Molecular and stratification effects on the evolution of concentration fluctuations in decaying homogeneous turbulence with transverse mean-concentration gradient

Transport of a passive scalar contaminant in nearly isotropic non-decaying turbulence was first studied theoretically by Corrsinl, and in that study it was predicted that an imposed passive linear cross-stream mean temperature profile will maintain itself and will be independent of the downstream distance. Corrsin’s prediction of constancy of the cross-stream temperature gradient, ß, has been confirmed experimentally for decaying turbulent flows^2,3,4. Despite the constancy of ß there has been confusing experimental data on the streamwise evolution of passive scalar contaminants. The heated grid method used by Wiskind2 to study the streamwise evolution of passive scalar has been found to be far from ideal because significant transverse variation of temperature variance was observed in Wiskind’s data^3,4. The use of differentially heated screens downstream of a grid^3,4 has aided the study of the streamwise evolution of passive scalar fluctuations, but there still remains some uncertainties in the physics of this type of flow particularly at large decay times.