This study investigates the aerodynamic benefits of integrating trailing edge camber morphing on the strut of a regional strut-braced wing aircraft designed to cruise at Mach number of 0.5. Strut-braced wings are recognized for their weight advantages in high aspect ratio designs compared to the equivalent cantilever wings since the strut decreases the main wing’s bending moment. Hence, the induced drag component can be reduced due to the high aspect ratio without increasing the weight of the main wing. However, the strut increases the parasite drag component highlighting the need for innovative methods to improve the strut-braced wing overall aerodynamic efficiency. Recent studies have shown the significance of strut shape in the overall drag reduction and the necessity of maintaining high aerodynamic efficiency in off-design conditions. In this work, a genetic algorithm was utilized in conjunction with a mid-fidelity aerodynamic model to optimize the morphing strut trailing edge geometry across a range of climb and cruise conditions. The optimization objective was the minimization of drag and the design variables were the equivalent trailing edge deflection angles in seven sections of the strut. The results demonstrate a drag reduction of 0.5% to 3% both in climb and cruise. For lift coefficients below 0.8, the drag reduction is mainly attributed to the redistribution of the loading and the induced drag component reduction. In contrast, at lift coefficients above 0.8, the parasite drag component decreases due to the increased region of laminar flow over the upper wing surface.@en

High aspect ratio strut-braced wing aircraft can significantly reduce the induced drag while limiting the weight penalty of increasing the wingspan. As part of the Hybrid Electric Regional Wing Integration Novel Green Technologies (HERWINGT) project, a multifunctional morphing strut is being investigated. In this study, an optimization framework is proposed to define the thickness distribution of the morphing trailing edge of the strut to achieve the desired operational shapes while considering laminate manufacturing guidelines and material allowables. The optimizer finds designs capable of achieving the objective shapes and provides load and mass estimations that can be used to make design decisions.

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Large wind turbines face more intricate atmospheric conditions with turbulent coherent structures sized similarly to the rotor diameter, posing loading challenges. The present study assesses twelve distinct wind fields using the Large Eddy Simulations (LES) and International Electrotechnical Commission (IEC) Kaimal model scaled to their LES counterpart. The hub height wind speed in the different cases was set to 8.5 m/s (below-rated), 11.5 m/s (at-rated), and 14.5 m/s (above-rated). In a previous study, it was found that the unscaled IEC model-based wind field is conservative and scaled IEC model-based wind fields were found to yield different loads than upon use of LES-based wind fields in different atmospheric stability conditions. The present study aims to understand these differences. Utilizing Spectral Proper Orthogonal Decomposition (SPOD), the original wind fields were decomposed and reconstructed to study the influence of large and small coherent structures represented by their distinct frequencies. SPOD analysis was complemented by wind field spectral analysis considering atmospheric surface layer height, integral length scales, and co-coherence estimates. Integral length scales in the scaled IEC Kaimal model were found to be half of those in unstable atmosphere LES wind fields. The aero-elastic impact on the IEA 22 MW reference wind turbine with a 280 m rotor diameter was evaluated. The analysis reveals that large coherent structures, particularly low-frequency (≤0.06 Hz) ones, significantly impact wind turbine loads, contingent upon atmospheric stratification. Compared to the scaled IEC Kaimal model wind field, the maximum tower fore–aft bending moment and the maximum blade root flap-wise bending moment were found to be higher, for example, by 10% and 5% respectively in an unstable atmosphere during below-rated wind turbine operation. In the same scenario, standard deviation of the tower fore–aft bending moment was found to be higher by up to 50% while standard deviation of the blade root flap-wise bending moment was found to be lower by up to 25%. These findings underscore the critical importance of accurately modeling atmospheric turbulence and its coherent structures for more reliable design and operation of large wind turbines.

