Impeller for centrifugal turbomachine and centrifugal turbomachine

1. An impeller for a centrifugal compressor, comprising:

a hub having a small-diameter portion positioned at a first end portion in an axial direction and a large-diameter portion positioned at a second end portion in the axial direction, the large-diameter portion having a greater diameter than the small-diameter portion; and

a plurality of blades disposed on an outer peripheral surface of the hub,

wherein the plurality of blades includes:

two or more blades each of which has a first edge positioned at an axial-directional position of the small-diameter portion so as to define an inlet for to-be-compressed gas flowing into the impeller and a second edge positioned at an axial-directional position of the large-diameter portion,

wherein for each of the two or more blades:

the blade has a first radial-directional cross section which is a cross section orthogonal to the axial direction at an axial-directional position passing a tip of the first edge and a portion of the blade disposed on a radially-inner side of the tip, at least a part of the portion of the blade disposed on the radially-inner side of the tip included in the first radial-directional cross section in a blade-height range of 50% or more being inclined downstream in a rotational direction of the impeller with respect to a radial direction,

wherein the first radial-directional cross section includes:

a first hub-side reference point which is a radial-directional position of the blade at the hub on a first reference line connecting midpoints of the first radial-directional cross section in a blade thickness direction; and

a first tip-side reference point which is a radial-directional position of the tip on the first reference line and is positioned downstream of the first hub-side reference point in the rotational direction, and

wherein, for each of the two or more blades, the first reference line includes a curved portion which has a curvature center at a downstream side, in the rotational direction of the first radial-directional cross section.

2. The impeller according to claim 1 ,

wherein, for each of the two or more blades, the first reference line includes a linear portion.

3. The impeller according to claim 1 ,

wherein, for each of the two or more blades, the first reference line is configured such that:

when an angle θ 1 between a first tangent to a respective midpoint of the first reference line and a radial-directional line passing the respective midpoint is defined such that a sign of the angle θ 1 is positive when the first tangent extending radially outward from the respective midpoint is positioned downstream of the radial-directional line in the rotational direction, and

the angle θ 1 has a maximum value of not smaller than 20 degrees.

4. The impeller according to claim 1 ,

wherein, for each of the two or more blades, when, on a second reference line connecting midpoints of the second radial-directional cross section in a blade thickness direction, a second hub-side reference point is defined as a radial-directional position of the blade at the hub and a second tip-side reference point is defined as a radial-directional position of the tip at the second edge,

the second-tip side reference point is positioned upstream of the second hub-side reference point in the rotational direction.

5. A centrifugal turbomachine, comprising:

the impeller according to claim 1 ; and

a casing disposed so as to cover the impeller.

6. The centrifugal turbomachine according to claim 5 ,

wherein the first edges are leading edges,

wherein the second edges are trailing edges, and

wherein the centrifugal turbomachine is a centrifugal compressor.

7. An impeller for a centrifugal compressor, comprising:

a hub having a small-diameter portion positioned at a first end portion in an axial direction and a large-diameter portion positioned at a second end portion in the axial direction, the large-diameter portion having a greater diameter than the small-diameter portion; and

a plurality of blades disposed on an outer peripheral surface of the hub,

wherein the plurality of blades includes:

two or more blades each of which has a first edge positioned at an axial-directional position of the small-diameter portion so as to define an inlet for to-be-compressed gas flowing into the impeller and a second edge positioned at an axial-directional position of the large-diameter portion,

wherein for each of the two or more blades:

the blade has a first radial-directional cross section which is a cross section orthogonal to the axial direction at an axial-directional position passing a tip of the first edge and a portion of the blade disposed on a radially-inner side of the tip, at least a part of the portion of the blade disposed on the radially-inner side of the tip included in the first radial-directional cross section in a blade-height range of 50% or more being inclined downstream in a rotational direction of the impeller with respect to a radial direction,

wherein the first radial-directional cross section includes:

a first hub-side reference point which is a radial-directional position of the blade at the hub on a first reference line connecting midpoints of the first radial-directional cross section in a blade thickness direction; and

a first tip-side reference point which is a radial-directional position of the tip on the first reference line and is positioned downstream of the first hub-side reference point in the rotational direction, and

wherein, for each of the two or more blades, a phase angular difference Δθ 1 between the first tip-side reference point and the first hub-side reference point is not smaller than 20 angular degrees.

