Mechanisms of Hysteresis in the Acceleration and Deceleration Processes of Hypersonic Inlets

To broaden the stable operating range of hypersonic aircrafts, this work examined the mechanisms of the hysteresis phenomenon for hypersonic inlets under acceleration/deceleration process conditions. Guided by unsteady flowfield simulations on two typical 2D hypersonic inlets with different critical unstart modes of hard unstart and soft unstart, two dominant characteristics of the hysteresis phenomenon during the acceleration/deceleration processes were identified. The first characteristic is that, at the same free-stream Mach number in the hysteresis range, the main separation bubble at the cowl-lip station or the internal contraction section of the inlet during the acceleration process is considerably larger than that induced by the cowl shock wave/boundary layer interaction (SWBLI) during the deceleration process. The second characteristic is that the self-starting Mach number during the acceleration process exceeds the unstart Mach number during the deceleration process. Two mechanisms are proposed to explain such hysteresis. First, in the unstarting flowfield at relatively high incoming Mach numbers, the large-scale separation bubble under the unstarted state stems from the self-coupled SWBLI, instead of the throat blockage or the isolated SWBLI, the dimensionless pressure rise through the self-coupled SWBLI during acceleration is much larger than that of the isolated SWBLI during deceleration. Second, the transition between the unstarted state and the started state in the hysteresis range is, in essence, the conversion between the self-coupled SWBLI and the isolated one.

Automated summary

In order to expand the stable operating range of hypersonic aircrafts, the mechanisms of hysteresis phenomenon in hypersonic inlets under acceleration/deceleration conditions were investigated. By conducting unsteady flowfield simulations on two typical 2D hypersonic inlets, two dominant characteristics of the hysteresis phenomenon during the acceleration/deceleration processes were identified. Two proposed mechanisms were used to explain the hysteresis phenomenon.