"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:be865e1e-4643-4239-950f-ccbb53ded8c7","http://resolver.tudelft.nl/uuid:be865e1e-4643-4239-950f-ccbb53ded8c7","Helical mode interactions and spectral energy transfer in magnetohydrodynamic turbulence","Linkmann, M.F.; Berera, A.; McKay, M.E.; Jäger, J.","Linkmann, M.F. (author); Berera, A. (author); McKay, M.E. (author); Jäger, J. (author)","2015","Spectral transfer processes in magnetohydrodynamic (MHD) turbulence are investigated by decomposition of the velocity and magnetic fields in Fourier space into helical modes. In 1992, Waleffe (Phys. Fluids A, 4:350 (1992)) used this decomposition to calculate triad interactions for isotropic hydrodynamic turbulence and determined whether a given triad contributed to forward or reverse energy transfer depending on the helicities of the interacting modes. The problem becomes more difficult in MHD due to the need to treat a coupled system of partial differential equations and the energy transfers between the magnetic and velocity fields. This requires the development of techniques that extend Waleffe's work, which are subsequently used to calculate the direction of energy transfer processes originating from triad interactions derived from the MHD equations. In order to illustrate the possible transfer processes that arise from helical mode interactions, we focus on simplified cases and putting special emphasis on interactions resulting in reverse spectral energy transfer. This approach also proves to be helpful in determining the nature of certain energy transfer processes, where transfer of energy between different fields and between the same field can be distinguished. Reverse transfer of magnetic energy was found if the helicities of two modes corresponding to the smaller wavenumbers are the same, while for reverse transfer of kinetic energy Waleffe's result is recovered. Reverse transfer of kinetic to magnetic energy is facilitated if the interacting magnetic field modes are of opposite helicity, and no reverse transfer of magnetic to kinetic energy was found. More generally, the direction of energy transfer not only depends on helicity but also on the ratio of magnetic to kinetic energy. For the magnetically dominated case reverse transfer occurs of all helicities are the same, the kinetically dominated case two modes need to have the same helicity while the third mode is of opposite helicity to allow reverse transfer.","spectral methods; magnetohydrodynamics; turbulence; helical mode decomposition","en","conference paper","","","","","","","","","","","","","",""
"uuid:9e32b3d5-eae0-4012-9020-7b32079b4787","http://resolver.tudelft.nl/uuid:9e32b3d5-eae0-4012-9020-7b32079b4787","A Feature Tracking Velocimetry algorithm to determine the velocities in Negatively Buoyant Jets","Ferrari, S.; Badas, M.G.; Besalduch, L.A.; Querzoli, G.","","2013","We present a novel algorithm, namely Feature Tracking Velocimetry (FTV), which is less sensitive to the appearance and disappearance of particles and to high velocity gradients than classical Particle Image Velocimetry (PIV). The basic idea of FTV is to compare windows only where the motion detection may be successful, that is where there are high luminosity gradients. The FTV algorithm is suitable in presence of different seeding densities, where other techniques produce significant errors, due to the non-homogeneous seeding at the boundary of a flow. The FTV algorithm has been tested for the analysis of laboratory experiments on simple jets (SJs) and negatively buoyant jets (NBJs), both issuing from a sharp-edged orifice. Among the others, the velocity and Turbulent Kinetic Energy profiles, orthogonal to the jet axis, the mean streamwise centerline velocity decay and the integral Turbulent Kinetic Energy along the jet axis have been measured and analyzed. These quantities have been employed to study the differences between simple jets and NBJs, and to investigate how the increase in buoyancy affects the NBJ behavior. Moreover, mean velocity fields have been used to study the geometrical dimensions of the jet, while second order statistics, such as Turbulent Kinetic Energy, have been analyzed to characterize the turbulence structure governing the mixing processes.","Feature Tracking Velocimetry (FTV); simple jet; negatively buoyant jet; turbulence","en","conference paper","","","","","","","","","","","","","",""
