Wind tunnel investigations of a pitch-free flexible high aspect ratio aircraft model

Banneheka Navaratna, Punsara D.; Pontillo, Alessandro; Rezgui, Djamel; Lowenberg, Mark H.; Neild, Simon A.; Cooper, Jonathan E.

Abstract

This paper presents low Reynolds number experimental wind tunnel investigations of flexible high aspect ratio aircraft models with body pitch degree-of-freedom. The aim is to assess nonlinear dynamic interactions of highly flexible wings with aircraft dynamics. Two sets of wings, one designed to be highly flexible and the other to be near-rigid, were considered for comparison. The first test category involves the aircraft being trimmed for three lift cases of 20, 25, and 30N within a wind speed range of 18 to 30 m/s. The second category involves a trimmed pitch sweep ranging from -3.5 to 10.7 degrees at a single wind speed of 25 m/s. The aircraft mode frequencies and damping were identified experimentally using the Eigensystem Realization Algorithm on autocorrelated responses to random excitation of the model using gust vanes. Highly nonlinear trends in the short-period mode frequency and damping with respect to wind speed and pitch angle were observed, as well as differences between the wing design cases. A low-order geometrically-exact structural model was employed for numerical comparisons. Three aerodynamic models were considered: steady Vortex Lattice Method (VLM), steady 2-state Leishman, and unsteady 2-state Leishman aerodynamics. It was found that wing-to-tail influence captured by VLM aerodynamics is vital to accurately simulate the short-period mode and for its frequency magnitude to match with experiments. However, the local nonlinearity observed experimentally is not captured by any of the aerodynamic models considered. Introducing aerodynamic unsteadiness significantly reduces the damping of the short-period mode and has very minor impact on the wing-bending dominant mode. The trends in wing-bending mode were captured well by all aerodynamic models, with minor differences between them. In general, the short-period mode frequency increases with wind speed and decreases with pitch angle (for wings-up deflections). An increase in the magnitude of wing deflection results in an increase in wing-bending mode frequency and a decrease in damping. A reduction in wing stiffness or increase in flexibility reduces the frequency of the short-period mode. Increasing the magnitude of wing deflection also reduces the short-period mode frequency, which was observed to be more significant in experiments than in numerical results.

• 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
• Book Title: AIAA SCITECH 2024 Forum
• DOI: https://doi.org/10.2514/6.2024-2819
• Public URL: https://uwe-repository.worktribe.com/output/11886161