Compressibility effects in free shear layers

Abstract

High Reynolds number compressible free shear layers were studied experimentally to explore the effects of compressibility on the turbulence field. Previous preliminary results reported by the authors showed that the level and the lateral extent of turbulence fluctuations are reduced as the compressibility, which is characterized by a convective Mach number, is increased. The two convective Mach numbers used in the previous study were relatively close, Mc=0.51 and 0.64, and as a result the conclusions were not concrete. The present results with Mc=0.86 strongly support the earlier results, showing even higher reductions in the level and the lateral extent of Reynolds stresses. The higher-order moments of turbulence fluctuations such as skewness and flatness are reported, which show that the intermittency resulting from the excursion of large-scale structures into the free streams at the edge of shear layers was significantly reduced (both in the level and the extent) because of increased Mc. In the developing region of shear layers, development of mean flow and turbulence fluctuation profiles are reported that have similar trends seen in incompressible shear layers.