JPH0533793A - Mixed flow pump - Google Patents

Abstract

(57) [Summary] [Object] To provide a mixed flow pump which suppresses the occurrence of flow separation in a diffuser with vanes to improve pump efficiency and, at the same time, can reduce the outer diameter dimension of the pump. [Structure] An impeller 1, an impeller cover 2, and a casing 3 surrounding the impeller cover, and a diffuser blade 6a in a circular blade row in a discharge passage 5 opened on the circumference of the impeller cover. For a mixed flow pump provided with aligned vaned diffusers 6, the blade leading edges of the diffuser vanes are extended to near the impeller and arranged parallel to the end face of the impeller outlet, and the outlet of the diffuser with vanes Is provided with auxiliary wings 7 between the rows of diffuser blades.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mixed flow pump applied to a boiler water circulation pump of a steam turbine facility, and more particularly to the structure of a vaned diffuser incorporated in the pump.

[0002]

2. Description of the Related Art In a mixed flow pump that handles high temperature and high pressure hot water, such as the boiler water circulation pump described above, the casing is a robust hemispherical casing and the outlet of the impeller is connected to the casing. As described above, a structure in which a diffuser with blades is provided in a discharge passage opened on the circumference of an impeller cover to improve pump characteristics has been widely used.

3 and 4 show the structure of a conventional boiler water circulation pump, wherein 1 is an impeller, 2 is an impeller cover, 3 is a hemispherical casing surrounding the outer circumference of the impeller cover 2, and 4 is The drive shaft of the impeller, which faces the discharge side end surface of the impeller 1 and has a radial discharge passage 5 in the cover 2.
Is opened, and a diffuser 6 with vanes is provided in the discharge passage.

FIG. 4 shows the conventional structure of the diffuser 6 with blades. A large number of diffuser blades 6a are formed in the radial passage portion downstream of the discharge passage 5 leaving a space at the inlet side portion. Circular blade rows (deceleration blade rows) arranged above are arranged. In FIG. 3, D1 is the outer diameter of the casing 3,
d1 is the outer diameter of the impeller cover 2, and in the blade row of FIG. 4, β1 is the inlet angle of the diffuser blade 6a, L is the chord length, F1 is the inflow direction of the fluid, and F2 is the outflow direction.

[0005]

By the way, FIG. 3 and FIG.
The conventional vaned diffuser shown in (1) has the following drawbacks. (1) When the chord length L of the diffuser blade is increased so as to enhance the pressure recovery in the diffuser, the outer diameter d1 of the impeller cover 2 and thus the outer diameter D1 of the casing 3 also inevitably increase, and the whole body of the pump is drawn. To become larger.

(2) Outlet line AB (line connecting the outer peripheral edges of shroud 1a and hub 1b) to impeller 1 and inlet line CD of diffuser 6 with blades (diffuser blade 6)
In the inlet side space area P of the discharge passage 5 remaining between the blade a and the blade leading edge (a), the direction of the fluid flow suddenly changes because the radius of curvature r1 of the passage wall is extremely small, and the impeller 1 and the diffuser blade 6
and a interfere with each other to form a complicated three-dimensional flow. Especially when looking at the velocity distribution on the inlet line CD of the diffuser, the flow velocity on the side of the impeller 1 close to the shroud 1a becomes extremely higher than the flow velocity on the side close to the hub 1b. For this reason, it is extremely difficult to design the inlet angle β1 of the diffuser vane 6a so as to match the flow direction of the fluid flowing from the impeller 1, and as a result, the surface of the inlet side of the diffuser vane 6a is not affected during pump operation. Separation of the flow occurs in the flow path and the separation vortex v1 is easily generated. Also, on the outlet side of the diffuser blade 6a, if the chord length L is not sufficient, the flow is separated from the surface of the diffuser blade 6a due to the rapid decrease of the flow velocity in the diffuser, and the separation vortex v2 is likely to occur as described above. .. Moreover, in this way the separation vortexes v1, v2
In addition to the above, the pump efficiency decreases due to an increase in the energy loss of the fluid flow, and when the separation vortex grows, cavitation occurs and causes noise.

The present invention has been made in view of the above points, and an object thereof is to improve a diffuser with vanes to suppress the generation of flow separation vortices in the diffuser to improve pump efficiency and also to improve the pump efficiency. An object is to provide a mixed flow pump whose outer diameter size can be reduced.

