A method for reducing flow separation with actively actuated flaps inspired by bristling shark scales was studied experimentally using digital particle image velocimetry (DPIV). The flaps in this study had a rectangular shape and were designed with a protrusion height in the bottom 10% of the boundary layer height, which is similar to that of the flexible scales found on the mako shark. The flaps were embedded into a flat plate, actuated in unison with frequencies from 0.48 Hz to 5.13 Hz within a water tunnel in a separating turbulent boundary layer flow. These tests were then compared to a corresponding smooth plate case. In the first set of tests, a zero pressure gradient case, it was found that the actuation of the flaps increased the overall momentum in the boundary layer near the wall, when compared to the flat plate case. This momentum increase helps support the hypothesis that the flexible scales of the mako shark help to energize the boundary layer when self-actuated by the flow. In the second set of tests the model was placed in a separated region induced by a rotating cylinder to impose the presence of an adverse pressure gradient. The cases with the actuating flaps showed a reduction in the size of the separated region compared to the smooth wall case. These results suggest that the bristling action of the scales induce mixing within the turbulent boundary layer and is thus an important component of the mechanism by which flexible shark scales control flow separation.
展开▼
