Department of Chemical Engineering, Kyoto University, Kyoto 615-8510, Japan.
J Chem Phys. 2013 May 14;138(18):184905. doi: 10.1063/1.4804186.
The velocity relaxation of an impulsively forced spherical particle in a fluid confined by two parallel plane walls is studied using a direct numerical simulation approach. During the relaxation process, the momentum of the particle is transmitted in the ambient fluid by viscous diffusion and sound wave propagation, and the fluid flow accompanied by each mechanism has a different character and affects the particle motion differently. Because of the bounding walls, viscous diffusion is hampered, and the accompanying shear flow is gradually diminished. However, the sound wave is repeatedly reflected and spreads diffusely. As a result, the particle motion is governed by the sound wave and backtracks differently in a bulk fluid. The time when the backtracking of the particle occurs changes non-monotonically with respect to the compressibility factor ε = ν∕ac and is minimized at the characteristic compressibility factor. This factor depends on the wall spacing, and the dependence is different at small and large wall spacing regions based on the different mechanisms causing the backtracking.
使用直接数值模拟方法研究了在两个平行平板壁限制的流体中受脉冲力作用的球形颗粒的速度弛豫。在弛豫过程中，颗粒的动量通过粘性扩散和声波传播传递到环境流体中，并且每种机制伴随的流体流动具有不同的特征，并且对颗粒运动的影响也不同。由于边界壁的存在，粘性扩散受到阻碍，伴随的剪切流逐渐减小。然而，声波被反复反射并扩散。因此，颗粒运动受声波控制，并在主体流体中以不同的方式回溯。颗粒回溯的时间与压缩因子 ε = ν∕ac 不是单调变化的，并且在特征压缩因子处最小化。该因子取决于壁间距，并且基于引起回溯的不同机制，在小壁间距区域和大壁间距区域中的依赖性是不同的。
