城市街道峡谷大气流动与污染物扩散的研究

随着我国城市汽车保有量的逐年增多,城市中心街区的空气质量越来越引起人们关注。通过CFD数值模拟方法研究了4种不同屋顶形状对街区污染物流动与扩散的影响。结果表明,屋顶形状不同,街区空气流动轨迹会有明显变化。平顶建筑物污染物主要集中在街道峡谷中间,污染物浓度分布指数背风侧更高,而斜屋顶污染物主要集中在迎风侧,污染物浓度分布指数迎风侧更高,楼层越低,污染物浓度分布指数越高。     

太阳电池组件自然通风冷却的数值模拟

建立了光伏建筑一体化系统中太阳电池组件自然通风冷却的理论模型,在运行环境、系统结构变化等情况下利用模型对太阳电池温度进行了数值模拟。模拟结果表明,适宜的环境风速对太阳电池的散热能起到积极效果;0．30m的通风流道宽度在上海地区是BIPV中太阳电池一个合适的安装宽度。     

街道峡谷内污染物对流扩散模拟分析

采用数值模拟和现场实验观测相结合的方法,对街道峡谷内汽车污染物的扩散规律进行研究。在进行数值模拟时,依据污染物对流扩散的基本理论,对不同风速下污染物的对流扩散特征进行模拟分析。将结果与现场观测结果进行比较,从而验证了数学模型的正确性,同时也获得了城市街道峡谷内污染物对流扩散规律。研究结果可为城市街道规划建设、建筑高度和密度控制、机动车尾气的排放控制和交通流量控制提供科学依据。     

紊流数值模拟的现状及进展

讨论了紊流数值模拟的发展历史、现状及趋势。比较了各类紊流模型的优缺点及适用范围 ,并对特殊效应 (曲率、近壁区 )的处理作了介绍和评述。为了提高模型的预报能力 ,多重尺度和非线性模型正逐步应用于工程计算。随着计算机的发展 ,大涡和直接数值模拟也取得了一些研究成果     

阳极焙烧炉内煤气流动和燃烧的数值模拟

采用计算燃烧学的原理和模型以及CFD软件对燃烧煤气的阳极焙烧炉炉内的流动和燃烧过程进行了数值模拟计算,讨论了炉内温度场、流场、O2浓度场的分布规律,分析了这些因素对阳极炭块焙烧质量的影响。研究表明,在设计阳极焙烧炉时应考虑对气流分布有影响的各种因素。     

光伏太阳能电池板自然通风冷却的数值模拟

为了解光伏太阳能电池板在有无肋片下的自然冷却过程中的散热情况,对其进行了数值模拟研究,着重分析了肋片及其与风道的组合结构对背板散热的强化效果。研究结果表明,在室外温度、环境风速和电池板发热量均相同的前提下,在背板处设置肋片和肋片与风道组合结构均能够有效改善散热效果,同时,仅在背板处设置肋片时的散热效果最好。     

建筑高度对建筑群行人高度处的风场及污染物扩散影响的数值模拟

选取规则的高层建筑群,数值模拟了7种建筑高度布排下目标域内行人高度处的风场和污染物浓度场。建筑高度对风场和污染物浓度场有显著的影响,当域内建筑与周围建筑高度相同时,行人高度处的风速较小而污染物浓度在所有工况中最大;当域内建筑高度采用渐次或交错变化的布排方式且至少有1排建筑高度是周围建筑的2倍时,行人高度处的风速明显增强而污染物浓度变小;在域内建筑高度渐次增加的工况下,地面附近风速均匀且最强而污染物浓度最低。行人高度处的主流方向大多与来流方向一致或相反,与来流垂直方向的流动相对较弱。对流情况基本决定了污染物的分布特点,受地面回流和污染源位置的影响,7种工况下污染物浓度均较低。     

基于遗传算法的指数时空插值法在某渠道污染物扩散模拟中的应用

在考虑污染物扩散影响因素自身物理特性的基础上,提出一种新的时空插值方法线性反距离时空插值方法,但线性反距离时空插值结果与污染物扩散实测结果存在一定误差。因此利用遗传算法对线性反距离时空插值方法进行优化得到指数时空插值方法。实例应用结果表明,基于遗传算法优化的指数时空插值方法的预测精度较单一时空插值方法提高约10%,且计算时间更短,能够为突发性水污染预警系统提供一种新思路。     

