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对空间模式发展的气固两相圆孔射流中颗粒与流体双相耦合作用进行了并行环境下的直接数值模拟算法研究。气相流场采用可压缩的N-S方程直接求解。计算颗粒场时,采用Lagrangian方法跟踪实际的颗粒运动。利用并行求解算法,实现了颗粒穿越边界面的模拟。为了模拟颗粒对流体的作用,考虑了颗粒和流体的双相耦合。在本文的计算条件下,颗粒的直径远小于网格的间距,平均的Kolmogorov尺度和网格的间距在一个量级,保证了DNS的要求。气相和颗粒相的应力与实验的对比研究表明,本文的颗粒并行程序是可信的。 相似文献
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本文对空间发展的湍流气固两相平面混合层流动进行了大涡模拟研究,其中气相亚网格尺度(SGS)使用结构函数模型,气相控制方程组采用SIMPLE方法求解,固体颗粒运动用拉格朗日方法计算。计算结果正确重现了流体涡结构的卷起、合并和破碎过程,以及小尺寸颗粒在涡边缘(低涡度区)的局部富集现象。对直径分别为42μm、72μm和135μm分别进行了模拟,并将统计结果和实验测量结果(Hishida et al[1])比较,表明两者的平均速度吻合很好,但颗粒数密度和脉动速度存在较明显的差异,因此有必要对亚网格应力和颗粒之间的耦合作用以及拟序结构的三维性对颗粒运动的影响开展深入研究。 相似文献
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采用硬球模型对三维气同两相射流中Stokes数为10的中等颗粒的碰撞行为进行了直接数值模拟,以初步考察两相流动中颗粒碰撞的特件.颗粒的跟踪采用单向耦合的Lagrangian方法,计算分析了颗粒碰撞随空间、时间的演化及其对颗粒分布不均匀性的影响.模拟结果表明颗粒碰撞主要分布在流场巾颗粒局部浓度较高的区域;由于射流初期大尺度涡结构的影响,颗粒的浓度分布最为不均,因此碰撞次数在这一时期随时间呈线性增加,达到最大值后逐渐回落趋于平缓.此外,对网格中颗粒个数分布的矩的统计发现,碰撞对颗粒分布不均匀性的影响随时间呈现不同的特性. 相似文献
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An Incompressible Three-Dimensional Multiphase Particle-in-Cell Model for Dense Particle Flows 总被引:1,自引:0,他引:1
D. M. Snider 《Journal of computational physics》2001,170(2):523
A three-dimensional, incompressible, multiphase particle-in-cell method is presented for dense particle flows. The numerical technique solves the governing equations of the fluid phase using a continuum model and those of the particle phase using a Lagrangian model. Difficulties associated with calculating interparticle interactions for dense particle flows with volume fractions above 5% have been eliminated by mapping particle properties to an Eulerian grid and then mapping back computed stress tensors to particle positions. A subgrid particle, normal stress model for discrete particles which is robust and eliminates the need for an implicit calculation of the particle normal stress on the grid is presented. Interpolation operators and their properties are defined which provide compact support, are conservative, and provide fast solution for a large particle population. The solution scheme allows for distributions of types, sizes, and density of particles, with no numerical diffusion from the Lagrangian particle calculations. Particles are implicitly coupled to the fluid phase, and the fluid momentum and pressure equations are implicitly solved, which gives a robust solution. 相似文献
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利用外加声场促进悬浮在气相中的细颗粒发生相互作用,进而引起颗粒的碰撞和凝并,使得颗粒平均粒径增大、数目浓度降低,是控制细颗粒排放的重要技术途径.为探究驻波声场中单分散细颗粒的相互作用,建立包含曳力、重力、声尾流效应的颗粒相互作用模型,采用四阶经典龙格-库塔算法和二阶隐式亚当斯插值算法对模型进行求解.将数值模拟得到的颗粒声波夹带速度和相互作用过程与相应的解析解和实验结果进行对比,验证模型的准确性.进而研究颗粒初始条件和直径对相互作用特性的影响.结果表明,初始时刻颗粒中心连线越接近声波波动方向、颗粒位置越接近波腹点,颗粒间的声尾流效应就越强,颗粒发生碰撞所需要的时间就越短.研究还发现,颗粒直径对颗粒相互作用的影响取决于初始时刻颗粒中心连线偏离声波波动方向的程度.当偏离较小时,颗粒直径越大,颗粒发生碰撞所需要的时间越短;当偏离很大时,直径较小的颗粒能够发生碰撞,而直径较大的颗粒则无法发生碰撞. 相似文献
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工业过程中粉体颗粒不可避免地会相互摩擦碰撞而荷电. 荷电颗粒的存在可能会危害正常的工业生产过程, 也可能对工业过程起促进作用. 因此, 荷电粉体颗粒及其特性受到了广泛的关注, 但目前对粉体颗粒的荷电机理依然缺乏透彻的了解, 尤其是在气固两相流动中的粉体颗粒荷电现象. 事实上, 工业中存在的粉体颗粒的运动都受到流体的影响, 是典型的气固两相流系统, 流体对粉体颗粒的作用使粉体颗粒接触的荷电现象变得更为复杂, 因此从两相流动的观点来研究粉体颗粒荷电的物理本质就显得越来越重要. 本文介绍了工业过程中的几种不同类型的粉体颗粒荷电行为, 回顾了颗粒的荷电机理与描述颗粒荷电的数学模型. 对于工业过程中颗粒的荷电现象及颗粒在多相流体中的动力学行为, 介绍了研究颗粒受流体影响时荷电特性的数值模拟方法. 本文旨在对粉体颗粒的荷电机理、应用以及研究方法进行梳理与探讨, 为正确认识工业过程中粉体颗粒的荷电现象并加以控制利用提供理论借鉴. 相似文献
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湍流边界层中重粒子弥散的随机模型 总被引:1,自引:0,他引:1
在重粒子轨道模型的基础上,引入了Saffman力,并考虑了粒子-固壁碰撞和粒子-粒子碰撞的影响,建立了重粒子运动方程,耦合湍流脉动的随机方程,发展了重粒子弥散的随机模型,并在湍流边界层中考察该模型.将数值计算结果与实验结果进行比较,同时考察了Saffman力和粒子碰撞对计算结果的影响. 相似文献
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由于Lagrange粒子法的本质, 固壁边界条件的施加一直是光滑粒子动力学方法的难点之一. 本文从固壁边界的物理原理出发, 应用多层虚粒子表征固壁边界, 提出了一种新型固壁边界施加模型. 将虚粒子看作流体的扩展, 计算中虚粒子密度保持不变, 压力、速度等参数通过对流体粒子的插值获得, 虚粒子有条件的参与控制方程的计算, 对流体的密度/压力产生影响, 通过压力梯度隐式地表征壁面与流体之间的作用强度并对流体粒子施加沿壁面法线方向的斥力作用, 防止流体粒子对壁面的穿透. 数值算例测试结果表明, 与现有固壁边界施加方法相比, 本文方法更加符合流体与固壁边界作用的物理原理, 可以简单、有效地施加固壁边界条件, 方便地应用于具有复杂几何边界的问题, 获得稳定的流场形态、规则的粒子秩序及良好的速度、压力等参量的分布. 相似文献
