共查询到20条相似文献,搜索用时 171 毫秒
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流化床内颗粒聚并和破碎将影响颗粒相的流动特性.本文运用基于颗粒动理学理论的欧拉一欧拉气固多相流模型,利用直接矩积分方法求解颗粒数平衡方程,建立颗粒数密度与连续性方程、动量方程之间的关系,数值模拟流化床内两种不同直径颗粒发生聚并时气固两相流动特性。计算结果表明,颗粒聚并伴随着床内颗粒直径逐渐增大,床内颗粒流化状态逐渐变为固定床状态,两种颗粒直径均增加,且小颗粒的体积分数逐渐减小、大颗粒的体积分数增加。当仅考虑聚并过程时增加流化速度将导致床内颗粒体积平均直径变大。随着颗粒密度减小,床内体积平均直径增加。 相似文献
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《工程热物理学报》2015,(7)
本文介绍一种采用光纤式高速摄影测量装置获取三维柱锥形冷态喷动床试验台内部气固两相流颗粒瞬时速度的测量方法、及其测量不确度的分析。基于获取的颗粒相运动视频,计算出颗粒瞬时速度、颗粒相速度和颗粒温度,它们分别用于表征测量区域中颗粒群流动的快慢和脉动的强弱。测量结果表明:镜头畸变校正环节是影响颗粒瞬时速度测量的主要因素,本测量装置的颗粒瞬时速度的测量不确定度为士2.383%;颗粒相速度在喷泉核心区(r/R≤0.2)为正,绝对值较大,沿半径方向减小到零,然后在r/R=0.45处转变方向并逐渐增大;颗粒温度在区域r/R≤0.2和r/R≥0.65变化显著,对应着喷动床内颗粒喷射上行和下落的主要区域,这证实了公开文献中喷动床内颗粒脉动动能分布的数值模拟结果。 相似文献
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静止水中单个上升气泡的直接数值模拟 总被引:5,自引:2,他引:3
本文发展了基于Front Tracking的直接数值模拟方法研究气液两相界面的迁移特性,该方法对气液两相采用半隐式的分步法直接求解N-S方程,耦合Front Tracking Method获得两相界面的三维变形。针对无边界以及垂直壁面附近静止水中的单个气泡上升过程进行模拟,研究气泡运动的机理以及气泡与壁面的相互作用。数值模拟准确再现了气泡的上升过程和变形,不同Re数下气泡的上升速度计算结果同经验关联式非常吻合,验证了该方法的有效性。随后分析了气泡周围流场的结构,发现壁面对气泡周围流场的抑制是壁面对气泡作用力的主要原因,将导致气泡逐渐偏离垂直壁面。 相似文献
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《中国物理 B》2019,(2)
Based on the volume of fluid(VOF) method, we conduct a numerical simulation to study the hydrodynamic binary coalescence of droplets under air flow in a hydrophobic rectangular microchannel. Two distinct regimes, coalescence followed by sliding motion and that followed by detaching motion, are identified and discussed. Additionally, the detailed hydrodynamic information behind the binary coalescence is provided, based on which a dynamic mechanical analysis is conducted to reveal the hydrodynamic mechanisms underlying these two regimes. The simulation results indicate that the sliding motion of droplets is driven by the drag force and restrained by the adhesion force induced by the interfacial tension along the main flow direction. The detachment(i.e., upward motion) of the droplet is driven by the lift force associated with an aerodynamic lifting pressure difference imposed on the coalescent droplet, and also restrained by the adhesion force perpendicular to the main flow direction. Especially, the lift force is mainly induced by an aerodynamic lifting pressure difference imposed on the coalescent droplet. Two typical regimes can be quantitatively recognized by a regime diagram depending on Re and We. The higher Re and We respectively lead to relatively larger lift forces and smaller adhesion forces acting on the droplet, both of which are helpful to detachment of the coalesced droplet. 相似文献
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Zimmermann R Gasteuil Y Bourgoin M Volk R Pumir A Pinton JF 《Physical review letters》2011,106(15):154501
The motion of a large, neutrally buoyant, particle freely advected by a turbulent flow is determined experimentally. We demonstrate that both the translational and angular accelerations exhibit very wide probability distributions, a manifestation of intermittency. The orientation of the angular velocity with respect to the trajectory, as well as the translational acceleration conditioned on the spinning velocity, provides evidence of a lift force acting on the particle. 相似文献
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We consider the motion of a heavy particle in interaction with an infinite ideal gas of slow atoms. We prove that the velocity of the heavy particle is, in a suitable limit, modeled by a deterministic process. We also treat the process of rescaled velocity fluctuations around a certain deterministic motion and show that this is appropriately modeled by a nonhomogeneous diffusion process.Supported in part by NSF grants PHY-8201708 and DMR81-14726.Supported in part by NSF grant PHY-8003298 and the Seton Hall University, Research and Faculty Development Council. 相似文献
