Diffusers and Centrifugal Pumps

Abstract

To suppress the occurrence of rotating stall while suppressing a decrease in efficiency of a centrifugal pump. [Solution] The diffuser 7 is a diffuser arranged adjacent to the impeller in the axial direction of the rotating shaft of the centrifugal pump. The diffuser has a flow passage forming portion 84 and a plurality of vanes 9 that divide a plurality of diffuser flow passages. Each vane has a positive pressure surface 91a-98a, a negative pressure surface 91b-98b, and a front end 91c-98c, 95c-98d. The vane has a plurality of long vanes 91-94 and at least one short vane 95-98 that is shorter than the long vane. The long vane has at least one specific length vane arranged adjacent to the positive pressure surface side of the short vane corresponding to the long vane. In the axial direction, the front end of the short vane is arranged rearward of the front end of the long vane. The specific length vane has a communication flow passage 91d that opens to the positive pressure surface and the negative pressure surface of the specific length vane.

Description

[Technical field]

[0001] The present invention relates to a diffuser and a centrifugal pump. [Background technology]

[0002] A diffuser is attached to the discharge side of the impeller of the centrifugal pump, converting the velocity energy given to the handled liquid by the impeller into pressure energy. The diffuser has a plurality of vanes. The vanes form a plurality of diffuser passages for decelerating the handled liquid discharged from the impeller and increasing its pressure. The shape of the vanes (i.e., the shape of the diffuser passage) is designed based on the design point of the centrifugal pump. Therefore, when the centrifugal pump is operated at a flow rate smaller than the design point, the flow of the handled liquid in the diffuser passage separates from the vane surface. As the area where the separation occurs increases, a stall occurs in which the flow in the diffuser passage stagnates. The stall does not occur in all the diffuser passages of the diffuser, but mainly in one diffuser passage. As a result, the symmetry of the flow of the handled liquid with respect to the central axis of the centrifugal pump is lost, and a force acting on the centrifugal pump in the radial direction of the rotating shaft is generated. The stall propagates to the adjacent diffuser passage so as to rotate in the circumferential direction of the rotating shaft over time. As a result, the direction of the force acting on the centrifugal pump changes, causing vibrations in the centrifugal pump. This phenomenon is called rotating stall.

[0003] In order to prevent this rotating stall, a technique is known in which a slit is formed in the vane to divide the vane into two in the longitudinal direction of the vane (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-26496 Summary of the Invention [Problem to be solved by the invention]

[0005] In the technology disclosed in Patent Document 1, when a centrifugal pump is operated at a small flow rate, the forced flow straightening force of the vane is reduced by the slits, and the occurrence of rotating stall is suppressed. However, when a slit is formed in the vane, a part of the vane is chipped, and the pressure boosting function of the vane is reduced, and the efficiency of the centrifugal pump is slightly reduced. In recent years, as environmental issues have become a hot topic, a method for suppressing the occurrence of rotating stall while suppressing the decrease in efficiency of the centrifugal pump is desired.

[0006] An object of the present invention is to suppress the occurrence of rotating stall while suppressing a decrease in efficiency of a centrifugal pump. [Means for solving the problem]

[0007] In one embodiment of the present invention, a diffuser is disposed adjacent to an impeller in an axial direction of a rotating shaft of a centrifugal pump, the direction in which the impeller is disposed relative to the diffuser in the axial direction is a forward direction, and the direction in which the diffuser is disposed relative to the impeller is a rearward direction, the diffuser comprising: a flow passage forming portion having a cylindrical outer peripheral surface; and a plurality of vanes disposed on the outer peripheral surface and defining a plurality of diffuser flow passages, through which handled fluid discharged from the impeller flows, each of the plurality of vanes comprising a pressure surface, a suction surface which is a surface opposite to the pressure surface, and a front end portion disposed continuous with the pressure surface and the suction surface, the plurality of vanes comprising a plurality of long vanes and at least one short vane which is shorter than the long vane, The multiple long vanes include at least one specific length vane arranged on the positive pressure side of the short vane corresponding to the long vane, adjacent to the short vane corresponding to the long vane, and in the axial direction, the front end of the short vane is arranged rearward of the front end of the long vane, and the specific length vane includes a communicating flow passage that opens to the positive pressure side of the specific length vane and the negative pressure side of the specific length vane.

[0008] A centrifugal pump in one embodiment of the present invention includes a motor, a rotating shaft rotated by the motor, an impeller attached to the rotating shaft, and the diffuser described in the above embodiment that is disposed adjacent to the impeller in the axial direction of the rotating shaft. Effect of the Invention

[0009] The present invention suppresses the occurrence of rotating stall while suppressing a decrease in efficiency of a centrifugal pump. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view of a centrifugal pump showing an embodiment of the centrifugal pump according to the present invention. [Diagram 2] FIG. 2 is a partial schematic enlarged cross-sectional view of the centrifugal pump. [Diagram 3] 1 is a perspective view of a diffuser showing an embodiment of a diffuser according to the present invention. FIG. [Figure 4] FIG. 4 is a bottom view of the diffuser. [Diagram 5] FIG. 2 is a side view of the diffuser. [Figure 6] FIG. 2 is a schematic development view of the diffuser. [Figure 7] FIG. 2 is a partially enlarged schematic view of the diffuser showing the vicinity of a long vane and a short vane of the diffuser. [Figure 8] FIG. 4 is a schematic diagram showing an example of a method for designing the length of a short vane of the diffuser. [Figure 9] 4 is a schematic diagram showing a flow of a handled fluid in a diffuser flow passage formed by the diffuser. FIG. [Figure 10] 1 is a graph showing the results of measuring the rotating stall occurrence flow rate in an embodiment of the present invention, a reference example, and a comparative example. [Figure 11] 1 is a graph showing actual measurement results of pump efficiency at design points in an embodiment of the present invention, a reference example, and a comparative example. [Figure 12]6 is a graph showing a result of a simulation analysis of the flow rate of the diffuser passage at a design point of a reference example of the present invention. [Figure 13] 6 is a graph showing a result of a simulation analysis of a flow rate of the diffuser passage at a design point of an embodiment of the present invention. [Figure 14] 10 is a graph showing a result of a simulation analysis of a flow rate in the diffuser passage at a design point in another embodiment of the present invention. [Figure 15] 13 is a graph showing a simulation analysis result of a flow rate of the diffuser passage at a design point of another embodiment of the present invention. [Figure 16] 13 is a graph showing a simulation analysis result of a flow rate of the diffuser passage at a design point according to still another embodiment of the present invention. [Figure 17] 13 is a graph showing a result of a simulation analysis of a flow rate in the diffuser passage at a design point of still another embodiment of the present invention. [Figure 18] 13 is a graph showing the results of a simulation analysis of the flow rate of the diffuser passage at a flow rate of 30% in an embodiment of the present invention. [Figure 19] 13 is a graph showing the results of a simulation analysis of the flow rate of the diffuser passage at 30% flow rate in another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An embodiment of a diffuser and a centrifugal pump according to the present invention will be described below. In the following description, the drawings will be referred to as appropriate. In the drawings, the same members and elements are given the same reference numerals, and duplicated descriptions will be omitted. In addition, the dimensional ratios of the elements may be exaggerated for convenience of explanation, and are not limited to the ratios shown in the drawings.

[0012] In the following description, a submerged pump will be described as an example of a centrifugal pump according to the present invention. The submerged pump is attached to a storage tank in which liquefied gas is stored, and pumps the liquefied gas from the storage tank to the outside. That is, the submerged pump is an example of a centrifugal pump according to the present invention, and the liquefied gas is an example of a handled liquid in the present invention.

[0013] In the following description, the "downward direction" refers to the direction of gravity and is an example of the forward direction in the present invention. The "upward direction" refers to the direction opposite to the downward direction and is an example of the backward direction in the present invention.

[0014] ●Centrifugal pump● ●Configuration of centrifugal pump 1 is a schematic cross-sectional view of a centrifugal pump according to an embodiment of the present invention, in which a cross section of a portion of the centrifugal pump 1 is not shown.

