Stationary Crossflow and Traveling Instabilities for a Slab Delta in Hypersonic Flow

Stationary crossflow and traveling instabilities on a ‘slab delta’ model were investigated in a hypersonic flow. Experiments were conducted in the AFOSR–Notre Dame Large Mach-6 Quiet Tunnel at nominally zero angle of attack and yaw at unit Reynolds numbers from 4.1 · 10^6 /m to 12.2 · 10^6 /m. Infrared thermography was employed to measure the surface heat-flux distribution, assess the boundary-layer state, track the paths of the stationary crossflow waves, and quantify the flow uniformity. These measurements visualized characteristic streamwise heating streaks and outboard transition lobes. Linear Stability Theory (LST) calculations using the Linear Parabolized Stability Equation (LPSE) at Re∞ = 11.78 ·10^6 /m predicted the most-amplified waves would have a wavelength of 6 mm, a frequency of 13.75 kHz, and propagate towards the centerline with a wave speed of 81 m/s. Traveling waves were measured using surface-flush Kulite pressure transducer trios. Cross-spectral analysis of the pressure signals yielded wave angles and phase speeds as functions of frequency. Traveling waves were observed at Reynolds numbers ranging from 4.1 · 10^6 /m to 9.8 · 10^6 /m, with peak frequencies centered in the range from 7 to 10 kHz. Within experimental uncertainties, the wave angle and phase were found to be largely invariant with Reynolds number. The variation with frequency of experimentally obtained wave angle and phase speed agreed with LST predictions, but experiments exhibited mild left/right differences and phase-speed discrepancies not predicted by LST.