Hydrodynamic benefit of impulsive bursting in a self-propelled flexible plate

Abstract

The hydrodynamic benefit of impulsive bursting in a self-propelled flexible plate was explored using the penalty immersed boundary method. A self-propelled flexible plate was realized by enforcing a prescribed harmonic oscillation in the vertical direction but allowing the plate to move freely in the horizontal direction. In impulsive bursting, the motion trajectory in the first half of one locomotion period was not symmetric with that in the second half. Simulations with symmetric bursting were also performed for comparison, where the motion trajectory was symmetric in the first and second halves of one period. The underlying propulsion mechanism for impulsive bursting was analyzed by examining the phase of the heaving stroke. The elastic energy (Eb), x-direction kinetic energy (Ekx), and y-direction kinetic energy (Eky) were determined to characterize the energy transformation of the self-propelled flexible plate. Vortical structures and pressure distributions were visualized to elucidate the hydrodynamic benefit of impulsive bursting. The phenomenon of impulsive bursting suppressed plate deformation, and Eb was transferred to Ekx and Eky. A strong negative vortex was formed via impulsive bursting, which was beneficial to the enhancement of cruising speed. The effect of bending rigidity (ζ) on impulsive bursting was examined. The cruising speed of the plate with impulsive bursting was 10.7% greater than that with symmetric bursting.