旋转流场中颗粒运动与分布的特性研究

发布时间：2018-04-15 20:26

本文选题：碰撞 + 圆筒　；参考：《东南大学》2016年博士论文

【摘要】：液(气)固两相流广泛存在于电力、化工、制药、食品等传统领域及生物、材料等新兴工业领域.旋转流场中颗粒运动是液(气)固两相流研究中的重要课题。在实际过程中,由于流体与颗粒间及颗粒与颗粒间复杂的相互作用使得流场中颗粒运动与分布往往呈现出多态性和复杂性,其物理机制和内在规律特性仍未被全面认识。因此,对旋转流场中颗粒运动与分布的特性进行理论及实验研究,不仅对于探索颗粒与液(气)体间及颗粒与颗粒的相互作用机制具有重要的科学意义,并且对指导工程实际中颗粒流的优化与设计具有重要的工程应用价值。流场中颗粒流动的量化实验研究成本较高、难度较大,因此数值模拟逐渐成为了研究流场中颗粒流动的重要手段。目前,射流撞击激励产生旋转流场中颗粒碰撞、运动及分布尚不清晰。此外,对于气-液两相共存旋转流场及扭曲管内自激励旋转流场中颗粒行为机理与规律的研究还缺乏深入、充分的研究。为此,本文引入直接模拟蒙特卡洛(DSMC)方法描述射流撞击激励产生旋转流场中稠密颗粒间碰撞行为,建立了考虑颗粒旋转的射流撞击激励产生旋转流场中稠密颗粒的流动理论模型并进行了数值模拟,并对射流撞击激励下圆筒内旋转流场中颗粒运动及其碰撞行为进行了可视化观测；基于VOF(Volume of Fluid)和DEM(Discrete Element Method)方法建立了部分充液圆筒内旋转流场中颗粒流动的VOF-DEM理论模型并进行了数值模拟,利用实验手段对流场中颗粒运动、流动模式及分布特性进行了可视化研究；同时,采用CFD-DEM方法对方形截面扭曲管流内旋转流场中颗粒运动及分布特性进行了数值模拟。概括起来,本论文主要研究内容及结论如下：1.利用DSMC方法研究了射流撞击激励作用下圆筒内旋转流场中颗粒行为特性,分析了气体射流速度和颗粒旋转对射流撞击激励作用下圆筒内旋转流场中颗粒运动与分布特性的影响。此外,对射流撞击激励作用下圆筒内旋转流场中颗粒行为进行了实验观察。结果表明：射流撞击激励作用下圆筒内旋转流场中颗粒存在碰撞、渗透及旋转运动；碰撞使颗粒直接离开碰撞区域或在碰撞区域来回运动：入口气体速度增加能够强化颗粒从碰撞区域分散到其他区域；颗粒旋转驱使颗粒更快地离开碰撞区域,导致在碰撞区域中心颗粒浓度的最大值有所减少。2.开展了充液圆筒内旋转流场中颗粒运动与分布特性的可视化实验,研究了圆筒转速、液体高度对颗粒运动与分布特性的影响规律。结果表明：部分充液圆筒内旋转流场中颗粒出现滑移运动、塌落运动和抛落运动,满液圆筒内旋转流场中颗粒还出现了离心运动；在圆筒内液相流场中存在一个明显的漩涡结构；圆筒转速较低时几乎没有颗粒运动到液体旋入侧,而转速增加到一定值时颗粒会运动到液体旋入侧,并随转速增加其数量有所增加；在充液高度低时,颗粒主要分布液体的旋出侧区域；在充液高度较高时,颗粒在圆筒内液体的旋出侧运动,颗粒的分布趋于分散,而随着充液高度进一步增加,颗粒的分布范围扩大到圆筒内液体的旋入侧,颗粒的分布呈现环形分布。3.利用VOF-DEM方法研究了部分充液圆筒内旋转流场中颗粒群运动与分布特性,分析了颗粒液体密度比、液体粘度、液相高度及圆筒转速对液体中固体颗粒分散特性的影响。结果表明：在部分充液旋转圆筒内液相流场中存在涡流,颗粒群在旋转流场及涡流的作用下运动并逐渐分散至整个液相区域。液体黏度的增加,能有效改善旋转圆筒内液相中颗粒群的分散性；颗粒密度的增加,导致颗粒分散驱动力下降,使得液相中颗粒群分散性减弱：液相高度较低或较高时,颗粒在液相旋出侧或者在液相与壁面接触区域和气液界面区域发生聚积；圆筒旋转角速度小时,颗粒聚积在液相的旋出侧；旋转角速度增加,部分颗粒会运动到液相的旋入侧,且颗粒群的分散性能够得到一定的改善。4.利用CFD-DEM方法数值模拟了方形截面扭曲管内旋转流场中颗粒运动,分析了几何结构、入口速度、颗粒液体密度比对扭曲管内固液流动、颗粒运动及颗粒分布的影响。结果表明：扭曲管截面内存在一个逆时针的旋流,而四个角落的二次流是其重要的组成部分；扭曲管内大部分颗粒有相对明显的螺旋运动；对比直管,扭曲管内的旋流能够改善颗粒速度的一致性；在入口速度较小且扭曲比小时,速度对颗粒分散性影响较少,而在速度较大且扭曲比大时,速度对颗粒分散性影响较大；在扭曲比小时,颗粒液体密度比对颗粒分散性影响较大,而在扭曲比大时,颗粒液体密度比对颗粒分散性影响相对较少。
[Abstract]:This paper introduces direct simulation Monte Carlo ( DSMC ) method to describe the particle motion and distribution in the rotating flow field .
Based on the VOF ( Volume of Fluid ) and DEM ( Discrete Element Method ) method , the VOF - DEM theoretical model of particle flow in partial liquid filled cylinder was established and the numerical simulation was carried out .
In this paper , the particle motion and distribution characteristics of a rectangular cross - section twisted tube flow are numerically simulated by using the CFD - DEM method . The main research contents and conclusions are as follows : 1 . Using the DSMC method to study the particle behavior characteristics in the rotating flow field of the cylinder under the action of jet impact excitation , the particle behavior in the rotating flow field of the cylinder under the action of jet impact excitation is analyzed .
