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Hydrodynamic benefits of intermittent locomotion of a self-propelled flapping plate.

Intermittent locomotion is a widely used behavioral strategy for fish and birds to reduce the cost of movement. The intermittent locomotion performance of a self-propelled flapping plate is investigated numerically. Two intermittent swimming modes, namely, the multiple-tail-beat mode (MT mode) and the half-tail-beat mode (HT mode), as well as the continuous swimming mode (CT mode), are considered. Performance is evaluated from propulsive speed, efficiency, and cost of transport. The hydrodynamic performances of the intermittent modes are found to be better than the hydrodynamic performance of the CT mode when the bending stiffness K is moderate [i.e., K≈O(1)] and the duty cycle is not too small. For the two intermittent modes, the performance of the HT mode is better than that of the MT mode when K is small or moderate, while the situation is opposite when K is large. It is found that compared to the asymmetric wake of the MT mode, the symmetric wake of the HT mode is favorable to generate more thrust force and therefore achieve better performance. Besides, at moderate K, the largest bending deformation of the plate in the HT mode, as well as the large normal force, produces the largest thrust during the flapping. The present results can help us to better understand the intermittent locomotion of animals and may be helpful for bionic design.