Experimental Study of the Unstable-Unstarted Condition of a Hypersonic Inlet at Mach 6

Wind-tunnel tests were conducted to better understand the flow pattern of a hypersonic inlet at an unstable-unstarted condition that is caused by the downstream mass flow choking. High-speed shadowgraph flow visualization and instantaneous pressure measurements are employed to reveal the oscillations of the shock system and the unsteady process of the duct flow. Results show that the shock system both inside and in front of the inlet duct oscillates intermittently when the inlet is unstarted. With the increase of the downstream throttling ratio, the fundamental frequency of the unsteady flow process goes up and the shock-on-lip time goes down, but the process whereby the shock system is disgorged and swallowed remains unchanged, lasting for 15 ms. When the throttling ratio is 89 and 91%, the fundamental frequency is 8 and 23 Hz, respectively. At the smaller throttling ratio, the aerodynamic oscillatory phenomenon of the inlet can be divided into three stages: namely, mass filling up, shock system disgorging and swallowing, and near-throat flow pattern establishing and backpressure propagating. At the larger throttling ratio, the first stage disappears and the third one shortens.