[0015] The centrifugal pump 1 discharges the treated liquid stored in a storage tank (not shown, same below) into a pump column C. The centrifugal pump 1 is accommodated in the lower part of the pump column C, which is extended from the ceiling of the storage tank into the storage tank, and is immersed in the treated liquid. The configuration of the centrifugal pump 1 is the same as that of a known submerged pump, except for the configuration of a diffuser 7 (described later). The centrifugal pump 1 includes an outer housing 2, a motor 3, a rotating shaft 4, two inner housings 5 ​​(one not shown, same below), two impellers 6 (one not shown, same below), and two diffusers 7 (one not shown, same below). That is, the centrifugal pump 1 is a two-stage centrifugal pump including two impellers 6. That is, the inner housing 5, the impeller 6, and the diffuser 7 constitute a first-stage pump section M1, and the inner housings, impellers, and diffusers not shown constitute a second-stage pump section (not shown, same below). The second stage pump section is disposed above the first stage pump section M1.

[0016] The external housing 2 houses the motor 3, the rotating shaft 4, the internal housing 5, the impeller 6, and the diffuser 7. The shape of the external housing 2 is a generally cylindrical shape extending in the vertical direction. The external housing 2 has an intake port 21 and an exhaust port (not shown, same below). The lower end of the external housing 2 has a reduced diameter to form the intake port 21.

[0017] In the following description, the “upstream side” refers to the upstream side in the flow of the treated fluid flowing inside the external casing 2, and the “downstream side” refers to the downstream side in the flow of the treated fluid flowing inside the external casing 2.

[0018] The motor 3 is driven at a predetermined drive voltage and drive frequency to rotate the impeller 6. The motor 3 includes a rotor 31 and a stator 32. The motor 3 is a known motor that includes the rotor 31 attached to the rotating shaft 4, and the stator 32 that rotates the rotor 31.

[0019] The rotating shaft 4 rotates by the rotation of the motor 3 and transmits the rotational power to the impeller 6. The rotating shaft 4 has a cylindrical shape extending in the vertical direction. A lower portion 4a of the rotating shaft 4 extends downward from the motor 3 toward the inside of the inner housing 5.

[0020] In the following description, the term "axial direction" refers to the axial direction of the rotating shaft 4 (vertical direction).

[0021] FIG. 2 is a partially enlarged schematic cross-sectional view of the centrifugal pump 1. As shown in FIG. In the figure, the flow of pumped fluid is indicated by arrows. In the following description, Figure 1 will be referred to together with Figure 2 as appropriate.

[0022] The inner housing 5 holds the diffuser 7 and, together with the diffuser 7, defines a flow path through which the handled fluid discharged from the impeller 6 flows. The inner housing 5 has a generally double-tube shape with the upper end of a cylinder along the vertical direction folded back inward. That is, the inner housing 5 includes a cylindrical outer tube portion 51, a cylindrical inner tube portion 52 disposed inside the outer tube portion 51, and a ring-shaped connecting portion 53 connected to the upper ends of the outer tube portion 51 and the inner tube portion 52. The inner housing 5 is accommodated in the outer housing 2 and attached to the outer housing 2.

[0023] The impeller 6 imparts velocity energy to the handled liquid sucked in from below, and discharges the handled liquid radially outward. The impeller 6 is housed in the external housing 2, and is attached to the lower part 4a of the rotating shaft 4. The impeller 6 is disposed above the suction port 21 in the axial direction.

[0024] The diffuser 7 converts the velocity energy imparted to the handled fluid by the impeller 6 into pressure energy by decelerating and pressurizing the handled fluid discharged from the impeller 6. The diffuser 7 is attached to the inner housing 5 and disposed above the impeller 6 and adjacent to the impeller 6 in the axial direction. In other words, the diffuser 7 is a so-called axial type diffuser. The specific configuration of the diffuser 7 will be described later.

[0025] ●Diffuser● Diffuser configuration FIG. 3 is a perspective view of a diffuser 7 showing an embodiment of a diffuser according to the present invention (diffuser 7). FIG. 4 is a bottom view of the diffuser 7. As shown in FIG. FIG. 5 is a side view of the diffuser 7. In the following description, FIGS. 1 and 2 will be referred to together with FIGS. 3 to 5 as appropriate.

[0026] The diffuser 7 is made of a metal such as an aluminum alloy, etc. The diffuser 7 includes a main body 8 and a plurality of (for example, eight) vanes 9.

[0027] The main body 8 has a cylindrical shape with a bottom. The main body 8 includes a bottom 81, an insertion hole 82, a plurality of (for example, four) flow straightening plates 83 (see FIG. 2; the same applies below), and a cylindrical portion 84.

[0028] In the following description, the “radial direction” is the direction along the diameter (radius) of the main body portion 8, and the “circumferential direction” is the direction along the circumference of the main body portion 8.

[0029] The shape of the bottom 81 is substantially a disk shape. The center of the bottom 81 protrudes upward in a truncated cone shape, and an insertion hole 82 is disposed in the center. A part of the bottom 81 protrudes upward in a plate shape to form a current plate 83.

[0030] The outer edge of the bottom 81 protrudes upward in a cylindrical shape to form a cylindrical portion 84. The cylindrical portion 84 has a cylindrical outer peripheral surface 84a. A part of the outer peripheral surface 84a protrudes in the radial direction to form a vane 9. The cylindrical portion 84 is an example of a flow path forming portion in the present invention.

[0031] FIG. 6 is a schematic development view of the diffuser 7. As shown in FIG. This figure shows a schematic view of the diffuser 7 developed in the circumferential direction. In the following description, FIGS. 1 to 5 will be referred to together with FIG.

[0032] The vane 9 defines a diffuser flow passage Ch together with an outer cylinder portion 51 (see FIG. 2) and a cylindrical portion 84. The vane 9 includes a plurality of (for example, four) long vanes 91, 92, 93, and 94 and a plurality of (for example, four) short vanes 95, 96, 97, and 98.

[0033] When viewed from below, the long vanes 91-94 and the short vanes 95-98 are arranged alternately in a clockwise direction in the order of their reference symbols. That is, the long vanes 91-94 and the short vanes 95-98 are arranged alternately and at equal intervals in the circumferential direction on the outer circumferential surface 84a of the cylindrical portion 84. In other words, one long vane 91-94 is arranged between the short vanes 95-98 that are arranged closest to each other in the circumferential direction.

[0034] Fig. 7 is a partially enlarged schematic diagram of the diffuser 7, showing the vicinity of the long vane 91 and the short vane 98. The figure shows a schematic diagram of a part of the diffuser 7 in a circumferentially developed state. In the figure, the flow of the handled fluid is indicated by arrows. In the following description, Figs. 3 to 6 will be referred to as appropriate together with Fig. 7.

[0035] The long vane 91 has a generally arcuate plate shape extending from the lower end to the upper end of the cylindrical portion 84. The long vane 91 includes a positive pressure surface 91a, a negative pressure surface 91b, an end surface 91c, a communicating flow passage 91d, a first portion 91e, and a second portion 91f.

[0036] When viewed from below, the pressure surface 91a is a surface that faces in the counterclockwise direction. The suction surface 91b is a surface on the opposite side of the pressure surface 91a. When viewed in the radial direction, the shape of the pressure surface 91a is concave. When viewed in the radial direction, the shape of the suction surface 91b is convex so as to substantially conform to the pressure surface 91a. The end surface 91c is the surface located most upstream of the long vane 91. The shape of the end surface 91c is parallel to the radial direction and is curved when viewed in the radial direction. The end surface 91c is disposed between the pressure surface 91a and the suction surface 91b so as to be continuous with the pressure surface 91a and the suction surface 91b. The end surface 91c is an example of the "front end portion of the long vane" in the present invention.

[0037] The communication passage 91d is a passage for the handled fluid that communicates with a space (first space) arranged on the positive pressure surface 91a side of the long vane 91 and a space (second space) arranged on the negative pressure surface 91b side of the long vane 91. The communication passage 91d is shaped like a slit along the circumferential direction (parallel). That is, the communication passage 91d opens to the positive pressure surface 91a and the negative pressure surface 91b. The communication passage 91d is arranged in the front part of the long vane 91. In the radial direction, the communication passage 91d is arranged so as to cross the long vane 91 from the end on the inner side to the end on the outer side. That is, the communication passage 91d is arranged so as to divide the long vane 91 into two parts with the communication passage 91d as a boundary. That is, the long vane 91 is divided into a first portion 91e disposed below (upstream) the communicating passage 91d and a second portion 91f disposed above (downstream) the communicating passage 91d. The communicating passage 91d has an inlet 91g disposed (open) on the positive pressure surface 91a and an outlet 91h disposed (open) on the negative pressure surface 91b.

