Centrifugal turbomachine

Abstract

This centrifugal turbomachine comprises an impeller, a diffuser disposed on an outer peripheral side of the impeller, and a casing accommodating the impeller and the diffuser. The casing has: a volute that is disposed on the outer periphery of the diffuser and collects fluid discharged from the diffuser; and a discharge pipe connected to a terminal end of the volute. The discharge pipe has a first opening connected to the terminal end of the volute, and a second opening extending along an extension direction of the discharge pipe. The casing has a connection part that is disposed on the outer periphery of the diffuser and forms a tongue-part flow passage which connects a starting end of the volute and the second opening of the discharge pipe.

Description

centrifugal turbomachinery

[0001] The present disclosure relates to the configuration of centrifugal turbomachines.

[0002] Conventionally, centrifugal turbomachines have been known that transfer mechanical work and hydrodynamic energy through pressure on the blade surfaces. Examples of centrifugal turbomachines include compressors, superchargers, pumps, etc. Patent Document 1 discloses a turbine pump, which is a type of centrifugal turbomachine.

[0003] The centrifugal turbomachine disclosed in Patent Document 1 includes an impeller, a casing in which the impeller is journaled, a plurality of guide vanes arranged radially between the outer periphery of the impeller and the inner wall of the casing, an outlet volute that forms a scroll passage around the plurality of guide vanes, and a discharge pipe connected to the end of the outlet volute. In this centrifugal turbomachine, fluid that flows axially into the impeller is imparted with energy by centrifugal force as it passes radially through the rotating impeller. The fluid that has passed through the impeller flows into the volute through gaps between the plurality of guide vanes. The fluid that is collected in the volute is discharged to the outside through the discharge pipe.

[0004] JP 2017-214838 A

[0005] In centrifugal turbomachines, a tongue exists at the connection between the volute and the discharge pipe, separating the scroll flow in the volute from the discharge flow in the discharge pipe. The fluid around the tongue flows through the tongue in one direction toward the scroll and in the other direction toward the discharge. Near the tongue, the flow field becomes turbulent, resulting in a loss of fluid energy. Furthermore, some of the fluid may flow back beyond the tongue and into the discharge pipe. In this case, the discharge flow contracts due to the backflow into the discharge pipe. As a result, the effective cross-sectional area of ​​the discharge pipe decreases, increasing the flow velocity of the discharge flow and resulting in a loss of fluid energy.

[0006] The present disclosure has been made in consideration of the above circumstances, and its purpose is to reduce turbulence in the flow field in the confluence region of the discharge flow in the discharge pipe and the backflow from the volute in a centrifugal turbomachine.

[0007] In order to solve the above problems, a centrifugal turbomachine according to one aspect of the present disclosure comprises: an impeller; a diffuser arranged on the outer periphery of the impeller; and a casing that houses the impeller and the diffuser, wherein the casing has a volute arranged on the outer periphery of the diffuser to collect fluid discharged from the diffuser, and a discharge pipe connected to an end of the volute, the discharge pipe having a first opening connected to the end of the volute and a second opening extending along the extension direction of the discharge pipe, and the casing further has a connecting portion arranged on the outer periphery of the diffuser that forms a tongue flow path that connects the start end of the volute and the second opening of the discharge pipe.

[0008] According to the present disclosure, in a centrifugal turbomachine, it is possible to reduce turbulence in the flow field in the confluence region of the discharge flow in the discharge pipe and the backflow from the volute.

[0009] Fig. 1 is a meridian plane view showing the overall configuration of a centrifugal turbocompressor according to one embodiment of the present disclosure. Fig. 2 is a radial cross-sectional view of a volute and its periphery according to a first example. Fig. 3 is a perspective view of the volute and its surrounding flow passage according to the first example. Fig. 4 is a radial cross-sectional view of a volute and its periphery according to a second example. Fig. 5 is a diagram explaining the flow of fluid in the volute and its periphery according to the first example. Fig. 6 is a diagram showing a numerical analysis model of a conventional volute. Fig. 7 is a Mach number distribution diagram of the center cross-section of the pipe obtained by numerical analysis.

