建筑街区重密度气态污染物通风稀释过程研究

发布时间：2018-04-10 02:01

本文选题：建筑参差比　切入点：重密度气态污染物　出处：《湖南工业大学》2017年硕士论文

【摘要】：随着计算机和数值模拟技术的飞速发展和广泛应用,利用计算流体动力学方法研究城市街区中的污染物扩散问题已经成为一种高效、便利的研究手段。在城市街区的污染问题中,污染物自身的特性是决定其在街区峡谷中的扩散方式的重要因素。重密度气态污染物不同于能够轻易被城市风携带进而被稀释的密度近或轻于空气的气态污染物,其因受限于本身密度大、重量大的特性,缺乏良好的跟随性,因此,重密度气态污染物在城市街区中的扩散方式有一定的研究意义。本文主要利用计算流体动力学方法,分别选用参差比为0.0,0.2,0.4,0.6和0.8等5种建筑模型,探讨了分别位于城区外的重密度污染源和位于城区中心的重密度气态污染源,在水平自然风条件下于不同参差比建筑物间的沉积过程,以及探究街区内行人区重密度气态污染物的分布与建筑参差比之间的关系。本文首先通过对位于城市街区外的汞源受郊外来风影响在城市街区中扩散的稳态情况进行模拟,研究城市街区建筑物高低错落分布的布局对汞蒸气在城区中扩散的影响。模拟结果发现,城市街区不同高度建筑物错落分布会促进高空汞污染源在行人区的聚集,使得街区行人区汞浓度明显增大;并且随着街区建筑物参差比的增大,最高汞浓度值所在的街道逐渐向汞源方向靠近,较高建筑物背风面街道行人区汞质量流量明显高于较矮建筑物背风面街道行人区汞质量流量。然后结合时间线对街区中心爆发的甲苯在城市风作用下于街区中的扩散情况进行非稳态模拟,探究甲苯的扩散与时间与城区建筑参差比的关系。结果发现,当街区建筑高度一致时,甲苯扩散到下风向街道所花费的时间比建筑高度不一致时短;当街区建筑高度不一致时,位于较高建筑背风面街道的甲苯浓度普遍高于位于较矮建筑背风面街道的浓度;当建筑高度一致时,各街道的甲苯浓度随时间延长而降低,但当建筑高度不一致时,位于下风向街道的甲苯甚至会重新聚集回到行人区;经过一段时间后,爆发源所在街道的甲苯浓度属建筑参差比为0.4的街区甲苯浓度最高,其次为建筑参差比为0.6和0.8的街区,最后为建筑参差比为0.2和0的街区。最后还利用PIV粒子图像测速系统测量了缩比例尺的城市街区水箱模型内的流场,验证了计算流体动力学(computational fluid dynamics,CFD)在研究城市街区气流组织问题上的准确性。本文结合稳态和非稳态的数值模拟,探究了重密度气态污染物在建筑物高低不同错落分布的城市街区中的扩散规律。研究结果城市街区人居环境中的针对重密度气态污染物的治理工作提供了理论依据,有利于城区中受污染街道的具体位置和不同街道受污染的程度等级的确定,具有一定的实际意义。
[Abstract]:With the rapid development and wide application of computer and numerical simulation technology, the use of computational fluid dynamics (CFD) to study pollutant diffusion in urban blocks has become an efficient and convenient means of research.In the problem of urban district pollution, the characteristic of pollutant itself is an important factor to determine its diffusion mode in the district canyon.Heavy density gaseous pollutants are different from gaseous pollutants which can be easily carried and diluted by urban wind. Because they are limited by their own characteristics of high density and heavy weight, they lack good follow-ability.The diffusion of heavy density gaseous pollutants in urban blocks is of great significance.In this paper, using computational fluid dynamics (CFD) method, five kinds of building models, such as 0. 0. 2 0. 2, 0. 4, 0. 6 and 0. 8, are selected, respectively. The heavy density pollution sources located outside the urban area and the heavy density gaseous sources located in the center of the city are discussed, respectively.Under the condition of horizontal natural wind, the deposition process between buildings with different staggered ratios and the relationship between the distribution of heavy density gaseous pollutants in pedestrian areas and the building staggered ratios in the pedestrian areas were investigated.In this paper, firstly, the steady state of mercury source located outside the city block is simulated to study the influence of the distribution of building height and height on the diffusion of mercury vapor in the urban area.The simulation results show that the distribution of buildings with different height in urban blocks will promote the accumulation of high-altitude mercury pollution sources in pedestrian areas, and make the mercury concentration in pedestrian areas increase obviously, and with the increase of the ratio of buildings to buildings,The street with the highest mercury concentration value gradually approached to the mercury source, and the mercury mass flux in the pedestrian area of the street with higher building leeward was obviously higher than that in the pedestrian area on the leeward street of the lower building.Then unsteady simulation of toluene diffusion in the block under the action of urban wind is carried out with time line, and the relationship between toluene diffusion and time and the ratio of urban buildings to the difference between toluene diffusion and urban buildings is explored.The results showed that when the building height of the block was consistent, the time taken by toluene to spread to the downwind street was shorter than that when the building height was inconsistent, and when the building height of the block was not consistent,The concentration of toluene in the street at the higher building leeward was generally higher than that in the street at the lower building. When the building height was consistent, the toluene concentration in each street decreased with time, but when the building height was inconsistent, the concentration of toluene in the street decreased with time, but when the height of the building was not consistent,The toluene in the downwind streets even regrouped back into the pedestrian area; after a while, the toluene concentration in the street where the outbreak occurred was the highest in the block with a building staggered ratio of 0.4, followed by the block with the building disparity ratios of 0.6 and 0.8.The last block is a block with a staggered ratio of 0.2 and 0.Finally, the flow field in the water tank model of urban block is measured by using PIV particle image velocimetry system, which verifies the accuracy of computational fluid dynamics (CFD) in the study of urban block airflow organization.Based on the numerical simulation of steady and unsteady state, the diffusion law of heavy density gaseous pollutants in urban blocks with different distribution of buildings is studied in this paper.The results of the study provide a theoretical basis for the treatment of heavy density gaseous pollutants in the residential environment of urban blocks, which is beneficial to the determination of the specific location of polluted streets and the degree of pollution of different streets in urban areas.Has certain practical significance.
【学位授予单位】：湖南工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X51;TU834

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