JP2021025476A - Centrifugal pump and impeller for centrifugal pump - Google Patents

Abstract

To provide a centrifugal pump with a low specific speed, capable of improving pump efficiency.SOLUTION: In a centrifugal pump with a low specific speed in which the specific speed Ns is set to 50≤Ns<100, a negative pressure surface part 42 of an impeller blade 36 constituting a groove flow path 37 of an impeller 23 comprises a first curved part 42a, a straight part 42b and a second curved part 42c from a radial inside end part 36a, and is formed in a surface shape in which the straight part 42b and the first curved part 42a widens the width of the groove flow path 37 from the extension line of the second curved part 42c when viewed from the second curved part 42c side.SELECTED DRAWING: Figure 4

Description

The present invention relates to a centrifugal pump and an impeller for a centrifugal pump.

In the centrifugal pump, an impeller having a plurality of blades is arranged in the pump case, and the working fluid introduced from the axis center side is subjected to centrifugal force based on the rotation of the impeller through the groove flow path between the blades. It operates so as to discharge outward in the radial direction (see, for example, Patent Document 1).

By the way, in a centrifugal pump, it is common to set an impeller or the like so that the specific speed Ns representing the pump characteristics is 100 or more. However, there is also a request to use a centrifugal pump for a pump having a specific speed Ns setting of less than 100, and such a low specific speed centrifugal pump is also being studied.

Japanese Unexamined Patent Publication No. 2004-278311

The pump efficiency of a centrifugal pump decreases as the specific speed decreases. That is, in the centrifugal pump set to the low specific speed as described above, the pump efficiency tends to be low, and how to improve the efficiency has been one of the issues to be examined.

An object of the present invention is to provide a low specific speed centrifugal pump and an impeller for a centrifugal pump, which can be expected to improve pump efficiency.

A centrifugal pump that solves the above problems has a plurality of blade blades (36) arranged at predetermined intervals in the circumferential direction, and a plurality of groove flow paths (37) formed between the adjacent blade blades. The impeller (23) is provided with an impeller (23) for discharging the working fluid from the introduction port (39) on the inner side in the radial direction toward the discharge port (40) on the outer side in the radial direction via the groove flow path, and the specific velocity Ns is high. A low specific velocity centrifugal pump (10) set to 50 ≦ Ns <100, in which the vane of the impeller rotate the radial outer end (36b) more than the radial inner end (36a). It has a rearward blade structure located on the downstream side in the direction, and has a pressure surface portion (41) formed on one side surface of the blade blade when viewed from the groove flow path, and a negative pressure formed on the other side surface of the adjacent blade blade. The surface portion (42) is configured to have a substantially uniform curved shape, and the negative pressure surface portion is a first curved portion (42a) and a straight portion from the radial inner end portion of the blade blade. (42b) and the second curved portion (42c) are included, and the straight portion and the first curved portion widen the width of the groove flow path from the extension line of the second curved portion when viewed from the second curved portion side. It is composed of the surface shape of the aspect.

An impeller for a centrifugal pump that solves the above problems includes a plurality of blade blades (36) arranged at predetermined intervals in the circumferential direction, and a plurality of groove flow paths (37) formed between the adjacent blade blades. The working fluid is discharged from the introduction port (39) on the inner side in the radial direction toward the discharge port (40) on the outer side in the radial direction through the groove flow path, and the specific velocity Ns is 50 ≦ Ns <. An impeller (23) for a centrifugal pump having a low specific velocity set to 100, and the impeller blades of the impeller have a radial outer end (36b) in a rotation direction rather than a radial inner end (36a). A pressure surface portion (41) having a rearward blade structure located on the downstream side and formed on one side surface of the blade blade when viewed from the groove flow path, and a negative pressure surface portion formed on the other side surface of the adjacent blade blade. (42) and (42) are each formed to have a substantially uniform curved shape, and the negative pressure surface portion includes a first curved portion (42a) and a straight portion (42a) from the radial inner end portion of the blade blade. 42b) and the second curved portion (42c) are included, and the straight portion and the first curved portion widen the width of the groove flow path from the extension line of the second curved portion when viewed from the second curved portion side. It is composed of the surface shape of.