[0010] Next, an embodiment of the present disclosure will be described with reference to the drawings. Here, a centrifugal turbo compressor will be used as an example of a centrifugal turbo machine. However, the configuration of the centrifugal turbo machine according to the present disclosure is not limited to a compressor, and may be applied to a pump, a blower, or the like.

[0011] Figure 1 is a meridian plane view showing the overall configuration of a centrifugal turbo compressor 1 according to one embodiment of the present disclosure. The centrifugal turbo compressor 1 shown in Figure 1 includes a casing 2, a rotating shaft 3 rotatably supported by the casing 2, and multiple impellers 4 disposed inside the casing 2 and fixed to the rotating shaft 3. The multiple impellers 4 are aligned in an axial direction X of the rotating shaft 3. Here, the direction in which a central axis A of the rotating shaft 3 extends is referred to as the "axial direction X," the radial direction relative to the central axis A is referred to as the "radial direction," the direction approaching the central axis A in this radial direction is referred to as the "radially inward direction," the direction moving away from the central axis A in the radial direction is referred to as the "radially outward direction," and the circumferential direction about the central axis A is referred to as the "circumferential direction."

[0012] The casing 2 is provided with an intake passage 22 that draws in fluid and sends it to the first-stage impeller 4. The casing 2 also has a stationary passage 5 that sends the fluid discharged from the impeller 4 to the next-stage impeller 4. A combination of the impeller 4 and the stationary passage 5 constitutes a stage, which serves as a unit of pressure increase in the centrifugal turbo compressor 1. The fluid drawn into the intake passage 22 is pressurized each time it passes through a stage made up of the impeller 4 and the stationary passage 5.

[0013] A diffuser 45 is provided on the outer periphery of the final-stage impeller 4. The flow of fluid discharged from the final-stage impeller 4 passes through the diffuser 45 radially outward. A scroll passage 46 is connected to the outlet of the diffuser 45. The scroll passage 46 is a spiral-shaped passage that surrounds the diffuser 45. The outlet of the scroll passage 46 is connected to the inlet of the discharge passage 23 that is connected to the outside. The fluid that has discharged from the final-stage impeller 4 is decelerated by the diffuser 45 to restore static pressure, collected in the scroll passage 46, and discharged to the outside through the discharge passage 23. However, the passage shapes and number of stages of the centrifugal turbo compressor 1 described above are merely examples.

[0014] The basic configuration of the centrifugal turbo compressor 1 described above is the same as that of a conventional centrifugal turbo compressor. In the centrifugal turbo compressor 1 according to the present disclosure, an ingenious connection structure between the scroll passage 46 and the discharge passage 23 is provided. The connection structure between the scroll passage 46 and the discharge passage 23 will be described in detail below.

[0015] Fig. 2 is a radial cross-sectional view of the volute 31 and its surroundings according to the first example. Fig. 3 is a perspective view of the volute 31 and its surrounding flow passages according to the first example. As shown in Figs. 1, 2, and 3, the casing 2 has a volute 31 connected to a diffuser 45. The volute 31 forms a scroll flow passage 46 surrounded by a volute inner wall 32. The scroll flow passage 46 is a spiral flow passage, and the winding direction corresponds to the rotation direction R of the impeller 4.

[0016] The cross-sectional area of ​​the scroll passage 46 gradually increases from the start end 33 to the end end 34 of the volute 31. Here, the cross-sectional area of ​​the scroll passage 46 is a plane perpendicular to the center line along the direction of fluid flow in the scroll passage 46. The start end 33 of the volute 31 corresponds to the outlet of the scroll passage 46.

