| There is intensive shock wave/boundary layer interaction in the hypersonic inlet flowfield, especially the boundary layer separation on the body side of the vehicle induced by the impinged lip shock. The boundary layer separation severely depraved the quality of the inlet flowfield, which can make the inlet unstart at low Mach number or high backpressure. The most prominent characteristic of the unstarted inlet flowfield is the large-scale separation at the entrance of the inner contraction segment. In this thesis, the shock induced boundary layer separation and unstarted large-scale separation in hypersonic inlet flow are studied experimentally and numerically.The shock induced boundary layer separation and unstarted large-scale separation in hypersonic inlet flows are not only impacted by the flow parameters, but also depend highly on the inlet configuration. The flow structure and flow mechanics are much complicated, which is difficult to investigate. In this thesis, the indraft supersonic wind tunnel for flow mechanics research and the high enthalpy free-stream experimental system simulating real flight flow conditions are used together to carry out experimental study. The modern high resolution flow visualization system like the Nano-tracer Planar Laser Scattering(NPLS) technique is introduced to inlet flowfield visualization, combining with the traditional technique like schlieren system. The flow field is also investigated by numerical simulation.Firstly, the flow of turbulent boundary layer separation induced by incident shock is investigated. The boundary layer separation induced by the lip shock will make further compression to the main supersonic flow in the inner contraction segment of the inlet, which can easily lead to inlet unstart at low Mach number or high backpressure, so the flow characteristic and scale of the separation need to be studied. In this thesis, the mathematical model predicting the separation angle is built based on the simplified flow structure model of the incident shock induced turbulent boundary layer separation. The relations of the separation length with the relevant flow parameters are studied and the mathematic model predicting the separation length of the turbulent boundary layer is built.Secondly, based on the simplified two-dimensional inlet configuration, the large-scale separation at the entrance of the inner contraction segment, which is the most prominent characteristic of unstarted inlet, is studied. The flow structure model of the large-scale separation is proposed and the mathematical model predicting the large-scale separation angle is built base on the flow structure model. The fine three-dimensional structure of the large-scale separation is visualized by the NPLS technique and the “strip separation†structure in the spanwise direction of the large-scale separation is revealed. The transverse jets located downstream of the inlet is used to induce backpressure for the inlet and the formation and disappearance procedure of the large-scale separation in the process of inlet unstart/restart is captured.At last, the shock induced boundary layer separation and the unstarted large-scale separation in the side-compression hypersonic inlet is studied and the flow control for inlet start is investigated based on the inlet. It is shown that the laminar boundary layer transients first and then separates under the action of the swept shock, and the separated flow is in a semi-cone configuration. The afterward sidewall of the side-compression inlet is more propitious to avoid the unstarted large-scale separation than the forward sidewall, which make the starting ability of the afterward inlet better than the forward inlet. Bleeding the unstarted large-scale separation can restrain the formation of the separation, which can enhance the inlet starting ability notably. With bleeding the large-scale separation, reducing the spillage between the sidewalls can improve the starting ability and mass flow capture ratio of the inlet at the same time. |
