Buoyancy-Driven Homogeneous Turbulence Under Sharp Acceleration Changes

The effects of sharp acceleration changes on variable-density mixing are investigated using direct numerical simulations of buoyancy-driven homogeneous variable-density turbulence (HVDT). Such sharp changes, including acceleration reversal or a total removal of the acceleration field, occur in the high-energy-density applications such as inertial confinement fusion, blast waves, and astrophysical flows. HVDT is known to mimic the core regions of the mixing layers produced by the acceleration-driven Rayleigh-Taylor and the shock-driven Richtmyer-Meshkov instabilities by isolating the problem from edge effects. In this study, we explore the effects of acceleration switches on variable-density mixing in HVDT. The flow contains unique coupled transitory effects between the turbulent mixing and turbulence intensity which arise due to the sharp acceleration switches. These effects will be discussed in detail benefiting from the joint probability density functions (jPDF) of the density and momentum fields. Finally, the short- and long-term similarities between the effects of acceleration reversal on the Rayleigh-Taylor instability and HVDT will be discussed.