AERODYNAMIC AND AEROELASTIC MODELING OF HORIZONTAL AXIS WIND TURBINES USING PANEL METHODS

Wind energy is one of the most reliable renewable energy sources and constitutes
a viable alternative to fossil and nuclear fuels for the generation of
electricity. Over the last couple of decades the increasing demand for wind
energy has resulted in increasingly large and sophisticated wind turbines. Accurate
but efficient aerodynamic and aeroelastic modelling at the design stage
has become a key issue. The surface panel and vortex lattice methods are efficient
aerodynamic modelling tools that are routinely employed in design
calculations by the aerospace industry. They constitute a good compromise
between fidelity and computational cost in the preliminary design and optimization
phase. However, these approaches have not been widely adopted for
wind turbine modelling due to their inability to represent separated flow.
The main objective of this thesis is the development of a 3D unsteady viscous-inviscid
interaction technique that couples panel methods to a boundary layer
solution and can be used to model separated flow over the blades of a wind
turbine rotor. The technique is based on a quasi-3D, quasi-steady integral
boundary layer solution, coupled to a 3D unsteady surface panel method by
means of a two-way interaction scheme. The boundary layer solution results
in an estimate of the separation line on the suction surface of the blade. A
separated shear layer made up of doublet panels is shed from this line and
allowed to propagate freely at the local flow velocity, exactly like the wake shed
at the trailing edge. Aerodynamic pressure and load predictions obtained from
this method are validated through comparison to experimental measurements
from the NREL phase VI wind turbine.
The thesis also describes the development of a complete methodology for the
unsteady aeroelastic and aeroservoelastic modeling of horizontal axis wind
turbines at the design stage. The methodology is based on the implementation
of unsteady aerodynamic modeling, advanced control strategies and
nonlinear finite element calculations in the Siemens LMS Samcef for Wind
Turbines design package. The aerodynamic modelling is carried out by means
of the unsteady Vortex Lattice Method. The complete methodology is used
to perform full aeroservoelastic simulations of a 2MW prototype wind turbine
model.