The skin of Tursiops Truncatus is corrugated with small, quasi-periodic
ridges running circumferentially about the torso. These ridges extend into the
turbulent boundary layer and affect the evolution of coherent structures. The
development and evolution of coherent structures over a surface is described by
the formation and dynamics of vortex filaments. The dynamics of these filaments
over a flat, non-ridged surface is determined analytically, as well as through
numerical simulation, and found to agree with the observations of coherent
structures in the turbulent boundary layer. The calculation of the linearized
dynamics of the vortex filament, successful for the dynamics of a filament over
a flat surface, is extended and applied to a vortex filament propagating over a
periodically ridged surface. The surface ridges induce a rapid parametric
forcing of the vortex filament, and alter the filament dynamics significantly.
A consideration of the contribution of vortex filament induced flow to energy
transport indicates that the behavior of the filament induced by the ridges can
directly reduce surface drag by up to 8%. The size, shape, and distribution of
cutaneous ridges for Tursiops Truncatus is found to be optimally configured to
affect the filament dynamics and reduce surface drag for swimming velocities
consistent with observation.Comment: 71 pages, 27 encapsulated figure
