb4-00332c7d08ff","Inundation modelling for fluvial and pluvial flooding during typhoons: a case study in Shanghai city","Ke, Q. (TU Delft Hydraulic Structures and Flood Risk); Bricker, J.D. (TU Delft Hydraulic Structures and Flood Risk); Ye, Q. (Deltares); Acevedo Goldaracena, F. (TU Delft Hydraulic Structures and Flood Risk); Hohmann, T. (ETH Zürich); Kallioras, A. (Student TU Delft)","Uijttewaal, W. (editor); Franca, M.J. (editor); Valero, D. (editor); Chavarrias, V. (editor); Arbos, C.Y. (editor); Schielen, R. (editor); Crosato, A. (editor)","2020","The co-occurrence of storm surge, high tides and heavy precipitation increases flood probability and potential consequences compared to each hazard separately in Delta cities. The Huangpu River (HP) is a tributary of the Yangtze River in China, which drains Tai Lake to the west of Shanghai city, and meanders through downtown Shanghai. During typhoon events, storm surge reverses the river flow and pushes the water level up as far as 100km upstream. If storm surge (1-2 m above msl) co-occurs with high tide (2-3 m above msl), it poses great threats to the HP floodwall (crest level from ~3-5.5m above msl). At the same time, typhoons cause heavy precipitation (up to 70-80mm/hour) in the city, which increases urban drainage discharge in the pipeline system. In order to prevent elevated water levels in the river, stormwater drainage is ceased to effectively work in this situation. Pluvial and fluvial flooding occur simultaneously. The objective of this paper is to develop a hydrodynamic model to simulate simultaneous pluvial and fluvial flooding and to produce inundation maps due to failure of floodwalls and the urban drainage system. We apply the Delft3D FM numerical model to compound flood events in Shanghai. Results raise risk awareness for decision-makers during compound flood events and demonstrate the importance of compound flood modelling at a city scale.","","en","conference paper","CRC Press / Balkema - Taylor & Francis Group","","","","","Accepted Author Manuscript","","2021-07-10","","","Hydraulic Structures and Flood Risk","","",""
"uuid:5562b95c-42bd-476c-9956-2b8d87c7fa26","http://resolver.tudelft.nl/uuid:5562b95c-42bd-476c-9956-2b8d87c7fa26","Numerical analysis of fan noise for the NOVA boundary-layer ingestion configuration","Romani, G. (TU Delft Wind Energy); Ye, Q. (TU Delft Wind Energy); Avallone, F. (TU Delft Wind Energy); Ragni, D. (TU Delft Wind Energy); Casalino, D. (TU Delft Wind Energy)","","2020","Aim of this paper is to investigate the effects of the turbulent flow developing over a fuselage on fan noise for BLI embedded propulsion systems. Such configurations can suffer from inlet flow distortions and ingestion of turbulence at the fan plane with consequent impact on both broadband and tonal fan noise. The analysis is performed on a modified version of the Low-Noise NASA SDT fan-stage integrated into the ONERA NOVA fuselage in order to reproduce the NOVA BLI configuration. The numerical flow solution is obtained by solving the explicit, transient and compressible lattice-Boltzmann equation implemented in the high-fidelity CFD/CAA solver Simulia PowerFLOW®. The acoustic far-field is computed by using the Ffowcs-Williams & Hawkings integral solution applied to a permeable surface. All simulations are performed for an operating condition representative of a take-off with power cut-back. Installation effects due to the BLI configuration are quantified by comparison with an isolated configuration of the modified Low-Noise SDT fan-stage at the same operating condition. It is found that the BLI fan-stage, which is not optimal, is characterized by strong azimuthal fan blade loading unsteadiness, less axisymmetric and coherent rotor wake tangential velocity variations and higher levels of in-plane velocity fluctuations compared to the isolated engine. This resulted in no distinct tonal components and higher broadband levels in the far-field noise spectra, as well as in an increment of cumulative noise levels up to 18 EPNdB. This study, which represents the first high-fidelity CFD/CAA simulation of a full-scale aircraft geometry comprehensive of a BLI fan/OGV, provides with a clear understanding of the change of the noise sources in BLI integrated configurations.","Aeroacoustics; Aerodynamics; Boundary-layer ingestion; Lattice-Boltzmann method; Turbofan","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:42318268-8e69-43e0-9a5b-89b19c9c4f46","http://resolver.tudelft.nl/uuid:42318268-8e69-43e0-9a5b-89b19c9c4f46","Effect of drag