CN113236607B - A design method of a large engineering pump volute and its volute - Google Patents

Abstract

The invention discloses a design method of a large-scale engineering pump volute and the volute, which comprises a volute outlet, a diffusion section (2), a throat (3), a movable guide vane (5), and a fixed guide vane (6). , outlet guide vane (7), separating tongue (8), the outer periphery of the movable guide vane is provided with a plurality of fixed guide vanes, the outlet guide vane is generally tangent to the base circle D3 of the inlet of the pressurized water chamber, and the inlet end of the outlet guide vane has Section I, the separation tongue has section II, from section II to section I in the flow direction, the volute is an annular volute, and the flow area of the flow passage of the volute is basically the same. The annular volute structure with fixed guide vanes and movable guide vanes is adopted. According to the given working conditions, the geometric parameters of the volute are determined based on the volute velocity coefficient method, including the base circle diameter D ₃ of the inlet of the pressurized water chamber, and the inlet of the pump pressurized water chamber. The width B ₃ , the radius R of the outer contour of the scroll chamber, the number of movable guide vanes Z ₁ , the number of fixed guide vanes z _2' , and the diffusion angle θ. It can reduce the pressure pulsation and radial force during the operation of the pump, and enhance the operation safety and stability of the pump under various working conditions.

Description

A design method of a large engineering pump volute and its volute

technical field

The invention relates to the technical field of a volute of a hydraulic engineering pump and a volute of a centrifugal pump, in particular to a design method of a volute of a large engineering pump and the volute thereof.

Background technique

In recent years, my country's water conservancy and hydropower projects have developed by leaps and bounds, which has laid a solid foundation for the implementation of my country's sustainable development strategy while meeting the supply and demand of electricity and energy in my country. The volute is an important flow component of the centrifugal pump, which has a great influence on the efficiency index of the pump. When the fluid enters the volute from the impeller, due to the small gap between the impeller and the volute separating tongue/tongue, a strong interaction will occur, causing high-amplitude and low-frequency pressure pulsation in the area of the conventional spiral volute separating tongue; The geometric structure of the volute is asymmetrical. When the head and flow rate are high, large pressure pulsation and radial force will be generated, resulting in large vibration or noise, which will affect the operation stability of large-scale hydraulic engineering pumps. In response to this problem, Chinese Patent Application Publication No. CN201218236Y discloses a high-speed water pump volute, which contains a flat volute circular volute bottom with an involute or Archimedes volute and a continuous side wall to form a continuous volute and a pump. A volute with a pump inlet and outlet, the center of the volute is a water inlet, and the continuous side wall is a water baffle, which enhances the lift height and water flow, and has the characteristics of light weight, corrosion resistance, easy manufacturing and low cost; Chinese Patent Application Publication No. CN111894903A discloses a serialized single-stage centrifugal pump volute and a design method. When designing different pump flows with the same impeller outer diameter, the axial wall thickness of the pump body on the side of the pump cover can be the same, and the pump cover can be Designed in a universal shape. The pressurized water chamber adopts an axially asymmetric cross-section, taking the center line as the benchmark. The cross-section on the side of the pump cover is rectangular, and the other side is a right-angled trapezoid, which effectively reduces the disturbance of the rotating shaft, improves the reliability of the seal, and reduces the vibration of the pump. However, although this improves production efficiency, improves mechanical strength, and reduces pressure pulsation to a certain extent, the use of trapezoidal or rectangular section pump head and efficiency is low. Therefore, it is necessary to design a large-scale hydraulic engineering pump volute structure that can be widely used and can operate stably and efficiently with small pressure pulsation and radial force.

