Hydrodynamics of water entry for a bio-inspired array of horizontal cylinders at intermediate Reynolds numbers

Many organisms use arrays of long semi-parallel bristles to capture food and facilitate locomotion. The function of these bristled appendages depends on how fluid flows between adjacent bristles: they may be hydrodynamically solid “paddles” or porous “rakes”, depending on Reynolds number and bristle spacing. Some flying insects use such appendages to facilitate takeoff from the water surface; however, our understanding of bristled appendages at an air-water interface is limited, as previous work has been confined to fully submerged arrays. Inspired by the hairy legs of aerial-aquatic insects, we experimentally investigate the surface tension-dominated interaction of a parallel array of horizontally oriented cylinders with the air-water interface. We use high speed videography and Particle Image Velocimetry (PIV) to measure the deformation of the interface and the flow under the array across a range of intermediate Reynolds numbers, and explore the effects of cylinder spacing and impact velocity. We find that lower Re corresponds to more flow through the array, in contrast to previous work on submerged arrays. Our results provide insight into the biomechanics of aerial-aquatic locomotion as well as a new avenue for bio-inspired design in semi-aquatic environments.