典型体型体育场风荷载数值模拟分析

为了给体育场初步设计阶段选取风压系数提供参考,构造了马鞍形、平屋盖矩形、单侧看台月牙形和双侧看台月牙形4种典型体型体育场模型,并引用<欧洲张力薄膜结构设计指南>的罩棚标准化分区,采用计算流体力学(CFD)方法对4种典型体型体育场的风压系数和分布形式进行了系统研究,绘制了设计取值图供工程参考使用,并总结了各类体型体育场风荷载的规律.     

CFD study of exhaled droplet transmission between occupants under different ventilation strategies in a typical office room

This paper investigated the transmission of respiratory droplets between two seated occupants equipped with one type of personalized ventilation (PV) device using round movable panel (RMP) in an office room. The office was ventilated by three different total volume (TV) ventilation strategies, i.e. mixing ventilation (MV), displacement ventilation (DV), and under-floor air distribution (UFAD) system respectively as background ventilation methods. Concentrations of particles with aerodynamic diameters of 0.8 μm, 5 μm, and 16 μm as well as tracer gas were numerically studied in the Eulerian frame. Two indexes, i.e. intake fraction (IF) and concentration uniformity index R_C were introduced to evaluate the performance of ventilation systems. It was found that without PV, DV performed best concern protecting the exposed manikin from the pollutants exhaled by the polluting manikin. In MV when the exposed manikin opened RMP the inhaled air quality could always be improved. In DV and UFAD application of RMP might sometimes, depending on the personalized airflow rate, increase the exposure of the others to the exhaled droplets of tracer gas, 0.8 μm particles, and 5 μm particles from the infected occupants. Application of PV could reduce R_C for all the three TV systems of 0.8 μm and 5 μm particles. PV enhanced mixing degree of particles under DV and UFAD based conditions much stronger than under MV based ones. PV could increase the average concentration in the occupied zone of the exposed manikin as well as provide clean personalized airflow. Whether inhaled air quality could be improved depended on the balance of pros and cons of PV.     

Measurement of thermal environment in Kyoto city and its prediction by CFD simulation

In the summer of 2002, measurements were simultaneously performed to investigate the characteristics of heat flow in urban areas at three locations in Kyoto city: (1) a commercial urban area mixed with low-rise traditional residential buildings that represents the urban area of Kyoto; (2) a university campus area with lots of green zones; and (3) a plaza covered with a concrete slab which was used as a reference point of measurement. Heat flux of boundary layer over the three locations and the surface temperatures of building walls and streets were measured to investigate the urban thermal environment. For the analysis, a new simulation code was developed by combining unsteady state heat conduction of building walls and grounds, radiation heat exchange between them, and airflow by computational fluid dynamics (CFD). By using this code, the thermal environment of the urban areas such as air temperature, humidity, wind velocity, and boundary layer heat flux was predicted and compared with the measured results. It was found that this model could predict the real thermal environment of the urban area. Using this code, the effect of additional green on roofs and grounds can be investigated in order to mitigate urban heat island and to improve urban thermal environment at the street level.     

基于CFD建筑热环境模拟的建筑方案优化设计研究

考虑了影响建筑热环境的6个建筑设计要素:窗墙面积比、窗类型(传热系数)、水平遮阳板尺寸、外墙传热系数、屋顶传热系数及房间尺寸(长∶高∶宽)。根据设定的室内热环境评价指标:室内温度平均值、PMV平均值、温度不均匀系数和速度不均匀系数,通过正交试验和CFD模拟,得到了自然通风建筑设计中,使建筑热环境相对最优化的6个建筑设计要素的最优搭配方案。     

CFD study of the effects of furniture layout on indoor air quality under typical office ventilation schemes

The relative freshness of indoor air in breathing zone can be measured by ventilation effectiveness. Numerous research articles in literature have investigated ventilation effectiveness under different ventilation schemes, different inlet/outlet positions, and different diffusor types. These researches seem to have a goal to find a solution to optimize ventilation effectiveness through manipulating ventilation system. In reality, however, the occupants of a rented office room have no right to manipulate the ventilation system; instead, they have to accept whatever rented to them. An important issue thus arises: how to improve ventilation effectiveness without changing ventilation system? This paper has built a CFD model about a typical office room, validated it by published experimental data in literature, and then applied it to twelve typical office situations/cases of different furniture layouts under different ventilation schemes. The simulation results of twelve cases show that furniture layout is an important factor in indoor airflow and temperature fields, and the quality of air in breathing zone can be significantly improved by adjusting furniture layout without making any change in ventilation system.     

