Meeting Abstract

76.3  Sunday, Jan. 6  Unsteady computational fluid dynamics computation of fish suction feeding on stationary prey SKORCZEWSKI, T.L.*; CHEER, A.Y.; WAINWRIGHT, P.C.; CHEUNG, S.H.; University of California, Davis; University of California, Davis; University of California, Davis; University of California, Davis

During a suction feeding event, a fish rapidly expands its buccal cavity, thus creating a pressure gradient and inducing a fluid flow field. It is this flow field that exerts force upon the prey. Here unsteady fully viscous 3-D Navier-Stokes computations of a suction feeding event using an overset grid approach are performed. Instead of trying to represent the geometry with one large complex computational grid, several simple overlapping grids, one representing the fish, one the prey and one the surrounding fluid are used. In this study the prey is modeled as a stationary sphere placed one gape distance from the mouth and is allowed to influence the flow. The fish has a 15 cm length with a fixed 15 mm gape. The suction is simulated by prescribing a time dependent fluid velocity from experimental data of feeding Bluegill on the mouth of the fish. No slip boundary conditions are applied to all other surfaces. Drag forces on the prey are calculated by integrating the stress, &sigma = -P + &tau, over the surface of the prey. Computations with prey of varying diameters, D = 1, 2.5, 5, 10 mm, along with a computation with no prey are performed. Results show the impact of allowing the prey to influence the flow field, namely a negligible pressure gradient force. Computations where the peak suction time varies, t = 100, 200, 300, 400, 500 ms, with a 5 mm diameter prey are also run. Results from this parameter study indicate that the total forces on the prey, drag plus acceleration reaction, are inversely related to peak suction time and that the acceleration reaction force controls the total force. This supports previous claims that fish can increase the force exerted on prey by decreasing the time to peak suction.