Investigating the effects of the change in the angle of attack on the Mack mode frequencies in a Mach 6 wind tunnel on a slender cone

Abstract

An experimental investigation is conducted to examine the influence of angle of attack on the Mack mode (second-mode) instability over a slender cone in hypersonic flow. Experiments are performed in the University of Maryland HyperTERP Ludwieg tube facility at a nominal freestream Mach number of 6.2 using a 5-degree half-angle cone. The angle of attack is varied between -3 degrees and +5 degrees, with schlieren-based spectral measurements obtained in the range -1 degrees to +2 degrees. Z-type schlieren imaging combined with high-speed visualization at 800,000 frames per second is used to capture the boundary-layer disturbance field on the upper surface of the cone. At zero incidence, a clear second-mode spectral peak is identified at approximately 300 kHz. At -1 degrees angle of attack, where the upper surface becomes the windward side and the boundary layer is compressed, a visible increase in second-mode frequency is observed, consistent with boundary-layer thinning on the windward surface. At positive angles of attack, where the upper surface is leeward and the boundary layer thickens, no distinct second-mode peak is identifiable in the spectra.