Three-dimensional Shock Interactions In Hypersonic Internal/External Integration Flows

Shock interactions are prominent in hypersonic internal and external flows during hypersonic flight and significantly challenge the performance or even safety of the vehi-cle,therefore should be well studied to satisfy the application requirements.For the case of two-dimensional shock interactions,the existing research results are relatively suffi-cient,which are capable of providing a conceptual and methodological support for the understanding of the flow mechanism and engineering application of hypersonic two-dimensional inlet.However,an inward-turning inlet which becomes a research hotspot,has strong three-dimensional characteristics of the flow and the internal contraction ge-ometric constraint effect that pose great challenges to the existing shock interaction the-ory.These challenges make it difficult to accurately describe the flow mechanism and predict the performance of the three-dimensional compression system,and also make the related control and optimization design more difficult.Therefore,mechanistic and fundamental studies focused on the three-dimensional shock interaction phenomena are certainly of great significance.In this paper,focused on the integration flow of the air-breathing hypersonic vehicle with an inward-turning inlet,we strive to highlight the key points and decouple the difficult complexities,and several typical simplified models are proposed from different perspectives to cover the main features of the three-dimensional shock interactions.Through a combination of numerical simulations,theoretical anal-ysis and shock tunnel experiments,the research is carried out from several aspects such as flow feature recognition,flow mechanism discussion and key influencing factors analysis.Firstly,a two-dimensional simplified feasibility analysis is carried out for the fea-tures of the three-dimensional shock interference.The plane perpendicular to the tan-gential direction of the shock intersection line is chosen as the analysis plane,and a general theory for the three-dimensional shock interference is established based on the local two-dimensional analysis.Based on this theory,a simplified cone shock reflection model is adopted to examine the three-dimensional shock reflection transition boundary between regular/Mach reflection,and the hysteresis phenomenon in three-dimensional shock reflection is recognized.Results show that the aforementioned three-dimensional shock interaction theory based on two-dimensional local analysis can predict the tran-sition trend of shock reflection type fairly well.However,when there is strong three-dimensional flow near the transition point of the shock reflection type,the influence of the lateral flow parameters variation cross the analysis plane is significant,which may lead to inaccurate results from two-dimensional local analysis.The V-shaped cowl of an inward-turning inlet is a critical region due to its inter-nal/external flow coupling characteristics and complicated shock interactions.In the present work,a plate with a V-shaped blunt leading edge(VsBLEP)is proposed to explore the mechanism of shock interaction and vortex generation mechanism on the V-shaped cowl and its influence on the downstream flowfeld.The experiments are con-ducted in a shock tunnel with a nominal Mach number of 6,and planar laser scattering technique(PLS)and Schlieren photographic system are adopted to acquire the flow images.A complex saddle-shaped shock front is observed on this VsBLEP under the interactions between the detached shock(DS)induced by the swept blunt leading edge and the bow shock(BS)induced by the crotch.It is demonstrated that a new type of spatial transition exists on this saddle-shaped shock front,which involves the transition of shock interactions(i.e.,DS and BS)from the same family upstream of the crotch to opposite families downstream of the crotch.The inward crossflow induced by the swept blunt leading edge is enhanced in the region where the DS and BS are from the same family,and the shear layers generated in this region converge gradually to the spanwise symmetry plane,which results in the formation of a streamwise counter-rotating vor-tex pair(CVP).The CVP trails downstream,showing a far-reaching influence on the flowfeld.In addition,experimental observations in conjunction with numerical simula-tions were conducted to examine the shock interactions generated by the variation of the relative position of a wedge induced forebody shock and the V-shaped cowl.It is found that the interaction between the wedge-induced forebody shock and the bow shock of the V-shaped cowl is coupled with the self-induced shock interaction on the V-shaped cowl,resulting in a rather complicated flow structure.The shock interaction in the near circular converging flow is different from the plane shock interaction,and is also different from the axial singularity of the axisym-metric converging flow.In the present work,an elliptical cross-section is selected as a typical simplified configuration deviating from axisymmetric condition,and the shock interaction in elliptical converging flows are investigated.The effects of cross-section aspect ratio,leading edge compression angle and incoming angle of attack on shock wave evolution are investigated by a combination of experiments and numerical simu-lations.Three patterns of shock interaction types are discovered,which contain type A Mach reflection,type B regular reflection,and type C critical reflection.Through the theoretical and numerical analysis of the non-uniform development of the circumfer-ential shock strength and their converging characteristics,the main influencing factors and flow mechanism inducing the transition of the shock interference type in elliptical converging flows are revealed.The stronger flow convergence effect induced by the larger shock curvature in the major plane causes the shock to approach the axis more quickly,competing with the smaller off-axis distance of the shock in the minor plane.In addition,the initial continuous curved elliptical shock surface evolves and collapes into a strong pair and a weak pair of shock segments during the shock enhancement process,which propagate towards the axis with different intensities and scales.These two pairs of shock segments intersect and interact at different streamwise positions,result in the formation of different shock interaction types.