Numerical Simulation of Turbulent Diffusion in Cities

Examples of numerical simulations on turbulent diffusion fields in cities are presented including comparison with wind tunnel experiments. The first example is the computation of the flow and diffusion fields around a cooling tower by k-e turbulence model. A composite grid technique, which connects two grids supported by a fortified solution algorithm, is adopted in this computation. The second example is the computations of flow over a heated urban area by Large Eddy Simulation (LES) and k—e model. In the k-e model computations, two different modellings for buoyancy effect are adopted; first is the model proposed by Rodi (1984), and second is the one proposed by Viollet (1987). The last example is the LES computations of turbulent diffusion of buoyant (lighter-than-air) and heavy gases discharged in the wake region behind a building model. Results given from two types of Smagorinsky models, i.e., the standard one and its modified version proposed by Mason et al. (1989, 1990), are compared here. In the concluding remarks, the relative abilities of various turbulence models are discussed.