[0038] The communication passage 91d (at least the outlet 91h) in the long vane 91 is disposed within a range from the upstream limit position P1 to the downstream limit position P2. In this embodiment, the outlet 91h of the communication passage 91d passes through the lowest end (lower surface 98d: described later) of the short vane 98 corresponding to the long vane 91, and is disposed adjacent to the imaginary line C1 along the circumferential direction below the imaginary line C1. In other words, the outlet 91h is disposed at a position adjacent in the circumferential direction to a position adjacent to the position where the communication passage 91d is disposed in the axial direction. The imaginary line C1 is an example of a specific imaginary line in the present invention.

[0039] The "upstream limit position P1" is the most upstream position among positions where the flow F2 of treated fluid that has passed through the communication passage 91d can merge with the flow F1 of treated fluid flowing into the diffuser passage Ch1. Here, "the position where the flow F2 can merge with the flow F1" means a position where most of the flow F2 (e.g., 80% or more) can flow into the diffuser passage Ch1 together with the flow F1.

[0040] The "downstream limit position P2" is the most downstream position among the positions upstream of the vortex V (described later; the same applies below). Here, the "position upstream of the vortex V" means a position where the flow F3 of the handled fluid based on the vortex V does not directly flow into the communication flow passage 91d.

[0041] In the present invention, the communicating passage 91d (particularly the outlet 91h) in the long vane 91 is preferably located in the vicinity of the position P3 closest to the end face 98c of the corresponding short vane 98, and more preferably located at the position P3. Here, "located at the position P3" means that the outlet 91h is located so as to include the position P3.

[0042] The long vanes 92-94 have the same configuration as the long vane 91. Therefore, in the following description, a detailed description of each of the long vanes 92-94 will be omitted. The long vane 92 has a positive pressure surface 92a, a negative pressure surface 92b, an end surface 92c, a communicating passage 92d, a first portion 92e, and a second portion 92f. The long vane 93 has a positive pressure surface 93a, a negative pressure surface 93b, an end surface 93c, a communicating passage 93d, a first portion 93e, and a second portion 93f. The long vane 94 has a positive pressure surface 94a, a negative pressure surface 94b, an end surface 94c, a communicating passage 94d, a first portion 94e, and a second portion 94f.

[0043] The short vane 95 is shaped like a generally arcuate plate extending from the lower end to the upper end of the cylindrical portion 84. The short vane 95 is shaped as if the long vane 91 was cut at a predetermined length position (the position of the imaginary line C1) upward from the end face 91c of the long vane 91. Here, the "predetermined length position" is the position where the communication passage 91d is disposed. Therefore, the shape of the short vane 95 is the same as the shape of the second portion 91f of the long vane 91. The short vane 95 includes a positive pressure surface 95a, a negative pressure surface 95b, an end face 95c, and a lower face 95d.

[0044] When viewed from below, the positive pressure surface 95a is a surface that faces in the counterclockwise direction. The negative pressure surface 95b is a surface on the opposite side of the positive pressure surface 95a. When viewed from the radial direction, the shape of the positive pressure surface 95a is concave. When viewed from the radial direction, the shape of the negative pressure surface 95b is convex so as to be substantially aligned with the positive pressure surface 95a. The end surface 95c is the surface located most upstream of the short vane 95. The end surface 95c is disposed between the positive pressure surface 95a and the lower surface 95d so as to be continuous with the positive pressure surface 95a and the lower surface 95d. The shape of the end surface 95c is a curved surface parallel to the radial direction. The lower surface 95d is a surface that faces downward. The shape of the lower surface 95d is a flat surface parallel to the circumferential and radial directions. The lower surface 95d is disposed between the suction surface 95b and the end surface 95c so as to be continuous with the suction surface 95b and the end surface 95c. In the axial direction, the end surface 95c and the lower surface 95d are disposed above the end surfaces 91c to 94c. The end surface 95c and the lower surface 95d are an example of the "front end portion of the short vane" according to the present invention.

[0045] FIG. 8 is a schematic diagram of the diffuser 7, showing an example of a method for designing the positions of the end surface 95c and the lower surface 95d (that is, the length of the short vane 95). The broken lines in the figure indicate the positions of an end surface 95c and a lower surface 95d of the short vane 95. In the following description, Figures 3 to 7 will be referred to together with Figure 8 as appropriate.

[0046] The positions of the end surface 95c and the lower surface 95d (that is, the length of the short vane 95) are designed based on the ratio of the second length L2 to the first length L1 (L2 / L1: hereinafter referred to as the "throat ratio").

[0047] The "first length L1" is the length of the inlet Chi of the diffuser passage Ch (diffuser passage Ch2) arranged on the negative pressure surface 95b side of the short vane 95 as viewed in the radial direction. The "inlet Chi" is the narrowest part of the diffuser passage Ch. The cross-sectional area perpendicular to the flow direction of the treated liquid in the diffuser passage Ch is smallest at the inlet Chi, and increases as the position of the cross-sectional area moves downstream. When the lower surface 95d is located upstream of the end surface 91c, the first length L1 is the length of an imaginary line segment that connects the end surface 91c and the negative pressure surface 95b at the shortest distance. When the lower surface 95d is located downstream of the end surface 91c, the first length L1 is the length of an imaginary line segment that connects the positive pressure surface 91a and the boundary between the negative pressure surface 95b and the lower surface 95d at the shortest distance. The first length L1 changes depending on the position of the end surface 95c.

[0048] The "second length L2" is the length of the inlet Chi of the diffuser passage Ch (diffuser passage Ch3) disposed on the pressure surface 95a side of the short vane 95. The second length L2 is the length of an imaginary line segment connecting the end surface 95c and the suction surface 92b at the shortest distance. The second length L2 changes depending on the position of the end surface 95c.

[0049] The throat ratio increases (becomes greater than "1") as the positions of the end face 95c and the lower face 95d of the short vane 95 move downstream, is maximum when the end face 95c and the lower face 95d are located at a predetermined position (hereinafter referred to as the "maximum position"), and decreases as the position moves downstream from the maximum position. The positions of the end face 95c and the lower face 95d may be any position that provides a throat ratio of "1" or more and that can maintain the static pressure capacity required for the diffuser 7. The position may be preferably above the position of the end face 92c of the long vane 92 corresponding to the short vane 95 and within the range up to the maximum position, and more preferably be the maximum position.

[0050] The configuration of the short vanes 96-98 is the same as that of the short vane 95. Therefore, in the following description, a detailed description of each of the short vanes 96-98 will be omitted. The short vane 96 has a pressure surface 96a, a suction surface 96b, an end surface 96c, and a lower surface 96d. The short vane 97 has a pressure surface 97a, a suction surface 97b, an end surface 97c, and a lower surface 97d. The short vane 98 has a pressure surface 98a, a suction surface 98b, an end surface 98c, and a lower surface 98d.

[0051] Among the vanes 9, the long vanes 91-94 correspond to the short vanes 95-98 arranged adjacent to each other on the negative pressure surfaces 91b-94b of the vanes 9. Therefore, the long vanes 91-94 are arranged adjacent to the corresponding short vanes 95-98 on the positive pressure surfaces 95a-98a of the corresponding short vanes 95-98. That is, the long vane 91 corresponds to the short vane 98, the long vane 92 corresponds to the short vane 95, the long vane 93 corresponds to the short vane 96, and the long vane 94 corresponds to the short vane 97. That is, the long vanes 91-94 are an example of the specific length vanes of the present invention.

[0052] The main body 8 is attached to the inner housing 5 with the lower part 4a of the rotary shaft 4 inserted through the insertion hole 82. At this time, the outer cylinder part 51 of the inner housing 5 is disposed radially outward from the cylindrical part 84 so as to face the outer circumferential surface 84a of the cylindrical part 84. That is, the space between the adjacent long vanes 91-94 and short vanes 95-98 in the circumferential direction is covered by the outer cylinder part 51. As a result, the opposing positive pressure surfaces 91a-98a and negative pressure surfaces 91b-98b, the outer circumferential surface 84a, and the outer cylinder part 51 form a diffuser flow passage Ch that decelerates and pressures the handled fluid discharged from the impeller 6. In other words, the vane 9, together with the inner housing 5 and the outer circumferential surface 84a of the cylindrical part 84, defines the diffuser flow passage Ch. In the following description, when the diffuser flow passages Ch are to be particularly distinguished from one another, the suffixes "1" to "8" are added to the names of the diffuser flow passages Ch.

