地铁岛式站台空调气流CFD模拟

为给岛式站台的气流组织设计提供依据,评价气流组织设计方案,确定合适的送风温差以优化岛式站台空调系统的设计。建立典型岛式站台的三维几何模型,应用标准湍流模型作为站台气流的物理模型,根据实际测试的站台热湿负荷设定数值模拟的边界条件,应用CFD（计算流体力学）对地铁岛式站台空调系统进行模拟。岛式站台的温度场模拟结果与实际测试的站台温度场吻合较好,表明在合理的简化条件下,采用标准湍流模型的计算流体力学模拟能够较为准确地模拟和预测地铁岛式站台的温度场,可以为岛式站台空调系统的气流组织设计提供依据。     

带风口屏蔽门地铁车站自然通风特性的数值模拟

建立了全尺寸几何模型,采用动网格方法模拟了地铁列车运行时引起的非稳态流动,分析了屏蔽门风口、隧道区域、站台楼梯口的气流特性及活塞风井特性。结果表明,带风口屏蔽门的地铁车站可以利用活塞风带走隧道及站台余热,从而降低通风能耗。     

室内有毒有害气体扩散的数值模拟

采用基于RNGKε湍流模型的CFD方法,模拟了通风模型房间内的气流运动和由固定点释放的示踪气体CO2的浓度分布,分析了送风速度和释放源位置对浓度场的影响。气流速度场的模拟结果与文献中的流动显示实验结果比较吻合。     

地铁站台两种送回风方式下热环境对比分析

本文使用计算流体力学(CFD)的方法,建立典型岛式站台的三维几何模型,用标准k-ε湍流模型作为站台气流的物理模型,按实测的热湿负荷、温度\速度等作为边界条件,对地铁闭式系统岛式站台环控系统中两种典型送回风方式的气流组织方案在夏季工况最不利情况下进行对比分析。结果表明:两侧送中间回的气流组织方案在对站台的温度控制上要优于单送单回的气流组织方案,而在气流温度\速度均匀性和能耗系数上,后者更加满足舒适性和能耗方面的要求。研究成果为地铁环控系统设计运营提供参考。     

地铁车站火灾的烟气流动状况研究

以地铁火灾与烟气发展过程的数学模型为基础,建立CFD模拟的物理模型,对岛式无屏蔽门的地铁车站列车火灾进行了数值模拟。分析了火灾发生后的烟气流动规律及温度场和气流场的分布,并与实体燃烧试验的结果进行了对比。结果表明,如果方程模型选用恰当,边界条件设置合理,CFD模拟火灾的结果是能够令人满意的。     

CFD在地铁站台空调系统设计中的应用

以典型的北京地铁建国门站为研究对象,以Navier-Stokes方程为基础,引入了广泛应用的标准的k-ε湍流模型,建立用于求解典型地下铁道站台内流场的计算流体力学模型。采用计算流体力学场模拟软件ANSYS CFX为计算工具,建立典型地铁车站的物理与数学模型,以试验测试与大量参考文献综合计算的活塞风结果为计算边界条件,模拟计算城市地铁空调系统的气流场,得出地铁站台典型断面的温度场、速度场以及候车区关键位置的空气温度与速度分布规律。     

深圳地铁5号线环控系统的模拟辅助设计

以大浪站为研究对象,建立了地铁车站的物理和数学模型,根据设计条件确定模型的边界条件,分别对地铁车站正常工况和火灾工况的温度场和气流场进行了模拟分析.结果表明:正常工况下,站台层和展厅层的平均温度和气流速度满足设计要求;站厅火灾工况下,站台补风可不开启,站台火灾时,区间风机需开启.     

不同环境工况下密闭式冷却塔的数值模拟

基于CFD软件和逆流密闭式冷却塔相关理论,对气流运动采用标准k-ε湍流模型,填料区,雨区和盘管区采用离散相模型计算,对填料区的膜状流动用滴状流动近似模拟,并且通过控制水滴粒子速度来得到所需要的传质传热过程.基于该模型,对设计制冷量为10t/h的逆流式密闭冷却塔的气水流动与热质交换进行数值模拟.分析环境条件对冷却塔热力特性的影响.计算结果表明:基于CFD软件的冷却塔数值求解模型有很好的适用性,环境条件对逆流密闭式冷却塔的换热效果影响很大.     

