Scroll casing and centrifugal compressor

1. A scroll casing which forms a scroll flow passage of a centrifugal compressor,

wherein, provided that, in a cross section of the scroll flow passage, Ei is an inner end of the scroll flow passage in a radial direction of the centrifugal compressor, and Mh is a middle point of a maximum flow-passage height Hmax of the scroll flow passage in an axial direction of the centrifugal compressor,

the scroll flow passage has a separation suppressing cross section in which the inner end Ei is disposed on an inner side, in the radial direction, of a diffuser outlet, and the inner end Ei is disposed on a back side, in the axial direction, of the middle point Mh, in a section disposed at least partially in an upstream region of a connection position of a scroll start and a scroll end,

wherein, provided that an angular position about a scroll center of the scroll flow passage is zero degree at the connection position and the angular position is θ at a position upstream of the connection position,

the separation suppressing cross section is disposed at least in a section from θ=zero degree to a

predetermined angular position,

wherein the separation suppressing cross section is not disposed in a section upstream of the predetermined angular position,

wherein the predetermined angular position is an angular position of not less than 60 degrees and not more than 150 degrees.

2. The scroll casing according to claim 1 ,

wherein the scroll flow passage includes a section having a circular cross section at an upstream side of the predetermined angular position.

3. A centrifugal compressor, comprising:

an impeller; and

the scroll casing according to claim 1 , the scroll casing being disposed around the impeller and forming the scroll flow passage into which a fluid flows after passing through the impeller.

4. A scroll casing which forms a scroll flow passage of a centrifugal compressor,

wherein, provided that, in a cross section of the scroll flow passage, Ei is an inner end of the scroll flow passage in a radial direction of the centrifugal compressor, and Mh is a middle point of a maximum flow-passage height Hmax of the scroll flow passage in an axial direction of the centrifugal compressor,

the scroll flow passage has a separation suppressing cross section in which the inner end Ei is disposed on an inner side, in the radial direction, of a diffuser outlet, and the inner end Ei is disposed on a back side, in the axial direction, of the middle point Mh, in a section disposed at least partially in an upstream region of a connection position of a scroll start and a scroll end,

wherein, provided that an angular position about a scroll center of the scroll flow passage is zero degree at the connection position and the angular position is θ at a position upstream of the

connection position,

the separation suppressing cross section is disposed at least in a section from θ=zero degree to a predetermined angular position,

wherein, at least in a part of the section of the scroll flow passage from θ=zero degree to the predetermined angular position, the inner end Ei of the separation suppressing cross section is shifted backward in the axial direction with a distance from an upstream side toward the connection position.

5. A scroll casing which forms a scroll flow passage of a centrifugal compressor,

wherein, provided that, in a cross section of the scroll flow passage, Ei is an inner end of the scroll flow passage in a radial direction of the centrifugal compressor, and Mh is a middle point of a maximum flow-passage height Hmax of the scroll flow passage in an axial direction of the centrifugal compressor,

the scroll flow passage has a separation suppressing cross section in which the inner end Ei is disposed on an inner side, in the radial direction, of a diffuser outlet, and the inner end Ei is disposed on a back side, in the axial direction, of the middle point Mh, in a section disposed at least partially in an upstream region of a connection position of a scroll start and a scroll end,

wherein, provided that an angular position about a scroll center of the scroll flow passage is zero degree at the connection position and the angular position is θ at a position upstream of the connection position,

the separation suppressing cross section is disposed at least in a section from θ=zero degree to a

predetermined angular position,

wherein, at least in a part of the section of the scroll flow passage from θ=zero degree to the predetermined angular position, a flow-passage wall portion connecting the inner end Ei and a front end Ef of the scroll flow passage with respect to the axial direction has a curved surface portion which protrudes toward a cross-sectional center of the separation suppressing surface.

6. The scroll casing according to claim 5 ,

wherein the curved surface portion is formed so as to have a curvature radius which decreases from an upstream side of the scroll flow passage toward the connection position.

