Leading-edge separation in hypersonic flow

Leading-edge separation and the resulting unsteadiness are a byproduct of flow turning around a blunt body with a sharp axial protrusion at hypersonic speed. The resulting flow dynamics impose severe fluid-structure interaction and substantial heat transfer on the immersed body. A hypersonic Ludweig tunnel is built to produce an impulse flow at M_∞=6. An axisymmetric flat-face cylinder of diameter D=35 mm is equipped with a sharp-tip spike of different lengths and spike diameters to induce the leading-edge separation. Unsteady pressure measurements on the base body along with high-speed images from the schlieren and the laser-based Rayleigh scattering resolve the flow field spatiotemporally. Two different forms of unsteadiness involving pulsation and flapping are observed. Flapping unsteadiness is observed for a wide range of Reynolds numbers (Re_D) and geometrical configurations. The signature of the shock oscillation during flapping depends on the nature of the separated shear layer undergoing a transition from laminar to a turbulent state. Analysis of shock-foot oscillations using x-t diagrams from the high-speed schlieren images for the longest spike reveals a change in spectra from discrete to broadband while varying from low to high Re_D. Similarly, unsteady pressure measurements show a four-order reduction in the power spectra while increasing the spike length by two times. More details on the experiments and discussions will be presented at the conference.