UC Santa Barbara

Aquatic organisms extensively rely on hair-covered surfaces to perform functions ranging from chemical sensing to filter feeding. The flow over such hair-covered surfaces has traditionally been studied with a macroscopic array of rigid cylindrical hairs in a long flow channel. This channel geometry is a great starting point but does not necessarily provide a flow profile that matches the ones found in nature. Flow through such finite porous medium exhibits three regimes, with increasing fluid transport through the array: rake, deflection, and sieve. In the rake regime, the bulk flow is diverted around the array, while in the sieve regime, the flow goes through the array. The deflection regime is a transition regime where some of the streamlines exit the array laterally. The regimes depend on the Reynolds number of the flow, porosity, and confinement of the array. The channel geometry has previously been used as a model configuration to study transport. Here we 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. Variables such as the flow rate entering the array through the first row and the drag on the hair array allow for the definition of the three regimes and the efficiency of the filtration process. These variables are first measured in Chapter 2 with 2D finite element analysis simulations using COMSOL Multiphysics. The filter efficiency increases with the volume of fluid entering the array and decreases with the drag on the array. The filtered volume and drag coefficient exhibit a non-linear dependence on the rotation speed. In Chapter 3, we discuss the experimental methods used to obtain preliminary results that are able to quantify the transition from rake to deflection regimes for two arrays with different cylinder spacings. Our finding verify that the rake to deflection regime change can be experimentally found and measured.