Shock Interactions And Aerothermal Heating/Pressure Behaviors On V-shaped Blunt Leading Edges

Shock interactions phenomena are widely encountered in the internal and external flow of an air-breathing hypersonic vehicle,which can lead to abrupt changes in flow fields and significant increase of local heating/pressure loads.Therefore,it is one of the key factors challenging the long-time of hypersonic flight.The three-dimensional air capture system,which is typically represented by an inward-turning inlet,has become a highly promising design scheme due to its high compression efficiency and excellent flow capture performance.However,severe shock interactions on its V-shaped cowl lip are gradually revealed with the deepening of research.It is difficult to evaluate and predict new features of shock interactions on the V-shaped cowl lip using classic theories.Therefore,the shock interaction on the V-shaped cowl lip becomes one of the most challenging subjects in the aircraft design and the scientific research.More efforts are required to enrich the knowledge of the shock interaction on the V-shaped cowl lip,reveal the physical mechanisms,and provide guidelines for the design.A series of V-shaped blunt leading edges are employed here to focus on shock interactions.Comprehensive investigations,including the shock structures,heating/pressure loads,and unsteady oscillations,are performed using a combination of theoretical analysis,numerical simulations,and wind tunnel experiments.Wave configurations and transitions of shock interactions on V-shaped blunt leading edges are analyzed at a freestream Mach number of 6.Three types of shock interactions,i.e.,regular reflection(RR),Mach reflection(MR),and regular reflection from the same family(sRR),are observed in both experiments and numerical simulations.Transitions from RR to MR and from MR to sRR are identified with the increasing of radius ratio(i.e.,the crotch radius over the leading edge radius)and the half-span angle.It is revealed that the specific geometric constraints of the model,rather than the classic detachment and von Neumann criteria,govern the transitions of shock interactions.From theoretical analyses of the relative geometric positions of the shock structures near the crotch,transition criteria of the shock interactions from RR to MR and from MR to sRR are established.These theoretical transition criteria achieve good agreement with the experimental and numerical results.In addition,an abnormal hysteresis(i.e.,below the von Neumann criterion)is observed near the transition boundary between RR and MR.Shock interactions cause severe aerothermal heating loads on the V-shaped blunt leading edge,in which four types of generation mechanisms for local heating peaks are revealed,including supersonic jet impingement,shock wave or expansion waves/boundary layer interaction,shear layer attachment,and the collision of the robust jets.The results show that the heating peaks generally increase first and then decrease with the increasing of the radius ratio,whereas the heating peaks generally decrease with the increasing of the half-span angle.Thus,the model with a large half-span angle and a large radius ratio has the potential to reduce local extremely high heating loads.Furthermore,correlations between the local heating and pressure peaks are established according to different generation mechanisms of the heating peaks,which provide an important method to rapidly predict the local heating peaks on V-shaped blunt leading edges.Shock oscillations are observed on V-shaped blunt leading edges,which causes fluctuating pressure loads.To understand these unsteady characteristics in different shock interactions(i.e.,RR,MR,and sRR),a combination of high-speed schlieren and image processing technologies is used.Four types of oscillation patterns,i.e.,global swing oscillation,mixed oscillation of swing and arch-recover,global arch-recover oscillation,and local arch-recover oscillation,are observed with the increasing of the radius ratio.It is revealed that the competition of the two opposite jets near the stagnation point and the breathing-like motion of the flow at the crotch region are the underlying key factors activating the shock oscillations.Transitions of the four oscillation patterns are quantitatively identified by analyzing the fluctuations of characteristic points on the shocks.The measurements of the fluctuating pressure confirm that the shock oscillations have a dominant middle-frequency.The Strouhal number correspondingly collapse to about 0.09.Moreover,it is demonstrated that the fluctuating pressure loads can be reduced by increasing the radius ratio and the sideslip angle,and by decreasing the freestream Mach number.The adjusted shock structures are responsible for these reductions.