Numerical investigation on air/SF$_{\textbf 6
Abstract
Evolution of an SF$_6$ square block accelerated by a planar shock with different Mach numbers (<i>Ma</i>=1.18, 2.50) is numerically investigated using VAS2D algorithm, focusing on the compressible effect on the flow instability development. The wave patterns show that different shock strengths will result in the difference in location of shock-shock interaction occurring, and consequently have a prominent influence on interface morphology, especially on the jet structure. The results indicate that for a low Mach number, complicated shock-shock interaction occurs inside the volume, causing an outward jet formation. For a high Mach number, on the contrary, complicated shock-shock interaction occurs outside the volume, inducing an inward jet formation. Meanwhile, the shock reflection and refraction at interface for the high Mach number are so complicated that several additional jets generate and the interface is disturbed heavily. As shock Mach number increases, the compressible effect increases and vorticity amplitude and distribution also behave differently. More vorticity will deposit at the interface after impacted by a stronger shock wave, resulting in the vortex pair growing faster. Besides, vorticity is also clearly observed at the slip surface for the stronger shock wave, indicating that the obvious difference in velocity amplitude occurs at both sides of slip surface. Compressed by the stronger shock wave, the interface acquires a larger velocity, and the interface width and height also change greatly. Furthermore, the impact of the stronger shock wave greatly increases the mixing between two gases. Qualitative and quantitative results in this work demonstrate that the compressible effect has a significant influence on wave pattern and interface evolution.
