We use feature-based modeling framework for control of loads on aeroelastic wings in the presence of unsteady wind gust disturbances, leveraging interpretable reduced-order-model system identification techniques without relying on black-box machine learning techniques. Unlike prior formulations, we explicitly include the dominant disturbance, such as a gust, as a control input within the model, allowing the controller to respond adaptively and in anticipation to external forcing. To this end, model predictive control (MPC) could be used in the low dimensional latent space of features, whose dynamics are identified partly by sparse identification of nonlinear dynamics with control (SINDYc) and linear parameter-varying system (LPV). As a proof of concept, the methodology is applied to system identification of smart vortex generators (SVGs) for mitigating transient gust loads on an aeroelastic wing section in CFD simulations. This methodology offers a promising path toward real-time mitigation of atmospheric disturbances in next-generation flight systems.

Accurate modeling of atmospheric turbulence is critical for the design and operation of next-generation large-scale wind turbines, particularly those exceeding 15 MW rated capacity and spanning well above the atmospheric surface layer (typically 10 − 20% of the atmospheric boundary layer (ABL)). In this study, Large Eddy Simulations (LES) were performed to investigate turbulence characteristics at high altitudes, up to 300 m above ground level — a region increasingly relevant for large turbine rotors. Turbulence coherence was analyzed and compared with field measurements to assess the fidelity of numerical predictions. Coherence estimates from LES were validated against lidar-based measurements obtained under stable, neutral, and unstable atmospheric conditions. Results show good agreement in the coherence decay rates and cross-spectral characteristics, with notable discrepancies only at very low frequencies (on the order of several 10^(−4) Hz) and large spatial separations (on the order of several 10^(2) m). Consequently, a LES-tuned empirical lateral coherence model is proposed, featuring distinct coherence decay rates for each atmospheric stability regime (stable, neutral, and unstable ABL), offering improved representation of turbulence structures across a range of operating conditions. These findings provide a valuable reference for refining turbulence models for improving load estimation methodologies for next-generation wind turbines operating at hub heights above 200 m.

Current advances in the structural optimization of aircraft structures have led to the introduction of sandwich panels into the optimization process. This study attempts to extend the possibilities of sandwich optimization by proposing an analytical model which predicts the homogenized properties of a sandwich panel with a honeycomb core and CFRP skins. The model is based on a combination of Classical laminate theory and a 1-D beam model of the honeycomb core. The finite-element equivalent of tensile and shear tests is used to validate the proposed model on a broad range of core geometries with different combinations of core thickness, wall angle, cell elongation, and cell wall thickness. The results of 425 different geometries showed the overall precision of the proposed model, highlighted effects in the behavior of the core that drive the sandwich properties further from the predicted values, and suggested which parts of the model are suitable for optimization and where are their limits of applicability.

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.

This paper investigates the impact of introducing a switchable vortex generator (SVG), acting as a minitab, 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 two-dimensional simulations, focusing on the aerodynamic effects of changing the chordwise 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 minitabs can strongly affect the aerodynamic forces produced by the wing section, showing great potential for load alleviation and control, but also emphasizing 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 chordwise 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 (greater than or equal to 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 (less than 1% chord length) can generate normal shock waves on the upper surface, with limited lift reduction in cruise conditions and at higher incidence.

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.

Correction notice The CL in the title of Fig. 7(b) was corrected from 0.4 in the original version to CL=1.0. (a) Climb local lift spanwise distribution at CL=1 0 0.2 0.4 0.6 0.8 1 0 5 10 10-3 0 0.2 0.4 0.6 0.8 1 0 5 10 10-3 (b) Solid line (suction side)-dashed line (pressure side) Fig. 7 Local lift coefficient distribution with a selected friction coefficient of one section.

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.

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.

There are technical applications where structures undergo deformation in the geometrically non-linear domain. This is the case for high-aspect-ratio wings, which may play a more important role in the future aircraft designs. Shape sensing methods can estimate the deflection of these structures during operation, if a direct measurement of the displacements is inconvenient or not possible. For the geometrically nonlinear range, the modal rotation method has been proposed as a candidate suitable for slender structures. The method superposes modal rotation increments of segments along the length of the structure, typically obtained from a finite element model. If the method is applied model-free, based on modal rotations identified from test data, the variability of the modal rotations leads to uncertainty in the displacement estimates. The present study illustrates how displacement output uncertainty can be expressed using linearised propagation formulae, relying on the prerequisite that the modal rotations exhibit a normally distributed and independent scatter around their mean. This uncertainty propagation is investigated in the shape sensing of a high-aspect-ratio wing model, and verification through Monte Carlo simulations demonstrates that the derived expressions accurately propagate the uncertainty from variable modal rotations. Consequently, these expressions can be applied to specific shape sensing tasks in experiments where this variability can be recorded.

