An Investigation of Turbomachinery Shrouded Rotor Blade Flutter

Turbomachinery shrouded rotor blade design has been widely used in fans, compressors, and turbines. By using shroud design, the blade structural damping can be increased to prevent blade flutter. However, the shrouded rotor blade design will cause the blade mode shapes to be complex, and in some cases both bending and torsion mode components can be present at the same time in a single mode. Therefore, a complex mode analysis was developed to predict shrouded rotor blade flutter with these bending and torsion combined system modes. Using the blade natural frequencies and mode shapes from a finite element model, and the blade aerodynamic flow-field, the unsteady aerodynamic forces of the system mode can be calculated. A complex mode flutter analysis was then performed using a modal solution to determine the stability of the system. The analysis system was applied to two shrouded rotor blade applications. The bending and torsion combined system mode was decomposed into a real mode component and an imaginary mode component. Bending-dominated or torsion-dominated mode shapes can be analyzed using single mode approach to obtain consistent flutter stability results. However, for the bending and torsion combined mode shape cases, the single mode analysis can be misleading, and the complex mode analysis can be a useful tool.