Evaluation of a mechanical drag coefficient formulation in the complex urban area of Beijing

The constant building drag coefficient was replaced by a mechanical drag coefficient formulation in a multilayer urban canopy system coupled with the Rapid-refresh Multiscale Analysis and Prediction System to improve the wind speed prediction performance in complex urban areas. Although this formulation has been assessed in idealized urban areas by computational fluid dynamic simulations, the applicability of this formulation has not been sufficiently evaluated, especially in complex urban areas with inhomogeneously distributed tall buildings. The main objective of this study is to evaluate the performance of the coupled system in the Beijing urban area. The results show that the average wind speed model performance is improved by 40% in summer and 36% in winter by introducing a drag coefficient into the regional forecast model.