This thesis describes the different steps needed to design a steadystate
computational fluid dynamics (CFD) wind farm wake model.
The ultimate goal of the project was to design a tool that could
analyze and extrapolate systematically wind farm measurements to
generate wind maps in order to calibrate faster and simpler
engineering wind farm wake models. The most attractive solution
was the actuator disc method with the steady state k-ε turbulence
The first step to design such a tool is the treatment of the forces.
This thesis presents a computationally inexpensive method to apply
discrete body forces into the finite-volume flow solver with
collocated variable treatment (EllipSys), which avoids the pressurevelocity
The second step is to distribute the body forces in the
computational domain accordingly to rotor loading. This thesis
presents a generic flexible method that associates any kind of
shapes with the computational domain discretization. The special
case of the actuator disc performs remarkably well in comparison
with Conway’s heavily loaded actuator disc analytical solution and
a CFD full rotor computation, even with a coarse discretization.
The third step is to model the atmospheric turbulence. The
standard k-ε model is found to be unable to model at the same time
the atmospheric turbulence and the actuator disc wake and performs
badly in comparison with single wind turbine wake measurements.
A comparison with a Large Eddy Simulation (LES) shows that the
problem mainly comes from the assumptions of the eddy-viscosity
concept, which are deeply invalidated in the wind turbine wake
region. Different models that intent to correct the k-ε model’s issues
are investigated, of which none of them is found to be adequate.
The mixing of the wake in the atmosphere is a deeply non-local
phenomenon that is not handled correctly by an eddy-viscosity
model such as k-ε .
- Wind turbine structures
- Wind energy
- AAU-DCE Thesis no. 22
- AAU-DCE Thesis 22