A Comparative Numerical Study on the Performances and Vortical Patterns of Two Bioinspired Oscillatory Mechanisms: Undulating and Pure Heaving.

Mohsen Ebrahimi,Madjid Abbaspour

doi:10.1155/2015/325934

Abstract

The hydrodynamics and energetics of bioinspired oscillating mechanisms have received significant attentions by engineers and biologists to develop the underwater and air vehicles. Undulating and pure heaving (or plunging) motions are two significant mechanisms which are utilized in nature to provide propulsive, maneuvering, and stabilization forces. This study aims to elucidate and compare the propulsive vortical signature and performance of these two important natural mechanisms through a systematic numerical study. Navier-Stokes equations are solved, by a pressure-based finite volume method solver, in an arbitrary Lagrangian-Eulerian (ALE) framework domain containing a 2D NACA0012 foil moving with prescribed kinematics. Some of the important findings are (1) the thrust production of the heaving foil begins at lower St and has a greater growing slope with respect to the St; (2) the undulating mechanism has some limitations to produce high thrust forces; (3) the undulating foil shows a lower power consumption and higher efficiency; (4) changing the Reynolds number (Re) in a constant St affects the performance of the oscillations; and (5) there is a distinguishable appearance of leading edge vortices in the wake of the heaving foil without observable ones in the wake of the undulating foil, especially at higher St.

Highlights

The hydrodynamics and energetics of bioinspired oscillating mechanisms have received significant attentions by engineers and biologists over the past decades
From the arbitrary LagrangianEulerian (ALE) viewpoint, the nodes of the computational domain mesh may be moved with the continuum, same as normal Lagrangian manner, be held fixed in Eulerian fashion, or be moved in some arbitrarily specified way to give a continuous rezoning capability [38]
The solutions are continued to multiple periods of oscillations to ensure the repetitive periodic time dependent results. This systematical investigation reveals the comparative behaviors of the energetics of the heaving and undulatory oscillations as well as their flow patterns

Summary

Introduction

The hydrodynamics and energetics of bioinspired oscillating mechanisms have received significant attentions by engineers and biologists over the past decades. The oscillating mechanisms which are used by animals in nature can provide forces and moments efficiently [2,3,4]. This is due to the evolution process of these animals and their adaptation with operating medium [5]. Heaving (or plunging) and undulation are two significant mechanisms which are commonly used by body and/or fins of aquatic animals and wings of aerobic animals for propulsion, maneuvering, and stabilization purposes [2]. In some fish species (some kinds of carangiform and Thunniform swimmers, e.g., some of the dolphins, tunas, or sharks), the caudal fin has pure heaving motions, while in some other species (anguilliform and subcarangiform swimmers like spinny dogfish shark) it has undulating motions [5, 6]

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