Impact of urban canopy characteristics on turbulence dynamics: Insights from large eddy simulation

Abstract

In this study, a series of large-eddy simulations are conducted to explore the dynamics of turbulence within the urban canopy. Two idealized urban-like geometries (staggered and aligned arrays of cubes) and one real urban region (located on the Southern University of Science and Technology campus in China) are simulated under neutral atmospheric conditions. The results show a significant difference in the dispersive momentum fluxes between OpenFOAM and PALM within the ultra-dense arrays. Furthermore, it is found that the spatial layout does not exert a significant effect on the budget of turbulent kinetic energy. Instead, it mainly depends on the ratio of the building surface area to the total surface area, i.e., packing density. In addition, a multi-scale coupled inflow boundary condition is introduced in this study to simulate the flow in a real urban area. This boundary condition yields a better match to the LiDAR measurements than the Weather Research and Forecasting model data. Finally, this study shows that the mean velocity obtained from the campus of SUSTech is in satisfactory agreement with the data from low-density idealized cube arrays and the corresponding urban canopy model. This observation suggests that mean wind speeds within partially occupied urban areas are relatively independent of wind direction, thus greatly improving the application of urban canopy models to such scenarios.