According to the centrifugal pump and the impeller for the centrifugal pump, the negative pressure surface portion of the blade blade constituting the groove flow path of the impeller includes the first curved portion, the straight portion and the second curved portion from the radial inner end portion. The straight portion and the first curved portion are formed in a surface shape in which the width of the groove flow path is widened from the extension line of the second curved portion when viewed from the second curved portion side. As a result, the flow velocity of the working fluid at the inlet side of the groove flow path is suitably reduced, and the effect of reducing the wall friction loss of the working fluid flowing through the groove flow path can be obtained, so that the total pressure of the centrifugal pump can be improved. It can be expected (see FIG. 5 (b) and the like).

The schematic block diagram of the centrifugal pump in one Embodiment. (A) is a perspective view of the impeller of one embodiment, and (b) is a side view thereof. The plan view for demonstrating the detailed structure of the impeller of one Embodiment. A partially enlarged view of FIG. 3 for explaining a detailed configuration of an impeller of one embodiment. (A) is a partially enlarged view of FIG. 4 for explaining the detailed configuration of the impeller of one embodiment, and (b) is a graph for explaining the pump characteristics when the impeller is used. (A) is a partially enlarged view of FIG. 3 for explaining the detailed configuration of the impeller of one embodiment, and (b) is a schematic diagram for explaining the flow of fluid when the impeller is used. (A) is an enlarged view equivalent to FIG. 6 for explaining the detailed configuration of the impeller of the comparative example, and (b) is a schematic view for explaining the fluid flow when the impeller is used. (A) is a vertical sectional view for explaining the detailed configuration of the impeller of one embodiment, and (b) is a graph for explaining the pump characteristics when the impeller is used. (A) is a side view for explaining the detailed configuration of the impeller of one embodiment, and (b) is a graph for explaining the pump characteristics when the impeller is used. (A) is a partially enlarged view of FIG. 3 for explaining the detailed configuration of the impeller of one embodiment, and (b) is a graph for explaining the pump characteristics when the impeller is used.

Hereinafter, an embodiment of the centrifugal pump and the impeller for the centrifugal pump will be described.
The centrifugal pump 10 of the present embodiment shown in FIG. 1 is an air pump that discharges air as a working fluid. The centrifugal pump 10 includes a motor unit 11 composed of an electric motor and a pump unit 21 driven by the motor unit 11 to supply air, and the motor unit 11 and the pump unit 21 are integrally configured. There is.

The motor unit 11 includes a motor case 12, a stator 13, and a rotor 14. The motor unit 11 includes a stator 13 and a rotor 14 in a motor case 12. The motor case 12 is fixed to the pump case 22 of the pump unit 21. In the motor unit 11, the rotor 14 rotates based on the power supplied to the stator 13, and the rotating shaft 15 rotates together with the rotor 14. The rotating shaft 15 is provided so as to project toward the pump portion 21 side, and transmits the rotational force to the pump portion 21 side.

The pump unit 21 includes a pump case 22 and an impeller 23. The pump unit 21 includes an impeller 23 in the pump case 22. That is, the pump case 22 includes a pump chamber 24 in which the impeller 23 is rotatably housed. The impeller 23 has a substantially disk shape that is flat with respect to its own axial direction. Correspondingly, the pump chamber 24 also has a substantially circular space flat in the axial direction.

The pump case 22 includes a shaft insertion hole 25 that communicates with the pump chamber 24. The tip of the rotating shaft 15 protruding from the motor portion 11 is inserted into the shaft insertion hole 25. The tip of the rotating shaft 15 reaches the pump chamber 24 and is rotatably connected to the support of the impeller 23 arranged in the pump chamber 24 and the impeller 23.

