Low Reynolds Number Flows Through Flexible Hair Arrays

Many aquatic organisms utilize arrays of hair-like structures on their appendages to perform essential tasks such as chemical sensing and particle capture from surrounding flows. The particle capture is called filter feeding and is controlled by the flow interaction with the hair-like structures. This fluid interaction exhibits three distinct flow regimes: rake, where the flow is diverted around the hair array; sieve, where the flow passes through the array; and deflection, a transitional regime in which the flow partially penetrates the array and is redirected laterally. The regime is dependent on both the Reynolds number and the porosity of the array.

This study investigates flow through arrays of flexible hairs at Reynolds numbers from 0.5 to 20. In the experiments, flexible hairs are rotated around a large water tank to mimic flow conditions found in the environment. Fluid velocity and hair deflection are experimentally measured and compared to results from numerical simulations.

Results from varying the flow speed and array geometry demonstrate how hair flexibility affects the flow regimes. These findings will contribute to a better understanding of how hair-covered surfaces on aquatic organisms modulate flow to sample the surrounding fluid. It should provide insight into bio-filtration and bio-inspired filters.