Study On Richtmyer-Meshkov Instability Of Heavy/Light Interface

When an interface between two fluids with different densities is subjected to a shock wave,initial perturbations on the interface will grow persistently with time and eventually develop into turbulent mixing.This type of interface instability is usually called the Ricthimer-Meshkov(RM)instability.The study of RM instability has important academic significance in fields of shock dynamics,flow instability,and compressible turbulence,and also is of great importance in many engineering applications such as inertial confinement fusion,supersonic combustion and supernova explosion.Previous studies on the RMI mainly focused on the development of a light/heavy interface and several linear and nonlinear models have been developed to describe the perturbation growth.However,only few studies(especially experimental studies)on the growth of a heavy/light interface were reported.The accuracy of the related theoretical models for predicting the growth of a heavy/light interface has not been well validated.Also,different from the evolution of light/heavy interface,for the light/heavy interface,after the shock impact the perturbation amplitude decreases gradually to zero,which is called phase inversion.Such a phase inversion process has not been observed in previous experiments(limited by the space and time resolutions),and the underlying physical mechanisms are unknown.This paper studies the RM instability at a heavy/light single-mode interface both experimentally and theoretically.The first part of this thesis focuses on the interaction of an incident planar shock with a well-defined light/heavy single-mode interface.The differences between the evolution of heavy/light interface and that of light/heavy interface are emphasized.Different from the light/heavy case,after the shock impact,the heavy/light interface immediately enters the phase reversal process.After the phase reversal,the interface experiences successively the linear and nonlinear growths,which is similar to the light/heavy case.The reliable experimental and numerical results here allow us to examine the validity of the previous linear and nonlinear models for the heavy/light RM instability growth.It is found that the linear model of Meyer&Blewett gives a good prediction of the perturbation growth at linear stage up to a dimensionless time of 0.7,and the empirical model of Dimonte&Ramaprabhu reasonably predicts the perturbation growth at the nonlinear stage,which is different from the light/heavy case where the model of Zhang&Guo gives the best prediction as suggested by an elaborate experimental study.The second part of this thesis focuses on the interaction between a reflected shock wave and a heavy/light single-mode interface,which is also called reshock RM instability.The reshock RM instability exists widely in various engineering applications.Here,we mainly study the reshock RM instability at a heavy/light interfaced with different amplitude-over-wavelength ratios and the reflection distances through numerical simulations.After the heavy/light single-mode interface is impacted by the reflected shock,its perturbation amplitude first decreases and then increases at a larger growth rate than that before the reshock.It is also found that the post-reshock growth rate is weakly correlated to the initial interface wavelength,amplitude and reflection distance.The existing empirical models(Charakhch' an model,Mikaelian model,Cha-Uk model,and Mik-Uk model)are found to be not suitable for predicting the growth of reshock RM instability at a heavy/light interface.