JP2013213410A - Centrifugal fluid machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a centrifugal fluid machine that can reduce a shaft thrust load.SOLUTION: A centrifugal fluid machine includes: a casing; a disk-like hub stored in the casing, rotates on a surface vertical to a rotary shaft, and includes a back surface facing the casing; and an impeller having a plurality of vanes fixed to an opposite back surface of the hub, from an outer circumference of which working fluid flows and in which the working fluid is flowed out to an opposite direction of the back surface of the hub. A ring-shaped member is provided on a surface facing the back surface of the hub of the casing to be operable toward the back surface of the hub.

Description

  Embodiments described herein relate generally to a centrifugal fluid machine.

Centrifugal fluid machines such as pumps and Francis turbines generate axial thrust force (axial thrust force) due to the unbalance of the force opposite to the force pushing the impeller toward the suction pipe.
From the balance of the total force in the rotation axis direction, it is generally known that a thrust force is applied to the suction pipe side in the rotation axis direction. In addition, since the impeller rotates during operation, the flow in the back pressure chamber swirls in the direction of rotation of the impeller due to the rotational friction of the hub, and due to the centrifugal force acting on the fluid on the meridional section. A flow toward the outer diameter direction is generated along the hub surface, and a circulating flow is generated. Further, it is known that the pressure acting on the surface of the hub of the back pressure chamber increases toward the outer peripheral side due to this centrifugal force (see, for example, Patent Document 1).

JP 2009-8021 A

Under normal operation, a thrust force acts on the impeller toward the axial direction. But,
During transient operation such as startup, a thrust force may act in the opposite main shaft side direction, and the impeller may be lifted and come into contact with the casing. Therefore, in order to prevent contact with the impeller even if it moves to the main shaft side in the axial direction under such circumstances, it is usually designed with a certain gap between the impeller and the casing.

However, since the clearance is widened, the circulation on the meridian plane caused by the rotation of the impeller is strengthened. Therefore, the pressure increases with the strength of the flow, and the thrust force is increased.

The problem to be solved by the present invention is to provide a centrifugal fluid machine capable of reducing the axial thrust force.

The centrifugal fluid machine according to the present embodiment includes a casing, a disc-shaped hub that is accommodated in the casing, rotates on a plane perpendicular to the rotation axis, and includes a rear surface facing the casing, and the rear surface of the hub. A plurality of blades fixed on the opposite side, the working fluid flows from the outer peripheral side,
An impeller for flowing a working fluid in a direction opposite to the rear surface of the hub, and a ring-shaped member operable toward the rear surface of the hub on a surface of the casing facing the rear surface of the hub. .

FIG. 3 is a meridional sectional view of the centrifugal fluid machine according to the first embodiment. Sectional drawing which expanded the back pressure chamber vicinity shown in FIG. Sectional drawing which expanded the back pressure chamber vicinity shown in FIG. The horizontal axis is the length along the hub, and the vertical axis is the pressure acting on the hub surface. FIG. 6 is a cross-sectional view of a centrifugal fluid machine according to a second embodiment. FIG. 6 is a cross-sectional view of a centrifugal fluid machine according to a third embodiment. FIG. 6 is a cross-sectional view of a centrifugal fluid machine according to a fourth embodiment. FIG. 10 is a schematic view of a back pressure chamber of a centrifugal fluid machine according to a fifth embodiment when viewed from the outer peripheral side. FIG. 10 is a schematic diagram of a back pressure chamber of a centrifugal fluid machine according to a sixth embodiment viewed from the outer peripheral side.

  Embodiments will be described with reference to the drawings.

<Embodiment 1>
FIG. 1 is a meridional sectional view of a centrifugal fluid machine according to a first embodiment. Here, a Francis type turbine will be described as an example of a centrifugal fluid machine.

A Francis-type impeller 3 is connected to a lower end of a main shaft 2 that is a rotation shaft of the water turbine 1. A generator (not shown) is connected to the top of the main shaft 1. The impeller 3 fixes a plurality of blades 3a arranged at predetermined intervals in the circumferential direction, a disk-shaped hub 3b for fixing these blades 3a from one side, and the blades 3a from the other side. And a shroud 3c functioning as an annular member. The hub 3 b is connected to the main shaft 1 and rotates on a plane perpendicular to the main shaft 1.

The impeller 3 is accommodated in the casing 4. The casing 4 includes a snail-shaped (annular) annular portion 4 a disposed on the outer periphery of the impeller 3, and an upper cover 4 disposed above the impeller 3.
b and a discharge ring 4 c disposed below the impeller 3. A plurality of stay vanes 5 are provided in the circumferential direction on the inner peripheral portion of the annular portion 4a. A plurality of guide vanes 6 are arranged between the stay vanes 5 and the impeller 3 in the circumferential direction. Below the impeller 3, a suction pipe 7 connected to the discharge ring 4c is disposed.

