CFD–DEM simulation of gas-driven sampling on asteroid regolith: Dependence of collected mass on gas ejection

Asteroids are the remnants of the process by which planets formed from the protoplanetary disk. Laboratory analyses of materials originating from asteroids give us the unique opportunity to reveal the formation history of our Solar System about 4.6 billion years ago. To obtain surface regolith in the low-gravity and vacuum environment, a gas-driven sampling strategy has been proposed, but the relation between the collected mass and the gas ejection remains to be explored, which is important for the development of efficient sampling mechanism designs. In this paper, we simulate the gas–particle two-phase flow in the gas-driven sampling process by using the coupled Computational Fluid Dynamics and Discrete Element Method (CFD–DEM) method. The results show that the sampling process can be divided into three stages according to the mass of particles that are sampled. Initially, the impact ejection of the pressurized gas on the regolith layer dominates, during which the sampling speed increases to a maximum value rapidly. After that, the gas flow transports the ejected particles to the collection chamber. In this stage, the conveyance effect of gas plays a primary role. As grains accumulate near the entrance of the collecting tube, jamming state happens and obstructs the particle flow, making the sampling rate drop to a stable value. By varying the inlet gas velocity, we show that higher gas velocity increases the collected mass rate greatly at the first stage while no significant differences are found after the development of jamming state inside the chamber. The position of the inlets affects the flow field and thus could be used to prevent the unfavorable aggregation of particles near the collecting tube, which facilitates the sampling. The influence of the inlet gas angle is also explored. We find two inward tilting gas inlets could increase the sampling efficiency considerably through striking a balance between ejected mass and ejecting velocity. The results presented in this article are expected to provide important information on the optimal designs of gas-driven sampling devices for future asteroid space mission.