Near-body flow dynamics in swimming fish

We consider the motions and associated flow patterns of a swimming giant da nio (Danio malabaricus). Experimental flow-visualization techniques have be en employed to obtain the unsteady two-dimensional velocity fields around t he straight-line swimming motions and a 60 degrees turn of the fish in the centerline plane of the fish depth. A three-dimensional numerical method is also employed to predict the total velocity field through simulation. Comp arison of the experimental and numerical velocity and vorticity fields show s good agreement, The fish morphology, with its narrow peduncle region, all ows for smooth flow into the articulated tail, which is able to sustain a l arge load for thrust generation. Streamlines of the flow detail complex pro cesses that enhance the efficiency of flow actuation by the tail. The fish benefits from smooth near-body flow patterns and the generation of controll ed body-bound vorticity, which is propagated towards the tail, shed prior t o the peduncle region and then manipulated by the caudal fin to form large- scale vortical structures with minimum wasted energy. This manipulation of body-generated vorticity and its interaction with the vorticity generated b y the oscillating caudal fin are fundamental to the propulsion and maneuver ing capabilities of fish.