Flow through an array of rigid hairs

Hair-covered surfaces serve a variety of purposes in Nature, from chemical sensing on the antennules of a crustacean to flow generation in our respiratory system. Confining structures, walls or larger hairs, are believed to focus the flow on the hair-covered region. We investigate the influence of the confinement on the flow through an array of passive hairs. Previous work has shown that the flow exhibits three regimes: rake, deflection, and sieve. The regimes describe the relative amount of fluid traveling through and around the finite array of hairs, and depend on the Reynolds number and the porosity of the array. To explore the effects of confinement experimentally, we vary the hair spacing, channel dimension and flow rate. We measure the velocity field using Particle Image Velocimetry. We also conduct numerical simulations for a wider sweep of the parameters. Our experimental results agree well with results of finite element simulations and reveal that the confinement of an array of hairs can shift the Reynold’s number at which the flow regimes are observed and limit which regimes can occur. These results should provide insight into the morphology of hairy surfaces and have implications in the design of bio-inspired flow sensors and filters.