This thesis presents a new medium-fidelity ducted fan analysis code, to bridge the current gap in compressible-flow analysis methods. The existing Multi-passage ThroughFLOW software is integrated into a unified code to extend its capabilities. This unified code forms part of a newly developed ducted fan optimisation framework that utilises a modern genetic algorithm. Validation against experimental data shows a significantly improved accuracy in both thrust and power coefficient modelling compared to currently used panel methods.

The optimisation framework is applied to several case studies, demonstrating the capabilities of the developed tools. Propulsor efficiency improvements up to 10% are obtained, with significant associated frontal area reductions. Single-objective and multi-objective single-point optimisations were demonstrated, and suggestions are made to improve the flight profile multi-point optimisation.

The framework's robustness and computational efficiency can make it suitable for broader applications, including multidisciplinary optimisation and integration into complete aircraft design workflows.
Related dataset 4TU.ResearchData: https://doi.org/10.4121/efc63362-65e5-4c5d-b787-27e44dafa52a

Research into propellers has been rejuvenated recently, as the efficiency of propulsive systems becomes increasingly important. A drawback of propellers is their aeroacoustic noise, which can be reduced by adding blade sweep. This thesis investigates the effect of sweep on the aerodynamic performance of propellers by comparing a swept and a new, unswept propeller utilising a wind tunnel experiment and lifting-line methods.
The wind tunnel results show no significant differences in the integrated performance between the two propellers, although the slipstreams are different. It was found that the swept propeller has an outboard shift in the blade loading from flowfield measurements. The lifting-line results indicate a greater effect of sweep on performance than the experimental results. These differences can primarily be attributed to the 2D airfoil polar data used in the lifting-line simulations. The shift in outboard loading due to the sweep distribution is present in the computational results.

The increasing demand for sustainable, efficient, and versatile air mobility solutions has accelerated research into Vertical Take-off and Landing (VTOL) configurations. While tilt-rotor and tilt-wing designs offer high cruise efficiency by employing the same propulsion units for lift and thrust, conventional implementations rely on complex and heavy actuation systems, limiting payload capacity and endurance. This thesis proposes a novel passive tilt-wing concept based on offset Distributed Electric Propulsion (DEP), in which asymmetric propeller placement and differential thrust are used to control wing tilt without dedicated actuators. The configuration aims to reduce structural complexity and weight while enhancing aerodynamic performance.

However, effective modeling of coupled propeller–wing aerodynamics across a wide AoA range, which is critical for tilt-wing VTOL aircraft, remains lacking. Existing methods either lack accuracy at high AoA (low-order models) or are too computationally expensive for early-stage design (high-fidelity CFD), limiting their applicability to tilt-wing DEP systems. To address this issue, a data-driven aerodynamic modeling framework is developed to predict propeller–wing interactions over a wide angle-of-attack range. The approach combines a physics-informed propeller digital twin—constructed from wind tunnel load and Particle Image Velocimetry (PIV) measurements—with computational fluid dynamics (CFD)-based clean-wing aerodynamic results, corrected for slipstream effects. This model enables accurate and computationally efficient estimation of aerodynamic loads under conditions typical of VTOL transition flight, and is validated against wind tunnel experiments. Parametric studies are conducted to explore the influence of propeller installation parameters on cruise and take-off efficiency, revealing optimal placements for both performance and control authority.

The thesis is organized as follows: Part I presents the scientific paper, focusing on the principal innovations of this project in the field of propeller–wing interaction analysis, detailing the development, validation, and application of the modeling of propeller-wing aerodynamic interaction. Part II covers other aspects of the project, including the literature review, the conceptual design of the passive tilt-wing VTOL configuration, preliminary explorations of propeller–wing modeling, and the feasibility analysis and optimization of the proposed passive tilt-wing design.

With the resurgence of interest in propeller-powered aircraft for short-haul and regional missions, understanding the aerodynamic interaction between propellers and nearby surfaces has become increasingly crucial. While propellers offer superior propulsive efficiency and sustainability benefits, their integration introduces complex unsteady flow phenomena that remain insufficiently explored. Additionally, concepts related to regenerative braking and the negative thrust regime aim to harness the full potential of propellers in the pursuit of sustainable aviation. However, the interactions are more complex in the negative thrust regime and need to be accounted for.