Shape sensing techniques allow for the time-efficient reconstruction of displacements based on measured strain data. There are technical applications, where the structure of interest is deformed in the geometrically non-linear domain. In aeronautics, this is the case for high-aspect-ratio wings, which are more frequently found in future designs. Only shape sensing methods that specifically take the non-linearity into account, can deliver appropriate displacement estimates for such application. A shape sensing method based on the linear modal approach can be utilised incrementally to capture the geometric non-linearity; it has therefore been denoted incremental modal method (IMM). This paper presents analytical relations for the uncertainty propagation for the various input quantities of the method, specifically strain mode shapes, displacement mode shapes, and measured strain. Deterministic shape sensing and uncertainty propagation are demonstrated using data obtained with a finite element model of a high-aspect-ratio wing experiencing geometric non-linear deflections in flapwise bending. Virtual strain and acceleration sensors are assumed for this setup, imitating the instrumentation conceivable for experimental work. The results obtained by analytical propagation are compared to Monte Carlo simulations for the purpose of validation. The derived propagation formulas make it possible to follow the evolution of the uncertainties over the number of increments. Given that the variability of the input quantities is known, the number of increments that minimise uncertainties can be determined for a model-free application of the shape sensing. Together with the deterministic estimates provided by an FE model, it is possible to determine the ideal number of increments for a specific shape sensing application in the geometrically non-linear domain.

Synthetic wind fields generated for wind turbine simulations do not satisfy incompressibility condition, thus, are not divergence-free. This results in spurious pressure fluctuations when input as a boundary condition to, for example, incompressible large eddy simulations (LES). This study investigates the impact of divergence-free correction on synthetic wind fields and their influence on wind turbine loads. Although divergence-free correction methods exist, they often modify the wind field energy spectrum and unsteady characteristics. Ongoing research addresses these challenges, but the acceptability of such changes and their impact on wind turbine loads has not been adequately studied. This work enforced incompressibility using the Helmholtz–Hodge decomposition, solved through spectral and spatial methods. An efficient Fourier-based spectral method was implemented, validated, and tested against the traditional finite difference method used for the spatial approach. Synthetic wind fields based on three coherence models were analyzed under three turbine operating conditions. An aeroelastic analysis of the IEA (Formula presented.) MW wind turbine was performed in the (Formula presented.) wind fields before and after divergence correction. Spectral analysis revealed a reduction in energy at specific frequencies after the correction for incompressibility. Additionally, the standard deviations of the wind velocities changed (despite similar means), consequently affecting the aeroelastic turbine response. A new iterative correction method is proposed to mitigate these effects, which preserves first- and second-order statistics while enforcing a divergence-free condition. This method is recursively applied, maintaining RMSE changes to the wind field within user-specified bounds. Key findings show that the iterative method yields an excellent match in the longitudinal wind field energy spectrum and a closer match in wind field standard deviation across the rotor, reducing discrepancies in turbine response. Some discrepancies in the lateral and vertical velocity components' higher order statistics were observed. Standard divergence correction (without RMSE constraints) led to a decrease of up to 20% in the tower fore-aft moment, while the proposed method reduces this change to −10%. The tower top side-side moment was found to increase by (Formula presented.) % by using the former approach, while the proposed correction reduced this increase to (Formula presented.) %. Blade root flap-wise bending moment was less affected (up to 5% reduction). Divergence-free wind fields, even with similar statistical properties, influence aeroelastic loads. The proposed method aims to achieve physically consistent and more comparable wind field analyses and resulting wind loads.

In the development of large battery-electric aircraft, integrating the batteries into the wing is a crucial decision, as it results in a lighter wing structure due to bending relief. To understand the influence of wing-integrated batteries on wing structures, this paper presents a study on the wing structural design and sizing of the Elysian E9X aircraft configuration. In this study, the baseline wing design is defined, and the critical load cases for wing sizing are identified. Wing structural sizing is performed using an in-house aeroelastic optimization tool. The objective of the optimization is to minimize wing mass by adjusting the thickness of the wing design sections, subject to various design constraints, including structural strength, buckling, and aeroelastic instability. Sensitivity studies on wing mass with respect to key design parameters are conducted. The study results confirm that placing the batteries in the wing results in a significant wing structural mass reduction compared to housing the batteries in the fuselage. The wing mass sensitivities to other design parameters, such as the spanwise position of the main landing gear, may serve as input for the next round of aircraft design.

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.

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.

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.

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.

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 (

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.