Computational Fluid Dynamics (CFD) simulations of objects like the Kitepower V3A Leading Edge Inflatable (LEI) kite require accurate experimental data for validation. However, for these kites, particularly in steady-state simulations, such data is scarce. LEI kites are soft and deform continuously during flight, making validation complex. To address this, a unique experiment in the Open Jet Facility (OJF) at TU Delft, testing a rigidized subscale model of the V3A kite, marking the first wind tunnel test on a rigid kite.

The rigid model was made of carbon fiber reinforced polymer and mounted on a custom support structure that allowed adjustments to the kite’s angle of attack and sideslip. Aerodynamic forces and moments were measured at different wind speeds and orientations, with and without zigzag tape to study its effects on low Reynolds number flow.

The results were compared to existing CFD simulations, including Reynolds-Averaged Navier-Stokes (RANS) and vortex step methods. The experimental data aligned well with these simulations at low Reynolds numbers, validating the setup. However, some discrepancies highlighted areas for improvement, such as reducing interference from the support structure and better matching Reynolds numbers between simulations and experiments.

Using renewable energy to power a Mars habitat is a technological challenge because resources such as solar and wind are significantly weaker than on Earth. This work investigates the feasibility of using airborne wind energy (AWE) systems in combination with solar photovoltaic (PV) modules to power a Mars habitat. The Luchsinger model and the higher fidelity QSM are used to simulate the performance of the AWE system and compared. This thesis builds upon two earlier design synthesis exercise (DSE) projects by implementing a version of the quasi-steady model (QSM) that accounts for the transition phase, models a realistic retraction trajectory, and accounts for the mass of the airborne components. Additionally, the results of the first DSE indicate that the Luchsinger model used did not appear to consume any energy during the reel-in phase, which is not realistic and led to an over-prediction of mean cycle power. However, this thesis aims to implement the Luchsinger model correctly.

Creating a road map for sizing AWE kite systems on Mars is the main objective of this thesis. Since the performance of the AWE system is varying in time and space, the Mars Climate Database (MCD) is used to retrieve atmospheric and surface solar flux data including wind Weibull probability distribution functions (PDF). The second DSE used the MCD and validated the results against wind data from various Mars landers. The MCD is based on numerical simulations of the Martian atmosphere using a general circulation model and validated with available observational data. Seasonal vertical wind profiles are generated from the meteorological data to characterise the boundary layer over time. A scaling study assesses how AWE on Mars differs from that on Earth, performing dimensional analysis. In the system characteristics chapter, the initial sizing of the kite area and mass is computed using the scaling study. The performance models create the power curves, which together with the wind PDFs and surface solar flux data are used in the habitat energy model to verify whether the power requirements are met. Due to an insufficient amount of quantitative information on the energy consumption of the robotic construction of the habitat, the design of the microgrid is covering only the use of the habitat, which is 10 kW of continuous power. This is similar to remote off-grid solutions on Earth, with the additional challenge of having lower resource availability, both for wind and solar. This thesis concludes that various configurations of a hybrid power plant can continuously provide 10 kW of power throughout the entire Martian year. Moreover, the results indicate that using kites alone could generate sufficient power for the habitat without using solar PV.

Rhizome project: http://www.roboticbuilding.eu/project/rhizome-development-of-an-autarkic-design-to-robotic-production-and-operation-system-for-building-off-earth-habitats/

Published poster on thesis for Airborne Wind Energy Conference in Milano, Italy,: https://repository.tudelft.nl/islandora/object/uuid%3A4013ca0b-5508-4413-b8cb-5251ca1e7781

Video made to illustrate how Mars flight would look like.: https://www.youtube.com/watch?v=YS20vHhqgKk&ab_channel=AirborneWindEnergyOnline

