Detailed Computational Modelling of Thermal and Wind Environment in an Urban Area

Urban microclimate is the local climate found in the lower atmosphere of urban areas. It is influenced by building geometry, vegetation and human activities. Urban microclimate alters the wind and thermal environment of urban areas affecting thermal comfort and energy demand of buildings. This study uses a coupled multi-physics solver in OpenFOAM to model wind and temperature fields over an 800m by 700m domain in the urban area of a midsized city. The domain is a real city block with building geometry, terrain and vegetation extracted from Geographic Information System (GIS) data. Buildings are treated as solid obstructions and trees as porous volumes. Computational Fluid Dynamics (CFD) simulations are performed using a custom transient solver which solves Reynolds-Averaged Navier Stokes (RANS) equations with the standard k-epsilon turbulence model. Time-varying wind conditions are defined at the domain boundaries using data obtained from weather stations. Appropriate boundary conditions for different surfaces (such as building walls, ground, and trees) are also included to capture the potential development of urban heat island effects. Preliminary results show that weather-dependent time-varying wind conditions at boundary and domain features such as buildings, trees and terrain influence wind patterns and surface heat distribution within the city block. Recirculation zones and velocity reduction are observed near obstacles, while temperature changes across the domain suggest localized heating and cooling effects. The use of a real city terrain and geometry and real weather-driven boundary conditions increase the model's ability to capture key flow and thermal features of the urban microclimate.