【作者】 邓启红；

【导师】 汤广发；

【作者基本信息】 湖南大学 ， 供热、供燃气、通风及空调工程， 2003， 博士

【摘要】 本文主要讨论建筑室内空气环境中对流问题的模拟方法与基本特征。主要内容分为七章,研究要点如下:第一章探讨如何描述对流系统中热与质的传输过程?由于传统的温度与浓度等值线分布仅展示了对流传热传质系统所达到的最终状态,而没有提供热与污染物的传输信息或结构,因此我们无法知道对流行为的本质特征。本章提出的对流传输过程模拟与可视化方法则是直接显示对流系统内部流体、热与污染物的传输结构或过程,使我们清楚地看到对流行为特征。作者在对流控制方程的基础上定义了描述流体、热、质传输统一的对流传输函数(流函数、热函数、质函数),并分析了传输函数及其传输路径(流线、热线、质线)的基本性质。应用算例充分说明了对流传输函数及其传输路径的价值与意义。第二章是将对流传输可视化技术应用于建筑环境领域,为室内空气环境评价提供一种更为简单有效的工具与方法。室内热与污染物的传输结构给我们提供了一种视觉上的环境质量评价,如我们可以直观地看到:室内有害的热与污染物能否尽快排除?有害的热与污染物是否对我们身体健康产生影响?如何布置或控制热源与污染源,以避免它们对我们身体造成侵害或使室内空气环境质量更好?作者以二维层流双扩散混合对流模型——置换通风——进行了数值模拟与分析,并利用上述对流可视化技术来观察热源、污染源、外部机械通风三个因素对室内空气环境的影响。建筑室内热源表现出很大的特殊性:一方面呈离散分布状态,另一方面热源的大小、类型与强度各不相同。如何描述室内大小、类型与强度不同的离散热源之间的相互作用及其对室内空气环境的影响即是第三章的主要内容。作者首先提出了组合温度尺度法,它有效地将离散热源之间抽象的相互作用转换为边界条件之间明确的物理关系。其次,通过广泛意义上的贡献因子概念来描述/鉴别不同的离散热源。最后,在热源统一的传热特性基础上定义了热源强度概念,它决定了离散热源在相互作用中的地位。本章分别讨论了壁面离散热源之间及壁面离散热源与内部体积热源之间的相互作用。由于人类活动的复杂性和舒适性需要,建筑室内离散热源与污染源的位置与强度往往是不断变化的,从而对室内空气环境产生重要影响。第四章研究了室内双扩散自然对流系统中离散热源与与污染源之间的相互作用随强度与位置的变化关系。模拟结果表明双扩散自然对流系统的空气流动与传热传质特性完全是由离散热源与污染源浮升力之间的相互作用关系决定的:当离散热源与污染源浮升力协同作用时,自然对流呈比较稳定的单一流动结构;而当热源与污染源浮升力对抗作用时,自然对流系统随它们之间强度变化呈现出多种流动状态。第五章是讨论如何模拟室内复杂的对流问题?室内空气对流行为的复杂性与状态的多样性通常是多种物理过程相互作用的结果,如离散热源的热浮升力、离散污染源的浓度浮升力及机械通风等。因此,模拟室内空气对流传热传质系统最自然的方法是分析室内可能发生的各种物理过程之间的相互作用,而在相互作用中明显占优的物理过程将决定室内对流的基本特性。本章提出的处理复杂对流问题的自然模拟法即是根据物理过程之间的相互作用分析对流的行为特征。第六章是研究对流问题求解的SIMPLE算法。作者从连续性守恒的本质出发,详细分析了压力修正方程的求解特殊性及其对SIMPLE算法收敛性能的影响。尽管从方程结构上看,压力修正方程与动量方程具有相同的离散形式,可以采用相同的迭代方法求解,但在迭代求解的三个方面——迭代初值、边界条件、迭代过程——都表现很大的特殊性:首先压力修正方程的迭代初值具有独立性而不象动量方程的迭代初值具有继承性;其次,压力修正方程的边界条件类型应该与动量方程的速度边界相反;最后,必须增加压力修正方程的内循环迭代求解次数,才能提高算法收敛过程的稳健性。作者通过无开口、局部开口与完全开口三种典型流场来验证SIMPLE算法中压力修正方程特殊处理方法的准确性与有效性。第七章是实验研究,主要利用先进的粒子图像速度场PIV设备对室内空气对流进行实验研究并验证数值模拟结果的可靠性。作者根据无因次控制方程的解处处相等原则建立了小尺度水模型实验与大尺度空气真实对象之间的对应关系。结果比较表明,水模型实验测试与空气模型数值模拟基本吻合。更多还原