[0053] The diffuser passage Ch1 is disposed between the long vane 91 and the short vane 98. The diffuser passage Ch2 is disposed between the long vane 91 and the short vane 95. The diffuser passage Ch3 is disposed between the long vane 92 and the short vane 95. The diffuser passage Ch4 is disposed between the long vane 92 and the short vane 96. The diffuser passage Ch5 is disposed between the long vane 93 and the short vane 96. The diffuser passage Ch6 is disposed between the long vane 93 and the short vane 97. The diffuser passage Ch7 is disposed between the long vane 94 and the short vane 97. The diffuser passage Ch8 is disposed between the long vane 94 and the short vane 98.

[0054] The diffuser passages Ch arranged on the pressure surface 91a-98a side of the long vanes 91-94 and short vanes 95-98 function as pressure surface diffuser passages. The diffuser passages Ch arranged on the suction surface 91b-98b side of the long vanes 91-94 and short vanes 95-98 function as suction surface diffuser passages. That is, for example, the diffuser passage Ch2 functions as the pressure surface diffuser passage for the long vane 91, and functions as the suction surface diffuser passage for the short vane 95. In other words, the diffuser passage Ch includes a pressure surface diffuser passage and a suction surface diffuser passage.

[0055] Furthermore, the connecting portion 53 of the inner housing 5 is disposed above the vane 9 and the cylindrical portion 84, and the inner cylindrical portion 52 of the inner housing 5 is disposed radially inward of the cylindrical portion 84. As a result, the inner cylindrical portion 52, the connecting portion 53, and the cylindrical portion 84 form a flow path that guides the handled fluid flowing out from the diffuser flow path Ch to the inside of the cylindrical portion 84. Furthermore, the bottom portion 81, the straightening plate 83, and the inner cylindrical portion 52 form a flow path that guides the handled fluid guided to the inside of the cylindrical portion 84 to the second-stage pump section.

[0056] The configuration of the second-stage pump section is the same as that of the first-stage pump section M1, and therefore a description of the inner casing, impeller, and diffuser (not shown) constituting the second-stage pump section will be omitted.

[0057] ● Operation of centrifugal pump Next, the operation of the centrifugal pump 1 will be described below, focusing on the flow of the handled liquid in the diffuser 7 (particularly in the vicinity of the long vane 92 and the short vane 95). In the following description, Figures 1 to 8 will be referred to as appropriate.

[0058] FIG. 9 is a schematic diagram illustrating the flow of the handled liquid in the diffuser flow passage Ch. In the figure, the flow of the handled fluid is indicated by arrows. The figure also shows a schematic view of a portion of the diffuser 7 in a circumferentially developed state.

[0059] The handled fluid sucked into the impeller 6 is discharged radially outward from the impeller 6. The handled fluid discharged from the impeller 6 has its flow direction changed to an upward direction by the outer casing 2, and flows into each diffuser flow passage Ch while swirling in the circumferential direction.

[0060] When the centrifugal pump 1 is operating at the design point, the inlet angle "α" of the handled liquid flowing into the diffuser flow passage Ch is adjusted to be close to a suitable angle in design (e.g., α≒β1: a range in which the attack angle is several degrees) with respect to the inlet angle "β1" of the long vanes 91-94. As described above, the shape of the short vane 95 is the same as the shape of the second portion 92f of the long vane 92. Therefore, the inlet angle "β2" of the short vanes 95-98 is slightly larger (e.g., about 1° to 10°) than the inlet angle "β1" of the long vanes 91-94.

[0061] The handled liquid flows into the diffuser passages Ch2 and Ch3. As described above, the long vane 91 is disposed on the negative pressure surface 95b side of the short vane 95, and the long vane 92 is disposed on the positive pressure surface 95a side. Therefore, the inlet Chi of the diffuser passage Ch3 on the positive pressure surface 95a side of the short vane 95 is larger than the inlet Chi of the diffuser passage Ch2 on the negative pressure surface 95b side. As a result, the flow rate of the handled liquid flowing into the diffuser passage Ch3 is larger than the flow rate of the handled liquid flowing into the diffuser passage Ch2. In other words, the diffuser 7 is designed so that the flow rate of the handled liquid flowing into the diffuser passage Ch3 is larger (larger) than the flow rate of the handled liquid flowing into the diffuser passage Ch2.

[0062] A part of the handled liquid also flows into the communication passage 92d. The flow F2 of the handled liquid flowing out from the outlet 92h to the upstream side of the inlet Chi of the diffuser passage Ch3 merges with the flow F1 of the handled liquid flowing into the diffuser passage Ch3 on the upstream side. Therefore, the flow rate of the handled liquid flowing into the diffuser passage Ch3 increases by the amount of the merged flow. The handled liquid flowing into the diffuser passages Ch2 and Ch3 is decelerated and pressurized by passing through the diffuser passages Ch2 and Ch3. As shown in FIG. 2, the handled liquid that has passed through the diffuser passages Ch2 and Ch3 is guided to each passage formed by the inner tube portion 52, the connecting portion 53, the bottom portion 81, and the cylindrical portion 84, and is introduced into the second-stage pump section. The handled liquid discharged from the second-stage pump section is discharged from the discharge port into the pump column C and flows upward in the pump column C.

[0063] An inlet 92g of the communicating passage 92d opens to the positive pressure surface 92a. Therefore, a part of the handled liquid flowing into the diffuser passage Ch4 flows into the communicating passage 92d. As a result, the effect of increasing the pressure of the handled liquid in the diffuser passage Ch4 may be slightly reduced. Also, the flow of the handled liquid flowing into the diffuser passage Ch3 may be slightly disturbed. However, the diffuser passage Ch3 is designed to have a large flow rate. Therefore, the influence of the flow F2 of the handled liquid from the communicating passage 92d on the flow F1 of the handled liquid flowing into the diffuser passage Ch3 is reduced. As a result, the pump efficiency of the centrifugal pump 1 is improved compared to the pump efficiency of a conventional centrifugal pump (hereinafter referred to as "conventional pump A") having only a conventional vane with no communicating passage formed therein, and the pump efficiency of a conventional centrifugal pump (hereinafter referred to as "conventional pump B") having only a vane (long vane) with a communicating passage formed therein.

[0064] Next, when the centrifugal pump 1 is operating at a flow rate smaller than the design point, the inflow angle "α" of the handled liquid flowing into the diffuser passage Ch becomes smaller, and the difference between the inflow angle "α" and the inlet angles "β1", "β2" becomes larger (the attack angle becomes larger). As a result, in the region in contact with the suction surfaces 92b, 95b, separation of the handled liquid occurs starting from the upstream end of the suction surfaces 92b, 95b.

[0065] Generally, when the angle of attack increases and separation occurs, the area where separation occurs (hereinafter referred to as the "separated area") increases over time. At this time, a phenomenon occurs in which a part of the handled liquid flows back from the adjacent diffuser passage Ch arranged on the suction surface 91b-98b side of the diffuser passage Ch where separation occurs, on the downstream side of the diffuser passage Ch where separation occurs. At this time, a vortex V is formed on the downstream side of the diffuser passage Ch due to the backflow. Eventually, the diffuser passage Ch is blocked by the separated area, and a stall in which the flow in the diffuser passage Ch stagnates may occur.

[0066] In this embodiment, the flow rate of the handled liquid flowing into the diffuser passage Ch3 is increased by the short vane 95 and the communication passage 92d. That is, the flow of the handled liquid is strong in the diffuser passage Ch3. Therefore, even if separation occurs in the diffuser passage Ch3, the separation area does not increase, and the diffuser passage Ch3 is not blocked by the separation area. In addition, the flow of the handled liquid flowing out from the diffuser passage Ch3 toward the downstream side of the diffuser passage Ch3 becomes strong. Therefore, the flow (backflow) of the handled liquid flowing out from the diffuser passage Ch3 toward the downstream side of the diffuser passage Ch2 is also suppressed. As a result, in the diffuser passage Ch2, the separation area does not increase to the extent that the diffuser passage Ch2 is blocked, and the diffuser passage Ch2 is not blocked by the separation area.

[0067] In addition, a vortex V is formed in the diffuser passage Ch3 due to the backflow. The position of this vortex V is not significantly affected by an increase or decrease in the flow rate of the centrifugal pump 1, and is substantially the same regardless of the flow rate. As described above, the communicating passage 92d is disposed upstream of the vortex V. Therefore, the flow F3 of the handled fluid based on the vortex V does not directly flow into the communicating passage 91d. Therefore, the communicating passage 91d is not blocked by the flow F3, and the flow F2 is not obstructed by the flow F3.

