The Richtmyer-Meshkov Instability Of Multi-mode Interfaces Accelerated By A Planar Shock Wave

When an interface that separates two fluids with different densities is impacted by a shock wave,the disturbances initially existing on the interface will develop imme-diately.With the continuous evolution of the interface structures at various scales and the coupling between different modes,the flow will eventually enter a turbulent mixing state.This is generally referred to as the Richtmyer-Meshkov(RM)instability.RM instability plays an important role in multi-scale scientific and engineering issues,such as supernova explosions,supersonic and hypersonic air-breathing engines and inertial confinement fusion(ICF).In ICF,specifically,RM instability is one of the important reasons for ignition failure.Because the single-mode interface is fundamental and is convenient for theoretical analysis,it has received widespread attention.However,a multi-mode interface is ubiquitous in both science and engineering.As a result,it is of great significance to understand the evolution of a multi-mode interface for revealing scientific laws and guiding engineering practice.At present,the studies of multi-mode interfaces are rare and also lack of systemicity.This dissertation focuses on the RM in-stability of a V-shaped interface,which is a fundamental configuration of a multi-mode interface.The initial interface is generated by the soap film technique,and the flow field is recorded by the high-speed schlieren system.All the experiments are conducted in a planar shock tube.First,the evolution of a V-shaped interface with a bubble configura-tion in the linear and nonlinear stages is studied.Second,the two-bubble competition in the initial stage of RM instability is investigated.Third,the effects of transverse waves on the RM evolution of the multi-mode interface are highlighted.Fourth,the similar-ities and differences of RM dynamics between heavy-light and light-heavy interfaces are compared.Finally,the RM characteristics of the interfaces with different shapes(single-mode,trapezoid,V-shape)after reshock are studied.The main contents are as follows:1.The evolution of the V-shaped interface with a bubble configuration in linear and nonlinear stages is studied experimentally.It reveals the evolution characteristics of a multimode interface with sharp corners.The impulsive model can predict the linear growth rate of the V-shaped interface with small amplitudes,but it needs to be modified for large amplitudes.Due to the existence of high-order modes in the initial interface,the existing nonlinear models underestimate the nonlinear growth rate of the V-shaped interface.Based on the Sohn potential model,a new nonlinear model is proposed and gives a satisfactory prediction to the amplitude growth rate.2.The bubble competition of multimode interfaces in the initial stage of RM in-stability is studied experimentally for the first time,and the influence of the bubble competition effect and the nonlinear effect on the interface evolution is clarified.For large interfaces(bubbles),the nonlinear effect has a stronger influence on the interface growth than the bubble competition effect has,while for small interfaces(bubbles),the conclusion is just the opposite.The effect of the initial bubble size difference on the bubble competition in the streamwise direction is not significant.However,with the increase of the initial bubble size difference,the growth rate of large bubbles in the spanwise direction is faster than that in the streamwise direction.3.The influence of transverse waves on the interface modes evolution is studied for the first time.The transverse waves and the shock proximity effects are responsible for the flattening of the bubble front.They introduce additional force to the flow,resulting in the reduction of the first mode amplitude and the increase of the high-order modes amplitudes,and consequently the change of the interface shape.From spectrum,the increase of the amplitude of the second harmonic mode leads to the flattening of the bubble front.4.Experiments of accurately defined interfaces(sinusoidal,trapezoidal and V-shaped interfaces)impacted by reshock are conducted for the first time,and the evo-lution features of the interface before and after reshock are analyzed.Before reshock,the similarities and differences of the interface evolution in linear and nonlinear stages between the heavy/light and the light/heavy cases are compared.The phase reversal af-fects the evolution of higher-order modes of heavy/light interfaces,but it has a limited influence on the evolution of the first fundamental mode.After reshock,the RM behav-iors of the interfaces maintain a strong memory of the initial conditions.The differences in the bubble growth rates among different interfaces result in the overall mixing width growth rates ranking as:V-shape>single mode>trapezoid.Our experiments verify the two-dimensional single mode reshock model for the first time.