【Abstract】 Indoor air environment (IAE) is closely related to our health and work efficiency and hence has attracted considerable attention in the recent years. IAE is mainly a hybrid process of air flow and heat/mass transfer. Therefore, the knowledge of indoor air convective heat and mass transfer or indoor air convection, is fundamental to control our indoor air environment. The objective of the present dissertation is to investigate the modeling and characteristics of indoor air convection. The layout of the dissertation is as follows:The first chapter is to model and visualize the convective heat and mass transport. The traditional distributions of temperature and concentration just mark the final state that a convection system has reached but convey the information about how the heat and contaminant is transported across the system, and therefore we cannot get to know the natural characteristics of convection. The concept of convection transport is proposed to‘see’the nature of the convective phenomena. The ability to see is very attractive, for the engineers and customers are much convinced by their seeing. Unified convection transport functions (streamfunction, heatfunction and massfunction) are derived from the governing equations to describe the fluid, heat and mass transport respectively.In chapter two, the visualization of convection transport provides a simple but effective way to evaluate the indoor air environment. The heat and contaminant transport structures indoors give us a bird-eye to see (a) if the heat and contaminant could be swept out as soon as possible, (b) if the harmful heat/pollutant sources do harm to our health, and (c) how to organize the heat and pollutant sources so as to achieve a high indoor air quality. A two-dimensional double diffusive laminar mixed convection, displacement ventilation, is fully investigated by the means of heat and contaminant transport structures to see the effects of the heat and pollutant sources and the external mechanical ventilation.Chapter three focuses attentions on the interaction between discrete heat sources (DHSs) indoors and their effects on IAE. In order to identify the discrete heat sources of different strength, type and size, a combined temperature scale is first developed. The advantage of the method is that the implicit interaction between DHSs is transformed to the explicit relations between their contribution ratios. The contribution ratio of the surface heat source is expressed by its boundary condition and that of the inner volumetric source expressed by the source term in the governing equation, and the total contribution ratios from all the discrete heat sources are unity. A related concept of thermal strength of DHS is then introduced to determine its role in the interaction between others.The effect of the position and strength of indoor heat and pollutant sources on indoor air environment is then numerical studied in chapter four. A two-dimensional double diffusive laminar natural convection in rectangular enclosure is detailed analyzed. The results show that when the thermal and solutal buoyancies aid each other, the airflow consists of one main cellular structure and is steady, regardless of the relative strength variation between the heat and pollutant sources. There are multiple flow structures, however, according to the relative strength when the buoyancies opposing each other.Natural modeling is suggested in chapter five to deal with the complicated indoor air convection. The complicated behavior and multiple states of indoor air convection are mainly related to the multiple physical processes, such as the thermal buoyancy, the solutal buoyancy and the mechanical ventilation. Therefore a natural modeling of indoor air convection is to analyze the interaction between all the possible physical processes. The basic characteristics of indoor air convection are then determined by the prevailing physical process.The SIMPLE algorithm for the numerical solution to convection problem is then investigated in the following chapter. The special features of pressure-correction equation and their effects on the performance of the SIMPLE algorithm have been thoroughly studied based on the principle of continuity conservation. The last chapter focuses on the experiment study. A small-scale water experiment is first set up by the particle image velocimetry and then validates the numerical simulation of the full-scale airflow indoors.更多还原