Interactions between compressible jet and granular surfaces under rarefied atmospheres

Plume-Surface Interactions (PSI) are ubiquitous in scenarios involving the take-off and landing of inter-planetary vehicles. These can be observed when the compressible exhaust plumes discharged by the vehicle interact with the granular planetary surface leading to the formation of craters and high-speed ejecta. This, in turn, can be detrimental to the vehicle and the structures around the landing sites. This study uses stereo photogrammetry to characterize the cratering dynamics and planar particle tracking velocimetry to characterize the kinematics of particles ejected from the crater. Time-resolved and full-domain experiments were performed in a vacuum chamber facility to understand the effects of nozzle height and ambient pressure conditions on cratering and ejecta dynamics. Compared to the Earth’s atmospheric conditions, the jet under rarefied conditions was highly under expanded leading to the formation of much wider and shallower craters. As a result, the ejecta also had higher velocities and shallower angles under rarefied atmospheres suggesting that the damage from ejecta, especially to the surrounding structures, will likely be much more severe than encountered on Earth. Finally, a strong correlation between the ejecta properties and crater geometry was observed, providing valuable insights into the initial characteristics of particle ejection.