Calibrating passive scalar transport in shear-flow turbulence

TL;DR

This study uses numerical simulations to determine the turbulent diffusivity tensor in shear-flow turbulence, revealing how its components depend on flow parameters and are unaffected by helicity, with implications for modeling scalar transport.

Contribution

It provides a detailed numerical analysis of the turbulent diffusivity tensor in shear flows, including its dependence on flow parameters and the effects of helicity.

Findings

Diagonal components increase quadratically with Peclet and Reynolds numbers below 10.

Diffusivity components decrease Lorentzian with wave number.

Components are unaffected by turbulence helicity.

Abstract

The turbulent diffusivity tensor is determined for linear shear flow turbulence using numerical simulations. For moderately strong shear, the diagonal components are found to increase quadratically with Peclet and Reynolds numbers below about 10 and then become constant. The diffusivity tensor is found to have components proportional to the symmetric and antisymmetric parts of the velocity gradient matrix, as well as products of these. All components decrease with the wave number of the mean field in a Lorentzian fashion. The components of the diffusivity tensor are found not to depend significantly on the presence of helicity in the turbulence. The signs of the leading terms in the expression for the diffusion tensor are found to be in good agreement with estimates based on a simple closure assumption.