The impact of heat and inflow wind variations on vertical transport around a supertall building - The One Vanderbilt field experiment.

The impact skyscrapers have on wind flow remains poorly characterized, thus affecting atmospheric dispersion predictions in dense urban centers. A new mobile observatory equipped with remote sensors controlled by a smart sampling protocol was developed to collect high-resolution (18 m, 15 s) observations throughout the atmospheric layer below 1.5 km. A series of four deployments was performed around the One Vanderbilt skyscraper (H = 427 m) located in Manhattan, NY to document wind flow and temperature in canyons with relatively high width-to-depth ratios (H/W ~ 1.2-7.5; H being the height of the adjacent building) and steepness (H/H= 2.1-11.2) and that under a range of inflow wind and solar heating conditions. A series of flow features were common to all case studies with head-on winds. A stagnation point was observed 2/3 of the way up the impeded portion of the One Vanderbilt, pointing to the importance of the upwind building height in controlling vertical air flow. In the canyons parallel to the flow, three sets of mirroring counterrotating vortices were detected pointing to the fact that H is not as important a parameter in controlling flow in canyons parallel to the inflow wind. Plumes of rapidly rising air were detected near building heat vents under both 10 m s and 3 m s inflow wind conditions, at night and in the morning respectively. This suggests that anthropogenic heat may be an important energy source especially in the absence of solar heating. In the presence of solar heating, a systematic tendency for upward flow was observed above H. We associate this pattern to the presence of rising thermals, a common mechanism for planetary boundary layer growth. Below H, complete flow reversal (relative to mechanically driven circulations) was detected ~20 % of the time, showing evidence of dominant thermal effects even under 7 m s inflow wind conditions.