Thesis title: Integrated experimental and numerical investigation of unsteady aerodynamics and aeroelasticity in horizontal and vertical axis wind turbines
This thesis presents a comprehensive investigation into the unsteady aerodynamic and aeroelastic behaviour
across vertical- and horizontal-axis wind turbines. A stall-driven vertical-axis Darrieus rotor is probed
with time-resolved Particle Image Velocimetry (PIV) system to establish quantitative vortex life-cycle and
blade-resolved metrics for like-for-like model-experiment cross validation; aeroelastic analysis addresses
horizontal-axis NREL 5 MW and IEA 15 MW Reference Wind Turbines (RWTs) operating in on/offshore
configurations. At the convergence of scale and turbine type, dynamic stall emerges as the binding thread.
The first part focuses on a two-bladed H-type vertical-axis Darrieus Wind Turbine (DWT) operating in
a stall-dominated regime. A time-resolved PIV campaign is conducted to capture statistically-robust phaseresolved velocity fields and vortex dynamics, complemented by an enhanced Double-Multiple Streamtube
(DMST) model with high-thrust correction and a dynamic stall sub-model. Comparisons against present
PIV data, legacy experiments, and 2D Reynolds average Navier-Stokes (RANS) simulations highlight the
role of dynamic stall in shaping Vertical Axis Wind Turbines (VAWTs) aerodynamics and demonstrate both
the potential and limitations of low-order models in stalled conditions.
The second part examines Horizontal Axis Wind Turbines (HAWTs) across scales and operating regimes.
The in-house aeroelastic solver, AEOLIAN (coupling blade-element–momentum theory, BEMT, with a
lumped-mass multibody structure), is verified on NREL Phase VI (NASA Ames Unsteady Aerodynamics
Experiment, UAE) and validated at utility scale on the NREL 5 MW RWT under uniform, sheared and
yawed inflow, as well as floating-offshore operation. These studies show that engineering-fidelity tools can
be reliable when aero–structural coupling and blade deformation are treated consistently. Building on this,
the analysis is extended to the IEA 15 MW RWT to benchmark aerodynamic solvers from BEMT through
actuator-line and free-vortex wake to blade-resolved RANS. Comparisons with BEMT–Geometrically-Exact
Beam Theory (GEBT) highlight torsional deformation as a key driver of local angle of attack and load
changes, especially outboard.
Finally, dynamic stall modelling—central to both horizontal- and vertical-axis turbine aerodynamics—is
revisited through a systematic review and calibration of the Beddoes–Leishman (BL) model on classical
pitching-airfoil data. A physics-informed calibration strategy is shown to significantly extend the predictive
range of the model, supporting its use across a broad spectrum of operating conditions.
Hence, this thesis contributes to the study of unsteady aerodynamics and aeroelasticity in wind turbines,
spanning from time-resolved experiments to utility-scale rotor simulations. The main outcomes are: (i)
an experimental–numerical assessment of stall-driven Darrieus turbine aerodynamics at the blade level,
(ii) tailored post-processing methodologies to extract blade phase, circulation, and relative velocity from
time-resolved PIV, providing quantitative metrics for like-for-like model-experiment comparisons and a
regime-aware validation of low-order Darrieus models, specifying conditions under which the quasi-steady
assumptions are valid and when additional unsteady physics are required, (iii) development and verification
of AEOLIAN aeroelastic solver for on/offshore horizontal axis wind turbines, (iv) an aeroelastic analysis
and verification of the next generation of utility scale RWTs operating under complex conditions and (v) a
systematic reassessment of the Beddoes–Leishman dynamic stall model.
These efforts collectively support a more consistent evaluation of higher-fidelity industrial models for
the analysis of next-generation wind turbines.
Keywords: Offshore, Wind Turbine, Aerodynamics, Unsteady, Aeroelasticity, Darrieus, Experiment,
PIV, Stall.