"uuid:05820775-31c5-4aa5-8d68-cfd1103f99fc","http://resolver.tudelft.nl/uuid:05820775-31c5-4aa5-8d68-cfd1103f99fc","Stereo-PIV Measurement of Turbulence Shear Stress in a Stirred Flow Mixer","Shekhar, C.; Nishino, K.; Iso, Y.","","2013","The turbulence dissipation rate and turbulence shear stress are estimated inside a cylindrical, stirred flow mixer by carrying out Stereo PIV measurements in twelve vertical and three horizontal planes. The flow domain is vertically oriented, filled with the water. A commercially-available, three-blade impeller, HR-100, is used as the agitator. The impeller is mounted near the tip of a thin, rigid shaft, which is aligned along the central axis of the flow domain. The impeller rotates with the constant angular speed of 150RPM, and the Reynolds number based on the impeller diameter and the blade's tip-velocity is equal to 59400. The turbulence statistics in the vertical measurement planes are reported before (Shekhar C, Nishino K, Yamane Y and Huang J, Stereo-PIV measurement of turbulence characteristics in a flow mixer Journal of Visualization 15 (2012) pp.293~308), which revealed that the rotation induces a downward, as well as tangential, bulk flow motion, which convects the turbulence generated at the blade-water interface, causing the turbulence level below the impeller to be much higher than the level above it. The present study is the second part of the same project, and reports the turbulence statistics in the horizontal measurement planes. The results show that the turbulence level is high in the area swept by the rotating impeller blades and underneath. However, in the outside region, the turbulence damps down and becomes negligible. The vertical and horizontal measurement results are also combined to estimate the production, convection, viscous diffusion, and turbulence dissipation terms of the turbulence kinetic energy's budget equation, along with the turbulence shear stress, along the lines where the different vertical and horizontal planes intersect.","stirred mixer; stereo PIV; turbulence; budget equation; dissipation rate; shear stress","en","conference paper","","","","","","","","","","","","","",""
"uuid:c8dcce2e-159d-45be-ae23-c84f7a022d65","http://resolver.tudelft.nl/uuid:c8dcce2e-159d-45be-ae23-c84f7a022d65","Numerical modeling for the accurate computations of arc-heater flows","Lee, J.I.; Kim, C.; Kim, K.H.","","2006","The purpose of this paper is to develop an accurate analysis code for the flow of arc-heater by employing advanced numerical models. Governing equations are hyperbolic-type axisymmetric Navier-Stokes equations which include joule heating by arc, radiation and turbulent transport effect. Joule heating is simply calculated by Ohms law with the given distribution of current. Radiation is computed by the three-band model which accounts for self-absorption and is consistent with the detailed line-by-line radiation model. Turbulence effect is incorporated by two-equation turbulence models which can describe the transport of turbulence. In order to assess the performance of the newly developed code, AHF and IHF are calculated in various operating conditions. And, it is confirmed that two-equation turbulence models combined with the three-band radiation model simulate the flow physics in arc-heater more accurately than any other previous models and the influence of the turbulence is as much as or bigger than radiation effect.","plasma wind tunnel; arc-heater; joule heating; radiation; turbulence","en","conference paper","","","","","","","","","","","","","",""
"uuid:5e85afbc-e6c8-47c7-b39c-6dfe8652d04c","http://resolver.tudelft.nl/uuid:5e85afbc-e6c8-47c7-b39c-6dfe8652d04c","A new Eulerian Monte Carlo method for the joint velocity-scalar PDF equations in turbulent flows","Soulard, O.; Sabel'nikov, V.","","2006","In the field of turbulent combustion, Lagrangian Monte Carlo (LMC) methods (Pope, 85) have become an essential component of the probability density function (PDF) approach. LMC methods are based on stochastic particles, which evolve from prescribed stochastic ordinary differential equations (SODEs). They are used to compute the one-point statistics of the quantities describing the state of a turbulent reactive flow: namely, the velocity field and the reactive scalars (species mass fractions and temperature). Numerous publications document the convergence and accuracy of LMC methods. They have been used in many complex calculations (including LES), and for several years now, they have been implemented in commercial CFD codes. Nonetheless, the development of a new Eulerian Monte Carlo (EMC) method is useful and stimulating, since the competition between LMC and EMC methods could push both approaches forward. EMC methods have already been proposed by Sabel'nikov and Soulard (2006) in order to