Computational Simulation of Wind Microclimate in Complex Urban Models and Mitigation using Trees

Due to a rapid increase in urbanisation, accurate wind microclimate assessment is of crucial importance. Evaluating wind flows around buildings is
part of the planning applications in design of new developments. In this study, Computational Fluid Dynamics (CFD) simulations are carried out
for a case study, representing the east village in the London Olympic park. Following a validation test against an experimental data for a simpler urban configuration, the key input parameters including appropriate boundary conditions, mesh setting and type of turbulence model are selected for the Olympic park model. All the simulations are conducted by the commercial code, STAR-CCM+ under steady state condition with the Reynolds Average Navier-Stokes (RANS) method. The turbulence is modelled using different common variants of Eddy-Viscosity Models (EVM) including standard k-", realizable k-", standard and SST k-!. The results demonstrated that standard and realizable k-" models correlate very well with the experimental data, while some discrepancies were found with standard and SST k-!. Following the determination of areas of high velocity, appropriate tree planting is proposed to overcome the effect of corner and downwash acceleration. With the arrangement of trees and using specific type of trees (e.g. birch), the wind speed at the pedestrian level is reduced at different regions. With the optimized arrangement of trees and using specific type of trees (e.g. birch), the wind speed at pedestrian level are reduced by 3.5%, 25%, 66% in 3 main regions of interest . Moreover, we investigated the effects of tree heights. The obtained results illustrated that the wind velocity reduces when the crown of the trees are located closer to the buildings and the ground. Our high-resolution CFD simulation and results offer a quantitative tool for wind micro-climate assessment and optimized design and arrangement of trees around the buildings to improve pedestrian comfort.