40 | ORBIT | 2Q01 Rotor Dynamics of Centrifugal Compressors in Rotating Stall

his paper discusses rotating stall in centrifugal compressors from the standpoint of rotor dynamics. The literature survey shows insufficient understanding of rotor dynamic implications of rotating stall. Most of the literature on the subject addresses only aerodynamic aspects of the problem, thus putting an emphasis on stall cells, with exclusion of the rotor vibrational response. This paper treats a compressor as a coupled mechanical-aerodynamic system. For the rotor/fluid system, the results of Dynamic Stiffness identification of an experimental centrifugal compressor in rotating stall and in normal operating conditions are presented. It is shown that the aerodynamically-induced radial (direct spring) stiffness coefficients are negative in normal operating conditions. The negative radial stiffness effect in the case of rotating stall is even more profound. The result is that the rotor system’s mechanical resonance could be reduced to as low as 5 % to 10 % of running speed. The conclusion is that the rotor dynamic stability margin during rotating stall is reduced