Flow through a confined array of rigid hairs

A variety of aquatic organisms use appendages covered with arrays of hairs to capture food, smell, and move the fluid around them. At the hair level, the flow is characterized by a low Reynolds number (Re), whose value controls the transport through the array. The array acts either as a rake forcing the fluid around at low Re or small hair spacing or as a sieve letting the fluid through at higher Re or large hair spacing. We study the influence of confinement on the flow regimes through the finite porous structure. We investigate the flow through an array of hairs in a rectangular channel in the presence of a developed Poiseuille flow field. We vary the geometry of the array, flow rate through the channel, and confinement through numerical simulations and experiments. We show that the transition between the rake and sieve regimes depends on the geometry of the system and rationalize the results using a Darcy-Brinkman model.