Secondary instabilities of Görtler vortices in high-speed boundary layer flows

Abstract eng:
Gortler vortices developed in laminar boundary layer experience remarkable changes when the flow is subj ected to compressibil- ity effect. In the present study, five Ma numbers, covering incompressible to hypersonic flows, at Ma : 0.015, 1.5, 3.0, 4.5 and 6.0 are specified to illustrate this compressibility effect. G'ortler vortices in subsonic and moderate supersonic flows (Ma : 0.015, 1.5, 3.0) are governed by the conventional wall-layer mode (mode W). In hypersonic flows (Ma : 4.5, 6.0), the trapped-layer mode (mode T) becomes dominant. This difference maintains and intensifies downstream leading to different scenarios of secondary instabilities. The secondary instabilities of G'ortler vortices set in when the resulting streaks are adequately developed. The secondary perturbations become unstable downstream following the sequence of sinuous mode type I, varicose mode and sinuous mode type 11 indicating an increasing threshold amplitude. Onset conditions are determined for these modes. The above three modes each can have the largest growth rate under the right conditions.

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