463 / 2019-03-12 19:17:47

Bubble Competition in Richtmyer-Meshkov Instability

Bubble competition; Richtmyer-Meshkov instability; Self-similar evolution

全体主题 > Interface Instabilities at Extremes

The Richtmyer-Meshkov (RM) instability occurs when a shock wave passes through an interfacial perturbation between two fluids of different densities. After the shock wave impact, the perturbation growth generally experiences a linear phase, and then a nonlinear state with the formation of bubbles and spikes, and eventually a turbulent mixing state. The RM instability plays an important role in many scientific areas such as inertial confinement fusion (ICF) and astrophysical problems. In ICF, RMI encompasses multiple modes generated by random perturbations on the interface. After the random disturbances on an interface develop, a competition between bubbles will occur, and this behavior is usually referred to as bubble competition. Two-bubble competition is the simplest type of bubble competition, in which two bubbles with a large and small size are periodically arranged. In this work, two-bubble competition experiments of an inverse-chevron interface with the initial vertex angle θ = 60° are carried out, and a periodic inverse-chevron interface is also considered for comparison. The initial interface is generated with a soap film technique, and a high-speed Schlieren system is used to observe the postshock interface evolution.
In the evolution of bubble competition, the large bubble expands and the small bubble shrinks. The small bubble is completely merged at late stage. The interface width evolution of large and small bubbles is studied. Large and small bubbles are determined to develop independently in the early stage, and both the dimensionless linear growth rates of large and small bubbles are 1. Bubble competition promotes the evolution of the large bubbles for p = 1.5 and 2, but inhibits the evolution of the large bubbles for p = 3, which is attributed to different spike developments in the late stage. The dominant bubble grows self-similarly with time in the competition process. The self-similar parameter β is first studied experimentally in RM instability and has a range of 3-3.4, which is in the range of the theoretical result of Alon et al.. The evolution of bubble front width of the large bubble obeys a power law with the power law exponent in a range of 0.31-0.42. The range of the power law exponent is consistent with previous results.