Centrifugal turbomachinery

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.