Browsar Examensarbeten för kandidatexamen // Bachelor Theses efter Författare "Alatalo, Viktor"
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- PostCFD Modelling of the Neutral Atmospheric Boundary layer above and inside Forest Regions(2020) Alatalo, Viktor; Eriksson, Sara; Johansson, Tim; Larsson, Oscar; Larsson, Viktor; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Davidson, Lars; Abedi, HamidrezaAs the demand for wind power increases, more areas are being investigated for construction of wind farms. The forest covered landscape of Sweden offers plenty of room for expansion, but comes with certain difficulties. One important factor to consider is that the forest canopies are sources of turbulence in the air flow. The turbulence causes fatigue in wind turbines and may affect their power production, it therefore needs to be taken into account when constructing them. One cost-effective method for recreating and measuring the effects of this turbulence is Computational Fluid Dynamics (CFD). In this project, the commercial software STAR-CCM+ was used for all simulations. Using CFD, the turbulence may be modelled in several different ways. Large-Eddy Simulations (LES) is a turbulence model that accurately predicts turbulent, unsteady flow, but at the cost of computational power. Another model uses the Reynolds-Averaged Navier-Stokes equations (RANS) which solve for the mean velocity field by modelling the fluctuations in the flow. LES was used for reference data, but the main part of the project was performed using RANS in combination with the k- model. Several different simulations were performed aiming to replicate the real physical conditions. In addition to bare terrain, two different forests were simulated, ’sparse’ and ’dense’. This project employed four canopy models: Sanz, Svensson, Green and Liu. Of these models, Sanz was found to correspond best with the LES data. After choosing a canopy model, a wind turbine was simulated by employing the ’virtual disk’ model available in STAR-CCM+. The forest density was found to have little impact on the streamwise velocity of the wind. The turbulent kinetic energy, however, differed with the forest density. For the wind turbine simulations the same relation was observed, as the turbulent kinetic energy was higher when the forest was included compared to bare terrain. This increase bears significance on the lifespan of wind turbines, and by extension, their design. Testing a wider range of wind speeds, as well as investigating whether wake regions yield similar effects may be topics for future studies.