Quasi-direct numerical simulation of lift force-induced particle separation in a curved microchannel by use of a macroscopic particle model
Quasi-direct numerical simulation of lift force-induced particle separation in a curved microchannel by use of a macroscopic particle model
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DOI：
10.1016/j.ces.2007.01.031
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发表时间：
2007-05
影响因子：
4.7
通讯作者：
S. Ookawara;M. Agrawal;D. Street;K. Ogawa
中科院分区：
文献类型：
--
作者：
S. Ookawara;M. Agrawal;D. Street;K. Ogawa
采用基于有限体积法的宏观颗粒模型(MPM)验证了弯曲微通道中升力诱导颗粒分离的机理。在非定常模拟中，MPM根据每个时间步长的质点速度，对接触到质点物理边界的流体单元给予动量。给定动量与反号之和除以时间步长，即可得到作用在质点上的流体动力。也就是说，颗粒的存在和运动导致了颗粒周围的流体流动，而颗粒所产生的流场通过流体动力决定了颗粒的运动。因此，MPM可以看作是在静态计算单元上实现的准直接数值模拟。剪切流中作用在球形颗粒上的升力是由颗粒周围的流场引起的纯流体动力。因此，预计MPM可以在不增加任何额外模型的情况下预测升力效应。首先，研究表明，MPM模型能够预测由于升力的作用，颗粒在直线微通道壁面上的迁移。随后，在弯曲的微通道中，将MPM预测的典型释放点的粒子轨迹与没有任何升力模型的普通粒子跟踪方法预测的粒子轨迹进行了比较。MPM预测粒子的运动轨迹被限制在沟道截面的外部区域。另一方面，由于Dean涡产生的离心力，跟踪方法预测的环流轨迹有扩展的趋势。因此，陡峭的剪切速率所产生的升力是导致弯曲微通道内颗粒分离的一个重要因素。
The macroscopic particle model (MPM) based on the finite volume method is employed to validate a mechanism of lift force-induced particle separation in a curved microchannel. According to the particle velocity at each time step in the unsteady simulation, the MPM gives momentum to those fluid cells touching the particle physical boundary. The summation of the given momentum with the reversed sign is divided by the time step to obtain the hydrodynamic force acting on the particle. Namely, the existence and motion of the particle causes fluid flow around the particle, while the flow field caused by the particle determines the particle motion by means of the hydrodynamic force. Therefore, the MPM can be regarded as implementing a quasi-direct numerical simulation over the static computational cells. The lift force acting on a spherical particle in a shear flow is a purely hydrodynamic force caused by the flow field around the particle. It is expected, therefore, that the MPM could predict the lift force effect without any additional model. At first, it is shown that the MPM is capable of predicting particle migration away from the wall of a straight microchannel due to the lift force. In a curved microchannel, subsequently, the particle trajectories from representative release points predicted by the MPM are compared to those predicted by a common particle tracking method without any lift force model. The MPM predicted that the particle trajectories are confined in the outer region of the channel cross-section. On the other hand, the circulating trajectories predicted by the tracking method tend to expand due to centrifugal force caused by the Dean vortices. It is concluded, therefore, that the lift force due to the steep shear rate is a significant factor to cause particle separation in a curved microchannel.