FIG. 2 is an enlarged cross-sectional view of the vicinity of the back pressure chamber 22 shown in FIG. Hub 3b and upper cover 4
A back pressure chamber 22 is formed in a space surrounded by b. A ring-shaped member 21 is provided on the surface of the upper cover 4b that faces the back surface of the hub 3b. The ring-shaped member 21 is configured to be operable by an elevating device that is a driving mechanism (not shown) in the direction of the rotation axis of the impeller 3 toward the rear surface of the hub 3b. That is, the ring-shaped member 21 is configured to be movable up and down in the rotation axis direction of the impeller 3.

The pressure water which is the working fluid introduced from the upper pond through the iron pipe is the casing 4 shown in FIG.
And the guide vane 6 where the flow rate is adjusted and guided to the impeller 3. The impeller 3 converts the pressure energy of the introduced pressure water into rotational energy, rotates about the main shaft 2 as a rotation shaft, and rotates a generator (not shown) connected to the main shaft 2 to generate electric power. The working fluid that flows in from the outer periphery of the impeller 3 and passes through the impeller 3 passes through the suction pipe 7 below the impeller 3 and is discharged to the downstream basin.

The ring-shaped member 21 shown in FIG. 2 avoids contact with the impeller 3 by moving the ring-shaped member 21 to the upper cover 4b side during transient operation such as startup. During normal operation, the distance between the ring-shaped member 21 and the hub 3b is made sufficiently small.

FIG. 3 is an enlarged cross-sectional view of the vicinity of the back pressure chamber 22 shown in FIG. 1, and arrows in the drawing schematically show the flow of the working fluid. The ring-shaped member 21 is lowered, and the ring-shaped member 21 and the hub 3
By making the distance to b sufficiently small, the flow in the outer peripheral direction along the surface of the hub 3b caused by the rotation of the impeller 3 can be suppressed on the meridional section, so that the hub 3b at the corresponding location due to the centrifugal force. The pressure on the surface also decreases.

FIG. 4 is a diagram in which the horizontal axis represents the length along the hub 3b and the vertical axis represents the pressure acting on the surface of the hub 3b. When the embodiment is applied, the pressure applied to the surface of the hub 3b at the relevant location due to the centrifugal force is lower than in the conventional case where the embodiment is not applied.

According to this embodiment, it is possible to reduce the thrust force acting on the impeller 3 in the direction of the suction pipe 7 of the rotating shaft. Further, during transient operation such as startup, the ring-shaped member 21 can be moved to the upper cover 4b side, and contact between the ring-shaped member 21 and the impeller 3 can be reduced.

<Embodiment 2>
FIG. 5 is a cross-sectional view of a centrifugal fluid machine according to the second embodiment. The same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. In the second embodiment, the surface of the ring-shaped member 31 facing the hub 3b is formed in a shape along the upper surface (back surface) of the hub 3b.

When the ring-shaped member 21 is lowered, the ring-shaped member 21 and the hub 3b are compared with the first embodiment.
The distance between and becomes even smaller. Therefore, since the flow in the outer peripheral direction along the surface of the hub 3b caused by the rotation of the impeller 3 on the meridional section can be further suppressed as compared with the first embodiment, the flow on the hub 3b surface at the corresponding location due to the centrifugal force is reduced. Such pressure can be further reduced.

<Embodiment 3>
FIG. 6 is a cross-sectional view of a centrifugal fluid machine according to the third embodiment. The same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. In the third embodiment, a cylindrical rib 42 is provided on the surface facing the upper cover 4 b of the ring-shaped member 41.

The cylindrical rib 42 can reduce the flow 43 (FIG. 3) passing between the ring-shaped member 41 and the upper cover 4b. Further, the flow 44 (FIG. 3) that passes through the back pressure chamber 22 and is discharged from between the main shaft 2 and the upper cover 4b can be reduced. Therefore, the amount of high-pressure water (leakage flow rate) can be reduced.

According to this embodiment, in addition to the effects of the first embodiment, the leakage flow rate that does not act on the impeller 3 can be reduced, so that the volume efficiency of the fluid machine can be improved.

<Embodiment 4>
FIG. 7 is a cross-sectional view of a centrifugal fluid machine according to a fourth embodiment. The same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. In the fourth embodiment, the protrusion 52 is provided on the surface of the ring-shaped member 51 on the side facing the hub 3b. A plurality of protrusions 52 are provided concentrically, and the heights of the protrusions differ depending on the distance between the ring-shaped member 51 and the hub 3b. In this embodiment, the height decreases as it goes to the outer periphery, and the flow in the outer peripheral direction along the surface of the hub 3b caused by the rotation of the impeller 3 is suppressed as much as possible at each position of the protrusion 52. Is formed.

