球形颗粒在微管流中惯性迁移现象的数值研究

NUMERICAL STUDY OF INERTIAL MIGRATION OF SPHERICAL PARTICLES IN MICROPIPE FLOW

全列

11849033

硕士

力学

王连平

2020-05-28

2020-07-17

哈尔滨工业大学

深圳

在管道泊肃叶流动里，悬浮颗粒与流动相互作用，会由于流体惯性力作用导致颗粒有序迁移和聚集现象，从而自动实现颗粒的分离、移除或者处理。在当前快速发展的微流控领域里，利用颗粒的惯性聚集行为可以实现低成本、高效率的颗粒被动筛分技术，具有广阔的应用前景。颗粒在管道中的输运属于多相流动，除了在极小雷诺数下将惯性作用线性化后能够利用渐近展开法得到近似解，对于工程应用中有限雷诺数下的颗粒输运问题目前还没有理论解。另外，实验观察难以获得颗粒和流场全时空的物理信息。 得益于计算机技术和数值方法的快速发展，近年来各类数值方法已经被用来研究惯性迁移，并取得了一定进展。本文采用格子玻尔兹曼方法，对中性悬浮球形颗粒在不同壁面几何形状的管道中的输运过程进行直接数值模拟，获得流场和颗粒的全时空信息。本论文的特色是系统模拟和比较单颗粒、双颗粒和多颗粒在圆管、槽道、方管和矩形管中的输运过程，从而从应用角度更全面地理解颗粒惯性迁移的流体力学机理。本文首先研究了单颗粒在不同壁面形状、雷诺数、颗粒尺寸中的惯性迁移特点。其次对双颗粒在管道流动中的相互影响进行研究，发现在平衡位置的平面内，双颗粒由于颗粒尾流而发生的横向迁移后对齐成链和颗粒轴向距离趋于定值的现象。最后在双颗粒基础上进一步模拟了多颗粒输运过程，分析了多颗粒在管道流动中对齐并形成轴向距离一致的链条的原因。在这些数值模拟过程中，研究了管道雷诺数、颗粒阻塞比、颗粒体积分数等对颗粒惯性迁移和聚集的影响。研究发现多颗粒成链现象随着雷诺数增加变得更加明显。一个有趣的发现是，在轴对称的圆管里颗粒惯性迁移的轨迹在横截面投影是直线，但是在矩形管中颗粒惯性迁移的轨迹在横截面投影可以是一条曲线；造成曲线轨迹的原因和颗粒旋转角速度因流场缺乏对称性而发生较为微妙的变化有关。以上结果为微流控技术中的被动颗粒筛分技术设计提供了理论指导。本论文的另一个工作是独立推导出矩形管道单相层流的非定常理论解，为矩形管道层流直接数值模拟提供了验证基准。

When suspended particles are transported in a Poiseuille flow, due to fluid inertial forces they might migrate and accumulate at certain radial positions, causing them to naturally separate or to be easily removed or processed. In the rapidly developing field of microfluidic control, this passive particle screening technology has a low cost and high efficiency, which has a broad application prospect.Suspended particles moving in a viscous flow is a topic of multiphase flow. When the flow Reynolds number is very small and the fluid inertia effect can be linearized, approximate analytical solution can be obtained by using the method of asymptotic expansion. However, for the particle migration problem in engineering applications at finite Reynolds numbers, theoretical solution is no longer achievable. Experimental observations of both particle migration and local flow field are also difficult due to instrument limitations. With the rapid developments of computer technology and numerical algorithms, numerical simulations can now be conducted to study particle inertial migration. In this thesis, the Lattice Boltzmann method is used as a direct simulation method to study the migration of neutrally buoyant, spherical particles in microscale pipes with different cross-sections. The unique feature of this work is to systematically simulate and compare particle transport processes involving one, two, and multiple particles in different pipes including a circular tube, groove tube, square and rectangular tube, in order to gain a deep understanding of the mechanisms governing the particle inertial migration.Firstly, the inertial migration of a single particle is simulated in pipes of different shapes, Reynolds numbers and particle sizes. Secondly, the interaction between two particles in pipe flow is studied, and it is found that in the lateral plane of the equilibrium position, the axial migration and alignment of the two particles occur due to the wake flow and the axial distance of the particles approaches a constant value. Finally, the transport process of multiple particles is simulated, and the alignment of multiple particles in a pipe and the formation of a particle chain with uniform inter-particle axial distance are examined. The simulations consider the effects of pipe Reynolds number, particle blocking ratio and particle volume fraction. It is found that the chain formation is enhanced as the flow Reynolds number is increased. An interesting observation is that, while for axisymmetric circular pipe the particle migration trajectory project on the cross section is a straight line, the migration trajectory in the rectangular pipe projected onto the cross section plane can be a curved path due to change of particle angular velocity in response to the subtler local shear rate distribution in the flow. The above results provide theoretical guidance for the design of passive particle screening technology in microfluidic devices.Another contribution of this thesis is the derivation of a theoretical solution for unsteady unidirectional laminar flow in a rectangular pipe, which provides a benchmark case for the validation of transient laminar flow in a rectangular duct.

多相流 格子玻尔兹曼方法 泊肃叶流动 惯性迁移

Multiphase flow Lattice Boltzmann method Poiseuille flow inertial migration

中文

联合培养

南方科技大学

全列. 球形颗粒在微管流中惯性迁移现象的数值研究[D]. 深圳. 哈尔滨工业大学,2020.