Nguyen Thomas, Manikantan Harishankar
Department of Chemical Engineering, University of California Davis, Davis, CA 95616, USA.
Soft Matter. 2024 Feb 21;20(8):1725-1735. doi: 10.1039/d3sm01499a.
The complex dynamics of elastic fibers in viscous fluids are central to many biological and industrial systems. Fluid-structure interactions underlying these dynamics govern the shape and transport of flexible fibers, and understanding these interactions can help tune flow properties in applications such as microfluidic separation, printing and clogging. In this work, we use slender-body theory to study micromechanical dynamics that arise from the coupling between the elastic backbone of a fiber and the local straining flow that contributes to filament flipping and cross-streamline migration. The resulting transverse drift is unbiased in either direction in simple shear flow. However, a non-uniform shear rate results in bias towards regions of high shear, which we connect to the shape transitions during flips. We discover a depletion layer that forms near the boundaries of pressure-driven channel flow due to the competition between such a cross-streamline drift and steric exclusion from the walls. Finally, we develop scaling laws for the curvature of filaments during flip events, demonstrating the origin of the drift bias in non-uniform flows, and confirm this behavior from our simulations. Put together, these results shed light on the role of a local and dominant coupling between elasticity and viscous resistance in dictating long-term dynamics and transport of elastic fibers in confined flows.
粘性流体中弹性纤维的复杂动力学是许多生物和工业系统的核心。这些动力学背后的流固相互作用决定了柔性纤维的形状和传输，理解这些相互作用有助于在微流体分离、打印和堵塞等应用中调节流动特性。在这项工作中，我们使用细长体理论来研究由纤维的弹性主干与导致细丝翻转和跨流线迁移的局部应变流之间的耦合产生的微观力学动力学。在简单剪切流中，产生的横向漂移在任一方向上都是无偏的。然而，不均匀的剪切速率会导致偏向高剪切区域，我们将其与翻转过程中的形状转变联系起来。我们发现，由于这种跨流线漂移与来自壁面的空间排斥之间的竞争，在压力驱动通道流的边界附近形成了一个耗尽层。最后，我们为翻转事件期间细丝的曲率制定了标度律，证明了不均匀流中漂移偏差的起源，并从我们的模拟中证实了这种行为。综上所述，这些结果揭示了弹性与粘性阻力之间局部和主导耦合在决定受限流中弹性纤维的长期动力学和传输方面的作用。
