TECHNICAL FIELD

The present disclosure relates to a centrifugal compressor and a turbocharger including the centrifugal compressor.

BACKGROUND ART

Centrifugal compressors include a closed type in which the entire blades are covered with a shroud cover and an open type in which the blades are not covered with a shroud cover. Patent Documents 1 to 3 disclose a centrifugal compressor in which the blades are covered with a shroud cover partially in the rotational axis direction of the impeller, for instance, on the leading edge side of the blades.

CITATION LIST

Patent Literature

Patent Document 1: JPH6-235398APatent Document 2: JPH6-193594APatent Document 3: JP3653054B

SUMMARY

Problems to be Solved

The shroud cover provided to the centrifugal compressor in Patent Documents 1 to 3 is cylindrical with a constant shape along the circumferential direction of the shroud cover. Covering the blades with such a shroud cover has an advantage of reducing the occurrence of clearance flow, but also has some disadvantages. The conventional cylindrical shroud cover cannot overcome these disadvantages.

In view of the above, an object of at least one embodiment of the present disclosure is to provide a centrifugal compressor which includes blades covered with a shroud cover partially in the rotational axis direction of an impeller but can reduce disadvantages caused by the provision of the shroud cover, and a turbocharger including the centrifugal compressor.

Solution to the Problems

(1) A centrifugal compressor according to at least one embodiment of the present disclosure comprises: an impeller rotatably disposed and having a plurality of first blades; and a shroud cover disposed on a leading edge side of the first blades partially in a rotational axis direction of the impeller and connecting the first blades circumferentially adjacent to each other. The shroud cover is shaped such that a position of at least one of an upstream edge or a downstream edge of the shroud cover in the rotational axis direction changes along a circumferential direction of the shroud cover.

With the above configuration (1), since the shroud cover has a shape that can deal with disadvantages caused by the provision of the shroud cover, it is possible to reduce the disadvantages.

(2) In some embodiments, in the above configuration (1), a portion of the shroud cover connected to a pressure side of each first blade and a portion of the shroud cover connected to a suction side of each first blade are each in a range of 30% or less of a meridional length of each first blade from the leading edge toward a trailing edge of the first blade.

The present inventors have performed CFD analysis and consequently found that the clearance flow mainly occurs in a range of 30% or less of the meridional length of the first blade. With the above configuration (2), by the shroud cover disposed in the range of 30% or less of the meridional length of the first blade from the leading edge toward the trailing edge of the first blade, it is possible to reduce the occurrence of clearance flow.

(3) In some embodiments, in the above configuration (1) or (2), one of a portion of the shroud cover connected to a pressure side of each first blade or a portion of the shroud cover connected to a suction side of each first blade is longer than the other.

A first natural mode of vibration of the first blade consists of vibration of a leading edge portion of the first blade. Accordingly, when the shroud cover is disposed on the leading edge side of the first blade, the mass is applied to the vibrating portion, which leads to a reduction in eigenvalue. However, with the above configuration (3), since the shroud cover has a portion with a narrow width in the rotational axis direction, it is possible to reduce the mass of the shroud cover, and as a result, it is possible to reduce vibration of the blade, compared with the case where the width of the shroud cover in the rotational axis direction is constant along the circumferential direction.

Further, the clearance flow at the leading edge of the first blade occurs from the pressure side to the suction side of the first blade. Accordingly, in order to reduce the occurrence of loss due to clearance flow, the shroud cover has only to cover a necessary range of the first blade on either the pressure side or the suction side of the first blade. With the above configuration (3), the occurrence of loss due to clearance flow is suppressed by the portion connected to the pressure side or the suction side of the first blade.

(4) In some embodiments, in any one of the above configurations (1) to (3), a portion of the upstream edge of the shroud cover between a portion connected to a pressure side of one of two circumferentially adjacent first blades of the plurality of first blades and a portion connected to a suction side of the other of the two circumferentially adjacent first blades is positioned further toward a trailing edge side of the first blades than a throat position.

When the blade is covered with the shroud cover, the throat area may be reduced, so that the flow rate may be reduced. With the above configuration (4), since the shroud cover is disposed away from the throat position, it is possible to suppress the reduction in flow rate.

(5) In some embodiments, in the above configuration (4), a leading end of the portion of the shroud cover connected to the pressure side of the first blade is positioned at the leading edge of the first blade, and a leading end of the portion of the shroud cover connected to the suction side of the first blade is positioned further toward the trailing edge side of the first blades than the throat position.

With the above configuration (5), since the shroud cover is disposed away from the throat position, it is possible to suppress the reduction in flow rate.

(6) In some embodiments, in any one of the above configurations (1) to (5), the impeller further includes a plurality of second blades each of which is disposed between two circumferentially adjacent first blades of the plurality of first blades, each second blade having a leading edge positioned further toward a trailing edge side than the leading edge of each first blade, each second blade having a meridional length shorter than each first blade. The shroud cover connects the circumferentially adjacent first blades and the second blades disposed between the first blades.

With the above configuration (6), since the shroud cover connects the first blade with the second blade having a different vibration mode from the first blade, it is possible to reduce vibration in the natural mode of the first blade.

(1) A centrifugal compressor according to at least one embodiment of the present disclosure comprises: an impeller rotatably disposed and having a plurality of first blades and a plurality of second blades each of which is disposed between two circumferentially adjacent first blades of the plurality of first blades; and a shroud cover disposed on a leading edge side of the first blades partially in a rotational axis direction of the impeller. Each second blade has a leading edge positioned further toward a trailing edge side than a leading edge of each first blade and has a meridional length shorter than each first blade. The shroud cover connects the circumferentially adjacent first blades and the second blades disposed between the first blades.

With the above configuration (7), since the shroud cover connects the first blade with the second blade having a different vibration mode from the first blade, it is possible to reduce vibration in the natural mode of the first blade.

(8) A turbocharger according to at least one embodiment of the present disclosure comprises: the centrifugal compressor described in any one of the above (1) to (7).

With the above configuration (8), since the shroud cover has a shape that can deal with disadvantages caused by the provision of the shroud cover, it is possible to reduce the disadvantages.

Advantageous Effects

According to at least one embodiment of the present disclosure, since the shroud cover is shaped such that the position of at least one of the upstream edge or the downstream edge of the shroud cover in the rotational axis direction changes along the circumferential direction of the shroud cover, the shroud cover has a shape that can deal with disadvantages caused by the provision of the shroud cover. Thus, it is possible to reduce the disadvantages.

