Appropriate boundary conditions for computational wind engineering models revisited

At the first Computational Wind Engineering conference in 1992 “Appropriate boundary conditions for computational wind engineering models using the k–ε turbulence model” were proposed. In this paper it is shown that these conditions can be directly derived by treating the onset flow as a horizontally homogeneous turbulent surface layer, with the flow being driven by a shear stress at the top boundary. This approach is extended to provide the inlet profiles and boundary conditions appropriate for modelling the flow using the standard k–ε, RNG k–ε, Wilcox k–ω and LRR QI turbulence models. Means for their application within the commercial CFD code CFX 12.0 are given. It is shown that within the flow the various turbulence model constants set the effective value of von Kármán's constant, which does vary slightly between models. The discrepancy between the turbulence level set by the standard turbulence model constants and that observed in the atmosphere is discussed. Problems with excessive turbulence generation near the ground and the over-prediction of stagnation pressures are discussed and possible solutions proposed.