大涡模拟方法下的四圆柱绕流数值模拟

采用了Fluent软件和大涡模拟LES方法进行了在雷诺数下Re=15000的四圆柱绕流数值模拟。计算分析显示本文的计算结果与他人的实验结果吻合良好,可为类似圆柱结构的流体绕流问题设计提供参考。     

湍流边界层中低矮建筑绕流大涡模拟

通过对平板湍流边界层进行大涡模拟,采用拟周期边界条件维持湍流边界层厚度稳定,提取速度和压力时程作为低矮建筑绕流模拟之脉动入流边界条件,研究脉动入流下的低矮建筑绕流特性。研究结果表明：入流边界特性对网格变化适应性良好,其平均速度剖面、湍流强度、流速频谱特性基本符合空旷地貌风场特性;脉动入流下,建筑表面的平均风压系数、脉动风压系数的计算结果与风洞试验结果基本吻合。受雷诺数及湍流强度的影响,流动分离区负压与试验值存在一定差别;屋盖上分离区风压时程具有非高斯概率特性,尤以气流分离较剧烈的屋盖迎风边缘及屋盖两侧风压的非高斯特性明显,该特征与风洞试验基本一致;受非高斯特性的影响,建议峰值因子g取4.5~5.5。     

矢流洁净室二维流场的大涡模拟

采用大涡模拟技术对矢流洁净室二维流场进行了数值模拟，分析了模拟结果，确定了空态洁净室的送风口半径、回风口高度、送风速度等参数，指出湍流大涡模拟能准确得到洁净室流场中旋涡的位置和尺度，适用于对洁净空调多种工作环境的数值模拟。     

火羽流轴向温度大涡模拟与实验比较

为了验证基于大涡模拟的FDS技术研究火羽流中心线轴向温度的可靠性,建立FDS模型对某实体厂房中640、1 080kW的池火灾进行数值模拟,并与实验室开展的全尺寸池火灾数据及经典理论模型预测值比较。研究结果发现,基于大涡模拟的FDS技术得到的火羽流中心线轴向温度与试验数据变化趋势基本吻合;与经典羽流模型预测的数据相比,FDS模拟得到的火羽流中心线轴向温度吻合度最高,其相对误差值普遍偏小,仅仅在个别点会出现相对误差偏大的现象。     

基于大涡模拟的火羽流轴向流速预测

为了验证基于大涡模拟的FDS技术研究火羽流中心线轴向流速的可靠性,建立FDS模型,对某实体厂房中0.6、1.2、1.8、2.4 W的池火灾进行数值模拟,并与经典理论模型预测值进行分析比较,发现:基于大涡模拟的FDS技术得到火羽流中心线轴向流速的变化趋势与经典理论模型的结果较为吻合;不同火源功率的模拟值与Heskestad模型预测值的最小误差分别为0.020、0.130、0.106、0.293m/s,且相对误差平均值仅为2.928%、6.069%、5.545%、8.050%。研究表明,基于大涡模拟的FDS技术能准确有效地预测大空间池火灾中心线轴向流速。     

建筑物绕流的非稳态数值模拟研究

建筑物绕流是一种典型的钝体绕流形式,而钝体绕流通常具有非稳态流动特征,本文主要工作是对建筑物绕流的非稳态流场进行数值模拟研究。首先采用了RNG k-ε模型对方柱绕流进行非稳态数值模拟研究,通过与实验以及大涡模拟结果进行比较,发现RNG k-ε模型可以获得满意结果;接着又对一种典型的建筑物绕流形式进行数值模拟研究,分别采用了稳态和非稳态模拟方法,模拟结果表明了采用非稳态数值模拟方法可以获得与实验以及大涡模拟更为接近的结果。     