[0017] The casing 2 has a discharge pipe 24 connected to a terminal end 34 of the volute 31. A discharge flow path 23 is formed within the discharge pipe 24. The discharge flow path 23 is a flow path in which a fluid flows in a direction other than the circumferential direction. The discharge pipe 24 has a first opening 25 and a second opening 26 at its upstream end. The first opening 25 is a substantially circular pipe end opening with an opening axis parallel to the extension direction of the discharge pipe 24. The terminal end 34 of the volute 31 is connected to the first opening 25. Meanwhile, the second opening 26 is a slit-shaped opening in the pipe wall of the discharge pipe 24 that extends parallel to the extension direction of the discharge pipe 24. The size of the second opening 26 in the axial direction X is the same as or larger than the size of the start end 33 of the volute 31 in the axial direction X.

[0018] The casing 2 has a connection portion 29 arranged circumferentially between the start end 33 of the volute 31 and the second opening 26 of the discharge pipe 24. The connection portion 29 forms a tongue flow passage 27 that circumferentially connects the start end 33 of the volute 31 in the counter-rotational direction to the second opening 26 of the discharge pipe 24. The tongue flow passage 27 connects the scroll flow passage 46 and the discharge flow passage 23. The tongue flow passage 27 has a delta shape in which the cross-sectional area of ​​the flow passage gradually decreases radially outward from the central axis A. Here, the cross-section of the tongue flow passage 27 is a surface formed by gathering points of the tongue flow passage 27 that are the same distance from the central axis A.

[0019] The connection portion 29 of the casing 2 has a connection portion outer peripheral wall 28 that forms the outer peripheral edge of the tongue flow path 27. The connection portion outer peripheral wall 28 connects the outer peripheral edge of the start end 33 of the volute 31 and the downstream end edge of the second opening 26 of the discharge pipe 24. The connection portion 29 of the casing 2 also has a pair of connection portion side walls that sandwich the tongue flow path 27 from both sides in the axial direction X. The distance in the axial direction X between the pair of connection portion side walls is the same as or greater than the dimension in the axial direction X of the start end 33 of the volute 31.

[0020] The angle of the rotation direction R of the volute 31 from the starting end 33 to the ending end 34 is 270° or more and 310° or less. In other words, the angle of the rotation direction R of the volute 31 from the ending end 34 to the starting end 33 is 50° or more and 90° or less.

[0021] At the connection between the starting end 33 of the volute 31 and the connection portion outer peripheral wall 28, the connection portion outer peripheral wall 28, as viewed from the axial direction X, is located on a tangent to the outer peripheral edge of the starting end 33 of the volute 31, or is located radially outward of the tangent.

[0022] At the intersection of the connection portion outer wall 28 and the discharge pipe 24, the angle formed by the tangential direction of the connection portion outer wall 28 and the extension direction of the discharge pipe 24 as viewed from the axial direction X (hereinafter referred to as the connection angle θ) is a right angle or an obtuse angle, and preferably is greater than or equal to 90° and less than or equal to 135°.

[0023] In the volute 31 according to the first example shown in Figure 2, the angle of the rotation direction R from the starting end 33 to the ending end 34 is approximately 290°, and the angle of the rotation direction R from the inlet of the discharge pipe 24 to the starting end 33 of the volute 31 is approximately 70°. The connection angle θ between the connecting portion outer peripheral wall 28 and the discharge pipe 24 is approximately 90°. The connecting portion outer peripheral wall 28 is disposed along a tangent to the outer peripheral edge at the starting end 33 of the volute 31.

[0024] Figure 4 is a radial cross-sectional view of a volute 31A and its periphery according to the second example. In the volute 31A according to the second example shown in Figure 4, the angle of the rotational direction R from the start point 33 to the end point 34 of the volute 31 is approximately 290°, and the angle of the rotational direction R from the inlet of the discharge pipe 24 to the start point 33 of the volute 31 is approximately 70°. The connection angle θ between the connection portion outer peripheral wall 28 and the discharge pipe 24 is approximately 120°. When viewed from the axial direction X, at the intersection of the connection portion outer peripheral wall 28 and the discharge pipe 24, the tangent direction of the connection portion outer peripheral wall 28 has a component parallel to the direction in which the fluid in the discharge pipe 24 flows downstream. Furthermore, the connection portion outer peripheral wall 28 is located radially outward of the tangent to the outer peripheral edge at the start point 33 of the volute 31.