Collision causes the particles to move directly out of the collision zone or back and forth in the collision zone : the increase in the velocity of the inlet gas can enhance the dispersion of the particles from the collision zone to other areas ;
In this paper , the effects of cylinder speed and liquid level on particle motion and distribution are studied .
There is an obvious vortex structure in the liquid phase flow field in the cylinder .
When the rotation speed of the cylinder is low , little particles move to the liquid spinning side , while the rotation speed is increased to a certain value , the particles move to the liquid spinning side , and the number of the particles increases with the rotating speed ;
When the liquid filling height is low , the particles mainly distribute the spinning - out side area of the liquid ;
The effects of particle swarm and particle size distribution on the dispersion of solid particles in liquid are studied by using VOF - DEM method .
the increase of the particle density causes the particle dispersion driving force to decrease , so that the particle group dispersibility in the liquid phase is reduced : when the liquid phase height is lower or higher , the particles are accumulated in the liquid phase rotation - out side or in the contact area between the liquid phase and the wall surface and the gas - liquid interface area ;
the cylinder rotates angular velocity for hours , and the particles are accumulated on the rotary - out side of the liquid phase ;
The effects of geometric structure , inlet velocity and liquid density ratio on the solid - liquid flow , particle movement and particle distribution in the twisted tube are analyzed by using the CFD - DEM method .
the majority of the particles in the torsion tube have relatively obvious helical movement ;
Compared with the straight tube , the swirl in the twisted tube can improve the consistency of the particle velocity ;
When the inlet velocity is small and the twist ratio is small , the effect of the velocity on the particle dispersion is less , and when the speed is large and the distortion ratio is large , the velocity has great influence on the particle dispersion ;
When the twist ratio is small , the density ratio of the particles is larger than that of the particles , and when the twist ratio is large , the density ratio of the particles is relatively less than that of the particles .

【学位授予单位】：东南大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TK12

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