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Hydrodynamic diffusion in apolar active fluids

Time: Tue 2025-06-17 10.00 - 11.00

Location: Faxén, Teknikringen 8

Video link: https://kth-se.zoom.us/j/3366544548

Participating: Zhouyang Ge (University of British Columbia)

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Abstract: When bacteria swim in a fluid, they generate flows that not only propel themselves but also interact with each other over a distance, resulting in highly nonlinear and diffusive dynamics. Using the Fast Stokesian Dynamics method, I will present two numerical studies showing how such diffusion depends on the concentration of the swimmers as well as the presence of an external shear. Specifically, I will focus on apolar active suspensions of squirmers, particles that are individually immotile but undergo activity-induced hydrodynamic diffusion. Extensive simulations show that these particles diffuse fastest at an intermediate concentration, where the suspension is relatively dilute; however, surprisingly, the diffusion can slow down under shear. I will discuss the physical origins of these phenomena and, particularly, explain how an interplay of shear and activity leads to the reduced diffusion, which may be a general feature of any fluid endowed with an underlying microstructure and internal persistence.