Impacts of uneven surface heating of an ideal street canyon on airflows and indoor ventilation:Numerical study using OpenFOAM coupled with EnergyPlus

In the daytime,building facades and ground surfaces are heated by solar radiation,and the resulting buoyancy can change the flow field inside street canyons.In this study,the impacts of uneven and time-varying heating of surfaces inside an ideal urban street canyon(aspect ratio=1)on single-sided indoor natural ventilation are analyzed.This work introduces a methodology for a numerical approach based on the coupling between a computational fluid dynamics(CFD)model and an energy balance model.First,EnergyPlus is employed to calculate the time-varying and uneven surface heating.Simulations are performed at four typical study times(05:00,09:00,15:00,20:00)during a hot summer day(July 15)in Wuhan,China.Second,the surface temperature results are transferred to OpenFOAM for CFD simulation.Two inlet wind velocities(U_(ref))are investigated.The results show that for a relatively strong ambient wind(U_(ref)=3 m/s),the buoyancy caused by surface heating does not significantly change the airflow structures and indoor ventilation compared with those in the isothermal case.However,for a weak ambient wind(U_(ref)=0.5 m/s),the airflow structures inside the street canyon vary with the time of day.Moreover,the average air exchange rate(ACH)differs by-25.0% to 15.9%compared with that in the isothermal case,and the ACH of a single room increases by up to 2710%.The results indicate that the surface-heating-induced buoyancy is nonnegligible and should be carefully investigated,especially for weak ambient winds.