[0068] Furthermore, the handled fluid flowing out from the communicating passage 92d rectifies a part of the separated region, suppressing the increase of the separated region. As a result, the size of the separated region is suppressed to a size that does not cause stall. Therefore, the occurrence of rotating stall is suppressed. Here, a part of the handled fluid collides with the end face 95c of the short vane 95. At this time, the fluid pressure around the end face 95c decreases. Therefore, the closer the position of the outlet 92h is to the end face 95c, the easier it is for the handled fluid to flow out of the communicating passage 92d and into the communicating passage 92d.

[0069] Example: Next, examples of the present invention will be described below together with reference examples and comparative examples. In each of the following examples, the configuration of a part of the pump device is different from that of the centrifugal pump 1. Therefore, the reference numerals attached to each component are omitted, except for the diffuser flow path Ch. ● Examples 1 to 3 (Comparison of rotating stall occurrence flow rate and pump efficiency) FIG. 10 is a graph showing the results of actual measurements of the rotating stall occurrence flow rate for the embodiment of the present invention, the reference example, and the comparative example. FIG. 11 is a graph showing the results of actual measurement of pump efficiency at design points for an embodiment of the present invention, a reference example, and a comparative example. In FIG. 10, the "flow rate at which rotating stall occurs" is the ratio of the flow rate at which rotating stall occurs to the flow rate at the design point, when the flow rate at the design point is taken as 100%.

[0070] In these figures, in Examples 1 to 3, the number of short vanes is set to three types, 1, 2, and 3. In the axial direction, the position of the lower surface of the short vane is set to the same position as the position of the lowermost end of the long vane (the most upstream end of the long vane: the lower end of the cylindrical part of the diffuser) 11 mm (throat ratio: 2.61). Here, the width of the communication passage is set to 2 mm, and the length of the cylindrical part in the axial direction is set to 76 mm. In the axial direction, the position of the upper end of the communication passage is set to the same position as the position of the lower surface of the short vane. In Reference Examples 1 to 4 and 8, the number of short vanes is set to five types, 1, 2, 3, 4, and 8. No communication passage is arranged. In Comparative Example 1, no short vane and no communication passage are arranged. That is, the pump device of Comparative Example 1 is the same as the conventional pump A. In Comparative Example 2, no short vane is arranged. The width of the communication passage is set to 2 mm. That is, the pump device of Comparative Example 2 is the same as the conventional pump B.

[0071] As shown in Fig. 10, in Examples 1 and 2, rotating stall did not occur even when the flow rate was 0% (a state in which the discharge side of the pump device was closed). In other words, rotating stall did not occur. In Example 3, the flow rate at which rotating stall occurred was reduced to 2%. On the other hand, in Comparative Example 1, rotating stall occurred at a flow rate of 50% or less. In Comparative Example 2, the flow rate at which rotating stall occurred was reduced more than in Comparative Example 1, but rotating stall occurred at a flow rate of 44% or less.

[0072] Reference Examples 1 to 4 and 8 are for verifying the effect of the number of short vanes on the flow in the diffuser passage Ch. As shown in Reference Examples 1 to 4, when the number of short vanes is one to three, the rotating stall occurrence flow rate is reduced to 8%. Even when the number of short vanes is four, the rotating stall occurrence flow rate is reduced to 14%. On the other hand, as shown in Reference Example 8, when the number of short vanes is eight, that is, when all vanes are short vanes, rotating stall occurs at a flow rate (90%) near the design point. It is presumed that these phenomena occur because the design point flow rate increases as the number of short vanes increases, and when the number of short vanes exceeds half the total number of vanes, the design point changes to a large flow rate corresponding to the short vanes (the effect of the short vanes on the flow of the handled liquid becomes dominant over the effect of the long vanes). Therefore, in order to suppress rotating stall, the number of short vanes is preferably half or less of the total number of vanes.

[0073] As shown in Fig. 11, in Examples 1 to 3, the pump efficiency increased as the number of short vanes increased, and was higher than the pump efficiency of Comparative Examples 1 to 2. In Reference Examples 1 to 4 and 8, the pump efficiency increased as the number of short vanes increased up to three, and then decreased as the number of short vanes increased. The pump efficiency increased above the pump efficiency of Comparative Examples 1 to 2 up to four short vanes. The vanes were provided with a communicating flow path, so the pump efficiency was slightly reduced.

[0074] These results show that the present invention, by combining short vanes and communicating passages, is able to suppress the occurrence of rotating stall while suppressing the decrease in centrifugal pump efficiency more than conventional pumps A and B.

[0075] Reference Examples 1 to 8 (Comparison of diffuser flow rate: design point) FIG. 12 is a graph showing the results of simulation analysis of the flow rate of each diffuser passage at the design point of the reference examples (reference examples 1 to 8) of the present invention. For ease of explanation, the figures are labeled with the symbols "Ch1 to Ch8" for each diffuser passage (as in Figs. 13 to 19). The figures indicate the positions of the short vanes with thick dashed lines (as in Figs. 13 to 19). The figures also show the results of Comparative Example 1 for comparison. In the figures, the vertical axis represents the flow rate of the handled liquid passing through the axial cross section along the circumferential direction of each diffuser passage Ch1 to Ch8 at the downstream end of each diffuser passage Ch1 to Ch8 (as in Figs. 13 to 19). In Reference Examples 5 to 7, the number of short vanes is set to three types: five, six, and seven. No communication passage is provided.

[0076] As shown in Fig. 12, when the number of short vanes is four or less (when the number of short vanes is half or less of the total number of vanes), the flow rate of the diffuser passages Ch1, Ch3, Ch5, and Ch7 arranged on the pressure side of the short vanes increases, while the flow rate of the diffuser passages Ch2, Ch4, Ch6, and Ch8 arranged on the suction side of the short vanes decreases. On the other hand, when the number of short vanes is five or more (when the number of short vanes is greater than the total number of vanes), the above-mentioned tendency varies. This result shows that in order to control the flow rate of the diffuser passages Ch1 to Ch8, it is preferable that the number of short vanes is half or less of the total number of vanes.

[0077] ●Examples 1 to 3 (Comparison of flow rate of diffuser passage: design point) FIG. 13 is a graph showing the results of a simulation analysis of the flow rate of each diffuser passage at the design points of Examples 1 to 3 of the present invention. The figure also shows the results of Reference Examples 1 to 3 for comparison.

[0078] 13, the flow rates of the diffuser passages Ch3, Ch5, and Ch7 in Examples 1 to 3 were higher than the flow rates of the diffuser passages Ch3, Ch5, and Ch7 in Comparative Examples 1 to 3. That is, this result shows that the flow rates of the diffuser passages Ch3, Ch5, and Ch7 arranged on the pressure surface side of the short vane are increased by providing a communication passage in the long vane corresponding to the short vane.

[0079] Reference Example 9 (Comparison of diffuser flow rate: design point) FIG. 14 is a graph showing the results of a simulation analysis of the flow rate of each diffuser passage at a design point of another embodiment (embodiment 9) of the present invention. For comparison, the figure also shows the results of Reference Example 2. In Reference Example 9, the number of short vanes is two, and they are arranged adjacent to each other.

[0080] 14, the flow rate of the diffuser passage Ch5 arranged between the short vane and the long vane was increased compared to the same flow rate in Reference Example 2, but the flow rate of the diffuser passage Ch4 arranged between the short vanes was decreased compared to the same flow rate in Reference Example 2. This result shows that the flow rate of a specific diffuser passage Ch5 increases even when two short vanes are arranged next to each other, and that it is preferable to arrange one long vane between two short vanes.

[0081] Example 4 (Comparison of diffuser flow rate: design point) FIG. 15 is a graph showing a simulation analysis result of the flow rate of each diffuser passage at a design point in another embodiment (embodiment 4) of the present invention. For comparison, the figure also shows the results of Example 3. In Example 4, three short vanes are arranged alternately with long vanes. The outlet of the communication passage is arranged downstream (position P3) from the position in Example 3.

[0082] As shown in Fig. 15, the flow rate of the diffuser passages Ch3, Ch5, and Ch7 located on the pressure side of the short vane increases slightly as the outlet of the communication passage is located closest to the bottom end of the corresponding short vane. This result shows that the flow rate of the diffuser passages Ch3, Ch5, and Ch7 located on the pressure side of the short vane increases as the outlet of the communication passage approaches position P3.