[0008]

The above object is achieved according to the invention by extending the blade leading edge of the diffuser vane close to the impeller and parallel to the outlet end of the impeller. Further, in the above configuration, auxiliary blades may be arranged between the diffuser blades at the outlet of the diffuser in combination with the blade row of the diffuser blades.

[0009]

In the above structure, first, the blade leading edge of the diffuser blade is extended to the vicinity of the impeller and is arranged in parallel with the end face of the discharge port of the impeller so that the diffuser impinges from the impeller into the diffuser. The three-dimensionality of the flowing fluid is weakened, and a uniform velocity distribution can be obtained for the fluid flowing on the inlet line. Therefore, it becomes easier in terms of design to more accurately predict the inflow angle of the fluid at the diffuser inlet and match the inlet angle of the diffuser blade with the inflow angle of the fluid. Can be suppressed well. Also, since the chord length of the diffuser blade, that is, the effective flow path length of the diffuser, can be increased by the amount of extending the leading edge of the diffuser blade toward the inner diameter side (smaller radius), the outer diameter dimension of the diffuser, The pump can be made compact by reducing the outer diameter of the impeller cover and casing. Furthermore, by arranging auxiliary blades at the outlet of the diffuser in combination with the cascade of diffuser blades,
Even if the chord length is not designed to be long, the divergence angle with respect to the fluid passage in the diffuser becomes small, and the separation of the flow generated in the outlet side region can be favorably prevented.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 are block diagrams of an embodiment of the present invention.
The same members corresponding to those in FIGS. 3 and 4 are denoted by the same reference numerals. That is, in the configuration of FIGS. 1 and 2, in the curved discharge passage 5 opened in the impeller cover 2, the vaned diffuser 6 is provided in the entire length region from the inner diameter (inlet side) to the outer diameter (outlet side). Circular blade rows of the diffuser blades 6a are provided, and the blade leading edge of the diffuser blades 6a (inlet line C-
D) approaches the discharge port end of the impeller 1 and its exit line AB
Is formed so as to be parallel to. Further, at the outlet of the diffuser 6 (a region on the downstream side of the throat of the diffuser), auxiliary blades 7 each having a short chord length are provided between the diffuser blades one by one with respect to the circular blade row of the diffuser blades 6a. is there. The radius of curvature r2 of the wall surface of the discharge passage 5 is designed to be larger than the radius of curvature r1 in FIG.

With such a configuration, the operation and effect described in the above section [Operation] can be obtained, the flow loss in the diffuser 6 is reduced to improve the pump characteristics, and the outer diameter d2 of the impeller cover 2 is improved. , The outer diameter D2 of the casing 3 is the outer diameter of FIG.
The entire pump can be made smaller by making it smaller than d1 and D1.

[0012]

Since the mixed flow pump of the present invention is constructed as described above, the separation of the flow of the fluid generated in the diffuser can be suppressed to improve the pump efficiency, and also the conventional construction. Compared with, the outer diameter of the entire pump can be made smaller.

[Brief description of drawings]

FIG. 1 is a sectional view showing the configuration of an embodiment of the present invention.

FIG. 2 is a sectional view taken along the discharge passage showing a blade row of the vaned diffuser in FIG.

FIG. 3 is a sectional view showing the structure of a conventional mixed flow pump.

FIG. 4 is a sectional view taken along the discharge passage showing a blade row of the vaned diffuser in FIG.

[Explanation of symbols]

1 impeller 2 impeller cover 3 casing 4 drive shaft 5 discharge passages 6 Diffuser with blade 6a diffuser blade 7 Aileron F1 fluid inflow direction F2 fluid outflow direction Exit line of AB impeller Entrance line of CD diffuser

Claims (2)

[Claims] 1. A blade comprising an impeller, an impeller cover, and a casing surrounding the impeller cover, and a diffuser blade arranged in a circular blade row in a discharge passage opened on the circumference of the impeller cover. A mixed-flow pump provided with a diffuser, wherein the blade leading edge of the diffuser blade is extended to near the impeller and arranged parallel to the discharge port end of the impeller. 2. The mixed flow pump according to claim 1, wherein auxiliary blades are arranged between the diffuser blades at the outlet of the diffuser in combination with the blade row of the diffuser blades.