WO2007123406A1

WO2007123406A1 - Centrifugal pump impeller

Info

Publication number: WO2007123406A1
Application number: PCT/NL2007/050181
Authority: WO
Inventors: Hasan Hüseyin Bugdayci
Original assignee: IHC Holland I.E. B.V.
Priority date: 2006-04-25
Filing date: 2007-04-25
Publication date: 2007-11-01
Also published as: EP2010787A1; CN101432527A; NL1031687C2

Abstract

A centrifugal pump comprises a housing as well as a rotor which is arranged so as to be able to rotate about an axial axis of rotation in the housing. The rotor is provided with at least two rotor blades, each of which extends substantially radially with respect to the axis of rotation between a radial outer end and a radial inner end. The outer ends of at least two rotor blades are at radially different distances to the axis of rotation.

Description

CENTRIFUGAL PUMP IMPELLER

The invention relates to a centrifugal pump, comprising a housing as well as a rotor, which is arranged so as to be able to rotate about an axial axis of rotation in the housing, which rotor is provided with at least two rotor blades, each of which extends substantially radially with respect to the axis of rotation between a radial outer end and a radial inner end.

A centrifugal pump of this type is known. The housing of this centrifugal pump has an axial inlet and a tangential outlet. The rotor is provided with an axial supply or intake, which is aligned with respect to the axial inlet of the housing, and a radial discharge. The rotor blades extend between a radial inner end and a radial outer end. The radial discharge is situated between the outer ends of the rotor blades.

In operation, the rotor rotates about the axial axis of rotation. Between the rotor blades, the mass to be pumped is forced radially outwards on account of centrifugal forces. The pumped mass flows into the housing via the radial discharge of the rotor. Subsequently, this mass is carried along to the tangential outlet of the housing in the circumferential direction of the housing.

The housing has a circumferential wall, in which the tangential outlet is disposed. The transition between the inner wall of the tangential outlet and the inside of the circumferential wall of the housing determines a so-called cutwater. The pumped mass which is entrained from the radial discharge of the rotor in the circumferential direction of the housing largely flows out of the tangential outlet of the housing. A small amount of the entrained mass recirculates, that is to say flows back into the housing via the cutwater.

While the rotor blades are rotating, a pulsating pressure is created near the cutwater. When a rotor blade moves past the cutwater of the housing, the local pressure at the cutwater initially increases up to a maximum value. After all, the pumped mass is forced between the surfaces of the moving rotor blade and the cutwater facing one another. Shortly after this rotor blade has passed the cutwater, this local pressure decreases. In this manner, the rotor blades exert a pulsating force onto the cutwater.

In order to ensure the pump action, the outer ends of the rotor blades are at a minimum distance to the axis of rotation. This minimum distance determines the amplitude of the pulsating pressure.

Li addition, the pump system comprising the centrifugal pump, the pumped substance as well as possibly a part of the pipe system, at the suction and delivery side of the pump, has a natural frequency which depends on various variables. These variables comprise, for example, the density of the pumped mass and/or the configuration of the pipe system. Depending on these variables, the pressure peaks caused by the rotor blades, in combination with the natural frequency of the system, may result in undesired vibrations of components of the pump or the pipe system connected to the latter. This problem can occur in particular when pumping dredge spoil.

It is an object of the invention to provide a centrifugal pump which is less susceptible to undesired vibrations.

According to the invention, this object is achieved in that the outer ends of at least two rotor blades are at radially different distances to the axis of rotation. As a result, these rotor blades produce different pressure peaks at the cutwater of the housing. The pump system will thus not be impinged on by each rotor blade with the maximum occurring pressure. Per rotation, in addition to the maximum pressure, a pressure will also occur which is lower with respect to the former and which corresponds to one or more radially inwardly staggered rotor blades. This makes the centrifugal pump less susceptible to undesired vibrations.

