INVESTIGATION OF FREQUENCY LOCK-IN PHENOMENA ON A SUPERCRITICAL AEROFOIL IN THE PRESENCE OF TRANSONIC SHOCK OSCILLATIONS

摘要

Within a narrow band of the transonic flight regime, shock-wave/boundary layer interactions yield large amplitude, self-sustained shock oscillations. When this transonic buffet instability interacts with a forced or freely oscillating structure, frequency lock-in between the aerodynamic and structural modes can occur, resulting in large amplitude limit cycle oscillations of the structure. In this study, the lock-in phenomenon is investigated by means of Reynolds-Averaged Navier-Stokes simulations. Harmonically driven pitching simulations are performed for a range of driving frequencies and amplitudes for the supercritical OAT15A aerofoil section. The results show that for a band of driving frequencies near the buffet, frequency synchronisation develops for sufficient driving amplitudes. The flow topology within the lock-in regions differs for driving frequencies above and below the buffet. This is attributed to a phase reversal of the aerodynamic coefficients as the excitation frequency passes through the fundamental flow frequency. Analysis of the gain and phase relationships of the aerodynamic coefficients supports the findings of prior studies, where the lock-in phenomenon is related to bounded single degree-of-freedom flutter.