HYDRODYNAMICS OF 'THERMAL' GRANULAR CONVECTION

摘要

We employ the Navier-Stokes granular hydrodynamics for determining the threshold of "thermal" convection in a horizontal layer of fluidized granular medium. A recent experiment with a highly fluidized three-dimensional granular flow gives strong evidence for thermal convection. In the simplest model of inelastic hard spheres, the convection sets in when the restitution coefficient becomes smaller than a critical value. When gravity goes to zero, the convection instability turns into a recently discovered phase separation instability. A lower bound for the convection threshold is determined using the Schwarzschild criterion of stability of classical compressible fluid.