A modified k-ω turbulence model for improved predictions of neutral atmospheric boundary layer flows

Abstract

A modified k-ω turbulence model is developed for neutral atmospheric boundary layer flows by introducing additional source terms to the equations of the standard model to remove its inconsistency with the inlet conditions. Rough wall functions based on aerodynamic roughness are adopted to overcome the limitations of the standard wall functions that are based on sand grain roughness. Moreover, the diagnostic and prognostic approaches are considered when simulating the flow. The diagnostic approach is approximate, relying on satisfying mass conservation by solving an optimization problem, whereas the prognostic approach resolves the Navier-Stokes equations with a turbulence model. The performances of the developed modified k-ω model, an existing modified k-ε model, and the standard SST k-ω model are compared. To calculate the concentration field, the Eulerian approach which solves a concentration transport equation, and the Lagrangian approach which adopts the particle method with core radius spreading for computing diffusion are used. Results generated with the diagnostic approach demonstrate its unsuitability to calculate wind flows over complex geometries. On the other hand, the prognostic approach, with the three mentioned turbulence models, was successful in reproducing the flow data of CEDVAL A1 and B1 experiments in domains composed of one building and an array of buildings. In addition, a good agreement with the concentration measurements is obtained when using the newly modified k-ω and the SST k-ω models to account for turbulence, with the Eulerian method outperforming the Lagrangian dispersion approach.