Time-Accurate Experimental Investigation of Hypersonic Inlet Buzz at Mach 5

Abstract

Hypersonic inlet buzz is investigated experimentally in a ramjet intake at Mach 5. A two-dimensional planar inlet featuring a double-compression ramp with 10 and 22° inclination to the freestream direction and a rectangular-cross-section duct is tested. A solenoid is used to raise a barrier into the flow and initiate buzz at high throttling ratios. Static pressure is measured at a data sample rate of 10 kHz, and schlieren images are collected at an image frame rate of 30 kHz. Oscillations in the flow not linked to buzz are present at both zero and full throttle, and they cause a high-amplitude pressure peak at very high frequency (higher than 3 kHz). At full throttle, buzz is spotted, in the contemporary presence of shear layers being ingested by the intake (Ferri criterion) and of separated flow lying on the second compression ramp (Dailey criterion). Both features are analyzed by means of the standard deviation of the frames captured. The kind of buzz hereby observed activates high-amplitude pressure oscillations at both low frequencies and high frequencies. The unstarted flowfield is largely subsonic inside the intake and allows for the use of the linear acoustic theory. Indeed, one of the peaks recorded matches the quarter-wave resonator frequency (1411 Hz) of the inlet, suggesting that the barrier acts as a solid wall and that the inlet model behaves as a duct with a closed end.