Compressibility and mixing in turbulent free shear layers

Experimental and numerical results from an investigation of compressible, turbulent shear layers are presented. In particular, the issues of compressibility and mixing in these flows are addressed. Two-component laser Doppler velocimeter (LDV) measurements reveal that the transverse turbulence intensity and normalized Reynolds shear stress decrease with increasing relative Mach number (compressibility), while the Reynolds stress correlation coefficient remains constant and the anisotropy increases. Two-dimensional digital images of Mie scattering signals demonstrate that large-scale, organized structures occur less frequently and are less well defined at high relative Mach numbers. Statistical processing of these images suggests that a preferred mixed fluid concentration does not occur in the shear layer under the current conditions. A new one-equation algebraic stress turbulence model with improved pressure-strain modeling is presented that accounts for variations in the anisotropy of the normal stresses. Results from the proposed model agree well with the detailed LDV data. In addition, transport modeling of a passive scalar is considered, with special emphasis given to modeling the unmixedness.