Reinitiation and feedback in global instabilities of subsonic spatially developing mixing layers

Abstract
Two-dimensional numerical simulations of compressible, spatially evolving, unforced planar shear flows are used to investigate the role of feedback in the reinitiation of vortex roll up. The calculated pattern of coherent structures shows global self-sustaining instabilities in which new vortex roll ups are triggered in the initial shear layer by pressure disturbances originating in the fluid accelerations downstream. This reinitiation mechanism, absent in the linear treatments of stability, is demonstrated conclusively here.

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