Effect of an adverse pressure gradient on hypersonic wall pressure fluctuations

Measurements based on a plate-perpendicular fin model were conducted to investigate the effect of an adverse pressure gradient on hypersonic wall pressure fluctuations. The leading edge diameter of the perpendicular fin is designed to be 25 mm with a height of 200 mm. A linear sensor-array was used to measure the wall pressure fluctuation, and a numerical computation was carried out to validate the measurement. Wall pressure fluctuations were discussed in terms of two aspects: the time-frequency domain and spatial correlation. The flow types on the plate could be estimated by the sound pressure level distribution, and the dominant flow type that substantially contributes to the wall pressure fluctuations could be determined. The spatial correlation of wall pressure fluctuations was analyzed using the phase array technique, and two disturbance modes could be identified from the wavenumber map obtained using the beamforming algorithm. The investigation results revealed that the change in the unit Reynolds number caused by the variation in the inflow dynamic pressure leads to the change in the flow type and the distribution of wall pressure fluctuations. The small-scale vortices within the hypersonic laminar flow lead to the difference in the signs of the convective mode wavenumber and that generated by hypersonic turbulence.