Further, the pump case 22 includes an introduction flow path 26 for introducing air, which extends from the pump chamber 24 on the side opposite to the shaft insertion hole 25 in the axial direction and opens. The introduction flow path 26 is provided coaxially with the shaft insertion hole 25, in this case coaxially with the impeller 23. Further, the pump case 22 includes a discharge flow path 27 for air discharge that extends from the pump chamber 24 on one side in the direction orthogonal to the axis, in this case, extends outward in the circumferential direction of the impeller 23. The discharge flow path 27 is connected to, for example, a vehicle air cleaning device (not shown) that receives air supply via a hose.

As shown in FIGS. 1, 2 (a), 2 (b) and 3, the impeller 23 includes an impeller body 31, a closing plate 32, and a connecting member 33. The impeller body 31 and the closing plate 32 are made of, for example, a resin material, and the connecting member 33 is made of, for example, a metal material. The impeller body 31 is formed by, for example, 11 blade blades 36 having the same shape arranged side by side at equal intervals in the circumferential direction on one side surface of a bottom plate portion 35 having a circular plate shape. The space between the adjacent blades 36 is configured as an air groove flow path 37. Each blade blade 36 is appropriately provided with a lightening portion 38 for the purpose of reducing the weight of the impeller 23. The detailed shapes of each blade blade 36 and each groove flow path 37 will be described later.

A cylindrical connecting member 33 is assembled to the central portion of the bottom plate portion 35 of the impeller body 31 so as not to rotate relative to each other. The tip of the rotating shaft 15 of the motor portion 11 is internally fitted into the cylindrical connecting member 33, and is fixed so as to rotate integrally with the rotating shaft 15. That is, when the rotating shaft 15 is rotated by the rotational drive of the motor unit 11, the impeller body 31, that is, the impeller 23 is integrally rotated via the connecting member 33.

The closing plate 32 has a circular plate shape having substantially the same diameter as the bottom plate portion 35. A circular introduction port 39 is provided at the center of the block plate 32. Then, such a closing plate 32 is integrally assembled with the impeller body 31 so as to be in contact with the upper surface of each blade blade 36 so as to be parallel to the bottom plate portion 35 of the impeller body 31. As a result, the impeller body 23 is configured as a so-called closed type impeller 23 in which each groove flow path 37, which has been opened upward by itself, is closed by mounting the closing plate 32. Each groove flow path 37 has a radial direction because a portion other than the introduction port 39 at the center of the closing plate 32 and the discharge port 40 that opens radially outward of the groove flow path 37 is closed by the closing plate 32. Independent groove flow paths 37 are established adjacent to each other from the inner introduction port 39 toward the outer discharge port 40 in the radial direction.

Such an impeller 23 rotates in the pump chamber 24 so that its own introduction port 39 always faces the introduction flow path 26 of the pump case 22 and its own discharge port 40 faces the discharge flow path 27. Arranged as possible. Then, when the impeller 23 rotates based on the rotational drive of the motor unit 11, in this case, the rotary drive in one direction, the air introduced from the introduction flow path 26 to the introduction port 39 is based on the centrifugal force of the impeller 23. Air is discharged from each groove flow path 37 via the discharge port 40 and the discharge flow path 27, and air is supplied to an in-vehicle device (not shown).

[Detailed configuration of blade blade 36 and groove flow path 37 of impeller 23 of the present embodiment]
As a premise, the centrifugal pump 10 using the impeller 23 of the present embodiment is set to have a specific speed Ns representing pump characteristics of 50 or more and less than 100, that is, a lower specific speed than a general centrifugal pump of 50 ≦ Ns <100. ing. The specific speed Ns is a well-known index showing the pump characteristics, and is expressed by the following equation.

