Description
- Abstract:
- Using a minimal hydrodynamic model of active fluids in an isotropic phase, we study the stability of a thin active gel film, and two-dimensional Couette flows in straight and annular channels. Using a linear stability analysis of the active fluid film, we calculate the growth rates of the modes assuming zero Frank elasticity. We show that activity-driven instability occurs even in the presence of an interface. For sufficiently large activity, some of the modes have an oscillatory character. Using theoretical and computational analyses of active gels in straight and annular channels, we find that an externally imposed shear flow can stabilize an extensile fluid that would be unstable to spontaneous flow in the absence of shear flow, and destabilize a contractile fluid that would be stable against spontaneous flow in the absence of shear flow. The gels are isotropic in the absence of externally- or activity- driven shear, but develop nematic order that increases with increasing shear rate. We also determine the possible flow states for a range of activities and shear rates using the finite element method. For extensile gels, we find three kinds of nonlinear flow states in the range of parameters we study: unidirectional, oscillatory and dancing flows, and we characterize these states by the average volumetric flow rate and wall stress. For contractile gels, we find only one kind of nonlinear state in the range of parameters studied: unidirectional flow. For large values of activity, the unidirectional contractile flow develops a boundary layer. Our analysis of annular channels shows how the curvature of the streamlines in the base flow affects the transitions among flow states.
- Notes:
- Thesis (Ph. D.)--Brown University, 2023
Citation
Luo, Wan,
"Hydrodynamics of active gels: interfacial instabilities, and two-dimensional Couette flow in straight and annular channels"
(2023).
Fluid, Thermal, and Chemical Processes Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://repository.library.brown.edu/studio/item/bdr:xpwf7rjh/
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Collection:
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Fluid, Thermal, and Chemical Processes Theses and Dissertations
Theses and Dissertations for the Fluid, Thermal, and Chemical Processes department....