Streamwise Vortex And Its Interaction With Shock Wave In Hypersonic Flow

Streamwise vortex/shock wave interactions characterized by the vortex breakdown and the deformation of the shock wave are widely encountered in the internal and external flows of a hypersonic vehicle.These phenomena can lead to abrupt changes in aerodynamic forces and a sudden reduction in the engine performance,and thus become one of the key factors challenging the performance promotion of the hypersonic vehicle.Moreover,it is difficult to predict different types of streamwise vortex/shock wave interactions encountered in the wide-speed-range flight using classic theories.To enrich the knowledge of streamwise vortex/shock wave interactions and provide guidelines for the design,a combination of numerical simulations,shock tunnel experiments,and theoretical analysis is employed in this work to focus on the physical features of the wing-tip vortex and the streamwise-vortex-pair generated in the internal and external flows of the hypersonic vehicle.The phenomena of wing-tip vortex/shock wave interactions and streamwise-vortex-pair/shock wave interactions are analyzed,the physical mechanisms of streamwise vortex/shock wave interactions and the law of vortex breakdown are revealed,and new theories predicting the breakdown of the wingtip vortex and the streamwise-vortex-pair induced by an oblique shock wave are proposed.First,distributions of circulation within the wing-tip vortex at various streamwise locations are analyzed in a wide-speed-range.It is found that the classic relationship for the circulation of the wing-tip vortex in low-speed flows can be further extended to supersonic/hypersonic flows.Moreover,a swept-ramp vortex generator is used to generate counterrotating vortex pairs(CVPs)with an absence of a boundary layer in the hypersonic regime.In contrast to the CVPs immersed in the boundary layer,it is identified that the maximum of transverse velocity in the spanwise symmetry plane induced by the CVPs without the boundary layer changes slowly and the minimum of transverse velocity increases obviously along the streamwise direction.Therefore,the scaling law for the transverse velocity in the spanwise symmetry plane induced by CVPs immersed in the boundary layer is not suitable for CVPs in the present study.A new scaling law is proposed based on the new features of CVPs without the boundary layer and demonstrated to work well.Additionally,the planar laser scattering images show the enhanced mixing between CVPs without the boundary layer and outside highmomentum fluids is earlier than that immersed in the boundary layer.Second,wing-tip vortex/oblique shock wave interactions and streamwise-vortexpair/oblique shock wave interactions are analyzed and compared with each other.When the strength of the incident oblique shock wave keeps constant,the intensity of the streamwise vortex/shock wave interactions can be classified into strong,moderate,and weak types due to the decay of the vortex intensity with streamwise locations.For the strong interaction between the oblique shock wave and the streamwise-vortex pair,a Tshaped bulged-forward shock front,which is a new feature,is identified in a threedimensional view.Compared with the strong interactions induced by wing-tip vortex/oblique shock wave,differences are highlighted by the shapes of the bulged-forward shock front,the locations of the localized normal shock wave,and the positions of the subsonic recirculation region/stagnation point.For the moderate interactions,differences in the shapes of the bulged-forward shock front and the locations of the localized normal shock wave are distinguished.For the weak interactions,differences are observed in the shapes of the bulged-forward shock front.Finally,the breakdown of the wing-tip vortex and the stream wise-vortex-pair induced by the oblique shock wave is studied.For the wing-tip vortex/oblique shock wave interaction,it is shown that the wing-tip vortex with a greater pressure deficit is easier to break down.However,the existing theories for predicting the onset of vortex breakdown induced by an oblique shock wave neglect the impact of the pressure deficit,which leads to the inaccurate predictions of the vortex breakdown.Hence,the pressure difference term of the existing theory for the oblique shock wave-induced vortex breakdown is improved by considering the pressure deficit,and a new theory is proposed and demonstrated to work well in the freestream Mach number range of 2～6.Moreover,it is shown that the trestles at the bottom of the swept-ramp vortex generator have a great impact on the flow fields of strong interaction between the oblique shock wave and the streamwise-vortex-pair.As a result,the existing theory of the shock waveinduced vortex breakdown is suitable for the flow fields with a single trestle and without a trestle,whereas it is invalid in the flow fields with double-trestles.