A Study On Instability And Jet Development Of Shock-Accelerated Gas Interface

Richtmyer-Meshkov(RM) instability is an important problem in many fields such as inertial confinement fusion(ICF). weapon and astrophysics. This instability has important scientific significance and wide background. Shock tube experiment of RM instability have many merits:less money, short period, high resolution diagnosis, controlled condition. Thus, shock tube experiment is paid much attention in the world, and is thought as an important means to validate code and understand the complex mechanism of RM instability. Currently, in the relative domestic research, much attention are paid to the numerical simulation and less experimental progress are made.In this thesis, based on widely reading relative literatures, summarization and analysis, gas interfacial instability laboratory are developed starting from scratch. By using of experimental, computational cooperated with theoretical methods, the RM instability and jet development occurring on gas interface are comprehensively investigated. Initial gas interface configuration contains gas cylinder, sinusoidal interface and spherical gas bubble.Construction of the RM instability experimental platform:From building the house, two shock tubes with square cross-sectional area of50mm×50mm and100mm X200mm are developed. Initial membraneless gas cylinder and nitrocellulose sinusoidal interface techniques are explored and mastered. High speed photograph, shadowgraph and particle image velocimetry(PIV) diagonsis systems are established. Thus, RM instability experimental apparatus and technique are generally constructed, and the all-round experimental ability are formed.Evolution process of shock-accelerated gas cylinder:Circular gas cylinder experimental results show initial interface evolves into the typical vortex-pair structure. The size of gas cylinder increases with time, and the width increases faster than the height. In the elliptic gas cylinder evolution study, when the vertical axis is much longer than the horizontal axis, the vorticity production is mainly concentrated at the upper and lower corners, which rolls up in time, and results in a structure of big vortex-pair. When the horizontal axis is much longer than the vertical axis, the baroclinic vorticity production distributes at almost every position along the interface which leads to a faster rolling up of vortices, a spike caused by shock focusing appears in the early stage, and even second vortex and bifurcation structure are exhibited at later times. The PIV velocity field results demonstrate that the maximal velocity locates on the symmetrical axis of gas cylinder. The streamwise convective velocity is symmetric and the spanwise velocity is antisymmetric. The longer the axis perpendicular to the shock front, the larger the absolute values of vorticity. the stronger the effect of convergence, the smaller the distance between the two vortex cores, the larger the maximal value of velocity field, the faster and the severer the deformation of the gas cylinder.Sinusoidal interface RM instability:In the single mode RM instability study, the velocity of bubble is larger than that of the spike. The perturbation amplitude increases faster in the linear stage, and develops slower later because the spike evolves into a mushroom structure due to the baroclinic vorticity mechanism. The experimental disturbance amplitude is in good agreement with the results of Zhang-Sohn model and PPM numerical simulation. In the double mode RM instability study, the difference of interface shape, location and shock front between the initial uniform and nonuniform flows are analyzed. It is found that the flow field nonuniformity as well as the initial perturbation plays a significant role on the interface evolution.Interfacial evolution and jet development of shocked spherical gas bubbles:The shock-heavy bubble interactions are numerically studied. In the evolution of SF6bubble, many typical flow structures are exhibited gradually such as shock collision, focusing, outward jet, main vortex ring, secondary vortex ring, neck shrink effect and break of jet, disappear of jet head and secondary vortex ring. The evolutionary process of R12bubble is similar to SF6case except that the typical structure appears earlier. R22bubble evolution images are also similar to that of SF6case except for secondary vortex ring. In the Kr-0.83bubble evolution, jet phenomenon is absent because two high pressure zone are balanced each other on the left and right of downstream pole at the nearly ideal shock focusing time. A inward jet is found in the evolution of Kr bubble. Furthermore, quantitative results show the smaller gas bubble density, the earlier the jet appears. In the late stage, the outward jet moves at a constant velocity. The velocity of the inward jet is much smaller than that of the outward jet. As the gas bubble density increases, the shock collision time remains a constant, the focusing time increases, the maximal pressure and density also increase, and the total circulation and the baroclinic torque increase too. Compared with the secondary wave pattern, the incident shock wave brings on intenser vorticity.As mentioned above, many progress of theoretical, experimental and computational studies about RM instability is made in this thesis. Those progress contributes a solid basis to further study on strong incident shock, high density ration, convergent driving, metal interfacial instability, and investgation on the mechanism of RM instability. Those work also provides reliable support for instability problem of many important fields such as ICF, astrophysis etc.Some highlights of this thesis are innovative and first presented in theworld or in China. The main innovations are listed as follows:(1) From building the house, many shock tube apparatuses and diagnosis methods are developed. Initial membraneless gas cylinder and nitrocellulose sinusoidal interface techniques are explored and mastered. The comprehensive experimental ability of RM instability are formed. Two national invention patents are authorized. Those work are pioneering in China.(2) Elliptic gas cylinder RM instability problem is put forword. Seven cases of elliptic gas cylinder interface evolution process are first studied and ideal experimental results are obtained. Some typical phenomenon, such as big vortex-pair, second vortex and bifurcation structure, are found and the evolution mechanism of vortex are further clarified. Numerical simulation results validate the experimental phenomenon and deepen the physical understanding. Those research results are admitted by foreign colleagues.(3) By using of experimental, computational cooperated with theoretical methods, RM instability in nonuniform flow field is first investigated in the world. It is found that the flow field nonuniformity as well as the initial perturbation plays a significant role on the interface evolution. Those work exploit new research field of hydrodynamic instability and deepen the understanding of RM instability in complex flows.(4) Jet problem of shocked heavy bubbles is first quantatively studied employed finite volume method code VAS2D and reliable, comprehensive results are presented. The computational results reveal the intrinsic mechanism of jet phenomenon. Those work are much beneficial to understand thoroughly shock focusing and high speed jet of shock accelerated inhomogeneous flows.