Aeroelastic Damping Estimation for a Flexible High-Aspect-Ratio Wing

Estimation of aeroelastic damping for a very flexible high-aspect-ratio wing using wind-tunnel test data is presented in this work through the comparison of four different methods: half-power, half-quadratic gain, an adapted version of random decrement, and the least-square complex exponential method. A model with an aspect ratio of 18.8 was tested in the Cranfield 2.4 x 1.8-m (8 x 6-ft) low-speed wind tunnel across a Reynolds number range of 2.33 x 10(5)-4.66 x 10(5) and dynamically excited using the step relaxation technique. Analysis of the results provides a view of the benefits and limitations of each method, which were seen to differ between 3% and 25% relative to the half-power for the dominant first mode. The trends in predicted damping show clear dependency on freestream velocity. Structural damping of the first mode was also obtained using ground vibration test data to separate the aerodynamic and structural contributions to the overall aeroelastic damping. Structural damping was found to be around 5% and the aerodynamic component was found to add approximately 7.5% at one specific test condition. Although the half-power method is widely used in the community for calculating structural damping, this work shows that when aeroelastic damping is higher than 5%, the other three examined methods yield more consistent results. (C) 2021 American Society of Civil Engineers.