Dynamic overset 2D CFD numerical simulation of a small vertical axis wind turbine

ABSTRACT

The environmental friendly sources of power have been explored due to increased environment degradation. In this regard, wind energy may be a viable option. A renewed involvement in Vertical axis wind turbines (VAWT) was found. A wide variety of factors such as the cut-in, cut-out wind speed will decide the beneficence of VAWT as a function of energy production and reliability. In this research work, 2D computational fluid analysis of an aggregate small type of vertical axis wind turbine is performed using pecuniary codes of GAMBIT 2.3 and FLUENT 6.3. At starting, the simulation model and numerical method of small type of vertical axis wind turbine is presented in detail having classical NACA0018, NACA0021 and NACA0025 three-bladed rotor. The result shows that NACA0025 bladed rotor has the highest moment of 2.9195?Nm and power 43.7924?W at a tip speed ratio?=?6.     

Analysis of thermal comfort in an office room by varying the dimensions of the windows on adjacent walls using CFD: A case study based on numerical simulation

Ventilation provides a more comfortable thermal environment for occupants inside of buildings. The growing demand for electricity has encouraged research focused on natural ventilation. In this study, we analyze the thermal comfort in an office room with varied window opening dimensions using the computational fluid dynamics (CFD) technique. We created a 3-dimensional model room with windows on adjacent walls and an atmospheric zone. The flow equations were solved using the control volume method. Steady k-ɛ turbulence model and incompressible fluid flow of constant property have been considered, neglecting the variation due to temperature. We examined the effects of the window openings’ area and aspect ratio on thermal comfort. The CFD code was compared with the network model and its discrepancy value was less than 8%. Air temperatures along the various midlines of the room were predicted and compared for a range of window sizes. We identified the room areas occupied by the low temperature zone at various planes. Finally, we determined the predicted mean vote (PMV) contours at the midplane to identify the comfort zone. Areas other than the room corners and the areas nearest to the windowless walls are identified as the most comfort zone. Results from this study indicate the optimum window opening area and aspect ratio for maintaining thermal comfort in an office room.     

空调水蓄冷温度分层动态特性模拟

分析了空调水蓄冷温度分层的特性,建立了相应的数学模型,并利用该模型模拟了竖直放置的圆柱形蓄冷桶内的温度分布规律,认为该模型可为空调水蓄冷系统的设计和运行提供理论依据。     

电缆燃烧典型火源模拟方法综述

针对电缆火灾问题,综述了国内外电缆火灾模拟试验及电缆燃烧测试中使用的火源模拟方法,并对比探讨了多种火源模拟方法的点火时间、火源温度、火源面积、火源功率、可扩展性、可移动性以及可持续使用性等方面的差异:燃气喷灯法和辐射加热法(锥形量热计)所需点火时间短;电加热法火源温度高,操作简便易移动;燃油点火法的点火面积大,可扩展性...     

Dynamic thermal simulation of a glass-covered semi-outdoor space with roof evaporative cooling

In the hot season solar radiation impinging on a glass roofing may overheat the underneath space to temperature values which may generate a high stress environment. To moderate the extreme microclimate which may occur in a glass covered semi-outdoor space, evaporative cooling to be applied to the glass roof is suggested. The analysis is performed under both the thermal and the energetic point of view, by accounting for the actual climate of the considered location. The results point out that roof evaporative cooling coupled with glass sheet high solar radiation absorptivity may offer an attractive way for the control of a semi-outdoor environment.     

Optimization of a hospital room by means of CFD for more efficient ventilation

This paper analyses the ventilation airflow pattern in a two-bedded hospital room. The whole space of the room is divided in modules by means of curtains and internal partition walls. This configuration has many advantages from the point of view of comfort and medical assistance, but it implies an important restriction as far as ventilation is concerned. The ventilation system consists of an induction unit placed inside the hall ceiling blowing into the room and an exhaust fan in the bathroom. Numerical model solves mass, momentum and mean age of air equations assuming isothermal and stationary flow. Ventilation is evaluated analysing the age of air and the velocity fields inside the room. The results with the initial architectural design of the room show a very deficient ventilation at the patients site. Alternative configurations have been studied, allowing for correct ventilation without renouncing to the assistance advantages. Finally, the optimum configuration of the room is provided, regarding both the comfort of the patients and the cost of execution.     

Effects of double glazed facade on energy consumption,thermal comfort and condensation for a typical office building in Singapore

Fully glazed facade that has been increasingly used in Singapore causes higher energy consumption and thermal discomfort due to higher solar gain. The use of double glazed facade system with ventilation system is one way to solve these problems. The objective of this paper is to investigate the effects of double glazed facade with ventilation system on the energy consumption, thermal comfort and condensation and compare to single glazed facade system. TAS and CFD software were utilized to calculate energy consumption, thermal comfort and condensation for single glazed facade building as well as double glazed facade building. The simulation results showed double glazed facade with natural ventilation were able to minimize energy consumption as well as to enhance the thermal comfort. Turning the mechanical fans on could also solve the condensation problem due to high humidity.     

