The linear aeroelastic stability of a simplified mass-spring model representing the basic dynamics of a sector of Na airfoils is analyzed. The degree of multiplicity of the eigenvalues of the simplified structural model is Na−1 and hence its mode-shapes are not determined in a unique way. The aerodynamic damping strongly depends on the mode shape and hence its accurate determination is essential in order to obtain realistic values of damping. This in-determination is removed when the aerodynamic forces associated to the motion of the airfoils are added or a platform with finite stiffness is considered. In both cases the problem is not degenerated anymore and the mode-shapes of the system are uniquely determined. It is shown that the expected stabilizing effect due to the packets may be negligible, depending on the relative strength of the aerodynamic forces and the stiffness of the lower platform. It is also shown that, for the most unstable situation, the aeroelastic behaviour of the problem may be, in first approximation, very similar to that of a continuous ring.

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