compute the one-point PDF of turbulent reactive scalars. EMC methods are based on stochastic Eulerian fields, which evolve from prescribed stochastic partial differential equations (SPDE) statistically equivalent to the PDF equation. The extension of EMC methods to include velocity still remains to be done. Thus, the purpose of this article is to derive SPDEs allowing to compute a modeled one-point joint velocity-scalar PDF. To achieve this objective, we start from existing Lagrangian stochastic models. The latter are described by SODEs, which can be considered as modeled Navier-Stokes equations written in Lagrangian variables. Then, the idea is to transform these Lagrangian SODEs into Eulerian SPDEs, in the same way one transforms the Lagrangian Navier-Stokes equations into Eulerian equations, in classical hydrodynamics. However, our case differs from the classical one. Indeed, the stochastic velocity does not respect an instantaneous continuity constraint, but only a mean one. To account for this difference between the stochastic and the physical system, one must introduce a stochastic density, different from the physical density. As a result of this procedure, we eventually obtain hyperbolic conservative SPDEs giving the evolution of a stochastic velocity, of stochastic scalars, and of a stochastic density. In addition to the main result, an alternative EMC method for the scalar PDF is also derived as a special case of the full velocity-scalar method.","turbulence; combustion; probability density functions; stochastic partial differential equations; Eulerian Monte Carlo Method","en","conference paper","","","","","","","","","","","","","",""
"uuid:2b90abcc-3488-41f4-b70e-f2afdd8c3a0e","http://resolver.tudelft.nl/uuid:2b90abcc-3488-41f4-b70e-f2afdd8c3a0e","Particle Sedimentation in Wall-Bounded Turbulent Flows","Cargnelutti, M.; Breugem, W.A.; Portela, L.M.; Mudde, R.F.; Uijttewaal, W.S.J.; Stelling, G.S.","","2006","In this work, a comparison between the results of point-particle direct numerical simulations and PIV/PTV experiments of a particle-laden horizontal channel flow is presented. The numerical simulations were preformed trying to mimic as much as possible the experimental conditions. The accuracy of the point-particle approach was evaluated by comparison of the concentration, velocity and velocity fluctuation profiles. The agreement was good, both qualitatively and quantitatively, in the central part of the channel. However, in the near-wall region some differences were found. This can be explained by the lack of resuspension present in the simulations, because we considered only the fluid-particle interaction (one-way coupling) and neglected both the particle-fluid interaction (two-way coupling) and the particle-particle interaction (collisions).","particle-laden flows; turbulence; DNS; PIV","en","conference paper","","","","","","","","","","","","","",""
"uuid:39a5176c-4f4b-4fa9-8589-5fe7c7279544","http://resolver.tudelft.nl/uuid:39a5176c-4f4b-4fa9-8589-5fe7c7279544","Non reflecting boundary conditions for reacting flows","Prosser, R.","","2006","In this paper we explore the specification of time dependent boundary conditions suitable for the simulation of low Mach number reacting flows. The standard treatments used to date are based on the method of characteristics, and essentially set to zero the incoming characteristics; this practise has been shown to have deleterious effects on the flow evolution. The new approach, while still based on the method of characteristics, circumvents this problem through the application of a double expansion in terms of an appropriately defined Mach number. In the method, a low Mach number expansion of the dependent variables is coupled to a two-length scale decomposition. Through the double expansion, it is possible to separate inertial events (i.e. those moving at the local convection velocity) from acoustic events (those moving at the local sound speed). The paper highlights why previous treatments have encountered difficulties in turbulent flows, and provides a method by which heat release effects can be incorporated into a non-reflecting boundary condition framework. The accuracy of the method is demonstrated using a curved stagnating flame, in which the reaction zone crosses the boundary.","characteristics; turbulence; boundary conditions","en","conference paper","","","","","","","","","","","","","",""
