Frequency domain unsteady transonic aerodynamics for flutter and limit cycle oscillation prediction

The purpose of this study was to develop new approaches for predicting transonic flutter and limit cycle oscillations (LCO) using computational methods. The TSD equation is separated into the in-phase and out-of-phase components through a nonlinear harmonic averaging method. It is then solved in the frequency domain to obtain the aerodynamic forcing function which is needed in the flutter and LCO analyses. To predict flutter, equations are developed using the concept of generalized coordinates. The flutter speed is determined by examining the frequency-domain matrix equation eigenvalues. Flutter characteristics of the AGARD I-445.6 wing are analyzed. Flutter speed and frequency are well predicted in subsonic speed, but are overestimated in supersonic flow. To predict limit cycle oscillations, the frequency-domain aerodynamic coefficients are used to obtain a nonlinear time-domain expression for the aerodynamic force. Limit cycle oscillation characteristics of the DAST ARW-2 wing are analyzed. The results show LCO for Mach numbers ranging from 0.915 to 0.940