The structure of the traditional volute includes a volute casing, a water flow channel is arranged in the volute casing, and the water flow passage is generally composed of a pressurized water chamber and a diffusion section. The starting end of the pressurized water chamber is the separation tongue, the connection between the pressurized water chamber and the diffuser section is the throat, and the outlet of the diffuser section is the outlet of the pump body; the traditional pressurized water chamber is based on the design base circle outside the outer circle of the impeller. It is composed of a set of cross-section connections that gradually increase from the tongue part to the throat of the inlet of the pump diffusion section along the rotation direction of the impeller. and efficiency.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the deficiencies existing in the prior art, and to provide a design method for a large-scale engineering pump volute and the volute thereof, which can reduce the pressure pulsation and radial force during the operation of the pump, and strengthen the pump under various working conditions. operational security and stability.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A volute of a large engineering pump, comprising a volute outlet (1), a diffusion section (2), a throat (3), a fixed multi-flow channel (4), a movable guide vane (5), and a fixed guide vane ( 6), the outlet guide vane (7), the tongue/tongue (8), the flow channel gap (9), the outlet end of the pressure water chamber is provided with a diffusion section, the outlet end of the diffusion section has a volute outlet, and the pressure water chamber is provided with a volute outlet. The connecting part with the diffuser section is the throat, the outer periphery of the impeller is provided with a diffuser, the diffuser includes a plurality of movable guide vanes distributed along the circumferential direction, and a separation tongue is formed between the diffuser section and the volute wall, which is characterized in that : A plurality of fixed guide vanes (6) are arranged on the outer periphery of the movable guide vane (5). The fixed guide vane divides the volute flow channel into fixed multi-flow channels. The center line/axis of the outlet guide vane and the center line/axis of the diffuser section Collinear/parallel, the outlet guide vane is substantially tangent to the base circle D3 of the inlet of the pressurized water chamber, and the outlet end of the fixed guide vane is adjacent to the inlet end of the fixed guide vane on the radially inner side or the base circle D3 of the inlet of the pressurized water chamber There is a flow channel gap (9) between them, the inlet end of the outlet guide vane has a section I, and the tongue has a section II, in the flow direction from the section II to the section I, the volute is an annular volute, and the flow channel of the volute is The cross-sectional flow area is substantially the same.

Further, the volute adopts a generally eccentric elliptical cross-section annular volute, and in the direction of the long axis of the ellipse, the size of the eccentric long part of the ellipse is 2-4 times the size of the short part.

Further, the fixed guide vane (6) is an arc guide vane, and the fixed guide vane has different central angles, and the central angle gradually increases from section II to section I in the flow direction; II to section I, the central angle of the downstream is 1.05-1.25 times the central angle of the upstream.

Further, from section II to section I in the flow direction, the flow channel gap (9) gradually increases; and from section II to section I in the flow direction, the downstream flow channel gap is 1.05- of the upstream flow channel gap 1.2 times.

Further, the fixed guide vane (6) has a downstream end/trailing edge end (61), the downstream end is tapered in a tapered or arc shape, and the downstream end has a first groove (62), a second groove ( 63), a plurality of first grooves are arranged on the radially inner side of the downstream end, and a plurality of second grooves are arranged on the radially outer side of the downstream end; the first and second grooves are semicircular structures.

Further, the number of the first grooves (62) is greater than the number of the second grooves (63), and the number of the first grooves is 1.5-3.0 times the number of the second grooves.

Further, the diffusion section is the pump body outlet, the diffusion section is from the throat to the volute outlet, the area of the water flow channel gradually increases, and the cross section of the diffusion section includes a shape composed of a rectangle and/or a circular arc; the pressure water chamber at the throat position The cross-sectional shape of the radiator is the same as and coincides with the end face shape of the diffuser section. This structure ensures a smooth transition between the pressurized water chamber and the diffuser section.

A design method for a volute casing of a large engineering pump is characterized in that, an annular volute casing structure with fixed guide vanes and movable guide vanes is adopted, and the geometric parameters of the volute casing are determined based on the volute velocity coefficient method according to a given working condition, Including the base circle diameter D ₃ of the inlet of the pressurized water chamber, the width of the inlet of the pump pressurized water chamber B ₃ , the outer contour radius R of the volute chamber, the number of movable guide vanes Z ₁ , the number of fixed guide vanes Z ₂ , and the diffusion angle θ;

It includes the following design steps:

( ₁ ) Design the base circle diameter _D3 of the inlet of the pressure water chamber:

D ₃ =D ₂ +2b ₂

where:

b ₂ - radius of movable guide vane, mm;

D ₂ - Outer diameter of pump impeller, mm;

D ₃ - The diameter of the base circle of the inlet of the pump pressure water chamber, mm;

