Effects of compressibility on the characteristics of free shear layers

A high Reynolds number two-dimensional constant pressure compressible shear layer was formed at the trailing edge of a 0.5 mm-thick splitter plate. Convective Mach numbers of 0.51 and 0.64 were investigated using a two-component coincident LDV for the measurements. For the lower convective Mach number case, the nondimensionalized shear-layer and vorticity thickness growth rates were over 20% higher and the momentum thickness growth rate was over 30% higher than those of the higher convective Mach number case. Scaling the lateral dimension of shear layer with the local vorticity thickness collapsed all the mean velocity results for available convective Mach numbers between 0 and 1 from these experiments and the experiments of other investigators. However, when using the local momentum thickness instead of the vorticity thickness, a convective Mach number dependent linear transformation was necessary to collapse the velocity profiles. The lateral turbulence intensity, shear stress, and lateral transport of kinetic energy all nondimensionalized, with the velocity difference across the shear layer showing reduced levels for the higher convective Mach number case. The results seem to indicate that both small scale and large scale mixing are reduced with increasing convective Mach number.