LAUSR

Abstract Although the study of flow around buildings has a rich background, the development of construction material, the congestion of buildings, the urban ventilation and consideration of pedestrian wind condition make the necessity of further insightful flow-physic studies. This study numerically investigates the gap and wake flows associated with two inline non-identical-height (aspect ratios of 4 and 7 for the up- and downstream) buildings at a Reynolds number of 2.2 × 104 and gap spacing (G*) of 1, 3, and 5 through the large eddy simulation technique. It is found that an increase of G* mostly affects the flow pattern in the gap, so that the slender-body, alternate reattachment and semi-stable gap flow at the G* of 1 (or 3) turns into the co-shedding flow at the G* of 5. The pressure coefficients ( C ¯ p ) on the cylinders' faces show that an increase of G* from 1 to 3 increases/decreases the C ¯ p on the side (and top) faces of upstream/downstream cylinders, respectively. Further increasing G* from 3 to 5, however, drops the C ¯ p on the side and top faces of both cylinders. On the other hand, the flow regime produces a profound effect on the pedestrian level so that the strong wind condition appears in the small gap, and a very weak wind condition in the vortex cores. Hence a minimum gap of 3 is recommended for better pedestrian level wind conditions. Besides, increasing gap from 1 to 5 reduces the shielding effect of the interfering building markedly.