This study investigates the unsteady aerodynamic effects of a pusher-propeller operating upstream of a downstream airfoil, with a focus on both positive and negative thrust regimes. A flexible PCB embedded with microphones and pressure sensors was used to capture unsteady surface pressure fluctuations across different operating conditions. The motivation stems from the limited understanding of unsteady surface pressure fluctuations in negative thrust conditions.

The experimental campaign was conducted in two wind tunnel labs: the M-Tunnel and the Small Low-Turbulence Tunnel in the Low-Speed Wind Tunnel Laboratory of Delft University of Technology, Netherlands. The research was carried out in two experimental phases. In the first phase, the device was validated to verify the response of the microphones and the pressure sensors. A known tonal excitation case, along with a case involving an upstream cylinder, was conducted to assess whether the results aligned with theory and expected trends from the literature. These validation experiments confirmed the device’s capability to capture unsteady flow behaviour. However, certain limitations, such as overshoots in measured pressure data and restricted chordwise and spanwise resolution, were encountered. The second phase was conducted in the Small Low-Turbulence Tunnel featuring a fixed airfoil section downstream of a rotating propeller. The device, comprising the microphones and BMP390 pressure sensors, was wrapped around the leading edge of the airfoil to measure pressure fluctuations across the airfoil surface. Initial validation confirmed the reliability of the device in measuring the flow in the propeller slipstream, with good agreement with results from the literature. Comparative analysis was performed across multiple cases, including nacelle-only baselines and propeller-on conditions at two different advance ratios. In the positive thrust regime, the propeller generated a strong tip vortex trace, which significantly influenced the laminar separation bubble and led to elevated pressure fluctuations and peaks at the tonal harmonic of the blade passage frequency. In contrast, the negative thrust regime featured a weaker tip vortex trace and a broadband-dominated spectrum, with reduced suction observed on the upper surface due to lower dynamic pressure in the slipstream.

The study also highlights that the influence of the propeller slipstream extends well beyond its boundary across the span of the airfoil model. Key limitations included discrepancies in the data measured by two rows of microphones due to surface mounting issues.

Overall, the device proved to be a valuable measurement tool for investigating the unsteady surface pressure fluctuations associated with propeller–wing interaction. The insights gained contribute to a better understanding of surface pressure fluctuations on a body immersed in a propeller slipstream, particularly in energy-harvesting operating regimes. Recommendations for future work include improving sensor mounting fidelity, increasing chordwise resolution, and incorporating time-resolved flow visualisation techniques to complement the surface pressure measurements and provide additional insight into the spatial and temporal evolution of the flow field.

Growing interest in efficient short-haul and electric regional aviation has renewed focus on propeller-driven aircraft, although open rotors pose significant noise challenges. This study investigates how noise perception—quantified by the Effective Perceived Noise Level (EPNL)—influences propeller blade design, with particular attention to blade sweep. Aerodynamic modelling is carried out using a Vortex Lattice Method, while aeroacoustic analysis relies on Hanson’s frequency-domain tonal noise model.

A parameter study reveals that perceived noise plays a more critical role during take-off than cruise in guiding propeller design, and that blade sweep is more effective at reducing perceived noise than physical noise, especially at high rotational velocities.

In the second part of the study, multiple trade-off analyses are conducted through a series of optimisations that minimise EPNL under progressively loosened power requirements, all performed under take-off conditions. The results indicate that while reducing rotational velocity remains the most effective strategy for lowering both physical and perceived noise, the fundamental frequency becomes increasingly dominant in the total tonal noise. Consequently, optimisation for perceived rather than physical noise results in similar blade geometries, but with progressively greater reductions in perceived noise relative to physical noise because of the lowering Blade Passage Frequency, which the human ear is less sensitive to. Among various sweep-induced noise reduction mechanisms, fixing the blade radius—rather than the blade length—yields greater noise reduction, primarily due to reduced blade loading as the blade lengthens with introduced sweep.

