Implementation of Rooftop Recirculation Parameterization into the QUIC Fast Response Urban Wind Model

The QUIC (Quick Urban & Industrial Complex) dispersion modeling system has been developed to provide high-resolution wind and concentration fields in cities. The fast response 3D urban wind model QUIC-URB explicitly solves for the flow field around buildings using a suite of empirical parameterizations and mass conservation. The current model does not capture the rooftop recirculation region associated with flow separation from the leading edge of the building. In this work, a model for rooftop recirculation is implemented using parameters for the length, height and strength of velocities for the recirculation region, which are a function of the aspect ratio of the building. An ellipsoidal region formed by the length and height parameters which are derived from Wilson (1979), represent the rooftop recirculation region. A logarithmic profile with modifications in the first half of the total height of the recirculation region is implemented as an initial wind field in the ellipsoidal region. After mass consistency is applied, this parameterization models the rooftop velocities quite well. In addition, the capacity to incorporate the effects of varying incident wind angles on rooftop flow has been added. In off angle flows, a “delta wing” type vortex forms on the rooftop with a core that is not perpendicular to the incident wind angle. This vortex is specified using a parameterization based on an empirical model by Banks et. al (2000). The length and height of the vortex along the corresponding building edges are calculated from the angle formed by the vortex core and the leading edge of the building. This vortex is extended beyond the downwind building face where it is forced to diffuse into the wake region. The modified model is an improved version of the previous model as it accounts for an improved modeling of flow in the near rooftop region. The modified model when evaluated with the experimental data for various building geometry cases and the incident wind perpendicular to the building face, matches the experimental data quite well.