基于格子Boltzmann方法的椭球粒子在简单流体中的运动研究

发布时间：2018-04-02 15:39

本文选题：格子玻尔兹曼方法　切入点：椭球粒子　出处：《中国科学技术大学》2016年博士论文

【摘要】：本文采用格子玻尔兹曼方法,数值研究了椭球粒子在三种简单流动中的运动问题,包括椭球粒子在平板Couette流中的转动问题、无限长竖直管道内的沉降模态以及在Poiseuille流中的运动特性。主要工作及研究成果如下：(1)对两种形状的椭球粒子,即长条形和扁形的椭球粒子进行了细致的模拟,通过一系列的计算,发现了几种椭球粒子的周期性转动模态和稳定的转动模态。比较特殊的是,在305Re345区间内,长条形椭球粒子可能会出现一种特别的周期性转动模态。在这种模态中,长条形椭球粒子会绕着其比较靠近两平板中间面的倾斜轴转动,并且伴随有进动和章动运动。但是在345Re385内,长条形椭球粒子会围绕着涡矢量方向做章动运动。同时,本文还在较高Re445区间内,发现了长条形椭球粒子停转的现象。通过计算发现,椭球粒子的转动模态不仅仅和流场的Re有关,而且还依赖于椭球粒子的初始放置方位,因此,本文通过对流场Re分区讨论,给出了粒子在不同Re区间可能出现的转动模态,并对粒子的初始放置方位对粒子最终转动模态的影响进行了详细地讨论。在同一个Re区间内,椭球粒子可能会出现不同的转动模态,但是本文发现,当长条形椭球粒子在Re120和385Re445区间范围内,仅仅只出现一种转动模态,而在本文计算的其它范围内,由于不同初始条件的影响,可能会出现两种以上的转动模态。但是通过大量算例模拟,本文发现扁形椭球粒子的转动模态与其初始放置方位并无紧密联系。(2)讨论了几种不同管道,包括圆形管道和方形管道,以及长条形粒子和扁形粒子的沉降模态。通过模拟一系列算例,我们发现了几种典型的沉降模态,包括翻转模态、倾斜转动模态、水平沉降模态、螺旋沉降模态、非常规式沉降模态以及摆动模态。粒子对最终沉降模态的选择和管道与粒子宽度比以及Re有关,并不依赖于初始的放置位置和放置时的角度取向。通过比几种形状的管道,本文发现粒子在方形管道中存在很明显的对角面优势。本章中还详细讨论了粒子的沉降速度与粒子和流体密度比以及和模态转变之间的关系,发现在某些参数条件下存在一种特殊现象,由于模态的转变,略轻的粒子反而沉降速度比略重的粒子更大。本章通过计算一系列算例,给出了粒子沉降模态和伽利略数(Ga)以及管道宽度之间的相图关系。本章还尝试给出粒子选择某种沉降模态的原因,发现粒子可能趋向于使得粒子本身沉降速度更快的模态。本章的研究有助于理解粒子沉降模态与管道壁面效应之间的规律。(3)讨论了几种不同的管道,包括圆形管道、方形管道和矩形管道,以及长条形和扁形椭球粒子的运动特征。通过计算本文发现了椭球粒子的几种典型的运动模态。管道的大小和形状对椭球粒子的运动会产生很大影响。在圆形管道中本文发现对于长条形椭球粒子而言,翻转模态是稳定的而滚动模态是不稳定的,扁形椭球粒子恰好和其相反。本章详细对比研究了这两种不同形状的椭球粒子的转动特征并重点讨论了管道尺寸和Re对这两种粒子运动形态的影响。本章发现在中等宽度的方形管道中,椭球粒子的运动明显受到对角面效应的吸引,而在较窄和较宽的方形管道中对角面效应则不强烈,而是出现船桨式摆动模态和垂直于对角面的滚动式模态。在矩形管道中长条形椭球粒子的滚动模态可以稳定地存在。通过对比椭球粒子的模态转变过程,本章发现粒子运动过程中趋向于选择所获得的动能较小的模态。
[Abstract]:This paper uses the lattice Boltzmann method, numerical study of spheroidal particles in three kinds of simple flow motion, including rotational ellipsoid particles in plane Couette flow in the settlement mode of infinite length in vertical pipelines and the motion characteristics of Poiseuille flow. The main research results are as follows: and (1) of ellipsoidal particle two kinds of shapes, namely, elongated and flat ellipsoidal particles were detailed simulation, through a series of calculations, found several periodic rotation ellipsoid particles and stable rotation mode mode. Especially, in the range of 305Re345, elongated ellipsoid particles may appear a periodic special the rotation mode. In this mode, elongated ellipsoid particles will around the middle of the plate two closer to the rotation of the plane of the tilt axis, and the precession and nutation movement. But in 345Re385, long Bar spheroidal particles will surround the vorticity vector direction of nutation movement. At the same time, this paper also found high Re445 range, elongated ellipsoid particles stop phenomenon. It was found that the modal rotation ellipsoid particles and the flow field is related not only to Re, but also depends on the initial ellipsoid particles position, therefore, this article through the flow field of Re partition discussion, gives the possible modal particles in different rotation range of Re, and the initial particle effect on the particle rotation range placed the final mode is discussed in detail. In the same Re range, spheroidal particles may appear different rotation mode, but we found that when the long bar ellipsoid particles in Re120 and 385Re445 range, only a