PREDICTION OF FLUTTER STABILITY USING AEROELASTIC FREQUENCY-RESPONSE FUNCTIONS

This paper deals with the flutter stability of turbomachinery blading using aeroelastic frequency response functions (FRFs) which are obtain ed by inverting the dynamic stiffness matrix of the aeroelastic system . The structural model is a lumped parameter representation while the aerodynamic model is based on linearized 2D cascade theories for subso nic and supersonic flows. The advantages of identifying the aeroelasti c modes via a rational fraction modal analysis of the aeroelastic FRFs rather than using a standard complex eigensolution are discussed in s ome detail. It is found that significant natural frequency and mode sh ape differences can exist between the structural and aeroelastic syste ms, a characteristic which must be considered duly when predicting the flutter stability. The consequences of changing the elastic axis posi tion were discussed in the case of a 12-bladed disk and it was found t hat flutter occurred mainly in torsion for the system studied. Finally , the effects of random and alternate mistuning on flutter stability w ere also investigated using the same model and it was found that mistu ning had a stabilizing effect in some, but not all, cases.