In this paper the effects of mistuning on the flutter stability of a turbine blade are analysed. Two types of mistuning are considered, frequency mistuning and aerodynamic mistuning. The study concentrates on the the first family of modes (1F, first flap) as the blade fluttered in this mode during test. For the frequency mistuning analysis, the 1F frequency is varied around the annulus but the 1F mode shapes remain the same for all the blades. The mistuning analyses are performed by using a reduced order model (ROM) based on an eigenvalue analysis of the linearized modal aeroelastic system with the aerodynamic matrix calculated from the aerodynamic influence coefficients. The influence coefficients required for this algorithm are obtained from a three-dimensional, non-linear aeroelastic solver (AU3D) by shaking one blade in the datum (tuned) frequency and mode and recording aerodynamic forces on the other blades in the assembly. After the ROM is validated against the non-linear method for the tuned case, it is used for the mistuning and mis-staggering study as time-domain computations of such cases are very time consuming.
The results of this paper indicate that, frequency mistuning is always stabilizing but aerodynamic mistuning can be destabilizing under certain conditions. Moreover, it is shown that the effect of frequency mistuning is much higher than the one of aerodynamic asymmetries and that structural coupling limits the effects of mistuning.