A Library for Wall-Modelled Large-Eddy Simulation Based on OpenFOAM Technology

TL;DR

This paper introduces an open-source wall-modelled LES library based on OpenFOAM, enhancing turbulence simulation efficiency by accurately modeling near-wall regions with various wall-stress models, validated on channel flow and backward-facing step flow.

Contribution

The work presents a flexible, extensible OpenFOAM-based library for wall-stress modeling in WMLES, including algebraic and ODE-based models, with systematic validation on canonical flows.

Findings

Algebraic wall model based on Spalding's law performs well.

Second-order schemes with 27000 cells per δ³ yield accurate results.

Pressure-gradient-inclusive models are less accurate in tested cases.

Abstract

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-of-the-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 was achieved using a mildly dissipative second-order accurate scheme for the convective fluxes applied on an isotropic grid with 27000 cells per $\delta^3$-cube, where $\delta$ is the thickness of the TBL or the half-height of the channel. 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.