Numerical study of stable stratification effects on the wind over simplified tall building models using large-eddy simulations

Abstract

Atmospheric stratification is a critical factor affecting wind around buildings. However, very few studies have dealt with the atmosphere under stable stratification. In addition, the building model is typically simplified as a cubic block in previous studies concerning stable stratifications; however, the building aspect ratio (height/width) in the downtown area is often larger than 1. Furthermore, the spatial correlation of the velocities in tall buildings, which is important in determining the length scale of the flow and in evaluating pollutant dispersion, has seldom been studied. Therefore, in the present study, the flow around a simplified tall building and the flow around two groups of buildings with the plan area densities of 12.5% and 25.0%, were investigated under stable stratifications with stratified numbers K equaling to 0, 1, 2, and 3, using large eddy simulations (LES). The aspect ratio of the building models is 2. It was found that, for a single building model, the average wind acceleration above the building is directly proportional to K. Regarding the fluctuating wind velocity, the stratification effect has a weak impact. For building groups, the impact region of stratified flow usually appears when z/H < 1.2. A higher building density reduces the streamwise fluctuating wind velocity and the streamwise velocity spatial correlation.