Shock Waves And Shock Interactions In Inward-Turning Inlet Flow

Hypersonic inlet is a very important component of scramjet for the air breathing hypersonic propusion.Three-dimensional inward-turning inlets,owing to their high compression ratio,small wetted area,and the ability to be easily integrated with a circular cross-sectional engine,have attracted wide attention in both industrial and academic communities.However,due to the complex geometry structure of an inward-turning inlet,many kinds of curved shock waves(such as compression shock,cowl shock,separation shock,reattached shock,etc.)are inevitably generated,which make the flow obviously different from the traditional two-dimensional inlet,especially the Shock Wave-Boundary-layer Interactions(SWBLIs)which has a three-dimensional complex feature of spatial curvature.Previous knowleges of plane shock wave and its interaction with the boundary layer in two-dimensional flow field can hardly be appled in three-dimensional inward-turning inlet.The previous works on inward-turning inlet are insufficient,particularly the experimental visualization which plays a key role in understanding of the phenomena.Therefore,the present work starts from the efforts of flow visualization for inward-turning inlet to obtain the three-dimensional inner flow structures.With the combination of numerical simulation,some typical flow fields observed in the experiments are analyzed.Furthermore,the complex interactions between curved shock wave and curved wall are decoupled to highlight the key points,in which the incident shock is simplified as a planar oblique shock to emphasize the role of concave cylinder wall in the reflection process.The main findings are summarized as follows.First a truncated segmented visualization method is proposed to observe the internal flow field of an inward-turning inlet.The internal flow field structure at the truncated section can be obtained by segmenting,and then the overall spatial structure of the internal flowpath can be obtained by combining the multi segments.A planar laser scattering(PLS)technique is developed for the inlet flow visualization in shock tunnel,in which nano-particles produced by condensation of water vapor in nozzle are used as tracers.The tests show that PLS method is an effective flow visualization method in hypersonic flow;where through properly arranged light path,it is the first time to observethe flow field of the three-dimensional inward-turning inlet.In addition,the pressure-sensitive paint(PSP)technic is used to measure the pressure distribution on the surface of the model and obtain the flow field distribution on the wall.Combined with Schlieren.PLS and other different methods.the flow field can be obtained with multiple informations which are helpful for the correlated analysis.Secondly,based on the experimental observation of the flow field,the complex flow structure of the inward-turning inlet is further characterized by means of numerical simulation.It is found that the complex wave interactions at the V-shaped blunt leading edge not only cause local high thermal load,but also forms streamwise counter-rotating vortex pair(CVP)on both sides of the inlet,which affect long distance downstream.On the other hand,a relatively large low speed region on the compression side is not only related to the development of the long-distance compression surface boundary layer,but also the interaction between the shock wave inside the cowl and the curved side wall,which results in the accumulation of the boundary layer of the side wall to the bottom.In addition,the three-dimensinal wave structures produced by the reflection of oblique shock wave on a concave cylinder is investigated by inviscid numerical simulation.With the help of local two-dimensional analysis method,the transition of regular-Mach reflection of oblique shock wave on concave cylinder is predicted and analyzed.The results show that the reflection on side wall of concave cylinder is mainly Mach reflection,whereas the region near the symmetry is more prone to regular reflection,and the transition region is accompanied by complex structures such as bridging shock and shear layer.With increase of the incident oblique shock intensity,the regular reflection region gradually decreases and eventually disappears.At this time,the reflection type at the symmetry plane will switch from regular reflection to Mach reflection,and then full Mach reflection mode will appear.The Mach stem near the symmetry plane produces a high-pressure and low-speed region,which is similar to normal shock.The total pressure loss is significant in this region,and the flow field non-uniformity becomes obvious.Therefore,the full Mach reflection should be avoided in the design and operation of inward-turning inlet.