Plume-Surface Interaction in Rarefied Environments

Plume-surface interaction during propulsive landings on unprepared regolith in extra-terrestrial environments is recognized as a major risk factor facing exploration missions. Dust and debris particles are liberated and may strike the landing vehicle and surrounding assets and may obscure ground observation for safe landing. In addition, craters are formed on the landing surface, posing an additional challenge to vehicle stability and surface operations. CFDRC has developed the Gas-Granular Flow Solver (GGFS) capable of simulating the multi-phase gas-particle interaction and the complex granular physics within Moon and Mars regolith. Eulerian-Eulerian models are applied to efficiently model the gas and particle phases as continuum fluids. This capability has successfully been introduced into NASA project applications for Mars lander development including the InSight lander and future human Mars lander architectures.nbsp; With the current focus on returning to the Moon in the near future, this plume-surface effects simulation capability must be extended for applicability to lunar vacuum environments where a mixed continuum/rarefied approach must be used to properly simulate the gas-phase dynamics. In Phase I, the gas-granular capability was adapted for use in mixed continuum/rarefied regimes by coupling with a kinetic solver using a novel multi-fluid coupling approach. This combination facilitates a local switch to continuum or rarefied gas flow in a seamless automated process, distinctively accounting the gas-particle interactions. In Phase II, the multi-fluid continuum and rarefied gas and solid particles coupling algorithm will be implemented and extended for use with realistic gas and granular mixtures. A procedure will be implemented for generating realistic lunar regolith composition material models. The validation effort will include simulations with reduced gravity, varied atmospheric rarefication, supersonic flow, realistic and ideal granular mixtures.