JP2010190080A - Centrifugal compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To further increase the operating range of a centrifugal compressor 1 while increasing the efficiency thereof. <P>SOLUTION: An annular extraction groove 27 is formed in the shroud wall 5 of a casing 3 further on the downstream side than the leading edge of a blade 15. An outflow hole 29 is formed in the shroud wall 5 of the casing 3 further on the upstream side of the leading edge of the blade 15. An annular treatment cavity 31 is formed inside the casing 3. An annular shroud step surface 35 is formed in the shroud wall 5 of the casing 3 in such a manner that the inner diameter of the opening downstream side end 27a of the extraction groove 27 is larger than the inner diameter of the opening upstream side end 27b thereof. A plate step surface 37 corresponding to the shroud step surface 35 is formed at the outer edge of the blade 15. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a centrifugal compressor that is used in a supercharger, a gas turbine, an industrial air facility, and the like, and compresses a gas such as air using centrifugal force.

  In recent years, various studies have been made to expand the operating range of a centrifugal compressor, and there are those shown in Patent Document 1 and Patent Document 2 as centrifugal compressors having an expanded operating range.

  Hereinafter, a centrifugal compressor according to the prior art will be described with reference to FIG.

  Here, FIG. 5 is a schematic cross-sectional side view of the main part of the centrifugal compressor according to the prior art. In the drawings, “F” indicates the forward direction, and “R” indicates the backward direction.

  A centrifugal compressor 101 according to the prior art includes a casing 103, and the casing 103 has a shroud wall 105 on the inner side. An impeller 107 is rotatably provided in the shroud wall 105 of the casing 103, and the impeller 107 rotates around an axis (an axis of the impeller 107, in other words, an axis of the casing 103). A possible hub 109 and a plurality of blades 111 (only one is shown) provided at intervals on the outer peripheral surface of the hub 109 are provided. Here, the outer edge of each blade 111 extends along the shroud wall 105 of the casing 103.

  A suction port 113 for sucking air (an example of gas) to the impeller 107 side is formed at the upstream peripheral edge of the shroud wall 105 of the casing 103, and compressed at the downstream peripheral edge of the shroud wall 105 of the casing 103. An annular diffuser passage 115 (one of the exhaust passages) for exhausting air is formed. Further, on the downstream side (rear side) of the blade 111 on the shroud wall 105 of the casing 103 on the downstream side (rear side), an extraction hole 117 capable of extracting backflowed air is formed, and the blade on the shroud wall 105 of the casing 103 is formed. An outflow hole 119 through which air can flow out to the impeller 107 side is formed on the upstream side (front side) of the front edge position of 111. An annular treatment cavity 121 that allows air to flow from the extraction hole 117 side to the outflow hole 119 side is formed in the casing 103.

  Therefore, when the centrifugal compressor 101 is operated, for example, by rotating a plurality of blades 111 integrally with the hub 109 by rotating a turbine wheel (not shown) or the like, in other words, by rotating the impeller 107. The air sucked from the suction port 113 toward the impeller 107 can be compressed using centrifugal force. The compressed air is decelerated from the diffuser channel 115 and exhausted.

  During operation of the centrifugal compressor 101, if the operating point of the centrifugal compressor 101 moves to an off-design region where the air flow rate on the inlet side of the impeller 107 is small, air in the impeller 107 (part of the air sucked into the impeller 107 side). ) Occurs, and the backflowed air is extracted from the extraction hole 117 and flows into the treatment cavity 121. Then, the air flowing into the treatment cavity 121 flows from the extraction hole 117 side to the outflow hole 119 side, flows out from the outflow hole 119 to the inlet side of the impeller 107, and is again sucked into the impeller 107 side. Thereby, a part of the air sucked into the impeller 107 side can be circulated between the extraction hole 117 and the outflow hole 119, and the operation of the centrifugal compressor 101 can be stabilized. As a result, the operation of the centrifugal compressor 101 can be stabilized. The area can be expanded to the low flow rate side.

JP 2006-342682 A JP 2003-31496 A

  By the way, when the backflow of air becomes large in the impeller 107, the backflowed air cannot be sufficiently extracted from the extraction holes 117, and the operation of the centrifugal compressor 101 becomes unstable, and the centrifugal compressor 101 becomes surging. Will come. In recent years, there has been an increasing demand for further expanding the operating range of the centrifugal compressor 101 by sufficiently suppressing the surging of the centrifugal compressor 101.

  Then, an object of this invention is to provide the centrifugal compressor of a novel structure which can solve the above-mentioned subject.

