Significant risks result from the plume-surface interaction during propulsive landings on unprepared regolith in extra-terrestrial environments. 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 physics within the regolith compositions found on Moon and Mars. 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. With the current focus on returning to the Moon in the near future, this plume-surface effects simulation capability must now be applied in the lunar vacuum environments. In this case, a mixed continuum/rarefied approach must be used to properly simulate the gas-phase dynamics. This project will combine existing capabilities for gas-granular flows with mixed continuum/rarefied gas flows into a coupled toolset using a novel micro/macro coupling approach. This combination facilitates a local switch to continuum or rarefied gas flow in a seamless automated process. During Phase I, the mixed continuum-rarefied gas flow capability will be implemented and its influence on the particle phase response demonstrated. A plan will be devised for modeling the reverse effects of the particle phase on the state of the mixed rarefied gas phase. A list of required validation cases for this new capability and suitable experimental facilities will be identified to generate validation data in Phase II. Phase II effort will complete implementation of all models and perform extensive validation and application demonstrations.
Potential NASA commercial applications include all NASA led lunar lander development projects. Small commercial lander activities and NASA sponsored instrument payloads under the CLEPS program will require accurate definition of the plume-particle distribution environment below the landers near the surface encountered by the landers and the payload instruments. The development of medium/large size robotic and human class landers, in the context of the Lunar Gateway outpost, will require detailed information on plume-surface interaction risks.
Potential non-NASA applications include mixing in pharmaceutical industries, where flow and heat transfer through particle beds can force local conditions to be non-continuum due to the small length scales. The tool will be relevant to multiple applications that encounter ablation through porous media in low-pressure environments such as terminal high-altitude National Missile Defense vehicles.