reducing riblet surface on coherent structure in turbulent boundary layer","CUI, Guangyao (Beihang University); PAN, C. (Beihang University); WU, Di (Beihang University); Ye, Q. (TU Delft Wind Energy); WANG, Jinjun (Beihang University)","","2019","The characteristics of turbulent boundary layer over streamwise aligned drag reducing riblet surface under zero-pressure gradient are investigated using particle image velocimetry. The formation and distribution of large-scale coherent structures and their effect on momentum partition are analyzed using two-point correlation and probability density function. Compared with smooth surface, the streamwise riblets reduce the friction velocity and Reynolds stress in the turbulent boundary layer, indicating the drag reduction effect. Strong correlation has been found between the occurrence of hairpin vortices and the momentum distribution. The number and streamwise length scale of hairpin vortices decrease over streamwise riblet surface. The correlation between number of uniform momentum zones and Reynolds number remains the same as smooth surface.","Coherent structures; Particle image velocimetry; Riblet; Riblet surface; Turbulent boundary layer; Uniform momentum zones","en","journal article","","","","","","","","","","","Wind Energy","","",""
"uuid:bd154cd4-9a82-457b-b459-4b456f58ebec","http://resolver.tudelft.nl/uuid:bd154cd4-9a82-457b-b459-4b456f58ebec","Effect of Surface Roughness on Boundary Layer Transition and Far Field Noise","Ye, Q. (TU Delft Wind Energy); Avallone, F. (TU Delft Wind Energy); Ragni, D. (TU Delft Wind Energy); Choudhari, Meelan (NASA Langley Research Center); Casalino, D. (TU Delft Wind Energy)","","2019","Surface roughness elements are often used to force laminar to turbulent transition during aerodynamic and aeroacoustic experiments in wind tunnels. The statistical features and frequency content of the forced turbulent boundary layer can influence the far-field trailing edge noise. To study this dependence, boundary layer transition induced by randomly distributed roughness elements and a zigzag strip of the same height over a NACA 0012 airfoil is investigated experimentally. The effects of roughness type on the near-field flow topology, transition location, and far-field noise are addressed. At a fixed roughness height, the distributed roughness elements are less effective in forcing transition than the zigzag trip at low freestream velocity (u∞ < 20 m/s). As u∞ increases, the transition front for the distributed roughness elements moves close to the roughness location, reaching the same or even further upstream location compared with the zigzag strip. The far-field noise intensity depends on the transition location. For u∞ < 20 m/s, a higher noise level is measured for the distributed roughness with respect to the zigzag strip. Whereas, for u∞ <20m/s, the earlier onset of transition leads to a lower noise level for the distributed roughness elements with respect to the zigzag strip. The data confirms that an adequate characterization of the state of the boundary layer is necessary when measuring far-field noise in wind tunnel experiments.","","en","conference paper","","","","","","","","","","","Wind Energy","","",""
"uuid:fcc3e754-84ef-40a7-8e25-4435c659288f","http://resolver.tudelft.nl/uuid:fcc3e754-84ef-40a7-8e25-4435c659288f","Boundary layer transition induced by distributed roughness array","Ye, Q. (TU Delft Wind Energy); Avallone, F. (TU Delft Wind Energy); Ragni, D. (TU Delft Wind Energy); Choudhari, Meelan (NASA Langley Research Center); Casalino, D. (TU Delft Wind Energy)","","2019","The effects of a finite, spanwise-periodic array of cylindrical roughness elements on boundary layer transition over a NACA 0012 airfoil are investigated at a chord-based Reynolds number of 1.44×105 by using hotwire anemometry and infrared thermography. Both the number and the spanwise spacing of roughness elements in the array are varied in order to study their effect on the wake flow topology. Spanwise interaction between the roughness elements has an effect on the connection and the merging of neighbouring low-speed regions, which results in the formation of merged low-speed blobs (MLSs) that modify the spatial distribution and the amplitudes of the velocity streaks. When the spanwise distance between adjacent roughness elements equals 1.5 times the cylinder diameter, the transition location moves rapidly upstream. In this case, the two neighbouring low-speed regions overlap with each other in the near wake of the roughness, leading