Simulations of Flow over Idealized Urban Street Canyons

Urban modeling can roughly be divided into two categories. In the first, urban effects in mesoscale models are incorporated in terms of parameterizations. In the second, CFD models are used to resolve the flow field at building and street scales. An assumption of neutral atmospheric stability is usually made in the CFD models, which may not hold true for every scenario. In this study, a standard equation set governing the atmospheric flows is used to simulate flows around idealized street canyons. The effect of atmospheric stability on the development of flow is described. A higher-order Godunov-type scheme is developed and applied on unstructured triangular meshes to discretize the Navier-Stokes equations and Smagorinsky-Lilly method is implemented for prameterization of eddy diffusivities. The primary benefit of the unstructured grid technique over a conventional structured grid lies in its ability to discretize complex topologies with relative ease. Meshes for arbitrary surfaces and volumes in three dimensions can be generated. This capability is essential for resolving urban features, such as buildings. The results of this study will be presented during the symposium.