Boundary layer turbulence near an actively controlled deformable surface

摘要

Recent advances in technology, in particular soft robotics and micro-electronics, 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 those found in dolphin skin, are known to have the potential to reduce boundary drag, by delaying the transition from laminar to turbulent flow in the boundary layer around the body and minimizing boundary layer turbulence. The possible mechanisms to reduce boundary layer turbulence include counteracting boundary layer coherent structures or impacting momentum transfer near the boundary. Actuating a deformable membrane in a 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, as well as numerical simulations (see companion paper). Boundary actuation is shown to impact the boundary layer velocity profile and near boundary momentum transfer. We characterize the parameter space most likely to reduce boundary layer turbulence in a natural environment, which could lead to more energy-efficient platforms and underwater vehicles.