Department of Mechanical Engineering, Santa Clara University, Santa Clara, California, 95053, USA.
Soft Matter. 2021 Apr 14;17(14):3829-3839. doi: 10.1039/d0sm02130j. Epub 2021 Mar 19.
Some micro-organisms and artificial micro-swimmers propel at low Reynolds numbers (Re) via the interaction of their flexible appendages with the surrounding fluid. While their locomotion has been extensively studied with a Newtonian fluid assumption, in realistic biological environments these micro-swimmers invariably encounter rheologically complex fluids. In particular, many biological fluids such as blood and different types of mucus have shear-thinning viscosities. The influence of this ubiquitous non-Newtonian rheology on the performance of flexible swimmers remains largely unknown. Here, we present a first study to examine how shear-thinning rheology alters the fluid-structure interaction and hence the propulsion performance of elastic swimmers at low Re. Via a simple elastic swimmer actuated magnetically, we demonstrate that shear-thinning rheology can either enhance or hinder elastohydrodynamic propulsion, depending on the intricate interplay between elastic and viscous forces as well as the magnetic actuation. We also use a reduced-order model to elucidate the mechanisms underlying the enhanced and hindered propulsion observed in different physical regimes. These results and improved understanding could guide the design of flexible micro-swimmers in non-Newtonian fluids.
一些微生物和人工微型游泳者通过其柔性附肢与周围流体的相互作用，在低雷诺数（Re）下推进。虽然已经广泛研究了它们在牛顿流体假设下的运动，但在现实的生物环境中，这些微型游泳者不可避免地会遇到流变复杂的流体。特别是，许多生物流体，如血液和不同类型的粘液，具有剪切稀化的粘度。这种普遍存在的非牛顿流变学对柔性游泳者性能的影响在很大程度上仍然未知。在这里，我们进行了首次研究，以检查剪切稀化流变学如何改变低 Re 下弹性游泳者的流固相互作用，从而改变其推进性能。通过磁性驱动的简单弹性游泳者，我们证明剪切稀化流变学可以增强或阻碍弹性流体动力学推进，这取决于弹性力和粘性力以及磁驱动之间的复杂相互作用。我们还使用简化模型阐明了在不同物理区域观察到的增强和阻碍推进的机制。这些结果和改进的理解可以指导在非牛顿流体中设计柔性微型游泳者。
