On the use of the k –εε model in commercial CFD software to model the neutral atmospheric boundary layer

The k  –εε model is routinely used by wind engineers to computationally model the atmospheric boundary layer (ABL). Commercial software is typically used, with the default law of the wall used to model the rough ground surface. By setting appropriate profiles for wind velocity and the turbulence quantities at the inlet, it is often assumed that the boundary layer will be maintained up to the buildings or obstructions in the flow. This paper shows that this is not the case, even in the absence of obstructions, and that the velocity and turbulence profiles decay along the fetch under these default conditions.By revisiting previous work, it is shown that the neutral ABL can be maintained along a lengthy fetch but only with a modified law of the wall and with a shear stress applied to the top boundary of the domain. For those practitioners who are not able to adopt this more thorough approach, some measures are suggested to mitigate the decay of the boundary layer.