大涡模拟及其在室内空气流动换热中的应用

介绍了国内外大涡模拟的亚格子湍流模式和在室内空气流动换热中的研究现状给出了大涡模拟室内空气流动的应用实例。认为大涡模拟有广阔的发展前景。     

数值风工程应用中湍流模型的比较研究

湍流封闭模型是影响建筑风工程数值模拟计算结果精度的至关重要的影响因素之一,本文针对数值风工程研究中最常见的钝体绕流问题,比较研究了基于RANS方法的标准κ-ε模型、Realizableκ-ε模型、RNGκ-ε模型、v2-f模型及RSM模型等五种湍流模型对风压和风速计算结果的影响.比较研究的对象是SRI完成的6m立方柱建筑模型,风压数值计算结果的比较参考值为该研究项目的场地实测值,风速比较则采用文献的风洞试验结果.通过比较分析得出结论：在研究比较的五种湍流模型中,RNGκ-ε模型和v2-f模型的数值预测结果相对较好,它们基本可以反映这一典型钝体结构绕流的复杂流动特性.     

密闭腔室火灾温度的大涡模拟

应用大涡模拟方法模拟全尺寸的密闭腔室火灾场景。提出应用平均燃烧效率的概念模拟密闭腔室火灾的方法,选取平均燃烧效率为0.75进行大涡模拟,得到密闭腔室室内温度场以及烟气运动的模拟数据。通过分析密闭腔室内竖直方向上的温度分布,发现在竖直方向上存在温度分层现象。将模拟结果与实验数据进行对比可以看出,大涡模拟可以较好地模拟密闭腔室内火灾的发生发展情况。     

基于大涡模拟的三维高层建筑结构气弹响应数值模拟

以宽高比为1∶6的方形截面高层建筑为研究对象,采用弱耦合分区交错算法,流体域采用大涡模拟方法,进行了紊流边界层风场内三维高层建筑结构多自由度模型的气弹数值模拟,计算中考虑了来流紊流,以及结构的顺、横风向响应。将结构静止时大涡模拟结果与刚性模型测压风洞试验进行比较,验证了该方法在准确预测结构风荷载方面的可行性。通过与气弹模型风洞试验结果的比较表明,本文数值分析方法可用于求解风与结构的相互作用,且具有较高的精度。进行了高折减风速下的气弹数值模拟,研究了结构顶部顺、横风向位移响应随折减风速的变化规律。结果表明：结构风振气弹响应主要为来流紊流引起的顺风向抖振和旋涡脱落引起的横风向涡激振动;折减风速较小时,结构顺、横风向位移振幅相当,且位移响应均相对较小;随着折减风速的增加,结构位移响应增大,横风向涡激振动逐渐占据主导地位,并经历了从“拍”到“涡激共振”的转化。     

中庭火灾烟气流动的大涡模拟

采用大涡模拟的方法,对中庭火灾烟气的流动过程进行了模拟,了解了中庭烟气的蔓延过程,得到了烟气的速度场和温度场、顶棚射流的速度和温度的详细结果。模拟结果表明,大涡模拟能比较准确地预测中庭内烟气的流动状态,可用于指导中庭建筑的防火设计。     

Large eddy simulation of the backdraft phenomenon

A sub-grid scale model for partially premixed combustion has been adapted and applied to simulate the backdraft phenomena. A fast deflagration or backdraft is produced when into a hot, fuel-rich compartment an inflow of fresh air is suddenly allowed through an opening. It is essentially a violent combustion process involving both premixed and non-premixed regimes. The present model is based on the coupling of independent approaches for non-premixed and premixed turbulent combustion. The ‘flame index’ concept was used to separate the two different combustion regimes. This index describes the structure of the flame based on fuel and oxygen gradients. Due to the lack of detailed experimental measurements, the results were largely analysed qualitatively. The predictions have provided valuable insight into the backdraft phenomenon suggesting that the development of backdraft can be divided into five phases, i.e. initial condition, free “spherical propagation, “plane” front propagation, stretching of the flame front through the opening and fireball outside the container. Quantitatively, the experimentally measured and predicted lapse of time between the maximum over- and under-pressure at the opening of the container is found to be in reasonably good agreement.     

