On the energy dissipation rate of ensemble eddy viscosity models of turbulence: Shear flows

TL;DR

This paper investigates whether ensemble eddy viscosity models for turbulence, which directly compute turbulent viscosity from ensemble averages, tend to over-diffuse solutions, especially near walls.

Contribution

It analyzes the energy dissipation rate in ensemble eddy viscosity models for shear flows, addressing the potential over-diffusion issue.

Findings

Ensemble models can accurately capture near-wall behavior.

The study provides conditions under which over-diffusion occurs.

Ensemble approach offers a simpler alternative to classical models.

Abstract

Classical eddy viscosity models add a viscosity term with turbulent viscosity coefficient developed beginning with the Kolmogorov-Prandtl parameterization. Approximations of unknown accuracy of the unknown mixing lengths and turbulent kinetic energy are typically constructed by solving associated systems of nonlinear convection-diffusion-reaction equations with nonlinear boundary conditions. Often these over-diffuse so additional fixes are added such as wall laws or using different approximations in different regions (which must also be specified). Alternately, one can solve an ensemble of NSE's with perturbed data, compute the ensemble mean and fluctuation and simply compute directly the turbulent viscosity parameterization. This idea is recent, seems to be of lower complexity and greater accuracy and produces parameterizations with the correct near wall asymptotic behavior. The question then arises: Does this ensemble eddy viscosity approach over-diffuse solutions? This question is addressed herein.