DSMC simulation of near-field enceladus plumes from tiger stripe fractures

The Saturn orbiter, Cassini, during its flyby of Saturn's moon, Enceladus, in 2005 discovered plumes of water vapor and ice grains in the south-polar region, primarily originating from four prominent fractures known as tiger stripes. Significant differences between gas and grain velocities suggest that the plume source lies beneath the satellite's surface. In this paper we model the subsurface gas and ice grain mixture flow from a subterranean source through a 45 m long subsurface channel. The gas flow inside the channel is continuum and inviscid in nature and is solved using an equilibrium direct simulation Monte Carlo (eDSMC) approach. Assuming that the ice grains are present in small mass concentration in the plume, an overlay technique to model the ice grain number density and size distribution along the channel is employed. A second more rigorous method, denoted as eDSMC-condensation, is developed to model ice grain collisions with water molecules and ice grain size growth directly in the water molecular flow as the two-phase flow evolves. The difference of gas and ice grains properties obtained with the two methods for a conical nozzle shape are found to be large. The ice grain size and mass fraction are compared at the surface exit with different method and nozzle shapes. Finally, it is observed that the eDSMC condensation simulations of the double-throated nozzle show that the flow properties strongly depend on the drag coefficient.