A numerical study on flow in street canyons using a second-order turbulence closure model

Computational fluid dynamics (CFD) model has been widely used for the study of urban flow and pollutants dispersion. Air flow and pollutants dispersion in the street canyon in urban area was studied using mostly RANS (Reynolds-Averaged Navier-Stokes equations) models and LES (Large-Eddy Simulation) models. RANS model was used more popularly than LES model which requires more computation time. RANS models such as standard k-ε turbulence models and modified ones can be classified as one and half-order closure model. We have developed a two-dimensional 2nd-order turbulence closure model that can be effectively used for investigating the characteristics of air flow and turbulence in the urban street-canyon. This model is composed of equations for Reynolds stress and velocity variance as well as mean wind velocities. The patterns of air flow inside urban street-canyon depend on the geometric shape, especially the building aspect ratio, defined by the ratio of the building height to the width between two buildings. The second-order closure model is tested for various values of aspect ratio. The results are compared to those from k-ε model.