A comparison of EPNL-optimised designs requiring 1% additional power shows that allowing the blade length to vary under a fixed radius enables a further 7.2 dB reduction in perceived noise. When examining the effectiveness of sweep versus twist under constant blade radius conditions, and again allowing 1% extra required power, blade twist achieves a 1.3 dB reduction in perceived noise, while blade sweep provides an additional 4.6 dB reduction.

While experimental studies typically ensure the proper scaling of the advance ratio, testing under ambient conditions often leads to a reduced free-stream Mach number and, if the advance ratio is maintained, to a reduced tip Mach number. This research analyzed the sensitivity of a propeller's far-field tonal noise emissions to variations in helical tip Mach number when operating at a non-zero angle of attack and experiencing wake encounter, using low-fidelity methods. The chosen aeroacoustic solver, based on Hanson's time-domain theory, allowed to capture physical insights via waveform analyses.
The analyses conducted showed that variations in tonal noise amplitude, directivity, and spectral content due to a flow non-uniformity depend on the propeller helical tip Mach number. An enhanced influence of steady noise sources at higher Mach numbers was observed. Waveform analyses suggest that, as Mach number increases, the effect of temporal variations in the acoustic planform—determined by blade element positions at their retarded times—on unsteady loading noise diminishes relative to steady loading noise, thereby amplifying the influence of the latter. These results highlight that propeller aeroacoustic data obtained at low helical tip Mach numbers in experiments cannot be directly scaled to full-scale propellers operating at high Mach numbers.

The present study investigates the deformation of propeller blades in the presence of a wing, specifically analysing the lift-induced upwash effects through experimental measurements conducted in a wind tun- nel. The objective is to quantify the impact of non-uniform inflow on blade bending, with a particular focus on the aerodynamic interactions between the rotor and the wing. Image Pattern Correlation Tech- nique (IPCT) was employed to measure blade deformation, leveraging high-resolution optical methods to capture structural response under varying flight conditions. The experimental campaign was conducted at the Large Low-speed Facility (LLF) of the German- Dutch Wind Tunnels (DNW), a closed-circuit wind tunnel with an open test section measuring 6 × 8 m. The facility provides high flow uniformity, low turbulence levels, and a Mach number range up to 0.2, allowing for detailed aerodynamic and structural measurements. A range of rotor pitch angles and operating conditions were tested to assess how blade deformation varies with changes in aerodynamic loading. Preparatory work was done at DLR in Göttingen to test all the necessary assumptions. Results indicate that inflow incidence angle (αC) corrections, which account for the effective angle of attack due to the lift-induced upwash at the rotor, effectively account for deformation effects, includ- ing in swept-wing configurations. The propwash was found to significantly influence the wing lift and consequently the induced upwash and angle of attack at the rotor. The location of maximum bending, defined as the displacement normal to the plane defined by the rotor span and its root chordline, was verified for both the wing-on and wing-off cases, with the wing sweep being directly responsible for an increase in mean bending and a clockwise rotation in the deformation distribution. Furthermore, mea- surements revealed that the upgoing blade, closer to the wing leading edge, exhibited larger deviations between clean and wing-on setups due to both the rotation of the deformation distribution and to the increase in deformation which were not accounted for by the lift-induced α correction computed for the rotor centre. The effect of the component of lift-induced upwash field due to the wing sweep resulted in a 10% increase in mean bending at the worst case scenario of high angle of attack and advance ratio. These results highlight the importance of wing-rotor integration for aerodynamic efficiency and struc- tural resilience, particularly in higher disk loading configurations, such as open-rotor designs. The find- ings suggest that wing sweep and propwash interactions, identified as the main cause of the non-uniform inflow component, strongly influence blade deformation and could be relevant for future propulsion sys- tem designs. This has implications not only for structural analysis, as the rotor is more stressed, but also for aerodynamics, as the measured displacement can affect the twist distribution. Strain gauges were considered a complementary method to digital image correlation, offering data to correlate IPCT measurements across the rotor disk and reconstruct deformation fields in occluded areas. Furthermore, linking in-plane loads from the RSB with rotor disk deformation could improve the understanding of blade behaviour. The study also underscores the feasibility of using optical measurement techniques for partially occluded stator blades, provided that phase-dependent rotor wake effects on deformation remain negligible. In the investigated configuration with steel stator blades, deformation appeared negligible, falling within the measurement accuracy range. Future work should focus on integrating strain gauge data with IPCT to improve measurement coverage, exploring correlations between vibrational modes and blade deformation. These advancements would refine predictive aerodynamic models, provide insight into rotor-wing interactions and contribute to the development of more efficient propulsion systems for next-generation aircraft

