Influence of inlet pressure conditions on supersonic turbulent mixing layers

The effect of nonisobaric initial conditions on a highly compressible (M(c)=1), supersonic mixing layer is studied experimentally. Mean flow characteristics and turbulent fields are measured with a two-dimensional laser Doppler velocimeter in a high Reynolds number supersonic wind tunnel. Mean longitudinal velocity profiles, vorticity thickness growth rate, longitudinal and lateral turbulent intensities, shear stress, and flatness and skewness factors of longitudinal velocities fluctuations are given for the isobaric and nonisobaric configurations. Results show that the asymptotic state of the mixing layer is the same whatever the inlet pressure condition is (in the range covered by the present experiment). The only apparent effect of the initial pressure ratio is to accelerate the transition between the initial boundary-layer state and the asymptotic mixing-layer configuration. The present results are also compared with existing literature. Both the isobaric and nonisobaric data collapse quite well with other experiments. It has to be noted that the present results confirm that the Reynolds stress tensor anisotropy seems to be unaffected by compressibility until convective Mach number close to unity. (C) Elsevier Science Inc., 1997.