Turbulent, mixing of a scalar quantity in a 2-d mixing layer using matched asymptotic expansions

Abstract

In this note analytical solutions for the turbulent mixing of a scalar quantity (mass, temperature, etc.) for a 2-d, free shear flow are developed. Approximate, i.e. thin shear layer self-similar forms for mass, momentum and the scalar quantity are derived, linearized using Göertler’s [ZAMM 22 (1942) 244] perturbation argument and examined. Though successful for the mean velocity field, the regular expansion yields inconsistent solutions for the transport of a scalar. Sources of the non-uniformity are identified and a consistent result is obtained using matched asymptotic expansions. This result explains the success of semi-empirical convective velocity closures used by several researchers for a turbulence length scale equation.