Fluid-mode flutter in plane transonic flows

We investigate the flutter behavior of 1) a typical-section OAT15A airfoil with a heave and a pitch degree of freedom and 2) a generic symmetric airfoil of variable thickness equipped with a flexible trailing-edge plate by means of RANS simulations. The linearized flutter stability problem in the pre-buffet region is approached with three different techniques: A Newton-based root search involving the p-k approximation (NPK), a rational function approximation (RFA) of the fluid-structure coupled frequency response and a time-domain eigenvalue identification on the coupled impulse response obtained via succesive convolution (SCM). We emphasize on flutter instabilities resulting from the coupling of a structural mode and a fluid mode in separated flow. We conclude that the buffet onset should be regarded as the flutter boundary in the limiting case of zero density and buffeting is essentially flutter.