to the maximum growth in the velocity streak amplitude and the velocity fluctuations. The number of roughness elements affects the total number of MLSs within the boundary layer. For a single MLS behind a pair of cylinders, the Kelvin-Helmholtz instability dominates the growth of velocity fluctuations around the three-dimensional shear layers. When three cylinders are placed in the array, two MLSs appear in the near wake, which coalesce in to one low-speed blob downstream before the onset of transition, revealing the importance of Kelvin-Helmholtz instability.","","en","conference paper","","","","","","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.","","2021-12-08","","","Wind Energy","","",""
"uuid:6a999983-98b3-4ca5-bcb9-93596bb4c4f4","http://resolver.tudelft.nl/uuid:6a999983-98b3-4ca5-bcb9-93596bb4c4f4","Linear and Non-Linear Dynamics of a Micro-ramp Wake","Groot, K.J. (TU Delft Aerodynamics); Casacuberta Puig, J. (TU Delft Aerodynamics); Ye, Q. (TU Delft Aerodynamics); Hickel, S. (TU Delft Aerodynamics)","","2019","Micro-ramps are deployed to prevent boundary layer separation by creating a momentum excess close to the wall. Through Direct Numerical Simulations (DNS) of the base, instantaneous and mean flow, we identify that the perturbation dynamics in the wake of the microramp play an essential role in creating the near-wall momentum excess. To identify the origin of the perturbations, we deploy BiGlobal stability analysis on the laminar base flow. We demonstrate that the amplification of the most unstable linear mode is closely related to the time-averaged amplitude of the unsteady perturbations. The flow structure corresponding to this mode has a varicose symmetry with respect to the symmetry plane and matches with the early development of the hairpin vortices in the instantaneous flow field. It is concluded that the varicose instability supported by the laminar base flow represents the mechanism that generates the hairpins.","","en","journal article","","","","","","","","","","","Aerodynamics","","",""
"uuid:71616d00-fe37-4f43-8509-93e82eb5a65b","http://resolver.tudelft.nl/uuid:71616d00-fe37-4f43-8509-93e82eb5a65b","Transitional Flow Dynamics Behind a Micro-Ramp","Casacuberta Puig, J. (TU Delft Aerodynamics); Groot, K.J. (TU Delft Aerodynamics); Ye, Q. (TU Delft Wind Energy); Hickel, S. (TU Delft Aerodynamics)","","2019","Micro-ramps are popular passive flow control devices which can delay flow separation by re-energising the lower portion of the boundary layer. We compute the laminar base flow, the instantaneous transitional flow, and the mean flow around a micro-ramp immersed in a quasi-incompressible boundary layer at supercritical roughness Reynolds number. Results of our Direct Numerical Simulations (DNS) are compared with results of BiLocal stability analysis on the DNS base flow and independent tomographic Particle Image Velocimetry (tomo-PIV) experiments. We analyse relevant flow structures developing in the micro-ramp wake and assess their role in the micro-ramp functionality, i.e., in increasing the near-wall momentum. The main flow feature of the base flow is a pair of streamwise counter-rotating vortices induced by the micro-ramp, the so-called primary vortex pair. In the instantaneous transitional flow, the primary vortex pair breaks up into large-scale hairpin vortices, which arise due to linear varicose instability of the base flow, and unsteady secondary vortices develop. Instantaneous vortical structures obtained by DNS and experiments are in good agreement. Matching linear disturbance growth rates from DNS and linear stability analysis are obtained until eight micro-ramp heights downstream of the micro-ramp. For the setup considered in this article, we show that the working principle of the micro-ramp is different from that of classical vortex generators; we find that transitional perturbations are more efficient in increasing the near-wall momentum in the mean flow than the laminar primary vortices in the base flow.","BiLocal stability; DNS; Hairpins; Laminar-turbulent transition; Micro-ramp; Roughness; SFD; Tomo-PIV","en","journal article","","","","","","","","","","","Aerodynamics","","",""
