468 / 2019-03-15 19:47:52

Experimental Investigation on Nonlinear Converging Richtmyer-Meshkov Instability

RM instability; Nonlinear effect; BP effect

全体主题 > Interface Instabilities at Extremes

The perturbation growth of the interface with different densities impacted by the shock is always referred to as the Richtmyer-meshkov(RM) instability. Many investigations have been devoted to the converging RM instability due to its extensive applications in the fields of inertial confinement fusion(ICF) and astrophysics. Bell and Plesset respectively analyzed the development of an accelerated interface under the linear regime in cylindrical and spherical geometries. The geometry convergence was found to continually modify the growth rate of a radially-moving interface, which is later called as the BP effect. Previous experiments and simulations have also observed an evident interface deceleration and reshock. The presence of Bell-Plesset (BP) and Rayleigh-Taylor (RT) effects as well as the second impact by reshock make the converging RM instability much more complicated than the planar counterpart. The existence of the RT effect covers almost the nonlinear effect of short-term interface evolution. Hence, rare studies have been related to the nonlinear RM instability, which motivates the present study.
A unique shock tube is first established to remove the converging shock reflection from the convergence center. A smooth concave-oblique-convex wall profile is employed to carefully control the propagation of the shock wave in the tube. Specifically, a concave segment first transforms the incident planar shock into a cylindrical arc. Then, the cylindrical shock formed propagates along the oblique wall with its strength increasing gradually. Later, a convex wall connected to the end of the oblique section bends the cylindrical shock back into a planar one again. The new-formed planar shock, which is much stronger than the incident one, moves forward and later exits the shock tube. Three sinusoidal air/SF6 interface with different amplitude are located at the convergent test section. And the interface evolution are well captured by a high-speed schlieren photography. A long-term linear development of the interface amplitude is obtained, which indicates the RT effect is greatly inhibited in our experiment. The amplitude growth can be ascribe to the dominant role of the nonlinear effect in the later times. The interaction of the BP effect and the nonlinear effect illustrates the linear evolution of the interface.