According to this embodiment, the hub 3 caused by the rotation of the impeller 3 on the meridional section.
Since the flow in the outer peripheral direction along the b surface can be further suppressed as compared with the first embodiment, the pressure applied to the surface of the hub 3b at the location associated with the centrifugal force can be further reduced.

<Embodiment 5>
FIG. 8 is a schematic view of the back pressure chamber 22 of the centrifugal fluid machine according to the fifth embodiment viewed from the outer peripheral side. The same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. In the fifth embodiment, a plurality of protrusions 62 arranged radially at equal intervals on the surface of the ring-shaped member 61 facing the hub 3b.
Is provided.

The protrusion 62 receives a swirling flow due to rotational friction, and a force acts in a direction away from the hub 3b.
As the distance between the ring-shaped member 61 and the hub 3b decreases, the upward force received by the projection (force in the direction away from the hub 3b) increases. Since the ring-shaped member 61 is provided with a drive mechanism (not shown), the ring-shaped member 61 slightly rises due to play or a damper function of the drive mechanism. Therefore, stable operation can be performed while keeping the distance between the ring-shaped member 61 and the hub 3b small.

According to this embodiment, the hub 3 caused by the rotation of the impeller 3 on the meridional section.
Since the flow in the outer peripheral direction along the b surface can be further suppressed as compared with the first embodiment, the pressure applied to the surface of the hub 3b at the location associated with the centrifugal force can be further reduced.

<Embodiment 6>
FIG. 9 is a schematic view of the back pressure chamber 22 of the centrifugal fluid machine according to the sixth embodiment viewed from the outer peripheral side. The same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. In the fifth embodiment, a plurality of grooves 72 arranged radially at equal intervals are provided on the surface of the ring-shaped member 71 facing the hub 3b.

The groove 72 receives a swirling flow due to rotational friction, a force acts in a direction away from the hub 3b, and an upward force (hub 3) received by the projection as the distance between the ring-shaped member 71 and the hub 3b decreases.
force in the direction away from b). Since the ring-shaped member 71 is provided with a drive mechanism (not shown), the ring-shaped member 71 is slightly lifted by play or a damper function of the drive mechanism. Therefore, stable operation can be performed while keeping the distance between the ring-shaped member 71 and the hub 3b small.

According to this embodiment, the hub 3 caused by the rotation of the impeller 3 on the meridional section.
Since the flow in the outer peripheral direction along the b surface can be further suppressed as compared with the first embodiment, the pressure applied to the surface of the hub 3b at the location associated with the centrifugal force can be further reduced.

According to the centrifugal fluid machine of at least one embodiment described above, it is possible to reduce the thrust force acting in the suction pipe side direction of the rotating shaft with respect to the impeller. In addition, the ring-shaped member can be moved to the upper cover side during transitional operation such as startup, and contact between the ring-shaped member and the impeller can be reduced.

Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions can be made without departing from the spirit of the invention.
Can be replaced or changed. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  For example, Embodiments 3 to 6 can be combined with all other embodiments.

DESCRIPTION OF SYMBOLS 1 ... Water wheel, 2 ... Main shaft, 3 ... Impeller, 3a ... Blade, 3b ... Hub, 4 ... Casing, 4b ... Upper cover, 21, 31, 41, 51, 61, 71 ... Ring-shaped member, 42 ... Rib, 52, 62
... projections, 72 ... grooves.

Claims (5)

A casing,
A disc-shaped hub that is housed in the casing and rotates on a plane perpendicular to the rotation axis and includes a rear surface facing the casing; and a plurality of blades fixed to the opposite side of the rear surface of the hub; An impeller from which a working fluid flows in from an outer peripheral side and flows out in a direction opposite to the back surface of the hub,
A centrifugal type fluid machine having a ring-shaped member operable toward a back surface of the hub on a surface of the casing facing the back surface of the hub. 2. The centrifugal fluid machine according to claim 1, wherein a surface of the ring-shaped member facing the hub is formed along the shape of the back surface of the hub. 2. The centrifugal fluid machine according to claim 1, wherein a cylindrical rib is provided on a surface of the ring-shaped member facing the casing. The centrifugal fluid machine according to claim 1, wherein concentric protrusions are provided on a surface of the ring-shaped member facing the hub. The centrifugal fluid machine according to claim 1, wherein a radial protrusion or a radial groove is provided on a surface of the ring-shaped member facing the hub.

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