Simulation of Diluted Flow Regimes in Presence of Unsteady Boundaries

The main feature of diluted flows is the presence of both continuum and kinetic regimes in the same field. TheES-BGKmodel is a kinetic model that preserves the asymptotic properties towards compressible Euler equations in the hydrodynamic regime, yet modeling momentum and kinetic energy diffusion for low Knudsen numbers. Here, this model is discretized by a finite-volume scheme on Cartesian meshes. The scheme is second order up to the possiblymoving boundaries. To ensure a smooth transition between the hydrodynamic and the kinetic regime up to the walls, appropriate boundary conditions are devised. As an application, we present the simulation of an unsteady nozzle plume in a very low pressure environment.