[0025] FIG. 5 is a diagram illustrating the volute 31 according to the first example and the flow of fluid around it. As shown in FIG. 5 , the volute 31 according to the first example of the present disclosure does not have a conventional tongue separating the scroll passage 46 and the discharge passage 23 between the start end 33 of the volute 31 and the discharge pipe 24. Instead, the portion corresponding to the conventional tongue is a tongue passage 27 through which fluid flows. Fluid flowing into the scroll passage 46 from the diffuser 45 becomes a scroll flow 92 that flows downstream through the scroll passage 46 while swirling. The scroll flow 92 flows from the outlet of the scroll passage 46 into the discharge passage 23 and becomes a discharge flow 91. The discharge flow 91 then passes through the discharge passage 23 and flows out to the outside. Here, fluid flows in the counter-rotating direction from the start end 33 of the volute 31 into the tongue passage 27, generating a backflow 93. Fluid flows directly into the tongue passage 27 from the diffuser 45 without passing through the scroll passage 46, and merges with the backflow 93 from the scroll passage 46. The backflow 93 from the tongue passage 27 flows into the discharge passage 23 through the second opening 26 of the discharge pipe 24. In the discharge passage 23, the discharge flow 91 (i.e., the main flow) and the backflow 93 from the tongue passage 27 merge near the second opening 26. However, compared to when the discharge flows merge at a conventional tongue, the inlet area for the backflow 93 is larger, and the backflow 93 is rectified by the tongue passage 27, so that turbulence in the flow field at the merger region of the discharge flow 91 and the backflow 93 is suppressed. This suppresses flow contraction of the discharge flow 93 in the discharge passage 23, suppresses a decrease in the effective cross-sectional area of ​​the discharge passage 23, and as a result, suppresses energy loss of the fluid. In the volute 31 and discharge pipe 24 of the second example shown in FIG. 4 , the fluid flows in the same way as in the volute 31 and discharge pipe 24 of the first example.

[0026] <<Evaluation of Flow Field of Volute>> Here, the results of a numerical analysis of Mach number conducted to evaluate the flow field, particularly in the confluence region of the discharge flow and the reverse flow, for a conventional volute and the volutes 31, 31A according to the present disclosure will be described.

[0027] FIG. 6 is a diagram showing a numerical analysis model of a conventional volute 131. In the numerical analysis, a typical conventional volute 131 shown in FIG. 6 was used as a comparative example. The numerical analysis model of the conventional volute 131 includes a diffuser 145, a volute 131 surrounding the outer periphery of the diffuser 145, and a discharge pipe 124 connected to the terminal end 134 of the volute 131. Fluid that flows from the outer periphery of the diffuser 145 into a volute passage 146 in the volute 131 passes from the volute passage 146 through a discharge passage 123 in the discharge pipe 124 and is discharged to the outside. The terminal end 134 of the volute 131 is connected to the discharge pipe 124, and a tongue 150 that divides the fluid flow into a scroll flow and a discharge flow is provided at the connection between the starting end 133 of the volute 131 and the discharge pipe 124.