(2) Design the inlet width B ₃ of the pump pressure chamber:

B ₃ =B ₂ +0.05D ₃

where:

B ₂ - the axial width of the pump impeller outlet, mm;

D ₃ - The diameter of the base circle of the inlet of the pump pressure water chamber, mm;

B ₃ - Inlet width of pump pressure water chamber, mm;

(3) The outer contour line radius R of the designed scroll chamber:

where:

A _I - the area value of the first section of the volute, mm;

R- the radius of the outer contour of the volute chamber, mm;

(4) Design the number of movable guide vanes Z ₁ :

Z ₁ =8～14

where:

Z ₁ - the number of active guide vanes, pcs;

(5) Design the number of fixed guide vanes Z ₂ :

Z ₂ =3～5

where:

Z ₂ - the number of fixed guide vanes, pcs;

(6) Design the diffusion angle of the diffusion section:

where:

A _I - the area value of the first section of the volute, mm;

D _S - volute outlet diameter, mm;

L - the length of the diffuser section of the volute, mm;

θ-diffusion angle, °;

Use θ to take 6° to 12°.

The present invention has beneficial technical effects as follows:

(1) The structure of the annular volute is adopted. Compared with the typical spiral volute, the annular volute has a symmetrical flow passage and has a larger gap between the separation tongue and the impeller outlet, which is replaced by an annular volute. The traditional volute can reduce the pump pressure pulsation and radial force, and improve the operation stability. The gap between the outer periphery of the impeller and the volute separation tongue is increased, which has the advantage of reducing the collision of the water flow on the volute separation tongue. The increase in the gap between the separation tongue and the impeller can reduce pressure pulsation and overall radial force.

(2) By further designing the fixed guide vanes to have different central angles, and from section II to section I in the flow direction, the central angle gradually increases. From section II to section I in the flow direction, the runner gap gradually increases. It can further reduce the pressure pulsation and radial force during the operation of the pump, reduce the corner vortex at the outlet of the fixed guide vane, reduce the pressure fluctuation and pressure loss of the annular volute, and enhance the operation safety and stability of the pump under various working conditions. . Through the design of the first groove and the second groove, the present invention can further reduce the corner vortex at the outlet of the fixed guide vane, reduce the pressure fluctuation and pressure loss of the annular volute, thereby enhancing the operation safety of the pump under various working conditions and stability.

(3) There are double rows of guide vanes (movable guide vanes, fixed guide vanes) in the volute to collect the high-speed liquid thrown out by the impeller, and evenly guide the inlet or pressure chamber of the impeller of the next stage, and can be used in the guide. Part of the kinetic energy of the liquid is converted into pressure energy in the vane, thereby improving the efficiency of the pump. Compared with no fixed guide vanes or single-row fixed guide vanes, the hydraulic performance of the double-row guide vanes is greatly improved. Combined with the eccentric elliptical cross-section of the volute, the influence of the cross-sectional shape on the hydraulic performance of the centrifugal pump was analyzed, and it was found that the elliptical cross-sectional shape under the annular volute can provide higher efficiency than trapezoidal, semicircular or rectangular shapes. pump head.

Description of drawings

Fig. 1 is the structural representation of the pump annular volute of the present invention;

Figure 2 is a partial comparison diagram of an annular volute and a helical volute, (a) an annular volute and (b) a helical volute;

Fig. 3 is the comparison diagram of the spiral volute and the annular volute section, (A is the spiral volute, B is the annular volute);

Figure 4 is a comparison diagram of the performance of the annular volute and the helical volute to the pump;

FIG. 5 is a partial enlarged structural schematic diagram of another embodiment of the fixed guide vane of the present invention.

