How fish power swimming – a 3D computational fluid dynamics study*

In undulatory swimming of fish, muscles contract sequentially along the body to generate a bending wave that pushes against the water and produces thrust. Here we use 3D computational fluid dynamics coupled to the motion of the fish with prescribed deformation to study the force, torque, and power distributions along the fish's body. We find that forces on the bodies of both the anguilliform swimmer and the carangiform swimmer are dominated by reactive forces, and furthermore, the force on the caudal fin of the carangiform swimmer is dominated by drag-like forces. The torque exhibits a wave pattern travels faster than the curvature wave in both the anguilliform and carangiform swimmers but the wave speed is even higher for the carangiform swimmer. The power output for the anguilliform swimmer is concentrated on the anterior half of the body and is significantly negative on the posterior side of the body. In contrast, most of the power is generated by the posterior part of the body before the peduncle for the carangiform swimmer. The results may explain the differences in the observed electromyography patterns in fish with different swimming modes.