Computational fluid dynamics modeling used to assess mesoscale urban canopy drag and turbulence parameterizations

Since mesoscale numerical models do not have the spatial resolution to directly simulate the fluid dynamics and thermodynamics in and around urban structures, urban canopy parameterizations are sometimes used to approximate the drag, heating, radiation attenuation and enhanced turbulent kinetic energy (tke) produced by the sub-grid scale urban elements. In prior work, we have developed an urban canopy parameterization for mesoscale models in order to account for the area-average effects of buildings and urban materials on the flow field (Brown and Williams, 1998). However, the urban parameterizations are difficult to validate due to lack of area-averaged datasets. In this presentation, we test the assumptions associated with the urban canopy drag and turbulence production schemes. Our approach is to use a computational fluid dynamics (CFD) model to explicitly simulate the flow field around clusters of buildings. The gridded CFD model-computed data is then area-averaged and compared to the mesoscale model profiles of velocity and turbulent kinetic energy. Although the CFD model produces high resolution data that is essential for the area-average calculation, the model-produced data is, of course, not real. Hence, we will also compare the CFD model results to a few idealized wind-tunnel experiments of flow around buildings in order to have more confidence in the CFD model-produced area-average profiles.