60 / 2020-02-27 17:26:44

Numerical investigations of interface instability and turbulent mixing under implosion

Richtmyer-Meshkov instability; Rayleigh-Taylor instability; Reshock; Convergent geometry,implosion,turbulent mixing

全体主题 > 极端条件下的物理学

The perturbed interface between two different fluids will be unstable and grows when it is driven by a shock wave or acceleration, this phenomenon is known as the Richtmyer-Meshkov instability (RMI) or Rayleigh-Taylor instability (RTI). They can induce the turbulent mixing at late times. These problems are very important in the inertial confinement fusion (ICF), supernova explosion, etc. In this paper, the dynamical behavior of interface instability and turbulent mixing in air/SF6 gas configuration driven by implosion in spherical geometry are investigated by using an in-house direct numerical simulation code MVFT.
The results show the complex evolving laws and physical mechanism of interface instability and turbulent mixing due to the evolution of complex waves in this case. The RM instability is induced when the perturbed Air/SF6 interface is driven by the incident shock wave. And the perturbed interface moves toward the center acceleratedly, the RT instability occurs. Then the perturbed interface slows down and moves towards the center deceleratedly, and the RT stabilization appears and suppress the development of interface instability and turbulent mixing. When the RT stabilization acts an absolutely dominant role, the growth of turbulent mixing zone (TMZ) width is restrained completely, and its width reduces. After the rebound of transmitted shock wave, the secondary loading from heavy fluid to light fluid is a combination of quasi-isentropic ramp wave, shock wave and Taylor wave in time series. The loading of quasi-isentropic ramp wave also contributes to the RT stabilization mechanism, the drive of rebound shock wave induces the RM instability too, and the impact of Taylor wave results in the RT instability once again. In the following, the reflected waves move towards the center and bounces again, the third loading process is same as the secondary one, the TMZ width repeat the same growth laws. The Bell-Plesset (BP) effect belonging to the conergent geometry can promote the development of TMZ. In the spherical converegent geometry, the competition mechanism among RM instability, RT instability, BP effect and RT stabilization controls the evolution of interface instability and turbulent mixing. The distributions of turbulent kinetic energy indicate that the TMZ evolves asymmetrically along the radial direction. The distributions of three direction components of turbulent kinetic energy and energy spectra also exhibit the evolution of TMZ is strong anisotropic.