屏蔽门开启模式对地铁火灾烟气流动的影响

采用Fluent软件,选择RNG k-ε模型对某地铁站站台端部火源强度为5 MW的不同火灾工况进行数值模拟,在站台原有的通风系统加上屏蔽门作为排烟口的通风模式下,分别分析了屏蔽门不同开启模式对烟气速度、温度、浓度的影响。研究结果表明,地铁站台着火6 min时,屏蔽门作为排烟口进行排烟可使站台层的楼梯口处温度小于452 K,气流流动速度大于1.5 m/s;屏蔽门的开启可以实现将站台层的烟气向隧道抽吸,扩大站台安全区域。     

逆流密闭式冷却塔热力特性数值模拟

基于CFD软件和逆流密闭式冷却塔相关理论,对气流运动采用标准k-ε湍流模型,填料区、雨区和盘管区采用离散相模型计算,对填料区的膜状流动用滴状流动近似模拟。基于该模型,对设计制冷量为10 t/h的逆流密闭式冷却塔的气水流动与热质交换进行数值模拟。模拟分析了淋水密度和环境条件对冷却塔热力特性的影响,并分析得到了使冷却塔性能达到最优的无量纲参数气水比的取值。数值模拟结果表明:淋水密度和环境条件对逆流密闭式冷却塔的换热效果影响很大。     

Sensitivity of the predicted convective heat transfer in a cooled room to the computational fluid dynamics simulation approach

Computational fluid dynamics (CFD) plays an increasingly important role in the design, analysis and optimization of engineering systems. However, CFD does not necessarily provide reliable results. The most crucial numerical solution error is caused by inadequate grid resolution, and the key modelling error sources in CFD in ventilated indoor environments are turbulence modelling and diffuser modelling. Many researchers already proposed guidelines, but they based their analyses on local variables. In response, underlying study intended to verify the impact of the CFD simulation approach on the convective heat flux, an integral quantity. The authors tested several grids, Reynolds averaged Navier–Stokes turbulence models and diffuser models for three convection regimes in a cooled room. The diffuser modelling had a much larger impact than the grid and the turbulence modelling, as long as the jet dominated the airflow. So, CFD users, who want to model forced/mixed convection airflow indoors, certainly need to pay attention to the diffuser modelling.     

CFD modelling of an industrial air diffuser—predicting velocity and temperature in the near zone

This article describes experimental and modelling results from CFD simulation of an air diffuser for industrial spaces. The main objective of this paper is to validate a manufacturer model of the diffuser. In the air diffuser, the low velocity part is placed on top of a multi-cone diffuser in order to increase airflow rates and maximize the cooling capacity of a single diffuser unit. This kind of configuration should ensure appropriate performance of industrial air diffusers, which is discussed briefly at the end of the article. The paper illustrates the importance of a simulation model jointly with the manufacturer's product model and the grid layout near the ventilation device to achieve accurate results. Parameters for diffuser modelling were adapted from literature and manufacturer's product data. Correct specification of diffuser geometry and numerical boundary conditions for CFD simulations are critical for prediction. The standard k–ε model was chosen to model turbulence because it represents the best-known model utilized and validated for air diffuser performance. CFD simulations were compared systematically with data from laboratory measurements; air velocity was measured by ultrasonic sensors. Results show that CFD simulation with a standard k–ε model accurately predicts non-isothermal airflow around the diffuser. Additionally, smoke tests revealed that the flow around the diffuser is not completely symmetrical as predicted by CFD. The cause of the observed asymmetry was not identified. This was the main reason why some simulation results deviate from the measured values.     

入口紊乱参数对室内空气分布的影响研究

文中采用计算机流体动力学（ＣＦＤ）的方法就风口入流参数对通风空调房间内空气流动和分布情况的影响作了数值研究,通过对条缝二维平面射流特性及其作为送风口的空调房间室内空气分布的数值计算结果与有关实验数据对比指出：在相当大的紊流入流参数范围内,最终的室内空气流动及平面射流特性的计算结果变化不大,藉此可以指导对室内空气流动进行数值模拟时的边界条件描述。     

Feasibility of utilizing numerical viscosity from coarse grid CFD for fast turbulence modeling of indoor environments

