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Analysis of the unsteady boundary-layer flow over urban-like canopy using large eddy simulation

Abstract : The rapid development of urbanization raises social and environmental challenges related to air pollution and urban climate. Understanding the physical processes of momentum, heat, and mass exchanges between the urban canopy and the atmospheric boundary-layer is a key to assess,predict and prevent negative impacts of urbanization. The turbulent processes occurring in the urban boundary-layer are investigated using computational fluid dynamics (CFD). The unsteady flow over an urban-like canopy modelled by a staggered arrangement of cubes is simulated using large eddy simulation (LES). Considering the highspatial and temporal in homogeneity of the flow, a dynamic Smagorinsky subgrid-scale model is implemented in the code to allow energyback scatter from small to large scales. The Reynolds number based on the domain height and free-stream velocity is 50000. The near-wall viscous sub-layers are resolved and the grid is refined in the canopy resulting in about 28 million grid cells. LES results are assessed by comparison with literature and data recently acquired in the wind tunnel of the LHEEA. The turbulent kinetic energy budget in which all contributions are independently computed is investigated. These rarely available data are used to analyse the turbulent processes in the urban canopy. By taking advantage of the three-dimensionality of the simulated flow, the complex 3D time-averaged organization of the flow (recirculation, vorticesor singular points) is analyzed in relation with production of turbulence. Finally a drag approach where obstacles are replaced by an equivalent drag force is implemented in the same domain and results are compared to obstacle-resolved data.
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Submitted on : Thursday, April 11, 2019 - 4:51:08 PM
Last modification on : Tuesday, January 28, 2020 - 3:35:38 AM

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  • HAL Id : tel-02096983, version 1

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Geng Tian. Analysis of the unsteady boundary-layer flow over urban-like canopy using large eddy simulation. Fluids mechanics [physics.class-ph]. École centrale de Nantes, 2018. English. ⟨NNT : 2018ECDN0062⟩. ⟨tel-02096983⟩

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