In one embodiment of the invention, the length of at least two rotor blades differs with respect to one another. By varying the length of the rotor blades, undesired vibrations of the centrifugal pump or the pipe system connected thereto can be effectively counteracted. It is preferable that the rotor comprises at least three rotor blades, the inner end of each rotor blade being at the same radial distance from the axis of rotation, and the length of each rotor blade differing from the length of both rotor blades which adjoin said rotor blade in the circumferential direction. In a common flow design for the supply of the rotor, the inner ends of the rotor blades are in each case at the same radial distance from the axis of rotation. By varying the length of the rotor blades, the outer ends of the rotor blades according to the invention are at different radial distances to this axis of rotation. As a result, the reduction of the associated pressure peaks can be achieved without modifying the flow design of the supply of the rotor according to the invention. The flow properties of the supply of the rotor according to the invention are still maintained.

For example, the rotor may comprise at least five rotor blades, with the outer end of at least three rotor blades being situated in each case radially inside the outer end of at least one of the rotor blades. In this embodiment of the invention, at least one of the rotor blades forms the outer rotor blade, that is to say the rotor blade which extends furthest radially outwards with respect to the axis of rotation. The outer ends of the other rotor blades are at a smaller radial distance from the axis of rotation. The outermost rotor blade then produces the maximum pressure, while the pressure peaks associated with the other rotor blades are lower than the maximum pressure.

In this embodiment of the invention, it is also possible that the rotor has several outermost rotor blades. For example, the rotor having five rotor blades has two outermost rotor blades, as a result of which the maximum pressure is reached twice and a relatively low pressure peak is reached three times per rotation. In this case as well, the risk of undesired vibrations due to resonance remains limited.

The number of rotor blades of the centrifugal pump and the number of outermost rotor blades thereof may vary according to the invention. The degree to which the distances of the outer ends of the rotor blades to the axis of rotation differ also depends on the use.

According to the invention, it is preferable that the rotor is balanced with respect to the axis of rotation. Thus, the rotor will not go out of balance while rotating in the housing. This can be achieved in various ways, for example by suitably distributing the rotor blades over the circumference and/or locally milling and/or increasing the weight of the rotor.

According to the invention, it is possible that the rotor is provided with a hub which defines the axis of rotation, a first wall which is attached to the hub, as well as a second wall which is arranged at an axial distance from said first wall, in which the rotor blades are arranged between said walls, in which the radial discharge is formed between said walls, and in which the axial supply is arranged in the second wall. Between the walls and in each case two adjoining rotor blades, in each case one flow passage is formed.

According to the invention, it is possible that the radial inner end of each rotor blade is located inside the axial supply of the rotor. As a result thereof, the mass to be pumped is subjected to an appreciable sucking force in the supply. The sucking action is caused by the reduced pressure which prevails between the rotor blades. This reduced pressure is caused by the pumped mass being forced away.

In order to reduce the risk of undesired vibrations occurring further, it is preferable, according to the invention, that the rotor blades are arranged at irregular distances with respect to one another in the circumferential direction. With the known rotor, the rotor blades are distributed evenly over the circumference of the rotor. As a result thereof, the pumped mass is subjected to a substantially radial counterpressure at a fixed frequency at the location of the cutwater. This impingement frequency of the rotor blades is equal to the product of the rotation frequency and the number of rotor blades. If the impingement frequency of the rotor blades substantially corresponds to the natural frequency of the system, this may cause undesired vibrations of components of the pump or the pipe system connected thereto. However, according to this embodiment of the invention, the time between the successive rotor blades moving past the tangential outlet of the pump, in particular past the cutwater thereof, is variable as a result of the irregular distances between said rotor blades. Thus, the pump system is only impinged on at the rotation frequency, which reduces the risk of resonance occurring. If the rotor blades are arranged at irregular distances with respect to one another in the circumferential direction, the distance between a pair of rotor blades which adjoin one another in the circumferential direction may differ from the distance between a further pair of rotor blades which adjoin one another in the circumferential direction. According to the invention, the rotor blades are unevenly distributed over the circumference of the rotor, so that the impingement frequency of the rotor is substantially equal to the rotation frequency thereof. If a rotor blade moves past the tangential outlet, in particular the cutwater of the housing, in each case a different time elapses until a subsequent rotor blade moves past that cutwater. The risk of undesired vibrations is greatly reduced according to the invention.

In one embodiment according to the invention, the rotor comprises at least three rotor blades, and the angles between the pairs of rotor blades are in each case different. According to the invention, however, the rotor may comprise a different number of rotor blades, for example four, five, six, seven or more rotor blades.