  The present invention is characterized in that, in a centrifugal compressor that compresses gas by utilizing centrifugal force, a casing having a shroud wall on the inside thereof, and a rotatable inside the shroud wall of the casing, and rotating around an axis. A possible hub, and an impeller provided with a plurality of blades that are circumferentially spaced on the outer peripheral surface of the hub and whose outer edges extend along the shroud wall of the casing, A suction port (air supply port) for sucking (supplying) gas to the impeller side is formed in the upstream peripheral edge of the shroud wall of the casing, and the compressed gas is exhausted to the downstream peripheral edge of the shroud wall of the casing. An exhaust passage is formed, and an annular bleed groove is formed that can bleed the gas that has flowed back downstream from the front edge position of the blade in the shroud wall of the casing. An outflow hole through which gas can flow out to the inlet side of the impeller is formed on the shroud wall of the casing on the upstream side of the front edge position of the blade, and the bleed groove side to the outflow hole side in the casing. An annular treatment cavity that allows gas flow (circulation) is formed, and an annular shroud step surface on the shroud wall of the casing such that the inner diameter of the downstream end of the extraction groove is larger than the inner diameter of the upstream end of the opening And a blade step surface corresponding to the shroud step surface is formed on the outer edge of the blade.

  Here, in the claims and the specification, the “upstream side” means the upstream side when viewed from the flow direction of the mainstream gas, and the “downstream side” refers to the flow direction of the mainstream gas. This is the downstream side. Further, the “plurality of blades” may be composed of a plurality of types of blades having different axial lengths. In this case, the “leading edge position of the blade” refers to the blade having the longest axial length. It is the position of the leading edge, and the “outer edge of the blade” is the outer edge of the blade having the longest axial length. Further, the “outflow hole” includes an outflow groove, the “opening downstream end” refers to the downstream end of the opening, and the “opening upstream end” refers to the upstream end of the opening. That is.

  According to a first aspect of the present invention, when the centrifugal compressor is operated, a plurality of the blades are rotated together with the hub, in other words, the impeller is rotated to rotate the suction. The gas sucked from the mouth to the impeller side can be compressed using centrifugal force. The compressed gas is exhausted from the exhaust passage.

  During operation of the centrifugal compressor, when the operating point of the centrifugal compressor moves to an off-design region where the gas flow rate on the inlet side of the impeller is small, gas in the impeller (part of gas sucked into the impeller side) Backflow occurs. The backflowed gas is extracted from the bleed groove, flows from the bleed groove side to the outflow hole side in the treatment cavity, flows out from the outflow hole to the inlet side of the impeller, and again the impeller 7 Inhaled to the side. Thereby, a part of the air suck | inhaled to the impeller side can be circulated between the said extraction groove | channel and the said outflow hole, and the operation | movement of the said centrifugal compressor can be stabilized.

  The annular shroud step surface is formed on the shroud wall of the casing so that the inner diameter of the opening downstream end of the bleed groove is larger than the inner diameter of the upstream opening end, and the shroud step surface is formed on the outer edge of the blade. Since the blade step surface corresponding to is formed, while suppressing the so-called clearance flow that flows relatively from the pressure surface side of the blade to the suction surface side, even if the back flow of gas in the impeller increases, The gas flowing back by the shroud step surface is blocked to sufficiently extract air from the extraction groove.

  According to the present invention, the clearance flow relatively flowing from the pressure surface side to the suction surface side of the blade is suppressed, and even if the back flow of gas in the impeller becomes large, the air is sufficiently extracted from the extraction groove. Therefore, while maintaining the efficiency of the centrifugal compressor (compressor efficiency), surging of the centrifugal compressor can be sufficiently suppressed, and the operating range of the centrifugal compressor can be further expanded.

It is a typical sectional side view of the centrifugal compressor which concerns on embodiment of this invention. It is a typical sectional side view of the principal part of the centrifugal compressor which concerns on embodiment of this invention. FIG. 3A is an enlarged view of the arrow portion III in FIG. 2, and FIGS. 3B and 3C are diagrams showing blade steps of different modes. It is a figure which shows compressor performance. It is a typical sectional side view of the principal part of the centrifugal compressor which concerns on a prior art.

  An embodiment of the present invention will be described with reference to FIGS. In the drawings, “F” indicates the forward direction, and “R” indicates the backward direction.

  As shown in FIG.1 and FIG.2, the centrifugal compressor 1 which concerns on embodiment of this invention is used for a supercharger, and compresses air (an example of gas) using a centrifugal force. And the specific structure of the centrifugal compressor 1 which concerns on embodiment of this invention is as follows.

  The centrifugal compressor 1 includes a casing 3, and the casing 3 has a shroud wall 5 inside. The casing 3 is integrally attached to another casing (not shown).

