Contrasting flow dynamics between stationary and moving clapping bodies

Flow dynamics of pulse-jetting aquatic animals are often studied with apparatus kept stationary. This paper examines whether the stationary configuration captures the mechanics of the swimming animal. A clapping body, simulating a pulse-jet animal, is tested in freely propelled (dynamic) and forward motion constrained (stationary) conditions. Significant differences are observed in body motion and wake structure: clapping motion is nearly twice as fast in dynamic cases, while mean thrust coefficient and vortex circulation are higher in stationary cases, varying with body depth but which remain constant in dynamic cases. Care is needed in extrapolating data from stationary to swimming bodies.