Numerical Study on Relaminarization in Fish-Like Locomotion

Unsteady viscous flow field around a fish-like advancing NACA wing is numerically studied. The main objective is to study the abilities of a flexible fish-like body to produce thrust, achieve higher propulsive efficiency as well as to catch the basic flow characteristics in viscous flow field. The Reynolds numbers based on the oncoming velocity and the body length range from 10 6 to 3x10 6 . The flow is simulated by solving two-dimensional unsteady Reynolds averaged Navier-Stokes equation in a primitive value formulation, while the turbulence transportation is described by updated algebraic eddy-viscosity model and transitional zone is computed by empirical formula. The numerical scheme is based on the MAC method with a body fitted coordinate system. The simulation shows that the high propulsive efficiency of fish-like locomotion comes from relaminarization and effective vorticity control. Relaminarization reduces the frictional force at higher Reynolds number. Fish-like locomotion can recapture energy contained in the eddies by skillfully controlling vorticity generation, travel and shed through the body undulation.