Numerical investigation of the flow field around low rise buildings due to a downburst event using large eddy simulation

The transient lift and drag coefficients around a low rise cube of dimension 60mm and a portal building of dimensions 240x130x53mm with eaves height of 42mm, which arise from the numerical simulation of an impinging jet or downburst are investigated. The numerical results were validated against a experimental results from a laboratory impinging jet simulator operating at the same scale. Having found the CFD simulation to match well with the laboratory scale the CFD was then used to visualise and interpret the flow field around the buildings. Common transient atmospheric boundary layer flow features, such as conical vortices, vortices on the rear face of a building, flow separation and vortex shedding were observed and could be used to explain the lift and drag results obtained. In particular, motion of the primary vortex from the downburst and its effect on the transient pressures on the building were identified, with strong pressure gradients observed for a number of configurations. Aspects of the flow phenomena were identified, which along with the strong pressure changes on the building surfaces, indicate areas of further research due to their potential impact on building and cladding design