Experimental Subsonic Flutter of a Linear Turbine Blade Cascade With Various Mode Shapes and Chordwise Torsion Axis Locations

Abstract

Axial flow turbomachinery is susceptible to self-excited vibrations known as flutter, primarily affecting high-aspect ratio rotor blades. Experimental studies of blade flutter are essential to understanding the phenomenon. The existing research has shown that the most critical factor in determining the aerodynamic stability of the blade is the mode shape. In this work, measurements of subsonic flutter of a linear turbine blade cascade with various mode shapes and torsion axis locations in a chordwise direction are carried out. The cascade consists of eight blades representing the reduced tip sections of the last stage blade of the steam turbine rotor, and central four flexibly mounted blades are forced to vibrate in pure bending and pure torsion modes and a combined motion. Both the traveling wave mode approach and the influence coefficient method are tested. The results show that the pure torsion mode is insensitive to increasing reduced frequency and is aerodynamically unstable for each positive angle of incidence tested, while pure bending and combined modes become less stable with the increased angle of incidence. In addition, high sensitivity of blade behavior to changes in torsion axis position and phase shift between bending and torsion motions is demonstrated.