摘要
目的:颗粒-壁面冲击碰撞是近似混沌运动的液固耦合问题。针对传统建模方法难以描述颗粒-壁面碰撞运动过程所涉及的壁面效应问题,本文旨在提出一种液固耦合建模方法,以揭示流固耦合条件下的颗粒-壁面接触规律,探讨碰撞过程中环境变量(流道结构和流体粘度)对碰撞壁面效应的作用机理;得到在约束及非约束空间流场中,流体粘度与颗粒-壁面碰撞行为的内在联系,为流体光整加工、轮机叶片及反应器内壁面磨损所涉及的流场调控提供技术支持。创新点:1.建立适用于液固两相流的计算流体力学和离散单元法(CFD-DEM)耦合动力学模型;2.通过捕捉颗粒-壁面碰撞点分布,得到不同流道结构及流体粘度下的颗粒-壁面作用范围;3.建立无量纲化材料去除方程,探明非约束及约束空间流场内流体粘度对材料去除分布的影响。方法:1.将颗粒视为理想刚体,对流体运动及颗粒运动分别进行建模,通过求解流体对颗粒的作用力以及网格单元内流体体积分数实现两者之间的交互耦合,进而得到流场内颗粒的运动规律;2.采用软球接触模型描述颗粒-壁面碰撞过程,进而得到不同流道结构及流体粘度下的颗粒-壁面碰撞落点分布;3.计算颗粒-壁面冲击速度及冲击压力,通过无量纲化材料去除方程,得到约束空间及非约束空间内不同流体粘度下的工件表面材料去除分布。结论:1.流道结构及流体粘度会极大影响颗粒-壁面碰撞落点分布;在本文算例中,为获得均匀的工件加工效果,应采用较低粘度流体,并使抛光盘做周期性自转运动。2.随着流体粘度的升高,流体输运颗粒的能力增强,在非约束空间内的颗粒对壁面的碰撞冲击越剧烈,但在约束空间内的碰撞作用力减弱;在本文算例中,为获得更为均匀的材料去除分布,应采用较低粘度流体。3.借助粒子图像测速法得到了壁面处颗粒速度分布,并与模拟结果进行对比,验证了建模方法的有效性。
Particle-wall collision is a complex liquid-solid coupling matter approximating to a chaotic state. Previous research mainly focused on the issues of particle trajectory and near-wall flow field, but the particle-wall collision mechanism and contact effects are unclear. To address this, a coupled computational fluid dynamics and discrete element method （CFD-DEM） modeling method is proposed. Firstly, flow field profiles are acquired by the CFD method as the initial motion conditions. Then, the particles are regarded as rigid bodies, and the data interactions between CFD and DEM are implemented by calculating for interaction force and void fraction. The results show that there are radial texture phenomena on the particle trajectories caused by the flowing interference; the central region has the lowest velocity and can be regarded as the rigid core of a Rankine vortex; if inlet diameter is 20 mm, the contacting distribution with rotating superposition can reach the best uniformity; the higher viscosity can carry more particles, and the transporting ability of the fluid medium is improved; the uniform contact effects can be more easily performed by the low viscosity fluid. This research can offer theoretical relevance to the modeling for multi-phase particle fluid, and provide technical support for flow regulation in the areas of fluid-based processing, turbine blade erosion, and reactor wall abrasion.
基金
supported by the National Natural Science Foundation of China(Nos.51375446 and 51575494)
the Zhejiang Provincial Natural Science Foundation of China(Nos.LR16E050001 and LZ14E050001)
关键词
壁面接触效应
CFD-DEM
颗粒-壁面冲击
两相颗粒流
Wall contact effects
Computational fluid dynamics and discrete element method （CFD-DEM）
Particle-wall colli- sion
Two-phase particle fluid
