Forest Simulation with Industrial CFD Codes

Sammanfattning: Much of the planned installation of wind turbines in Sweden will be located in the northern region, characterized by a lower population density so that problems related to sound pollution and visual acceptance are of lower concern. This area is generally distinguished by complex topography and the presence of forest, that significantly affects the wind characteristics, complicating their modelling and simulation. There are concerns about how good an industrial code can simulate a forest, a question of paramount importance in the planning of new onshore farms. As a first step, a sensitivity analysis was initially carried out to investigate the impact on the ow of different boundary conditions and cell discretization inside the forest for a 2D domain with a homogeneous forest. Subsequently, a comparative analysis between the industrial code WindSim and Large Eddy Simulation (LES) data from Segalini. et al. (2016) was performed with the same domain. Lastly, simulations for a real Swedish forest, Ryningsnäs, was conducted to compare a roughness map approach versus modelling the forest as a momentum sink and a turbulence source. All simulations were conducted for neutral stability conditions with the same domain size and refinement. The main conclusions from each part can be summarized as follows. (i) The results from the sensitivity analysis showed that discretization of cells in the vertical direction inside the forest displayed a correlation between an increasing number of cells and a decreased streamwise wind speed above the canopy. (ii) The validation with the LES data displayed good agreement in terms of both horizontal mean wind speed and turbulence intensity. (iii) In terms of horizontal wind speed for Ryningsnäs, forest modelling was prevailing for all wind directions, where the most accurate simulation was found by employing a constant forest force resistive constant (C2) equal to 0.05. All forest models overestimated the turbulence intensity, whereas the roughness map approaches underestimated it. Based solely on the simulations for Ryningsnäas, a correlation between lower streamwise wind speed and higher turbulence intensity can be deduced.