题目：Dynamic Flow Structures in Active Viscoelastic Liquids

报告人：钱铁铮 教授（香港科技大学数学系）

地点：致远楼108室

时间：2025年6月30日 10:00–11:30

Abstract: Active fluids encompass a wide range of non-equilibrium fluids, in which the self-propulsion or rotation of their units can give rise to large-scale spontaneous flows. Despite the diversity of active fluids, they are commonly viscoelastic. Therefore, we develop a hydrodynamic model of isotropic active liquids by accounting for their viscoelasticity. Specifically, we incorporate an active stress term into a general viscoelastic liquid model to study the spontaneous flow states and their transitions in two-dimensional channel, annulus, and disk geometries. We have discovered rich spontaneous flow states in a channel as a function of activity and Weissenberg number, including unidirectional flow, travelling wave, and vortex-roll states. The Weissenberg number acts against activity by suppressing the spontaneous flow. In an annulus confinement, we find that a net flow can be generated only if the aspect ratio of the annulus is not too large nor too small, consistent with the experiments of microtubule-based active fluids. In a disk geometry, we observe a periodic chirality-switching of a single vortex flow, resembling the bacteria-based active fluid experiments. As such, our active viscoelastic model offers a unified framework to elucidate diverse active liquids, uncover their connections, and highlight the universality of dynamic active-flow patterns. — This work is supported by Hong Kong RGC and completed through a collaboration with Dr. Zhe Feng and Prof. Rui Zhang.

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