On Grid Resolution Requirements for Les of Wall-Bounded Flows

Rezaeiravesh, Saleh; Liefvendahl, Mattias; Fureby, Christer

doi:10.7712/100016.2345.7105

Cited by 6 publications

(5 citation statements)

References 17 publications

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“…This motivates introducing special modelling for the inner region, essentially aiming to resolve only the larger flow structures in the boundary layer, on the length scale δ, and model the effect of smaller structures, of length scale δ ν . This general approach is referred to as wall-modelled LES (WMLES), for which the required number of grid points scales only linearly with Re [10,43], thus significantly extending the range of affordable Re-numbers.…”

Section: Introductionmentioning

confidence: 99%

A library for wall-modelled large-eddy simulation based on OpenFOAM technology

Mukha

Rezaeiravesh

Liefvendahl

2019

Computer Physics Communications

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This work presents a feature-rich open-source library for wall-modelled large-eddy simulation (WMLES), which is a turbulence modelling approach that reduces the computational cost of traditional (wall-resolved) LES by introducing special treatment of the inner region of turbulent boundary layers (TBLs). The library is based on OpenFOAM and enhances the general-purpose LES solvers provided by this software with state-ofthe-art wall modelling capability. In particular, the included wall models belong to the class of wall-stress models that account for the under-resolved turbulent structures by predicting and enforcing the correct local value of the wall shear stress. A review of this approach is given, followed by a detailed description of the library, discussing its functionality and extensible design. The included wall-stress models are presented, based on both algebraic and ordinary differential equations. To demonstrate the capabilities of the library, it was used for WMLES of turbulent channel flow and the flow over a backward-facing step (BFS). For each flow, a systematic simulation campaign was performed, in order to find a combination of numerical schemes, grid resolution and wall model type that would yield a good predictive accuracy for both the mean velocity field in the outer layer of the TBLs and the mean wall shear stress. The best result, ≈ 1% error in the above quantities, was achieved for channel flow using a mildly dissipative second-order accurate scheme for the convective fluxes applied on an isotropic grid with 27 000 cells per δ 3 -cube, where δ is the channel half-height. In the case of flow over a BFS, this combination led to the best agreement with experimental data. An algebraic model based on Spalding's law of the wall was found to perform well for both flows. On the other hand, the tested more complicated models, which incorporate the pressure gradient in the wall shear stress prediction, led to less accurate results. PROGRAM SUMMARYProgram Title: libWallModelledLES Licensing provisions:GPLv3 Programming language: C++ Nature of problem: Large-eddy simulation (LES) is a scale-resolving turbulence modelling approach providing a high level of predictive accuracy. However, LES of high Reynolds number wall-bounded flows is prohibitively computationally expensive due to the need for resolving the inner region of turbulent boundary layers (TBLs) [1]. This inhibits the application of LES to many industrially relevant flows [2] and prompts for the development of novel modelling techniques that would modify the LES approach in a way that allows it to retain its accuracy (at least away from walls) yet significantly lowers its computational cost. Solution method: Wall-modelled LES (WMLES) is an approach that is based on complementing LES with special near-wall modelling that allows to leave the inner layer of TBLs unresolved by the computational grid. Many types * Principal Corresponding Author

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Section: Introductionmentioning

confidence: 99%

A library for wall-modelled large-eddy simulation based on OpenFOAM technology

Mukha

Rezaeiravesh

Liefvendahl

2019

Computer Physics Communications

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“…To simultaneously evaluate the procedures to compute the outer scales and the growth rate of the boundary layer, the evolution of Re θ = θU 0 /ν in the streamwise direction is considered. The following power-law estimate connecting Re θ and Re x is used as reference data [28] Re θ = 0.0167 • Re 0.846 x + 373.83.…”

Section: Resultsmentioning

confidence: 99%

“…The obtained values are shown in Figure 13. The DNS data by Schlatter and Örlü [30] and a power law estimate from [28] are used as reference. Excellent agreement with both is found.…”

Section: Resultsmentioning

confidence: 99%

“…The strip of cells where the source term is active is 2 cm long, 3 mm high and stretches across the whole domain in the spanwise direction. For the purpose of mesh generation, the flow is considered fully turbulent at x 0 = 0.4 m. This estimate is inserted into the following power law [28] to obtain the distribution of δ in the domain:…”

Section: Flat-plate Turbulent Boundary Layer 421 Simulation Set-upmentioning

confidence: 99%

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Predictive Accuracy of Wall-Modelled Large-Eddy Simulation on Unstructured Grids

Mukha¹,

Bensow²,

Liefvendahl³

2020

Preprint

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The predictive accuracy of wall-modelled LES is influenced by a combination of the subgrid model, the wall model, the numerical dissipation induced primarily by the convective numerical scheme, and also by the density and topology of the computational grid. The latter factor is of particular importance for industrial flow problems, where unstructured grids are typically employed due to the necessity to handle complex geometries. Here, a systematic simulation-based study is presented, investigating the effect of grid-cell type on the predictive accuracy of wall-modelled LES in the framework of a general-purpose finitevolume solver. Following standard practice for meshing near-wall regions, it is proposed to use prismatic cells. Three candidate shapes for the base of the prisms are considered: a triangle, a quadrilateral, and an arbitrary polygon. The cell-centre distance is proposed as a metric to determine the spatial resolution of grids with different cell types. The simulation campaign covers two test cases with attached boundary layers: fully-developed turbulent channel flow, and a zero-pressure-gradient flat-plate turbulent boundary layer. A grid construction strategy is employed, which adapts the grid metric to the outer length scale of the boundary layer. The results are compared with DNS data concerning mean wall shear stress and profiles of flow statistics. The principle outcome is that unstructured simulations may provide the same accuracy as simulations on structured orthogonal hexahedral grids. The choice of base shape of the near-wall cells has a significant impact on the computational cost, but in terms of accuracy appears to be a factor of secondary importance.

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“…The discussion of the features of turbulucid, as well as its design and implementation, is continued in the sections below. Examples of applying turbulucid to post-processing of simulations of various flows can be found in [3][4][5][6]. This includes flat-plate turbulent boundary layer flow, flow around a ship hull, and also flow around a submarine-like axisymmetric body.…”

Section: Introductionmentioning

confidence: 99%

Turbulucid: A Python Package for Post-Processing of Fluid Flow Simulations

Mukha

2018

JORS

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A Python package for post-processing of plane two-dimensional data from computational fluid dynamics simulations is presented. The package, called turbulucid, provides means for scripted, reproducible analysis of large simulation campaigns and includes routines for both data extraction and visualization. For the former, the Visualization Toolkit (VTK) is used, allowing for post-processing of simulations performed on unstructured meshes. For visualization, several matplotlib-based functions for creating highly customizable, publication-quality plots are provided. To demonstrate turbulucid's functionality it is here applied to post-processing a simulation of a flow over a backward-facing step. The implementation and architecture of the package are also discussed, as well as its reuse potential.

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On Grid Resolution Requirements for Les of Wall-Bounded Flows

Cited by 6 publications

References 17 publications

A library for wall-modelled large-eddy simulation based on OpenFOAM technology

A library for wall-modelled large-eddy simulation based on OpenFOAM technology

Predictive Accuracy of Wall-Modelled Large-Eddy Simulation on Unstructured Grids

Turbulucid: A Python Package for Post-Processing of Fluid Flow Simulations

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