Root influence on the unsteady characteristics of swept impinging oblique sblis

The influence of the root region on the unsteadiness of a swept impinging oblique SBLI has been investigated. Experiments are conducted at a nominal Mach number of 2.3 with a fully turbulent boundary layer (Re_θ = 5.5×10³ ). The SBLI is generated using a shock generator with deflection angle θ = 12.5^◦ and sweep angle ψ = 30.0^◦ . Low-frequency unsteadiness has been observed near the separation shock at frequencies approximately one order of magnitude below the characteristic frequency of the incoming boundary layer. A nearly constant low frequency is observed across the SBLI span despite increasing separation length. The unsteadiness is broadband near the root and becomes more focused toward the tip. This is accompanied by spanwise traveling ripples having an average speed of approximately 0.20U_∞ that accelerate toward the tip and are coherent with the low-frequency unsteadiness. Collectively, this led to a hypothesis that the root is imposing some length scale or dynamics that influence the global SBLI behavior. The hypothesis is assessed by installing a sub-boundary layer microramp upstream of the root to reduce its size while not affecting the quasi-infinite flow structure near the tunnel centerline. It is found that PSDs, correlations, coherence, and shock rippling speeds are almost completely unaffected by significant changes to the root structure. The exercise is repeated at the tip for completeness, but also shows little influence on the SBLI dynamics. Our previous observations showed there is a lack of upstream influence on the low-frequency unsteadiness. The present study suggests the source of unsteadiness is within the interaction (downstream mechanism).