Ns = nQ ^1/2 / H ^3/4 (n: rotation speed, Q: flow rate, H: total head)
H = P / ρg (P: total pressure, ρ: density, g: gravitational acceleration)

As a detailed configuration of the impeller 23 used in the centrifugal pump 10 of the present embodiment having such a low specific speed, as shown in FIGS. 2 (a) and 2 (b) and 3, first, each blade blade 36 has a diameter. The directional inner end portion 36a is provided at a position corresponding to the inner peripheral edge portion of the introduction port 39 of the closing plate 32, and the radial outer end portion 36b is provided so as to continuously extend to the outer peripheral edge portion of the bottom plate portion 35. Between the radial inner ends 36a of the adjacent blades 36 is the inlet 37a of the groove flow path 37, and between the radial outer ends 36b of the adjacent blades 36 is the outlet 37b of the groove flow path 37. The outlet 37b of the groove flow path 37 is also the discharge port 40 of the impeller 23. The portion inside the radial inner end portion 36a of each blade blade 36 is a substantially circular space corresponding to the introduction port 39 of the closing plate 32, and the inlet 37a of each groove flow path 37 faces each other. Further, a connecting member 33 for connecting to the rotating shaft 15 is assembled to the bottom plate portion 35 of the radial inner end portion 36a of each blade blade 36.

Each blade blade 36 has a radial outer end than the radial inner end 36a with respect to the rotation direction of the impeller 23 in one direction, that is, the direction of the R1 arrow which is the counterclockwise direction of FIGS. The portion 36b is configured by a so-called rearward blade structure located on the downstream side. The side wall on the counterclockwise side of each blade 36 is a pressure surface portion 41 that applies pressure to the air in the groove flow path 37, and the side wall on the clockwise side is the side wall of the air in the groove flow path 37. The negative pressure surface portion 42 on which the negative pressure acts. When viewed from each groove flow path 37 side, the side wall of the blade blade 36 on the counterclockwise side is the negative pressure surface portion 42, and the side wall of the blade blade 36 on the clockwise side is the pressure surface portion 41. The pressure surface portion 41 and the negative pressure surface portion 42 are formed by surfaces orthogonal to the bottom plate portion 35 and the closing plate 32. That is, the groove flow path 37 surrounded by these has a rectangular cross section. Further, the pressure surface portion 41 and the negative pressure surface portion 42 have a mode in which the distance between the pressure surface portion 41 and the negative pressure surface portion 42 increases from the inner side in the radial direction to the outer side. Each corner between the pressure surface portion 41 and the bottom plate portion 35 and between the negative pressure surface portion 42 and the bottom plate portion 35 is an R surface.

The pressure surface portion 41 has a uniform curved shape using, for example, an involute curve or an approximate curve thereof. On the other hand, as shown in FIGS. 4 and 5A, the negative pressure surface portion 42 has the surface shapes of the first section A1, the second section A2, and the third section A3 smoothly and continuously as a whole. It is configured as a substantially uniform curved shape. The first section A1 is a section of about 1/4 of the entire negative pressure surface portion 42 from the radial inner end portion 36a of the blade blade 36, and is, for example, a first curved portion 42a using an involute curve or an approximate curve thereof. .. Next, the second section A2 is a section from the boundary portion 42x of the first section A1 with the first curved portion 42a to about 1/3 of the first section A1, for example, the boundary portion 42x with the first curved portion 42a. It is a straight line portion 42b along the tangent line in. Next, the third section A3 is the remaining section from the boundary portion 42y with the straight line portion 42b of the second section A2 toward the outside in the radial direction, and is, for example, a second curved portion 42c using an involute curve or an approximate curve thereof. There is. The straight line portion 42b is also a tangent line at the boundary portion 42y with the second curved portion 42c.

Further, as shown in FIGS. 2 (a) and 2 (b) and 6 (a) and 6 (b), the radial intermediate position of the impeller 23 is set as the starting position k, and one of the axial directions is directed toward the introduction port 39 inside the radial direction. An inclined portion 23a that gradually bulges the impeller 23 is configured on the side. The inclined portion 23a is formed in the closing plate 32 on a linear slope that gradually separates from the bottom plate portion 35 toward the introduction port 39, and the radial inner portion of each blade blade 36 is also included in the closing plate 32. It is gradually formed taller corresponding to the shape of the slope on the side surface. That is, the height of each groove flow path 37 is gradually increased toward the inlet 37a side, and the cross-sectional area of the flow path is also gradually increased toward the inlet 37a side. The distance between the block plate 32 and the block plate 32 is constant on the outer side in the radial direction from the starting point position k.

