11:00
Flutter 3
Chair: Rafael Palacios
11:00
30 mins
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Aeroelastic design of a drone for research on active flutter control
Nicolò Fabbiane, Vincent Bouillaut, Arnaud Lepage
Abstract: Within the project CONCERTO, funded by the European research program Clean Aviation, ONERA is responsible of the aeroelastic design of a flying demonstrator, aimed at providing a suitable platform for the test of active control techniques to delay the onset of the flutter instability. This leads to very peculiar specifications for the nominal flutter behaviour of the aircraft and, therefore, to adapted solutions in the design process.
The flutter behaviour of the drone has to be tuneable; in particular, three configurations are expected. First, a reference configuration is required without any flutter occurrence in the flight domain and any coupling between flight mechanics and structural dynamics. For the second one, the first flexible mode’s frequency is low enough to interact with the flight dynamics, still being flutter stable. Finally, the third one presents a flutter instability for a specific range of velocities in the flight domain.
Thus, the design has to include a way to tune separately the flexional and torsional natural vibration modes of the wing. To this end, a system of movable masses positioned at the tip of the wing is introduced, providing the degrees of freedom to pilot the structural dynamic and, hence, the aeroelasticity of the drone. Along these design parameters, the wing structure is also tailored to ensure the necessary sensitivity of the structural dynamics to the above-mentioned movable masses.
This paper summarizes the design process, starting from the structural configuration and the sizing of the structural elements of the wing, i.e. composite skin and spars. Once a feasible baseline is identified, some structural parameters are tuned to comply with the above-mentioned specifications. Finally, a thorough analysis of the (linear) flutter behaviour is presented, to verify and document the expected dynamic aeroelastic performance of the drone.
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11:30
30 mins
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Co-Design of the Aeroelastic Wing Parameters and the Flutter Control Law
Zsombor Wermeser, Béla Takarics, Bálint Vanek
Abstract: In an aircraft design process, the initial airframe design is iteraively refined going back and forth between structural and control design. Instead of this iteration, the simultaneous optimization of the structure and the control laws would be advantageous. This paper presents a co-design for a flutter suppression controller for a simple rectangular flexible wing. The wing is parametrized by seven geometric and structural variables. The controller is based on output feedback, whose parameters are simultaneously optimized with the structure. A solution to the same co-design problem was already proposed by Filippi et. al. (2018) [1] by directly syn- thesizing the optimal control input along with the optimal parameters. In this paper, a solution is presented for the design of a control law instead of the control signals. The paper uses the model parameterization by Filippi to achieve comparable results. The behavior of the wing is evaluated by time domain simulations. The objective of the co-design method takes into consid- eration the maneuverability, comfortability, and control cost of the wing for two types of wind gusts. In our concept, we have taken the preliminary investigation of Filippi further, in which we successfully used a controller to suppress the flutter phenomenon. In our results, we achieved a cost function reduction of 81% compared to the Direct Transcription method. Thus, the sensor-based flutter suppression control is successfully applicable for co-design purposes.
1. G.Filippi and J.Morlier, “Integrated structural and control system design for robust flutter performance”, ISAE-SUPAERO Institute Suprieur de l’Aronautique et de l’Espace, p.6, 2018
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12:00
30 mins
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Unsteady RANS-based Computational Aeroelastic Simulations of X-56A Flutter for the Third Aeroelastic Prediction Workshop
Iren Ani Mkhoyan, Peter Blom, Jos Aalbers, Huub Timmermans
Abstract: This paper presents a high-fidelity aeroelastic study of the the Multi-Utility Technology Testbed (MUTT) X-56A, designed to exhibit aeroelastic instabilities such as body free flutter (BFF). The primary objective of this work is to assess the use of high-fidelity CFD-based aeroelastic simulations for flutter prediction. This research was originally conducted as part of the Third Aeroelastic Prediction Workshop (AePW3) aiming to enhance the knowledge in aeroelastic predictions using mid to high-fidelity computational aerodynamics. This particular study details the contribution from the Flight Physics & Loads group at the Netherlands Aerospace Centre (NLR), exploring two computation methods for generating the Generalised Aerodynamic Forces (GAFs), namely, ZAERO solver (ZONA Technology) using higher-order panel code ZONA6, and an unsteady RANS-based Computational Fluid Dynamics (CFD) and Computational AeroElastic (CAE) simulations implemented within NLR's ENFLOW simulation system for multi-block flow domains. The high-fidelity CFD and CAE analyses were performed using the flow solver ENSOLV with unsteady Reynolds-Averaged Navier-Stokes (RANS) flow formulation implemented with Explicit Algebraic Reynolds Stress Model (EARSM) turbulence modelling based on the TNT $k-\omega$. The CAE computational procedure consists of four tool chains, involving structural dynamics (modal) analyses; grid interpolation procedure; steady CFD computations on the undeformed shape; unsteady CFD computations on a deforming grid under prescribed, small-amplitude sinusoidal excitations based on the structural mode shapes; and the transformation of the time-domain unsteady solutions to frequency domain in order to construct the GAF matrices. The X-56A configuration used for this study is the 10lb fuel state model released within the AePW-3 group. The resulting GAFs were compared to the ZAERO results, showing good agreement for both the rigid body and elastic modes. Earlier work on X-56A within AePW-3 conveyed the need for further refinement of the high-fidelity aeroelastic methodology. Improvement efforts in this regard, included alternative structural dynamics methods for modal model computations, CFD grid refinements, and adjustments to the (un)steady CFD/CAE simulation procedures and methods.
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