Wake effects are important to wind turbine design and wind farm design, because
they will affect the aerodynamic performance and structural loads of wind turbine
operating in a wind farm.
Wake effects were investigated extensively for horizontal axis wind
turbine(HAWT) in the past, but there has been very limited work done for the
vertical axis wind turbine(VAWT), whose wake effects are unique because the
blades will go through their own wake region during the operation. The presented
thesis aims to bridge this knowledge gap by modelling the VAWT wake effects
using CFD.
As for the general wind turbine wake effects study, four key aspects can be
identified: wake models, aerodynamics, structural dynamics, and structural
integrity. Relevant literature is reviewed in the thesis, and a comprehensive
framework of studying the VAWT wake effects is proposed. The framework
covers all the four key aspects of the wind turbine wake effects study, and two of
them will be addressed in the presented thesis, wake models and wake
aerodynamics.
CFD modelling in the thesis is based on RANS method. The near wake modelling
focuses on the aerodynamics prediction and the far wake modelling focuses on
the wake structure prediction.
As for the near wake study, wake effects of a circular cylinder at Re=140000 is
studied and validated. the aerodynamic performance of NACA0015 airfoil at
various angle of attack at Re=2000000 is modelled using different turbulence
models, dynamic stall effects of the airfoil at three different regimes are
investigated. They form the basis of analysing the aerodynamic performance of
VAWT rotor. A 17m 2-bladed VAWT designed based on such geometries (circular
cylinder and NACA0015 airfoil) is modelled thereafter, simulated aerodynamic
performance under different tip-speed ratios are compared with experiment data.
As for the far wake study, both rotor simplification using porous disk and full rotor
simulation are presented. A persistent symmetric wake region is observed from the porous disk modelling while the full rotor modelling predicts an asymmetric
wake region. The wake interaction is then studied in a two turbine VAWT array,
the influence of wake effects on the performance of VAWT at 3 diameters
downstream is investigated. Overlapping of wake region is analysed
