Sulfur hexafluoride bubble evolution in shock accelerated flow with a transverse density gradient

Abstract

Sulfur hexafluoride (SF6) is a colorless, odorless, non-toxic, non-flammable stable gas, which has been widely adopted as the heavy gas in the Richtmyer–Meshkov instability study. In this paper, a computational analysis of SF6 bubble evolution in shock-accelerated flow with a transverse density gradient is presented. The influences of different incident shock Mach numbers on various interactions were clarified using high-resolution computation schemes. The results showed that the incident shock wave becomes curved during propagation because of the transverse density gradient. Based on this, two separate shock-focusing processes were identified when Ma = 1.21 and three separate shock-focusing processes were identified when Ma = 2.0. However, the shock-focusing intensity was weaker than previously observed in a flow field with a uniform density distribution. High- and relevant-pressure impingement played vital roles in the formation of three jets near the downstream pole of the SF6 bubble in both cases. In addition, impingement by incident and reflected shocks could induce additional vorticities in the bubble region and promote increased bubble volumes, but these increased bubble volumes could weaken the average vorticity. Upon increasing the incident shock Mach number, the effective bubble volume decreased with the enhanced shock intensity, but the vorticities were strengthened. Furthermore, analyzing the factors that affected vorticity evolution allowed us to find that the compression term had a stronger influence on vorticity evolution than the baroclinic term or the viscosity term. All of these studies complement the Richtmyer–Meshkov instability study.