"uuid:7431c316-1511-4d8f-95e7-20a392e310fe","http://resolver.tudelft.nl/uuid:7431c316-1511-4d8f-95e7-20a392e310fe","Fan Noise Boundary Layer Ingestion Installation Effects for NOVA Aircraft Configuration","Romani, G. (TU Delft Wind Energy); Ye, Q. (TU Delft Wind Energy); Avallone, F. (TU Delft Wind Energy); Ragni, D. (TU Delft Wind Energy); Casalino, D. (TU Delft Wind Energy)","","2019","Aim of this paper is to investigate the effects of the turbulent flow developing over a fuselage on fan noise for Boundary Layer Ingestion (BLI) embedded propulsion systems. Such engine configurations can suffer from inlet flow distortions and ingestion of turbulence at the fan plane with consequent impact on both broadband and tonal fan noise. The analysis is performed by considering a modified version of the Low-Noise configuration of the NASA Source Diagnostic Test (SDT) integrated into the Nextgen ONERA Versatile Aircraft (NOVA) fuselage in order to reproduce the NOVA BLI configuration. The numerical flow solution is obtained by solving the explicit, transient and compressible lattice-Boltzmann equation implemented in the high-fidelity CFD/CAA solver Simulia PowerFLOW R®. The acoustic far-field is computed by using the Ffwocs-Williams & Hawkings integral solution applied to a permeable surface encompassing the fan-stage. Simulations are performed for an operating condition representative of a take-off with power cutback. Installation effects due to the BLI configuration are quantified by comparison with an isolated configuration of the modified Low-Noise SDT fan-stage geometry at same operating conditions. Comparisons are carried out in terms of fan-stage intake/interstage velocity fields, fan blades section air-loads and far-field noise; correlations between the fan-stage velocity field and noise emission for the BLI configuration are outlined. It is found that the BLI fan-stage is characterized by strong azimuthal fan blade loading unsteadiness, less periodic and coherent rotor wake tangential velocity variations and higher levels of in-plane velocity fluctuations compared to the isolated engine, resulting in far-field noise spectra with no distinct tonal components and higher broadband levels. This study represents the first high-fidelity CFD/CAA simulation of a full-scale aircraft geometry comprehensive of a BLI fan/Outlet Guide Vane (OGV) stage.","","en","conference paper","American Institute of Aeronautics and Astronautics Inc. (AIAA)","","","","","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.","","","","","Wind Energy","","",""
"uuid:0517ee26-8909-405b-82ad-8b0d669a895e","http://resolver.tudelft.nl/uuid:0517ee26-8909-405b-82ad-8b0d669a895e","On Reynolds number dependence of micro-ramp-induced transition","Ye, Q. (TU Delft Wind Energy); Schrijer, F.F.J. (TU Delft Aerodynamics); Scarano, F. (TU Delft Flow Physics and Technology; TU Delft Aerodynamics)","","2018","The variation of transitional flow features past a micro-ramp is investigated when the Reynolds number is decreased approaching the critical regime. Experiments are conducted in the incompressible flow spanning from supercritical to subcritical roughness-height-based Reynolds number ( , 730, 460 and 320) with tomographic particle image velocimetry. The effect of on three-dimensional flow behaviour is analysed in a domain encompassing 73 ramp heights in the streamwise direction. Above the critical , the primary vortex pair and induced central low-speed region in the mean flow field are active over longer range when decreasing. In the instantaneous flow, at <![CDATA[Reh, the hairpin vortices induced by Kelvin-Helmholtz (K-H) instability progress gradually from close to the micro-ramp into the region where the overall shear layer is destabilized, indicating the correlation between the K-H instability and the onset of transition. The breakdown of K-H vortices as observed at , does not occur at lower. Decreasing , the secondary vortex structures make their first appearance significantly downstream, postponing the formation of sideward disturbances, which destabilize the local shear layer by ejection events. Two major types of eigenmodes with symmetric and asymmetric spatial distribution of velocity fluctuations in the near wake are clearly identified by proper orthogonal decomposition. The symmetric and asymmetric modes correspond to the presence of vortex shedding and a sinuous wiggling motion respectively. It is found that is the key factor determining the importance of the symmetric mode. At , the disturbance energy of the symmetric mode decays before the onset of transition, suggesting that it is relatively insignificant in the process. However, decreasing to 730 and 460, the symmetric mode produces continuous growth of high level disturbance energy, leading to transition.","boundary layer stability; boundary layer structure; transition to turbulence","en","journal article","","","","","","","","","","Flow Physics and Technology","Wind Energy","","",""