In the figure: volute outlet 1, diffuser section 2, throat 3, fixed multi-channel 4, movable guide vane 5, fixed guide vane 6, outlet guide vane 7, tongue/tongue 8, runner gap 9, D2 the outer diameter of the impeller, D3 the diameter of the base circle of the inlet of the pressurized water chamber, the radius of the outer contour of the R scroll chamber, the downstream end/trailing edge end 61, the first groove 62, and the second groove 63.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments These are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The present invention will be further described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1-2, a design method of a large engineering pump volute and its volute, which includes a volute outlet 1, a diffusion section 2, a throat 3, a fixed multi-flow channel 4, a movable guide vane 5, Fixed guide vane 6, outlet guide vane 7, separating tongue/tongue 8, flow channel gap 9, the outlet end of the pressurized water chamber is provided with a diffuser section 2, the outlet end of the diffuser section 2 has a volute outlet 1, and the pressurized water chamber and the The connecting part between the diffuser sections 2 is the throat part 3, the outer periphery of the impeller is provided with a diffuser, and the diffuser includes a plurality of movable guide vanes 5 distributed along the circumferential direction, and a separation tongue 8 is formed between the diffuser section 2 and the volute wall , which is characterized in that: the outer periphery of the movable guide vane 5 is provided with a plurality of fixed guide vanes 6, the fixed guide vane 6 divides the volute flow channel into a fixed multi-flow channel 4, and the centerline/axis of the outlet guide vane 7 is connected to the diffuser section 2. The center line/axis are collinear/parallel, the outlet guide vane 7 is substantially tangent to the base circle D3 of the inlet of the pressurized water chamber, and the outlet end of the fixed guide vane 6 is adjacent to the radially inner fixed guide vane 6. There is a flow channel gap 9 between the inlet base circle D3 of the pressurized water chamber, the inlet end of the outlet guide vane 7 has a section I, and the separation tongue 8 has a section II, from the section II to the section I in the flow direction, the volute is an annular scroll. The cross-sectional flow area of the flow channel of the volute is the same.

Further, as shown in FIG. 3, the volute adopts a generally eccentric elliptical cross-section annular volute B, and in the direction of the long axis of the ellipse (in the direction of the X axis), the size of the long part of the ellipse eccentric is short. 2-4 times the size of the portion, preferably 2.5 times.

Further, the fixed guide vanes 6 are arc guide vanes, and the fixed guide vanes 6 have the same or different central angles. Preferably, the fixed guide vanes 6 have different central angles, and the central angles gradually increase from the section II to the section I in the flow direction. Specifically, from section II to section I in the flow direction, the central angle of the downstream is 1.05-1.25 times the central angle of the upstream.

Further, from the section II to the section I in the flow direction, the flow channel gap 9 gradually increases. Specifically, from section II to section I in the flow direction, the downstream flow channel gap 9 is 1.05-1.2 times the upstream flow channel gap 9 .

As shown in FIG. 1, the volute has substantially the same cross-sectional flow area from cross-section II to cross-section I in the flow direction, and then, the gap between the outer circle of the impeller and the volute tongue 8 is increased, which has the advantage of The collision of solid particles on the volute tongue is reduced, and the increase in the clearance between the diaphragm and the impeller can reduce pressure pulsation and overall radial force.

The diffuser section 2 is the pump body outlet, the diffuser section is from the throat 3 to the volute outlet 1, the area of the water flow channel gradually increases, and the cross section of the diffuser section includes a shape composed of a rectangle and/or a circular arc. The cross-sectional shape of the pressurized water chamber at the position of the throat 3 is the same as and coincident with the end face shape of the diffuser section 2. This structure ensures a smooth transition between the pressurized water chamber and the diffuser section.

As shown in Figure 2, the annular volute has a larger and more uniform flow cross-sectional area than a conventional helical volute. An excessively small cross-sectional area of the volute will cause a hump in the pump head curve, causing surge in the piping system. Under the rated operating conditions, the hydraulic performance decreases slightly with the increase of the flow area of the volute; when the operation of the pump deviates from the rated operating conditions, the hydraulic performance is improved when the volute flow area is large; in addition, As the flow area of the volute increases, the high-efficiency area will widen.

The volute does not have a traditional trapezoidal or semi-circular volute cross-section, but a substantially eccentric oval cross-section, which helps to reduce pressure pulsations in the volute.

As shown in Figure 4(a), by using annular volutes, radial forces can be reduced in the low flow range; again, these volutes generate more when the pump is operating below the optimum efficiency point lift and efficiency. The larger tip clearance in these volutes reduces the interaction between the impeller blades and the volute tangs, so the pressure distribution around the impeller becomes more uniform. At design time, due to the constant cross-sectional area volute, the pressure distribution around the impeller is not uniform, which causes the point of minimum radial force to be at low flow rather than design flow.