  An impeller 7 is rotatably provided in the shroud wall 5 of the casing 3. Specifically, a hub 9 is provided in the shroud wall 5 of the casing 3, and the outer peripheral surface of the hub 9 gradually increases from the axial direction of the casing 3 (in other words, the axial direction of the impeller 7). The casing 3 extends outward in the radial direction of the casing 3 (in other words, the radial direction of the impeller 7). The hub 9 is integrally connected to one end portion (front end portion) of a rotor shaft 11 rotatably provided in another casing via a tightening nut 13, and the shaft center (in other words, the impeller 7). Then, it can rotate around the axis 3 of the casing 3. Further, on the outer peripheral surface of the hub 9, a plurality of long blades (full blades) 15 (only one is shown) and a plurality of short blades (splitter blades 17) (splitter blades) 17 are spaced apart in the circumferential direction. Are provided alternately. Here, the front edge of the long blade 15 is located on the upstream side (front side) of the front edge of the short blade 17, and the outer edge of the long blade 15 and the outer edge of the short blade 17 are the shroud wall 5 of the casing 3. It extends so that. Instead of using two types of blades 15 and 17 having different axial lengths, blades having the same axial length may be used.

  A suction port (air supply port) 19 for sucking (supplying) air to the impeller 7 side is formed at the upstream peripheral edge (inlet peripheral edge of the impeller 7) of the shroud wall 5 of the casing 3. An annular diffuser flow path 21 (one of the exhaust flow paths) is formed on the downstream peripheral edge (outlet peripheral edge of the impeller 7) of the shroud wall 5 to decelerate and exhaust the compressed air. A spiral scroll channel 23 (one of the exhaust channels) for exhausting compressed air is formed on the peripheral side of the diffuser channel 21 inside the casing 3. A discharge port 25 for discharging compressed air is formed at an appropriate position of the casing 3, and this discharge port 25 communicates with the scroll flow path 23 and the diffuser flow path 21, and is connected to the internal combustion engine. It can be connected to an intake manifold (not shown).

  On the shroud wall 5 of the casing 3 on the downstream side (rear side) of the front edge position of the long blade 15 and on the upstream side of the front edge position of the blade 17, an annular extraction groove 27 capable of extracting backflowed air. Is formed. Further, on the upstream side of the front edge position of the long blade 15 in the shroud wall 5 of the casing 3, one or a plurality of (only one shown) outflow holes 29 through which air can flow out to the impeller 7 side are provided in the circumferential direction. Are formed along. An annular treatment cavity 31 that allows air flow (circulation) from the extraction groove 27 side to the outflow hole 29 side is formed inside the casing 3. Further, a narrowed portion 33 is formed between the impeller 7 and the outflow hole 29 in the shroud wall 5 of the casing 3, and the narrowed portion 33 is gradually reduced in inner diameter toward the downstream side.

  As shown in FIGS. 2 and 3A, the inner diameter of the opening downstream end (the downstream end of the opening) 27a of the bleed groove 27 is larger than the inner diameter of the opening upstream end (the upstream end of the opening) 27b. An annular shroud step surface 35 is formed on the shroud wall 5 of the casing 3. A blade step surface 37 corresponding to the shroud step surface 35 is formed on the outer edge of each long blade 15. Here, the step amount (step height) m of the blade step surface 37 is the same as the step amount k of the shroud step surface 35, and the blade step surface 37 is close to the shroud step surface 35.

  As shown in FIG. 3B, the blade step surface 37 is positioned between the opening downstream end 27a and the opening upstream end 27b of the bleed groove 27 in the axial direction of the casing 3 (left-right direction in FIG. 3). If so, it may not be close to the shroud step surface 35. Further, as shown in FIGS. 3A and 3B, the blade step surface 37 is formed between the opening downstream end 27a and the opening upstream end 27b of the bleed groove 27 in the axial direction of the casing 3 (left and right direction in FIG. 3). As shown in FIG. 3C, it may be located at the same position as the opening downstream end 27 a of the bleed groove 27 in the axial direction of the casing 3.

  Then, the effect | action and effect of embodiment of this invention are demonstrated.

  When the centrifugal compressor 1 is operated, for example, by rotating the rotor shaft 11 by rotating a turbine wheel (not shown), the blades 15 and 17 are rotated integrally with the hub 9, in other words, The impeller 7 is rotated. Thereby, the air suck | inhaled from the inlet 19 to the impeller 7 side can be compressed using a centrifugal force. The compressed air is exhausted from the diffuser flow path 21 and the scroll flow path 23 and is sent to the intake manifold of the internal combustion engine via the discharge port 25.

