Shark-Inspired Laminar Separation Control in an Unsteady Adverse Pressure Gradient

The 3D printed Micro-adaptive Array for Kinematic Optimization (MAKO) is a manufactured surface of flexible scales that are geometrically similar to shortfin mako scales from the flank region. Previous work suggests the MAKO model can reproduce the ability of shortfin mako shark scales in separation mitigation, specifically in turbulent boundary layers. The current study documents separation bubble formation and scale response for unsteady, laminar conditions in a boundary layer subjected to an increasing adverse pressure gradient (APG). Experiments were conducted in two different boundary layer configurations, considering Reynolds number and induced flow reversal effects. Reynolds number ranged from 1.22*10^5 to 4.5*10^5. The APG was induced to create a separation bubble using a spinning cylinder located just upstream from the MAKO surface, with unsteady effects induced by moving this spinning cylinder vertically toward the plate from a distance of 14 cm to 4 cm. Using DPIV, the formation of the separated region can be visualized, for both a smooth surface and over the MAKO model so this passive flow control mechanism can be studied. Instantaneous flow fields capture bristling of the scales that impede the formation of reversing flow, thus allowing this motion to be analyzed. All test configurations are compared to a smooth plate to better understand the extent of flow control.