Numerical Simulation of Plume-Regolith Interaction in Lunar Environment

• Numerical Simulation of Plume-Regolith Interaction in Lunar Environment • DASH/IDEA 2025 Background Current space exploration aims to establish permanent structures on the Moon, Mars, and eventually other planetary bodies. The successful design and execution of lunar missions relies heavily on understanding and predicting the behavior of lunar regolith, a fine granular material covering the Moon's surface. Lunar regolith exhibits highly irregular particle shapes, low cohesion, and a wide particle size distribution, making it significantly different from terrestrial soils. The reduced gravity (approximately 1/6th of Earth’s) and extreme vacuum conditions on the Moon further complicate the behavior of granular materials. Lunar regolith poses unique modeling challenges due to its composition, microstructure, and interaction with rarefied exhaust gases. The exploration, development of sustainable infrastructure, and eventual habitation of the Moon require a deep understanding of how lunar regolith—an unconsolidated layer of fragmented rock and dust—behaves under varying conditions and different mechanical and fluid dynamic influences. The study of under-expanded compressible flow from the rocket nozzle interacting with lunar regolith is critical for understanding the effects of rocket exhaust on lunar surfaces. This is particularly relevant for space exploration initiatives such as the Artemis program, which aims to establish sustainable operations on the Moon through multiple landings using largescale spacecraft. One of the critical challenges during surface operations on the Moon is the plume-regolith interaction (PRI) phenomenon, where high-velocity exhaust gases from descent engines disturb the regolith, causing erosion, ejecta dispersion, and crater formation. These effects can damage lander hardware, obscure sensors, and threaten nearby assets. To address these concerns, a robust, modular simulation framework was developed that provides accurate predictions for lunar regolith behavior and plume-regolith interactions, leveraging state-of-the-art software platforms MFiX-DEM and COMSOL Multiphysics®. MFiX-DEM can accurately model particle contact force, particle collision, cohesion, etc. that are relevant to granular regolith flows, and COMSOL can accurately model the interaction between the highly compressible supersonic plume and the lunar surface. Technical Approach The proposed approach focused on utilizing each tool's specialized capabilities relevant to the problem, without direct coupling, to achieve successful and accurate computationally intensive simulations of critical lunar surface phenomena. The approach captured the gas dynamics of the rocket plume, thermal field, and the particle-scale physics of regolith transport and deformation. Simulations were conducted under lunar gravity, with low atmospheric pressure mimicking vacuum boundary conditions and particle models. Conclusions This project modeled the flow behavior of granular materials representing lunar regolith in an hourglass hopper geometry (narrow-throat geometry) and simulated the high-velocity exhaust plume dynamics, thermal field, and their interaction with the lunar surface. Simulation models were validated by comparing numerical outputs with experimental observations and analytical predictions. Simulation results showed the COMSOL capability for simulating complex high-speed flows. The regolith flow simulations quantified the effect on particle-wall and particle-particle contact forces on AOR, clogging behaviors unique to reduced gravity granular systems in regolith particles with small diameters. The predicted AOR values matched well with values in the open literature. Results Debashis Basu, Akbar Whizin, Anthony Belzung, Michael Poston Southwest Research Institute® Acknowledgement This research was funded by the Advisory Committee for Research, Southwest Research Institute Mach number distribution of converging-diverging nozzle for different pressure ratios Plume-regolith interaction at different times and regolith particle lofting Plume-regolith interaction and displacement of regolith particles Change in AOR with frictional properties References • Chambers, W.A. and Korzun, “Plume-surface interaction testing for crewed lunar lander risk reduction.” In Applied Space Environments Conference Proceedings, October 2023. • Capecelatro, J. “Modeling high-speed gas-particle flows relevant to spacecraft landings: A review and perspectives,” International Journal of Multiphase Flow, Vol. 150, 104008, 2022. • Cuesta, C.J., Davies, J., Worrall, K., Cammarano, A. and Zare-Behtash, H., “Plume-surface interactions: A review of experimental work.” Acta Astronautica, Vol. 226, 892-912, 2025. Regolith flow and angle of repose (AOR) Diameter 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 13.37 s Y X Z Diameter 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 13.37 s Y X Z Lander module Diffused shock Continuum flow region Strong shock Polydispersed granular flow Entrained particles in the absence of atmosphere and consequent drag forces Viscous erosion region (Maximum dynamic pressure) Particle-Particle collision Stagnation region Expansion fan Nozzle wall Sonic line Nozzle Triple Point Jet Shock Wave Shear Layer Stagnation Bubble Wall Jet Recirculation Tail ShockImpingement Zone Bow Shock Gas Flow General physics in lunar plume-regolith interaction (Chambers and Korzun 2023, Capecelatro 2022, Cuesta et al. 2025) Plume-regolith interaction Computational Fluid Dynamics (CFD) using COMSOL Multiphysics: Solves the Navier– Stokes equations to simulate compressible gas dynamics of rocket plumes. Discrete Element Method (DEM) using MFiX-DEM: Models the motion and interaction of individual regolith grains, accounting for contact forces, collisions, and friction. This was exclusively used to simulate the flow of lunar regolith. Objectives This research project developed a numerical simulation tool that independently addresses two critical aspects of lunar regolith behavior in two phases: granular flow dynamics using DEM, and plume-regolith surface interaction (PSI) using the Eulerian-Lagrangian (Discrete Particle Model, DPM) approach. The simulation tool leverages the capabilities of two advanced computational platforms: MFiX for lunar regolith simulations with DEM and COMSOL Multiphysics® for plume surface interaction, without direct coupling between the two computational platforms. The main objectives of the research were: • Develop and validate a robust simulation approach using MFiX to simulate and analyze the granular flow behavior of lunar regolith while exploring the effects of regolith properties, such as particle size distribution, cohesion, and density, on granular flow behavior. • Simulate the high-velocity exhaust plume dynamics and their interaction with the lunar surface to assess the behavior of lunar regolith when subjected to high-velocity exhaust plumes, including particle ejection, regolith scouring, and plume-regolith interaction dynamics, using COMSOL Multiphysics and apply this to future Artemis landers. Pile-up and angle of repose (AOR) for lunar regolith particles Variation of AOR with reduced friction properties