Michael Breuer

Bio: Michael Breuer is an academic researcher from Helmut Schmidt University. The author has contributed to research in topics: Turbulence & Reynolds number. The author has an hindex of 40, co-authored 203 publications receiving 5974 citations. Previous affiliations of Michael Breuer include Karlsruhe Institute of Technology & University of Erlangen-Nuremberg.

Accurate computations of the laminar flow past a square cylinder based on two different methods : lattice-Boltzmann and finite-volume

Abstract: The confined flow around a cylinder with square cross-section mounted inside a plane channel (blockage ratio B=1/8) was investigated in detail by two entirely different numerical techniques, namely a lattice-Boltzmann automata (LBA) and a finite-volume method (FVM). In order to restrict the approach to 2D computations, the largest Reynolds number chosen was Re=300 based on the maximum inflow velocity and the chord length of the square cylinder. The LBA was built up on the D2Q9 model and the single relaxation time method called the lattice-BGK method. The finite-volume code was based on an incompressible Navier–Stokes solver for arbitrary non-orthogonal, body-fitted grids. Both numerical methods are of second-order accuracy in space and time. Accurate computations were carried out on grids with different resolutions. The results of both methods were evaluated and compared in detail. Both velocity profiles and integral parameters such as drag coefficient, recirculation length and Strouhal number were investigated. Excellent agreement between the LBA and FVM computations was found.

Large eddy simulation of the subcritical flow past a circular cylinder: numerical and modeling aspects

Abstract: SUMMARY The turbulent flow past a circular cylinder (Re=3900) was computed by large eddy simulation (LES). The objective was not to investigate the physical phenomena of this flow in detail but to study numerical and modeling aspects which influence the quality of LES solutions. Concerning the numerical method, the most important component is the discretization of the non-linear convective fluxes. Five different schemes were investigated. Also, the influence of different grid resolutions was examined. Two aspects play an important role on the modeling side, namely the near-wall model and the subgrid scale model. Owing to the restriction to low Reynolds numbers in this study, no-slip boundary conditions were used at solid walls. Therefore, only the second aspect was taken into account. Two different subgrid scale models were applied. Additionally, LES computations without any subgrid scale modeling were carried out in order to prove the performance of the models. The results were evaluated by comparison with available experimental data. © 1998 John Wiley & Sons, Ltd.

A challenging test case for large eddy simulation: high Reynolds number circular cylinder flow

Abstract: A thorough numerical investigation of high Reynolds number ( Re =140,000) circular cylinder flow was performed based on large eddy simulation (LES). The objective was to evaluate the applicability of LES for practically relevant high- Re flows and to investigate the influence of subgrid scale modeling and grid resolution on the quality of the predicted results. Because the turbulent von Karman vortex street past circular cylinders involves most of the characteristic features of technical applications, it is an ideal test case for this purpose. Based on a parallelized finite-volume Navier–Stokes solver, computations were carried out on a series of grids applying both the Smagorinsky and the dynamic subgrid scale model. The simulations yielded information on the time-averaged flow field, the resolved Reynolds stresses and integral parameters such as drag coefficient, recirculation length and Strouhal number. The results were analyzed in detail and compared with experimental data. In general, the LES results agreed fairly well with the experimental data, especially in the near wake. Owing to the coarse resolution in the far wake, larger deviations were observed here. As expected, the importance of the subgrid scale model significantly increased for the high- Re case in comparison with a low- Re case predicted earlier. A critical issue for LES is grid refinement which did not automatically lead to an improved agreement between the predicted results and the experimental measurements. Possible explanations are offered in the paper.

Flow over periodic hills – Numerical and experimental study in a wide range of Reynolds numbers

Abstract: The paper presents a detailed analysis of the flow over smoothly contoured constrictions in a plane channel. This configuration represents a generic case of a flow separating from a curved surface with well-defined flow conditions which makes it especially suited as benchmark case for computing separated flows. The hills constrict the channel by about one third of its height and are spaced at a distance of 9 hill heights. This setup follows the investigation of Frohlich et al. [Frohlich J, Mellen CP, Rodi W, Temmerman L, Leschziner MA. Highly resolved large-eddy simulation of separated flow in a channel with streamwise periodic constrictions. J Fluid Mech 2005;526:19–66] and complements it by numerical and experimental data over a wide range of Reynolds numbers. We present results predicted by direct numerical simulations (DNS) and highly resolved large-eddy simulations (LES) achieved by two completely independent codes. Furthermore, these numerical results are supported by new experimental data from PIV measurements. The configuration in the numerical study uses periodic boundary conditions in streamwise and spanwise direction. In the experimental setup periodicity is achieved by an array of 10 hills in streamwise direction and a large spanwise extent of the channel. The assumption of periodicity in the experiment is checked by the pressure drop between consecutive hill tops and PIV measurements. The focus of this study is twofold: (i) Numerical and experimental data are presented which can be referred to as reference data for this widely used standard test case. Physical peculiarities and new findings of the case under consideration are described and confirmed independently by different codes and experimental data. Mean velocity and pressure distributions, Reynolds stresses, anisotropy-invariant maps, and instantaneous quantities are shown. (ii) Extending previous studies the flow over periodic hills is investigated in the wide range of Reynolds numbers covering 100 ⩽ Re ⩽ 10 , 595 . Starting at very low Re the evolution and existence of physical phenomena such as a tiny recirculation region at the hill crest are documented. The limit to steady laminar flow as well as the transition to a fully turbulent flow stage are presented. For 700 ⩽ Re ⩽ 10 , 595 turbulent statistics are analyzed in detail. Carefully, undertaken DNS and LES predictions as well as cross-checking between different numerical and experimental results build the framework for physical investigations on the flow behavior. New interesting features of the flow were found.