As the aviation industry faces growing environmental challenges, there is a critical push for innovations to reduce its climate impact. Advances in propeller technology present a promising, more efficient alternative to traditional turbofans, especially for short to medium-range flights. Propellers offer high propulsive efficiency and flexibility, though they pose challenges like increased noise and performance limitations at higher speeds. Recent developments explore propeller integration into airframes to harness aerodynamic benefits, such as distributed propeller systems that enhance lift during take-off. The design of such integrations requires a comprehensive understanding of the highly complex flow dynamics involved in the interaction between a propeller, wing, and flap.
The objective of this dissertation is therefore to characterise the phenomena and mechanisms that govern the aerodynamic interaction between a propeller, wing, and flap. The propeller-wing-flap aerodynamic interaction can be viewed as a combination of two fields which are already established in literature: propeller-wing aerodynamic interaction and multi-element airfoil aerodynamics. Using these foundations, the present research approaches the problem from two perspectives: the extension of propeller-wing interaction to include a flap, and the influence of a non-uniform flowfield induced by a propeller on the aerodynamics of a multi-element airfoil. Special attention is paid to the slipstream deformation, which is known to be substantial in propeller-wing interaction at high angles of attack and is likely to be very significant for the flow over a deployed flap. Additionally, the explorations of additional components in the system, such as distributed propellers and the role of the nacelle integration, are included to provide a basis for further research in the field....

Future regional and short to medium-range aircraft are expected to use propellers for sustainable aviation, possibly with (hybrid-)electric propulsion systems. This will enable innovative integration of aero-propulsive systems, potentially increasing the overall aerodynamic efficiency of the airframe and propellers, resulting in a lighter airframe and increased passenger comfort. The presence of electric motors and propellers in such configurations, in addition, offers a unique opportunity to leverage propellers as airbrakes by operating them at negative thrust. This approach offers multiple potential advantages, including shorter landing runs, enhanced landing maneuverability, energy harvesting during braking operations, faster aircraft turnaround times, and reduced community noise exposure.

Despite these potential advantages, the aerodynamic and aeroacoustic characteristics of propellers operating in negative thrust mode remain largely unexplored. This dissertation addresses this knowledge gap through computational analysis, comparing the performance of isolated propeller configurations in negative thrust mode with the well-understood positive thrust mode. The results reveal that the distinct aeroacoustic characteristics of propellers operating in negative thrust conditions, compared to conventional positive thrust conditions, offer a promising avenue for reducing community noise, not only through the possibility of steeper descents but also through changes in the noise emissions from the propeller itself.

