Biological filtration systems offer a sustainable alternative to existing engineered solutions. In this 
computational work, we seek to optimize the surface coverage by an array of hair arrays to capture 
particles in channels. 
A variety of aquatic organisms rely on arrays of hairs to interact with their fluidic environments. The 
hair functionality can vary from sensing to smelling, filtration to flow control depending on the 
species considered. Amongst those organisms, filter-feeders use suspension-feeding which is not 
only one of the most widespread feeding mechanisms but also one of the oldest. Baleen whales are 
filter-feeders that catch their prey by using the baleen, which is a complex structure composed of 
plates and bristles in their mouth. The bristles are hollow cylindrical structures with a diameter of a 
few hundred micrometres that can extend over tens of centimetres. The baleen filters out the prey 
while letting the seawater through. The baleen is composed of flexible and elongated structures 
whose properties are adapted to the feeding habits of the whale. The porosity of the structure 
depends on the flow feature. Effectively, the flow can be used to tune the filter properties, which 
sets biological filters apart from their engineered counterpart. 
Previous mechanical studies have shown that an array of hairs can either act as a sieve, allowing all 
the fluid to flow through it, or as a rake, forcing the fluid to flow around it instead. For a given 
spacing of hair, as the Re increases, the behaviour shifts from rake to sieving. From a filtration 
perspective, the rake regime is not favourable as particles do not enter the array. For a fixed Re, the 
flow transitions from rake to sieve as the spacing between the hairs in the array increases. Our 
recent work has also demonstrated that the confinement of the channel influences the sieve to rake 
transition. The filtration mechanisms that filter-feeder organisms use to capture food particle exhibit 
complex fluid-structure interactions that have yet to be leveraged in engineered systems. 
To guide the development of hair-covered surfaces capable of trapping particles in channel flows, 
we investigate how different geometric factors affect the fluid transport and capture of particles by 
the array. In previous work, a small number of hairs, typically 25 were considered. Through 
numerical simulations, we vary the geometry of the array, the Re of the flow and the surface 
coverage to study the transport through this confined porous structure. We compare arrays based 
on their optimal efficiency and the (sub-optimal) operating conditions which make the filter 
versatile.

A Numerical Study of the Effect of Surface Coverage on the Filtration Performance of Hair Arrays

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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