Experimental Bifurcation Forecasting Using the Transient Response of an Airfoil in a Wind Tunnel

Aircraft wings can experience dangerous flutter instabilities due to fluid–structure interactions. These instabilities can occur before the typical flutter point, posing a significant risk as they involve multiple stable solutions with large amplitudes. Besides, they become more dominant with the increased nonlinearities that arise in novel flexible designs. Accurate prediction of such behavior is vital for aircraft safety. Traditional modeling methods for aeroelastic systems are computationally expensive and challenging when accurate models are lacking, especially for large and complex systems. On the other hand, in-flight flutter tests are risky and only provide approximate flutter speed estimates based on gradual vibration observation. As a result, safe and model-free methods for testing and evaluating experimental aeroelastic systems are desired. This chapter investigates application of a proposed data-driven forecasting method for predicting flutter and its bifurcation diagrams in a 2-degree-of-freedom experimental airfoil. The bifurcation forecasting approach, relying on measurements collected in safe pre-flutter regime, offers insights into post-bifurcation dynamics without relying solely on expensive and risky in-flight tests. The proposed stability analysis approach eliminates the need for complex models or unsafe wing oscillations by using pre-bifurcation transient measurements. Results show the strong potential of this approach to enhance aeroelastic systems safety and performance in a more efficient and cost-effective manner.