The present invention relates to a centrifugal compressor which increases a pressure of a fluid to generate a compressed fluid, and particularly, relates to a centrifugal compressor which includes a diffuser part provided on a discharge side of the compressor fluid.
A centrifugal compressor is mainly configured of an impeller which includes a rotating hub and a plurality of centrifugal blades attached to the outer peripheral surface of the hub, and a casing which accommodates the impeller and forms a flow path for a fluid.
In the flow path for the fluid, there are provided a suction flow path through which the fluid is sucked from the outside by rotation of the impeller and the fluid is introduced into the impeller, a diffuser part which is approximately annularly formed on the outer peripheral side of the impeller and recovers a static pressure by decreasing the speed of airflow discharged from the impeller, and a spiral volute part and a discharge pipe which are provided on the outer peripheral side of the diffuser part, are formed so that the cross-sectional areas are enlarged along the peripheral directions, decrease the speed of the airflow, and increase the static pressure of the airflow.
In this centrifugal compressor, when the impeller is rotated, the impeller compresses the fluid such as gas, air, or the like introduced from the outside. The flow (airflow) of the fluid formed in this way is discharged from the outer peripheral end of the impeller to the outside through the discharge pipe via the diffuser part and the volute part.
Meanwhile, in the centrifugal compressor, the compressed air is discharged during a specific period, and thus, the pressure and the flow rate are changed, and a phenomenon such as surging which generates self-excitation vibration occurs. The pressure and the flow rate generated by the surging determine an operation limit of a small flow rate side.
On the other hand, if the flow rate is increased, occlusion of the fluid referred to as choking occurs in the impeller or the diffuser part, and thus, the flow rate range of a large flow rate side is limited.
Accordingly, in order to realize a stable operation in the centrifugal compressor, it is necessary to operate an operational range so that the surging does not occur in the small flow rate side and the choking does not occur in the large flow rate side.
Then, in the diffuser part, seperation occurs on the low flow rate condition, a reverse flow from the volute part reaches the impeller when a reverse flow region generated due to the seperation reaches the rear edge of the diffuser part, and thus, surging occurs.
Accordingly, for example, in the technology disclosed in PTL 1, a circulation passage is provided on a rear side of a wall surface of a diffuser along the flow direction of a fluid, a first opening of the circulation passage is formed on a fluid outlet side of an impeller of the wall surface of the diffuser, and a second opening is formed on a discharge port side of the wall surface of the diffuser.
In this configuration, the fluid, which flows in the vicinity of the wall surface of the diffuser and in which the reverse flow easily occurs, becomes a circulation flow in which the fluid enters from the second opening to the circulation passage and is discharged from the first opening, and thus, an apparent flow rate of the diffuser is increased. Accordingly, the flow in the vicinity of the wall surface is smooth, occurrence of the reverse flow of the fluid is suppressed, and thus, it is possible to increase a flow rate range up to the surge. As a result, it is possible to suppress occurrence of the surging with certainty, due to the reverse flow of the fluid during a low flow rate without damaging the functionality of the diffuser.
In addition, a technology disclosed in PTL 2 includes a configuration in which a circulation flow path is provided, through which a part of a fluid flowing in a diffuser flow path is returned as a circulation fluid from a downstream side region to an upstream side region in the diffuser flow path, and the fluid flowing in the circulation flow path is cooled by cooling means.
Accordingly, the fluid flowing in the circulation flow path is cooled, and is returned to the upstream side region of the diffuser flow path. Therefore, compression performance of the centrifugal compression is improved.
However, it is constantly necessary to further expand an operational range of a centrifugal compressor, and thus, there is still needs for improvement.
In the technologies disclosed in PTL 1 and PTL 2, occurrence of the reverse flows of the fluid is suppressed by circulating a part of the fluid flowing in the diffuser flow path and increasing the flow rate of the appearance, and thus, operational efficiency is substantially decreased.
The present invention is made in consideration of the above-described circumstances, and an object thereof is to provide a centrifugal compressor capable of increasing the operational efficiency while suppressing occurrence of the surging and further expanding the operational range.
According to the present invention, a centrifugal compressor including: an impeller which includes a hub and a plurality of blades attached to the outer peripheral surface of the hub; and a casing which rotatably accommodates the impeller, in which the casing includes: a suction flow path through which a fluid sucked from the outside by rotation of the impeller is introduced to the impeller; a diffuser part which is annularly formed on an outer peripheral side of the impeller, and decelerates the flow of the fluid discharged to the outer peripheral side by the rotation of the impeller; a spiral volute part which is formed on an outer peripheral side of the diffuser part and in which a cross-sectional area is gradually increased along a circumferential direction; a discharge pipe which extends from a part having the largest cross-section area of the volute part toward the outer peripheral side; and a connecting part which is formed on a side wall surface of a diffuser flow path through which the fluid flows in the diffuser part, and causes the inner portion of the volute part and the inner portion of the diffuser flow path to communicate with each other, in which an opening part of the diffuser flow path side of the connecting part is formed on a downstream side of the diffuser flow path, and is formed in only a region from within 30° of a upstream side of the diffuser part to within 30° of a downstream side thereof based on a tongue which is formed between a minimum area part of the volute part and the discharge pipe.