A key challenge in the Airborne Wind Energy industry is the minimisation of the time and energy required for the transfer and return phases inherent to the power cycles of ground-generator-based kite power systems. This thesis contributes to solving this problem by exploring the use of bleed air spoilers during the return phase in terms of their potential to improve the average cycle performance. To this end, a mathematical model is first introduced to evaluate the individual phases of the characteristic power pumping cycles in a general sense. This model is further used to demonstrate that a given kite configuration with the capacity to selectively lower its glide slope and/or resultant aerodynamic loading could improve the net power output of the system by around 30%. A CFD-based simulation environment for investigations of the effects induced by bleed air spoilers is developed using Simcenter STAR-CCM+. To establish the reliability of the setup, a first study revolves around its validation with experimental data from independent wind tunnel tests on bleed air spoilers effects on ram-air parachutes. The second CFD study is based on a standard kite geometry employed by SkySails Power GmbH. Two parameter studies testing the influence of spoiler size and chordwise position are carried out to investigate how bleed air spoilers are best used to reach the desired aerodynamic effects. The results show that bleed-air spoilers should ideally be applied in the vicinity of the suction peak and that relatively small spoiler geometries can already entail a major effect on the resultant flow field. It is predicted that the evaluated configurations would improve the system's overall performance by 9 to 18.3%, mostly due to substantial reductions in the glide ratio.

Aeroelastic codes are fundamental for the design of wind turbines and the prediction of instabilities. Such codes rely on engineering models which limit their accuracy. With wind turbine blades becoming more slender to lower the costs, it is important to reduce these uncertainties to maintain a safe and stable turbine design. The dynamic stall model is one of these engineering models which simplifies the physics involved and so an improvement in accuracy might be possible. Various dynamic stall models have been published over the last 50 years. However, dynamic stall has proven to be a complex phenomenon to model accurately over a wide range of conditions and is an ongoing topic of research.
Here four semi-empirical dynamic stall models, the Øye, Risø, Snel and ONERA models, are compared first in 2D against wind tunnel data to understand their accuracy and limitations. The experimental data for this comparison uses the NACA0015, NACA0030 and NACA4415 airfoils over a variety of cases relevant to wind turbines. Hereafter the models are compared within an aeroelastic code as a part of complete horizontal axis wind turbine simulations for
an extreme load case (IEC design load case 1.4), standstill instabilities (IEC design load case 6.2) and the flutter speed to understand the effect of the different dynamic stall models. For the standstill cases the aerodynamic damping provided by each model is compared by reducing the structural damping of the blades to find the point where the blades become unstable. Next the Øye and Risø models are tuned to the wind tunnel data. The results from the 2D comparison are inconclusive with each model showing different strengths
and weaknesses. In general the attached flow physics in the Risø and ONERA models improves the fit for the 15% thick airfoils. The ONERA model captures the lift peak the best, although it usually has the largest least squares error to the data due to the drop in lift after this peak being too early and too sharp. Once in the aeroelastic code the ONERA model started to show unphysical behaviour by reducing the deflection in the extreme load case and adding negative
damping to the standstill cases. Snel’s model, on the other hand, adds so much damping that the blades remains stable even when the blades have only a small amount of structural damping, which is likely not physical. The Øye and Risø models show similar damping levels and reduce the required structural damping to prevent the standstill instabilities by at least a factor two with respect to no dynamic stall model being used. For the classical flutter analysis the Risø model shows an increase in flutter speed as expected from the implementation of Theodorsen’s theory, while the ONERA model decreases the flutter limit.
Overall the Risø model is seen as the best for in an aeroelastic code due to showing better behaviour in the full turbine cases than the ONERA and Snel models. Furthermore, it is superior to the Øye model due to correctly modeling the attached flow physics and improving the drag and moment coefficients.

