Wind tunnel testing of 3D printed shark scale surface for separation control

Low speed water tunnel studies have obtained favorable results of separation control with real shark skin and 3D printed models. However, the thinner boundary layers formed in wind tunnel studies have proved challenging for testing shark skin models in air. Sizing of shark scales within the boundary layer is an important parameter. Previously, the scales actuated to heights of over eight percent of the boundary layer, compared to within five percent in water tunnel studies and three percent as observed in nature. This experiment attempts to alleviate the sizing issue by growing a boundary layer over a long flat plate to a Reynolds number of 1,700,000 so that the smallest possible 3D printed scales (actuation height of 2 mm) will only reach within the bottom five percent of the boundary layer thickness. An array of over 5,000 scales is investigated on the suction side of a trailing edge flap at the end of the flat plate. Scales are locally actuated by reversing flow near the surface of the flap, impeding the development of separation. Force measurements are analyzed to determine if scales of this size are effective as a passive separation control mechanism.