Research On Hysteresis Phenomena In The Accelerating/Decelerating Process Of Two-dimensional Hypersonic Inlets

In order to study the hysteresis phenomena in the accelerating/decelerating process of two-dimensional hypersonic inlets,numerical simulation method were used to study the accelerating/decelerating processes of two hypersonic inlets with different cowl angles.Furthermore,to enlarge the starting speed envelop of two-dimensional hypersonic inlets,a forward-stretching splitter is implemented at the entrance of internal contraction duct to decrease the self-starting Mach number,and the feasibility of the method were verified by a series of numerical simulations.First,two hypersonic inlets with different cowl angles were designed,and the steady numerical simulations of the accelerating/decelerating processes were carried out.The differences of hysteresis loops between the two hypersonic inlets were analyzed and compared,and the cause of hysteresis phenomenon was also explored.The results show that there are significant differences between the hysteresis loops of the two different hypersonic inlets,and the hysteresis phenomenon not only exists in the transition between the unstart state and the start state,but also exists in the transition between the "hard" unstart state and the "soft" unstart state.Second,a method to improve the self-starting ability of two-dimensional hypersonic inlets by introducing a forward-stretching splitter at the internal contraction duct is proposed.By numerical simulations,the flow structure variations during the self-starting process and the self-starting performances of the hypersonic inlets with/without a splitter were compared and analyzed.The results show that there is a great difference between the self-starting processes of the baseline inlet and the inlet with splitter.The self-starting ability of the inlet with a splitter is significantly improved compared with that of the baseline inlet,and the self-starting Mach number decreases from 6.84 to 4.23.Hence the starting speed envelop of hypersonic inlets is enlarged obviously.Third,for the rectangular hypersonic inlet with a full-sidewall,the effects of the three-dimensionality on the self-starting performance improvement of the splitter were studied numerically.The results show that although the self-starting Mach number of the three-dimensional baseline inlet and the inlet with a splitter is slightly higher than those of the pure two-dimensional configurations,the self-starting performance improvement of the splitter for the three-dimensional configurations is not affected obviously.Finally,the effects of the relative location and the upside initial angle of the splitter on the self-starting performance improvement were studied.The results show that if the upper sub-duct always keeps the supersonic unstarting mode before reaching the starting state,the self-starting performance of the inlet is better overall.Within the scope of the study,the variation of the upside initial angle does not change the upper sub-duct unstarting mode,so the self-starting performance changes a little.Besides,the variation range of the relative location and the upside initial angle of the splitter with excellent self-starting ability are wide,hence the proposed method by introducing the splitter to improve self-starting ability of hypersonic inlets has strong practicality in engineering.