Centrifugal compressor

A centrifugal compressor comprising:

• a rotary shaft;
• a hollow casing that rotatably supports the rotary shaft and is provided with an intake port on one side in an axial direction of the rotary shaft and a discharge port on the other side;
• a first-stage inlet guide vane that is disposed in the intake port;
• a first-stage impeller that is disposed downstream of the first-stage inlet guide vane in the casing;
• a diffuser that is disposed downstream of the first-stage impeller in the casing;
• a return flow channel at which a fluid that flows from an inner side in a radial direction of the rotary shaft to an outer side in the radial direction after flowing through the diffuser is reversed to the inner side in the radial direction;
• return vanes that are disposed in the return flow channel;
• a second-stage inlet guide vane that is disposed downstream of the return vanes in the casing;
• and
• a second-stage impeller that is disposed downstream of the second-stage inlet guide vane in the casing,
• wherein the return vanes are arranged at predetermined intervals in a circumferential direction of the rotary shaft and a vane angle of each return vane is changed from a leading edge, at which the fluid is introduced, to a predetermined position and the vane angle is maintained constant from the predetermined position to a trailing edge, at which the fluid is discharged, in terms of meridian plane distance in a direction from the leading edge to the trailing edge, and
• wherein the predetermined position is set 50% to 70% from the leading edge.