From Fig. 4(b), the radial force distribution is shown as a quadrilateral, which is consistent with the impeller blade angle; in addition, as the flow increases, the quadrilateral rotates clockwise, and the increase of the volute flow area can reduce the force acting on the shaft. The magnitude of the radial force, especially under the conditions of nominal flow and large flow, can reduce the vibration of the pump, thereby improving the operating stability of the pump.

As shown in (c) of Figure 4, it can be seen from the polyline distribution of the wave intensity coefficient in the annular volute that the coefficient increases as a whole with the increase of the flow rate; in addition, the polyline shows four peaks, which Consistent with the number of impeller blades, the equivalent declination angle of the four peaks is 90°, and the maximum pressure pulsation occurs approximately 30° behind the volute diaphragm, implying the interaction between the trailing edge of the impeller and the volute diaphragm It is the main cause of pressure pulsation in the volute. In addition, the increased flow area of the volute will reduce pressure pulsations in the volute regardless of the operating state of the pump.

Preferably, by further designing the fixed guide vanes 6 to have different central angles, and from the section II to the section I in the flow direction, the central angles gradually increase. From section II to section I in the flow direction, the flow channel gap 9 gradually increases. It can further reduce the pressure pulsation and radial force during the operation of the pump, reduce the corner vortex at the outlet of the fixed guide vane, reduce the pressure fluctuation and pressure loss of the annular volute, and enhance the operation safety and stability of the pump under various working conditions. .

As shown in FIG. 5 , in one embodiment, the stationary guide vane 6 has a downstream end/trailing edge end 61 , the downstream end/trailing edge end 61 is tapered in a tapered or arc shape, and the downstream end 61 has a first groove 62. The second groove 63, a plurality of first grooves 62 are arranged on the radial inner side of the downstream end 61, and a plurality of second grooves 63 are arranged on the radial outer side of the downstream end 61; the first grooves 62, The second groove 63 has a semicircular structure. Through the design of the first groove 62 and the second groove 63, the corner vortex at the outlet of the fixed guide vane can be further reduced, the pressure fluctuation and pressure loss of the annular volute can be reduced, thereby enhancing the operating safety of the pump under various working conditions and stability.

Further, the number of the first grooves 62 is greater than the number of the second grooves 63 , and preferably, the number of the first grooves 62 is 1.5-3.0 times the number of the second grooves 63 .

A design method for a large engineering pump volute, which adopts an annular volute structure with fixed guide vanes and movable guide vanes, and determines the geometric parameters of the volute based on the volute velocity coefficient method according to a given working condition, including the inlet of the pressurized water chamber. Base circle diameter D ₃ , inlet width B ₃ of pumping water chamber, outer contour radius R of volute chamber, number of movable guide vanes Z ₁ , number of fixed guide vanes z ₂ , and diffusion angle θ;

It includes the following design steps:

(1) Design the base circle diameter D ₃ of the inlet of the pressurized water chamber:

D ₃ =D ₂ +2b ₂

where:

b ₂ - radius of movable guide vane, mm;

D ₂ - Outer diameter of pump impeller, mm;

D ₃ - The diameter of the base circle of the inlet of the pump pressure water chamber, mm;

(2) Design the inlet width B ₃ of the pump pressure chamber:

B ₃ =B ₂ +0.05D ₃

where:

B ₂ - the axial width of the pump impeller outlet, mm;

D ₃ - The diameter of the base circle of the inlet of the pump pressure water chamber, mm;

B ₃ - Inlet width of pump pressure water chamber, mm;

(3) The outer contour line radius R of the designed scroll chamber:

where:

A _I - the area value of the first section of the volute, mm;

R- the radius of the outer contour of the volute chamber, mm;

(4) Design the number of movable guide vanes Z ₁ :

Z ₁ =8～14

where:

Z ₁ - the number of active guide vanes, pcs;

(5) Design the number of fixed guide vanes Z ₂ :

Z ₂ =3～5

where:

Z ₂ - the number of fixed guide vanes, pcs;

(6) Design the diffusion angle of the diffusion section:

where:

A _I - the area value of the first section of the volute, mm;

D _S - volute outlet diameter, mm;

L - the length of the diffuser section of the volute, mm;

θ-diffusion angle, °;

Use θ to take 6° to 12°.