rotation mode, and the other range are calculated in this paper, the influence of different initial conditions, may two Turn the mode above. But through a lot of examples in this paper, simulation, rotational modal and initial flat ellipsoid particles placed no close contact. (2) discussed several different channels, including circular pipe and square pipes, and elongated particles and flat particles. Through a series of settlement mode simulation examples, we find that the settlement of several typical modes, including flip mode, tilt rotation mode, the level of settlement mode, spiral settlement mode, unconventional settlement mode and swing mode. The particles on the final settlement mode selection and pipeline and particle width ratio and Re, does not depend on the initial position and orientation angle. By placing the shape of the pipe is several, found that particles have obvious advantages in the diagonal plane of square pipe. This chapter also discusses in detail the velocity and particle settling particle The relationship between the change and the fluid density ratio and mode, we found that there exists a special phenomenon under certain parameter conditions, the modal transformation, but slightly lighter particles settling slightly more heavy particle velocity. This chapter through the calculation of a series of examples, gives the particle settling mode and Galileo number (Ga) phase diagram and the relationship between the width of the pipe. This chapter also tries to give the choice of a modal particle deposition, found particles may tend to make the particle itself faster. The settlement mode of this chapter helps to understand the effect of modal particle sedimentation between the surface and the pipe wall of the law. (3) discussed several different pipeline. Including the circular pipe, square pipe and rectangular pipe, and the elongated and flat ellipsoid particle movement characteristics. Through the calculation of this paper found several typical motion modes ellipsoid particles. The size of pipe And the shape of the ellipsoid particle motion will have a great impact. This paper found that in a circular pipe for elongated ellipsoid particles, turning mode is stable while the rolling mode is unstable, and the flat ellipsoid particles just opposite. This chapter detailed comparative study of the two different shapes of the spheroidal particle rotation characteristics and discusses the influence of pipe size and Re of the two kinds of particle morphology. This chapter found in the square pipe medium width, ellipsoidal particle motion obviously attracted diagonal plane effect, and in the square is narrow and wide pipe in the diagonal plane effect is not strong, but the paddle type the swing mode and perpendicular to the diagonal rolling mode. The rolling mode in rectangular pipeline in elongated ellipsoid particles can exist stably. Through the modal transformation process comparison of ellipsoid particles, the particles found In the process of motion, it tends to select the less kinetic modes obtained.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O35

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