Enhanced swimming performance by flow control in marine mammals.
Frank E. Fish, Ph.D.
Department of Biology, West Chester University
Optimization of energy by whales and dolphins requires adaptations that reduce drag, and improve thrust production and efficiency. The control of flow over and around the body of whales, therefore, is critical to efficient swimming performance. Drag is minimized by streamlining of the body and appendages. These highly derived aquatic mammals have body shapes close to the optimal hydrodynamic design for drag reduction. Oscillations of the flukes, which are caudal hydrofoils, generate thrust throughout the stroke cycle and maintain a propulsive efficiency over 80%. This high efficiency is dependent on the passive, self-adjusting spanwise and chordwise bending of the flukes. Variation in body design also affects stability and turning performance. Major features affecting maneuverability are positions of control surfaces (i.e., flippers, fin, flukes, peduncle) and flexibility of the body. Position of control surfaces provides a generally stable design with respect to an arrow model. Whales with flexible bodies and mobile flippers are able to turn tightly at low turning rates, whereas fast-swimming whales with less flexibility and relatively immobile flippers sacrifice small turn radii for higher turning rates. The humpback whale (Megaptera novaeangliae) is exceptional among the baleen whales in its ability to undertake acrobatic underwater maneuvers to catch prey. In order to execute these maneuvers, such as banking and turning, humpback whales utilize extremely mobile, wing-like flippers. The humpback whale flipper is unique because of the presence of large tubercles along the leading edge, which gives this surface a scalloped appearance. The position, size and number of tubercles suggest analogues with specialized leading edge control devices associated with improvements in hydrodynamic performance on lifting surfaces. The tubercles function to produce vortical flows over the surface of the flipper and control lift characteristics at high angles of attack, where stall would occur. The morphologies displayed by animal species represent compromises between structural materials, evolutionary constraints, and diverse functional requirements. However, due to the high level of performance engendered by the various morphological solutions displayed in whales, these biological designs are of particular interest for the potential development of new and superior technological designs.