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Several compressible mixing layers, with one supersonic and one subsonic streams, are experimentally analyzed by pressure measurements and laser anemometry. Detailed measurements of the mean and fluctuating velocity fields are provided and compared against data from incompressible flows. The effects of compressibility on the flows are observed. The spreading rate of the mixing layers decrease when the Mach number is increased, in good agreement with results found in the literature. Laser Doppler measurements are performed for three test cases. The compressibility effects on the fluctuation levels are discussed and compared with existing results. The evolution of the turbulence structure of the flow, when the convective Mach number increases, is considered in the analysis when separate LDA seeding regimens are employed on the two sides of the layers. Some modifications of the large scale organization are observed when supersonic and subsonic mixing layers are compared and the two sides of the supersonic mixing layers have different characteristics.

An experimental investigation of plane supersonic mixing layers is presented with emphasis on the compressibility effects on the large scale structures. It is well known that, in incompressible mixing layers, 2D large scale structures predominate and play a major role in the development of the flow. In the case of supersonic mixing layers, this organization seems to be strongly affected by the compressibility. In this study, laser-planogram visualizations are associated with hot-wire rake (HWR) measure ments to examine the turbulent organization of supersonic mixing layers for various regimes. From the HWR measurements, a scalar Proper Orthogonal decomposition (POD) based on the longitudinal component of the velocity is applied. The Pseudo-Flow-Visualization (PFV) is used to analyze the HWR signals. These results are then compared with equivalent ones obtained in the subsonic regime.

Three compressible mixing layers, with one supersonic and one subsonic streams, for convective Mach numbers of 0.525, 0.535 and 0.64 are experimentally studied by laser anemometry. Detailed measurements of the mean and fluctuating velocity fields are provided and compared with incompressible ones.