Unsteady Reynolds-Averaged Navier-Stokes simulation of turbulent flow fields around a line of trees and a steep hill using a new turbulent inflow generation method

In this study, mean and turbulent flow fields around a line of trees and a steep hill are investigated by unsteady Reynolds-Averaged Navier-Stokes (URANS) simulation with a new turbulent inflow generation method. First, an inflow generation method is presented for the URANS model, utilizing a prespecified averaging time to divide the turbulent flow fields into resolved and modelled parts and ensure conservation of the total turbulence kinetic energy. The turbulent flow fields reproduced by the URANS model are then evaluated over flat terrain, a line of trees and a steep hill to demonstrate the performance of the URANS model. A large averaging time can be applied to the URANS model for flat terrain and a line of trees because the turbulent flow field can be simulated well by the turbulence model, but suitable averaging times are required for the URANS simulation to predict large separation vortices behind the steep hill as resolved coherent structures. Finally, an indicator is proposed to assess the performance of turbulence models considering the prediction accuracy and computational efficiency. The proposed method exhibits the best performance in predicting the mean velocity and turbulence kinetic energy, compared to Reynolds-Averaged Navier-Stokes model and Large Eddy Simulation.