Vortical structures around a flexible oscillating panel for maximum thrust in a quiescent fluid

摘要: Abstract It has been agreed that a proper level of flexibility in moving appendages like fin swimming animals enhances their propulsive performance. However, few efforts have spent to characterize the criterion, as simple guideline for designing biomimetic propulsor, at which beneficial effect compliance is maximized. Recently, it was reported sinusoidally pitching panel produces enhanced thrust when passively bending angle trailing edge lags behind its by around π / 2 due compliance. To understand mechanism, we perform series particle image velocimetry measurements quiescent water, while varying compliance, planform shape and frequency. For all shapes frequencies considered, with phase delay about , region high streamwise velocity thrust-generating momentum retained farther (in direction) wake, caused large effective during accelerating stage rotation. When stiffer (or smaller than ) optimal condition, however, strong interaction between trailing-edge vortices (TEVs) formed successively each half strokes pushes surrounding fluid into transverse direction, thereby decay velocity. This TEVs weak case On other hand, over-compliance, rotates opposite indicates inertial work required rotate stroke-reversal becomes excessive expense rotational circulation eventually weakens thrust.