A new version of detached-eddy simulation, resistant to ambiguous grid densities

Abstract: Detached-eddy simulation (DES) is well understood in thin boundary layers, with the turbulence model in its Reynolds-averaged Navier–Stokes (RANS) mode and flattened grid cells, and in regions of massive separation, with the turbulence model in its large-eddy simulation (LES) mode and grid cells close to isotropic. However its initial formulation, denoted DES97 from here on, can exhibit an incorrect behavior in thick boundary layers and shallow separation regions. This behavior begins when the grid spacing parallel to the wall Δ∥ becomes less than the boundary-layer thickness δ, either through grid refinement or boundary-layer thickening. The grid spacing is then fine enough for the DES length scale to follow the LES branch (and therefore lower the eddy viscosity below the RANS level), but resolved Reynolds stresses deriving from velocity fluctuations (“LES content”) have not replaced the modeled Reynolds stresses. LES content may be lacking because the resolution is not fine enough to fully support it, and/or because of delays in its generation by instabilities. The depleted stresses reduce the skin friction, which can lead to premature separation.

Scale-Invariance and Turbulence Models for Large-Eddy Simulation

Abstract: ▪ Abstract Relationships between small and large scales of motion in turbulent flows are of much interest in large-eddy simulation of turbulence, in which small scales are not explicitly resolved and must be modeled. This paper reviews models that are based on scale-invariance properties of high-Reynolds-number turbulence in the inertial range. The review starts with the Smagorinsky model, but the focus is on dynamic and similarity subgrid models and on evaluating how well these models reproduce the true impact of the small scales on large-scale physics and how they perform in numerical simulations. Various criteria to evaluate the model performance are discussed, including the so-called a posteriori and a priori studies based on direct numerical simulation and experimental data. Issues are addressed mainly in the context of canonical, incompressible flows, but extensions to scalar-transport, compressible, and reacting flows are also mentioned. Other recent modeling approaches are briefly introduced.

Strategies for turbulence modelling and simulations

Abstract: This is an attempt to clarify and size up the many levels possible for the numerical prediction of a turbulent flow, the target being a complete airplane, turbine, or car. Not all the author’s opinions will be accepted, but his hope is to stimulate reflection, discussion, and planning. These levels still range from a solution of the steady Reynolds-Averaged Navier‐Stokes (RANS) equations to a Direct Numerical Simulation, with Large-Eddy Simulation in between. However recent years have added intermediate strategies, dubbed ‘‘VLES’’, ‘‘URANS’’ and ‘‘DES’’. They are in experimental use and, although more expensive, threaten complex RANS models especially for bluA-body and similar flows. Turbulence predictions in aerodynamics face two principal challenges: (I) growth and separation of the boundary layer, and (II) momentum transfer after separation. (I) is simpler, but makes very high accuracy demands, and appears to give models of higher complexity little advantage. (II) is now the arena for complex RANS models and the newer strategies, by which time-dependent three-dimensional simulations are the norm even over two-dimensional geometries. In some strategies, grid refinement is aimed at numerical accuracy; in others it is aimed at richer turbulence physics. In some approaches, the empirical constants play a strong role even when the grid is very fine; in others, their role vanishes. For several decades, practical methods will necessarily be RANS, possibly unsteady, or RANS/LES hybrids, pure LES being unaAordable. Their empirical content will remain substantial, and the law of the wall will be particularly resistant. Estimates are oAered of the grid resolution needed for the application of each strategy to full-blown aerodynamic calculations, feeding into rough estimates of its feasibility date, based on computing-power growth. ” 2000 Elsevier Science Inc. All rights reserved.

Detached-Eddy Simulation

Abstract: Detached-eddy simulation (DES) was first proposed in 1997 and first used in 1999, so its full history can be surveyed. A DES community has formed, with adepts and critics, as well as new branches. The initial motivation of high–Reynolds number, massively separated flows remains, for which DES is convincingly more capable presently than either unsteady Reynolds-averaged Navier-Stokes (RANS) or large-eddy simulation (LES). This review discusses compelling examples, noting the visual and quantitative success of DES. Its principal weakness is its response to ambiguous grids, in which the wall-parallel grid spacing is of the order of the boundary-layer thickness. In some situations, DES on a given grid is then less accurate than RANS on the same grid or DES on a coarser grid. Partial remedies have been found, yet dealing with thickening boundary layers and shallow separation bubbles is a central challenge. The nonmonotonic response of DES to grid refinement is disturbing to most observers, as is the absence of...