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This study investigates the aerodynamic performance of switchable vortex generators (SVGs) operated in spoiler configuration for load alleviation at transonic speeds. Using three-dimensional computational fluid dynamics (CFD) simulations, the effects of design parameters - including the height, aspect ratio, and spacing between the vortex vanes - are analysed on a simplified wing geometry, modelled as a straight extrusion of a supercritical airfoil. The analysis demonstrates that finite-span spoiler devices such as SVGs can effectively reduce the generated lift in cruise conditions, but their performance is strongly affected by geometric properties. Distinct aerodynamic regimes can be determined by placing a SVG of varying height and aspect ratio on the wing upper surface, characterised by different degrees of flow separation downstream of the device. Lift reduction becomes significant only when the size of the vortex vane is such to trigger full flow separation. The aerodynamic behaviour induced by a single SVG is further examined under high-speed off-design conditions, showing that larger vortex vanes induce full flow separation at lower angles of attack, while smaller SVGs can lead to sharp lift variations at higher incidence. The interaction between multiple SVGs is found to be significantly influenced by their spacing and aspect ratio, with the wall ratio emerging as a critical parameter. Smaller SVGs are most effective at high wall ratios, where they can generate a more uniform flow separation across the upper surface. In contrast, larger devices perform better at low wall ratios, where they can trigger full flow separation independently of their mutual interaction.@en

Hybrid- or fully-electric propeller-based propulsion systems have recently gained interest as an option to reduce greenhouse gas emissions within the rapidly expanding aerospace industry. The electrification of aircraft enables the possibility for energy harvesting during flight phases where no power input is required. The use of aircraft propellers to harvest energy was first suggested by Glauert [1] in 1926, although there was no feasible technology at the time of his research to implement the idea. Seventy years later, MacCready [2] and Barnes [3]–[5], revisited the concept in a battery electric and self-launching sailplane, which could operate its propellers as energy harvesters during descending flight. Both MacCready and Barnes found that the optimal propeller geometries for energy-harvesting and propulsive operation significantly differ from each other. Recently, Erzen et al. [6] were able to obtain a 19% decrease in energy consumption during the ascend/descend flight pattern with a rigid propeller designed specifically for propulsive and energy-harvesting operation in comparison to a conventional propeller. The observed performance improvement, however, heavily depends on the selected flight pattern. The proposed paper will investigate the potential for aeroelastic tailoring of composite blades to improve the performance of propellers operating in propulsive and energy-harvesting modes, considering a realistic mission profile of a typical general aviation type of aircraft. To assess the effect of the mission profile on the propeller design, the mission profile was varied by changing the length of the cruise phase relative to the ascend and descent flight phases. To obtain an optimal propeller design featuring tailored composites, an aeroelastic model [7] was assembled by closely coupling a nonlinear Timoshenko beam model with BEM theory. The model was embedded in an optimisation routine considering lamination parameters and pitch setting as design variables, while the propeller geometry in terms of spanwise chord and twist distribution was kept constant. In addition, both fixed- and variable-pitch propellers were considered during optimization studies involving the full mission, and optimal blade designs corresponding to each individual mission segment were also obtained. The collected results confirm that composite tailoring can noticeably improve the performance of dual-role propellers, especially for mission profiles featuring relatively short cruise flight phases through the reduction of energy consumption by up to 2.0% with respect to the baseline rigid propeller. As the cruise distance is increased, maximum decreases in energy consumption are reduced to 1.5%. Lastly, it is interesting to observe that composite tailoring dominated by cruise distance has a positive effect on the performance during the ascend flight phase as well.@en

