Physics of rheologically enhanced propulsion: Different strokes in generalized Stokes
Physics of rheologically enhanced propulsion: Different strokes in generalized Stokes
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DOI：
10.1063/1.4818640
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发表时间：
2013-08-01
影响因子：
4.6
通讯作者：
Loghin, Daniel
中科院分区：
文献类型：
--
作者：
Montenegro-Johnson, Thomas D.;Smith, David J.;Loghin, Daniel
剪切稀化是许多生物流体(如粘液)的重要流变性，因此流体的表观粘度随剪切而降低。研究表明，某些微观游泳者在使用剪切稀释液时进步更快，但这种行为对所有微观游泳者来说都是通用的吗？剪切稀释流变学通过什么物理机制影响游泳者的推进力？我们研究游泳者在二维无惯性Carreau流体中采用规定的泳姿运动学：剪切变稀的“广义Stokes”流。游泳者使用Femlet的方法，通过一组沉浸的、规则的力量来建模。然后在贴体网格上离散控制流体动力学的方程，并用有限元方法进行求解。我们分析了三类不同类型的微泳者的运动：(1)概念性游泳者，包括使用一维和二维泳姿的滑球，(2)纤毛虫的滑速包络模型，通常被称为“蠕动动物”，以及(3)单鞭毛推进器，如精子。我们发现，具有不同泳姿的形态相同的游泳者在剪切稀释液中可能比在牛顿流体中游得更快或更慢。我们通过考虑游泳者推进元件和有效载荷元件周围流体粘度的差异来解释这种运动学敏感性，并利用这一洞察力提出了两个相互滑动的球体游泳者，他们在剪切变稀流体中违反了珀塞尔的Scallop定理。我们还表明，剪切稀化流变学引起的流量衰减率的增加与滑移速度蠕动的游动速度的降低有关。对于像精子一样的游泳者来说，沿着鞭毛从粗到薄的液体梯度改变了它施加在液体上的力，使轨迹变平，增加了瞬时的游泳速度。(C)2013年作者(S)。除另有说明外，所有文章内容均按照知识共享署名3.0未移植许可进行许可。
Shear-thinning is an important rheological property of many biological fluids, such as mucus, whereby the apparent viscosity of the fluid decreases with shear. Certain microscopic swimmers have been shown to progress more rapidly through shear-thinning fluids, but is this behavior generic to all microscopic swimmers, and what are the physics through which shear-thinning rheology affects a swimmer's propulsion? We examine swimmers employing prescribed stroke kinematics in two-dimensional, inertialess Carreau fluid: shear-thinning "generalized Stokes" flow. Swimmers are modeled, using the method of femlets, by a set of immersed, regularized forces. The equations governing the fluid dynamics are then discretized over a body-fitted mesh and solved with the finite element method. We analyze the locomotion of three distinct classes of microswimmer: (1) conceptual swimmers comprising sliding spheres employing both one-and two-dimensional strokes, (2) slip-velocity envelope models of ciliates commonly referred to as "squirmers," and (3) monoflagellate pushers, such as sperm. We find that morphologically identical swimmers with different strokes may swim either faster or slower in shear-thinning fluids than in Newtonian fluids. We explain this kinematic sensitivity by considering differences in the viscosity of the fluid surrounding propulsive and payload elements of the swimmer, and using this insight suggest two reciprocal sliding sphere swimmers which violate Purcell's Scallop theorem in shear-thinning fluids. We also show that an increased flow decay rate arising from shear-thinning rheology is associated with a reduction in the swimming speed of slip-velocity squirmers. For sperm-like swimmers, a gradient of thick to thin fluid along the flagellum alters the force it exerts upon the fluid, flattening trajectories and increasing instantaneous swimming speed. (C) 2013 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.