Hypersonic transitional shock-wave–boundary-layer interaction on a flat plate

This work presents an experimental and numerical study of hypersonic transitional shock-wave–boundary-layer interaction, wherein transition occurs between separation and reattachment in the detached shear layer. Experiments were conducted in a free-piston compression-heated Ludwieg tube that provided a Mach 5.8 flow at a freestream Reynolds number of 7 × 10⁶ m⁻¹. A shock generator deflected the flow by 10°, resulting in an oblique shock impinging on a flat plate. The shock triggered transition in the boundary layer and the formation of Görtler-like vortices downstream of reattachment. Heat flux and pressure distributions on the plate were measured globally using infrared thermography and pressure-sensitive paint. Oil film visualization was employed to evaluate the boundary-layer reattachment. Numerical results consist of Reynolds-averaged Navier–Stokes and fully laminar steady-state three-dimensional simulations. Shock-induced transition is considered to be the cause of the overshoot in peak pressure and peak heating of approximately 15%, in agreement with previous studies. Görtler instability, triggered by the concave nature of the bubble at separation, is identified as the main mechanism leading to boundary-layer transition, resulting in heat-flux variations of less than 30%. By comparing numerical results against thermographic values it is possible to delineate the extent of transition. Within this region, the disturbance amplification factor was estimated to be approximately between 6 and 10, in reasonable agreement with other relevant numerical and experimental data.