Cratering of a Particle Bed by a Turbulent Subsonic Jet

Future space exploration necessitates improved gas-solid and solid-solid interaction models. Impinging rocket plumes from spacecraft interact with the lunar regolith surface and release a high velocity particle-spray that is potentially hazardous to surrounding surface structures and surface architecture. Experiments performed at NASA-KSC provide data on the cratering of a particle bed by a turbulent subsonic jet of gas. In order to model this system, an Eulerian treatment is employed using locally averaged equations of motion along with closure relations describing the solids-phase stress derived using concepts based on dense-phase gas kinetic theory. The solids phase frictional stresses, which occur at high solids volume fractions and result from sustained particle-particle contacts, are based on critical state theory. Standard commercial codes employ these frictional stress models, but poorly predict the cratering dynamics found experimentally and predict a particle bed that is too liquid-like. However, a continuum frictional stress model in which the normal frictional pressure and frictional viscosity is increased significantly improves the predictions for the cratering behavior. In addition, the effect of the changes in the jet velocity and density are explored and compared with experimental data for crater width and depth.