Influence of Transitional Flows at Transonic Mach Numbers on the Flutter Speed of a Laminar Airfoil

This paper presents a flutter analysis for a supercritical airfoil with free boundary layer transition based on CFD simulations with the gamma-Re_theta transition model. The results are compared to results obtained by fully turbulent simulations with the SST k-w model. Unsteady RANS simulations at Re = 2·10^6 are used to determine the aerodynamic derivatives, required to solve the flutter equation for a 2-dof model by a k-method. It is found that the flutter boundary decreases for a flow with free boundary layer transition compared to a fully turbulent flow in the transonic flight regime in the vicinity of the transonic dip, whereas the flutter boundary is raised in the subsonic region. Furthermore, an aerodynamic resonance in connection with an instability of the transition region is found