"uuid:b4f624be-50fa-475d-9615-15027916da4c","http://resolver.tudelft.nl/uuid:b4f624be-50fa-475d-9615-15027916da4c","Regularization modeling for large-eddy simulation of diffusion flames","Geurts, B.J.","","2006","We analyze the evolution of a diffusion flame in a turbulent mixing layer using large-eddy simulation. The large-eddy simulation includes Leray regularization of the convective transport and approximate inverse filtering to represent the chemical source terms. The Leray model is compared to the more conventional dynamic mixed model. The location of the flame-center is defined by the `stoichiometric' interface. Geometrical properties such as its surface-area and wrinkling are characterized using an accurate numerical level-set quadrature method. This allows to quantify flame-properties as well as turbulence modulation effects due to coupling between combustion and turbulent transport. We determine the active flame-region that is responsible for the main part of the chemical conversion in the flame and compare direct and large-eddy simulation predictions.","turbulence; combustion; large-eddy simulation; regularization modeling; iso-surface analysis","en","conference paper","","","","","","","","","","","","","",""
"uuid:9375fecd-4428-4a29-a4e6-8a0a1f3cc4be","http://resolver.tudelft.nl/uuid:9375fecd-4428-4a29-a4e6-8a0a1f3cc4be","Influence of the nozzle outlet face on near flow field mixing","Khan, I.M.; Gilbert, T.; Barigou, M.","","2006","The shape of the nozzle geometry is increasingly attractive in heating, ventilation and air conditioning applications. However an important consideration in the design of nozzle geometry is its effect on the dynamics of near flow field jet and to minimise the manufacturing cost for practical applications. In this investigation the effect of an identical 3d contraction of the nozzle geometry is investigated numerically with circular, square and rectangular outlets of similar effective area. Comparisons of the axial mean streamwise velocity decay, turbulence, entrainment and the temperature distribution were reported for a circular, square and rectangular outlet sections of the nozzle to evaluate its performance in the space. From the analysis of data, it was found that enhanced mixing between the jet flow and the still surrounding fluid was noticed for the JETs existing nozzle geometry with circular outlet section which generated relatively higher turbulence kinetic energy in the near flow field, which implies better diffusion of temperature for air conditioning and ventilation applications.","nozzle; turbulence; diffusion; near flow field","en","conference paper","","","","","","","","","","","","","",""
"uuid:c7f5a261-e698-4d69-8da9-3c2a17be505d","http://resolver.tudelft.nl/uuid:c7f5a261-e698-4d69-8da9-3c2a17be505d","Direct numerical simulation of the interaction between unsheared turbulence and a free-slip surface","Campagne, G.; Cazalbou, J.B.; Joly, L.; Chassaing, P.","","2006","In this paper, direct numerical simulation is used to study the interaction between turbulence and a free surface. The configuration is original due to the fact that a random force generates turbulence in the vicinity of a plane parallel to the free surface. Turbulence is therefore statistically steady and nearly isotropic at some distance of the surface. A detailed description of the flow is provided, including second-order statistics and full Reynolds-stress budgets. It is shown that the results obtained in this configuration can help the understanding of intercomponent energy-transfer mechanisms.","turbulence; direct numerical simulation; free surface; random forcing","en","conference paper","","","","","","","","","","","","","",""
"uuid:dccf9895-423d-4070-ba7c-adf4d92c8427","http://resolver.tudelft.nl/uuid:dccf9895-423d-4070-ba7c-adf4d92c8427","Magnitude control of commutator errors","Geurts, B.J.","","2006","Non-uniform filtering of the Navier-Stokes equations expresses itself, next to the turbulent stresses, in additional closure terms known as commutator errors. These terms require explicit subgrid modeling if the non-uniformity of the filter is sufficiently pronounced. We derive expressions for the magnitude of the mean flux, the turbulent stress flux and the commutator error for individual Fourier modes. This gives rise to conditions for the spatial variations in the filter-width and the filter-skewness subject to which the magnitude of the commutator errors can be controlled. These conditions are translated into smoothness requirements of the computational grid, that involve ratios of first -, second - and third order derivatives of the grid mapping.","turbulence; large-eddy simulation; non-uniform filter; commutator errors","en","conference paper","","","","","","","","","","","","","",""