燃油锅炉改烧瓦斯气炉内流动和燃烧过程的数值模拟

1引言近年来,石化行业生产工艺的可燃副气量越来越多,如何利用这些气体燃料已成为石化行业节能和环保所面临的一项必须解决的任务。为了回收利用工业可燃副气,将现有的燃油锅炉改烧可燃副气或油气混烧是一项良好的节能措施。然而,燃料成份的改变、燃烧器喷射状况的不同以及炉膛     

整车罩壳内空气流动的数值模拟研究

为提高冷却系统散热能力,探讨某装载机罩壳内空气流动的数值模拟方法。计算模型中综合考虑了各种对空气流动影响较大的因素,尤其对风扇-散热器组件作了重点分析。将数值模拟结果同整车热平衡风洞试验相验证,为冷却系统空气侧评估与改进提供完整方法。     

进口来流条件对单体建筑绕流时均流场影响的数值模拟

数值模拟了6种进口条件下单体建筑物模型附近的时均流场,模拟值与风洞试验值基本吻合,进口时均流参数对速度模拟值的影响较大,进口紊流参数对速度模拟值的影响则较小;当进口时均速度按照试验情况设置但紊流参数不同时,速度模拟值在建筑物前方和顶部几乎无差别,但在建筑物后方,其差别开始显现,且进口紊流参数按近地面情况或试验值设置时的模拟结果相对较好。由于标准k-ε紊流模型对来流动能的耗散模拟过大,导致速度模拟值比试验值略偏小,人为增加近地面动能的进口条件能有效改善上述情况,在依据进口流量确定的进口速度条件下,建筑物附近的速度模拟值与试验值最吻合。     

Numerical simulation of turbulent natural convection of nanofluid with thermal radiation inside a tall enclosure under the influence of magnetohydrodynamic

In the present study, the natural convective heat transfer in the turbulent flow of water/CuO nanofluid with volumetric radiation and magnetic field inside a tall enclosure has been numerically investigated. The thermophysical properties of nanofluid have been considered variable with temperature and the effects of Brownian motion of nanoparticles have been considered. The main objective of this work is an investigation of the effect of using water/CuO nanofluid and presence of magnetic field on turbulent natural convection in three types of enclosures (vertical, inclined, and horizontal) by considering the volumetric radiation. The governing equations on turbulent flow domain under the influence of the magnetic field and by considering the combination of volumetric radiation and natural convection have been solved by a coupled algorithm. For validating the present research, a comparison has been carried out with the laminar natural convection flow under the influence of the magnetic field and radiation effects and also, the natural turbulent convection flow of previous studies and a proper coincidence has been achieved. The results indicated that by increasing volume fraction and Hartmann number the average Nusselt number enhances and reduces, respectively. By adding 1% CuO nanoparticles to the base fluid, heat transfer improves from 10.59% to 17.05%. However, by increasing the volume fraction from 1% to 4%, heat transfer improves from 1.35% to 4.90%. By increasing Hartmann number from 0 to 600, heat transfer reduces from 9.29% to 22.07%. Also, the results show that the ratio of deviation angle of the enclosure to the horizontal surface has considerable effects on heat transfer performance. Therefore, in similar conditions, the inclined enclosure with a deviation angle of 45° compared to the vertical and horizontal enclosure has better thermal performance.     

自然通风的策略形式及模拟分析

介绍了自然通风的策略形式 ,阐述了采用网络法和CFD对自然通风的模拟分析。最后提出了自然通风的策略选择和模拟分析中要注意的几个问题。     

济南办公建筑自然通风工况下自然室温的研究

针对济南地区一办公房间,讨论不同的换气次数、围护结构和建筑朝向对自然室温影响的变化规律。指出夜间通风和节能50%的围护结构能获得适宜的自然室温,建筑朝向对自然室温的影响较小。     

自然通风条件下建筑围护结构及室内空气的温度计算

建立太阳照射和自然通风条件下建筑与室内、外环境的空气平衡方程与热平衡方程,以及沿围护结构厚度的非稳态一维导热方程,求解得到建筑围护结构和室内空气的温度。选取广州夏季某一天的气象参数,计算围护材料分别采用钢筋混凝土、灰砂砖砌体、浮石混凝土、橡木和平板玻璃情况下,从7时至19时一单室建筑围护结构及室内空气的温度。     

