A priori and a posteriori tests of subgrid scale models for scalar transport

Abstract

A priori tests of subgrid scale (SGS) models for the transport of scalars by turbulence are performed by studying the transfer of scalar fluctuations between resolved and subgrid scales in a temporal mixing layer. They confirm that both forward and backward transfer are present, what can be best represented by mixed models (eddy-diffusivity+scale-similarity). However, a posteriori tests show that eddy-diffusivity models, even if only able to dissipate fluctuations from resolved to subgrid scales, give very similar results to mixed models, provided that an appropriate model is used for SGS stresses.