CFD Modelling of the Neutral Atmospheric Boundary layer above and inside Forest Regions
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Typ
Examensarbete på kandidatnivå
Program
Publicerad
2020
Författare
Alatalo, Viktor
Eriksson, Sara
Johansson, Tim
Larsson, Oscar
Larsson, Viktor
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
As 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.
Beskrivning
Ämne/nyckelord
Wind power production , Turbulence modelling , RANS, LES , k-epsilon , STAR-CCM+ , Actuator disc , Canopy models , Neutral ABL