In recent years, the civil aviation sector has increasingly focused on optimizing propulsion designs to improve efficiency and reduce CO₂ emissions. Propellers have regained attention for their superior efficiency, particularly in applications like full-electric aircraft, though high noise emissions remain a significant challenge. This thesis investigates the aerodynamic and acoustic performance of a Boundary Layer Ingesting (BLI) propeller installed at the end of the fuselage of a transport plane, behind the vertical tail. The study focuses on the impact of unsteady blade loading on performance and explores whether increasing blade count or modifying blade sweep can mitigate drawbacks in a BLI configuration.
The development of numerical tools was the first step in this investigation. The aerodynamic tool, an enhanced Unsteady Non-Linear Vortex Lattice Method, accounts for viscosity and flow separation, while the acoustic solver uses Hanson's Helicoidal Surface Theory to model noise emissions from propellers in both isolated and installed conditions. Simulations were conducted on a modified 6-bladed XPROP-S. The velocity profiles at the propeller disk, used as inflow for the installed BLI analysis, were taken from CFD results of the fuselage with the vertical tail installed.
The complex inflow field led to periodic increases in blade loading, especially behind the vertical tail, causing oscillations in thrust and power. Increasing the blade count from two to six resulted in steadier performance and reduced force oscillations. In the installed configuration, the propellers exhibited a thrust-to-power ratio increase of 2% to 5%, with in-plane forces scaling with thrust and remaining within 3% of it. Noise emissions rose significantly after installation, with peak emissions shifting from the rotational plane to the propeller axis, where unsteady loading noise sources became more prominent. The noise level increase reached up to 46 dB during cruise for the 6-bladed baseline. While increasing the blade count reduced noise levels in isolated conditions due to lower propagation efficiency of steady loading noise, in installed conditions, unsteady loading noise sources counterbalanced this, leading to overall increased noise. Maximum noise emissions ranged from 32 dB (isolated, six blades) to 78 dB (installed, six blades). Sweeping the baseline blade backward at the tip and forward near the hub increased loading and thrust by up to 20%, particularly at the tips. In installed conditions, backward sweep reduced overall blade loading changes, while forward sweep increased them. Noise levels varied, with isolated conditions showing a slight increase and installed conditions experiencing up to a 4.7 dB reduction with backward sweep.
The analysis underscores the importance of accounting for unsteady blade loading and how the dominance of unsteady loading noise sources is influenced by loading oscillation amplitude, propeller geometry, and operating conditions.

An unintended yaw is a persistent accident characterised by an unexpected helicopter rotation around the yaw axis without the pilot’s intention and any technical malfunctions. Unintended yaw accidents are one of the top operational causes of helicopter accidents, causing serious damages and fatalities each year. This thesis in collaboration with Airbus Helicopters and the FAA does a numerical investigation of unintended yaw to provide a characterisation of the phenomena for different helicopter configurations with an open tail rotor and find an optimal recovery method. The simulations include trimmed flights and time domain flights to assess the yaw trim capabilities of the helicopter. Specific attention is placed on the tail rotor aerodynamics and demands. An uncontrollable unintended yaw did not appear for any of the evaluated flight cases and helicopter configurations, showing that the pilot always could trim the helicopter with sufficient pedal margin. In case of unintended yaw, applying immediate and maximum opposite pedal to the rotation of the helicopter could always recover the yaw rate to zero.

The effect of excluding the nacelle in tip-mounted propeller research can be modelled with Computational Fluid Dynamics (CFD) to quantify this effect on the wing performance and flow measurements. For this, the performance parameters of the wing in terms of lift and drag are analysed. Also, swirl angle and total pressure in the wake is investigated to understand the vortex behaviour. This is all done for a configuration set without a propeller, and also with a propeller installed in the form of a disk model.

Propeller-based propulsion technology is experiencing renewed interest owing to its superior propulsive efficiency in comparison to conventional jet engines. This phenomenon is attributed to the capacity to generate thrust by accelerating a significant volume of air through a small velocity differential. Additionally, owing to its compatibility with electrical power systems, propeller-based propulsion offers an opportunity to utilize more environmentally friendly energy sources and configurations like the distributed propulsion systems. To optimize the integration between the propeller-based propulsion system and the airframe, it is imperative to thoroughly understand the interactive aerodynamics of the propeller-wing system.

This thesis presents a comprehensive study on the aerodynamics of propeller-wing interactions, with a specific focus on leading-edge distributed propeller configurations.
The research was conducted through a comparative analysis, employing a single propeller-wing system, modeled based on the ATR 42/300 as the baseline. This involved comparing a conventional single tractor propeller configuration with a three-propeller leading edge distributed configuration. The methodology used is an unsteady panel method
solver, FlightStream, which is a commercially available software, allowing for an in-depth
examination of the two-way interactions between the propeller and wing (Full interaction mode), and allowing for a force-free wake.

The findings of the study highlighted significant aerodynamic benefits of the leading-edge distributed propeller configuration over the traditional single propeller setup. Notably, there was a 2.5% increase in wing efficiency and a 6.1% reduction in induced drag. Additionally, the propeller efficiency in the distributed system saw a 3% increase compared to the single propeller system. However, it’s crucial to note that these propellers operated at different, non-optimal points, which influences their comparative performance. A key result was the reduced power consumption of the three-propeller system, which required 8.1% less power to maintain steady level-flight conditions than the baseline single-propeller model. This finding suggests potential for increased efficiency in aircraft designs incorporating such configurations.