Life cycle energy assessment of a typical office building in Thailand

A typical office building in Thailand was analyzed using the life cycle energy analysis (LCEA) method to illustrate the argument. Results indicate that although life cycle energy (LCE) distribution is concentrated at the operating phase, the embodied energy of buildings is a non-negligible fraction of the LCE balance. Energy (electricity) used for lighting and HVAC systems in the operation phase and; the manufacture of concrete and steel were the most significant elements in the buildings life cycle. Application of a combination of energy saving measures, showed that 40-50% of energy (electricity) used in a typical office building in Thailand can be saved. Preliminary analysis indicated that recycling building materials can also contribute additional energy savings (about 8.9%) to a buildings LCE profile. Therefore reducing energy consumption should be a priority for not only the operation but also other life cycle phases. It is suggested that both embodied and operating energy should be accounted for within the context of energy efficiency through the incorporation of LCEA into the existing Thai building energy code.     

CFD analysis and energy simulation of a gymnasium

A computational fluid dynamics (CFD) program EXACT3 has been applied to investigate the temperature distribution and air movement within an air-conditioned gymnasium with four different, but commonly found, exhaust positions in Hong Kong. In this numerical study, the effects of thermal stratification on the energy performance (in terms of cooling load and electricity consumption) are examined with respect to the HVAC plant oversizing issue. It has been found that significant thermal stratification occurs in the gymnasium. The annual cooling load can be overestimated by 45.4% for the best exhaust position when the effect of thermal stratification is not considered. The corresponding peak cooling load and, hence, chiller plant size, will increase from 59.9 to 77.6 kW. The low energy efficiency of the oversized chiller at part-load operation results in a 7% increase in the annual energy use for the HVAC plant.     

大空间建筑室内热环境CFD模拟中壁温及室温的求解

应用PHOENICS软件模拟某体育馆的室内热环境,将壁温作为模拟的第一类边界条件。建立了室内表面对流辐射耦合换热方程,着重讨论了采用表面换热分析法求解表面传热系数以求解壁温的方法。因壁温计算和室温计算互相耦合,采用迭代计算的方法求解壁温和室温。模拟计算结果与实测结果基本吻合。     

某典型客厅火灾数值仿真模拟

采用大涡模拟(LES)方法,对典型客厅火灾进行全尺寸仿真模拟。通过模拟分析火灾时室内热释放速率、燃烧速率、壁面温度及烟气温度的变化特性,揭示客厅火灾的特殊性。     

Application of an array processor to the solution of transient thermal problems in buildings

The heat transfers occurring within buildings are described in terms of a lumped parameter model. A building's thermal properties can be represented by a simple resistance-capacitance network. Temperatures or heat flows resulting from imposed thermal conditions can be calculated by numerical solution of the equations representing the network. An implementation of the solution method on a conventional computer is presented and shown to be very time-consuming for a typical domestic multi-room building. An implementation on an array processor is also presented and it is shown that substantial savings in run time can be achieved without recourse to changes in the model or extensive reprogramming.     

北京汽车博物馆空调气流组织的CFD模拟研究

针对北京汽车博物馆跨度大、空间高、形状复杂、空调系统设计难度大的特点,采用CFD软件对高大空间的温度场和速度场进行了数值模拟和研究,最终达到调整和优化空调系统设计方案的目的.     

Study on indoor thermal environment of office space controlled by cooling panel system using field measurement and the numerical simulation

The purpose of this study was to analyze the performance of a cooling panel system installed in the vertical plane with condensation (hereinafter a cooling panel system) using field measurement and coupled simulation of convection and radiation (CFD). Unlike an all-air cooling system, the cooling panel system could remove the cooling load by convection and radiation. Since the surface temperature of the cooling panel analyzed in this study can be controlled under the dew point, this system is expected to be energy-saving and dehumidifying. In the first step of this study, the indoor thermal environment of the office space, which is air-conditioned by a cooling panel system, was analyzed by field measurement and CFD. By comparing both results, the expected precision of CFD for an indoor space with a cooling panel was examined and the CFD method verified from a practical point of view. In the next step, the thermal environment of the model office space, which is cooled by three types of HVAC system (cooling panel system, all-air cooling system, and hybrid air cooling system composed of cooling panel and natural ventilation), was analyzed using CFD. Installing a human model in the office, the characteristics of heat transportation from the human model were also analyzed. The analysis deals with only sensible heat in this study. The operative temperature in the cooling panel system was lower than that in the all-air cooling system when each of the sensible cooling loads of all types of HVAC system was the same. In conclusion, the cooling panel system was found to be very energy-efficient.     

CFD simulation on the air flow in a sauna

Sauna is the Finnish word for a wood-lined and insulated room, heated by a special stove containing stones, and erected specifically to create the right environment for a certain kind of dry bath. Its fundamental purpose is to induce perspiration and thus to cleanse the skin and body. The authors have now applied scientific data to the mystique and culture of the often misunderstood Sauna which has been used by the Finns for some two thousand years.