Laminar Boundary-Layer Development and Transition of Fish-Shaped Bodies of Revolution

Abstract

Since the major source of hydrodynamic drag of most fish is due to boundary-layer skin friction, it is expected that the magnitude of the drag is very sensitive to the position of transition from laminar to turbulent flow-at least in the range of body sizes and speeds where Reynolds numbers in the order of millions are achieved. It is the purpose of this paper to examine the effect of body shape on laminar boundary-layer development, transition position, and resulting drag to determine whether fish shapes have undoubtedly evolved from many requirements, the desirability of laminar flow over the nose and an attached flow over the afterbody to minimize drag and enhance pressure sensing (for control and detection) was probably a major requirement for certain sizes and types of fish.