Evaluating Shark Skin-Inspired Denticle and Riblets for Thrust Generation in Flapping Fins

Improving the efficiency of uncrewed underwater vehicles (UUVs) unlocks new possibilities for ocean exploration, monitoring, and restoration. We designed bioinspired fins that incorporate geometries modeled after the drag-reducing and lift-enhancing properties of shark skin. These hydrodynamic benefits stem from small, interlocking structures known as dermal denticles, which feature surface undulations (riblets) that alter vortex interactions in the boundary layer. To evaluate denticle and riblet textured fins, we built a multi-axis gantry system capable of precisely measuring forces acting on the fins. By varying stroke and pitch rotations, we simulated a range of biologically inspired flapping motions and assessed their impact on thrust generation. We examined how surface features influence performance across flow regimes, comparing results to a smooth control fin. Specifically, we tested inset versus raised riblet geometries and varied riblet spacing. We also evaluated the patterns of biomimetic denticle with widths of 1 mm and 2 mm to compare their performance to riblets. Drawing inspiration from sharks, turtles, and flying fish, we demonstrate how combining surface structures with flapping kinematics can inform the development of more efficient UUV propulsion systems.