Here, in examining the configuration of the groove flow path 37, for example, a comparison shown by a broken line in FIG. 5A in which the negative pressure surface portion 42 is formed only by the second curved portion 42c with the second curved portion 42c side as a reference. An example is compared with the present embodiment shown by the solid line in FIG. 5A, which is formed by connecting the first and second curved portions 42a and 42c with the straight portion 42b. In other words, let's compare the configurations in which the second curved portion 42c, which is the outlet 37b side of the groove flow path 37, is used as a reference, and the inlet 37a side of the groove flow path 37 is viewed from there.

Looking at the inlet 37a side from the outlet 37b side of the groove flow path 37, it is shown by the solid line in FIG. 5 (a) with respect to the extension line of the second curved portion 42c in the comparative example shown by the broken line in FIG. 5 (a). In the present embodiment, not only the height but also the width of the groove flow path 37 is set to be slightly wider from the straight portion 42b toward the first curved portion 42a, that is, the inlet 37a. As a result, as shown in FIG. 5B, it was found that the centrifugal pump 10 of the present embodiment can improve the total pressure of the centrifugal pump 10 when the same driving is performed as compared with the comparative example. It can be inferred that this is because the flow velocity of the air in the inlet side portion from the inlet 37a of the groove flow path 37 to the straight portion 42b is suitably reduced, and the wall friction loss of the air flowing through the groove flow path 37 can be reduced.

It should be noted that there is a concern that the smoothness of the surface shapes of the boundary portions 42x and 42y may be deteriorated by connecting the first and second curved portions 42a and 42c with the straight portion 42b to form the negative pressure surface portion 42. However, in the present embodiment, the common tangent line at the boundary portions 42x and 42y of the curved portions 42a and 42c is used for the shape of the straight portion 42b so as not to impair the smoothness. Therefore, even if the curved portions 42a and 42c are connected by a straight portion 42b to form a composite surface shape, the air flow in each groove flow path 37 is smoothly maintained.

Further, as described above, in the present embodiment, as shown in FIGS. 6A and 6B, the boundary portion where the starting point position k of the inclined portion 23a of the impeller 23 is the outlet portion of the straight portion 42b of the negative pressure surface portion 42. It is set to the outside in the radial direction from 42y. Here, as shown in FIGS. 7A and 7B, a comparative example and the present embodiment in which the starting point position k of the inclined portion 23a is set radially inside the outlet portion of the straight portion 42b of the negative pressure surface portion 42. Let's compare with.

In the present embodiment shown in FIG. 6B, the air flow through the outlet portion of the straight portion 42b is smooth, whereas in the comparative example shown in FIG. 7B, the air flows through the outlet portion of the straight portion 42b. A backflow vortex and a separation flow were observed in a part of the air flow. When a backflow vortex or a separation flow occurs, the groove flow path 37 is pseudo-blocked, the actual flow path is narrowed, and the wall friction loss of the air flowing through the groove flow path 37 is increased, which is not preferable. This is more than the comparative example in which the starting point position k of the inclined portion 23a is set radially outside the exit portion of the straight portion 42b in the present embodiment, and the starting point position k is set radially inside. It can be inferred that one of the reasons is that the change in the inclined surface of the closing plate 32 at the starting point position k is small. In the present embodiment in which the change in the inclined surface of the closing plate 32 is small, the air flow can follow the shape change, whereas in the comparative example in which the change in the inclined surface of the closing plate 32 is large, the air flow follows the shape change. This is thought to be because the flow becomes difficult to follow.

