Requirements and sensitivity analysis of RANS-free wall-modeled LES

TL;DR

This paper investigates how different modeling choices and numerical setups affect the accuracy and robustness of wall-stress predictions in RANS-free wall-modeled LES of turbulent channels, aiming to improve model reliability.

Contribution

It provides a systematic analysis of sensitivities in dynamic wall models to various simulation parameters and proposes mitigation strategies for enhanced robustness.

Findings

SGS model sensitivity is reduced when the SGS stress fraction is constant.

Hexagonal grids decrease numerical sensitivities.

Sensitivity to boundary conditions and numerics can be mitigated with specific configurations.

Abstract

We study the sensitivity of wall model input variables to the modeling choices of the outer LES. This work is motivated by sensitivities observed in dynamic slip wall models. These dynamic wall models use variables from the near-wall LES solution as inputs to predict the wall stress without relying on a priori coefficients or equilibrium assumption. Mitigating the sensitivities in the wall model inputs allows development of robust dynamic wall models. The effects of SGS model, boundary condition type, numerics, and mesh topology are assessed through a series of WMLES calculations of turbulent channels. Probability density functions are computed from planes of the WMLES solutions at a wall-normal sampling height and are used as a metric for sensitivity. Sensitivity to SGS model is alleviated when the fraction of total wall stress carried by the SGS model is held constant. Use of hexagonal close-packed grids mitigated numerical sensitivities.