Experimental and numerical studies of flows through and within high-rise building arrays and their link to ventilation strategy

Urban ventilation implies that wind from rural areas may supply relatively clean air into urban canopies and distribute rural air within them to help air exchange and pollutant dilution. This paper experimentally and numerically studied such flows through high-rise square building arrays as the approaching rural wind is parallel to the main streets. The street aspect ratio (building height/street width, H/W) is from 2 to 5.3 and the building area (or packing) density (λp) is 0.25 or 0.4. Wind speed is found to decrease quickly through high-rise building arrays. For neighbourhood-scale building arrays (1–2 km at full scale), the velocity may stop decreasing near leeward street entries due to vertical downward mixing induced by the wake. Strong shear layer exists near canopy roof levels producing three-dimensional (3D) vortexes in the secondary streets and considerable air exchanges across the boundaries with their surroundings. Building height variations may destroy or deviate 3D canyon vortexes and induced downward mean flow in front of taller buildings and upward flow behind taller buildings. With a power-law approaching wind profile, taller building arrays capture more rural air and experience a stronger wind within the urban canopy if the total street length is effectively limited. Wider streets (or smaller λp), and suitable arrangements of building height variations may be good choices to improve the ventilation in high-rise urban areas.