Experiment on nonliner growth of supersonic mixing layers

Abstract eng:
It is known that large scale structures play important role in the growth of supersonic mixing layer, and a great deal of experimental works focused on the characteristics and functions of large scale structure in the past, unfortunately, little experiments have been conducted on the spatial evolution of these structures up to now, which may be helpful to solve the issues of growth rate. In the present study, the evolution of large scale structures of the planar supersonic mixing layer at convective Mach numbers of 0.25, 0.5 and 0.7, respectively formed by the streams with the responding Mach number combination of 2.0 & 1.5, 3.0 & 2.0 and 2.0 & 0.6, is visualized using a planar laser Mie scattering (PLMS) technique. The instantaneous images at convective Mach number of 0.25 are respectively obtained by seeding ethanol vapor as a marker in one stream in each experiment, and those at convective Mach numbers of 0.5 and 0.7 were obtained by seeding the ethanol vapor in the stream of Mach number 2.0. The results show that the spatial evolution of large scale structures is comprised primarily of three parts, which is in some degree consistent with the structural investigations of linear stability theory. The different growth rates of large scale structure in the three parts suggest that only one coefficient used as previous investigations is not enough to represent the growth rate of supersonic mixing layer. Specific issues regarding the description of growth rate are discussed in detail.

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