A tightly coupled aeroelastic design code for composite propeller blades was developed, verified, and used to perform design sensitivity studies. The design code features a structural model that accounts for geometric nonlinearities through the application of a corotational framework, nonlinear responses to loads, and a cross-sectional modelling approach to accurately represent the detailed 3D blade structure as a reduced-order Timoshenko beam element model. Blade element momentum (BEM) theory was used to evaluate aerodynamic loads, which are mapped onto the structural mesh. The nonlinear aeroelastic analysis routine uses Newton’s method to converge on a solution, with analytical derivatives for all applied loads. Excellent agreement with other analysis methods was shown during verification studies for all developed models. During validation, performance trends obtained from BEM were consistent with experimental results, with a maximum error of 20% at operating conditions under consideration during this research. The use of either symmetric-unbalanced or symmetric-balanced laminates was considered during sensitivity studies. Small variations in performance compared to the rigid propeller were observed from blades constructed out of symmetric-balanced laminates, as the minimal amount of bend-twist and extension-shear coupling resulted in small twist deformations. Conversely, propellers constructed out of symmetric-unbalanced laminates were shown to yield a noticeable variation in thrust and power compared to the rigid propeller due to the presence of bend-twist and extension-shear coupling, which results in coupling between twist and blade axis deformations. The presence of an aerodynamic wash-out effect was also found to alleviate blade loads, resulting in a lower power requirement at a given thrust setting, and an opposite trend was observed in the presence of a wash-in effect. The proposed analysis framework may be applied towards more extensive design studies or optimization in future projects.

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Recently, Wilson et al. [1] suggested the use of an active hinged folding wingtip device on aircraft wings, with the goal of benefiting from the aerodynamic efficiency of high-aspect ratio wings while reducing the peak loads that are experienced at the wing root in the presence of gusts. The dynamic load reduction potential of this approach has been demonstrated successfully in several studies, e.g., in [2,3]. In these studies, the timing of the hinge release with respect to the gust encounter has been identified as an important performance parameter, motivating further research on this topic. So far, the experimental data from wind tunnel measurements on the hinged folding wingtip that are available in the published literature are limited to only a few parameters, such as the wing root bending moment or the wingtip fold angle. In this study, the aeroelastic gust response of a hinged folding wingtip device will be analyzed based on a wind tunnel experiment performed at Delft University of Technology (see Fig. 1). The measurements in the wind tunnel are conducted with an integrated optical approach [4] that provides measurements of the dynamic response of the structure via tracking optical markers, and for the first time, of the flow field around the folding wingtip. The goal of this research is to provide detailed insights into the aeroelastic gust response of the folding wingtip at different hinge release timings and to produce reference data for numerical prediction models, in particular with respect to the distribution of the unsteady lift force acting on the folding wingtip.@en

This paper provides an insight into ongoing research aimed at designing a morphing wing with the ability to continuously adapt its aerodynamic shape. The wing is targeted at a general purpose unmanned aerial vehicle. The morphing wing concept outlined in the paper is based on continuous camber changes of the wing leading and trailing edges, allowing optimal performance in different flight regimes. The aeroelastic tailoring method is used to design the load carrying structure of the wing in order to define the optimal stiffness and strength of the structure, which are considered as fixed in subsequent design steps. The research proposes a novel modular design approach that combines aerodynamic shape optimisation and aeroelastic considerations for designing morphing wing surfaces.@en

Shape sensing techniques enable the real-time reconstruction of wing displacements based on measured strain. As wing designs become more flexible, they may at some point exhibit geometric non-linear deformation. This eventually leads to erroneous displacement estimates if applied methods rely on the assumption of linear deformation. In this research, the Incremental Modal Method (IMM) is presented which accounts for the change of the employed mode shapes due to structural deformation. The method is applied on the finite element model of a high aspect ratio wing undergoing geometric non-linear deflections in flap-wise bending. In the process, a setup of virtual strain sensors is presumed which is representative as instrumentation in experiments. Along a reference line of the wing, the displacement estimates of IMM are compared to results obtained using the Modal Rotation Method (MRM), another shape sensing scheme recently developed for the non-linear regime. For the chosen segmentation and virtual instrumentation of the investigated wing, IMM proves to be a promising candidate for realtime displacement reconstruction in experiments, provided that mode shapes in intermediate deflected states can be determined. @en