Next, the key dimensions of the impeller 23 of the present embodiment will be examined.
As shown in FIG. 8A, the ratio b ₁ / b _{2 of the inlet height b 1} at the inlet 37 a of the groove flow path 37 of the impeller 23 and the outlet height b _{2 at the outlet 37 b of the groove flow path 37.} The change in the total pressure of the centrifugal pump 10 with respect to the above is shown in FIG. 8 (b). In the _{process of changing the ratio b 1} / b ₂ from "1.0" to "4.0", the total pressure of the centrifugal pump 10 becomes the desired value x 1 in the range X1 of "1.4" to "2.5". Beyond. Therefore, in the impeller 23 of the present embodiment, _{the inlet height b 1} and the outlet height b ₂ of the groove flow path 37 are set _{so that 1.4 ≤ b 1} / b _{2 ≤ 2.5.} , The total pressure of the centrifugal pump 10 is improved.

Further, as shown in FIG. 9A, the change in the total pressure of the centrifugal pump 10 with respect to the ratio b ₂ / D _{1 of the outer diameter D 1} of the impeller 23 and the outlet height b _{2 of the groove flow path 37 is shown.} It is shown in 9 (b). In the _{process of changing the ratio b 2} / D ₁ from "0.04" to "0.07", the total pressure of the centrifugal pump 10 is the desired value x2 in the range X2 of "0.045" to "0.06". Beyond. Therefore, in the impeller 23 of the present embodiment, the outer diameter D _{1 of the impeller 23 and the outlet height b 2 of the} groove flow path 37 are set _{so that 0.045 ≦ b 2} / D _{1 ≦ 0.06.} It is set to improve the total pressure of the centrifugal pump 10.

Further, as shown in FIG. 10A, the ratio l ₂ / l _{1 of the inlet width l 1} at the inlet 37 a of the groove flow path 37 of the impeller 23 and the outlet width l _{2 at the outlet 37 b of the groove flow path 37.} The change in the total pressure of the centrifugal pump 10 with respect to the above is shown in FIG. 10 (b). Here, the inlet width l ₁ is the innermost point which is the radial inner end portion 36a of the blade blade 36 and the negative pressure surface portion 42 of the blade blade 36 adjacent to the innermost point (in this case, the first curved portion 42a). ) Is defined as the width between the tangent line of the negative pressure surface portion 42 and the point orthogonal to it when the straight line is extended toward). Further, the outlet width l ₂ is the outermost point which is the radial outer end portion 36b of the blade blade 36, and the pressure surface portion when a straight line is extended from this outermost point toward the pressure surface portion 41 of the adjacent blade blade 36. It is defined as the width between the tangent of 41 and the point orthogonal to it.

In the _{process of changing the ratio l 2} / l ₁ to be larger than "1.0", the total pressure of the centrifugal pump 10 exceeded the desired value x 3 in the range X3 of "2.0" or more. As the upper limit of the ratio l ₂ / l ₁ , "3.0" is a realistic numerical value in terms of composition. Further, the inlet width l ₁ is "0.25" times or more, "0.5" times _{the ratio D 1 / Z of the outer diameter D 1 of the} impeller 23 and the number Z of the blade blades 36 shown in FIG. 9 (a). "Double or less is a realistic numerical value in terms of composition. From these, in the impeller 23 of the present embodiment, 0.25 · D ₁ / Z ≦ l ₁ ≦ 0.5 · D ₁ / Z and 2.0 ≦ l ₂ / l ₁ ≦ 3.0. _{The inlet width l 1} and the outlet width l ₂ of the groove flow path 37 are set so as to be such that the total pressure of the centrifugal pump 10 is improved.

