Unsteadiness in a leading-edge separated flow at supersonic speed

Supersonic flow separates across a sharp leading edge with a protrusion present at a downstream length of a few times its height. The resulting separation produces shock-related unsteadiness. The source of the instability is a topic of scientific interest, as any method to reduce or control the unsteady intensity will result in appropriate payload shielding from severe fluid-structure interaction. Spiked body in supersonic flow is a typical case where such a leading-edge flow separation occurs. In the present investigation, a two-dimensional spike fitted in front of a rounded rectangular forebody block is investigated in a supersonic freestream Mach number of M_∞=2.0. Such a configuration is preferred over the axisymmetric counterpart as the former offers flexibility in probing the flow around the spike. Experimentally, oil-flow visualization, high-speed shadowgraph imaging, steady and unsteady wall static pressure measurements are taken using a blow-down supersonic wind tunnel. Complementary two-dimensional computation is performed using the detached-eddy simulation method in a commercial flow solver package. Leading-edge flow separation at supersonic speed produces shocklets along with the separated shear layer. In the considered flow problem, the outer part of the shocklets is propagating along the supersonic flow stream. The other part of the shocklets is trapped inside the recirculation region (observed between the separation region on the spike and the reattachment region on the rounded forebody). Shocklets in the recirculation region are trapped in the subsonic flow region, and hence, travel forth and back between the separation and reattachment zones. The to-and-fro motion of the shocklets perturbs the separation zone and introduces disturbances in the shear layer, which further produces shocklets. The mechanism of self-sustained unsteadiness in a leading-edge separated flow is explained through carefully planned experiments and supplementary computations.