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