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

近年来，由于有害物质意外或故意释放到城市环境中而产生的污染物顺风向扩散进入大气的环境和毒物影响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涉及更深入地了解城市环境中动态演变的流动结构与复杂的建筑几何结构之间的相互作用，以及动量、热能和被动标量传输过程的耦合。与基于雷诺平均Navier-Stokes(RANS)方法的传统方法不同，该研究旨在开发新的动态线性和非线性亚格子尺度(SGS)应力和标量通量模型，用于高性能的城市流动和扩散的大涡模拟(LES)。为了达到本研究的目的，本建议分为两个部分。第1部分侧重于LES方法的基本方面，用于预测主动和被动标量的湍流输送；第2部分侧重于应用第1部分中开发的先进的SGS模拟方法，以改进复杂城市环境中危险物质的湍流输送的LES。为了验证本文提出的大涡模拟新方法的有效性，将得到的数值结果与实验数据和直接数值模拟数据进行了比较。预计拟议的研究将对现有和建议的SGS应力和标量通量模式进行系统的比较研究；推进LES用于高性能计算城市流量和弥散的方法；并导致对次网格尺度运动及其与城市冠层内外相干流动结构的相互作用的更深入的物理理解。预计拟议的研究将提供一个机会，在机械和环境工程、先进科学计算和国防科学和技术等领域培训高素质的人员。

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.