This study explores the implementation of aeroelastic tailoring in the design of a regional aircraft featuring a strut-braced wing (SBW). Making use of the aeroelastic optimisation framework from Delft University of Technology, PROTEUS, the research addresses two distinct cases. The first case involves a simplified SBW geometry to validate the modifications of PROTEUS, which were conducted to include the strut in the aeroelastic analysis. Static and dynamic load cases are compared with a NX Nastran aeroelastic model, showing good agreement in displacements, strains, and gust response. In the second case, the study investigates the weight-saving potential of aeroelastic tailoring in an SBW aircraft based on the ATR-72. Three optimisation scenarios, allowing various laminate types, are examined: unbalanced symmetric laminates, balanced symmetric laminates, and a thickness optimisation with a prescribed balanced symmetric stacking sequence. The results reveal that the prescribed stacking sequence limits stiffness tailoring, thereby also reducing potential weight savings. Moreover, the study shows how the presence of a strut reduces wing deflections, limiting the effectiveness of aeroelastic tailoring.@en

This paper presents an experimental investigation into the aeroelastic behavior of an innovative wind turbine design featuring a downwind two-blade rotor with a teetering hub mounted on a tower with adjustable tilt. The rotor model incorporates two sets of elastic blades—stiff and flexible—for scaling purposes, each instrumented with strain gauges and accelerometers. Ground and wind tunnel tests were conducted to analyze the aeroelastic response. Static tests exhibited discrepancies between measured and numerically predicted displacements, with maximum displacements near the tip exceeding numerical predictions by 14% and 31% for flexible and stiff blades respectively. Frequency differences between measured and numerically simulated elastic modes ranged from 0.5% to 18% for both blade sets, as determined by ground vibration tests. Wind tunnel tests revealed the dominance of rotational speed harmonics, particularly the second harmonic, in the blades’ periodic response. A sensitivity analysis was also carried out with respect to tower tilt angle, rotational speed and blade pitch angle, for both blade sets at a range of tip-speed ratio values. The static response of the system, as captured by the generated power and thrust, was primarily sensitive to tower tilt angle variation and to a lesser extent blade pitch angle. Conversely, the tip-speed ratio in conjunction with rotational speed were found to dictate the dynamic response, influencing the azimuthal position and magnitude of the maximum bending moment at the blade root. Finally, no dynamic aeroelastic instability was observed during wind tunnel tests.

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In line with recent advancements in aviation, which lead to more fuel-efficient aircraft, this paper presents a novel continuous movable parameterisation methodology. The methodology takes advantage of the ability of the doublet lattice method (DLM) to describe aerodynamic forces using downwash. The movables are described in the continuous space using a downwash distribution generated using a B-spline surface. To demonstrate and assess the movable modelling methodology, the U-HARWARD aircraft model has been used, with the performance of the continuous parameterisation compared to a reference movable parameterisation for roll control, manoeuvre load alleviation and cruise performance. The results show that the continuous parameterisation can determine a downwash distribution that is at least equal in performance – during roll – or has better performance – for manoeuvre load alleviation and cruise performance – than the reference parameterisation. The continuous parameterisation showed a 3 percentage points improvement with respect to the reference parameterisation for manoeuvre load alleviation and a 2.4 percentage points improvement for the induced drag coefficient. The results in the paper demonstrated the successful application of a movable parameterisation methodology, which can be applied to an aircraft for which only the planform and initial structural parameters are known.@en

Metamaterials show a considerable potential in the field of complex optimization of aerospace structures. To fully exploit this potential, the authors present a novel approach to modeling the structural response of a sandwich panel with metamaterial core and CFRP skins that could be used within a single-step optimization process. The proposed approach is illustrated using a model of a panel with aluminum honeycomb core. Obtained results confirm the high potential of the inclusion of the core optimization into the optimization framework. Simple preliminary validation utilizing the finite element analysis presented in the closure of this study yielded a satisfactory agreement with the results of the proposed analytical model. The maximum reached difference of five percent can be attributed to a different shape of deformation of the honeycomb core within the sandwich as opposed to a deformation of the honeycomb core alone. @en

