Experimental and numerical analysis of the bifurcation behaviour of a very flexible wing

Pontillo, Alessandro; Coetzee, Etienne; Lowenberg, Mark H.; Jones, Dorian; Cooper, Jonathan E.

Abstract

High aspect ratio wings promise greater aerodynamic efficiency with subsequent savings for airlines. However, these types of designs could be prone to unstable aeroelastic responses within the standard flight envelope, which may result from the reduction in the natural frequencies. This paper proposes a fully nonlinear low order aeroelastic framework able to predict the onset of any potential subcritical and supercritical limit cycle oscillations in very flexible wings, a critical tool required for the design of modern wings. Numerical continuation is used to detect unstable aeroelastic oscillations triggered by nonlinear geometrical effects, nonlinear aerodynamics or both. For this work, a 2-state aerodynamic model is used to predict the unsteady aerodynamic response of the model. Numerical results are verified and validated against wind tunnel data. The comparison shows a close match of the wing static response and the prediction of the flutter speed. The subject of this work is a very flexible wind tunnel model of 2.4 m span tested in 2018 in the 12 x 10 ft subsonic Airbus wind tunnel in Filton, which was part of the Agile Wing Integration (AWI) project. The model was specifically designed for the purposes of numerical code validation with certain dynamic characteristics and does not resemble any wing that would be used on an aircraft. It was equipped with accelerometers, strain gauges, pressure sensors and markers for video tracking to provide a complete picture of the onset of aeroelastic instabilities. The bifurcation analysis presents the equilibrium branches for the wing model in different configurations for different angles of attack and structural damping. Results show that the Hopf bifurcation velocity (flutter) strongly depends on the structural damping for the clean wing configuration, which also presents pitchfork-like behaviour at zero incidence due to the asymmetry in the inertia of the model.

• Presentation Conference Type: Conference Paper (published)
• Conference Name: AIAA SciTech Forum and Exposition, 2024
• Start Date: Jan 8, 2024
• End Date: Jan 12, 2024
• Acceptance Date: Jan 4, 2024
• Online Publication Date: Jan 4, 2024
• Publication Date: Jan 4, 2024
• Deposit Date: Apr 22, 2024
• ISBN: 9781624107115
• DOI: https://doi.org/10.2514/6.2024-1265
• Public URL: https://uwe-repository.worktribe.com/output/11886176