"uuid:16642e34-4ae6-4c38-a3ff-7fdc9d543fc4","http://resolver.tudelft.nl/uuid:16642e34-4ae6-4c38-a3ff-7fdc9d543fc4","Transitional flow dynamics behind a micro-ramp","Casacuberta Puig, J. (TU Delft Aerodynamics); Groot, K.J. (TU Delft Aerodynamics); Ye, Q. (TU Delft Wind Energy); Hickel, S. (TU Delft Aerodynamics)","","2018","We computed the base, instantaneous and mean flow around a micro-ramp immersed in an incompressible boundary layer. Results of our Direct
Numerical Simulations (DNS) are compared with an independent stability analysis and experiments. We analyse flow structures and mechanisms that contribute to the micro-ramp functionality and find that transitional perturbations increase the near-wall momentum in the mean flow more efficiently than the primary vortices in the laminar base flow.","","en","conference paper","","","","","","","","","","","Aerodynamics","","",""
"uuid:b1b5332a-33d5-4fd4-b386-3acc48e12003","http://resolver.tudelft.nl/uuid:b1b5332a-33d5-4fd4-b386-3acc48e12003","Mechanisms of boundary layer transition induced by isolated roughnes","Ye, Q. (TU Delft Aerodynamics)","Scarano, F. (promotor); Schrijer, F.F.J. (copromotor); Delft University of Technology (degree granting institution)","2017","Boundary layer transition is a relevant phenomenon in many aerodynamic and aero-thermodynamic problems and has been extensively investigated from the past century till recent times. Among the factors affecting the transition process, surface roughness plays a key role. When a roughness element with sufficiently large height (h) compared to the boundary layer thickness (δ) is immersed in a laminar boundary layer, it will produce spanwise varying disturbances with the potential to accelerate the transition process. In the thesis, a fundamental study is carried out to understand the physical mechanism of isolated roughness element induced transition. Experiments are performed in incompressible flow regime covering both critical and supercritical conditions. Tomographic particle image velocimetry (PIV) is employed as the main experimental diagnostic technique, returning the three-dimensional velocity and vorticity field of the flow.
The three-dimensional wake flow behaviour is firstly identified behind roughness element of micro-ramp geometry. The micro-ramp produces a pair of counter-rotating streamwise vortices in the wake, transporting low momentum fluid away from the wall by the central upwash motion, and sweeping the high momentum flow towards the near-wall region sideward. The shear layer around the central low-speed region is related to the growth of Kelvin-Helmholtz (K-H) instability. The active range of the primary vortices and the central low-speed region in the streamwise direction is associated to the selection of the dominant instability mechanism, which decreases with the increase of roughness-height based Reynolds number (Reh).
The instantaneous flow field reveals that the earliest unstable structures featuring hairpin shape are caused by the K-H instability at the separated shear layer. The evolution of K-H vortices is strongly influenced by Reh. At Reh = 1170, the K-H vortices are lift up under the upwash motion effect of the quasi-streamwise vortices, following by paring, distortion and finally breakdown. The active region of K-H vortices is separated from the inception of turbulent wedge, where early stage transition occurs. When Reh decreases approaching the critical value, the K-H vortices progressed gradually until the overall shear layer is destabilized, indicating the correlation between K-H instability and transition. The POD analysis yields the symmetric (K-H) and asymmetric mode. The disturbance energy associated to the symmetric modes changes with Reh. At higher Reh, the disturbance energy of the symmetric modes quickly decays, having a comparable contribution as the asymmetric modes. When Reh < 1000, the symmetric modes produce a remarkably higher level of disturbance energy until the onset of transition, indicating its dominance.
The effectiveness of roughness element on promoting transition is strongly influenced by its geometry. The bluff-front roughness elements induce horseshoe vortices due to upstream separation. The different rotation direction of these vortices compared to the micro-ramp leads to early inception of sideward growth of fluctuations, and more rapid transition process. While for the slender micro-ramp, significant longer distance is required to for the onset of transition.
Reh