The effect of this embodiment will be described.
(1) In the centrifugal pump 10 of the present embodiment having a low specific speed in which the specific speed Ns is set to 50 ≦ Ns <100, the negative pressure surface portion 42 of the blade blade 36 constituting the groove flow path 37 of the impeller 23 is formed. Includes the first curved portion 42a, the straight portion 42b and the second curved portion 42c from the radial inner end portion 36a, and the straight portion 42b and the first curved portion from the extension line of the second curved portion 42c when viewed from the second curved portion 42c side. The portion 42a has a surface shape that widens the width of the groove flow path 37. As a result, the flow velocity of the air at the inlet side of the groove flow path 37 is suitably reduced, and the effect of reducing the wall friction loss of the air flowing through the groove flow path 37 can be obtained. Therefore, the total pressure of the centrifugal pump 10 is improved. Can be expected (see FIG. 5 (b)).

(2) The straight portion 42b of the negative pressure surface portion 42 is formed along a common tangent line at the boundary portions 42x and 42y of the first and second curved portions 42a and 42c. Therefore, the surface shape of the negative pressure surface portion 42 in which the curved portions 42a and 42c are connected by the straight line portion 42b does not impair the smoothness even if it is a composite surface, and the air flow can be maintained smoothly.

(3) The negative pressure surface portion 42 is composed of three surfaces in which the first and second curved portions 42a and 42c are connected by a straight portion 42b. Therefore, the surface shape of the negative pressure surface portion 42 can be realized without being greatly complicated.

(4) The starting point position k of the inclined portion 23a of the impeller 23 is radially outside the boundary portion 42y with the second curved portion 42c, which is the outlet portion of the straight portion 42b of the negative pressure surface portion 42, that is, the introduction port 39. It is set away from. That is, since the inclined shape of the inclined portion 23a can be set gently and the change in the inclined surface at the starting point position k can be reduced, it becomes easy to make the air flow follow the change in the inclined surface, and the air flow is smoothly maintained. can do.

(5) The groove flow path 37 can be expected to improve the total pressure of the centrifugal pump 10 from the effect of _{optimizing the relationship between its own inlet height b 1} and outlet height b _{2 (FIG. 8).} See (b)).
(6) of the impeller 23 the relationship between the outlet height _{b 2} of the outer diameter _{D 1} and Mizoryuro 37, the flute 37 for the ratio between the number Z of the outer diameter _{D 1} and the vane blade 36 of the impeller 23 relationship inlet width l _1, and even from the effects due to each appropriate the relationship between the inlet width l ₁ and the outlet width l ₂ of Mizoryuro 37, improvement of the total pressure of the centrifugal pump 10 can be expected ( 9 (b) and 10 (b)).

This embodiment can be modified and implemented as follows. The present embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.
-The working fluid may be a gas other than air, water, another liquid, or the like.

An involute curve or an approximate curve thereof is used for the first and second curved portions 42a and 42c constituting the negative pressure surface portion 42, but the present invention is not limited to this, and other curves may be used.
-For the straight line portion 42b constituting the negative pressure surface portion 42, a common tangent line at each boundary portion 42x, 42y of the first and second curved portions 42a, 42c was used, but the present invention is not limited to this, and other straight lines are used. May be good.

The negative pressure surface portion 42 is composed of a composite surface composed of three surfaces, a first curved portion 42a, a straight portion 42b, and a second curved portion 42c, but the number and combinations of surfaces used are not limited to this, and may be changed as appropriate. You may.

-Although the impeller 23 was provided with the inclined portion 23a, the inclined shape of the inclined portion 23a may be appropriately changed or omitted.
-In addition to the above, the configuration of the impeller 23 may be changed as appropriate.

The configuration of the centrifugal pump 10 including the impeller 23 is an example, and may be changed as appropriate.
The technical idea that can be grasped from the above-described embodiment and modified example will be described.
(B) The ratio b ₂ / D ₁ of the outer diameter D _{1 of the} impeller to the outlet height b ₂ of the groove flow path is
0.045 ≤ b ₂ / D ₁ ≤ 0.06 and
_{The inlet width l 1} of the groove flow path with respect _{to the ratio D 1} / Z of the outer diameter D _{1 of the} impeller and the number Z of blade blades is
0.25 · D ₁ / Z ≤ l ₁ ≤ 0.5 · D ₁ / Z, and
The ratio l ₂ / l ₁ of the inlet width l ₁ and the outlet width l ₂ of the groove flow path is
It is set so that 2.0 ≤ l ₂ / l _{1 ≤ 3.0.}

