Patent ID: 8075260

Claim:
A centrifugal turbomachinery comprising: a rotating shaft, a plurality of centrifugal impellers mounted on said shaft, a diffuser having a plurality of diffuser blades, and introducing a fluid boosted by a preceding stage impeller to a following stage impeller, and a return flow path means, wherein the return flow path means comprises a side plate located on a back surface side of the preceding stage impeller, a stage plate opposing the side plate and located at a front surface side of the following stage impeller, and a plurality of return blades located between the side plate and the stage plate so as to be spaced in a peripheral direction, an outer diametral portion of the side plate being varied along the peripheral direction, a maximum outer diameter of the plurality of the return blades in the return flow path means is equal to or less than a minimum outer diameter of the side plate, each of said plurality of impellers has an impeller side plate located at a suction flow side, and an impeller core plate adjacent to a following stage having the following stage impeller, an outer diameter of the diffuser blades is varied along an axial direction with the outer diameter of each diffuser blade being smaller at a core plate side of the impeller and large at a side plate side of the impeller, a semi-open flow path is located between an outer periphery of the side plate and a maximum outer diameter of the side plate, a u-turn flow path which is disposed radially outward from the semi-open flow path, and wherein said u-turn flow path begins at the outer periphery of the side plate.