Impact of heterogeneous building arrangement on local turbulence escalation

Abstract

Turbulent wakes and the recirculatory flow induced by building arrays subjected to an atmospheric boundary layer flow were numerically studied to investigate the building arrangement impact on the urban air mobility (UAM) service. To mimic the atmospheric flow with realism, large-eddy simulation was employed along with an immersed boundary method to construct the presence of the building arrays. Four cases were studied which included an array of three high-rise buildings and three other combinations of high-rise and low-rise building arrays. Horseshoe vortex and recirculation flows were found in all building configurations whose intensity varied according to the upstream building height. In particular, the clockwise-rotating vortex was found to be dominant within the cavity between the buildings. In addition, the lateral vortex generated by the side walls of the nonuniform array tilted outward due to the secondary flow formed by the wake of the building, which additionally contributed to the downwash flow behind the building array. Elevated velocity fluctuations were found on top of and behind the high-rise buildings which persisted further downstream in parallel with the freestream flow. The largest velocity standard deviation was found to be 3.8 times that of the inflow which was due to the combination of flow recirculation and the wake from the further upstream building. Finally, the velocity spectra were analyzed to provide reference data for the deployment of vertiports and the UAM take-off and landing guidance.