Computational fluid dynamics (CFD) is a useful tool in building indoor environment study. However, the notorious computational effort of CFD is a significant drawback that restricts its applications in many areas and stages. Factors such as grid resolution and turbulence modeling are the main reasons that lead to large computing cost of this method. This study investigates the feasibility of utilizing inherent numerical viscosity induced by coarse CFD grid, coupled with simplest turbulence model, to greatly reduce the computational cost while maintaining reasonable modeling accuracy of CFD. Numerical viscosity introduced from space discretization in a carefully specified coarse grid resolution may have similar magnitude as turbulence viscosity for typical indoor airflows. This presents potentials of substituting sophisticated turbulence models with inherent numerical viscosity models from coarse grid CFD that are often used in fast CFD analysis. Case studies were conducted to validate the analytical findings, by comparing the coarse grid CFD predictions with the grid-independent CFD solutions as well as experimental data obtained from literature. The study shows that a uniform coarse grid can be applied, along with a constant turbulence viscosity model, to reasonably predict general airflow patterns in typical indoor environments. Although such predictions may not be as precise as fine-grid CFDs with well validated complex turbulence models, the accuracy is acceptable for indoor environment study, especially at an early stage of a project. The computing speed is about 100 times faster than a fine-grid CFD, which makes it possible to simulate a complicated 3-dimensional building in real-time (or near real-time) with personal computer.     

某高层建筑空调室外机的气流模拟及优化

运用CFD数值模拟方法和Airpak计算软件对建筑空调室外机进行气流模拟,根据其速度场、温度场、压力场的模拟结果,发现不同的出风方式以及风口形状对气流有较大影响。另外,通过对有室外风影响的情况的模拟,结果表明室外风速对气流有一定的影响,但是影响并不十分显著。经过对原方案的改进,满足了室外机的工作条件,基本达到了所需的要求。     

CFD simulations of gas dispersion around high-rise building in non-isothermal boundary layer

Urban heat island phenomena and air pollution become serious problems in weak wind regions such as behind buildings and within street canyons, where buoyancy effect cannot be neglected. In order to apply CFD techniques for estimation of ventilation and thermal and pollutant dispersion in urban areas, it is important to assess the performance of turbulence models adopted to simulate these phenomena. As the first step of this study, we carried out wind tunnel experiments and CFD simulations of gas and thermal dispersion behind a high-rise building in an unstable non-isothermal turbulent flow. The standard k-ε model and a two-equation heat-transfer model as RANS models, and LES, were used for the CFD simulation. One of the important purposes of this study was to clarify the effect of inflow turbulence (both velocity and temperature) on flow field and gas/thermal dispersion for the LES calculation. Thus, LES calculations with/without inflow turbulence were conducted. The inflow turbulence was generated through a separate precursor simulation. The calculated results showed that both RANS models overestimated the size of the recirculation region behind the building and underestimated the lateral dispersion of the gas. Turbulent flow structures of LES with and without inflow turbulence were completely different. The LES result with inflow turbulence achieved better agreement with the experiment.     

The effect of ceiling configurations on indoor air motion and ventilation flow rates

The purpose of this paper is to evaluate the effects of a building parameter, namely ceiling configuration, on indoor natural ventilation. The computational fluid dynamics (CFD) code Phoenics was used with the RNG k–? turbulence model to study wind motion and ventilation flow rates inside the building. All the CFD boundary conditions were described. The simulation results were first validated by wind tunnel experiment results in detail, and then used to compare rooms with various ceiling configurations in different cases. The simulation results generated matched the experimental results confirming the accuracy of the RNG k–? turbulence model to successfully predict indoor wind motion for this study. Our main results reveal that ceiling configurations have certain effects on indoor airflow and ventilation flow rates although these effects are fairly minor.     

山地风场特性及其对输电线路风偏响应的影响

山地风场的复杂性和显著的三维特性是困扰山区输电线路抗风设计的关键问题。该研究采用CFD数值模拟与风洞试验相结合的方法研究典型单山脉地形和双山脉峡谷型地形的三维平均风场和脉动风场特征。由于风洞试验测点数及试验风速的限制，输电线路沿线各点的三维平均风场基于CFD数值模拟得到。由风洞试验获取山脉地形的湍流度、湍流积分尺度、沿线路方向的衰减系数等脉动风场参数，在此基础上采用POD法重构生成输电线路沿线各点的三维脉动风速时程，并分析比较跨越峡谷、山脊的输电线路沿线风场特征。建立连续三跨输电线路有限元模型，采用时域法研究山地风场特性对输电线路风偏响应的影响。研究结果表明：山顶、峡谷处风速显著增大，且气流爬坡将导致局部位置产生上升气流；由于近地风场加速效应的影响，沿山脊布置的输电线路全档风偏响应增幅较大，跨峡谷输电线路其爬坡段风偏响应增幅较大；上升气流主要使导线竖向风偏位移增大；山地地貌下考虑脉动风速的影响，绝缘子串风偏角风振系数宜取1.2~1.3。该研究为完善山区输电线路的抗风偏设计提供借鉴。