Flow regimes in the rotational motion of an array of rigid hairs

Aquatic organisms extensively rely on hair-covered surfaces to perform functions ranging from chemical sensing to feeding. The flow over such hair-covered surfaces has traditionally been studied with a macroscopic array of rigid hairs in a long flow channel. The flow through such finite porous medium exhibits three regimes, with increasing fluid transport through the array: rake, deflection, sieve. The regimes depend on the Reynolds number of the flow, porosity and confinement of the array. Here we experimentally introduce a new flow geometry where the array of hairs is swept in a circular path around a cylindrical tank, through stationary fluid. This flow condition has a velocity profile that linearly increases from the inner to outer edge of the array. To study the influence of the flow geometry on the three regimes we vary the rotational velocity and array dimensions. Particle Image Velocimetry with dynamic masking is used to measure the velocity field through the array. The experimental results are compared with 2D numerical simulations conducted with the finite element analysis software Comsol. This experimental approach should provide new insights into the interactions of hairs and fluid.