Novel subgrid-scale modelling for large-eddy simulation of turbulent flow and dispersion in urban environments

由于意外或故意将有害物质释放到城市环境中，污染物下风扩散到大气中的环境和毒理学影响近年来已成为一个日益重要的问题。与这一重要问题相关的主要挑战包括对城市环境中动态发展的流动结构与复杂建筑几何结构的相互作用，以及动量、热能和被动标量传输过程的耦合有更深入的了解。与基于Reynolds平均Navier-Stokes （RANS）方法的传统方法相比，本研究旨在开发新的动态线性和非线性亚网格尺度（SGS）应力和标量通量模型，用于高性能的城市流和分散大涡模拟（LES）。为了达到本研究的目的，本提案分为两部分。第一部分着重于LES方法的基本方面，用于预测主动和被动标量的湍流输运；第2部分侧重于第1部分中开发的先进SGS建模方法的应用，以改进复杂城市环境中有害物质湍流运输的LES。为了验证本研究中开发的新颖LES方法，将获得的数值结果与实验和直接数值模拟（DNS）数据进行比较。预计本研究将对现有的和提出的SGS应力和标量通量模型进行系统的比较研究；提出了基于LES的城市流动和分散的高性能计算方法；并导致对亚网格尺度运动及其与城市树冠内部和上方连贯流动结构的相互作用有更深的物理理解。还预期拟议的研究将提供一个机会，在与机械和环境工程、先进科学计算和国防科学和技术有关的领域训练高度合格的人员。

The environmental and toxicological impact of the downwind dispersion of contaminants released into the atmosphere, resulting from an accidental or deliberate release of a hazardous material into an urban environment, has become an increasingly important problem in recent years. The major challenge associated with this important problem involves obtaining a deeper understanding of the interaction of the dynamically evolving flow structures with the complex building geometry in an urban environment, as well as the coupling of the momentum, thermal energy and passive scalar transport processes. In contrast to conventional methods based on the Reynolds averaged Navier-Stokes (RANS) approach, the proposed research aims at developing novel dynamic linear and nonlinear subgrid-scale (SGS) stress and scalar-flux models for high-performance large-eddy simulation (LES) of urban flow and dispersion. In order to achieve the goal of this research, this proposal is divided into two parts. Part 1 focuses on the fundamental aspects of the LES methodology for prediction of turbulent transport of active and passive scalars; and Part 2 focuses on application of the advanced SGS modelling approaches developed in Part 1 for improved LES of turbulent transport of hazardous substances in complex urban environments. In order to validate the novel LES approaches developed in this research, the obtained numerical results will be compared with experimental and direct numerical simulation (DNS) data. It is anticipated that the proposed research will provide a systematic comparative study of the existing and proposed SGS stress and scalar-flux models; advance the methodology of LES for high-performance computing of urban flow and dispersion; and lead to a deeper physical understanding of the subgrid-scale motions and their interactions with the coherent flow structures within and above the urban canopy. It is also anticipated that the proposed research will provide an opportunity to train highly qualified personnel in areas related to mechanical and environmental engineering, advanced scientific computing, and defence science and technology.