Role of collisions in erosion of regolith during a lunar landing

摘要

The supersonic gas plume of a landing rocket entrains lunar regolith, which is the layer of loose solids coveringnthe lunar surface. This ejection is problematic due to scouring and dust impregnation of surrounding hardware,nreduction in visibility for the crew, and spoofing of the landing sensors. To date, model predictions of erosionnand ejection dynamics have been based largely on single-trajectory models in which the role of interparticlencollisions is ignored. In the present work, the parameters affecting the erosion rate of monodisperse solids areninvestigated using the discrete element method (DEM). The drag and lift forces exerted by the rocket exhaustnare incorporated via one-way coupling. The results demonstrate that interparticle collisions are frequent in thenregion immediately above the regolith surface; as many as 20% of particles are engaged in a collision at angiven time. These collisions play an important role both in the erosion dynamics and in the final trajectories ofnparticles. In addition, a direct assessment of the influence of collisions on the erosion rate is accomplished via ancomparison between a “collisionless” DEM model and the original DEM model. This comparison shows that thenerosion dynamics change drastically when collisions are considered and that the erosion rate is dependent on thencollision parameters (coefficient of restitution and coefficient of friction). Physical explanations for these trendsnare provided.