Over recent decades, the wind energy sector has undergone rapid expansion, driven by escalating global energy demand and the widespread transition toward sustainable power generation. This development has been accompanied by a substantial increase in wind turbine rotor size. However, scaling up turbine dimensions introduces significant engineering challenges, particularly in achieving high aerodynamic performance while maintaining cost effective structures. The resulting trend toward longer and more slender blades has amplified both static and dynamic loading, making structural integrity a central concern in contemporary turbine design. To address these challenges, modern rotor concepts incorporate thicker inboard and mid-span airfoils, including flatback configurations, which improve structural efficiency and aerodynamic performance while reducing overall blade mass. At the same time, enlarging blade radii leads to greater elastic deformations, which further increase the dynamic loads experienced by the rotor.

Ensuring reliable turbine operation requires accurate load assessment, which depends heavily on aeroelastic and dynamic load simulations across a broad range of operating conditions. As blades become larger and more flexible, they are subjected to stronger inflow turbulence, more pronounced unsteady variations in angle of attack, and an increased likelihood of transient stall phenomena. These factors make accurate unsteady aerodynamic modeling essential. In this context, dynamic stall models are frequently employed to predict unsteady aerodynamic forces. Historically, however, most dynamic stall models were developed for thin airfoils in helicopter applications, and despite subsequent adaptations for wind turbine use, their suitability for thick airfoils remains limited. The aerodynamic response of thick airfoils, particularly those typical of large modern blades, still lacks comprehensive validation, resulting in uncertainties in load predictions. Moreover, thick mid‑span airfoils experience large unsteady angles of attack and are more susceptible to early stall, necessitating active or passive flow‑control strategies. Flatback airfoils and vortex generators have emerged as promising solutions, offering increased lift, delayed flow separation, and improved stall characteristics. Nevertheless, their combined impact on unsteady aerodynamics is not yet fully understood, revealing a critical gap in current aeroelastic modeling capabilities.

This knowledge gap compromises the reliability of current aeroelastic models and poses risks for the design, optimization, and structural assessment of large modern turbines. Consequently, this dissertation is motivated by the need to advance the understanding and modeling of dynamic stall phenomena in thick wind turbine airfoils, with particular emphasis on the combined effects of vortex generators under unsteady flow conditions. By addressing these gaps, the work aims to contribute improved physical insight and enhanced predictive capability for the aerodynamic behavior of next generation wind turbine blades.

Therefore, several wind tunnel campaigns were conducted to investigate the unsteady aerodynamic characteristics of two $35\%$ thick airfoil configurations, comprising a conventional airfoil and a flatback airfoil, tested in different setups in Low-speed, low-Turbulence wind Tunnel (LTT) of the Delft University of Technology.

The results show that flatback airfoils exhibit inherently more stable hysteresis loops, as evidenced by reduced force fluctuations, larger lift overshoots, and delayed separation compared to sharp trailing edge airfoils, primarily due to their more favorable suction side pressure gradients under the studied operating conditions. Dynamic stall on these thick airfoils is governed not by leading edge vortex formation, as seen in thin airfoils, but by a gradual trailing edge separation mechanism that produces moderated load transients. Reduced frequency strongly influences dynamic stall, i.e, higher frequencies delay separation, enhance lift overshoot, and stabilize flow evolution for both airfoils. The addition of vortex generators substantially improves flow attachment during the upstroke phase, increases lift overshoot, and suppresses force fluctuations, particularly when placed near the leading edge. Their effectiveness, however, depends sensitively on chordwise placement, the underlying airfoil geometry, and the oscillation regime. While flatback airfoils generally benefit from improved stall delay, they experience larger force excursions during fully separated flow, indicating both the potential and the risks of employing blunt trailing edge designs. The evaluation of the Beddoes–Leishman and Risø dynamic stall models demonstrates that both models are not capable to predict separated flow behavior on thick airfoils, especially regarding lift overshoot, lift drop, post-stall loads, drag, and pitching moment. Lack of modeling accuracy lead to systematic discrepancies in model predictions, even when tuning time constants. These findings highlight the need for new or revised separation and reattachment modules tailored specifically for thick airfoils for reliable load prediction in the inboard and mid-span regions of large modern wind turbine blades. ... Read more

