建筑开口率对自然通风流量系数的影响分析

开口的流量系数是自然通风计算中的重要参数,而大开口自然通风的开口率对流量系数又有一定的影响。对自然通风条件下室内外的速度场和压力场进行了数值模拟,通过模拟结果分析了开口率(ε)在不同来流角度时对全压差和流量系数的影响,并给出了流量系数的取值。     

基于LES的单开口非稳态自然通风模拟

本文对非稳态流场边界条件下的单开口建筑自然通风进行了大涡模拟,采用谐波叠加法生成随机脉动风速时程数据,同时考虑平均风速随高度呈指数分布,脉动风速经过零散度修正处理后作为数值模拟的入口边界条件。比较了不同开口面积,建筑体积以及平均风速对自然通风量的影响。研究结果表明:单开口建筑的自然通风量是风速和建筑开口面积的函数,还与体积相关。如果仍然采用常规稳态通风量模型会错误评估自然通风效果。     

大空间建筑上部开口节能潜力研究

利用大空间建筑上部开口自然通风降低室内空调能耗是大空间建筑节能的方向之一,利用上部开口有效利用系数定义了空调切换温度,并以某体育馆为研究对象分析了大空间建筑节能潜力.     

自然通风计算基础—表面风压系数和开口流量系数

表面风压系数和开口流量系数是多区域模型的自然通风计算基础。本文通过文献综述系统梳理两系数的研究结果。综述表明,流态变化与两系数密切相关,伯努利原理是理解两系数变化的重要依据。建筑体型与设计、风向、上游地貌和周边建筑遮挡是影响表面风压系数的关键因素。小开口具有恒定的静止空气流量系数。大开口热压通风下的流量系数与室内外温差、开口的垂直位置、宽度和厚度有关,风压通风下的流量系数与开口率、风向和进出风口面积比有关。房间内部流动阻力对流量系数有一定影响。     

自然通风开口流量系数影响因素探讨

开口特性参数———流量系数是影响建筑自然通风流场的关键因素之一。对影响流量系数的因素如开口长宽比、开度、内外压差和温差、开口上安装的纱窗等进行了分析,指出了常值计算的有限性,提出自然通风研究应进行变流量系数定性分析。     

顶部多开口隧道热压通风模拟研究

顶部多开口隧道能避免汽车尾气在隧道峒口集中排放,且利用自然通风降低隧道运行成本。而实际运用中自然通风作用能否达到隧道的需风量要求是不可知的。本文通过对称的隧道模型采用数值模拟的方法研究顶部多开口隧道阻滞工况自然通风规律。通过研究得到:可以用简化的尾气混合温度模型研究隧道热压通风;奇数对称顶部开口隧道有利于热压通风;对称分布的顶部开口数量超过3个时,隧道顶部开口通风量呈"中间小,两边大"的分布。     

上海地区某文化建筑中庭自然通风优化分析

采用CFD计算流体力学方法对上海市某文化建筑中庭室内自然通风进行了数值模拟计算,分析其室内中庭风速、空气龄分布情况,并设计三种优化方案改善其中庭内部自然通风效果.研究得出该建筑原设计方案中庭一层自然通风效果最好,随高度升高,二、三层自然通风效果逐渐变差.通过优化围护结构开口大小、开口高度两种设计参数能够显著改善二、三层自然通风效果和舒适性.可为本地区该类型建筑中庭的自然通风设计优化提供一定的参考.     

基于浮力效应的建筑顶部开口设计研究

风压和热压为建筑自然通风的两种基本形式,建筑自然通风往往是两种形式的综合作用。其中热压通风依托浮力效应原理,借助建筑顶部开口可以改善自然通风。论文从建筑环境对自然通风需求的提升、现代建筑对垂直通风的关注、设计科学与技术策略的丰富、零碳建筑的重要被动策略等方面梳理了其发展变迁的规律,探讨了建筑顶部开口改善自然通风作为设计策略的设计科学方法。     

计算机辅助高大空间自然通风设计

本文对南方地区高大空间的自然通风设计进行了讨论。高大空间建筑具有建筑面积大.人员密集.空调负荷大的特点.正确设计设计自然通风系统可以极大地减少空调系统的能耗。自然通风是一个复杂的流动与传热过程.应用CFD计算对高大空间自然通风进行科学的分析可以有效地确保设计方案的合理性。     

某办公建筑自然通风中拔风井的设计

办公建筑通过合理设置拔风井实现自然通风的利用,不仅能节省空调运行能耗,而且有助于改善建筑通风、提高室内空气品质和热舒适.以夏热冬暖地区某办公建筑为例,采用CFD数值模拟技术,对比分析了拔风井在不同位置、横截面积以及侧开口、顶部开口尺寸等参数下的自然通风效果,可为类似建筑的自然通风优化设计提供思路和参考.     

