Study on micro-atmospheric environment by coupling large eddy simulation with mesoscale model

This paper investigates wind field and traffic pollutant dispersion at street level in a local urban area. A coupling method is employed that the time-varying boundary values of velocity and temperature at the local urban area are provided by the Weather Research and Forecasting (WRF) mesoscale model which computes the atmospheric flow over the entire city while the atmospheric environmental flows are computed by a large eddy simulation (LES) code developed by the authors in the local urban area. In order to reduce the LES computation cost, a combined model for buildings in the urban area is proposed that in a central area, where the wind and pollution is most concerned, the buildings are properly resolved in fine grids and non-slip flow condition is prescribed at rigid boundaries whereas in the surrounding region the buildings are treated as drag element and coarse grids are used in computation. The wind field, temperature and carbon monoxide concentration fields are computed from 9 a.m. of October 26, 2009 to 8 a.m. of the next day in a built-up district of Beijing and the results show good agreement with observations. The advantage of proposed approach is that the multi-scale effect of atmospheric motion is considered and temporal evolution of flow structure in local urban area can be simulated by large eddy simulation at moderate computation cost. (C) 2012 Elsevier Ltd. All rights reserved.