Experimental evidence for non-linear growth in compressible mixing layer

An experimental study of compressible mixing layers （CMLs） was conducted using planar laser Mie scattering （PLMS） visualiza- tions from condensed ethanol droplets in the flow. Large ensembles of digital images were collected for two flow conditions at convective Mach numbers Mc = 0.11 and 0.47. The coherent vortices, braids and eruptions in the mixing zone were observed, interpreted as evidence of multi-scale, three-dimensional structures at a high Reynolds number. The mixing layers with a large visualized range present two stages along the streamwise direction, corresponding to the initial mixing and the well-developed stage. A new method, the gray level ensemble average method （GLEAM）, by virtue of the similarity of the mixing layer, was applied to measure the growth rate of the CML thickness. New evidence for a nonlinear growth of CML is reported, providing an interpretation of previous observations of the scattering of the growth rate.