Hydrodynamic advantages of a low aspect-ratio flapping foil. (May 2017)

• Record Type: Journal Article
• Authors: Lee, Jeongsu; Park, Yong-Jai; Cho, Kyu-Jin; Kim, Daegyoum; Kim, Ho-Young
• Is Part Of: Journal of fluids and structures. Volume 71(2017)
• Page Start: 70
• Page End: 77
• Publication Date: 2017-05
• Subjects: Aquatic locomotion -- Caudal fin -- Vortical structure -- Flapping -- Propulsion; Fluid-structure interaction -- Periodicals; Fluid mechanics -- Periodicals; Structural dynamics -- Periodicals; Structural analysis (Engineering) -- Periodicals; 620.106
• DOI: 10.1016/j.jfluidstructs.2017.03.006
• Languages: English
• ISSNs: 0889-9746

Abstract

Abstract: A high aspect-ratio foil is known to be advantageous in terms of both thrust and efficiency in flapping propulsion. However, many species of fish have evolved a low aspect-ratio hydrofoil, which naturally leads one to search for its physical advantages in locomotion. Here we study the flow physics of a hydrofoil in angular reciprocating motion with negligible free-stream velocity to reveal the effects of an aspect ratio on hydrodynamic performance. By establishing a scaling law for the thrust of a foil of general shapes and corroborating it experimentally, we find that the thrust of an angularly reciprocating foil is maximized at a low aspect ratio of 0.7 while hydromechanical efficiency continuously increases with an aspect ratio. This result suggests that a low aspect-ratio foil can improve thrust produced by the foil when they start from rest, but at the expense of efficiency.