In order to reduce the volume of the pump and the diameter of the discharge pipeline, reduce the loss of the pipeline, thereby reduce the lift of the pump, reduce the power of the pump, save energy, and reduce operating costs, the discharge diameter is preferably smaller than the suction diameter. After the outlet diameter of the pump is initially determined, it should be rounded according to the standard pipeline diameter series. The height L of the diffuser tube/diffuser section should be as small as possible under the condition of ensuring the diffusion angle, processing and bolt connection to reduce the size of the pump. .

The present invention has beneficial technical effects as follows:

(1) The structure of the annular volute is adopted. Compared with the typical spiral volute, the annular volute has a symmetrical flow passage and has a larger gap between the separation tongue and the impeller outlet, which is replaced by an annular volute. The traditional volute can reduce the pump pressure pulsation and radial force, and improve the operation stability. The gap between the outer periphery of the impeller and the volute separation tongue is increased, which has the advantage of reducing the collision of the water flow on the volute separation tongue. The increase in the gap between the separation tongue and the impeller can reduce pressure pulsation and overall radial force.

(2) By further designing the fixed guide vanes to have different central angles, and from section II to section I in the flow direction, the central angle gradually increases. From section II to section I in the flow direction, the runner gap gradually increases. It can further reduce the pressure pulsation and radial force during the operation of the pump, reduce the corner vortex at the outlet of the fixed guide vane, reduce the pressure fluctuation and pressure loss of the annular volute, and enhance the operation safety and stability of the pump under various working conditions. . Through the design of the first groove and the second groove, the present invention can further reduce the corner vortex at the outlet of the fixed guide vane, reduce the pressure fluctuation and pressure loss of the annular volute, thereby enhancing the operation safety of the pump under various working conditions and stability.

(3) There are double rows of guide vanes (movable guide vanes, fixed guide vanes) in the volute to collect the high-speed liquid thrown out by the impeller, and evenly guide the inlet or pressure chamber of the impeller of the next stage, and can be used in the guide. Part of the kinetic energy of the liquid is converted into pressure energy in the vane, thereby improving the efficiency of the pump. Compared with no fixed guide vanes or single-row fixed guide vanes, the hydraulic performance of the double-row guide vanes is greatly improved. Combined with the eccentric elliptical cross-section of the volute, the influence of the cross-sectional shape on the hydraulic performance of the centrifugal pump was analyzed, and it was found that the elliptical cross-sectional shape under the annular volute can provide higher efficiency than trapezoidal, semicircular or rectangular shapes. pump head.

The above-mentioned embodiment is an illustration of the present invention, not a limitation of the present invention. It can be understood that various changes, modifications, replacements and modifications can be made to these embodiments without departing from the principle and spirit of the present invention. The protection scope of the present invention It is defined by the appended claims and their equivalents.

Claims (8)