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Using the method of multi-particle collision dynamics (MPCD), we investigate inertial focussing in microfluidic channels that gives rise to the Segré-Silberberg effect. At intermediate Reynolds numbers, we model the motion of a spherical colloid in a circular microchannel under pressure-driven flow. We determine the radial distribution function and show how its width and the location of its maximum are strongly influenced by the colloid size and the Reynolds number of the Poiseuille flow. We demonstrate that MPCD is well suited for calculating mean values for the lift force acting on the colloid in the cross-sectional plane and for its mean axial velocity. We introduce a Langevin equation for the cross-sectional motion whose steady state is the Boltzmann distribution that contains the integrated lift force as potential energy. It perfectly coincides with the simulated radial distribution function. 相似文献
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V. P. Kuznetsov I. Yu. Smolin A. I. Dmitriev D. A. Konovalov A. V. Makarov A. E. Kiryakov A. S. Yurovskikh 《Physical Mesomechanics》2013,16(1):62-72
Dynamics simulation of burnishing of a thin steel layer beneath an indenter applied with a constant force and then moving with a constant velocity was performed by the finite element method in the plane strain approximation. The indenter was modeled by a perfectly rigid body, and the steel was modeled by an elastoplastic body with isotropic hardening according to an experimentally defined law. The regularities of changes in the stressstrain state of the material near the treated surface were studied and mechanisms of the formation of a nanostructured layer were disclosed. The effect of the friction coefficient and the burnishing force on the height of a bulge of edged material was analyzed. The results of studies agree well with experimental data. 相似文献
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Laboratory experiments and numerical simulation reveal that a submerged intruder dragged horizontally at a constant velocity within a granular medium experiences a lift force whose sign and magnitude depend on the intruder shape. Comparing the stress on a flat plate at varied inclination angle with the local surface stress on the intruders at regions with the same orientation demonstrates that intruder lift forces are well approximated as the sum of contributions from flat-plate elements. The plate stress is deduced from the force balance on the flowing media near the plate. 相似文献
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综合考虑黏性夹带力、Basset力、虚拟质量力和压力梯度力,建立颗粒在声场中的动力学模型,利用变步长四阶RungeKutta算法和二阶隐式Adams插值算法对颗粒的受力和运动进行数值模拟。将模拟和实验得到的颗粒运动特性进行对比,验证数值模拟的正确性。在此基础上,研究气温和颗粒密度对颗粒动力学的影响规律。结果表明,黏性夹带力对颗粒运动起主导作用;气温升高,压力梯度力与黏性夹带力之间的相位差减小,Basset力、虚拟质量力与黏性夹带力之间的相位差增大。研究还发现,气温较低时,颗粒密度对颗粒运动有重要影响,夹带系数随着密度的增加而迅速下降;气温较高时,颗粒密度对颗粒运动的影响较小,颗粒位移振幅和夹带系数相对低温时明显增加。 相似文献
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P. Snabre F. Magnifotcham 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):379-386
The recirculation flow induced by the rising motion of a bubble stream in a viscous fluid within an open-top rectangular enclosure
is studied. The three-dimensional volume averaged conservation equations are solved by a control-volume method using a hybrid
finite differencing scheme to describe the liquid phase hydrodynamics. The momentum exhange between the bubbles and the liquid
phase is modeled with a source term equals to the volumetric buoyancy force acting on the gas in the bubble stream. The volumetric
buoyancy force accounts for in line interactions between bubbles through the average gas volume fraction in the gas liquid
column which depends on the size and the rising velocity of bubbles. The fluid flow within an open-top rectangular enclosure
is further investigated by particle image velocimetry for a bubble stream rising in a water-glycerol solution. The measured
fluid velocities in a vertical plane are compared with the predictions of the numerical model over a wide range of fluid viscosity
(43 mPa s-800 mPa s) and gas flow rates. Finally, the recirculation flows resulting from the interaction of two neighbouring
vertical bubble streams are studied.
Received: 23 July 1997 / Revised: 19 December 1997 / Accepted: 11 May 1998 相似文献