Flow Performance Study Of Scramjet Isolator At Distorted Incoming Flow Conditions

Scramjet isolators will be interfered with incident shock waves and corner expansion waves in the actual work situation which lead to multiple reflection shock waves and shock wave/turbulent boundary-layer interactions.These distorted factors will have serious influence on the flow in the isolation.In order to study the flow performance of isolators under the influence of oblique shock,expansion wave and asymmetric boundary layer,the flow field of the isolator is simulated with isolators at distorted incoming flow conditions.Firstly,the flow characteristics of the isolators at the distorted and symmetrical incoming flow conditions are comparatively analyzed in the case of the same length of isolators.The results indicate that the maximum back pressure and the total pressure recovery coefficient of the isolator at distorted incoming conditions decrease by 5.7% and 6.4% compared with that of the asymmetric model at Ma4,and the applicability of Waltrup formula is poor.With the increase of back pressure,the shape and intensity of the first shock of the shock trains are basically the same at distorted incoming conditions,but that of isolators at the distorted incoming conditions vary greatly.Secondly,influence of length on the performance of isolators at different incoming flow conditions is studied.The results indicate that the length of isolators at distorted incoming flow conditions is 2 times the height of the isolators longer than that of the isolators at symmetrical incoming flow conditions at Ma4 and 1 times the height of the isolators longer than that of the isolators at symmetrical incoming flow conditions at Ma6 under the same back pressure rise.For the various length of distorted incoming flow condition at Ma4,considering the maximum back pressure rise and isolator length,11 times the height of the isolator is selected as the optimum isolator length at Ma4,13 times the height of the isolator is selected as the optimum isolator length at Ma6.The maximum pressure rise of isolators with optimum length can reach more than 96% of the limited pressure rise at Ma4 and Ma6 conditions.In addition,the relationship between the momentum distortion index and the limiting back pressure is fitted,which can estimate the limited back pressure of isolators with different distorted entrances.Finally,the phenomenon of shock train hysteresis loop in isolators at distorted incoming flow conditions in the process of back pressure rise and fall is studied.The main reason of shock train hysteresis loop is the separation caused by multiple shock wave/turbulent boundary-layer interactions,by analyzing the simplified diagram of anti-pressure ability.