Research On The Richtmyer-Meshkov Instability Under Reshock

When a shock wave interacts with a perturbed interface, the vorticity occurs in the flow field because of the misalignment of the pressure gradient induced by the shock wave and the density gradient on the interface, and the accumulated vorticity leads to the increase of the perturbations on the interface which finally develops into the turbulent mixing, and the phenomenon is referred to as Richtmyer-Meshkov (RM) instability. The research on the RM instability is very important to the academic problem such as the instability, the compressible flow and the turbulent flow, and it also plays a key role in many engineering applications such as the inertial confinement fusion and the scramjet engine. Since proposed, much attention has been paid to the RM instability. However, most previous work focused on the RM instability induced by a single shock, while the RM instability induced by multiple shock waves occurs a lot in the engineering applications. Therefore this paper concentrates on the evolution of the RM instability induced by the impact of the reflected shock.The first work is on the RM instability induced by a planar shock and its reflected shock. An aluminium plate is used in the planar shock tube to produce the reflected shock, and then a laser sheet is applied to illuminate the interface with a high speed camera used to observe the flow field. The paper has studied the interface evolution of two different heavy gas cylinders under the planar shock and its reflected shock, and the emphasis is placed on the effect of both the reflected shock and the Atwood number on the evolution of heavy gas cylinder. The results find that the reflected shock accelerates the mixing between the two different fluids, and it also induces some new features in the flow field. The difference of the Atwood numbers leads to the difference of the vorticity induced by the first shock, which results in the difference of the extent of the interface evolution when the reflected shock arrives, and the reverse vorticity induced by the reflected shock is also different because of the different Atwood numbers. The difference of the Atwood numbers results in the great distinction in the evolution morphology, the evolution velocity and the interface size.The second work in the paper is on the RM instability under the cylindrical converging shock and its reflected shock. The emphasis here is to study the effect of the eccentricity on the RM instability, for the eccentricity widely exists both in the experimental research and the engineering practices. The paper employs the procedure VAS2D to simulate the evolution of four familiar-shape interfaces. The differences of the eccentric and concentric cases are compared from the interface morphology, the pressure history of the interface center and the history of the mixing zone area. The results show that the eccentricity set in the paper is just a small perturbation, and the development of the RM instability is the superposition of the evolutions both in the concentric and eccentric cases. For the circular cylinder without the initial perturbation, the eccentricity results in the appearance of the tiny perturbation structures, and for the interfaces with the initial perturbation, the eccentricity makes the perturbation structures show the asymmetry and distortion. The eccentricity evidently changes the interface evolution and the parameters in the flow field. Two simple experiments on the eccentricity are supplemented and compared with the relative simulations, and the phenomena similar to the simulation are found in the experiments.