Detailed investigation of subgrid scale models in large-eddy simulation using high aspect-ratio grid spacing

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2 Citations (Scopus)

Abstract

In large eddy simulation (LES), we generally use information of the grid width in representing a filter width (Δ) to evaluate a subgrid scale (SGS) model. In practical applications, however, the grid widths are largely different in the streamwise and cross-streamwise directions, resulting in grid cells having high aspect ratios. In such a case, we often adopt the cube root of the grid-cell volume for the filter width; i.e., Δ = (Δ x Δ y Δ z)1/3 in the Cartesian grid system. Although this has been regarded as a standard way to determine the filter width, its superiority over other strategies, such as using the maximum width in all directions (i.e., Δ = max (Δ x, Δ y, Δ z)), has not always been made clear. In this paper, to investigate the effect of the definition of a filter width on the prediction accuracy of an SGS model, we report on a priori tests of several SGS models using highly resolved LES data of a backward-facing step flow. We focus particularly on the model performance in the shear layer downstream of a step, where there exists a strong velocity gradient and the aspect ratio of a grid cell is high despite the region being far from wall surfaces. This investigation enables us to distinguish the effect of the grid aspect ratio from that of near-wall damping. We make the important finding that the cube root of a grid-cell volume is not always appropriate for the filter width. To evaluate an SGS model properly, the effect of a grid width in one direction much smaller than in other directions must be excluded in determining the filter width.

Original languageEnglish
Article number115120
JournalPhysics of Fluids
Volume33
Issue number11
DOIs
Publication statusPublished - Nov 1 2021

All Science Journal Classification (ASJC) codes

  • Computational Mechanics
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering
  • Fluid Flow and Transfer Processes

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