"uuid:e055f69a-4edc-4f86-83fd-962465e71ee3","http://resolver.tudelft.nl/uuid:e055f69a-4edc-4f86-83fd-962465e71ee3","Multiscale Methods in Computational Fluid and Solid Mechanics","De Borst, R.; Hulshoff, S.J.; Lenz, S.; Munts, E.A.; Van Brummelen, E.H.; Wall, W.A.","","2006","The basic idea of multiscale methods, namely the decomposition of a problem into a coarse scale and a fine scale, has in an intuitive manner been used in engineering for many decades, if not for centuries. Also in computational science, large-scale problems have been solved, and local data, for instance displacements, forces or velocities, have been used as boundary conditions for the resolution of more detail in a part of the problem. Recent years have witnessed the development of multiscale methods in computational science, which strive at coupling fine scales and coarse scales in a more systematic manner. Having made a rigorous decomposition of the problem into fine scales and coarse scales, various approaches exist, which essentially only differ in how to couple the fine scales to the coarse scale. The Variational Multiscale Method is a most promising member of this family, but for instance, multigrid methods can also be classified as multiscale methods. The same conjecture can be substantiated for hp-adaptive methods. In this lecture we will give a succinct taxonomy of various multiscale methods. Next, we will briefly review the Variational Multiscale Method and we will propose a space-time VMS formulation for the compressible Navier-Stokes equations. The spatial discretization corresponds to a high-order continuous Galerkin method, which due to its hierarchical nature provides a natural framework for `a priori' scale separation. The latter property is crucial. The method is formulated to support both continuous and discontinuous discretizations in time. Results will be presented from the application of the method to the computation of turbulent channel flow. Finally, multigrid methods will be applied to fluid-structure interaction problems. The basic iterative method for fluid-structure interaction problems employs defect correction. The latter provides a suitable smoother for a multigrid process, although in itself the associated subiteration process converges slowly. Indeed, the smoothed error can be represented accurately on a coarse mesh, which results in an effective coarse-grid correction. It is noted that an efficient solution strategy is made possible by virtue of the relative compactness of the displacement-to-pressure operator in the fluid-structure interaction problem. This relative compactness manifests the difference in length and time scales in the fluid and the structure and, in this sense, the multigrid method exploits the inherent multiscale character of fluid-structure-interaction problems.","multiscale methods; fluid flow; turbulence; fluid-structure interaction; multigrid methods","en","conference paper","","","","","","","","","","","","","",""
"uuid:15a56eea-69bc-46e9-b24a-502fc697e9cc","http://resolver.tudelft.nl/uuid:15a56eea-69bc-46e9-b24a-502fc697e9cc","Application of Local Defect Correction in a 3d turbulent channel flow","De Hoogh, J.; Kuerten, J.G.M.","","2006","To investigate the behavior of the concentration of a passive scalar in a turbulent flow with realistic high Schmidt numbers, one needs a very fine grid to capture all length-scales that are present in the concentration. An efficient method to increase the spatial resolution without a drastic raise of the computational costs is to apply a Local Defect Correction method. To compute the velocity field of a turbulent channel flow, a Direct Numerical Simulation is used that consists of a pseudo-spectral method in two periodic directions and a Chebyshev expansion in the wall-normal direction. The concentration equation for the passive scalar is solved using a finite volume method. The main concern with an LDC method in a hyperbolic time-dependent problem is the interpolation of the concentration when the refinement area is moved. The interpolated solution has to be smooth and continuous to ensure numerical stability. Using the mean averaged radius and the total surface area of the concentration, the behaviour of several numerical methods can be investigated.","turbulence; local defect correction; passive scalar","en","conference paper","","","","","","","","","","","","","",""