[0028] FIG. 7 shows Mach number distribution diagrams of the pipe center cross section obtained by numerical analysis for the volute 31 according to the first example (see FIG. 2), the volute 31A according to the second example (see FIG. 4), and the conventional volute 131 according to the comparative example (see FIG. 6). In FIG. 7, the Mach numbers are indicated by different colors. In the volute 131 according to the comparative example, a high Mach number occurs locally at the tip of the tongue 150. In the volute 131 according to the comparative example, at the confluence region between the backflow that has entered the discharge flow path 23 beyond the tongue 150 and the discharge flow in the discharge flow path 123, the backflow extends into the discharge flow path 123, causing a contraction in the discharge flow, resulting in a high Mach number locally. On the other hand, in the volute 31 according to the first example and the volute 31A according to the second example of the present disclosure, the backflow from the scroll passage 46 to the tongue passage 27 mixes with the flow from the diffuser 45 while passing through the tongue passage 27, and then merges with the discharge flow in the discharge passage 23. In this confluence region, contraction of the discharge flow is suppressed, there is no local increase in the Mach number, and turbulence in the flow field in the confluence region is suppressed.

[0029] [Summary] A centrifugal turbomachine 1 according to a first item of the present disclosure comprises an impeller 4, a diffuser 45 arranged on the outer periphery of the impeller 4, and a casing 2 accommodating the impeller 4 and the diffuser 45, wherein the casing 2 has volutes 31, 31A arranged on the outer periphery of the diffuser 45 to collect fluid discharged from the diffuser 45, and a discharge pipe 24 connected to a terminal end 34 of the volute 31, wherein the discharge pipe 24 has a first opening 25 connected to the terminal end 34 of the volutes 31, 31A, and a second opening 26 extending along the extension direction of the discharge pipe 24, and the casing 2 further has a connecting portion 29 arranged on the outer periphery of the diffuser 45 and forming a tongue flow path 27 connecting a starting end 33 of the volute 31 and the second opening 26 of the discharge pipe 24.

[0030] In the centrifugal turbomachine 1 configured as described above, the backflow from the start end 33 of the volute 31 is rectified while passing through the tongue passage 27 of the connecting portion 29, and then flows into the discharge passage 23 from the second opening 26 to merge with the discharge flow in the discharge pipe 24. The backflow is rectified by passing through the tongue passage 27, and also flows into the discharge pipe 24 through the second opening 26 extending along the extension direction of the discharge pipe 24. Therefore, turbulence in the flow field in the merger region of the backflow and discharge flow is suppressed, and contraction of the discharge flow is suppressed. As a result, loss of fluid energy can be suppressed.

[0031] The centrifugal turbomachine 1 according to the second item of the present disclosure is the centrifugal turbomachine 1 according to the first item, wherein the connection portion 29 has a connection portion outer peripheral wall 28 that connects the outer peripheral edge of the starting end 33 of the volute 31, 31A and the downstream end edge of the second opening 26 of the discharge pipe 24, and when viewed from the axial direction X of the impeller 4, at the intersection of the connection portion outer peripheral wall 28 and the discharge pipe 24, the angle formed by the tangent direction of the connection portion outer peripheral wall 28 and the extension direction of the discharge pipe 24 is 90° or more and 135° or less.

[0032] The centrifugal turbomachine 1 according to the third item of the present disclosure is the centrifugal turbomachine 1 according to the second item, in which, when viewed from the axial direction X, at the intersection of the connection portion outer peripheral wall 28 and the discharge pipe 24, the tangential direction of the connection portion outer peripheral wall 28 has a component parallel to the direction in which the fluid in the discharge pipe 24 flows downstream.

[0033] The centrifugal turbomachine 1 according to the fourth item of the present disclosure is a centrifugal turbomachine 1 according to any one of the first to third items, in which the connection portion outer wall 28 is arranged along a tangent to the outer peripheral edge of the starting end 33 of the volute 31.

[0034] The centrifugal turbomachine 1 according to the fifth item of the present disclosure is a centrifugal turbomachine 1 according to any one of the first to fourth items, in which the connection portion outer wall 28 is positioned radially outward of the tangent to the outer peripheral edge of the starting end 33 of the volute 31.

[0035] In the centrifugal turbomachine 1 relating to the second to fifth items, the backflow flow flowing from the tongue flow path 27 into the discharge pipe 24 through the second opening 26 has a component parallel to the direction in which the fluid in the discharge pipe 24 flows downstream, and therefore, disturbance of the flow field can be suppressed in the confluence area of ​​the backflow and discharge flow.

