Screw-Powered Propulsion in Granular Media: An Experimental and Computational Study

Screw-Propelled Vehicles (SPV's) have been widely used for terrestrial applications such as transportation over mud, snow, and amphibious environments. Similar vehicles have also been applied to industrial processes such as dewatering. Typical designs rely on a large pontoon shaft and relatively small blades to prevent unwanted sinkage or blade damage. These types of vehicles were considered during the design of the first lunar rover, given their success in aqueous and arctic media and simplicity compared to tracked vehicles. Studies have looked at the mobility of SPV's on the surface of granular media but there are not any computational and experimental studies on propulsive buried screws. Understanding the role of screw design and its angular velocity on thrust force is key to the advancement and control of SPV's. This study presents experimental and computational results of a submerged, double-helix Archimedes screw generating propulsive force against a bed of soda-lime glass beads. Thus, this research forms the basis for design of a future miniaturized exploration vehicle for space applications. In our study, we used two different screw designs (5 cm radius, 10 cm length, 63 and 44 degrees helix angle corresponding to 4 cm and 8 cm pitch, respectively) submerged in 2mm glass beads (90% roundness with sizes 1.8 mm to 2.2 mm), For both screws, a similar trend is observed between rotational speed and thrust force. We used EDEM, a Discrete Element Modeling (DEM) software for computational studies of the screw interactions with granular media. There is 5-20% discrepancy between our computational and experimental results. We will discuss possible sources of error and the potential for using DEM as a design tool for SPV's.