Abstract Quantification of the dispersion rate and extent of gaseous substances leaked into the atmosphere is important for public safety and risk management as industrial facilities are being situated ever closer to populated areas. The complex interaction between atmospheric conditions and built environments makes urban dispersion prediction challenging in nature. Computational fluid dynamics (CFD) has emerged as a credible tool for urban dispersion analysis over the past two decades as it provides greater detail and accuracy than traditional methods, albeit usually at greater cost in terms of time, computing power and expertise. This paper describes a multigrid acceleration method for three-dimensional CFD that ensures robustness when resolving the interaction between the atmospheric boundary layer and complex urban environments, including terrain, buildings and obstacles. The solver is segregated, pressure-based and is uniquely applied to structured grids with Cartesian anisotropic mesh refinement and an immersed boundary method (IBM). This work describes novel adaption of a geometric multigrid method (MGM) to an immersed boundary representation of the urban environment features of real cities. The innovative multigrid treatment selectively uses the immersed boundaries at coarse multigrid levels with the advantage of enhancing computational stability while maintaining efficient convergence rates. The novel CFD techniques are demonstrated at three flow scales (laboratory, model-urban and real-world scale), and comparisons of velocity, turbulence levels and gas concentrations are made to published numerical and experimental measurements. The unique combination of MGM, IBM and adaptive mesh refinement (AMR) has not previously been documented and shows a speed-up factor of seven in convergence, relative to single grid, at the laboratory scale. At the urban scale, the combination of numerical methods makes city-scale Reynolds-Averaged Navier-Stokes (RANS) turbulence CFD solutions possible in hours on a workstation computer and is shown to match experimental concentration measurements within acceptable statistical limits.

中文翻译：

---

用于模拟复杂城市环境中大气扩散的浸入边界的几何多重网格处理

摘要 随着工业设施越来越靠近人口稠密地区，量化泄漏到大气中的气态物质的扩散率和范围对于公共安全和风险管理非常重要。大气条件和建筑环境之间复杂的相互作用使得城市扩散预测在本质上具有挑战性。在过去的二十年中，计算流体动力学 (CFD) 已成为城市分散分析的可靠工具，因为它比传统方法提供了更多的细节和准确性，尽管通常在时间、计算能力和专业知识方面的成本更高。本文介绍了一种用于三维 CFD 的多重网格加速方法，该方法可确保在解决大气边界层与复杂城市环境之间的相互作用时具有鲁棒性，包括地形、建筑物和障碍物。该求解器是隔离的、基于压力的，并且独特地应用于具有笛卡尔各向异性网格细化和浸入边界方法 (IBM) 的结构化网格。这项工作描述了几何多重网格方法 (MGM) 对真实城市城市环境特征的浸入式边界表示的新适应。创新的多重网格处理有选择地使用粗多重网格级别的浸入边界，其优点是提高计算稳定性，同时保持有效的收敛速度。新的 CFD 技术在三个流量尺度（实验室、模型城市和现实世界尺度）上进行了演示，并将速度、湍流水平和气体浓度与已发表的数值和实验测量值进行了比较。米高梅的独特组合，IBM 和自适应网格细化 (AMR) 以前没有被记录过，并且在实验室规模上显示，相对于单个网格，收敛速度提高了 7 倍。在城市尺度上，数值方法的组合使得城市尺度雷诺平均纳维-斯托克斯 (RANS) 湍流 CFD 解决方案在数小时内在工作站计算机上成为可能，并显示在可接受的统计范围内与实验浓度测量相匹配。