Planar Particle Tracking Velocimetry of Soil Erosion in Small Scale PSI Experiments*

During the powered descent of a human-class lander onto an extraterrestrial body a supersonic jet impinges on a surface generally conformed of loose regolith. The plume surface interaction (PSI) changes the surface topsoil geometry and causes entrainment of regolith into a complex multiphase flow that extends well above the surface and radially away from impingement. PSI effects have been identified to pose significant hazards throughout the history of manned spaceflight. The primary risks include, the alteration of the landing site surface, the obstruction of crew and sensor visibility during descent, and the damage by ejecta to vehicle instrumentation and nearby assets. High fidelity numerical simulation of plume-surface interactions is hindered by the complexity of accounting for four-way coupling interactions for a realistic number of particles and in a wide range of volume loadings and flow regimes. Lander scale numerical simulations require constitutive models for these multiphase flow interactions, which rely on experimental data. Historically, PSI experiments have relied on half-domain geometries to avoid the challenges of optical diagnostics in optically dense media. To advance the knowledge on PSI through quantitative measurements we have developed a subscale full-domain experiment with the ability to reproduce the main aerodynamic non-dimensional parameters of full-scale landers. Optical techniques such as high-speed schlieren, molecular tagging velocimetry, PLIF and planar particle tracking velocimetry are used to measure the flow and particle dynamics. Results at varying jet expansion ratios and nozzle-to-surface impingement distances highlight the very distinct flow and soil erosion features at conditions representative of Lunar and Martian landings.