[0036] The centrifugal turbomachine 1 according to the sixth item of the present disclosure is a centrifugal turbomachine 1 according to any one of the first to fifth items, in which the tongue flow passage 27 has a flow passage cross-sectional area that gradually decreases radially outward.

[0037] In the centrifugal turbomachine 1 configured as described above, the backflow from the volute 31 that has flowed into the tongue passage 27 is rectified in the tongue passage 27 together with the backflow from the diffuser 45. Therefore, turbulence in the flow field at the confluence region of the backflow that has flowed into the discharge pipe 24 and the discharge flow in the discharge pipe 24 can be suppressed.

[0038] The centrifugal turbomachine 1 according to the seventh item of the present disclosure is a centrifugal turbomachine 1 according to any one of the first to sixth items, in which the angle of the rotation direction R from the starting end 33 to the ending end 34 of the volute 31 is 270° or more and 310° or less.

[0039] In the centrifugal turbomachine 1 configured as described above, the end 34 and the starting end 33 of the volute 31 are spaced apart in the direction of rotation R, allowing the tongue flow passage 27 provided between the end 34 and the starting end 33 to be made larger, and also making it possible to increase the connection angle θ between the outer peripheral wall 28 of the connection portion of the tongue flow passage 27 and the discharge pipe 24.

[0040] The foregoing discussion of the present disclosure has been presented for purposes of illustration and description and is not intended to limit the present disclosure to the form disclosed herein. For example, in the foregoing detailed description, various features of the present disclosure are grouped together in a single embodiment for the purpose of streamlining the disclosure, but some of the features may also be combined. Furthermore, the features included in the present disclosure may be combined into alternative embodiments, configurations, or aspects other than those discussed above.

Claims

1. A centrifugal turbomachine comprising: an impeller; a diffuser arranged on the outer periphery of the impeller; and a casing that houses the impeller and the diffuser, wherein the casing has a volute arranged on the outer periphery of the diffuser to collect fluid discharged from the diffuser, and a discharge pipe connected to an end of the volute, the discharge pipe having a first opening connected to the end of the volute and a second opening extending along the extension direction of the discharge pipe, and the casing further has a connecting portion arranged on the outer periphery of the diffuser that forms a tongue flow passage that connects the start end of the volute and the second opening of the discharge pipe.

2. A centrifugal turbomachine as set forth in claim 1, wherein the connection portion has a connection portion outer peripheral wall connecting the outer peripheral edge of the starting end of the volute and the downstream end edge of the second opening of the discharge pipe, and when viewed in the axial direction of the impeller, at the intersection of the connection portion outer peripheral wall and the discharge pipe, the angle formed between the tangent direction of the connection portion outer peripheral wall and the extension direction of the discharge pipe is between 90° and 135°.

3. A centrifugal turbomachine according to claim 2, wherein, as viewed in the axial direction, at the intersection of the outer peripheral wall of the connection portion and the discharge pipe, the tangential direction of the outer peripheral wall of the connection portion has a component parallel to the direction in which the fluid in the discharge pipe flows downstream.

4. A centrifugal turbomachine according to claim 2 or 3, wherein the outer peripheral wall of the connection portion is disposed along a tangent to the outer peripheral edge of the starting end of the volute.

5. A centrifugal turbomachine according to claim 2 or 3, wherein the outer peripheral wall of the connection portion is located radially outward of a tangent to the outer peripheral edge of the starting end of the volute.

6. A centrifugal turbomachine according to any one of claims 1 to 3, wherein the tongue flow passage has a flow passage cross-sectional area that gradually decreases radially outward.

7. A centrifugal turbomachine according to any one of claims 1 to 3, wherein the angle in the rotational direction from the start end to the end end of the volute is equal to or greater than 270° and equal to or less than 310°.

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