Drag characteristics of a penguin's body under heaving motion

Abstract

Penguins are species of flightless seabirds that mainly use their flippers to generate thrust and change directions, which consequently induce unsteady lateral motion on the bodies. This study aims to investigate the drag characteristics of a penguin’s body under such motion, in particular heaving motion. Gentoo penguin’s actual body shape and swimming motions were obtained from recent bio-logging data, which were then scaled and replicated in a circulating water tunnel. Drag in the free stream direction was measured for various reduced frequencies and dimensionless amplitudes of heaving, revealing the existence of critical reduced frequency at which body drag undergoes characteristic change. Based on this critical parameter, quasi-steady mode and unsteady mode of heaving were defined. Scaling analysis was utilized to confirm Lighthill's relationship and also derive empirical formula for the drag of the penguin's body under unsteady heaving mode. Quasi-steady analysis reinforced findings that body drag increases significantly past the critical reduced frequency, where unsteady effects dominate.