  Aquatic animals have developed effective strategies to reduce their body drag
over a long period of time. In this work, the influence of the scales of fish
on the laminar-to-turbulent transition in the boundary layer is investigated.
Arrays of biomimetic fish scales in typical overlapping arrangements are placed
on a flat plate in a low-turbulence laminar water channel. Transition to
turbulence is triggered by controlled excitation of a Tollmien-Schlichting (TS)
wave. It was found that the TS wave can be attenuated with scales on the plate
which generate streamwise streaks. As a consequence, the transition location
was substantially delayed in the downstream direction by 55% with respect to
the uncontrolled reference case. This corresponds to a theoretical drag
reduction of about 27%. We thus hypothesize that fish scales can stabilize the
laminar boundary layer and prevent it from early transition, reducing friction
drag. This technique can possibly be used for bio-inspired surfaces as a
laminar flow control means.

Fluid Dynamics