With the growing trend towards larger wind turbine rotor diameters, the impact of wind shear on rotor performance and loads becomes increasingly significant. Atmospheric stability strongly influences wind shear, leading to higher wind shear under stable atmospheric conditions. In this study, the aeroelastic performance of the IEA 22 MW rotor is assessed under inflow conditions generated by different methods. Inflow conditions were generated using turbulence models specified in the IEC Standards and also by Large Eddy simulations. Standalone OpenFAST simulations were conducted with the respective inflow conditions. It was found that at rated and above-rated wind speeds, the time-averaged wind turbine design loads were higher in stable atmospheric conditions, in comparison to the IEC NTM inflow conditions, while the opposite held for below-rated wind speeds. Specifically, the time-averaged root flapwise bending moment and rotor thrust were found to be higher by up to 7% in stable atmospheres. However, maximum design and fatigue loads were considerably higher in the IEC NTM case due to elevated turbulence levels. Compared to the IEC NTM case, the damage equivalent root flapwise bending moment was found to be 30% to 70% lower in the different scenarios.

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In modern aircraft design, electro-mechanical actuators are increasingly being considered as an alternative to conventional, hydraulic actuation systems for flight control surfaces. While offering advantages in terms of weight reduction and increased efficiency, these actuators are also characterised by a higher sensitivity to nonlinear effects. Actuator models can strongly affect the effectiveness of control function such as gust load alleviation or flutter suppression, it is essential to correctly understand, model and identify nonlinearities in the actuator response, as well as to integrate nonlinear actuator models into aeroservoelastic models. This contribution explores the nonlinear effects of rate and acceleration limits in actuation systems, focusing on the actuator steady-state response to sinusoidal input and the effectiveness of closed-loop control systems. The saturation regimes determined by rate and acceleration limits are investigated, and analytical formulations are derived for the nonlinear actuator response and the boundaries of these regimes within the two-dimensional parameter space defined by non-dimensional rate and acceleration limits. Describing functions for each regime are determined in a closed form, establishing the relationship between actuator input and output in the frequency domain. Combined rate and acceleration limits are found to induce a low-pass filter behaviour in the actuator, with a -40 dB/decade roll-off, and can lead to nonsmooth phase dependence on frequency. The describing functions of combined rate and acceleration limits are applied to the analysis of an aeroservoelastic wing model developed for gust load alleviation (GLA) purposes. The effect of the actuator limits is investigated by evaluating the onset point of the nonlinear behaviour and an equivalent describing function for the entire actuator-plant-control feedback loop. The resulting findings illustrate that rate and acceleration limits can substantially affect the performance of closed-loop systems, leading to phenomena such as jump resonances when partial-to-full saturation regime transitions occur, and thereby constraining the effective frequency range of the GLA control systems. @en

This research investigates the application of aeroelastic tailoring to enhance the post-control surface reversal regime on a mid-range aircraft. Conventionally, active Maneuver Load Alleviation (MLA) is achieved through control surface actuation, while passive MLA utilizes structural modifications at the material or layout level to exploit wing wash-out deformation. Previous studies have demonstrated the significance of high control effectiveness in active MLA and the limitations of composite tailoring in passive MLA due to roll control authority constraints which typically result in stiffer wings with moderate mass savings. The aeroelastic optimization framework PROTEUS, developed at TU Delft, is employed to enhance operation in the post-control surface reversal regime. This is done to capitalize on increased control authority and thus promote load alleviation. The approach taken in this study is to identify critical constraints and assess the advantages of this strategy while acknowledging the technology’s immaturity, particularly its challenges in maintaining roll control effectiveness in certain flight envelope sectors. The results demonstrate significant mass savings in active MLA within the post-control surface reversal regime compared to conventional active MLA and highlight the substantial impact of the cruise-twist constraint on enhancing this regime. @en