[0083] ● Examples 5 to 10 (Comparison of flow rate of diffuser passage: design point) FIG. 16 is a graph showing the results of a simulation analysis of the flow rate of each diffuser passage at the design point of still other examples (Examples 5 to 10) of the present invention. The figure also shows the results of Examples 1 and 3 for comparison. In Examples 5 to 7, the number of short vanes is one. In Examples 8 to 10, the number of short vanes is three. In Examples 5 to 10, the lower surfaces of the short vanes are located at the same positions in the axial direction as 5.5 mm (throat ratio: 1.83), 22 mm (throat ratio: 2.38), and 33 mm (throat ratio: 2.22) from the bottom end of the long vane.

[0084] As shown in FIG. 16, in Examples 1, 5 to 7, when the position of the lower surface of the short vane is in the range of 5.5 mm to 33 mm, the flow rate of the diffuser passage Ch3 arranged on the positive pressure side of the short vane is increased more than the flow rate of the other diffuser passages Ch. Similarly, in Examples 3, 8 to 10, when the position of the lower surface of the short vane is in the range of 5.5 mm to 33 mm, the flow rate of the diffuser passages Ch3, Ch5, C7 arranged on the positive pressure side of the short vane is increased more than the flow rate of the other diffuser passages Ch. Also, in Examples 1, 5 to 7, when the position of the lower surface of the short vane is moved from 5.5 mm to 11 mm (when the short vane becomes shorter), the flow rate of the diffuser passage Ch3 is increased. When the position of the lower surface of the short vane is 11 mm and 22 mm, the flow rate of the diffuser passage Ch3 is approximately the same. When the position of the short vane's lower surface moved from 22 mm to 33 mm (when the short vane became shorter), the flow rate of the diffuser passage Ch3 decreased. On the other hand, in Examples 3, 8 to 10, when the position of the short vane's lower surface moved from 5.5 mm to 11 mm, the flow rate of the diffuser passages Ch3, Ch5, and Ch7 arranged on the pressure side of the short vane increased slightly. When the position of the short vane's lower surface was in the range of 11 mm to 33 mm, the flow rate of the diffuser passages Ch3, Ch5, and Ch7 decreased as the position of the short vane's lower surface moved upward. The reduction rate of the flow rate of the diffuser passages Ch3 (Ch3, Ch5, and Ch7) arranged on the pressure side of the short vane when the position of the short vane's lower surface moved from 22 mm to 33 mm decreased as the number of short vanes increased. Here, the throat ratio is maximum when the position of the short vane's lower surface is in the range of 11 mm to 16.5 mm from the lowest end of the long vane. These results show that if the position of the underside of the short vane is the maximum position where the throat ratio is maximum or below (upstream) the maximum position, the flow rate of the diffuser passages Ch3, Ch5, Ch7 located on the pressure side of the short vane increases. Also, these results show that even if the position of the underside of the short vane is above (downstream) the maximum position, the flow rate of the diffuser passages Ch3, Ch5, Ch7 located on the pressure side of the short vane increases if the throat ratio is 2 or more.

[0085] Reference Examples 10 to 15 (Comparison of diffuser flow rate: design point) FIG. 17 is a graph showing the results of simulation analysis of the flow rate of each diffuser passage at the design point of further examples (Examples 10 to 15) of the present invention. The figure also shows the results of Reference Examples 1 and 3 for comparison. In Reference Examples 10 to 12, the number of short vanes is one. In Reference Examples 13 to 15, the number of short vanes is three. In Reference Examples 10 to 15, the lower surfaces of the short vanes are positioned in the axial direction at the same positions as those of 5.5 mm (throat ratio: 1.83), 22 mm (throat ratio: 2.38), and 33 mm (throat ratio: 2.22) from the bottom end of the long vane.

[0086] As shown in FIG. 17, in Reference Examples 1, 10, and 11, the flow rate of the diffuser passage Ch3 arranged on the pressure surface side of the short vane was approximately the same. On the other hand, in Reference Example 12, the flow rate was significantly reduced compared to the flow rates of Reference Examples 1, 10, and 11. In Reference Examples 3, 13 to 15, the flow rates of the diffuser passages Ch3, Ch5, and Ch7 arranged on the pressure surface side of the short vane decreased as the position of the lower surface of the short vane moved upward. In particular, the flow rate significantly decreased when the position of the lower surface of the short vane was 22 mm or more from the lowest end of the long vane. The flow rate of the diffuser passage Ch3 (Ch3, Ch5, Ch7) arranged on the pressure surface side of the short vane decreased compared to the same flow rate in Examples 5 to 10. This result shows that the flow rate of the diffuser passage Ch3 (Ch3, Ch5, Ch7) arranged on the pressure surface side of the short vane is increased by the communication passage.

[0087] ● Examples 1 to 3 (Comparison of diffuser flow rate: 30% flow rate) FIG. 18 is a graph showing the results of a simulation analysis of the flow rate of each diffuser passage at a flow rate of 30% in Examples 1 to 3 of the present invention. The figure also shows the results of Reference Examples 1 to 3 and Comparative Example 1 for comparison.

[0088] 18, in Examples 1 to 3, the flow rate of the diffuser passages Ch3, Ch5, and Ch7 arranged on the pressure surface side of the short vane was increased more than the flow rate of the diffuser passages Ch2, Ch4, and Ch6 arranged on the suction surface side of the short vane. On the other hand, in Reference Examples 1 to 3, the same increase in flow rate was not obtained except for Reference Example 3. This result shows that by arranging a communication passage in the long vane corresponding to the short vane, the flow rate of the diffuser passages Ch3, Ch5, and Ch7 arranged on the pressure surface side of the short vane is increased even at a small flow rate.

[0089] Example 4 (Diffuser flow rate comparison: 30% flow rate) FIG. 19 is a graph showing the results of a simulation analysis of the flow rate of each diffuser passage at a flow rate of 30% in another embodiment (Example 4) of the present invention. The figure also shows the results of Example 3 for comparison.

[0090] As shown in Fig. 19, by positioning the outlet of the communication passage closest to the bottom end of the corresponding short vane, the flow rate of the diffuser passages Ch3, Ch5, Ch7 located on the pressure side of the short vane increases slightly even at a flow rate of 30%. This result shows that by positioning the outlet of the communication passage closer to position P3, the flow rate of the diffuser passages Ch3, Ch5, Ch7 located on the pressure side of the short vane increases even at a small flow rate.

[0091] Summary According to the embodiment described above, the vanes 9 of the diffuser 7 include long vanes 91-94 and short vanes 95-98. Each of the long vanes 91-94 is disposed adjacent to the corresponding short vane 95-98 on the pressure surface 95a-98a side of the corresponding short vane 95-98. In the axial direction, the end surfaces 95c-98c and lower surfaces 95d-98d of the short vanes 95-98 are disposed above the end surfaces 91c-94c of the long vanes 91-94. The long vanes 91-94 include communication passages 91d-94d that open to the pressure surfaces 91a-94a and suction surfaces 91b-94b.

[0092] According to this configuration, the flow rate of the handled liquid flowing into the diffuser passages Ch1, Ch3, Ch5, and Ch7 arranged on the positive pressure surfaces 95a-98a of the short vanes 95-98 increases. Therefore, even if separation occurs in the diffuser passages Ch1, Ch3, Ch5, and Ch7, the separated area does not increase, and the diffuser passages Ch1, Ch3, Ch5, and Ch7 are not blocked by the separated area. The handled liquid flowing out of the diffuser passages Ch1, Ch3, Ch5, and Ch7 is also prevented from flowing (backflowing) downstream of the diffuser passages Ch2, Ch4, Ch6, and Ch8. As a result, the separated area does not increase in the diffuser passages Ch2, Ch4, Ch6, and Ch8 to the extent that the diffuser passages Ch2, Ch4, Ch6, and Ch8 are blocked, and the diffuser passages Ch2, Ch4, Ch6, and Ch8 are not blocked by the separated area.

[0093] In addition, the diffuser flow paths Ch1, Ch3, Ch5, and Ch7 are designed to have a large flow rate. Therefore, the influence of the flow F2 of the handled fluid from the communicating flow paths 91d-94d on the flow F1 of the handled fluid flowing into the diffuser flow paths Ch1, Ch3, Ch5, and Ch7 is reduced. As a result, the pump efficiency of the centrifugal pump 1 is improved compared to the conventional pumps A and B.

