A consistent steady state CFD simulation method for stratified atmospheric boundary layer flows
An effective methodology for CFD simulations of stratified atmospheric boundary layer flows is presented, based on the Poiseuille-type zero pressure gradient boundary layer. The concept of precursor inflow generation is applied in the scope of Reynolds Averaging Navier-Stokes (RANS) simulations, and combined with mean temperature control via explicit global heat correction in the energy equation. We thus obtain solutions that are fully consistent with the equation system in a one-dimensional computational domain, which then serve as inlet profiles for the three-dimensional calculation. The resulting inflow profiles are furthermore utilized for turbulence model validation and the calibration of the modeling parameters. This yields an extension of the standard k-e turbulence model, incorporating buoyancy induced turbulence production and dissipation terms. Additionally, modified turbulent wall functions are applied, which consistently model wall roughness and heat transfer, in agreement with the similarity law. We demonstrate that the obtained turbulence model reproduces the expected analytical profiles from the Monin-Obukhov similarity theory, and also that the representation of turbulent kinetic energy shows a realistic evolution over a wide range of stratification parameters. The presented method is then applied to study flow over inhomogeneous surfaces, among others a cosine shaped hill and ridge, where lee wave patterns are observed in the expected range of Obukhov lengths. The final validation demonstrates quantitatively good agreement of the simulation results at a complex on-shore site in Germany with data from a 200 m met mast.