National Natural Science Foundation of China under Grants 51179183 and 61233013
This paper presents a design of foldable propellers for a hybrid-driven underwater glider. The design ensures that the propellers are fully closed when the glider is working in buoyancy-driven gliding mode, and become fully open to provide propulsion when necessary. The hydrodynamical moments during the folding and unfolding processes is analyzed and computed using computational fluid dynamics (CFD) methods. Torsion springs are used as key components in the folding and unfolding mechanism. The stiffness of the torsion springs are designed to achieve balance between the mechanical and hydrodynamical moments acting on the propellers. It is shown that comparing to a conventional unfoldable design, the foldable propellers may achieve a significant reduction in drag force when the glider is operating in the gliding mode. Pool experiment results demonstrate the effectiveness of the folding mechanism when installed on an underwater glider.