Effects of building wall arrangements on wind-induced ventilation through the refuge floor of a tall building

Wind-induced natural ventilation plays an important role in the fire and smoke safety of a refuge floor. This paper reports a computational fluid dynamics study to investigate the effect of building wall arrangements on the amount of wind-induced ventilation through a refuge floor which is located at the building mid-height. The refuge floor analysed has a large service core at its centre and is surrounded by exterior building walls, which are arranged in nine configurations that represent varying degrees of opening to wind flow. Results of computed flow patterns show that the wind-induced natural ventilation rate of a refuge floor varies significantly depending on the number of enclosing external walls and the incidence wind angle. A refuge floor, having only one side open, results in the worst natural ventilation and is not recommended.     

Experimental study based on large-scale smoke propagation fire tests through a horizontal opening connecting two mechanically ventilated compartments

This work describes an experimental study of the flow through a horizontal opening (also referred to as a vent), applicable to specific situations typically encountered in nuclear installations. The configuration consisted of two rooms, which were mechanically ventilated and connected to each other by a horizontal opening, the fire being located in the lower room. The flow was governed by buoyancy due to the heat release from the fire, inertia resulting from the mechanical ventilation, and local momentum from the ceiling jet. Two flow regimes (bi-directional and uni-directional) were encountered depending on the fire power and the ventilation set-up. This study presents 17 large-scale fire tests, investigating the behaviour of the flow at the horizontal opening according to several fire scenario parameters: the fire heat release rate, the fire location, the ventilation configuration and the ventilation flow rate. This range of parameters enabled us to focus on different flow regimes, from pure natural convection (bi-directional) to forced convection (uni-directional). The new set of data obtained, based on detailed flow measurements, offers new insights for understanding the flow and developing sub-models to be used in zone codes.     

Multiple steady states in stack ventilation

We investigate the natural ventilation of an occupied open-plan space, which is ventilated through two stacks connected to the roof of the space and a low-level opening or doorway located at the base of the space. The occupants at the floor level act as the source of heat and provide buoyancy driving the ventilation with a nearly uniform distribution of heat. These conditions can produce up to three steady state displacement ventilation regimes. In the first regime, colder air from the outside is drawn into the space through the shorter stack and bottom opening, while warm air inside the room leaves through the taller stack. In the second regime, colder outside air is drawn through the bottom opening and displaces warm air in the room upwards and out through both stacks. In the third regime, outside air is drawn through the taller stack and bottom opening, while warm interior air is displaced out through the shorter stack. A quantitative model is developed to describe these three steady state ventilation regimes. The model is successfully tested with laboratory experiments, and shows that the ventilation regime that actually develops in the room depends on the geometry of the room and the history of the flow. We discuss how these multiple ventilation regimes may be manipulated to bring about ventilation and thermal comfort to the occupants inside the ventilated space.     

Passive cooling in hot,arid regions in developing countries by employing domed roofs and reducing the temperature of internal surfaces

Natural ventilation due to wind effects through buildings employing domed roofs was estimated by a flow network analysis. The dome was assumed to have an opening at its crown. When compared with flat roofs, the domed roofs always increase the air flow rate through the building. The increase in natural ventilation becomes significant in buildings with doors and windows all in one wall, or whenever the wind effects on the building envelope do not produce large pressure differences at the openings.The large air flow rate in the buildings with domed roofs may be utilized to store night air coolness in the structure more effectively and keep the mean radiant temperature of the interior surfaces low for thermal comfort in summer. The lowest internal surface temperatures can be obtained when the surfaces are kept moist and evaporatively cooled.Through a one-dimensional energy analysis the inside surface temperature of a horizontal slab was estimated for various slab materials and thicknesses and external and internal conditions. The inside surface temperature was compared with the case of employing a roof pond. It was found that lower temperatures can be obtained by evaporatively-cooled moist internal surfaces than that which can be obtained by unshaded roof ponds: For a building whose internal surfaces (walls and ceiling) are kept moist a large ventilation rate is needed to prevent water vapor build-up in the space. A domed roof with a hole in its crown can produce the necessary ventilation for such a building.     

