TAEHYOUN KIM
DOI Number: N/A
Conference number: IFASD-2024-232
During design and analysis phases of aircraft flutter boundaries are computed using analysis tools such as the p-k iterations or eigenvalue analysis. Also, for the purpose of certification flight flutter test (FFT) is conducted to predict the onset of flutter experimentally. However, from the practical perspective aeroelastic vibrations with finite amplitudes known as the Limit Cycle Oscillation (LCO) are more critical because they reveal the true nonlinear nature of the fluid- structure interaction. Previously, based on the concept of the Dynamic Eigen Decomposition (DED) and a frequency domain stability theorem, a new flutter prediction methodology was developed for applications to FFT with limited actuators and sensors. In this study, this technique is extended to include LCOs originating from a nonlinearity existing in a control surface freeplay. First, a linear flutter boundary is predicted using the DED method and data available at subcritical flight conditions. Next, a simple harmonic analysis of the control surface freeplay is carried out to extract important harmonic contents of the nonlinearity, and a new DED is formulated in two parameters, i.e., the variable dynamic pressure and the effective stiffness of the control surface hinge. Using the formulation, it is possible to predict LCO by extrapolating the dynamic eigenvalues obtained at the subcritical data points. The proposed methodology is demonstrated using computational simulations of a tapered wing with four flaps and a freeplay in one of the hinges. It is shown that the new approach yields accurate predictions of LCO without need for taking additional data, with only the data obtained during the FFT.