In recent years, the research on Vertical Axis Wind Turbines (VAWTs) have been paving the way for the very large-scale (10-20 MW) floating offshore applications. For a cost effective utilization, VAWTs need to deliver superior aerodynamic and structural performance. Nowadays, the complex ow phenomenon of VAWTs have been better understood and the computational tools have reached to a mature level. It is time to explore the capabilities of this concept and improve its aerodynamic features by innovative design ideas. The main goal of this thesis is to enhance the performance of the lift-driven VAWTs by customized airfoil design and the active ow control with trailing edge aps. To achieve the research goals, four main lines of work are carried out: 1) performance exploration of an actuator cylinder, 2) design of the azimuthal flap control sequences, 3) comparison between the Actuator Cylinder Model and Panel Model in the presence of the active flap control and 4) airfoil design that is specified for effective flap operation on a VAWT blade. The flap control sequences are optimized with the use of the Actuator Cylinder Model for three aerodynamic objectives. These objectives are aiming to improve the power efficiency by maximizing the CP , provide a rated power control by minimizing the CP and decrease the cyclic load ranges by minimizing the CT . Whereas, RFOIL and NSGA-II genetic algorithm are coupled for the airfoil design, which aims for objectives such as superior single airfoil performance, extended flap sensitivity and high flap-wise bending stiffness. For a rotor solidity of 0.1 operating at tip speed ratio of 4, a 10% active flap is able to increase the CP by 7% , decrease the CP by 10% and alleviate 12% of the CT by sacrificing 3% of the CP . It is shown that depending on the solidity, tip speed ratio and the flap authority these figures could be increased. It is possible to brake the rotor with a relatively larger flap authority. The airfoils designed in this work are slightly cambered and span from 27% to 35% thickness, deliver higher maximum CP than a NACA 0018, show good performance in the dirty conditions and have high flap effectivity. Overall, the performance gains acquired by the new airfoils and flap control promises extensive improvements in multiple features of VAWTs such as power effciency, power control, load control that lead to reduced weight and decreased Cost of Energy.

The renewable energy need facilitates the development of offshore wind power. The abundant wind resource has pushed the wind farms into deep water sites. The floating VAWT concept is emerges as the times require. This research is part of Deepwind concept development. The project focuses on verifying the feasibility of using flap control to increase the power conversion of a VAWT through the numerical investigation. As a preliminary implementation, only a 2-D section is taken out from the Darrieus rotor as the modeled object. The report concentrates on the purely aerodynamic modeling of a VAWT. All the blades are assumed to be fully rigid in order to exempt the structural response. VAWTs present a distinct aerodynamic pattern from HAWT. To start up, a historical review on the aerodynamic models of VAWTs is performed to recap the critical issues in the aerodynamic modeling. The study mainly emphasizes on the momentum models, covers SST, MST, DMST and Actuator Cylinder (AC) models. AC mainly advantages on including the lateral inductions, and the wake interaction. Its precise prediction was confirmed in the simulation results of the aerodynamic model comparison study [10]. Hence, AC has been chosen as the numerical tool for VAWT modeling, both for the self-developed routine and HAWC2. A promising solution to determine the load-form for optimal power is constructing a uniform distribution so that the power coefficient could reach Betz limit. The normal load distribution on the blade path is the link between the power conversion and the blade force. At the moment of the determination of the load distribution that leads to the optimal power, the required blade force at the different azimuth positions are also settled. The simulations are performed with TSR=2, 3, 4, and 5 to verify the possibility on achieving the ideal power production in order to draw up an optimized control option. The result of the study is presented as a form of different flap angles at discretized azimuth positions. Even though the load-form is universal, the resultant flap variation only works for the specific rotor because of the introduction of airfoil data in the computation. An H-rotor VAWT with aps is set up in HAWC2 to validate the control strategy. As the supplement to AC model, a dynamic stall model called ATEFlap is integrated in HAWC2 to calculate the dynamic stall impact, and the influences from flap detection for the given airfoil. The model is supposed to return the aerodynamic loading of the blades under the dynamic stall. Hence, the deviations between the target load distribution obtained from the quasi-steady environment and the semi-dynamic one is observed as expected. In the end, the aps running with the given function could almost give the desired loading, but the deviations are observed in downwind part. It is mainly the hysteresis of the lift coefficient causes the difference. It is proven to be partly made up by increasing the flap deflections in the downwind side.