In the centrifugal compressor, the fluid sucked from the outside by the rotation of the impeller is discharged to the diffuser part of the outer peripheral side of the impeller via the suction flow path and is decelerated, and thus, the fluid flows into the volute part. In the volute part, the fluid flows from the side in which the cross-sectional area is small to the side in which the cross-sectional area is large, and is discharged from the discharge pipe to the outside as a high-pressure compressed fluid.
In this case, in the diffuser part, the high-pressure compressed fluid inside the volute part is discharged into the diffuser flow path through the connecting part. Accordingly, a flow rate in which a reverse flow region due to seperation occurring on the diffuser wall surface reaches a rear edge of the diffuser part is further decreased, and thus, it is possible to increase the flow rate range up to the surge. In addition, since the high-pressure compressed fluid passing through the diffuser part is circulated from the volute part, efficiency in the diffuser part is not decreased.
Preferably, a plurality of the connecting parts are formed at set intervals along the circumferential direction of the diffuser part. The connecting part may be a through hole, and may be a slit which is continuous in the circumferential direction of the diffuser part.
Then, in many cases, an axially asymmetrical structure such as a volute part in which the cross-sectional area is spirally increased along the circumferential direction, may exist in the downstream side of the diffuser. According to this influence, a non-uniform static pressure distribution in the circumferential direction exists in the downstream side of the diffuser. According to the non-uniform static pressure distribution, lengths in a radial direction of the reverse flow region with respect to the diffuser flow path wall are different from each other in the circumferential direction. In addition, it is considered that the surging is generated from a location at which the reverse flow region reaches the rear edge the earliest.
Accordingly, preferably, the connecting part is formed at least on an inner peripheral side of the part having the largest cross-section area of the volute part.
In addition, preferably, in the connecting part, at least an end part of the side wall surface side is formed so as to be inclined from the inner peripheral side of the diffuser part toward the outer peripheral side. Accordingly, the high-pressure compressed fluid discharged into the diffuser flow path from the connecting part can flow along the diffuser wall surface, and thus, it is possible to effectively suppress occurrence of the reverse flow of the fluid.
Moreover, in the connecting part, at least the end part of the side wall surface side may be formed so as to be parallel with an outer peripheral side end part of a diffuser vane.
According to a centrifugal compressor of the present invention, occurrence of the surging is suppressed, and it is possible to increase the operational efficiency while further expanding the operational range.
Hereinafter, embodiments of a centrifugal compressor according to the present invention will be described with reference to the drawings.
A centrifugal compressor 10 according to a first embodiment of the present invention will be described.
As shown in
The impeller 12 includes a hub 13 which is integrally provided with the rotary shaft 11 and a plurality of blades 14 which are provided on an outer peripheral surface of the hub 13. In the hub 13, a curved surface 13c in which the outer diameter is gradually increased from an end part 13a of one end side of the rotary shaft 11 toward an end part 13b of the other end side is formed. The plurality of blades 14 are disposed on the curved surface 13c of the hub 13 in the circumferential direction. Here, as shown in
The casing 20 includes a suction flow path 21 which is continuous along an axial direction of the rotary shaft 11 from a suction port 29 formed on one end 20a side toward the impeller 12, a diffuser part 30 which is annularly formed on the outer peripheral side of the impeller 12, a spiral volute part 22 which is continuously formed in the circumferential direction on the outer peripheral (downstream) side of the diffuser part 30 and in which a cross-sectional area in a cross-section orthogonal to the circumferential direction is gradually increased along the circumferential direction, and a discharge pipe 23 which is connected to a maximum area part 22b of the volute part 22 and extends in a tangential direction.
Here, a minimum area part 22a and the discharge pipe 23 are adjacent to the maximum area part 22b in the circumferential direction of the volute part 22. In addition, a tongue 28 is formed between the minimum area part 22a of the volute part 22 and the discharge pipe 23.
The diffuser part 30 is opened to the inner peripheral side (impeller 12 side) and the outer peripheral side (volute part 22 side) over the entire circumference of the outer peripheral part of the impeller 12. The diffuser part 30 includes an annular disk part 31 which is formed on a part of the casing 20, an annular disk 32 which is disposed to oppose the annular disk part 31 at a set interval, and diffuser vanes 33 which are integrally formed with the annular disk 32 and provided at equal intervals in the circumferential direction of the annular disk 32. The diffuser vanes 33 are formed so as to be inclined in the radial direction of the annular disk 32. Accordingly, the interval between the diffuser vanes 33 and 33 adjacent to each other in the circumferential direction of the annular disk 32 is gradually increased from the inner peripheral side toward the outer peripheral side.
In the diffuser part 30, the diffuser flow path 35 is formed between the annular disk part 31 and the annular disk 32.
In the present embodiment, a diffuser member 34 which includes the annular disk 32 and the diffuser vanes 33 is separately formed with the casing 20, and the diffuser member is provided to be interposed between the annular disk part 31 which forms a part of the casing 20 and a holding part 24 of the casing 20 which is formed to oppose the annular disk part 31. Moreover, an inner peripheral side end part 32a of the annular disk 32 is formed in a curved surface shape in which the interval between the inner peripheral side end part 32a and the annular disk part 31 is gradually decreased from an outer peripheral part 12a of the impeller 12 toward the outer periphery.