The European Union's vision of a single market is expanding to the free movement of research, innovation, data, and knowledge, an ambition that depends on effective cross-organisational collaboration and, consequently, on a high degree of interoperability. As organisations increasingly collaborate through Collaborative Networked Organisations (CNOs) and move into the digital domain, their success grows ever more dependent on the ability to interact towards mutually beneficial goals by sharing information, knowledge, and data. Yet despite considerable technical progress, many barriers to interoperability are institutional or governance-related rather than purely technical. Because research and practice continue to privilege technical solutions, the solution space remains narrow, and interoperability initiatives are undermined. This thesis therefore reframes interoperability as a governance challenge, consistent with the view of CNOs as socio-technical systems and adopts an Engineering and Policy Analysis perspective at the intersection of digital technologies and governance. It proposes commons scholarship, traditionally concerned with shared tangible resources but recently extended to intangible ones such as data and knowledge, as a lens for studying interoperability in CNOs, asking: how can commons scholarship inform the governance of interoperability in Collaborative Networked Organisations? Through two desk analyses and a case study, the thesis finds that interoperability is multidimensional yet often addressed in isolation; that only CNOs with a deliberate organisational structure and a long-term horizon are suited to a commons analysis; and that several commons frameworks, supported by the European Interoperability Framework, can systematically expose divergences between formal institutional arrangements and daily practice. The thesis contributes three replicable guideline tools, a decision tree, a set of application guidelines, and a checklist, demonstrated through a detailed case study. ... Read more

Glass is endlessly recyclable, yet only a fraction of container glass is recycled globally, while countries such as Brazil simultaneously face a severe shortage of affordable housing. In response, low-income communities have begun embedding used glass bottles in earthen mortars to construct walls. However, scientific investigation of glass bottles as structural components in earthcrete blocks is virtually absent from the literature. This thesis investigates the influence of different bottle configurations on the mechanical behavior of earthcrete building units embedded with long-neck beer bottles, using a combined numerical and experimental approach. Finite element models were developed in Abaqus using the Concrete Damage Plasticity model, calibrated on experimental data from earlier research on single-bottle blocks. A parametric study of cubic blocks (240 mm) was performed in which the number of vertically oriented bottles (0–9) and the earthcrete cover (2–6 cm) were varied. Based on these simulations, three configurations were fabricated and tested under uniaxial compression. The experiments proved highly repeatable: the plain block reached a mean capacity of 401 kN, whereas the four- and five-bottle blocks reached 330 kN and 349 kN respectively, corresponding to a capacity reduction of 18 and 13% and a distinctly more brittle post-peak response. The calibrated numerical model over-predicted the experimental capacities by 42–125% and incorrectly predicted that capacity increases with bottle
count. Recalibration improved the agreement but remains a fit rather than a validation. A Eurocode 6 case study demonstrates that a two- to three-storey residential building on bottle-embedded walls satisfies the ultimate limit state verification. It is concluded that embedded glass bottles act not as reinforcement but as functional voids: for a modest loss of compressive capacity,
they reduce material use and divert waste glass from disposal, making their value primarily economic and environmental rather than structural. ... Read more

Supercritical carbon dioxide (sCO₂) has significant potential as a working fluid for heat transfer applications, but its strongly varying thermophysical properties near the pseudo-boiling curve complicate the design of heat transfer equipment. Particle image velocimetry (PIV) could provide valuable measurements of the velocity field, but its application to sCO₂ is challenging due to low particle visibility and limited optical access. This thesis develops and experimentally characterizes an in-line PIV imaging system for an existing sCO₂ test cell. The system consists of a collimated light source, imaging lens, iris, light trap, and camera, and its optical performance is evaluated through measurements of focused beam diameter, depth of field, and image contrast. The results are compared with diffraction-limited optical theory and assessed through PIV measurements in simple flow configurations. The measured focused beam diameter and depth of field are substantially larger than theoretical predictions, which is attributed to non-idealities such as residual beam divergence and lens aberrations. PIV measurements in low-velocity flows produce highly correlated velocity fields with few outlying vectors, while higher velocities are limited by reduced particle signal relative to camera noise. The results show that diffraction-limited theory provides useful qualitative design trends but does not accurately predict the absolute optical performance of the system. Improved illumination intensity, reduced beam divergence, and lenses less sensitive to aberrations are recommended for further development. Additional investigation of tracer particle selection and refractive-index-induced image distortion is required before reliable PIV measurements can be performed in the sCO₂ test facility.
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