UCLA

Hydrodynamic interactions between respiratory fluid flows leaving the opercular openings and flows around the closely downstream pectoral fins of fishes are poorly understood. Labriform-swimming fishes that swim primarily by moving only their pectoral fins are good subjects for such studies. We did a high-fidelity two-dimensional computational investigation of these interactions using normal respiratory movements in both resting and slow steady swimming conditions based on representative values for parameters taken from experimental and computational work on the bluegill sunfish (Lepomis macrochirus) and largemouth Bass (Micropterus salmoides). We did a parametric study investigating the effects varying swimming speeds, strengths of opercular flows, and phase differences between pectoral fin and opercular opening and closing movements have on the thrust and side slip forces generated by the pectoral fins during both abduction and adduction portions of movement cycles. We analyzed pressure distributions on fin surfaces to determine physical differences in flows with and without opercular openings. Complex flow structures emerged from the coupling between opercular jets and vortex shedding from pectoral fins. The jets from the opercular opening appear to exert significant influence on the forces generated by the fins. These simulations and corresponding analysis establish a framework for study of these interactions in various labriform swimmers in a variety of flow regimes. These processes are likely significant in the maneuverability of these fishes.