Temperature gradient effects on the transition to turbulence in hypersonic flow

What is it about?

The prediction of boundary-layer transition from laminar to turbulent has repeatedly been placed in the forefront of design concerns for hypersonic vehicles. It has been predicted that the temperature ratio between the vehicle surface and the freestream can drastically alter the stability and transition of hypersonic boundary layers. It has also been shown that both blunt and slender bodies alike experience the condition where the surface is cooler than the freestream. While predictions indicate that lowering the wall-to-edge temperature ratio destabilizes instabilities known as the second mode, the majority of hypersonic tunnels are limited to relatively high wall-to-edge temperature ratios (3 or higher). In this study, we investigate the effect of the wall-to-edge temperature on the stability of a slender cone. Using active probe cooling, liquid-nitrogen injection, and thermal insulation, we construct a system capable of decreasing the model temperature by 85C. Four cooling levels are tested, and the resulting effects on boundary-layer height, structure angle, and second-mode frequency content, are compared. Spectral results are compared to numerical predictions computed using Linear Stability Theory.

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Photo by NASA on Unsplash

Photo by NASA on Unsplash