1. A volute of a large engineering pump, comprising a volute outlet (1), a diffuser section (2), a throat (3), a fixed multi-flow channel (4), a movable guide vane (5), a fixed guide Leaf (6), outlet guide vane (7), separating tongue/tongue (8), flow channel gap (9), the outlet end of the pressure water chamber is provided with a diffuser section, and the outlet end of the diffuser section has a volute outlet, the pressure The connection part between the water chamber and the diffuser section is the throat, and the outer periphery of the impeller is provided with a diffuser. The diffuser includes a plurality of movable guide vanes distributed along the circumferential direction, and a separation tongue is formed between the diffuser section and the volute wall, which It is characterized in that: the outer periphery of the movable guide vane (5) is provided with a plurality of fixed guide vanes (6), the fixed guide vanes divide the volute flow channel into fixed multi-flow channels, the center line/axis of the outlet guide vane and the center line of the diffuser section / The axis is collinear/parallel, the outlet guide vane is substantially tangent to the base circle D3 of the inlet of the pressurized water chamber, and the outlet end of the fixed guide vane is adjacent to the radially inner side of the fixed guide vane's inlet end or the base of the pressurized water chamber inlet There is a flow channel gap (9) between the circles D3, the inlet end of the outlet guide vane has a section I, and the tongue has a section II, from section II to section I in the flow direction, the volute is an annular volute, and the volute of the volute is an annular volute. The cross-sectional flow area of the flow channel is basically the same. 2. The volute of a large-scale engineering pump as claimed in claim 1, wherein the volute adopts a generally eccentric elliptical cross-section annular volute, and in the direction of the long axis of the ellipse, the elliptical eccentric The size of the long part is 2-4 times the size of the short part. 3. The volute of a large-scale engineering pump according to claim 2, wherein the fixed guide vane (6) is an arc guide vane, and the fixed guide vane has different central angles and is in the flow direction. From section II to section I, the central angle gradually increases; and from section II to section I in the flow direction, the downstream central angle is 1.05-1.25 times the upstream central angle. 4. the volute of a kind of large-scale engineering pump as claimed in claim 3 is characterized in that, from section II to section I in the flow direction, the flow channel gap (9) gradually increases; and in the flow direction from the section II to section I, the downstream runner gap is 1.05-1.2 times the upstream runner gap. 5. The volute of a large engineering pump according to claim 4, characterized in that, the fixed guide vane (6) has a downstream end/trailing edge end (61), and the downstream end is a tapered tapered or Arc-shaped, the downstream end has a first groove (62) and a second groove (63), a plurality of first grooves are arranged on the radially inner side of the downstream end, and a plurality of second grooves are arranged on the radially outer side of the downstream end Side; the first groove and the second groove are semicircular structures. 6. The volute of a large engineering pump according to claim 5, wherein the number of the first grooves (62) is greater than the number of the second grooves (63), and the number of the first grooves The number is 1.5-3.0 times the number of the second grooves. 7. The volute of a large-scale engineering pump as claimed in claim 5, wherein the diffusion section is the pump body outlet, the diffusion section is from the throat to the volute outlet, the area of the water flow channel increases gradually, and the section of the diffusion section is It includes shapes composed of rectangles and/or arcs; the cross-sectional shape of the pressurized water chamber at the throat is the same and coincident with the end face shape of the diffuser section, and this structure ensures a smooth transition between the pressurized water chamber and the diffuser section. 8. The method for designing the volute of a large engineering pump according to claim 1, wherein an annular volute structure with a fixed guide vane and a movable guide vane is adopted, and according to a given working condition, based on the speed of the volute The coefficient method is used to determine the geometric parameters of the volute, including the base circle diameter D ₃ of the inlet of the pressurized water chamber, the width of the inlet of the pump pressurized water chamber B ₃ , the radius of the outer contour line of the volute chamber R, the number of movable guide vanes Z ₁ , and the number of fixed guide vanes Z ₂ , the diffusion angle θ; It includes the following design steps: (1) Design the base circle diameter D ₃ of the inlet of the pressurized water chamber: D ₃ =D ₂ +2b ₂ where: b ₂ - radius of movable guide vane, mm; D ₂ - Outer diameter of pump impeller, mm; D ₃ - The diameter of the base circle of the inlet of the pump pressure water chamber, mm; (2) Design the inlet width B ₃ of the pump pressure chamber: B ₃ =B ₂ +0.05D ₃ where: B ₂ - the axial width of the pump impeller outlet, mm; D ₃ - The diameter of the base circle of the inlet of the pump pressure water chamber, mm; B ₃ - Inlet width of pump pressure water chamber, mm; (3) The outer contour line radius R of the designed scroll chamber:

where: A _I - the area value of the first section of the volute, mm; R- the radius of the outer contour of the volute chamber, mm; (4) Design the number of movable guide vanes Z ₁ : Z1=8～14 where: Z ₁ - the number of active guide vanes, pcs; (5) Design the number of fixed guide vanes Z ₂ : Z ₂ =3～5 where: Z ₂ - the number of fixed guide vanes, pcs; (6) Design the diffusion angle of the diffusion section:

where: A _I - the area value of the first section of the volute, mm; D _S - volute outlet diameter, mm; L - the length of the diffuser section of the volute, mm; θ-diffusion angle, °; Use θ to take 6° to 12°.

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