Toward Dolphin-Inspired Frictional Drag Reduction: A Novel Actuator Device for Boundary Layer Modulation

Drag reduction is of significant interest in the design of marine vehicles. Viscoelastic boundary materials and compliant surfaces, such as those found in dolphin skin, have the potential to reduce frictional drag by delaying the transition from laminar to turbulent flow and minimizing turbulence. To investigate the effect of boundary modulation on turbulence, we developed and tested a novel device that generates wave-like deformations on a flow boundary. This device, enabled by a 5×5 voice coil motor array, was embedded in the wall of a flow channel and overlaid with a flexible membrane in direct contact with the water. The boundary displacement was quantified using a computer vision approach. The deformable membrane system was tested across a range of flow tank speeds and boundary actuation patterns, and the impact on near-boundary velocity was assessed. The resulting data indicate that boundary actuation alters the boundary layer velocity and turbulent stresses both under the region of actuation and in its wake. The effect was most pronounced in regions with boundary layer coherent structures, and certain actuation parameters were consistent with a reduction in frictional drag. A numerical model of the flow tank showed a 10% reduction in average shear stress over the actuated boundary and one actuation wave period, supporting the laboratory experiments and corroborating the findings. This work supports efforts to develop dolphin-inspired methods to reduce near-boundary turbulence and drag, which, if successfully applied in a natural environment, can lead to more energy-efficient platforms and underwater vehicles.