Propulsive mechanism of forward and backward free swimming of angulla angulla*

Eels can swim backward by reversing the direction of the traveling wave along the body. The propulsive mechanism of an eel, angulla angulla, during its free forward swimming and switching direction to backward swimming has been studied numerically. The problem is reasonably simplified to a loose-coupling problem of fish swimming dynamics and hydrodynamics only in the heading direction. The approach involves the simulation of the flow by solving the two- dimensional unsteady incompressible N-S equations and the solution of fish motion dynamics problem by the Newton's Second Law. Visualizations of flow fields and vortex structures are presented. The results show that thrust is associated with vortex structures in the wake.