Impeller and rotary machine

1. An impeller comprising:

a disk that has a disk shape and is configured to rotate around an axis;

a plurality of blades that are provided at intervals in a circumferential direction on a side of a surface of the disk toward a direction of the axis and extend to a rear side in a rotation direction as the plurality of the blades go toward an outer side in a radial direction; and

a cover that covers the plurality of blades in the direction of the axis, wherein

each of the plurality of the blades has:

a primary blade which extends to the rear side in the rotation direction as the primary blade goes from an inner side toward the outer side in the radial direction and of which a rear edge is positioned on the inner side with respect to an outer circumferential edge portion of the disk in the radial direction, and

a secondary blade which is provided at intervals on a side in front of the primary blade in the rotation direction to correspond to the primary blade, of which a front edge is positioned on the outer side with respect to a front edge of the primary blade in the radial direction, and of which a rear edge is positioned on the outer circumferential edge portion of the disk,

a region between the disk and the cover facing each other in the direction of the axis is divided into a disk side region, a cover side region, and a central region between the disk side region and the cover side region, and

the secondary blade is not provided in the central region but is provided in at least one of the disk side region and the cover side region.

2. The impeller according to claim 1 , wherein a rear edge side region on a pressure surface of the primary blade and a front edge side region on a suction surface of the secondary blade corresponding to the primary blade face each other.

3. The impeller according to claim 2 , wherein the secondary blade has a plurality of stages of secondary blade pieces sequentially arranged toward the outer side in the radial direction, and a front edge of the secondary blade piece on a rear stage side of adjacent secondary blade pieces is positioned on a side in front of a rear edge of the secondary blade piece on a front stage side in the rotation direction.

4. The impeller according to claim 1 , wherein the secondary blade is disposed close to the corresponding primary blade of a pair of primary blades adjacent to each other.

5. The impeller according to claim 4 , wherein the secondary blade has a plurality of stages of secondary blade pieces sequentially arranged toward the outer side in the radial direction, and a front edge of the secondary blade piece on a rear stage side of adjacent secondary blade pieces is positioned on a side in front of a rear edge of the secondary blade piece on a front stage side in the rotation direction.

6. The impeller according to claim 1 , wherein the secondary blade has a plurality of stages of secondary blade pieces sequentially arranged toward the outer side in the radial direction, and a front edge of the secondary blade piece on a rear stage side of adjacent secondary blade pieces is positioned on a side in front of a rear edge of the secondary blade piece on a front stage side in the rotation direction.

7. The impeller according to claim 1 , wherein a chord length of the secondary blade is within a range of 5% to 30% of a chord length of the primary blade.

8. A rotary machine comprising:

the impeller according to claim 1 .

9. The impeller according to claim 1 , wherein the secondary blade is not provided in the central region but is provided in the disk side region and the cover side region.

10. The impeller according to claim 1 , wherein the cover forms a flow channel of the impeller along with the surface of the disk on which the plurality of blades are provided.

11. An impeller comprising:

a disk that has a disk shape and is configured to rotate around an axis;

a plurality of blades that are provided at intervals in a circumferential direction on a side of a surface of the disk toward a direction of the axis and extend to a rear side in a rotation direction as the plurality of the blades go toward an outer side in a radial direction, wherein

each of the plurality of the blades has:

a primary blade which extends to the rear side in the rotation direction as the primary blade goes from an inner side toward the outer side in the radial direction and of which a rear edge is positioned on the inner side with respect to an outer circumferential edge portion of the disk in the radial direction, and

a secondary blade which is provided at intervals on a side in front of the primary blade in the rotation direction to correspond to the primary blade, of which a front edge is positioned on the outer side with respect to a front edge of the primary blade in the radial direction, and of which a rear edge is positioned on the outer circumferential edge portion of the disk, and

when an angle formed by line segments respectively connecting the rear edges of the adjacent primary blades and the axis viewed in the direction of the axis is θ 1 , and when an angle formed by the line segment connecting the rear edge of the primary blade and the axis and a line segment connecting the front edge of the secondary blade corresponding to the primary blade and the axis viewed in the direction of the axis is θ 2 , θ 2 /θ 1 ≤0.1 is established.