Centrifugal compressor

1. A centrifugal compressor provided with an impeller which is configured to have a plurality of blades arranged at a predetermined interval in a circumferential direction of a hub rotating together with a rotation shaft,

wherein a blade angle relative to a meridian plane on a shroud side of the blade distributes to have a minimum value at a position between a leading edge of the blade and a midpoint of a camber line on the shroud side, and a maximum value at a position between the midpoint of the camber line on the shroud side and a trailing edge of the blade;

wherein the blade angle of the blade relative to the meridian plane on a hub side distributes so as to have a maximum value at a position between a leading edge and a midpoint of a camber line on the hub side;

wherein if a blade loading at an arbitrary point of the camber line on the shroud side is a derivative of a product of a circumferential average absolute velocity C θ and a radius r differentiated with respect to a camber line length x as shown by the following formula,

ⅆ

(

r

·

C

θ

)

ⅆ

x

where, r is a radius from an axis center of the rotation shaft at an arbitrary point of the camber line on the shroud side, C θ is a circumferential average absolute velocity of a working fluid flowing in a passage formed in the impeller, and x is a camber line length which is a length measured along the camber line on the shroud side from the leading edge to the arbitrary point of the camber line on the shroud side,

then the blade angle on the shroud side distributes such that the blade loading has a minimum value at the leading edge, increases from the minimum value along the camber line on the shroud side and reaches a maximum value, and decreases from the maximum value toward the trailing edge along the camber line on the shroud side, while maintaining a magnitude of the minimum value of the blade loading so that a reversed flow of the working fluid at the leading edge is suppressed;

wherein a distribution of the blade loading along the camber line on the shroud side has an inflection point at which a rate of rise of the blade loading changes or has a folding point where a rate of rise of the blade loading discontinuously increases at a position between a minimum point of the minimum value of the blade loading and a maximum point of the maximum value of the blade loading, the position being between the leading edge and the midpoint of the camber line on the shroud side;

wherein the blade loading at the inflection point or the folding point is not more than ⅓ of the maximum value of the blade loading; and

wherein the inflection point is a throat position of the blade.

2. The centrifugal compressor according to claim 1 ,

wherein the blade angle on the shroud side has a maximum value at the trailing edge.

3. The centrifugal compressor according to claim 1 ,

wherein the blade angle on the hub side is larger than the blade angle on the shroud side at a position between the leading edge and the midpoint of the camber line on the hub side, and smaller than the blade angle on the shroud side at a part of a position between the midpoint and the trailing edge of the camber line on the hub side.

4. The centrifugal compressor according to claim 1 , wherein the blade loading increases from the minimum value along the camber line on the shroud side and reaches a maximum value at a position between the leading edge and the midpoint.

5. The centrifugal compressor according to claim 1 , wherein the blade loading increases from the minimum value along the camber line on the shroud side and reaches a maximum value at a position between the midpoint and the trailing edge.

6. The centrifugal compressor according to claim 1 ,

wherein a suction flow coefficient is in a range from 0.09 to 0.15.

7. A method for manufacturing a centrifugal compressor provided with an impeller which is configured to have a plurality of blades arranged at a predetermined interval in a circumferential direction of a hub rotating together with a rotation shaft, the method comprising steps of:

distributing a blade angle relative to a meridian plane on a shroud side of the blade to have a minimum value at a position between a leading edge of the blade and a midpoint of a camber line on the shroud side, and a maximum value at a position between the midpoint of the camber line on the shroud side and a trailing edge of the blade; and

distributing a blade angle of the blade relative to the meridian plane on a hub side so as to have a maximum value at a position between a leading edge and a midpoint of a camber line on the hub side;

providing a distribution of the blade loading along the camber line on the shroud side to have an inflection point at which a rate of rise of the blade loading changes or to increase a folding point where a rate of rise of the blade loading discontinuously at a position between a minimum point of the minimum value of the blade loading and a maximum point of the maximum value of the blade loading, the position being between the leading edge and the midpoint of the camber line on the shroud side; and

being the inflection point a throat position of the blade.

8. The method for manufacturing a centrifugal compressor according to claim 7 , further comprising a step of:

determining a distribution of the blade angle on the shroud side from a distribution of the blade loading along the camber line on the shroud side by using an inverse design method.