Impact of inflow methods and aerodynamic roughness lengths on the streamwise homogeneity of flow profiles in LES of the neutral ABL

In Computational Fluid Dynamics (CFD) simulations of the atmospheric boundary layer (ABL) the relation between inflow conditions and wall boundary conditions has been thoroughly investigated for Reynolds-averaged Navier-Stokes (RANS) modeling, whereas it yet needs to be evaluated for Large Eddy Simulations (LES). In the present paper streamwise homogeneity of flow profiles for LES of the neutral ABL over surfaces with different aerodynamic roughness lengths in combination with three different inflow turbulence generation methods is investigated. Specifically, one precursor and two synthetic methods have been considered along with three aerodynamic roughness lengths. The results show that the precursor method satisfactorily preserves the homogeneity of both mean velocity and turbulence kinetic energy, with respective average deviations up to 0.7% and 3.5% from target profiles at the outlet of the domain. Among the synthetic methods, less accurate but also less computationally demanding than the precursor method, the Vortex Method greatly outperforms the Spectral Synthesizer in terms of both mean velocity and turbulence kinetic energy. Lastly, terrain roughness is found to have only a weak influence on the performance of the inflow methods considered.