【作者】 李勇；

【导师】 郭照立；

【作者基本信息】 华中科技大学 ， 热能工程， 2015， 硕士

【摘要】 细微颗粒在流体中的输运作为多相流领域的一类普遍现象,广泛存在于自然界与能源化工生产当中,例如近些年来越来越频发的雾霾天气。鉴于我国现在面临严峻的空气污染(主要是细微颗粒物的污染),对于颗粒污染的控制与治理越来越紧迫。因此,对细微颗粒物在流体中输运规律与特性的研究有重要的意义。随着大型计算机性能的不断提高,数值模拟方法也被迅速的应用到多相流领域的研究中,相对于传统的数值计算方法而言,基于介观模型的格子Boltzmann方法具有较多优点。因此这一方法被广泛的应用于计算流体力学的各个领域,其中包括气固两相流的数值模拟。对于细微颗粒在流体中的输运,很多学者作了相关工作。然而他们多数都是针对等温条件下的研究,对于非等温流场中细微颗粒运动的研究则相对较少。因此本文将采用不可压双分布热格子Boltzmann模型来研究细微颗粒在非等温流场中的输运与沉积特性。首先将格子Boltzmann方法与拉格朗日跟踪法结合,数值计算了等温条件下的细微颗粒在方腔中的输运,并与文献对比,结果吻合较好。然后对细微颗粒在由壁面温差引起的方腔自然对流中的运动进行了数值计算。结果表明,当Rayleigh数较小时,颗粒在流场中形成稳定的准平衡区域,此时粒径大小对颗粒的运动特性的影响较为明显;随着Rayleigh数增大,粒径大小的影响逐渐减弱,当Rayleigh数增大到6×105这一临界值时,粒径大小的影响基本可以忽略;同时,结果还显示,热泳力与布朗扩散效应是影响细微颗粒的主要作用力。最后,进一步研究了细微颗粒在由方腔内的方形冷热源引起的自然对流中的输运。结果发现:Rayleigh数一定时,颗粒的沉积率随着粒径的增加显著增加;Rayleigh数较小时,颗粒在流场方形冷热源周围形成一个环形;随着Rayleigh数增大,颗粒分布越来越均匀,且沉积率也随之减小;Rayleigh数一定时,随着方形冷热源数目的增加,颗粒沉积率增加;而保持冷热源单位长度的表面积一定,将其由竖直放置改为水平放置时,颗粒的沉积率也会增加。更多还原

【Abstract】 Particle transport in fluids is a typical multi-phase issue, and it appears in many natural and industrial process, such as the frequent haze, the motion of coal particles in fluidize bed and the dust removal system of flue gas etc. Due to the more and more serious particle pollution in the air in our country, it is of great importance to study how the particle transports in the air. With the rapid development of computer technology, numerical simulation has become an important means to study the gas-particle flow. And as a recently developed numerical method, the lattice Boltzmann method(LBM) has many advantages compared to the traditional method. So it’s widely used in the gas-particle simulation. The issue of gas particle flow has been studied by many researchers, however, most of them focus on the isothermal fluid. And study on the particle transport in fluid with temperature gradient is much less. In this paper, the particle transport in non-isothermal fluid will be studied with the Lattice Boltzmann Method.Firstly, the LBM with Lagrangian tracking method is used to simulate the particle transport in a square cavity, and the results are compared to previous work. A good agreement was gotten in the paper. Secondly, the particle transport in a square free convection is studied. The results show that a fraction of particles were trapped in a quasi-steady recirculation zone for a low Rayleigh number. And the particle diameter has a significant effect on the motion of particles. With an increasing Rayleigh number, the effect of particle diameter decreases. When the Rayleigh number increases to a critical value 6×105,the effect of particle diameter can be ignored. Our results also confirm the importance of the thermophoresis and the Brownian dispersion. Lastly, the particle transport in a cavity with internal heaters and coolers is numerically investigated. The results indicate that the particle distribution is strongly non-uniform at low Rayleigh number. Moreover, it is observed that the deposition rate of the particles increases as the number of the hearters and coolers increases or the orientation of heaters and coolers changes from vertical to horizontal.更多还原