Large-eddy simulations of air ventilation in parametric scenarios: comparative studies of urban form and wind direction

Abstract

ABSTRACTThis study evaluates effects of building form and wind direction on urban ventilation using a large-eddy simulation (LES) model. Numerical simulations of air flow in 80 sets of parametric scenarios are conducted and the results are cross-compared. Main findings and potential recommendations for urban planning are: First, high mean building height is generally not good for ventilation, as vertical momentum is prevented from penetrating inside the street canyon. Second, inhomogeneous building heights tend to decrease the variance of site-averaged velocity ratios compared to homogeneous scenarios. Horizontal ventilation is moderated by the vertical momentum generated by inhomogeneous building heights. Third, rectangular (1:2 horizontal size) building arrays may allow better ventilation than square (1:1 horizontal size) building arrays. Moreover, given a moderate ground coverage ratio in square building arrays, 45° wind input allows better ventilation than 0° wind input. Finally, in cases of square arrays, higher ground coverage ratios result in lower site-averaged velocity ratios. But in the case of rectangular arrays, this negative relationship may be reversed.