微喷管内气体流动的实验研究与数值模拟

通过实验和数值模拟来研究气体在渐缩微喷管内流动,基于连续介质模型研究了二维微喷管内的流场及推力特性,研究分析了流量和气体入口温度对微喷管流场结构和喷管性能的影响。研究结果表明,随着流量的不断增加,气体稀薄效应相应减小,粘性力对喷管流动的影响降低,边界层逐渐变薄,马赫数不断增大,微喷管的推力大小近似与流量成线性变化,但流量变化对微喷管流场结构影响并不显著。当温度增大时,粘性损失对喷管影响较大,导致边界层变厚,影响了微喷管推进性能,流场马赫数和微喷管推力随温度的升高而下降,说明低温气体有利于提高微喷管的推进性能。     

三维横向紊动射流流场结构的数值分析

对横向紊动射流流场结构、流动机理的研究具有重要的学术意义．同时对解决工程应用中存在的许多问题具有指导作用。利用RNG模型对横流中单股紊动射流流场的流动特性进行了数值模拟。运用SIMPLEC算法求解了适体坐标系下的控制方程．壁面函数法处理近壁区流动。得到了射流与主气流速度比为2和4的流场。结果表明：较大的射流速度对主气流流场影响大；射流内部已形成明显的反向涡旋对(CVP)；射流喷孔上游处出现了主气流向喷孔内部流动的趋势；射流喷孔背风侧存在尾迹区。图7表1参10     

Fluid flow and heat transfer of natural convection around large horizontal cylinders: Experiments with air

Natural convective flows of air around large horizontal cylinders were investigated experimentally. The main concerns were the turbulent transition mechanisms and the heat transfer characteristics of turbulent flows. The cylinders were heated with uniform heat flux and their diameters were varied from 200 to 1200 mm to enable experiments over a wide range of modified Rayleigh numbers, Ra_D^* = 1.0 × 10⁸ to 5.5 × 10¹¹. The flow fields around the cylinders were visualized with smoke to investigate the turbulent transition mechanisms. The results show that three‐dimensional flow separations occur first at the trailing edge of the cylinder when Ra_D^* exceeds 3.5 × 10⁹, and the separation points shift upstream with increasing Rayleigh numbers. These separations become a trigger to the turbulent transition and transitional and turbulent flows appear downstream of the separations at higher Rayleigh numbers. However, they occupy a relatively small portion of the cylinder surfaces even at the maximum Rayleigh numbers of the present experiments. The local heat transfer coefficients were also measured. The results show that the coefficients are increased significantly in the transitional and turbulent regions compared with the laminar coefficients. Moreover, the present results for air were compared with previous results for water and the effects of Prandtl number on the flow and heat transfer were discussed. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(4): 293–305, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10080     

被动式生态建筑中庭的自然通风设计策略

分析中庭设计存在的问题,将被动式生态设计与中庭结合,归纳总结了寒冷气候区、温和气候区、干热气候区、湿热气候区等4种典型气候类型对中庭被动式生态自然通风设计的影响,提出有效的通风策略和中庭自然通风的季节性调控技术。另外,还提出自然通风控制技术和构造策略,提供了一些新的视角,赋予中庭空间新的意义,为生态建筑中庭的自然通风设计提供参考。     

Numerical simulation of air flow field in high-pressure fan with splitter blades

For a deeper understanding of the flow characteristics in the high-pressure centrifugal blower of a fan of Model 9–26 with splitter blades, a three dimensional (3-D) numerical simulation of air flows in the fan was conducted with FLUENT software. The standard k-ε turbulent model and unstructured grids were used. The computational fluid dynamics (CFD) results showed that the performance of a fan could be improved by adding the splitter blades in the channel among the leaf blades. Under operational conditions, with the presence of splitter blades, the air flow rate of the fan increased about 5% and the total pressure at the outlet of the fan increased about 10% on average. It was also found that the length of the splitter blades affected the air flow and pressure drop. There is an optimal value for the length. The simulation results provide helpful information for improving the fan performance. __________ Translated from Fluid Machinery, 2007, 35(10): 29–32 [译自:流体机械]