2024
Wang, J., and You, R.* 2024. Evaluating different categories of turbulence models for calculating air pollutant dispersion in street canyons with generic and real urban layouts. Journal of Wind Engineering & Industrial Aerodynamics, 255: 105948.
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Abstract: Turbulence models are crucial for simulating urban pollutant dispersion by computational fluid dynamics (CFD) methods. This study aimed to evaluate the performance of steady-state and unsteady-state Reynolds-averaged Navier-Stokes simulation (SRANS/URANS) and large-eddy simulation (LES) in calculating air pollutant dispersion in street canyons with generic and real urban layouts. For each layout, wind tunnel experiments with measured wind speed and pollutant concentration were available as benchmarks. In addition, instantaneous concentration fields were analyzed to assess the transient models. The results showed that in both generic and real urban layouts, the RNG model and SST model provided similar results for time-averaged wind speed and concentration distributions in SRANS and URANS simulations. LES performed the best in calculating wind speed and pollutant dispersion. In a generic urban layout, URANS with the SST model captured large-scale fluctuations, while instantaneous results from URANS with the SST model did not change over time in a real urban layout. SRANS/URANS with the SST model can provide acceptable results for time-averaged pollutant concentration fields in a generic urban layout with simple building shapes and placements. However, for real urban layouts, the LES approach is the most accurate way to calculate air pollutant dispersion.
2023
Wang, J., Wang L., and You, R.* 2023. Evaluating a combined WRF and CityFFD method for calculating urban wind distributions. Building and Environment, 234: 110205.
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Abstract: Inflow boundary conditions are critical for simulating urban wind fields by CFD methods, and wind profiles within the atmospheric boundary layer are significantly affected by local atmosphere circulation and diurnal variation. The Weather Research and Forecasting (WRF) model is a powerful mesoscale weather prediction model that can be used to provide more realistic inflow boundary conditions. To investigate the potential of a combined WRF and CityFFD method (WRF-CityFFD), this study first validated the WRF and CityFFD models and then used the validated models in WRF-CityFFD to calculate the wind distribution in the Kowloon district of Hong Kong within an area of 3.5 km × 2.4 km. The wind speed data at two weather stations were used as a benchmark, and CityFFD with inflow boundary conditions from a semi-empirical method (semi-empirical-CityFFD) was also investigated for comparison. The WRF-CityFFD performed better than the semi-empirical-CityFFD in calculating wind velocities in urban microclimates. The power-law exponent for wind profiles should be carefully defined when conducting CFD simulations for complex urban layouts. Coastal areas with onshore wind conditions were more suitable for selection as inflow boundary conditions for WRF-CityFFD.
