Investigation of Low Speed Streaks Within a Turbulent Separated Boundary Layer over 3D-Printed Shark Denticles

Low speed, streamwise, turbulent streaks play an important role within turbulent boundary layers, aiding in the production and transport of turbulence. When the turbulent boundary layer separates, these low momentum streaks have been seen to be the first regions to experience reversing flow upstream global separation. A bio-inspired solution to decreasing a separated turbulent boundary layer is using 3D printed flaps inspired by shortfin mako shark denticles that passively actuate in reversing flow. Using a rotating cylinder, an adverse pressure gradient was generated over these scales upstream and in the vicinity of a turbulent separation bubble. DPIV was utilized to visualize the separation bubble itself and the streaks that occur upstream of global separation for Reynolds numbers ranging from 6.6e5 to 11.6e5. Data was analyzed to determine the spacing and thickness differences of this early reversing fluid over the scales to understand the mechanism that leads to global control.