7. A scroll casing which forms a scroll flow passage of a centrifugal compressor,

wherein, provided that, in a cross section of the scroll flow passage, Ei is an inner end of the scroll flow passage in a radial direction of the centrifugal compressor, and Mh is a middle point of a maximum flow-passage height Hmax of the scroll flow passage in an axial direction of the centrifugal compressor,

the scroll flow passage has a separation suppressing cross section in which the inner end Ei is disposed on an inner side, in the radial direction, of a diffuser outlet, and the inner end Ei is disposed on a back side, in the axial direction, of the middle point Mh, in a section disposed at least partially in an upstream region of a connection position of a scroll start and a scroll end,

wherein, in the cross section of the scroll flow passage, in a case where Lz is a line passing through a middle point Mw of a maximum flow-passage width Wmax of the scroll flow passage in the radial direction and parallel to the axial direction, Lr is a line passing through the middle point Mh and parallel to the radial direction, and the separation suppressing cross section is divided into four regions by the line Lz and the line Lr,

a flow-passage wall portion belonging to a region positioned on an outer side in the radial direction and on a front side in the axial direction of an intersection C of the line Lz and the line Lr, of the four regions, includes an arc portion having a first curvature radius R 1 ,

a flow-passage wall portion belonging to a region positioned on an inner side in the radial direction and on a front side in the axial direction of the intersection C, of the four regions, includes an arc portion having a second curvature radius R 2 which is greater than the first curvature radius R 1 , and

a flow-passage wall portion belonging to a region positioned on an inner side in the radial direction and on a back side in the axial direction of the intersection C, of the four regions, includes an arc portion having a third curvature radius R 3 which is smaller than the second curvature radius R 2 .

8. A scroll casing which forms a scroll flow passage of a centrifugal compressor,

wherein, provided that, in a cross section of the scroll flow passage, Ei is an inner end of the scroll flow passage in a radial direction of the centrifugal compressor, and Mh is a middle point of a maximum flow-passage height Hmax of the scroll flow passage in an axial direction of the centrifugal compressor,

the scroll flow passage has a separation suppressing cross section in which the inner end Ei is disposed on an inner side, in the radial direction, of a diffuser outlet, and the inner end Ei is disposed on a back side, in the axial direction, of the middle point Mh, in a section disposed at least partially in an upstream region of a connection position of a scroll start and a scroll end,

wherein, provided that an angular position about a scroll center of the scroll flow passage is zero degree at the connection position and the angular position is θ at a position upstream of the connection position,

the separation suppressing cross section is disposed at least in a section from θ=zero degree to a predetermined angular position,

wherein, at least in a part of the section of the scroll flow passage from θ=zero degree to the predetermined angular position, the maximum flow-passage height Hmax and a distance Δz between the inner end Ei of the separation suppressing cross section and the middle point Mh in the axial direction satisfies Δz≥0.1×Hmax.

9. A scroll casing which forms a scroll flow passage of a centrifugal compressor,

wherein, provided that, in a cross section of the scroll flow passage, Ei is an inner end of the scroll flow passage in a radial direction of the centrifugal compressor, and Mh is a middle point of a maximum flow-passage height Hmax of the scroll flow passage in an axial direction of the centrifugal compressor,

the scroll flow passage has a separation suppressing cross section in which the inner end Ei is disposed on an inner side, in the radial direction, of a diffuser outlet, and the inner end Ei is disposed on a back side, in the axial direction, of the middle point Mh, in a section disposed at least partially in an upstream region of a connection position of a scroll start and a scroll end,

wherein, provided that an angular position about a scroll center of the scroll flow passage is zero degree at the connection position and the angular position is θ at a position upstream of the connection position,

the separation suppressing cross section is disposed at least in a section from θ=zero degree to a predetermined angular position,

wherein the scroll flow passage is formed so that the inner end Ei is shifted forward in the axial direction with a distance from the connection position toward an outlet of the scroll flow passage, and

wherein, at least in a part of the section of the scroll flow passage from the connection position toward the outlet of the scroll flow passage, a flow-passage wall portion connecting the inner end Ei and a front end Ef of the scroll flow passage with respect to the axial direction has a curved surface portion which protrudes toward a cross-sectional center of the separation suppressing surface.