Evaluating a combined WRF and CityFFD method for calculating urban wind distributions

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.