Dynamics of a flexible helical filament rotating in a viscous fluid near a rigid boundary
Dynamics of a flexible helical filament rotating in a viscous fluid near a rigid boundary
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DOI：
10.1103/physrevfluids.2.034101
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发表时间：
2017-03
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影响因子：
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通讯作者：
M. Jawed;P. Reis
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文献类型：
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作者：
M. Jawed;P. Reis
研究了在低雷诺数条件(斯托克斯极限)下，无滑移刚性边界对柔性螺旋丝在粘性流体中旋转动力学的影响。该系统被认为是单鞭毛细菌推进的简化模型，其运动已知在固体边界附近被修改。具体地说，我们集中在由灯丝产生的推进力以及它的屈曲开始是如何被墙的存在所改变的。我们通过数值模拟来解决这个问题，数值模拟耦合了纤维的弹性、流体动力载荷和壁面效应。这三个部分分别由离散弹性杆法(对于细丝的几何非线性描述)、莱特希尔的细长体理论(对于非局部流体力模型)和镜像法(模拟边界)来模拟。通过在重定标宏观仪器上进行的精度实验，系统地验证了模拟结果的正确性。我们发现，在壁面附近，推力增大，而屈曲开始的临界转动频率通常降低。对螺旋丝的几何参数对壁面效应的影响进行了系统的参数研究。
We study the effect of a no-slip rigid boundary on the dynamics of a flexible helical filament rotating in a viscous fluid, at low Reynolds number conditions (Stokes limit). This system is taken as a reduced model for the propulsion of uniflagellar bacteria, whose locomotion is known to be modified near solid boundaries. Specifically, we focus on how the propulsive force generated by the filament, as well as its buckling onset, are modified by the presence of a wall. We tackle this problem through numerical simulations that couple the elasticity of the filament, the hydrodynamic loading, and the wall effect. Each of these three ingredients is respectively modeled by the discrete elastic rods method (for a geometrically nonlinear description of the filament), Lighthill's slender body theory (for a nonlocal fluid force model), and the method of images (to emulate the boundary). The simulations are systematically validated by precision experiments on a rescaled macroscopic apparatus. We find that the propulsive force increases near the wall, while the critical rotation frequency for the onset of buckling usually decreases. A systematic parametric study is performed to quantify the dependence of the wall effects on the geometric parameters of the helical filament.