Initial Development of Turbulent, Compressible Free Shear Layers

Abstract

The mixing zone between a two dimensional free stream and a fluid essentially at rest is studied experimentally and analytically. Turbulent shear layer velocity profiles were measured behind rearward facing steps and over cavities for equivalent free stream Mach numbers from 2.1 to 3.7, utilizing a wind tunnel wall boundary layer. Approximate methods are derived for calculating the shear layer change from an attached turbulent boundary layer to a fully developed free shear layer. A linearized equation of motion is used for the early stages of development, whereas the downstream stages are calculated by using a similarity profile. Both methods permit rapid calculations of the shear layer profile at any location along the mixing zone, without the necessity of determining the intermediate profiles. Comparison of the approximate methods with these experiments, and with experiments of other investigators, shows good agreement over the subsonic to supersonic Mach number range examined.