CFD Large Eddy Simulation을 이용한 실제 도시 스케일의 유동 및 확산 특성에 대한 연구

Turbulent flow and dispersion characteristics over a real urban street canyon are investigated by large-eddy simulation model. Two kinds of sub-grid scale (SGS) model, which are the constant coefficient Smagorinsky model and Vreman model, are assessed to evaluate SGS model performance. Turbulent statistics, particularly turbulent stresses, and wake patterns are compared between the two SGS models for three different wind directions. We found that while the role of the SGS model is small in average sense, local or instantaneous contribution to total stress near the surface or edge of the buildings is not negligible. Yielding smaller eddy viscosity near the walls than the Smagorinsky model, the Vreman model appears to be more appropriate for the simulation of a flow in a complex urban street canyon. In the following investigation of a flow field over a real urban street canyon, we found that depending on wind direction relative to the street canyon, wind fields, turbulence statistics, and dispersion patterns show very different characteristics. Particularly, tall buildings near the street canyon predominantly generate turbulence, leading to homogenization of the mean flow inside the street canyon. Furthermore, the release position of pollutants sensitively determines subsequent dispersion characteristics.