The invention also relates to a rotor for a centrifugal pump, comprising a hub which defines an axial axis of rotation of the rotor, an axial supply or intake, a radial discharge, as well as at least two rotor blades, each of which extends substantially radially with respect to the axis of rotation between a radial outer end and a radial inner end. According to the invention, the outer ends of at least two rotor blades are at radially different distances to the axis of rotation.

In a preferred embodiment of the rotor according to the invention, the rotor blades are arranged at irregular distances with respect to one another in the circumferential direction.

The invention will now be explained in more detail with reference to an exemplary embodiment illustrated in the figures, in which:

Figure 1 shows a cross sectional view of a centrifugal pump according to the invention; Figure 2 shows a front view along line II in Figure 1 , partially in cross section. The centrifugal pump according to the invention is denoted in its entirety by reference numeral 1. The centrifugal pump 1 comprises a housing 2, which is spiral-shaped (see Figure 2). The pump housing 2 comprises an axial inlet 6 and a tangential outlet 7. The tangential outlet 7 is located laterally with respect to the housing 2. hi this exemplary embodiment, the tangential outlet 7 is designed as a nozzle. Furthermore, a rotor 3 is provided which is arranged so as to be able to rotate about an axial axis of rotation 5 in the housing 2. The axial inlet 6 in the housing 2 is located centrally with respect to the rotor 3.

The rotor 3 is commonly formed by a single moulded piece. The rotor 3 comprises a hub 27, in which a shaft mounted outside the housing 2 can be accommodated (not shown). The hub 27 defines the axis of rotation 5 of the rotor 3. The rotor 3 furthermore has a first wall or shaft shield 30. The first wall 30 is connected to the hub 27. At an axial distance from this first wall 30, there is a second wall or suction shield 31. The rotor 3 furthermore comprises several rotor blades 14 which are fastened between said walls 30, 31. In this exemplary embodiment, five rotor blades 14 are shown (see Figure 2). The rotor blades 14, which have a curved shape, extend substantially radially with respect to the axis of rotation 5.

Each of the rotor blades 14 has a radial inner end 16 and a radial outer end 17.

Furthermore, each rotor blade 14 has an inner surface 20 and an outer surface 21. hi each case one flow passage 33 is formed between the inner surface 20 and the outer surface 21 of two adjoining rotor blades 14 and the walls 30, 31, respectively. The flow passage 33 extends substantially radially with respect to the axis of rotation 5.

An axial supply or intake 9 and a radial discharge 11 are provided in the rotor 3. The axial supply 9 is located in the second wall 31. The axial supply 9 is aligned with respect to the axial inlet 6 of the housing 2, that is to say the mass to be pumped can flow via the axial inlet 6 of the housing 2 into the axial supply 9 of the rotor 3. The radial outlet 11 is located between the walls 30, 31.

The transition between the inner wall of the tangential outlet 7 and the inside of the circumferential wall of the housing 2 determines the so-called cutwater 36. The cutwater 36 is thus formed by the elbow-shaped connection between the outlet 7 and the circumferential wall of the pump housing 2. A circumferential duct 39 is formed between the inside of the circumferential wall of the housing 2 and the rotor 3. The circumferential duct 39 has a surface area which increases slightly in the circumferential direction from the cutwater 36 to the discharge 7 (see Figure 2).

The action of the centrifugal pump according to the invention is as follows. During operation, the rotor 3 rotates inside the housing 2 of the centrifugal pump 1 in the direction of rotation, which is indicated by arrow A (see Figure 2). The fluid to be pumped, such as dredge spoil, flows into the centrifugal pump 1 through the axial inlet 6 of the housing 2. Subsequently, the fluid flows into the axial supply 9 of the rotor 3, following which the rotating rotor blades 14 exert forces on the fluid. These forces have a tangential component. During rotation of the rotor blades, the fluid is forced in a tangential direction and exerts a centrifugal force onto its environment. On account of these centrifugal forces, the fluid flows through the flow passages 33 radially outwards. Each of the flow passages 33 is delimited by two neighbouring rotor blades and the walls 30, 31.

