The present study is aimed at contributing to the development of supersonic mixing enhancement techniques for future scramjet engines. Since the compressibility effects strongly hampers the large scale turbulent motions it is indeed a real challenge to achieve the necessary mixing enhancement by means of turbulence control.
We have been working on the supersonic mixing enhancement using streamwise vortices in spanwise row-configuration experimentally at a freestream Mach number 2.5. Our experiments have shown a high possibility that the supersonic mixing can be much enhanced by using the streamwise vortices, in particular, a high rate of entrainment can be obtained during their formation stages. In the present study, a numerical simulation is conducted to verify the important conclusion obtained mainly from flow visualization. It is here stressed that the streamwise vortices in spanwise row-configuration are really powerful in enhancing the supersonic mixing.

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We have been working on the supersonic mixing enhancement using streamwise vortices. Experimentally at a freestream Mach number 2.5, this study examines the behaviour of wake shear layer and the small scale, alternately counter-rotating streamwise vortices in spanwise row, which are initially embedded in the shear layer. Another larger scale streamwise vortices are introdueced into the flow to observe their behaviour of interacting with and eventually engulfing these small scale vortices and shear layer. A number of Schlieren photographs show that the embedded vortices highly disturb the shear layer. The near-by large scale vortices are strongly disturbed by engulfing these smaller scale turbulent structures. It is inferred that strong vortical disturbances can develop within the large scale streamwise vortices at their formation when the weak shock waves governing the generation of streamwise vortices undergo oscillations. These results are very useful for the development of supersonic mixing enhancement techniques.

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