  During operation of the centrifugal compressor 1, if the operating point of the centrifugal compressor 1 moves to an off-design region where the air flow rate on the inlet side of the impeller 7 is small, air in the impeller 7 (part of the air sucked into the impeller 7 side) ) Occurs, and the backflowed air is extracted from the extraction groove 27 and flows into the treatment cavity 31. Then, the air that has flowed into the treatment cavity 31 flows from the extraction groove 27 side to the outflow hole 29 side, outflows from the outflow hole 29 to the inlet side of the impeller 7, and is again sucked into the impeller 7 side. Thereby, a part of the air sucked into the impeller 107 side is circulated between the extraction groove 27 and the outflow hole 29, and the operation of the centrifugal compressor 1 can be stabilized.

  Here, an annular shroud step surface 35 is formed on the shroud wall 5 of the casing 3 so that the inner diameter of the opening downstream end 27a of the bleed groove 27 is larger than the inner diameter of the opening upstream end 27b. Since the blade step surface 37 corresponding to the shroud step surface 35 is formed, the so-called clearance flow relatively flowing from the pressure surface side to the suction surface side of each long blade 15 is suppressed, and the air in the impeller 7 is suppressed. Even if the backflow increases, the backflowed air is blocked by the shroud step surface 35 and the air can be sufficiently extracted from the air extraction groove 27.

  Further, since the constricted portion 33 is formed between the impeller 7 and the outflow hole 29 in the shroud wall 5 of the casing 3, even if air flows out from the outflow hole 29 to the inlet side of the impeller 7, the rectifying action due to the contraction flow. This can reduce energy loss on the inlet side of the impeller 7.

  Therefore, according to the embodiment of the present invention, the clearance flow relatively flowing from the pressure surface side to the suction surface side of each long blade 15 is suppressed, and the energy loss on the inlet side of the impeller 7 is reduced, while the impeller 7 has an internal loss. Even if the back flow of air increases, the air can be sufficiently extracted from the extraction groove 27, so that the surging of the centrifugal compressor 1 can be sufficiently suppressed while improving the efficiency (compressor efficiency) of the centrifugal compressor 1. Then, as shown in FIG. 4, the operating range of the centrifugal compressor 1 can be further expanded by shifting the surge limit (surge line) of the centrifugal compressor 1 to the low flow rate side. In FIG. 4, Na, Nb, and Nc are the rotational speeds of the centrifugal compressor 1 and have a relationship of Na> Nb> Nc.

  The present invention is not limited to the description of the above-described embodiment, and can be implemented in various other aspects. Further, the scope of rights encompassed by the present invention is not limited to these embodiments.

DESCRIPTION OF SYMBOLS 1 Centrifugal compressor 5 Shroud wall 7 Impeller 9 Hub 15 Long blade 17 Short blade 19 Suction port 21 Diffuser channel 23 Scroll channel 25 Discharge port 27 Extraction groove 27a Opening downstream end 27b Opening upstream end 29 Outflow hole 31 Treatment cavity 33 Restriction Part 35 shroud step surface 37 blade step surface

Claims (3)

In a centrifugal compressor that compresses gas using centrifugal force,
A casing having a shroud wall on the inside;
A hub rotatably provided in the shroud wall of the casing and rotatable about an axis, and a circumferentially spaced outer peripheral surface of the hub and having an outer edge along the shroud wall of the casing An impeller having a plurality of blades extending in a manner
An inlet for sucking gas into the impeller side is formed at the upstream peripheral edge of the shroud wall of the casing, and an exhaust passage for exhausting compressed gas is formed at the downstream peripheral edge of the shroud wall of the casing,
An annular bleed groove is formed in the shroud wall of the casing so as to extract gas that has flowed back downstream from the front edge position of the blade, and upstream of the front edge position of the blade in the shroud wall of the casing. An outflow hole through which gas can flow out to the inlet side of the impeller is formed, and an annular treatment cavity that allows gas flow from the bleed groove side to the outflow hole side is formed inside the casing,
An annular shroud step surface is formed on the shroud wall of the casing so that the inner diameter of the opening downstream end of the bleed groove is larger than the inner diameter of the opening upstream end, and a blade corresponding to the shroud step surface on the outer edge of the blade A centrifugal compressor characterized in that a step surface is formed.   The step amount of the blade step surface is the same as the step amount of the shroud step surface, and the blade step surface is between the opening downstream end and the opening upstream end of the bleed groove in the axial direction of the casing, or 2. The centrifugal compressor according to claim 1, wherein the centrifugal compressor is located at the same position as a position of an opening downstream end of the bleed groove in the axial direction.   The centrifuge according to claim 1 or 2, wherein a constricted portion having an inner diameter gradually reduced toward the downstream side is formed between the impeller and the outflow hole in the shroud wall of the casing. Compressor.

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