Simulação do escoamento atmosférico sobre topografia urbana idealizada através do OpenFOAM.

Abstract

Given the complexity of the flow and turbulence structure over an urban surface, where flow and turbulence length scales and time scales can change dramatically from one obstacle configuration to the next, it seems reasonable to suggest that given increases in computational power enables affordable numerical simulations of these flows, providing valuable insights that could make the study of these flows easier and more effective. Large scale Computational Fluid Dynamics (CFD) models cannot represent in detail the atmospheric flow in a city or an urban environment. When the resolution in a computational mesh is bigger or equivalent than the scale characteristic of urban obstacles, these constitute sub grid disturbances. A manner to avoid this problem consists in the urban canopy parametrization in the flow through an inclusion of an additional drag in the large scale simulation. Such manner can be done increasing artificially the aerodynamic roughness length (z0) and displacing the ground level through a displacement height (d). This study simulates, through an open-source software OpenFOAM, the atmospheric boundary layer over a computational domain which consists of a square array of cubes representing an idealized urban topography, adopting the k-ω SST turbulence model in order to create a systematic. The pressure and viscous drag were quantified and then the urban drag coefficient (Cd) was defined. The values of d e z0 are calculated for the array of cubes and the results were validated with the parameterized simulation. The effects of a low Reynolds number are verified in the velocity profiles and in the drag coefficient, which were shown irrelevant. The results are obtained for a neutral atmospheric boundary layer and they are compared to bibliography data and wind tunnel experiments, obtaining a great validation with the calculated parameters. It also concludes that using a cyclic condition at the inlet and outlet the drag coefficient value tends to a minimum limit value.