Wind-induced natural ventilation of re-entrant bays in a high-rise building

This paper reports a systematic computational study of wind-induced natural ventilation and pollutant transport of re-entrant bays on a total of 30 generic building models of different building heights and with bays of different dimensions. Mean wind flow around each building model and wind-induced flow inside re-entrant bays are computed. To determine the ventilation efficiency of the bay, the computed flow field is used to disperse a scalar pollutant initially occupying the entire bay at a uniform concentration. The subsequent time decay of pollutant concentration inside the bay is studied and the ventilation efficiency is quantified by the retention time. The results show that wind-induced flow inside the bay, especially on the building side face, is complex and highly three-dimensional. Air exchange rates through the roof opening and vertical side opening are analyzed for each bay and their relationship to the ventilation efficiency is discussed. The bays on the building side faces are much worse ventilated than those on the windward or leeward building face. The deeper the side bay, the worse is the air exchange and ventilation. The building height is found to have a governing effect on the ventilation of the windward and leeward re-entrant bays.     

复杂通风方案设计计算方法研究

方案阶段的自然通风设计主要关注的是通风路径,而一般来说此阶段的部分开口信息未知.本文针对建筑设计的特点,提出了面向方案阶段复杂通风方案的设计计算方法,针对部分开口信息未知的情况,基于稳态热平衡模型和多区域通风网络模型建立了最优化计算模型,并以“未知开口平均面积的最小值”作为通风方案评估指标.将该设计计算方法用于比较单中庭和双中庭通风方案,发现单中庭方案部分楼层出现了气流“倒灌”现象,而双中庭方案可节省37.1％的开口面积.     

Wind-induced ventilation performances and airflow characteristics in an areaway-attached basement with a single-sided opening

In the present study, we performed both wind tunnel experiments and numerical simulations on a scale model with the focus on wind-driven natural ventilation in an areaway-attached basement with a single-sided opening. In the experiments, the mean value of the effective ventilation rate, purging flow rate (PFR) was measured for nine wind incidence angels based on the homogeneous emission rate method. The experimental results were used to validate two numerical approaches: Reynolds averaged Navier–Stokes (RANS) modeling and large-eddy simulation (LES). The influences of inflow turbulent fluctuations for LES modeling were also examined. The comparisons between the experiment and the numerical simulation indicate that LES can provide more accurate results than RANS and the inflow turbulent fluctuations should be taken into account for LES modeling. Based on LES with the inflow turbulent fluctuations, the mean airflow patterns within and around the areaway-attached basement were further studied for different wind incidence angles to investigate the influence of wind direction on ventilation performance in the areaway space. Furthermore, the relationships between the effective ventilation rate and the kinetic energy in the basement space were analyzed for three wind directions: 0°, 90° and 180°. A close correlation was found between the mean values, whereas the corresponding time variations showed large discrepancies. Finally, we compared the effective ventilation rate obtained using the homogeneous emission rate method and the airflow rates through the opening using two integration procedures. The effective ventilation rates were found lower than the airflow rates through the opening.     

居室热压自然通风应用探讨

采用风速法和示踪气体衰减法实测了某居室的自然通风量。得到了不同窗孔开度下的窗孔流量系数,给出了窗孔流量系数与窗孔开度的关系曲线,分析了室内外空气温差对窗孔流量系数的影响。     

建筑外窗自然通风流量系数的影响因素分析

流量系数是反映建筑开口自然通风量的一个重要参数。利用Fluent软件对不同形式的建筑开口在自然通风下的流量系数进行了模拟计算,分析其各项影响因素包括通风口面积、通风口高宽比、通风口开启角度、通风口两侧温差等的影响情况。再利用SPSS软件对模拟结果进行多元回归,定量分析平开窗、推拉窗以及悬窗3种开口的流量系数。