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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Force-free swimming of a model helical flagellum in viscoelastic fluids
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Force-free swimming of a model helical flagellum in viscoelastic fluids

机译：粘弹性流体中模型鞭毛的无力游泳

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We precisely measure the force-free swimming speed of a rotating helix in viscous and viscoelastic fluids. The fluids are highly viscous to replicate the low Reynolds number environment of microorganisms. The helix, a macroscopic scale model for the bacterial f lagellar filament, is rigid and rotated at a constant rate while simultaneously translated along its axis. By adjusting the translation speed to make the net hydrodynamic force vanish, we measure the force-free swimming speed as a function of helix rotation rate, helix geometry, and fluid properties. We compare our measurements of the force-free swimming speed of a helix in a' high-molecular weight silicone oil with predictions for the swimming speed in a Newtonian fluid, calculated using slender-body theories and a boundary-element method. The excellent agreement between theory and experiment in the Newtonian case verifies the high accuracy of our experiments. For the viscoelastic fluid, we use a polymer solution of polyisobutylene dissolved in polybutene. This solution is a Boger fluid, a viscoselastic fluid with a shear-rate-independent viscosity. The elasticity is dominated by a single relaxation time. When the relaxation time is short compared to the rotation period, the viscoelastic swimming speed is close to the viscous swimming speed. As the relaxation time increases, the viscoelastic swimming speed increases relative to the viscous speed, reaching a peak when the relaxation time is comparable to the rotation period. As the relaxation time is further increased, the viscoelastic swimming speed decreases and eventually falls below the viscous swimming speed.
机译：我们精确地测量在粘性和粘弹性流体中旋转螺旋的无力游泳速度。流体具有很高的粘性，可以复制低雷诺数的微生物环境。螺旋线是细菌薄片状细丝的宏观模型，是刚性的并且以恒定的速率旋转，同时沿其轴平移。通过调节平移速度以使净水动力消失，我们测量了无力游泳速度，该速度是螺旋转速，螺旋几何形状和流体特性的函数。我们比较了使用细长体理论和边界元方法计算的在高分子量硅油中螺旋线无力游泳速度的测量值与在牛顿流体中游泳速度的预测值。在牛顿情况下，理论与实验之间的极好的一致性证明了我们实验的高精度。对于粘弹性流体，我们使用溶解在聚丁烯中的聚异丁烯的聚合物溶液。该溶液是Boger流体，一种与剪切速率无关的粘度的粘弹性流体。弹性由单个松弛时间决定。当与旋转周期相比松弛时间短时，粘弹性游动速度接近粘性游动速度。随着弛豫时间的增加，粘弹性游泳速度相对于粘滞速度增加，当弛豫时间与旋转时间相当时达到峰值。随着弛豫时间的进一步增加，粘弹性游泳速度降低，并最终降至粘性游泳速度以下。

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