In addition, an outer peripheral side end part 32b of the annular disk 32 extends the outer peripheral side from the outer peripheral side end part 24a of the holding part 24 and is formed to protrude in the volute part 22. In the annular disk 32, a connecting part 40A through which a side wall surface 32c facing the diffuser flow path 35 and a backface 32d opposite to the side wall surface 32c communicate with each other is formed on the outer peripheral side from the outer peripheral side end part 24a of the holding part 24. A plurality of the connecting parts 40A are formed at set intervals in the circumferential direction of the annular disk 32, and each of the connecting parts 40A is formed of a slit 41 which is continuous in the circumferential direction.
Contrary to what is shown in
Here, preferably, the connecting part 40A configured of the slit 41 or the like is formed so as to be inclined from the inner peripheral side of the diffuser part 30 to the outer peripheral side, from an opening end 40a of the backface 32d side toward an opening end (opening part) 40b of the side wall surface 32c side.
Moreover, in the connecting part 40A, preferably, the opening end 40b of the diffuser flow path 35 side is formed on the downstream side of the diffuser flow path 35. More preferably, the opening end 40b is formed in the outer peripheral side from a position which is positioned 75% from the center side of the diffuser part 30 with respect to the radius of the outer peripheral part of the diffuser part 30. In the inner peripheral side, since a static pressure difference between the opening end 40a and the opening end 40b is increased, a speed of the flow introduced from the connecting part 40A to the diffuser part 30 is increased, and thus, the flow inside the diffuser deteriorates.
An operation of the centrifugal compressor 10 configured in this way will be described below.
The centrifugal compressor 10 rotationally drives the impeller 12 around the rotary shaft 11 by the driving device such as the motor (not shown) or a turbine (not shown). By the rotation of the impeller 12, the fluid taken in the casing 20 through the suction port 29 from the outside flows toward the impeller 12 in the suction flow path 21.
Centrifugal force is applied to the fluid introduced into the casing 20 by the rotation of the blades 14 integrally rotated with the hub 13, and is compressed. The compressed fluid flows from the outer peripheral end of the impeller 12 into the diffuser part 30 of the outer peripheral side. In the diffuser part 30, airflow discharged from the impeller 12 to the outer peripheral side passes between the diffuser vanes 33 and 33 adjacent to the each other in the circumferential direction, and thus, the airflow is decelerated, and the static pressure is recovered. In addition, the fluid flowing in the volute part 22 of the outer periphery from the diffuser part 30 flows from the minimum area part 22a toward the maximum area part 22b, and is discharged from the discharge pipe 23 as a high-pressure compressed fluid.
Here, as shown in
Therefore, it is possible to prevent occurrence of surging in the diffuser part 30, and it is possible to increase the operational range of the centrifugal compressor 10.
In addition, the diffuser member 34 including the annular disk 32 in which the connecting part 40A is formed and the diffuser vanes 33 may be separately formed with the casing 20. Accordingly, it is possible to easily process the connecting part 40A as a single body of the diffuser member 34.
Then, the plurality of slits 41 configuring the connecting part 40A is formed on only a part of the circumference.
On the downstream side of the diffuser part 30, it is known that static pressure distribution which is non-uniform in the circumferential direction exists in the vicinity of the tongue 28 in the volute part 22 in which the cross-sectional area is increased along the circumferential direction.
Accordingly, the slits 41 configuring the connecting part 40A may be formed only within a range from the tongue 28 to within 30° of the upstream side based on the tongue 28.
According to the invention, the slits 41 configuring the connecting part 40A must be formed only in an area from within 30° of the upstream side to within 30° of the downstream side based on the tongue 28 in which the pressure distribution exists.
Next, a second embodiment of the present invention will be described. In the second embodiment described below, in the drawings, the same reference numerals are assigned to the configurations common to the first embodiment, descriptions thereof are omitted, and differences between the first embodiment and the second embodiment are mainly described.
As shown in
Accordingly, the high-pressure compressed fluid flowing into the diffuser flow path 35 from the opening end 40b through the connecting part 40B can suppress turbulence in the flow between the diffuser vanes 33 and 33 adjacent in the circumferential direction. Therefore, it is possible to more certainly prevent occurrence of the surging in the diffuser part 30, and it is possible to further increase the operational range of the centrifugal compressor 10.
Also in this case, the connecting part 40B may be formed in only the range up to within 30° of the upstream side with respect to the tongue 28.
Moreover, the present invention is not limited to the above-described embodiments, and may be appropriately modified within the scope of the appended claims.
For example, the cross-sectional shapes, sizes, dispositions, or the like of the connecting parts 40A and 40B are not limited.
In addition, a plurality of rows (a plurality of plies) of the connecting parts 40A and 40B may be disposed on the inner peripheral side and the outer peripheral side.
Moreover, the diffuser vanes 33 may be removed, and the casing 20 and the holding part 24 may be an integral structure.
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.