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本文采用直接数值模拟的方法从颗粒所见的流场拓扑结构这一角度探讨了颗粒在不同拓扑结构下速度统计特性.结果表明,不同惯性的颗粒所见流体的速度特性类似,在Top1和Top2结构中,随时间演化而减少,而在Top3和Top4结构中随时间有波浪性的增长;由于颗粒惯性的差异引起的轨道交叉效应不同,颗粒与颗粒所见流体速度的关联随颗粒增大而衰减加剧,在颗粒与流体相之间的能量传递中,不同拓扑结构明显不同,从颗粒加入时能量由颗粒相向流体传递,各拓扑结构的相对强度为Top2>Top4>Top1>Top3,演化到后期能量由流体相向颗粒相传递,相对强度为Top1>Top2>Top3>Top4;st=1.0和st=10.0的颗粒差别在于演化后期Top2和Top3相对强度的转变. 相似文献
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We propose a new numerical method for modeling motion of open curves in two dimensions and open surfaces in three dimensions. Following the grid based particle method we proposed in [S. Leung, H.K. Zhao, A grid based particle method for moving interface problems. J. Comput. Phys. 228 (2009) 2993–3024], we represent the open curve or the open surface by meshless Lagrangian particles sampled according to an underlying fixed Eulerian mesh. The underlying grid is used to provide a quasi-uniform sampling and neighboring information for meshless particles. The key idea in the current paper is to represent and to track end-points of the open curve and boundary-points of the open surface explicitly and consistently with interior particles. We apply our algorithms to several applications including spiral crystal growth modeling and image segmentation using active contours. 相似文献
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Inertial focusing and rotating characteristics of elliptical and rectangular particle pairs in channel flow 下载免费PDF全文
Pei-Feng Lin 《中国物理 B》2022,31(8):80501-080501
The lattice Boltzmann method is used to study the inertial focusing and rotating characteristics of two-dimensional elliptical particles and rectangular particles in channel flow. The results show that both elliptical particles and rectangular particles initially located on one side and two sides of channel centerline migrate first towards the equilibrium position. Then, the single-line particle train with an increasing spacing and the staggered particle train with stable spacing are formed. The axial spacing of the staggered particle pair increases with aspect ratio and Reynolds number increasing. The staggered elliptical or rectangular particle pairs form perpendicular orientation angles, which will be more obvious at larger aspect ratio and lower Reynolds number. The single-line particle trains with different shapes seldom form the perpendicular orientation angle. 相似文献
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The interaction between finite-size particles and turbulent channel flow in the absence of gravity is studied by direct numerical simulations (DNS). The study is motivated by DNS observations of a turbulent channel flow with high-density, pointwise particles, that cluster in regions of high streamwise root-mean-square (RMS) acceleration close to the wall, contrary to what is observed in homogeneous isotropic turbulence. The aim of the present study is to explore if this is still the case when size effects are taken into account in the DNS. Based on the analysis of the velocity and acceleration statistics, the present DNS shows that, close to the wall, particles with ρp/ρf ranging from 2 to 4 are surrounded by regions with low streamwise RMS velocity but high streamwise RMS acceleration. According to the normalised particle acceleration probability density functions (PDFs), size effects become important in the near-wall region. As particle inertia increases, the normalised PDFs of particle acceleration tend to a Gaussian distribution. The tails of the normalised PDFs of the fluid conditioned by the presence of particles are higher than that of the unconditioned fluid close to the wall. 相似文献