Modelling and simulations of turbulent flows in urban areas with vegetation

A comparative assessment of the Reynolds-Averaged Navier–Stokes (RANS) two-equation k − ɛ model, with different proposals for a proper treatment of the vegetation (trees) effects in urban areas, is reported here. The most common variants proposed in the literature based on a two-equation k − ɛ eddy viscosity model are revisited. An extensive model validation is performed on generic cases with homogeneous and non-homogeneous vegetation and compared with available experimental data. It is shown that the minimal level of the proper modeling of the non-homogeneous (i.e. with the vertically variable leaf area density) vegetation requires a model with additional four terms in the equations for the turbulence kinetic energy and its dissipation rate. The proposed version of the model is then applied to a computational study of flow over the Delft University of Technology site with different scenarios of the vegetation islands. By performing series of simulations, some practical guidelines are suggested to reduce intensity of the side-wind gust within the campus. In conclusion, it is demonstrated that the adopted turbulence model for non-homogeneous vegetation, in combination with the passive element approach for buildings, proved to be a physically accurate and numerically robust method. The model is recommended for future use in simulating turbulent flows in complex urban areas with vegetation.