CFD simulation of “pumping” flow mechanism of an urban building affected by an upstream building in high Reynolds flows

"Pumping" flow, which is essentially induced by the periodic vortex shedding, was observed when natural wind blows across a single building with two leeward openings. This oscillating flow has been proposed for use to improve wind ventilation of buildings with single-sided openings. Existing studies are limited to a single building block. In this study, effect of an upstream building on the "pumping" ventilation is investigated for various obstacle spacings, by Computational Fluid Dynamics (CFD) simulations. Simulation results show that vortex shedding frequencies could be affected by the non-dimensional obstacle spacing W/B (gap distance/building width), whereas non-dimensional ventilation rate of the downstream building shows a non-linear correlation with the obstacle spacing W/B. Particularly, when W/B continuously increases to 2.0, the ventilation rate reaches the level comparable to that of the isolated block case. Further results also demonstrate that the "pumping" ventilation rates are determined by a combination of mean and fluctuating pressure differences between the leeward openings. The spacing W/B = 2 is the optimal spacing for largest ventilation rate and therefore lowest building energy consumption by Heating, Ventilation and Air Conditioning (HVAC) systems. Our findings could benefit sustainable building design in dense cities.