Effects of secondary instability on Mixing in a compressible shear layer were investigated, experimentally and analytically. In experiments, a blow down type wind tunnel was used. Air was injected at a subsonic speed in parallel direction with a co-flowing supersonic air stream, forming a compressible “double” shear layer. The Mach numbers of each stream were 0.29 and 1.78, respectively. By means of sine curved trailing edges, streamwise vortices are induced into the flow. In order to investigate effects of the phase differences, the in-phase and 180 deg out-of-phase trailing edges were used. While the distortions of the shear layer, due to the streamwise vortices, are the same amplitudes for the both cases, only for 180 deg out-of-phase trailing edge, growth rate of the shear layer is increased. The experimental results were investigated in the viewpoint of flow instability. The stability characteristics were investigated according to order of appearance of instabilities. A laminar shear layer is unstable to disturbances, and spanwise vortices are formed (Primary instability). The periodic flow containing such spanwise vortices are unstable to other disturbances and the vortices are distorted (Secondary instability). By the stability analysis, such vortex distortions are predicted.
展开▼
