Transonic aeroelastic limit cycles and their dependence on freestream conditions

In this paper, Unsteady Reynolds-Averaged Navier-Stokes (URANS) flow simulations are coupled to a single-degree-of-freedom rigid body structural solver to study the dependence of the transonic aeroelastic response of the OAT15A to variations in freestream conditions. The aeroelastic computations are validated against elastically-suspended profile wind tunnel experiments, with excellent correlation in the unsteady loads and surface pressure magnitude and phase. Mach number and angle of attack sweeps are performed for three distinct structural configurations, with the pitch eigenfrequency below, marginally above and wellabove the buffet frequency. The results find a rich spectrum of nonlinear dynamic behaviour, including mode-switching, asymmetric LCOs, and Hopf and jump bifurcations. Of significance is the emergence of nontypical LCOs for the structural composition in which frequency lock-in was observed. The origins of nontypical limit cycles, which grow and then reduce in amplitude with increases in Mach number, have been debated in literature and the findings of the present study indicate a potential connection between this transonic aeroelastic phenomenon and buffet lock-in.