35 / 2020-02-19 12:58:49

Richtmyer-Meshkov instability of a uniform interface driven by a perturbed shock: Reflected shock effect

perturbed shock,RM instability,reflected shock,theoretical model

全体主题 > 极端条件下的物理学

Richtmyer-Meshkov(RM) instability develops when a shock wave interacts with an interface separating two fluids with different densities. Over the past decades, the majority of the researches focus on the uniform shock hitting the perturbed interface and very little work is carried out to investigate the interaction of perturbed shock with uniform interface. Actually, the incident shock may be perturbed before it impacts the interface in many scientific fields such as inertial confinement fusion.
The talk will report an interesting experiment respecting a perturbed shock hitting a uniform N2/SF6 interface in a vertical shock tube and focus on the interface evolution during the reflected stage. Specifically, the perturbed shock is produced by diffracting a planar incident shock around a rigid cylinder, and the initial interface is formed by membraneless technique. Three different dimensionless distances η (the ratio of spacing from cylinder to interface over cylinder diameter) are considered. Features of the interface evolution after the impingement of the reflected shock are obtained using both schlieren photography and planar Mie scattering techniques.
Our previous work(Phys Rev E, 2017, 95, 013107), which concentrates on the evolution of the interface in the incident stage, indicated that, after the impact of the incident shock, the interface evolved into ‘Λ’ shape structure with two interface steps at both sides and a cavity and at the center. Here, the interface evolution during the reflected stage is discussed in detail and the result shows that, due to the impingement of reflected shock, the ‘Λ’ shaped interface first experiences a fast phase reversal and then increases gradually. For η = 2.0 case, the interface evolves into an overall bubble structure, while for η = 3.3 and η = 4.0 cases, a spike appears in the center of interface besides the overall bubble. The mixing width is further measured from Mie scattering images and compared with the theoretical values. It is found that at the early stage, the mixing width can be estimated well by the linear model proposed by Meyer & Blewitt(Phys. Fluids, 1972, 15: 753-759), and at the nonlinear stage, the mixing width can be reasonably predicted by the model proposed by Dimonte & Ramaprabhu(Phys. Fluids, 2010, 22, 014104). More over, the theoretical predictions and the experimental results coincide better with the increase of η number.