Hydrodynamic Analysis of Tandem Flapping Hydrofoils

Abstract

Flapping hydrofoils in tandem configuration find applications in wave gliders, dragonfly, dorsal-tail fin interaction in fishes, among others. The flapping motion consists of a combination of heaving and pitching motion. This type of motion involves complex interaction of the vortices shed from the upstream hydrofoil with the downstream hydrofoil, thus influencing the performance of the downstream hydrofoil. A two-dimensional stabilized finite element moving mesh framework is utilized for the current study. The important parameters which influence the flow interactions are the chord size ratio and the gap between the hydrofoils. The size ratio is defined as the ratio of the chord of the upstream hydrofoil to that of the downstream hydrofoil. The size ratio is varied from 0.25 to 1. The gap is varied from one chord length to 3 chord lengths of the downstream foil. The study focuses on the effect of the size ratio, gap and flapping kinematics based on sinusoidal heaving and pitching motion on the detailed flow dynamics of the tandem hydrofoils. The effect on the thrust coefficient and hydrodynamic efficiency is explored and compared with that of an isolated hydrofoil. The results obtained from the study can pave way for a better understanding with regard to engineering designs based on biomimetics.