The effects of injection and main flow conditions on the turbulent structure produced by a gaseous sonic transverse injection into a supersonic airstream were investigated. The turbulent structure inherent in the mixing flowfield was characterized by the single-time two-point spatial correlations based on the concentration fluctuation and measured with acetone planar laser-induced fluorescence. Results revealed that the most intensively fluctuating region appeared on the 50%-averaged-concentration track, irrespective of the injection conditions. The highly correlated region, which indicates an organized large-scale structure, appeared as a tilting ellipse in the lower-compressibility cases andan ellipse almost parallel to the streamline in the higher-compressibility cases. These differences in structure result in the difference of the averaged jet width. Theinjection with the higher-compressibility condition showedmore stable structures and slower development in the size due to suppression of the instability growth. The structure was likely to be stretched toward the averaged-velocity direction as the main flow Mach number increased. Increasing the velocity difference between the jet and main flow caused the large-scale eddies to appear more frequently.
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