[0094] In this way, in the centrifugal pump 1, the occurrence of rotating stall is suppressed while the decrease in efficiency is suppressed.

[0095] Also, according to the embodiment described above, the number of the short vanes 95-98 is half (or less) of the total number of the vanes 9. With this configuration, the influence of the long vanes 91-94 on the flow of the handled liquid becomes dominant over the influence of the short vanes 95-98. Therefore, the design point can be set to a flow rate according to the long vanes. Also, control of the flow rate of the diffuser flow passage Ch at the design point becomes easy.

[0096] Furthermore, according to the embodiment described above, one long vane 91-94 is disposed in the circumferential direction between each of the short vanes 95-98. With this configuration, the flow rates in the diffuser flow passages Ch1, Ch3, Ch5, Ch7 on the pressure surfaces 95a-98a of the short vanes 95-98 are reliably increased.

[0097] Furthermore, according to the embodiment described above, the outlets 91h-94h of the communication passages 91d-94d are disposed within a range from the upstream limit position P1 to the downstream limit position P2. With this configuration, the flow F2 reliably merges with the flow F1. Therefore, the flow rates of the diffuser passages Ch1, Ch3, Ch5, and Ch7 on the positive pressure surfaces 95a-98a of the short vanes 95-98 are reliably increased by the flow F2. In addition, the communication passages 91d-94d are not blocked by the flow based on the vortex V.

[0098] Furthermore, according to the embodiment described above, the outlets 91h-94h of the communication passages 91d-94d are disposed adjacent to the imaginary line C1 below the imaginary line C1. With this configuration, the flow F2 reliably merges with the flow F1. Therefore, the flow rates of the diffuser passages Ch1, Ch3, Ch5, and Ch7 on the pressure surfaces 95a-98a of the short vanes 95-98 are reliably increased by the flow F2.

[0099] Furthermore, according to the embodiment described above, the end faces 95c-98c and the lower faces 95d-98d of the short vanes 95-98 are disposed forward of the position where the throat ratio is maximized. With this configuration, the static pressure capacity required for the diffuser 7 is reliably maintained. Also, the flow F2 reliably merges with the flow F1. Therefore, the flow rates of the diffuser flow paths Ch1, Ch3, Ch5, and Ch7 on the pressure surfaces 95a-98a of the short vanes 95-98 are reliably increased.

[0100] Furthermore, according to the embodiment described above, the long vanes 91-94 are provided with the communication passages 91d-94d, respectively. With this configuration, the flow F2 merges with the flow F1 flowing into the diffuser passages Ch1, Ch3, Ch5, and Ch7 on the suction surfaces 91b-94b of all the long vanes 91-94. Therefore, the flow rates of the diffuser passages Ch1, Ch3, Ch5, and Ch7 are reliably increased.

[0101] Furthermore, according to the embodiment described above, the communicating passages 91d-94d are each shaped like a slit that divides the long vanes 91-94 into two with the communicating passages 91d-94d as a boundary. With this configuration, the communicating passages 91d-94d can be easily formed simply by forming a slit in the vane of an existing diffuser.

[0102] Furthermore, according to the embodiment described above, the long vanes 91-94 include first portions 91e-94e disposed below the communicating passages 91d-94d, and second portions 91f-94f disposed above the communicating passages 91d-94d. The shapes of the short vanes 95-98 are the same as the shapes of the second portions 91f-94f. With this configuration, the short vanes 95-98 can be easily formed by simply removing a portion of the vanes of an existing diffuser (portions corresponding to the first portions 91e-94e and the communicating passages 91d-94d).

[0103] Furthermore, according to the embodiment described above, the centrifugal pump 1 includes the diffuser 7. According to this configuration, in the centrifugal pump 1, the occurrence of rotating stall is suppressed while the decrease in efficiency is suppressed.

[0104] ●Other embodiments● In the present invention, the centrifugal pump 1 does not necessarily have to include a second-stage pump unit, or may include a third or more-stage pump unit.

[0105] In addition, in the present invention, the number of vanes 9 is not limited to "8".

[0106] Furthermore, in the present invention, among the multiple long vanes 91-94, it is sufficient that at least one long vane 91-94 corresponding to any of the short vanes 95-98 is provided with a communicating passage 91d-94d, and some of the long vanes 91-94 may not be provided with the communicating passages 91d-94d.

[0107] Furthermore, in the present invention, the shape of the communication passages 91d-94d is not limited to a slit shape. That is, for example, the communication passages 91d-94d may have the shape of one or more tubes (through holes) penetrating the long vanes 91-94.

[0108] Furthermore, in the present invention, the communication channels 91d to 94d do not have to be arranged parallel to the circumferential direction.

[0109] Furthermore, in the present invention, the communicating passages 91d to 94d may be located at different positions in the axial direction.

[0110] Furthermore, in the present invention, the number of the short vanes 95 to 98 is not limited to "4" as long as it is equal to or less than half the total number of the vanes 9. That is, for example, the number of the short vanes 95 to 98 may be "1" to "3".

[0111] Furthermore, in the present invention, the positions of the end faces 95c-98c and the lower faces 95d-98d of the short vanes 95-98 (the lengths of the short vanes 95-98) are not limited to those in this embodiment.

[0112] Furthermore, in the present invention, the shape of the lower surfaces 95d-98d of the short vanes 95-98 is not limited to a flat surface parallel to the circumferential and radial directions. That is, for example, the shape of the lower surfaces 95d-98d may be a curved surface convex downward.

[0113] Furthermore, in the present invention, among the short vanes 95 to 98, two or more of the short vanes 95 to 98 may be disposed adjacent to each other.

[0114] Furthermore, in the present invention, the short vanes 95 to 98 may each have a different length.

[0115] Furthermore, in the present invention, the diffuser flow passage Ch may be divided into two in the circumferential direction on the downstream side of the diffuser flow passage Ch.

[0116] Furthermore, in the present invention, the diffuser passage Ch may merge with an adjacent diffuser passage Ch on the downstream side of the diffuser passage Ch.

[0117] ●Embodiments of the present invention● Next, the embodiments of the present invention as understood from the above-described embodiments will be described below, using the terms and symbols described in each embodiment.

[0118] A first embodiment of the present invention is a diffuser (e.g., diffuser 7) arranged adjacent to an impeller (e.g., impeller 6) in the axial direction of a rotating shaft (e.g., rotating shaft 4) of a centrifugal pump (e.g., centrifugal pump 1). In the axial direction, the direction in which the impeller is arranged relative to the diffuser is a forward direction (e.g., downward direction), and the direction in which the diffuser is arranged relative to the impeller is a rearward direction (e.g., upward direction). The diffuser has a flow path forming portion (e.g., cylindrical portion 84) having a cylindrical outer peripheral surface (e.g., outer peripheral surface 84a), and a plurality of vanes (e.g., vane 9) arranged on the outer peripheral surface and partitioning a plurality of diffuser flow paths (e.g., diffuser flow paths Ch) through which the handled liquid discharged from the impeller flows, and each of the plurality of vanes has a positive pressure surface (e.g., positive pressure surfaces 91a to 98a) and a negative pressure surface ( The vanes each include a front end (e.g., end faces 91c-98c, lower faces 95d-98d) arranged so as to be continuous with the pressure surface and the suction surface, and the ... This diffuser comprises at least one specific length vane (e.g., long vane 91-94) arranged adjacent to the short vane corresponding to the long vane, the front end of the short vane being arranged rearward of the front end of the long vane in the axial direction, and the specific length vane having a communicating passage (e.g., communicating passage 91d-94d) opening to the positive pressure surface and the negative pressure surface of the specific length vane. According to this configuration, in the centrifugal pump, the occurrence of rotating stall is suppressed while a decrease in efficiency is suppressed.

[0119] A second embodiment of the present invention is the diffuser of the first embodiment, wherein the number of the short vanes is half or less of the total number of the vanes. This configuration makes it easy to control the flow rate in the diffuser passage at the design point.

[0120] A third embodiment of the present invention is a diffuser in the second embodiment, wherein the vanes include a plurality of short vanes, and one long vane is arranged between two of the short vanes in the circumferential direction of the outer circumferential surface. According to this configuration, the flow rate in the diffuser passage on the pressure surface side of the short vane is reliably increased.

