Role of internal flow in squid-inspired jet propulsion

Abstract

We numerically investigate the dynamics of a self-propelled system that swims by using intermittent jet propulsion through cyclic body deformations. Unlike existing studies, the focus of the current work is on characteristics of internal flow field and its effect on the thrust generation and energetics of the system. Our results indicate that the inertia of the internal flow plays a minor role in thrust generation in comparison with the momentum flux and the normal stress at the nozzle. By examining the energy pathways in both inflation (recovery) and deflation (power) phases, we illustrate that the energy dissipation inside the pressure chamber occurs mostly in the inflation phase, during which the energy transferred from the solid structure to the fluid is mostly damped out and wasted. Based on this analysis, we propose a novel performance enhancement method by using a variable nozzle to reduce the energy waste in the inflation phase. In a sample case, this strategy not only increases the propulsive efficiency by 118% but also increases the forward speed by 25%. Furthermore, we have studied the effect of solid structures inside the pressure chamber. Our results suggest these structures cause a decline in the efficiency, especially if they are close to the nozzle.