Ammonia shows great potential for decarbonizing the road transportation sector because it does not produce CO₂ emissions during combustion. On the other hand, ammonia-fueled engines emit gases such as (unburned) ammonia (NH₃), and nitrogen oxides (NO)_x, which contribute to air pollution and adversely impact human health, among other environmental effects. The aim of this work is to investigate the air quality impacts and human health trade-offs associated with potential emissions from an ammonia-fueled road transportation fleet of different vehicle categories. Specifically, we create a simplified emissions tool to quantify the NH₃ and NO_x spatial emissions from state-of-the-art ammonia engine developments. Next, the emissions are combined with spatial sensitivities, obtained from the adjoint of GEOS-Chem, to estimate the corresponding air quality impacts in terms of PM_2.5 formation and human health impacts with respect to premature mortalities.
The research findings indicate that the ammonia-fueled sector generally exhibits higher air quality and human health impacts compared to conventional transport. We estimate that the implementation of various ammonia engine configurations into the road transportation fleet in the USA in 2011 could lead to approximately 23 000 to 250 000 premature mortalities.
However, there is potential for mitigating air quality impacts of ammonia emissions through the use of post-combustion treatment methods or the adoption of ammonia-fueled heavy-duty vehicles. These approaches could help achieve air pollution levels comparable to those of fossil fuel vehicles while reducing the carbon footprint, offering future possibilities for an ammonia-fueled road transportation sector.

In recent years, there has been renewed interest in propeller research due to environmental concerns. Propellers are known for their low-speed efficiency and compatibility with electric motors. The utilization of regenerative energy during deceleration has been demonstrated to be beneficial for automobiles and has the potential to be applied to propeller-driven aircraft. This technology allows for the recharging of batteries and could increase the overall efficiency of the propulsion system by utilizing the regenerated energy in other flight maneuvers. The negative thrust mode of propellers has several additional advantages, including weight reduction, improved safety, and increased maneuverability. However, when operated in reverse thrust conditions, the performance of conventional propellers is suboptimal because they are designed for forward thrust. This suboptimal operation can lead to boundary layer separation on the blades, increasing broadband noise and potentially making it more dominant over tonal noise. To assess the relative importance between an isolated propeller's tonal and broadband noise sources under positive and negative thrust conditions, an experimental study was conducted using a scaled propeller setup in a low-turbulence wind tunnel (LTT). Aeroacoustic measurements were taken using a microphone array with 63 microphones placed in the floor and wall of the test section. The advance ratio was varied across different wind speeds at Reynolds numbers ranging from Re_c^0.7R = 0.8·10⁵ to Re_c^0.7R = 1.9·10⁵. Signal processing methods were used to analyze the data and quantify tonal and broadband noise sources, including fast Fourier transformation (FFT), phase averaging, beamforming, and blade element momentum (BEM) analysis. The results showed that the broadband noise component of the propeller significantly increased in negative thrust mode compared to positive thrust mode due to fully separated boundary layers. The tonal propeller components were often masked by interference from wind tunnel and motor noise, suggesting the need for further research to validate propellers in regenerative mode.

From the desire to reduce the impact of traveling on the environment and the increase in fuel prices over the past years, the propeller has regained interest as a propulsion mechanism in the aviation industry. Two main reasons can be found in their high propulsive efficiency and ability to combine with electric motors. The scaling of the motors is rather insensitive to the efficiency, allowing the propeller to be placed around the aircraft, resulting in new design freedoms.