[0121] A fourth embodiment of the present invention is a diffuser according to the second embodiment, wherein the vanes include a plurality of short vanes, and two of the short vanes are arranged adjacent to each other in the circumferential direction of the outer circumferential surface. According to this configuration, the flow rate in the diffuser passage on the pressure surface side of the short vane is reliably increased by the flow outflowing from the communication passage.

[0122] A fifth embodiment of the present invention is a diffuser according to the first embodiment, wherein the communication passage includes an outlet (e.g., outlets 91h to 94h) disposed on the negative pressure surface, the outlet is disposed within a range from an upstream limit position (e.g., upstream limit position P1) to a downstream limit position (e.g., downstream limit position P2), the upstream limit position is a position where a flow of the handled fluid flowing out from the outlet (e.g., flow F2) can join a flow of the handled fluid flowing into the diffuser passage (e.g., diffuser passages Ch1, Ch3, Ch5, Ch7) disposed on the negative pressure surface side of the specific length vane, and the downstream limit position is a position upstream of a vortex (e.g., vortex V) formed by a backflow of the handled fluid in the diffuser passage disposed on the negative pressure surface side of the specific length vane. According to this configuration, the flow out of the communication passage reliably joins the flow into the diffuser passage.

[0123] A sixth embodiment of the present invention is a diffuser in the fifth embodiment, wherein the upstream limit position is a position where the outlet is located forward of a specific imaginary line (e.g., imaginary line C1) and adjacent to the specific imaginary line, the specific imaginary line passing through the front end of the short vane corresponding to the specific long vane and along the circumferential direction of the outer circumferential surface. According to this configuration, the flow out of the communication passage reliably joins the flow into the diffuser passage.

[0124] A seventh embodiment of the present invention is a diffuser according to the sixth embodiment, wherein the short vane has an end face (e.g., end face 95c to 98c) located most upstream in the flow of the handled liquid in a first diffuser passage relative to the short vane, and the outlet is located at a position (e.g., position P3) of the short vane corresponding to the specific length vane that is closest to the end face. According to this configuration, the pumped fluid is more likely to flow out of the communicating flow passage and more likely to flow into the communicating flow passage.

[0125] An eighth embodiment of the present invention is a diffuser in the first embodiment, wherein the front end of the short vane is positioned forward from a position (e.g., maximum position) where a ratio (e.g., throat ratio) of a length (e.g., second length L2) of the inlet (e.g., inlet Chi) of the diffuser passage arranged on the pressure surface side of the short vane to a length (e.g., first length L1) of the inlet (e.g., inlet Chi) of the diffuser passage arranged on the suction surface side of the short vane is maximum. This configuration ensures that the required static pressure capacity of the diffuser is maintained.

[0126] A ninth embodiment of the present invention is a diffuser according to the first embodiment, wherein each of the long vanes is provided with the communicating passage. With this configuration, the flow rate in the diffuser passage on the suction surface side of all the long vanes is reliably increased.

[0127] A tenth embodiment of the present invention is a diffuser in the first embodiment, wherein the shape of each of the communicating passages is a slit shape that divides the specific length vane into two with the communicating passage as a boundary. According to this configuration, the communication flow passage can be easily formed in an existing diffuser.

[0128] An eleventh embodiment of the present invention is a diffuser in the tenth embodiment, wherein the specific length vane has a first portion (e.g., first portion 91e-94e) arranged forward of the communicating flow passage and a second portion (e.g., second portion 91f-94f) arranged rearward of the communicating flow passage, and the shape of the short vane corresponding to the specific length vane is the same as the shape of the second portion. According to this configuration, the short vanes can be easily formed in an existing diffuser.

[0129] A twelfth embodiment of the present invention is a centrifugal pump (e.g., centrifugal pump 1) comprising a motor (e.g., motor 3), a rotating shaft (e.g., rotating shaft 4) rotated by the motor, an impeller (e.g., impeller 6) attached to the rotating shaft, and a diffuser (e.g., diffuser 7) described in the first embodiment arranged adjacent to the impeller in the axial direction of the rotating shaft. According to this configuration, in the centrifugal pump, the occurrence of rotating stall is suppressed while a decrease in efficiency is suppressed. [Explanation of symbols]

[0130] 1. Centrifugal pump 3 Motor 4 Rotation Axis 6 Impeller 7 Diffuser 84 Cylindrical part 84a Outer surface 9. Vane 91~94 Long vane 91a~94a Positive pressure side 91b~94b Negative pressure side 91c~94c End face (front end) 91d~94d Connecting flow passage 91e~94e Part 1 91f~94f Part 2 91h~94h Exit 95~98 Short vane 95a~98a Positive pressure side 95b~98b Negative pressure side 95c~98c End face (front end) 95d~98d Lower surface (front end) Ch Diffuser passage Chi entrance C1 Virtual line F1 Trends F2 Flow P1 Upstream limit position P2 Downstream limit position P3 position L1 First length L2 Second length V Vortex

Claims

1. A diffuser disposed adjacent to an impeller in an axial direction of a rotary shaft of a centrifugal pump, a direction in which the impeller is disposed relative to the diffuser in the axial direction is a forward direction, and a direction in which the diffuser is disposed relative to the impeller is a rearward direction, A flow path forming portion having a cylindrical outer circumferential surface; a plurality of vanes disposed on the outer circumferential surface and defining, together with the outer circumferential surface, a plurality of diffuser flow passages through which the handled fluid discharged from the impeller flows; and Each of the plurality of vanes is A pressure surface; a suction surface which is a surface opposite to the pressure surface; a front end portion disposed so as to be continuous with the positive pressure surface and the negative pressure surface; With The plurality of vanes include A plurality of long vanes; at least one short vane shorter than the long vane; With The plurality of long vanes include At least one specific length vane is disposed adjacent to the short vane corresponding to the long vane on the pressure side of the short vane corresponding to the long vane; With In the axial direction, the front end portion of the short vane is disposed rearward of the front end portion of the long vane, The specific length vane is A communication flow passage opening to the positive pressure surface of the specific length vane and the negative pressure surface of the specific length vane; Equipped with Diffuser.

2. The number of the short vanes is half or less of the total number of the vanes. The diffuser of claim 1 .

3. The plurality of vanes include A plurality of said short vanes; With In the circumferential direction of the outer circumferential surface, one long vane is disposed between two of the short vanes. The diffuser of claim 2.

4. The plurality of vanes include A plurality of said short vanes; With In the circumferential direction of the outer circumferential surface, two of the short vanes are arranged adjacent to each other. The diffuser of claim 2.

5. The communication flow path is an outlet disposed on the suction side; With The outlet is disposed within a range from a maximum upstream position to a maximum downstream position, the upstream limit position is a position where the flow of the handled fluid flowing out from the outlet can join the flow of the handled fluid flowing into the diffuser flow passage arranged on the negative pressure surface side of the specific length vane, the downstream limit position is a position upstream of a vortex formed by a backflow of the handled fluid in the diffuser passage disposed on the negative pressure surface side of the specific length vane, in the flow of the handled fluid in the diffuser passage. The diffuser of claim 1 .

6. the upstream limit position is a position where the outlet is disposed forward of and adjacent to a specific imaginary line, The specific virtual line passes through the front end of the short vane corresponding to the specific length vane and extends along the circumferential direction of the outer circumferential surface. The diffuser of claim 5.

7. The short vane is an end surface located most upstream in a flow of the handled fluid in a first diffuser passage relative to the short vane; With The outlet is disposed at a position of the short vane corresponding to the specific length vane that is closest to the end face. The diffuser of claim 6.

8. the front end of the short vane is disposed forward from a position where a ratio of a length of an inlet of the diffuser flow passage disposed on the pressure surface side of the short vane to a length of an inlet of the diffuser flow passage disposed on the suction surface side of the short vane is maximized. The diffuser of claim 1 .

9. Each of the long vanes comprises: The communication flow path, Equipped with The diffuser of claim 1 .

10. The shape of each of the communication passages is a slit shape that divides the specific length vane into two with the communication passage as a boundary. The diffuser of claim 1 .

11. The specific length vane is A first portion disposed forward of the communication flow path; A second portion disposed rearward of the communication flow path; With The shape of the short vane corresponding to the specific length vane is the same as the shape of the second portion. The diffuser of claim 10.

12. A motor; A rotating shaft rotated by the motor; an impeller attached to the rotating shaft; a diffuser according to claim 1 , which is disposed adjacent to the impeller in an axial direction of the rotary shaft; It is made of Centrifugal pump.

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