不同强度平面激波冲击下正方形air／SF6界面演化的数值研究

Numerical investigation on air/SF_6 square block accelerated by planar shock with different strengths

本文采用VAS2D数值研究了两种强度平面激波(Ma=1.18,2.50)与air/SF6/air正方形界面作用后的RM不稳定性发展,重点考察流场可压缩性对界面不稳定性发展的影响.波系结构分析表明,激波强度不同会导致复杂的激波-激波干扰发生的位置不同,从而对界面形态,尤其是射流结构的产生有重要影响.低马赫数下复杂激波-激波干扰发生在界面内部,诱导向外射流结构的产生;而高马赫数下复杂激波-激波干扰发生在界面外部,诱导向内射流结构的产生.同时,高马赫数下复杂的激波反射折射对界面发展有着重要的影响,诱导多个射流结构的产生.随着入射激波强度增大,可压缩效应明显增强,界面上产生涡量大小和分布有所不同.强激波的冲击使得界面上累积更多的涡量,涡结构增长迅速,同时也观测到滑移面上有明显的涡量产生,表明滑移面两侧流体的运动速度有较大差异.强激波的压缩使得界面获得较高的运动速度,界面宽度和高度同样具有较大的变化率.此外,强激波的冲击会导致两种气体之间混合速率增大,极大地增强了气体之间的混合.定性和定量结果表明,可压缩性对流场的波系结构以及界面形态都有着重要的影响.

Evolution of an SF6 square block accelerated by a planar shock with different Mach numbers （Ma=l. 18, 2.50） is numer- ically 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 oc- curring, 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 in- creases, 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.