Experience With Empirical Criteria For Rotating Stall In Radial Vaneless Diffusers.

LecturePg. 97-106A seven stage, centrifugal compressor, for gas lift service on a North Sea oil production platform, exhibited subsynchronous shaft vibrations during full load, high density, factory tests. Pressure transducers in each stage characterized two stages as stalled and traced the cause of rotor vibration to rotating stall in the diffuser of the last stage. Modifications to that diffuser of the last stage corrected the subsynchronous shaft vibration. The other stage that exhibited characteristics of diffuser rotating stall was left unchanged as it did not yield harmful subsynchronous shaft vibration. The original compressor configuration was designed to meet Senoo and Kinoshita's criterion [1, 2] for inception of rotating stall in a vaneless diffuser. However, its diffuser widths, b3, were less than the impeller tip widths, b2, while b3 and b2 widths were equal in Senoo's experiment. Kobayashi, Nishida, et al. [3], and Nishida, et al. [4], extended Senoo's criteria by accounting for a b1/b2 ratio less than one. The subject compressor was analyzed using the Kobayashi, et al. [3], criterion. Data reduction of the testing condition producing diffuser rotating stall demonstrated significant margin to the criterion. The generous shape of the inlet diffuser contour was suggested as being the source of the disparity between the criterion and the data reduction values