Effects of Reynolds number on energy extraction performance of a two dimensional undulatory flexible body

Abstract

In this paper, a NACA0012 airfoil is used as a two-dimensional simplified model of a fish body undertaking undulating motion. Using numerical simulation and dynamic mesh method combined with the spring-based smoothing and the local remeshing, the effects of Reynolds number on energy extraction efficiency of an undulating flexible body are studied at different wave velocities and wavelengths. Based on unsteady incompressible Navier-Stokes (N-S) Equations, the flow field around an undulating two-dimensional fish-like body was simulated with the aid of CFD software Fluent 15.0. The present numerical results indicate that:1.Given the maximum amplitude, the tendency of the variation energy extraction efficiency with Reynolds number at different dimensionless wave velocity and wavelength are generally similar: as the Reynolds number increases, the energy extraction efficiency increases at first and then decreases. Relatively high efficiency always occurs at moderate Reynolds numbers;2.For each Reynolds number examined, when the wavelength is constant, the energy extraction efficiency first increases and then decreases with increasing dimensionless wave velocity. There is an optimum wave velocity at which the energy extraction efficiency achieve their maximum values;3.For a given Reynolds number, there is a threshold value of dimensionless wave velocity, at which the energy extraction efficiency becomes zero and this is a turning point from energy extraction to energy consumption.