Refraction Of Cylindrical Converging Shock Wave At An Air/helium Gaseous Interface

The refraction of shock wave at the interface between two fluids with differen-t speeds of sound is a classic and important issue.It plays a significant role in many engineering fields,such as inertial confinement fusion,shock-boundary layer interac-tion,shock-flame front interaction,and supersonic scramjet combustors.For past few decades,the formation mechanism of various irregular refraction wave patterns and the transition criterion between different refraction wave patterns have received much at-tention.In previous work,the studies of shock refraction mainly concentrated on the planar shock,and thus the phenomenon and laws got from them were confined to steady or quasi-steady conditions.However,the shock refraction under unsteady conditions is seldom investigated.The previous work has indicated that the shock intensity and incident angle are two primary ingredients that influence the wave patterns.When a converging shock wave propagates along an inclined interface,both the shock strength and incident angle change,and,therefore,the refraction phenomena and laws may dif-fer from those in steady and quasi-steady conditions.As a result,we aim to investigate the unsteady shock refraction by a cylindrically converging shock wave refracting over an inclined interface using both experimental and numerical methods.In experiment,a cylindrically converging shock wave with an initial shock inten-sity of 1.59 when encountering the interface is generated in a shock tube according to the shock dynamics theory,and the soap film technique is adopted to form the inclined air/helium interface with an incident angle of 30°,45° and 50°,respectively.The post-shock flow field is captured by a schlieren photography combined with a high-speed video camera,and the wave patterns are clearly displayed.Moreover,numerical sim-ulations based on an upwind space-time CE/SE method are also performed to compare with the experimental counterparts and to show details of refraction.The results show that both regular and irregular refractions occur when the converging shock moves along the interface.The flow unsteadiness will induce the transitions among wave patterns during the shock convergence,which is different from those in steady and quasi-steady conditions.It is found that the motion of the transmitted shock may be non self-similar when the transmitted shock becomes a free precursor shock wave.Quantitative results show that the motion of the transmitted shock is self-similar when the incident shock velocity along the interface is smaller than the counterpart of the transmitted shock.However,once the incident shock velocity passes the transmitted shock velocity along the interface,the motion of self-similar will be destroyed,and further causing the wave transitions.Furthermore,more cases are performed to investigate the shock refraction phe-nomena using the numerical method,considering the shock strength effect.The results indicate that compared with the incident angle,the shock strength has less influences on the wave patterns and the wave patterns are plentiful when the shock strength is moderate.