Equivalent wind incidence angle method: A new technique to integrate the effects of twisted wind flows to AVA

This paper presents a novel and cost-effective method to replicate modified pedestrian level wind (PLW) fields in twisted winds using a conventional wind profile with similar wind speeds and turbulent intensities. The novel method, namely the Equivalent Wind Incidence Angle (ϕEq) method was developed using data of PLW fields near five isolated buildings with aspect ratio (height:width) ranging from 4:1 to 0.5:1 subjected to two twisted wind profiles with the maximum clockwise yaw angles of 13° and 22°. The magnitude of ϕEq was found to be 6° and 14° for the two twisted wind profiles with maximum yaw angles of 13° and 22° and for any clockwise wind incidence angle ϕ, ϕEq is ϕ +6°, and ϕ +14°. The ϕEq method was applied for an Air Ventilation Assessment (AVA) done for an urban site in Hong Kong, and the outcomes were compared with two similar AVAs conducted using the two twisted wind profiles and a conventional wind profile without ϕEq. The comparison revealed that velocity ratios (VRs) and wind speeds with a 50% probability of exceedance are similar or slightly different from those in twisted winds if the conventional wind profile is combined with the ϕEq method.