10 ... Centrifugal pump, 23 ... Impeller, 23a ... Inclined part, 36 ... Blade blade, 36a ... Radial inner end, 36b ... Radial outer end, 37 ... Groove flow path, 39 ... Introduction port, 40 ... Discharge Outlet, 41 ... Pressure surface part, 42 ... Negative pressure surface part, 42x, 42y ... Boundary part, 42a ... First curved part, 42b ... Straight part, 42c ... Second curved part, Ns ... Specific speed, k ... Starting point position, b ₁ ... entrance height, b ₂ ... exit height.

Claims (6)

It has a plurality of blades (36) arranged at predetermined intervals in the circumferential direction and a plurality of groove flow paths (37) formed between the adjacent blades, and introduces a working fluid inside in the radial direction. It is provided with an impeller (23) for discharging from a port (39) toward a discharge port (40) on the outer side in the radial direction via the groove flow path.
A low specific speed centrifugal pump (10) in which the specific speed Ns is set to 50 ≦ Ns <100.
The vane blade of the impeller has a rearward blade structure in which the radial outer end portion (36b) is located on the downstream side in the rotational direction with respect to the radial inner end portion (36a), and the vane blade is viewed from the groove flow path. The pressure surface portion (41) formed on one side surface and the negative pressure surface portion (42) formed on the other side surface of the adjacent blade blade each have a substantially uniform curved shape. ,
The negative pressure surface portion includes a first curved portion (42a), a straight portion (42b), and a second curved portion (42c) from the radial inner end portion of the blade blade, and is viewed from the second curved portion side. The straight portion and the first curved portion are formed in a surface shape in such a manner that the width of the groove flow path is widened from the extension line of the second curved portion.
Centrifugal pump. The straight portion is formed along a common tangent line at each boundary portion (42x, 42y) of the first and second curved portions.
The centrifugal pump according to claim 1. The negative pressure surface portion is composed of three surfaces in which the first and second curved portions are connected by the straight portion.
The centrifugal pump according to claim 1 or 2. The impeller is configured with an inclined portion (23a) that gradually bulges the impeller on one side in the axial direction toward the introduction port on the inner side in the radial direction with its own radial intermediate position as the starting point position (k). And
The starting point position of the inclined portion is set radially outside the boundary portion with the second curved portion, which is the exit portion of the straight portion.
The centrifugal pump according to any one of claims 1 to 3. The groove flow path has a ratio b ₁ / b ₂ of its own inlet height (b ₁ ) and outlet height (b ₂ ).
It is set so that 1.4 ≤ b ₁ / b _{2 ≤ 2.5,}
The centrifugal pump according to any one of claims 1 to 4. It has a plurality of blades (36) arranged at predetermined intervals in the circumferential direction and a plurality of groove flow paths (37) formed between the adjacent blades, and introduces a working fluid inside in the radial direction. It is discharged from the port (39) toward the discharge port (40) on the outer side in the radial direction via the groove flow path.
A low specific speed centrifugal pump impeller (23) in which the specific speed Ns is set to 50 ≦ Ns <100.
The vane blade of the impeller has a rearward blade structure in which the radial outer end portion (36b) is located on the downstream side in the rotational direction with respect to the radial inner end portion (36a), and the vane blade is viewed from the groove flow path. The pressure surface portion (41) formed on one side surface and the negative pressure surface portion (42) formed on the other side surface of the adjacent blade blade each have a substantially uniform curved shape. ,
The negative pressure surface portion includes a first curved portion (42a), a straight portion (42b), and a second curved portion (42c) from the radial inner end portion of the blade blade, and is viewed from the second curved portion side. The straight portion and the first curved portion are formed in a surface shape in such a manner that the width of the groove flow path is widened from the extension line of the second curved portion.
Impeller for centrifugal pump.