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CFD evaluation of natural ventilation of indoor environments by the concentration decay method: CO_2 gas dispersion from a semi-enclosed stadium

机译：通过浓度衰减法对室内环境自然通风的CFD评估：半封闭体育场的CO_2气体扩散

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Computational Fluid Dynamics (CFD) simulations can be used to assess indoor natural ventilation by solving the interaction between the urban wind flow and the indoor airflow. The air exchange rate (ACH) can be obtained from the simulated volume flow rates through the ventilation openings or by the concentration decay method that is often used in experimental studies. This paper presents 3D unsteady Reynolds-averaged Navier-Stokes (RANS) CFD simulations to reproduce the decay of CO_2 concentration in a large semi-enclosed stadium. The study focuses on the hours after a concert, when the indoor CO_2 concentration generated by the attendants has reached a maximum. The wind flow, indoor airflow and dispersion of heat, water vapour and CO_2 are modelled on a high-resolution grid based on a grid-sensitivity analysis. The simulations are validated with on-site measurements of wind velocity and CO_2 concentration decay. The validated CFD model is used to analyse the significant horizontal and vertical CO_2 concentration gradients in the stadium, showing local differences at f = 300 s up to 700 ppm (i.e. 37% of the maximum of 1900 ppm). A specific piecewise-linear technique is applied for the concentration decay method to determine the ACH values for smaller time-intervals. This is needed because the plotted semi-logarithmic decay curve itself is not linear because the ventilation rate changes over time, due to the changing buoyancy forces. It shows that the ACH values decrease from about 2 h~(-1) at the beginning of the concentration decay simulations to about 0.3 h~(-1) at the end.
机译：通过解决城市风与室内气流之间的相互作用，可将计算流体力学（CFD）模拟用于评估室内自然通风。空气交换率（ACH）可以从通过通风口的模拟体积流量或通过实验研究中经常使用的浓度衰减方法获得。本文提出了3D非稳态雷诺平均Navier-Stokes（RANS）CFD模拟，以再现大型半封闭体育场内CO_2浓度的衰减。该研究着重于音乐会结束后的几个小时，当服务员产生的室内CO_2浓度达到最大值时。基于网格敏感度分析，在高分辨率网格上对风流，室内空气流以及热量，水蒸气和CO_2的扩散进行建模。通过现场测量风速和CO_2浓度衰减来验证模拟。经过验证的CFD模型用于分析体育场内显着的水平和垂直CO_2浓度梯度，显示在700 ppm的f = 300 s处的局部差异（即最大1900 ppm的37％）。将特定的分段线性技术应用于浓度衰减方法，以确定较小时间间隔的ACH值。这是必需的，因为绘制的半对数衰减曲线本身不是线性的，因为通风率随浮力的变化而随时间变化。结果表明，ACH值从浓度衰减模拟开始时的约2 h〜（-1）下降到结束时的约0.3 h〜（-1）。

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