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Aerodynamic loads estimation at extremes of the flight envelope

Periodic Report Summary - ALEF (Aerodynamic loads estimation at extremes of the flight envelope)

ALEF's goal to cover the extremes of the flight envelope has been genuinely addressed through the application of high-fidelity CFD/RANS methods to low-speed high-lift configurations, to high transonic speed and dive speed conditions, to configurations typical for high loads scenarios (i.e. necessitating control surface deployment), to conditions involving well established buffeting, to flows dominated by unsteady aerodynamics and for static and dynamic aeroelastic effects.

ALEF allowed extending the application range of high-fidelity RANS methods to the borders of the flight envelope including the deployment of control surfaces. The work performed provided a better picture of the capabilities and the limitations of RANS. Furthermore, thanks to the development of advanced fluid / structure coupled simulation procedures we no longer have to neglect static or aeroelastic effects. A wide range of high-fidelity simulation aspects have been addressed i.e. advanced meshing approaches (mesh deformation, Chimera meshing, ...) turbulence modelling, transition prediction methods.

In particular for unsteady aerodynamic loads, ALEF work has demonstrated the ability of unsteady CFD to shift from linear methods towards high-fidelity methods and to improve the prediction quality in aeroelastic analyses. Efforts were focused one tackling challenges for improving accuracy versus the standard practice. The research carried allowed to increase the overall confidence of methods by verification and validation thanks to test cases covering the flight envelope (including parts of the borders). Furthermore, several gust methods have been applied to complex aircraft configurations.

Further ALEF research focussed on the evaluation, enhancement and application guidelines of surrogate modelling (both for steady & unsteady purposes). In a first step, it resulted in the classification of present surrogate models and identification of potential fields of application for aero data production purposes. The Proper Orthogonal Decomposition technique was of particular interest and has been successfully applied in several fields by several partners. Research activities were carried out to enhance the technique in order to be able to account for deployed control surfaces or structural deformations. POD surrogate models proved to be a viable and fast alternative to CFD. Specific application guidelines and recommendations for further enhancement of POD techniques have been defined.

With regard to unsteady surrogate modelling a major technical achievement was the illustration of the potential of Linear Frequency Domain solvers to conduct fast flutter analysis thanks to significant time reduction versus unsteady time accurate simulations.

At the very end of the project, significant efforts were made to demonstrate the most promising steady, unsteady CFD developments and work on surrogate modelling through applications on industrially relevant and complex test cases. The methods and processes investigated in the ALEF project proved to be better than those available at the start of the project. The ability to use them in an industrial context was shown, which contributes to an improvement of the current state-of-the-art industrial aerodynamic data process. Last but not least the research conducted in ALEF clearly allowed a transfer of knowledge and methodologies from the project into industrial application.

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