Experimental Study of Swept Impinging Oblique Shock/Boundary-Layer Interactions

An experimental investigation has been conducted on swept impinging oblique shock/boundary-layer interactions at a nominal Mach number of 2.28 with a fully turbulent incoming boundary layer (Reθ=5500). The swept impinging oblique shock is induced by shock generators with x-y plane deflection angle θ=12.5 deg and various x-z plane sweep angles ψ=15.0, 22.5, 30.0, and 40.0 deg. Oil flow visualization, mean pressure measurements, and high-bandwidth pressure transducers are used to provide detailed characterization of the mean and unsteady features of the shock/boundary-layer interactions. Large-scale separation is observed in all cases with spanwise growth especially evident at high shock generator sweep angles. Near the onset of separation in the central region of the tunnel (quasi-infinite span zone), mean pressures are independent of span and scale cylindrically. However, mean pressures at reattachment for higher sweep angles display mild spanwise dependence, suggesting the overall mean flow topology of the shock/boundary-layer interaction is conical. Unsteady pressure measurements beneath the separation shock foot show clear low-frequency unsteadiness, orders of magnitude below that of the incoming boundary layer. As the sweep is increased, the frequency of the separation shock motion is also increased. Specific analysis of the ψ=30.0 deg configuration shows spanwise accelerating ripples of relatively constant frequency that propagate along the shock foot, suggesting that the wavelength of these ripples increases with span. Considerable coherence for this rippling motion is observed in the range associated with the low-frequency unsteadiness of the shock foot. Minimal influence of the incoming turbulent boundary layer on the low-frequency unsteadiness is present, suggesting an unsteadiness mechanism within the shock/boundary-layer interaction.