【作者】 李光辉；

【导师】 由长福；

【作者基本信息】 清华大学 ， 热能工程， 2005， 硕士

【摘要】 可吸入颗粒物危害人类健康,是目前我国大部分城市的主要污染物之一。因此,研究可吸入颗粒物的运动规律对其脱除工作具有非常重要的意义。本文采用直接数值模拟(DNS)方法对可吸入颗粒物的运动规律进行了研究,所得到的结果为以后进一步研究提高可吸入颗粒物的脱除效率等工作提供了基础。在以前的气固两相流动的数值研究中,一般采用湍流模型来模拟湍流流场,这对于大颗粒是比较适用的。但是,当颗粒直径远小于湍流的最小涡尺度时,这种方法就不能准确模拟出颗粒的运动。而直接数值模拟(DNS)不引入任何湍流模型,直接对N-S方程进行数值求解,可以求解出包含脉动尺度在内的不同尺度的瞬时速度场,已经被广泛的应用到了对微小颗粒的数值模拟中。本文对三维槽道两相流动进行了数值模拟。首先对于三维不可压缩无温差的槽道流动进行了直接数值模拟,采用Lagrangian方法跟踪颗粒的运动,颗粒的直径分别为1微米、2.5微米、10微米、20微米和100微米。发现了颗粒在近壁面附近浓度高的颗粒局部富集现象,同时槽道中心附近颗粒浓度较低,并且对不同直径的颗粒浓度分布在空间上的差异进行了讨论。然后在壁面温差为130℃和180℃情况下,模拟以上5种颗粒在热泳力作用下的运动规律和沉积规律,并且与温差为0℃的结果进行了比较。数值模拟的结果表明,相同的温差对于不同粒径颗粒的影响不同,较小的颗粒受热泳力的影响更大;同时,随着温差的增大,颗粒受到的热泳力也随着增大,热泳力对于颗粒的影响也越大。本文最后考虑颗粒间的相互碰撞,对粒径为1微米、2.5微米和10微米的颗粒在存在壁面温差的槽道中的运动进行了数值模拟。数值模拟结果表明,可吸入颗粒间的碰撞易于发生在颗粒浓度较高以及湍流动能较大的区域内,而在其它区域内,碰撞发生的概率很小。更多还原

【Abstract】 Inhalable particles can do great harm to people’s health which remain the keypollutant affecting the air quality in China. Therefore, it is necessary to study themotions of inhalable particles.In the earlier numerical study of two-phase flow, the turbulent models are oftenused to simulate the turbulent flow. It is an effective way to simulate the motions ofbigger particles which turns impossible when the particles are smaller than theKolmogorov length. The direct numerical simulation (DNS) solves the N-S equationdirectly and can provide all the data of the turbulent flow. Therefore, it had beenwidely used in the simulation of micro particles.Firstly, a three dimension, incompressible, turbulent channel flow without thetemperature difference is simulated. The Lagragian method is used to track themotions of particles. The particle diameters simulated in this study are 1 μm, 2.5 μm,10 μm, 20 μm and 100 μm. The numerical results reveal that the particles tend toaccumulate in the flow. The difference among the particle concentration is discussed.Secondly, the motions of the particles with the temperature difference of 130℃and 180℃ are simulated. The comparison with the date of no temperature differenceis made. The numerical results show that the effect of thermophoresis on thedeposition near the wall decreases with increasing particle diameter and the particledeposition increases as the temperature difference increases.Finally, the particle motions with mutual collisions are simulated. The resultsshow that the particles tend to collide in the region of higher particle concentration orin the region of higher kinetic energy.更多还原