Control of Turbulent Boundary Layer Separation by 3D Printed Dolphin Skin Models

A problem in many flow applications is boundary layer separation; this study investigates the passive separation control mechanism that could result from the micro-grooves found on dolphin skin. A water tunnel was used to grow a turbulent boundary layer over rigid 3D printed plastic models, and an adverse pressure gradient was created with a rotating cylinder to induce flow separation in the region of study. Each model consists of dynamically similar sinusoidal grooves in the streamwise direction inspired by dolphin skin. The groove period studied is 5 mm, and for this study, the groove amplitude is varied from 0.9 mm, corresponding to the dolphin skin, to 1.5 mm. The hypothesis is that the dolphin-inspired case will lead to maximal flow separation control with minimal skin friction drag penalty. Time-resolve digital particle image velocimetry (TR-DPIV) is used to track the development of the flow separation within the boundary layer and compared to the smooth plate (non-grooved) wall cases. The grooved surfaces form embedded vortices within the sinusoidal cavities which can lead to a partial slip condition effect in the wall vicinity. DPIV results quantify momentum adjacent to the grooved surface and the corresponding flow separation.