Restart Processes of Rectangular Hypersonic Inlets with Different Internal Contraction Ratios

Abstract

In this paper, the restart processes of two generic rectangular hypersonic inlets with different internal contraction ratios have been experimentally studied under a freestream Mach number of 5.0. The experimental results show that without downstream throttling, both inlets start successfully after the flowfield establishment of the wind tunnel. To obtain the restart processes of the two inlets, they are initially set at an unstarted state by a large downstream throttling ratio. Then, the throttling ratio is continuously decreased. For the inlet with a small internal contraction ratio, the restart process undergoes four stages: stable buzz, intermittent buzz, reestablishment of wave system in the inlet, and unthrottled flow; whereas for the inlet with a large contraction ratio, the internal flow cannot be normally reestablished after the intermittent buzz stage because a large-scale separation bubble consistently stands ahead of the inlet. That is, it cannot be restarted. In the stage of the intermittent buzz, there is a probability of the appearance of a quasi-steady flowfield when the pressure in the inlet reaches its maximum value, and the separation shock almost impinges on the cowl lip. For both inlets, the probability of buzz decreases continuously with time, and then it suddenly disappears. Furthermore, for the inlet with a large contraction ratio, two kinds of flowfields (that is, started or unstarted) occur at the same downstream throttling ratio and upstream flow conditions, which indicates that the inlet operates in the dual-solution region and the actual operating state of the inlet significantly depends on the historical flow. Therefore, the evaluation of hypersonic inlet starting capability must be examined carefully.