This paper investigates the impact of introducing a switchable vortex generator (SVG), acting as a mini-tab, on the aerodynamic performance of a high-aspect-ratio wing's outer section in transonic regime. A parametric study is conducted employing computational fluid dynamics 2D simulations, focusing on the aerodynamic effects of changing the chord-wise position and height of the vane of a SVG located on the airfoil upper surface in both nominal cruise conditions and for varying angles of attack. The analysis reveals that mini-tabs can strongly affect the aerodynamic forces produced by the wing section, showing great potential for load alleviation and control, but also emphasising the need for a careful parameter selection to reduce undesirable effects such as the generation of shock waves. In cruise conditions, lift reduction increases with the vane height and has its maximum for chord-wise positions at 60% of the chord-length. However, SVGs located in the first half of the chord-length yield more robust performance for varying angle of attack, without sharp lift variations or generated shock waves, and a delayed stall onset. High SVGs (≥3% chord-length) can also lead to strong shock waves on the airfoil lower surface at small or negative angle of attack, while small SVGs (@en

The present study regards a novel wind turbine design featuring a two-bladed rotor on ate etering hub and a yawed tower. A reduced order modelling methodology is proposed for the equation of motion, using a lumped parameter approximation to derive expressions for the structural, rotor dynamic and geometric stiffness terms. The analytical expressions are validated numerically. In addition, a methodology is developed for aero elastic scaling of the rotor for use in wind tunnel tests. This results in two blade design templates, a "stiff" and a "flexible" design focusing on the vibration behaviour and deflected shapes respectively. The templates are designed to be 3D-printable as a single part. Design optimisation was performed in MSCN as tran, yielding two rotor designs, each aiming to match the non-dimensional parameters of interest. The stiff rotor matches the flap wise and torsional natural frequencies within 2.7%error, but has a mismatch in the edgewise mode, as well as the mode shapes and anti-symmetric modes. The flexible rotor is capable of capturing the target normalised displacement profile, at reduced structural mass, partially alleviating the mismatch in Lock number.

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The ram air inlets flaps are used in some aircraft to modulate the amount of ram air cooling the Environmental Control System. The current flap design features two metallic plates connected with a hinge. The present work studies an alternative design that replaces the metallic plates with a single composite laminate with morphing capabilities. An optimization framework is proposed to define the thickness distribution of the laminate taking into account the desired operational shapes, manufacturing guidelines and maximum allowable strains. This framework combines linear and nonlinear simulations to account for the large deflections while limiting the computational cost of the optimization. The results of the optimization framework are discussed at the end of the paper and next steps are formulated.@en

A new flutter test version of the Parametric Flutter Margin (PFM) method, specifically applied to wings undergoing large deflections is presented. The PFM method adds a stabilising parameter, such as a stabilising mass, to the model such that the flutter velocity is increased. By exciting the stabilising mass in one of the primary (i.e., x, y and z) directions while simultaneously measuring the response in these directions and repeating the excitation in other directions, the flutter margins that are associated with the original model can be determined. To demonstrate the method a wind tunnel test campaign was performed at TU Delft using the Delft Pazy Wing which can exhibit large nonlinear deflection, onto which a flutter pod consisting of a shaker and stabilising mass was placed at the mid-span position at the leading edge of the wing. During the test campaign, three test series were performed. The first identified the flutter boundary through direct flutter tests, with the flutter onset and offset velocities being determined by actually hitting flutter that turned into an LCO. SISO and MIMO PFM tests were then performed to obtain the nominal flutter boundaries without actually hitting flutter, showing a maximum difference of 4.4 % between each other at an angle of attack of 6°. The difference between the MIMO and SISO PFM was found to be increasing with increasing angle of attack, which was as expected. Compared to the directly measured flutter tests, the MIMO PFM results identified a flutter velocity of 4.8 % lower than the directly measured flutter offset velocity at an angle of attack of 4°, and the SISO PFM results identified the flutter velocity to be 8.2 % lower than the offset velocity at 4° angle of attack. The PFM-identified flutter frequencies showed a difference of less than 2 % compared to the direct flutter test, with the difference in identified flutter frequency between the SISO and MIMO PFM reaching a maximum of 2 %. The acquired data shows the potential of the PFM method for performing safer, shorter and consequently cheaper flight tests for the certification procedure of new aircraft configurations.@en