16:00
Wind tunnel testing 2
Chair: Anders Karlsson
16:00
30 mins
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Aeroelastic Wind Tunnel Testing of 3D-Printed Semispan Wings
Alexander Pankonien, Nicholas Jones, Asa Palmer, Joshua Deslich, Kevin McHugh, Robert Taylor
Abstract: Additive manufacturing has lowered barriers associated with rapidly realizing complex shapes, such as the airfoils of wind tunnel models. To construct a flexible, aeroelastic wind tunnel model, these printed airfoils are typically affixed to an underlying structure, made with conventional fabrication techniques. However, the resultant design is not representative of the topologies typically found in aircraft, complicating actuation and sensing integration. This work details several years of exploring aeroelastic wind tunnels that leverage new, printed materials to build the underlying load bearing structure and skins. It is hoped that building all load bearing components simultaneously will reduce integration complexity, as well as lower overall fabrication cost and time, providing an opportunity for data assimilation into a conceptual vehicle design process. The method employed to design these models is a traditional conceptual aircraft sizing tool that allocates material thickness, and material stiffness when applicable to the printing process. This technique has been demonstrated for statically and dynamically scaled 20-inch semi-span models of a flying wing. Models in this work have been fabricated using one of two printing processes for comparison---polyjet or selective laser sintering. The models have been structurally tested experimentally, both quasi-statically and dynamically to validate their properties. The quasi-static deflection of the models under aerodynamic loading has been measured via digital image correlation measurement during wind tunnel testing, showing good agreement with expected stiffness, albeit with creep in the polyjet models. Initial efforts using the same experimental setup to characterize dynamic aeroelastic characteristics are also described, indicating the need for external excitation in these more highly-damped material systems. Finally, initial scanning of airfoil measurement for data assimilation is described, indicating good outer mold line agreement with the as-designed geometries in camber, but up to two degrees of erroneous twist. These results show promise for even larger models made with selective laser sintering of materials with higher glass transition temperatures.
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16:30
30 mins
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Analysis of the impact of forced pitching oscillations in transonic flow on the transition onset and the aeroelastic behaviour of an airfoil
Italo CAFARELLI, Cedric LIAUZUN
Abstract: The development and the validation of the numerical prediction tools for the aeroelastic behaviour of laminar wings goes first through the assessment and the potential updating of these tools on models undergoing forced harmonic motions. This implies the availability of an extended enough data base.
Within the European Clean Sky 2 Airframe ITD/NACOR project, a 2D model equipped with a laminar airfoil was thus designed, manufactured, highly instrumented and implemented in the Onera S2MA wind tunnel in order to study the behaviour of the laminar-turbulent transition on the model under forced dynamic pitch oscillations, mainly in transonic flow conditions.
The instrumentation includes amongst others, static pressure taps, unsteady pressure sensors, accelerometers, optical displacement sensors and a high density hot films sensor array. Several parameters were checked such as the inflow Mach number, the pitch angle (steady mean angle ranging from -3° to 3°, dynamic magnitude), the oscillation frequency and the Reynolds number.
The processing of the different time signals coming from steady and unsteady test configurations give an understanding of the effect of the above parameters on steady and unsteady aerodynamics and on the transition chordwise motion peculiarities.
The corresponding numerical simulations are performed using the Onera CFD code elsA with different turbulence and transition models (Arnal-Habiballah-Delcourt (AHD) criterion, Menter-Langtry,…). These simulations yield not only the variation of both steady and unsteady aerodynamic global forces and pressure chordwise distributions but also the steady and unsteady transition locations towards the pitch angle.
Experimental and numerical comparisons, relating to free transition and triggered turbulent flow, are also presented as they bring some clues on the most appropriate turbulent model and transition criterion to be used in simulations and provide some additional insight on the impact of laminarity on the overall steady and unsteady performances of such airfoils.
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17:00
30 mins
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Integrated Aerodynamic and Structural Measurements of the Gust Response of a Hinged Folding Wingtip
Christoph Mertens, Anna Biancotto, Jurij Sodja, Andrea Sciacchitano
Abstract: 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.
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