Imitating dolphins: Impact of active boundary modulation on near-boundary velocity in channel flow

Abstract Recent advances in technology have renewed the interested in the impact of viscoelastic boundaries and active boundary modulation on hydrodynamic drag and boundary layer turbulence. Viscoelastic boundary materials, such as found in dolphin skin, have the potential to reduce frictional drag by delaying the transition from laminar to turbulent flow in the boundary layer around the body and minimizing turbulence. Possible mechanisms to reduce boundary layer turbulence include counteracting coherent structures or impacting momentum near the boundary. Actuating a deformable membrane in channel flow allows the investigation of the impact of boundary actuation on boundary layer turbulence for a range of actuation parameters and flow channel speeds. We developed a deformable boundary and tested the system in channel flow, in direct contact with the water, actuating at various wave patterns and frequencies. The impact on boundary layer velocity was investigated with Particle Image Velocimetry. Numerical simulations from a companion model complement and support experimental results. Boundary actuation is shown to impact the boundary layer velocity profile and frictional drag, and to reduce near-boundary shear in the region of actuation. Achieving a reduction of boundary layer turbulence in a natural environment could lead to more energy-efficient platforms and underwater vehicles.