Large eddy simulation of thermal stratification effect on convective and turbulent diffusion fluxes concerning gaseous pollutant dispersion around a high-rise model building

In this paper, the large eddy simulation (LES) approach is employed to investigate the role of different thermal stratification conditions (stable, neutral and unstable) in the air flow and gaseous pollutant dispersion processes around a high-rise non-isolated model building with 1:1:2 shape placed within a non-isothermal boundary layer. The simulation results are initially validated with available experimental measurements and then applied to study the characteristics of pollutant dispersion. Predictions show a low-velocity zone behind the model building. The major effect of a stable stratification on flow field is the formation of a weak recirculation flow in the wake region. Results represent an intense temperature gradient close to the sides of the model building for both stable and unstable conditions. Moreover, the convective and turbulent diffusion fluxes are compared under different thermal stratification conditions, and it is shown that the LES approach is capable of predicting the counter-gradient mechanism.     

浅谈大空间火灾烟气运动规律的计算机模拟

分析并讨论了当前大尺度空间火灾烟气运动规律的计算机模拟研究现状。结果表明,采用大涡模拟方法结合多单元区域模拟是研究火灾烟气运动规律的发展趋势。     

Large eddy simulation of compartment fire with solid combustibles

For properly describing practical building fire processes with solid combustibles, the pyrolysis kinetics model of solid combustibles and the large eddy simulation (LES) approach are applied to the simulation of the thermal decomposition of the polyurethane foam (PUF) slab and the space fire spread in a compartment. The instantaneous variations of the heat release rate of the PUF slab, the smoke temperature, and the smoke interface height with time are obtained under different ventilation conditions. They are in agreement with the measured data. The ventilation conditions have distinct effects on the interactions between the pyrolysis of the PUF slab and the space fire spread. Influenced by the space fire spread, the heat flux on the top plane of the PUF slab exhibits a non-uniform distribution. The PUF slab is consumed in an asymmetric manner.     

深圳平安国际金融大厦风致响应大涡模拟分析

运用一种新的湍流脉动流场产生方法模拟了三种风场的湍流边界条件,采用一种新的大涡模拟的亚格子模型,基于Linux系统下软件平台Fluent 6.3的并行计算技术,对深圳平安国际金融大厦进行了全尺寸、高雷诺数（高达10×10⁸量级）的数值风洞模拟。计算了三种风场下建筑表面平均、脉动风压及风荷载时程数据。利用惯性风荷载（IWL）法得到三种风场下深圳平安金融大厦的基底等效静风荷载以及结构顶部峰值加速度响应。分析了不同的湍流来流对结构风压系数、风荷载及加速度响应的影响。分析结果表明：三种来流风场条件下,深圳平安金融大厦周围风场相差较大,来流的湍流强度越高,建筑物前方的脉动风速越高;顺风向等效风荷载主要受平均风速控制,横风向等效风荷载主要受脉动风控制;湍流强度越大,横风向等效风荷载越大;中国规范建议的湍流流场下,深圳平安金融大厦10年重现期顺风向、横风向峰值加速度响应满足居住者舒适度要求。     

Turbulence statistics in a fire room model by large eddy simulation

Fire and smoke movement in a room is influenced by the turbulence characteristics (such as Reynolds stress, turbulent heat flux, etc.) of the flow and temperature fields. In order to accurately predict fire and smoke movement by computational fluid dynamics (CFD), it is necessary to verify these turbulence quantities. The purpose of this study is to predict the turbulence structure of the flow and temperature fields due to a fire in the compartment by large eddy simulation (LES) using detailed experimental data to verify the simulation results. The results show reasonably good agreement with experimental data for both the mean flow properties and the turbulence quantities with the exception of the region near ceiling. This study provides useful information for verifying LES technique when applied to compartment fires.