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arXiv 1809.05459physics.flu-dyn
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Stokes流中两球体间的奇异水动力相互作用

The Singular Hydrodynamic Interactions Between Two Spheres In Stokes Flow

B. D. Goddard, R. D. Mills-Williams, J. Sun

摘要:

我们研究的精确解缓慢的粘性流动的无限液体所造成的两个刚性球接近每一个沿着或平行于他们的中心线,在所有分离有效。这超出了现有的解决方案的适用范围奇异的流体动力相互作用(HI),在实际应用中,仅限于近接触或远场区域的流动。对于HI的法向分量,通过使用双极坐标系,我们推导出流函数为$Re\to 0$和公式的奇异(挤压)力之间的球体作为一个无限级数。我们还获得了渐近行为的部队之间的无量纲分离的领域去到零和无穷大,严格确认和改进已知的结果有关的一个广泛接受的润滑理论。此外,作为一种特殊情况,我们恢复了垂直于平面运动的球体上的力。对于切向分量,再次利用双极坐标系,得到了球间(剪切)奇异力的无穷级数表达式。所有结果都适用于后退的球体,与斯托克斯流的可逆性一致。我们展示了大量的差异,在数值模拟的胶体流体时,使用本理论与现有的多极方法相比。此外,我们表明,本理论保持正定性的电阻矩阵$\boldsymbol{R}$在一些情况下,其中正性被破坏的多极/微扰方法。

英文摘要:

We study exact solutions for the slow viscous flow of an infinite liquid caused by two rigid spheres approaching each either along or parallel to their line of centres, valid at all separations. This goes beyond the applicable range of existing solutions for singular hydrodynamic interactions (HIs) which, for practical applications, are limited to the near-contact or far field region of the flow. For the normal component of the HI, by use of a bipolar coordinate system, we derive the stream function for the flow as $Re\to 0$ and a formula for the singular (squeeze) force between the spheres as an infinite series. We also obtain the asymptotic behaviour of the forces as the nondimensional separation between the spheres goes to zero and infinity, rigorously confirming and improving upon known results relevant to a widely accepted lubrication theory. Additionally, we recover the force on a sphere moving perpendicularly to a plane as a special case. For the tangential component, again by using a bipolar coordinate system, we obtain the corresponding infinite series expression of the (shear) singular force between the spheres. All results hold for retreating spheres, consistent with the reversibility of Stokes flow. We demonstrate substantial differences in numerical simulations of colloidal fluids when using the present theory compared with existing multipole methods. Furthermore, we show that the present theory preserves positive definiteness of the resistance matrix $\boldsymbol{R}$ in a number of situations in which positivity is destroyed for multipole/perturbative methods.

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