The influence of the propeller slipstream can increase the aerodynamic performance of a propeller-wing system. Propellers with inboard-up rotational configuration are found to reduce the induced drag of the wing in propeller-wing systems compared to isolated wings. To increase the aerodynamic performance of propeller-wing systems and certify design choices, a detailed understanding of the relative contribution of the lift-induced drag and swirl recovery to the induced drag of propeller-wing systems is desired. A low-order numerical model has been used for a parametric study on propeller-wing systems. From the results follow that the gradient of the spanwise wing lift distribution is of influence on the amount of net swirl recovery that the wing can obtain. It is shown that when a propeller is placed in front of a wing section where the gradient of the isolated spanwise wing lift distribution is positive from root to tip, more swirl recovery can be obtained by the inboard-down rotating configuration. In this case, the difference in lift between the wing sections behind the two propeller sides is increased. The increase of the difference in the lift also increases the lift-induced drag of the wing. With low disk loadings, the contribution of the swirl recovery is found to be higher than the increase in lift-induced drag. Increasing the disk loading results in more significant differences in lift between the wing sections behind the propeller sides, such that the gradient of the spanwise wing lift distribution increases. From this increase, the contribution of the lift-induced drag can become more significant than the contribution of the swirl recovery of the wing, increasing the induced drag of the system.

The angular momentum or swirl in the propeller slipstream is an energy loss. An effective method to recover the swirl and increase the propulsive efficiency is to use Swirl Recovery Vanes (SRVs). Former research showed an over-prediction in SRV thrust by a lifting line theory (LLT) model compared to wind tunnel experiments. The LLT model assumes an unbounded flow field from minus infinity to plus infinity, while in reality the SRV flow field is bounded due to a small axial spacing between the SRVs and the propeller plane. Using a 2D correction method, based on the application of the Kutta–Joukowski theorem in an axially confined domain combined with the thin airfoil approximation, a correction in the angle of attack can be computed for each blade element of the SRV. The LLT model including the correction method could match the SRV thrust of the experiments. Additionally, the original LLT thrust prediction was met with a corrected pitch angle of the SRVS. An SRV in off-design conditions would result in different correction angles. For a smaller thrust setting of the propeller, the thrust of the SRV will also be lower, hence the correction angle will be smaller. To make the correction method also applicable in off-design conditions, a fixed correction angle would be more practical since the whole vane can be rotated with a variable pitch to match the appropriate correction angle for the corresponding thrust setting. The fixed correction angle was determined by taking an average of all correction angles along the blade radius and the thrust prediction showed good agreement, with a negligible thrust loss of the SRV compared to correcting the pitch angle for each blade element separately. Finally, in the airfoil profile optimization, it was found that the profile drag of the profile is of less influence on the SRV thrust, hence more design freedom can be used to select the appropriate airfoil profile for the SRV.

This thesis investigates the aerodynamics of a propeller-wing-flap system, spurred by the growing interest in propeller-driven aircraft and the potential introduction of distributed electric propulsion. The research focuses on the complex flowfield involving the interaction of the propeller slipstream with the main wing and flap at high-lift conditions. Using unsteady RANS simulations at a chord based Reynolds number of 2 million, the study explores the impact of a propeller slipstream on flap time-dependent boundary layer variations. The computational results are validated against experimental data, showing good agreement. The analysis reveals intricate details of the flow field, including propeller slipstream shifts and complex vortex systems contributing to flap stall mechanics. The study highlights the influence of these phenomena on the spanwise lift distribution and flap flow separation areas. The findings contribute valuable insights into the understanding of propeller-wing-flap interactions, yet emphasizing the need for further research to confirm and expand upon the current discoveries.

The ever-growing aerospace industry's urgent need to reduce greenhouse gas emissions has ignited a surge of interest in hybrid or fully electric propulsion systems. The electrification of aircraft introduces the possibility for energy to be recovered during phases of flight where no power input is required, and previous research has demonstrated the potential for small energy balance enhancements using dual role propellers. The design and operation of dual-role propellers involves considering two opposing load cases: positive thrust and torque during propulsive operation, and negative thrust and torque in regenerative operation. Thus, the ideal blade shape for maximizing performance in each opposing operating condition will be very different. Structural tailoring of the composite blades may be an effective approach for reducing energy consumption during operation in both regimes. Accordingly, the primary objective of this research is to determine the extent of dual-role propeller performance improvements that may be obtained through the application of aeroelastic tailoring. Sensitivity studies were conducted to convey an understanding of how dual-role propeller performance is affected through variations in structural designs (ply orientations and thicknesses). Optimization studies were subsequently performed to identify the extent of performance enhancements yielded solely through aeroelastic tailoring for flexible constant- and variable-pitch propellers of fixed geometry, assuming installation on a reference aircraft, and evaluated over multiple cruise distances for a climb-cruise-descent mission.

