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 beha vior changes according to the relationship between the phase propagation ve locity of blade oscillation and the propagation velocity of rotating stall. The propagation of rotating stall is synchronized with, or entrained by, t he blade motion and becomes very regular when both propagation velocities a re close to each other. The oscillating blades are subjected to intense flu tter excitation when the synchronization occurs. On the other hand, when bo th propagation velocities are largely different from each other, the rotati ng stall propagates with an almost constant velocity regardless of the inst antaneous angles of blades. The propagation of rotating stall becomes irreg ular under the influence of blade oscillation when the difference of the pr opagation velocities is in between. The flutter excitation of blades does n ot occur in the latter two conditions.