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A comparison of three two-equation turbulence models namely the standard k-ε model, Renormalized Group Theory (RNG) k-ε model and the k-ω model of Wilcox for flow over three different types of topographies have been presented in this paper. The present work is also an attempt to propose best practices for simulating atmospheric boundary layer (ABL) flows over complex terrain. Numerical investigations are performed for three different topographies: (i) cosine Hill (ii) Bolund Hill and (iii) Askervein Hill. The commercial CFD solver PHOENICS and the wind farm design tool WindSim V-5.1.0 are used for solving the Reynolds Averaged Navier Stokes (RANS) equations with the turbulence closure. The profiles of velocity and turbulent kinetic energy obtained using the various turbulence models are compared with available experimental data. The numerical results clearly show the superiority of the k-ω model of Wilcox over the standard k-ε model and the RNG k-ε model for ABL flows. Though the velocity profiles obtained using all three models are alike there exists a significant variation in the turbulent kinetic energy profiles for the cases considered in this investigation. The models perform very well when the terrain orography is quite complex, except for the predictions on the leeward side of the Hill where the elliptic effects are more pronounced.

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