The fluid then flows from the radial discharge 11. The radial discharge 11 is substantially surrounded by the circumferential duct 39 in the housing 2 of the centrifugal pump 1. As the pumped mass has a tangential velocity, the rotor blades 14 carry the fluid along to the outlet 7 of the housing. At the location of the tangential outlet 7 the entrained fluid for the largest part flows into the tangential outlet 7, while a small amount of the entrained fluid recirculates, that is to say past the cutwater 36, and ends up back in the circumferential duct 39, on the right-hand side in Figure 2.

While a rotor blade 14 moves past the tangential outlet 7 and the cutwater 36, the pressure varies periodically. If the rotor blade 14 is far from the cutwater 36, a relatively low pressure prevails locally at the cutwater 36. As the rotor blade 14 rotates in the direction of the outlet 7, the local pressure at the cutwater 36 increases. When the rotor blade 14 is closest to the cutwater 36, the local pressure at the location of that cutwater 36 is at a maximum - the local pressure has then peaked. When the rotor blade 14 moves past the cutwater 36, the pressure decreases, after which a subsequent rotor blade 14 again causes a pressure increase.

With the known centrifugal pump, each rotor blade causes the same pressure peak. If the pressure peak of each rotor blade is sufficiently large, this pressure peak of the pulsating pressure may cause undesired vibrations. According to the invention, the occurrence of these undesired vibrations is counteracted by the fact that the outer ends 17 of at least two rotor blades 14 are at radially different distances to the axis of rotation 5.

In the exemplary embodiment illustrated, two outermost rotor blades 14 have a maximum radial distance to the axis of rotation 5, shown in Figure 2 as the rotor blade 14 on the outermost left-hand side and the outermost right-hand side. These outermost rotor blades 14 ensure the pump action, that is to say the maximum pressure.

Between these outermost rotor blades 14, there are two radially inwardly staggered rotor blades 14 and a single radially inwardly staggered rotor blade 14, respectively. The single inwardly located rotor blade 14 and one of the other two rotor blades 14 are at substantially 95% of the maximum radial distance to the axis of rotation 5 of the outermost rotor blades 14. The other rotor blade 14 is at a distance to the axis of rotation 5 of substantially 85% of this maximum distance of the outermost rotor blades 14. For example, the successive dimensions, viewed in the direction of rotation A, are 404 mm, 350 mm, 404 mm, 350 mm and 380 mm. These dimensions obviously depend on the use.

Ih this exemplary embodiment, the inner ends 16 of the rotor blades 14 are arranged at the same distance from the axis of rotation 5. As the outer ends 17 are at different distances from said axis of rotation 5, the rotor blades 14 are of different lengths.

In this exemplary embodiment, only the two outermost rotor blades 14 produce the maximum pressure at the cutwater 36 during rotation of the rotor 3. The other rotor blades 14 produce pressure peaks which are lower than said maximum pressure. Thus, the maximum pressure is reached only twice per rotation, which significantly reduces the risk of undesired vibrations.

In order to counteract the generation of undesired vibrations further, the centrifugal pump according to the invention has a second aspect.

With the known centrifugal pump, the rotor blades are evenly distributed over the circumference of the rotor, so that the rotor blades, during rotation thereof, impinge on the tangential outlet of the housing at a fixed frequency, which is equal to the product of the rotation frequency and the number of rotor blades. This impingement frequency may be close to the natural frequency of the pump system. If the pump system has been designed for pumping a fluid, i.e. the risk of resonance during pumping of that medium is minimal, pumping a different medium may still cause an increased risk of resonance and undesired vibrations. The fact is that the natural frequency depends on the density of the pumped medium. Incidentally, the natural frequency may also depend on further variables.

According to the second aspect of the invention, the occurrence of undesired vibrations is counteracted further by the fact that the rotor blades 14 are arranged at irregular distances with respect to one another in the circumferential direction (see Figure 2). The distance between a pair of rotor blades 14 adjoining one another in the circumferential direction in each case differs from the distance between a further pair of rotor blades 14 adjoining one another in the circumferential direction.

In the illustrated exemplary embodiment having five rotor blades 14, the angles between adjoining rotor blades 14 are in each case different. For example, these angles, viewed in the direction of rotation A, are successively substantially 72°, 50°, 94°, 51° and 92°.