The thesis objectives were achieved through the development and application of an aeroelastic analysis and optimization framework. Blade element momentum (BEM) theory was used for the aerodynamic model with engineering corrections for compressibility, effects of rotation, root- and tip-losses, and the turbulent wake state. Excellent agreement was obtained from comparisons with a previous BEM code, and reasonable agreement in performance trends was observed through comparisons with experimental data during verification and validation. A modified version of PROTEUS, an aeroelastic tailoring code that was developed at the TU Delft, was used for the structural model. The aerodynamic analysis routine of PROTEUS was modified to instead use the developed BEM code for the evaluation of loads, sensitivities, and performance. The structural model of PROTEUS was modified to feature centrifugal forces and different input structures that are more conducive to the analysis of rotor blades. The structural model implemented during this project accounts for geometric nonlinearities, as well as nonlinear loads through the application of a corotational framework, and it is capable of accurately representing the detailed 3D blade as a reduced-order Timoshenko beam element mesh through its use of a cross-sectional modeller. Finally, a tightly coupled aeroelastic analysis procedure was developed and applied, which ensures convergence through the minimization of a residual vector using Newton's method, and analytical sensitivities for all loads were included in the analysis. Excellent agreement was obtained during verification studies for both the structural and aeroelastic analyses.

Results from the optimization and sensitivity studies indicate that the flexible blades constructed out of symmetric-unbalanced laminates yield a significant variation in thrust and power through the presence of bend-twist and extension-shear coupling, which results in an increasing change in twist distribution with increasing deflection or elongation. Only small variations in performance were observed from symmetric-balanced laminates, as the minimal amount of coupling resulted in negligible twist deformations, which confirms that the presence of bend-twist and extension-shear coupling drives variations in performance obtained through aeroelastic tailoring. Furthermore, it was found that the presence of an aerodynamic wash-out effect augments the range of advance ratio values corresponding to high-efficiency operation during both propulsive and regenerative modes. An opposite trend was observed in the presence of a wash-in effect. Lastly, due to the significantly decreased loading in descent, combined with its small contribution towards the total mission energy consumption, effects of aeroelastic tailoring are significantly greater in propulsive conditions (climb and cruise) in comparison to regenerative conditions.

From optimization, it was found that the flexible constant-pitch propeller features an energy consumption that is between 0.7% and 1.5% lower than the energy consumption of the rigid propellers. Despite this consistent decrease in energy consumption, all optimal flexible constant-pitch propellers were found to regenerate between 3% and 25% less energy than the rigid variable-pitch propeller, and between 3% and 10% less energy than the rigid constant-pitch propeller. This further suggests that the application of aeroelastic tailoring is most-suitable for improving performance in propulsive mode, as the enhanced performance yielded in propulsive mode outweighs the degraded performance in descent by a significant enough margin to enable the flexible constant-pitch propeller to outperform all rigid propellers. Moreover, the flexible variable-pitch propeller naturally yielded an even better performance than the constant-pitch propeller, with a total mission energy consumption that is between 1.5% and 2.0% less than the energy consumption of the rigid propellers. It has thus been shown that aeroelastic tailoring can yield noticeable improvements in propeller performance, at least for the fixed mission profile and reference aircraft that was studied.

Propeller propulsion systems combined with Boundary layer ingestion (BLI) have been proposed as a propulsive system to reduce the CO2 emissions of aircraft by 50% by 2050. BLI leads to increased disturbances at the propeller disk and causes more noise due to the fluctuating blade loading. Using the APPU project as a test case, unsteady inflow is used to determine whether a metric to lower the blade loading fluctuation on an airfoil level is possible. Therefore, an optimisation was created using an Euler solver reliant on the harmonic balance method and the adjoint method to lower the computing time of the simulation. The combination of these methods has proven successful in turbomachinery applications. The optimisation scheme uses the modelled APPU inflow conditions to optimise for the drag coefficient while lowering the Root Mean Squared Error of the lift coefficient during the simulations by applying a constraint in various optimisation runs.