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

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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.