Meeting Abstract

S11.9  Wednesday, Jan. 6  Eddies: Potential impacts of turbulence on fish-swimming form and function WEBB, Paul W*; COTEL, Aline J; University of Michigan, Ann Arbor; University of Michigan, Ann Arbor pwebb@umich.edu

Ideas on the relationships between water flow and form of fishes over the past century are derived largely from assumptions of relatively steady flow. Instead, generating thrust and the natural habitat experienced by fishes are both characterized by unsteady water motions typical of turbulence. The occurrence of turbulence has received attention primarily in terms of boundary-layer control, delay of separation and similar drag-reducing forms and functions. A few historical studies have explored eddies, the structures of turbulent flow, in terms of their formation by propulsive movements. In the past decade, detailed study of eddy creation during swimming and in natural habitats has greatly increased, but consideration of the potential impacts of these eddies on form is very limited. Studies of fish wakes show that most of the mechanical energy associated with propulsive movements is dissipated to the wake, reversing the historical assumption that energy loss is associated with translocation of the body itself. Given the large energy loss in the wake, adaptations to minimize these losses would be anticipated. We suggest that requirements for fast-starts and other maneuvers limit the ability to minimize energy losses to the wake during steady swimming. In addition, we recognize that the archetypal streamlined “fish” shape not only minimizes resistance during glides and in turns, but also minimizes wake energy losses, and reduces linear and rotational perturbations as a result of swimming into eddies with circulation of magnitudes known to overwhelm fish stability control systems.