"uuid:ed4bd9db-f347-4173-8ccb-65634ac5fd25","http://resolver.tudelft.nl/uuid:ed4bd9db-f347-4173-8ccb-65634ac5fd25","Large-eddy Simulation of Isotropic Homogeneous Decaying Turbulence","Thornber, B.; Drikakis, D.","","2006","Simulations of three dimensional freely decaying homogeneous turbulence in a periodic cube have been used to examine in a detailed and quantitative manner the behaviour of a Large Eddy Simulation (LES) using implicit subgrid modelling. This paper details the form and behaviour of the implicit subgrid models for the Minmod and third order limiting methods at several mesh resolutions. It is shown that for simulations above 32^3 the decay of kinetic energy follows a power law with a decay exponent between 1:2 and 1:4, except in the case of turbulence with a constrained length scale for which the decay exponent is 2:1. This is in very good agreement with experimental data and theoretical analysis where the exponent ? 1:2 ? 1:4 unconstrained, and 2:0 when constrained. At a resolution of 32^3 the number of degrees of freedom are not sufficient to allow a turbulent flow, and velocity derivative statistics are Gaussian. The skewness of the velocity derivative is lower than existing explicit LES and Direct Numerical Simulation (DNS) simulations, but in good agreement with the most recent experimental results. There is a limited sub-inertial range with the three-dimensional Kolmogorov constant ? 1:9, also in agreement with DNS. The less dissipative nature of the third order limiter gives better skewness at a lower grid resolutions, however both give good results in terms of energy dissipation and growth of the length scales.","LES; implicit; isotropic; turbulence; decay; MUSCL","en","conference paper","","","","","","","","","","","","","",""
"uuid:e8c57b2f-74d8-402b-b3c6-e52d85344300","http://resolver.tudelft.nl/uuid:e8c57b2f-74d8-402b-b3c6-e52d85344300","On the required Reynolds-number dependence of variational multi-scale Smagorinsky models","Meyers, J.; Sagaut, P.","","2006","A theoretical analysis is presented on the dependence of the standard and variational multi-scale Smagorinsky models on the proximity of the LES filter width Delta to the integral length scale of turbulence L on the one hand, and to the Kolmogorov scale eta on the other hand. Moreover modifications of the models are formulated, which respond better to Delta/eta changes. Apart from a priori evaluations of L/Delta and Delta/eta effects, the quality of our proposed modifications to the models is further evaluated and corroborated based on LES of decaying homogeneous isotropic turbulence.","turbulence; modelling; large-eddy simulation; variational multi scale; Smagorinsky","en","conference paper","","","","","","","","","","","","","",""
"uuid:5e947fcf-c257-45c8-b750-0a942d5512d3","http://resolver.tudelft.nl/uuid:5e947fcf-c257-45c8-b750-0a942d5512d3","LES and URANS Unsteady Boundary Layer Strategies for Pulsating and Oscillating Turbulent Channel Flows Applications","Panara, D.; Porta, M.; Schoenfeld, T.","","2006","The use of wall functions has been investigated for LES and URANS numerical simulation in pulsating and oscillating channel flow applications. The results show that the wall function approach is accurate in the so-called quasi-steady regime but there are discrepancies with the experimental results in the intermediate frequency range. A special attention is given to the wall-shear stress prediction, and in particular on the wall-shear stress phase shift with respect to the free stream velocity. In order to capture such unsteady flow effects, the boundary layer needs to be resolved. Different approaches such as Low Reynolds Number near wall turbulence modeling (URANS) or the proposed Wall-Normal Resolved strategy (LES) seem to be suited for this purpose. The drawback is unfortunately the increasing of computational points in the boundary layer and consequently the higher computational costs.","fluid dynamics; turbulence; URANS; LES; pulsating flow; oscillating flow; near wall modeling; wall shear stress","en","conference paper","","","","","","","","","","","","","",""
"uuid:df2adbc6-0c02-4507-bf84-fbb7721916da","http://resolver.tudelft.nl/uuid:df2adbc6-0c02-4507-bf84-fbb7721916da","A Reinterpretation of the Non-Linear Galerkin Method as a Large Eddy Simulation Technique","Guermond, J.L.; Prudhomme, S.","","2006","The purpose of this paper is to show that the Fourier-based Nonlinear Galerkin Method (NLGM) constructs suitable weak solutions to the periodic Navier--Stokes equations in three dimensions. We re-interpret NLGM as a Large-Eddy Simulation technique (LES) and we rigorously deduce a relationship between the mesh size and the large-eddy scale.","NavierStokes equations; turbulence; large eddy simulation; nonlinear Galerkin method; suitable solutions","en","conference paper","","","","","","","","","","","","","",""