细微颗粒在方腔自然对流中输运的格子Boltzmann模拟

发布时间：2018-03-29 10:52

本文选题：气固两相流　切入点：细微颗粒　出处：《华中科技大学》2015年硕士论文

【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。
[Abstract]:As a common phenomenon in the field of multiphase flow, the transport of fine particles in fluid exists widely in nature and energy chemical industry. For example, in recent years, haze weather has become more and more frequent. In view of the severe air pollution in China (mainly the pollution of fine particles), the control and control of particulate pollution is becoming more and more urgent. It is of great significance to study the transport laws and characteristics of fine particles in fluid. With the continuous improvement of the performance of large scale computers, numerical simulation methods have been rapidly applied to the study of multiphase flow. The lattice Boltzmann method based on mesoscopic model has many advantages over traditional numerical methods, so it is widely used in various fields of computational fluid dynamics. This includes numerical simulation of gas-solid two-phase flows. Many scholars have done relevant work on the transport of fine particles in the fluid. However, most of them have been studied under isothermal conditions. Therefore, the incompressible double-distributed thermal lattice Boltzmann model is used to study the transport and deposition characteristics of fine particles in non-isothermal flow field. The Boltzmann method is combined with the Lagrangian tracking method. The transport of fine particles in a square cavity under isothermal conditions is numerically calculated, and the results are in good agreement with the literature. Then, the motion of fine particles in a square cavity caused by wall temperature difference is numerically calculated. The results show that, When the Rayleigh number was small, the particle formed a stable quasi-equilibrium region in the flow field, and the effect of particle size on particle motion was obvious, and the influence of particle size gradually weakened with the increase of Rayleigh number. When the Rayleigh number reaches the critical value of 6 脳 10 ~ 5, the influence of particle size can be neglected, and the results also show that the thermal swimming force and the Brownian diffusion effect are the main forces affecting the fine particles. The transport of fine particles in natural convection caused by square heat and cold sources in a square cavity is further studied. The results show that the deposition rate of fine particles increases significantly with the increase of particle size and decreases with the increase of particle size. The particles form a ring around the square heat and cold sources in the flow field, the particle distribution becomes more and more uniform with the increase of the Rayleigh number, and the deposition rate decreases with the increase of the number of the square cooling and heat sources, and the particle deposition rate increases with the increase of the number of the square cold and heat sources. When the surface area of the unit length of the heat and cold source is kept constant, the deposition rate of the particles will also increase when the unit length of the source is changed from vertical to horizontal.
【学位授予单位】：华中科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X513;O359

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