Numerical Study on Stall Flutter of a Compressor Cascade : 2nd Report, Relationship between Unsteady Aerodynamic Characteristics of Oscillating Blades and Rotating Stall

Stall flutter of a compressor cascade is studied by the numerical analysis of the unsteady separated flow around the blades oscillating in a torsional mode. When a cascade operates at a stall condition, the unsteady flow behavior changes according to the relationship between the propagation velocity of blade oscillation and the propagation velocity of rotating stall. The propagation of rotating stall is synchronized with, or entrained by, the blade motion and becomes very regular when both propagation velocities are close to each other. The oscillating blades are subjected to intense flutter excitation when the synchronization occurs. On the other hand, when both propagation velocities are largely different from each other, the rotating stall propagates with an almost constant velocity regardless of the instantaneous angles of blades. The propagation of rotating stall becomes irregular under the influence of blade oscillation when the difference of the propagation velocities is in between. The flutter excitation of blades does not occur in the latter two conditions.