Axial flow rotating machine and diffuser
An axial flow rotating machine has: a rotor with a plurality of rotor blades; a stator with a plurality of stator blades; an axial flow rotating portion defined by the rotor and the stator; and a diffuser connected to the axial flow rotating portion on a downstream side of the axial flow rotating portion. A final blade portion inner-circumferential inner wall, which is a portion of an inner-circumferential inner wall of the axial flow rotating portion, is defined such that a diameter thereof at a trailing edge position of a final blade is smaller than the diameter at a leading edge position of the final blade. In addition, a diameter of all or a portion of a diffuser inner-circumferential inner wall decreases in a direction of the downstream side in an axial direction.
1. A diffuser configured to be connected to a final-stage rotor blade of a turbine on a downstream side of the final-stage rotor blade, the diffuser comprising:
an outer-circumferential inner wall;
an inner-circumferential inner wall; and
a strut cover,
wherein:
the outer-circumferential inner wall is positioned on an outer circumferential side of the inner-circumferential inner wall such that the outer-circumferential inner wall is separated from the inner-circumferential inner wall and a circular flow path is defined between the outer-circumferential inner wall and the inner-circumferential inner wall;
the strut cover connects the inner-circumferential inner wall and the outer-circumferential inner wall in a radial direction inside the circular flow path;
the inner-circumferential inner wall includes a first inclination portion and a second inclination portion downstream of the first inclination portion;
the first inclination portion is a straight linear portion inclined at a first inclination angle in a cross section of the diffuser along an axial direction;
the second inclination portion is a straight linear portion inclined at a second inclination angle in the cross section of the diffuser along the axial direction;
the first inclination angle is different from the second inclination angle;
a diameter of the inner-circumferential inner wall along the second inclination portion decreases in a direction of a downstream side in the axial direction; and
an end of the first inclination portion is between a leading edge position of the strut cover and a trailing edge position of the strut cover in the axial direction.
2. The diffuser according to claim 1 , wherein the first inclination portion and the second inclination portion are connected at a position between the leading edge position of the strut cover and the trailing edge position of the strut cover in the axial direction.
3. The diffuser according to claim 2 , wherein the position between the leading edge position of the strut cover and the trailing edge position of the strut cover in the axial direction is a position between a throat position and the trailing edge position of the strut cover in the axial direction.
4. The diffuser according to claim 2 , wherein:
the second inclination angle is equal to or greater than the first inclination angle; and
the second inclination angle is less than 0 degrees.
5. The diffuser according to claim 1 , wherein:
the second inclination angle is equal to or greater than the first inclination angle; and
the second inclination angle is less than 0 degrees.
6. The diffuser according to claim 1 , wherein:
the diameter of the inner-circumferential inner wall along the second inclination portion is a second diameter; and
a first diameter of the inner-circumferential inner wall along the first inclination portion increases in the direction of the downstream side in the axial direction.
7. The diffuser according to claim 1 , wherein a cross section of the strut cover is blade-shaped.
8. A diffuser configured to be connected to a final-stage rotor blade of a turbine on a downstream side of the final-stage rotor blade, the diffuser comprising:
an outer-circumferential inner wall;
an inner-circumferential inner wall; and
a strut cover,
wherein:
the outer-circumferential inner wall is positioned on an outer circumferential side of the inner-circumferential inner wall such that the outer-circumferential inner wall is separated from the inner-circumferential inner wall and a circular flow path is defined between the outer-circumferential inner wall and the inner-circumferential inner wall;
the strut cover connects the inner-circumferential inner wall and the outer-circumferential inner wall in a radial direction inside the circular flow path;
the inner-circumferential inner wall includes a first portion and a second portion downstream of the first portion;
the first portion is a straight linear portion disposed at a first angle in a cross section of the diffuser along an axial direction;
the second portion is a straight linear portion disposed at a second angle in the cross section of the diffuser along the axial direction;
the first angle is different from the second angle;
a diameter of the inner-circumferential inner wall along the first portion decreases in a direction of a downstream side in the axial direction; and
the first portion and the second portion are connected at a position between a leading edge position of the strut cover and a trailing edge position of the strut cover in the axial direction.