Delaying Görtler-Vortex-Induced Hypersonic Boundary-Layer Transition Utilizing Streamwise Grooves

What is it about?

Grooves can attenuate secondary instability of Görtler vortices when placed at the center of Görtler streaks over a concave wall. Combined experimental studies with calculations are performed based on direct numerical simulations (DNS) and Bi-global stability analysis to discover the delaying mechanism. A delaying mechanism by grooves is proposed: grooves with spacings corresponding to the wavelength of primitive Görtler vortices reduce the streamwise velocity gradients, which act as the source of the disturbance energy. Thus, the growth rate of sinuous secondary instability mode of Görtler vortices is reduced efficiently, leading to the delay of boundary layer transition. Next, the effect of phase difference between grooves and stationary Görtler vortices on hypersonic boundary layer transition is also investigated. Finally, preliminary experimental results are obtained, showing a qualitative agreement with the numerical results.

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