Unsteady behavior of hypersonic inlet unstart caused by high angle of attack

Abstract

Unstart is an undesirable flow phenomenon at the inlet that severely reduces the air mass flow through engine, thereby causing thrust loss, engine surge, or combustor flameout. To better understand the flow evolution and unsteady behaviors of a hypersonic chin inlet caused by the angle of attack, an experiment was conducted in a blow-down-indraft wind tunnel at Mach 5.0. The unsteady flow patterns were observed simultaneously using a high-speed schlieren system and surface pressure measurement. The results showed that the forebody shock impinged on the inside of the cowl, and the inlet operated in the overrated mode when the angle of attack increased to 6°. Then, the inlet entered the unstarted state with a big buzz as the angle of attack reached 8.2°. During the big buzz, high-amplitude oscillations occurred throughout the entire duct with a dominant frequency of 318.3 Hz. In addition, the flow field periodically alternated between the unstarted mode driven by the large-scale separation region with supersonic spillage and the local unstarted mode characterized by subsonic spillage. Furthermore, cross-spectrum analysis revealed that the perturbation source was located in the throat and isolator, and the velocity of the upstream-propagating perturbation gradually decreased.