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The effects of the wing skin distortion on the boundary layer of a highly flexible wing are analyzed in a wind tunnel experiment using infrared thermography measurements. Considerable differences in the boundary layer flow are observed when comparing the sections of the wing near the ribs, where the design shape of the wing is preserved, and in between the ribs. At the spanwise locations between the ribs, the sectional wing shape distorts and triggers boundary layer transition close to the leading edge. The differences between the design behavior of the wing and the experimental results of the boundary layer analysis demonstrate the need for considering the skin deformation and its effects on the boundary layer flow when designing highly flexible wings., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Aerodynamics

This study presents an aeroelastic wind-tunnel experiment to identify the influence of the wing stiffness and hinge release threshold on the gust load alleviation performance of a folding wingtip design. Five models with different stiffness and tailoring properties are tested, and the wing root bending moment at different conditions is compared to the response with the locked-hinge condition to assess the impact on the gust load alleviation capabilities of the folding wingtip. The results show that the structural properties do not have an important impact on the peak load alleviation but the hinge release threshold and timing do. Releasing with the correct timing can reduce significantly the peak loads. However, the dynamics of the system are affected by this release; the flutter speed is decreased, and, although the performance can improve, load oscillations increase, which can be considered detrimental for reasons such as fatigue or passenger comfort., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Aerospace Structures & Computational Mechanics, Aerodynamics

The aeroelastic response of the Delft-Pazy wing to steady and periodic unsteady inflow conditions is analyzed experimentally. The Delft-Pazy wing is a highly flexible wing model based on the benchmark Pazy wing (Avin, O., Raveh, D. E., Drachinsky, A., Ben-Shmuel, Y., and Tur, M., “Experimental Aeroelastic Benchmark of a Very Flexible Wing,” AIAA Journal, Vol. 60, No. 3, 2022, pp. 1745-1768) and exhibits wingtip displacements of more than 24% of the span in the present study. The nonintrusive measurements are performed with an integrated optical approach that provides combined measurements of the structural response of the wing and the unsteady flowfield around it. The aeroelastic loads acting on the wing are derived using physical models and validated against force balance measurements, showing a good agreement for all considered inflow conditions. The analysis of the aeroelastic response of the wing to the unsteady inflow produced by a gust generator shows that both structural and aerodynamic responses depend strongly on the frequency of the gust. The results of this study provide a characterization of the aeroelastic behavior of the Delft-Pazy wing and can serve as a reference for the development of novel and improved nonlinear aeroelastic simulation models., Aerodynamics, Aerospace Structures & Computational Mechanics

This thesis presents a novel measurement approach for aeroelastic wind tunnel testing. The key novelty of this approach is the integrated measurement of aerodynamic and structural quantities using an optical technique. The considered approach consists of combined measurements of flow tracer particles and structural markers using a Lagrangian particle tracking system. Based on these measurements, the quantities of interest for the characterization of an aeroelastic interaction, which are the three forces in Collar’s triangle (aerodynamic, elastic, and inertial), are determined. Currently, measurements in aeroelastic wind tunnel tests are typically performed with individual sensors for each quantity of interest (pressure transducers, strain gauges, or accelerometers) that are installed inside the experimental model and/or with a force balance that measures the total loads acting on the model. The integrated optical measurement approach is an advancement over this existing measurement technology because it provides field measurements of the aeroelastic structural response and the unsteady flow field around the experimental model, based on which the aerodynamic and structural load distributions can be determined, without requiring an instrumentation of the model with sensors. This measurement approach is therefore an effective way to produce experimental reference data to support the development of novel aeroelastic prediction methods with a potential to accelerate the technological development process for innovations in aeronautics in the future. The development and applications of the integrated optical measurement in this thesis are based on the measurements that were performed in three experimental campaigns in the wind tunnel. Each of the three experiments corresponds to one of the three main chapters of this thesis. All three experiments are performed on a largemodel scale, with dimensions on the order of 1m, which is a scale of high practical relevance for aeroel, Aerodynamics

The Pazy Wing test case is a benchmark for the investigation of aeroelastic effects at very large deflections. Tip deformations in the order of 50% span were measured in wind tunnel tests which renders this model highly attractive for the validation of numerical aeroelastic methods and tools for geometrically nonlinear, large deflection analyses. The present work is focused on high fidelity aerodynamic and aeroelastic simulations of the wing using RANS and URANS with transition modeling in order to capture nonlinear effects originating from the shape of the wing and the low Reynolds number. Steady and unsteady aerodynamic as well as static coupling simulations with a nonlinear structural model are presented, the impact of the different transition and turbulence modeling techniques is depicted. This work supports the Large Deflection Working Group (LDWG), which is one of the sub-groups of the 3rd Aeroelastic Prediction Workshop (AePW3)., Aerodynamics

The laminar separation bubble (LSB) that forms on the suction side of a modified NACA 64 3-618 airfoil at a chord-based Reynolds number of Re = 200 , 000 is studied using wind tunnel experiments. First, the LSB is characterized over a range of static angles of attack, in terms of the locations of separation, transition and reattachment—using surface pressure measurements, particle image velocimetry (PIV) and infrared thermography (IT). For the conditions tested, excellent agreement between the techniques is obtained. Subsequently, a pitching motion is imposed on the wind tunnel model, with reduced frequencies up to k = 0.25. While surface pressure measurements and PIV are not affected by the change in experimental conditions, the infrared approach is impaired by the thermal response of the surface. To overcome this, an extension of the differential infrared thermography (DIT) method for detecting the three characteristics of an unsteady LSB is considered. All three experimental techniques indicate a hysteresis in bubble location between the pitch up and pitch down phases of the motion, caused by the effect of the aerodynamic unsteadiness on the adverse pressure gradient. However, the DIT measurements suggest a larger hysteresis, which is attributed to the thermal response time of the model surface. The experimental results measured with the pressure sensors reveal that the hysteresis in bubble location is larger than the hysteresis in lift, indicating that the observed bubble hysteresis is not purely due to instantaneous flow conditions, but has an inherent component as well., Aerodynamics

The aeroelastic response of a very flexible wing in steady and unsteady inflow conditions is measured in a wind tunnel experiment. An integrated aeroelastic characterization is performed with a non-intrusive optical setup that allows simultaneous measurements of the structural motion and the flow field around the wing. The experimental aerodynamic loads that are inferred from the flow field measurements are in very good agreement with reference data from a force balance. Prior to the wind tunnel experiment, results of the numerical modal analysis of a structural model of the wing are compared with the experimental results from a ground vibration test. An aeroelastic model validation is achieved by applying the experimental aerodynamic loads to the structural model of the wing. The results of this structural analysis are compared with the measured structural response in the wind tunnel for steady inflow conditions, yielding differences of around 15% in tip displacements when using a linear structural model., Aerodynamics, Aerospace Structures & Computational Mechanics