Prediction of transonic 2D wing flutter using the time-spectral computational fluid dynamics

Abstract

A new computation method to predict a transonic wing flutter under the limit-cycle oscillation (LCO) is developed using the time spectral (TS) method. The fluid and structural unknowns at a specified time interval in one cycle of the flutter are obtained by steady-state solutions of the aeroelastic TS equations, and thus higher computational efficiency is expected. Determining the frequency is the key for the flutter prediction, and we propose a method of minimizing the residuals of the fluid equation. The time histories of the plunge and pitch are reconstructed by the discrete Fourier transform, and compared with the existing time marching (TM) method. The effects of the number of harmonics in the TS and the time-step size in the TM are examined for the detailed comparison. The frequency, amplitude, and phase differences between the structural vibration modes all well agree between the two methods for a wide range of flutter speed index. Complex flutter boundaries are also predicted. The TS method is faster to reach the LCO than the TM method for the first vibration mode of the flutter. It is slower for the second vibration mode, but the increase in the computation time is much smaller than the reduction in the first mode. In general, the TS method is particularly advantageous for the prediction near flutter boundaries and is useful for aircraft design.

Keywords

• flutter
• transonic flow
• cfd
• fluid-structure interaction
• time-spectral method
• limit-cycle oscillation