Filtration and fundamental fluid mechanics inspired by the manta ray
Annette Hosoi (MIT)
| When |
Sep 25, 2023
from 11:00 to 12:00 |
|---|---|
| Where | Salle des Thèses |
| Attendees |
Annette Hosoi |
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Heating, ventilation, and air conditioning (HVAC) systems account for about 20% of energy consumption in the US of which at least 7% is consumed by fans. In addition, approximately 4% of US energy is consumed by the production, treatment, and distribution of water. A key component of the efficiency in all of these systems is the performance of filters in which reducing resistance can result in significant energy savings. In this talk, we will explore novel strategies for filtration inspired by the manta ray which has evolved a system for filtering zooplankton that appears to be unlike any filtration mechanism previously observed in biological or industrial settings. Rather than adopting a sieve strategy, the manta deploys microstructures which are hypothesized to instigate eddies that push particles away from the filtration pores, resisting clogging, and enabling the filtration of particles much smaller than the pore size.
In this talk we will examine two toy problems that mimic various features of the filtration strategies employed by manta rays. In the first, we examine the effect of microstructures in a "leaky pipe". In the second we analyze mechanisms that enable particles to cross streamlines, which is an essential component in separating the flow into particle-rich and particle-free streams. In particular, it is known that inertial lift forces can lead to particle focusing in channel flows; yet oscillatory straining effects have also been suggested as a mechanism for particle focusing in wavy channels. To determine which of these two mechanisms dominate, we decompose the particle-free channel flow into a primary Poiseuille flow and secondary eddies induced by the waviness. We calculate the perturbation of the particle on the particle-free flow and the resulting lateral lift force exerted on the particle using matched asymptotics. The interaction between the zeroth-order lift force and the particle-free flow largely determines the focusing locations. We find that experimental data from wavy channels are consistent with the asymptotic predictions of the focusing locations, which are primarily governed by the channel Reynolds number, the particle size, and the amplitude of the waviness.