Mixing Enhancement by an Actively Controlled Bristled Shark Scale Model in a Turbulent Boundary Layer*

The scales of the shortfin mako shark are capable of bristling up to 50 degrees. This bristling impedes flow reversal, which then leads to separation control and less drag. Previous research has confirmed that the actuation of the scales is a passive mechanism. Although the scales are actuated by the flow and not the shark, being able to actively actuate a shark skin model can help to isolate the momentum mixing that occurs between the turbulent boundary layer and cavities that form during scale actuation.  To closely match the cavity Reynolds number of the actual shark scales we have 3D printed a larger sized model. We tested the model at three free stream velocities, and at three different actuation timescales for each free stream velocity.  The effect on the turbulent boundary layer, with emphasis on changes in momentum of the flow near the wall, was studied using DPIV.