Steam turbine configured to recover static pressure of steam in diffuser

A steam turbine comprising:

• a rotor shaft that is configured to rotate about an axis;
• a plurality of rotor blade rows that are fixed radially outwards of the rotor shaft and disposed at intervals in an axial direction along which the axis extends;
• a casing that covers the rotor shaft and the plurality of rotor blade rows;
• and
• stator vane rows that are fixed to the casing, wherein each of the stator vane rows is disposed at intervals axially upstream of a respective rotor blade row of the plurality of rotor blade rows, wherein
• the casing has a diffuser that is configured to guide steam flowing out of the casing from a rotor blade row of a final stage that is disposed axially most downstream among the plurality of rotor blade rows,
• the diffuser comprises:
• an outer guide that gradually expands radially outwards of the diffuser from axially upstream of the diffuser to axially downstream of the diffuser, and
• an inner guide that is disposed at intervals radially inwards of the outer guide and gradually expands radially outwards of the diffuser from axially upstream of the diffuser to axially downstream of the diffuser,
• the inner guide has an inner curved diameter-expanded portion that gradually expands radially outwards of the diffuser while curving from axially upstream of the diffuser to axially downstream of the diffuser,
• the outer guide comprises:
• a first diameter-expanded portion that is disposed in a region closest to the rotor blade row of the final stage in the axial direction and gradually expands radially outwards of the diffuser with a first radius of curvature from an axially upstream end of the first diameter-expanded portion to an axially downstream end of the first diameter-expanded portion;
• and
• a second diameter-expanded portion that is connected to the first diameter-expanded portion axially downstream of the first diameter-expanded portion and gradually expands radially outwards of the diffuser with a second radius of curvature from an axially upstream end of the second diameter-expanded portion to an axially downstream end of the second diameter-expanded portion, the second radius of curvature being larger than the first radius of curvature,
• the second diameter-expanded portion forms a most axially downstream region of the outer guide, and
• a length of the second diameter-expanded portion in the axial direction is 0.5 to 2.0 times a length of the first diameter-expanded portion in the axial direction.