Valve-mediated flow control in salp-like locomotion

By using an axisymmetric model, we numerically investigate the underlying fluid dynamics of a salp-like swimmer consisting of a deformable shell, a front valve, and a back valve. Through coordinated shell inflation/deflation and valve opening/closing, uni-directional flow is created inside the body and in the wake, which provides thrust for forward motion. Our results prove that this method is capable of sustained locomotion. The uni-directional internal flow successfully reduces energy loss due to dissipation inside the body. Moreover, due to hydrodynamic interactions among different body parts (i.e., the shell and the two valves), the energy expenditure of one part may be recovered by others. In addition to its benefit to energy efficiency, this phenomenon also implies that the valves may be passively activated by harvesting energy spent by the shell, so that the mechanical design can be simplified. Parametric studies have been conducted to determine the effect of the stroke ratio. Furthermore, the locomotion performance of the salp-like system has been compared with that of a squid-like system in which the refilling flow and the jet are in opposite directions.