As a result of this irregular distribution of the rotor blades 14 over the circumference of the rotor 3, the time elapsed between two subsequent rotor blades 14 passing the tangential outlet 7, in particular the cutwater 36 thereof, differs in each case. Said cutwater 36 is only impinged on at the rotation frequency, which significantly reduces the risk of the impingement frequency corresponding to the natural frequency of the pump system. Resonance and undesired vibrations will thus occur less readily.

It will be clear that the rotor 3 should not get out of balance while it is rotating. Therefore, the rotor blades 14 are distributed over the circumference of the rotor 3 in such a manner that the rotor 3 is balanced with respect to the axis of rotation 5. In addition, the rotor 3 may comprise recesses and/or balance weights in order to ensure that the rotor remains balanced during its rotation. Balancing is important in order to prevent undesired vibrations.

Obviously, the above-described embodiment is only an example. The centrifugal pump according to the invention may be designed in many ways. For example, the number of rotor blades, the length of the rotor blades and/or the respective angle between the rotor blades may be modified.

The second aspect of the invention, i.e. the reduction of the risk of undesired vibrations by arranging the rotor blades 14 at irregular distances with respect to one another in the circumferential direction, is of independent importance. This second aspect is the subject of a patent application in the name of the Applicant, which was filed on the same date as the present patent application.

Claims

1. Centrifugal pump (1), comprising a housing (2) as well as a rotor (3) which is arranged so as to be able to rotate about an axial axis of rotation (5) in the housing (2), which rotor (3) is provided with at least two rotor blades (14), each of which extends substantially radially with respect to the axis of rotation (5) between a radial outer end (17) and a radial inner end (16), characterized in that the outer ends (17) of at least two rotor blades (14) are at radially different distances to the axis of rotation (5).

2. Pump according to Claim 1, in which the length of at least two rotor blades (14) differs with respect to one another.

3. Pump according to Claim 1 or 2, in which the rotor (3) comprises at least three rotor blades (14), and in which the inner end (16) of each rotor blade (14) is at the same radial distance from the axis of rotation (5), and in which the length of each rotor blade (14) differs from the length of both rotor blades (14) which adjoin said rotor blade (14) in the circumferential direction.

4. Pump according to one of the preceding claims, in which the rotor comprises at least five rotor blades (14), and in which the outer end (17) of at least three rotor blades

(14) is situated in each case radially inside the outer end (17) of at least one of the rotor blades (14).

5. Pump according to one of the preceding claims, in which the housing (2) is provided with an axial inlet (6) and a tangential outlet (7), in which the rotor (3) is provided with an axial supply (9), which is aligned with respect to the axial inlet (6) of the housing (2), and a radial discharge (11).

6. Centrifugal pump according to one of the preceding claims, in which the rotor (3) is balanced with respect to the central axis of rotation (5).

7. Pump according to one of the preceding claims, in which the rotor (3) is provided with a hub (27) which defines the axis of rotation (5), a first wall (30) which is attached to the hub (27), as well as a second wall (31) which is arranged at an axial distance from said first wall (30), in which the rotor blades (14) are arranged between said walls (30, 31), in which the radial discharge (11) is formed between said walls (30, 31), and in which the axial supply (9) is arranged in the second wall (31). 5

8. Pump according to one of the preceding claims, in which the inner end (16) of each rotor blade (14) is located inside the axial supply (9) of the rotor (3).

9. Pump according to one of the preceding claims, in which the rotor blades (14) are 0 arranged at irregular distances with respect to one another in the circumferential direction.

10. Pump according to Claim 9, in which the distance between a pair of rotor blades (14) which adjoin one another in the circumferential direction differs from the distance 5 between a further pair of rotor blades (14) which adjoin one another in the circumferential direction.

11. Pump according to Claim 10, in which the rotor comprises two or more rotor blades (14), and in which the angles between the pairs of rotor blades (14) are in each 0 case different.

12. Rotor (3) for a centrifugal pump (1), comprising a hub (27) which defines a axial axis of rotation (5) of the rotor (3), as well as at least two rotor blades (14), each of which extends substantially radially with respect to the axis of rotation (5) between a 5 radial outer end (17) and a radial inner end (16), characterized in that the outer ends (17) of at least two rotor blades (14) are at radially different distances to the axis of rotation (5).

13. Rotor according to Claim 12, in which the rotor blades (14) are arranged at i0 irregular distances with respect to one another in the circumferential direction.