Prediction of shrouded turbomachinery blade flutter by a complex mode analysis

[[abstract]]Turbomachinery shrouded rotor blade design has been widely used in fans, compressors, and turbines. By using either tip or mid-span shroud, the blade structural damping and natural frequencies can be increased to prevent flutter. However, shrouded rotor blade design sometimes results in complex system modes with both bending and torsion present at the same time. Consequently, a complex mode analysis was developed to analyze the shrouded rotor blade flutter. Since shrouded rotors are rotationally periodic, the bending and torsion combined system mode can be decomposed into a real component and an imaginary component. Using both the real and imaginary mode shapes, coupled with the blade surflace flow-field, a complex mode flutter analysis was developed using a modal solution to determine the stability of the system. This complex mode analysis was applied to two shrouded rotor blade applications. Bending-dominated or torsion-dominated simple blade modes in general can be analyzed using an existing single mode approach. However, for the bending and torsion combined system modes, the single mode analysis can be misleading. By using the complex mode analysis, it was demonstrated that the combined bending and torsion system mode plays an important role in determining the blade stability.[[fileno]]2020234010012[[department]]動機