Experimental Study of Unsteady Separation Control in a Laminar Boundary Layer by Shortfin Mako Shark Skin*

Flow separation, which results in higher drag, is an ongoing issue for flow control innovation. It has been demonstrated that shortifn mako shark scales are capable of being bristled by reversing flow occurring in separated regions resulting in a novel passive, flow actuated separation control mechanism.  An investigation of how this backflow forms and interacts with real shark skin specimens is of interest to further understand this mechanism and its potential to control separation.  A water tunnel experiment replicates separation with a focus on the reversing flow development near the wall within a laminar boundary layer.  Using a rotating cylinder, an unsteady and increasing adverse pressure gradient was induced creating a separated region over a flat plate.  Several laminar boundary layers of Re varying from 1.67*10^5 to 2.98*10^5 and approximate thickness of 10 mm were used making them more measurable to DPIV.  An unsteady and growing region of separated flow was induced over the plate for both smooth and shortifn mako shark skin surfaces.  The two are compared to see how the scales affect the formation, size, and separation point of the reversing flow region.