CFD study on hydrodynamics of three fish-like undulating hydrofoils in side-by-side arrangement

Abstract

Propulsive advantage in a three side-by-side (one above the other) arrangement as compared to single/isolated fish-like locomotion of a flexible hydrofoil is studied. A level set based immersed boundary method (LSIBM) is used for a transient 2D CFD simulation and analysis of hydrodynamics of fish like locomotion; modeled here by undulating NACA0012 hydrofoil. The study is undertaken for both antiphase and in-phase undulation (of the middle as compared to side foils) for various frequency (St = 0.4, 0.6 and 0.8) and gap ratios (d = 0.4, 0.6, 0.8 and 1), at a constant amplitude (Amax = 0.1), wavelength (λ = 1) and Reynolds number (Re = 400). Anti-phase as compared to in-phase undulation is found to give better propulsive performance. For side as well as middle hydrofoil, effect of frequency as compared to hydrofoil-spacing is found to be more dominant on the propulsive performance. Signature of thrust is shown with the help of momentum excess and reverse Von-Karman Street.