8. An impeller for a centrifugal compressor, comprising:

a hub having a small-diameter portion positioned at a first end portion in an axial direction and a large-diameter portion positioned at a second end portion in the axial direction, the large-diameter portion having a greater diameter than the small-diameter portion; and

a plurality of blades disposed on an outer peripheral surface of the hub,

wherein the plurality of blades includes:

two or more blades each of which has a first edge positioned at an axial-directional position of the small-diameter portion so as to define an inlet for to-be-compressed gas flowing into the impeller and a second edge positioned at an axial-directional position of the large-diameter portion,

wherein for each of the two or more blades:

the blade has a first radial-directional cross section which is a cross section orthogonal to the axial direction at an axial-directional position passing a tip of the first edge and a portion of the blade disposed on a radially-inner side of the tip, at least a part of the portion of the blade disposed on the radially-inner side of the tip included in the first radial-directional cross section in a blade-height range of 50% or more being inclined downstream in a rotational direction of the impeller with respect to a radial direction; and

the blade has a second radial-directional cross section which is a cross section orthogonal to the axial direction at an axial-directional position passing a tip of the second edge, at least a part of the second radial-directional cross section in a blade-height range of 50% or more being inclined upstream in the rotational direction of the impeller with respect to the radial direction,

wherein, for each of the two or more blades, when, on a second reference line connecting midpoints of the second radial-directional cross section in a blade thickness direction, a second hub-side reference point is defined as a radial-directional position of the blade at the hub and a second tip-side reference point is defined as a radial-directional position of the tip at the second edge, and

the second-tip side reference point is positioned upstream of the second hub-side reference point in the rotational direction,

wherein, for each of the two or more blades, the second reference line includes a curved portion which has a curvature center at an upstream side, in the rotational direction of the second radial-directional cross section.

9. The impeller according to claim 8 ,

wherein, for each of the two or more blades, the second reference line includes a linear portion.

10. The impeller according to claim 8 ,

wherein, for each of the two or more blades, the second reference line is configured such that:

when an angle θ 2 between a second tangent to a respective midpoint of the second reference line and a radial-directional line passing the respective midpoint is defined such that a sign of the angle θ 2 is positive when the second tangent extending radially outward from the respective midpoint is positioned upstream of the radial-directional line in the rotational direction; and

the angle θ 2 has a maximum value of not smaller than 30 degrees.

11. An impeller for a centrifugal compressor, comprising:

a hub having a small-diameter portion positioned at a first end portion in an axial direction and a large-diameter portion positioned at a second end portion in the axial direction, the large-diameter portion having a greater diameter than the small-diameter portion; and

a plurality of blades disposed on an outer peripheral surface of the hub,

wherein the plurality of blades includes:

two or more blades each of which has a first edge positioned at an axial-directional position of the small-diameter portion so as to define an inlet for to-be-compressed gas flowing into the impeller and a second edge positioned at an axial-directional position of the large-diameter portion,

wherein for each of the two or more blades:

the blade has a first radial-directional cross section which is a cross section orthogonal to the axial direction at an axial-directional position passing a tip of the first edge and a portion of the blade disposed on a radially-inner side of the tip, at least a part of the portion of the blade disposed on the radially-inner side of the tip included in the first radial-directional cross section in a blade-height range of 50% or more being inclined downstream in a rotational direction of the impeller with respect to a radial direction; and

the blade has a second radial-directional cross section which is a cross section orthogonal to the axial direction at an axial-directional position passing a tip of the second edge, at least a part of the second radial-directional cross section in a blade-height range of 50% or more being inclined upstream in the rotational direction of the impeller with respect to the radial direction,

wherein, for each of the two or more blades, when, on a second reference line connecting midpoints of the second radial-directional cross section in a blade thickness direction, a second hub-side reference point is defined as a radial-directional position of the blade at the hub and a second tip-side reference point is defined as a radial-directional position of the tip at the second edge, and

the second-tip side reference point is positioned upstream of the second hub-side reference point in the rotational direction,

wherein, for each of the two or more blades, a phase angular difference Δθ 2 between the second tip-side reference point and the second hub-side reference point is not smaller than 20 angular degrees.