An endwall treatment method for suppressing inlet recirculation in a centrifugal pump

Abstract

The present invention discloses an end wall treatment method for suppressing import backflow. By arranging arc-shaped slits on the front cover plate, the high-energy fluid through the arc-shaped slits impacts the import backflow, improving the import flow pattern. This method can effectively suppress the backflow of the centrifugal pump under small flow conditions. This end wall treatment method is simple and easy to implement, only requiring the machining of arc-shaped slits on the front cover plate, with low cost and good economy, which is beneficial to improving the stability of the semi-open impeller centrifugal pump under small flow conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of centrifugal pumps, and particularly relates to an end wall treatment method for suppressing inlet recirculation of a centrifugal pump. Background Art

[0002] When a low specific speed semi-open impeller centrifugal pump operates under a small flow rate condition, some of the fluid that has entered the impeller returns to the impeller inlet at a large radius, and then enters the impeller a second time along with the main flow. This phenomenon is called inlet recirculation. Many scholars at home and abroad have studied the inlet recirculation of centrifugal pumps and found that its essence is that fluid particles under the action of centrifugal force collide with the solid wall surface under partial load, resulting in changes in velocity and pressure in this area. Recirculation will generate additional hydraulic losses, reduce the efficiency of the pump, and the recirculation vortex will cause flow rate and pressure pulsations, exacerbate cavitation inside the impeller, generate vibrations and noises, thereby affecting the stability of the pump.

[0003] Scholars at home and abroad have adopted many methods for recirculation control. It is mainly divided into active control and passive control. Active control is the control of applying external energy, which requires energy input and sometimes the gain is not worth the loss. Passive control does not require external energy, but often affects the external characteristics. Most of the existing recirculation control methods have complex structures, and the control effect on recirculation varies with working conditions, so the applicable range is limited. Summary of the Invention

[0004] The purpose of the present invention is to provide an end wall treatment method for suppressing inlet recirculation of a centrifugal pump, and solve the problem that the centrifugal pump in the prior art is prone to generate recirculation under small flow rate conditions, thereby leading to poor inlet flow pattern.

[0005] The technical solution adopted by the present invention is an end wall treatment method for suppressing inlet recirculation of a centrifugal pump, which is specifically implemented according to the following steps:

[0006] Step 1: Define the axial length of the front cover plate of the semi-open impeller centrifugal pump as H. Make a longitudinal vertical line on the axial section of the front cover plate, and intersect with the inner surface of the front cover plate at point M. Make an auxiliary circle with point M as the center.

[0007] Step 2: The auxiliary circle intersects the generatrix of the inner surface of the front cover plate at points A and B. Connect points A and B to form a straight line. Take the midpoint C of the straight line, connect point M with the midpoint C and extend it to intersect with the auxiliary circle at point D to obtain the MD straight line.

[0008] Step 3: Make a parallel line of the AB straight line through point M to obtain the ab straight line. Rotate the MD straight line 45 degrees in the impeller rotation direction with the ab straight line as the axis to obtain the Md straight line. Make a circle M1 with M as the center.

[0009] Step 4: Draw a perpendicular line from point M to the axis, and the foot of the perpendicular is F. At 2 / 3H of the front cover plate axial section, draw a circle F1 with F as the center and MF as the radius; with M as the center, draw a circle F2 at 2 / 3H of the front cover plate axial section, and it intersects with circle F1 at point E.

[0010] Step 5: Taking point E as an endpoint, draw a parallel line to the Md straight line to obtain the straight line Ed1, and draw a circle E1 with E as the center and Ed1 as the radius.

[0011] Step 6: Use the straight line ME, circle M1, and E1 to create an annular ring and circular surfaces respectively, and they intersect with the inner surface of the front cover plate at curves L1 - L4.

[0012] Step 7: Remove the parts of the annular ring surface and circular surfaces that exceed the inner surface of the front cover plate along the intersection lines L1 - L4 to obtain the shape of the arc seam to be machined. Then, evenly machine multiple arc seams of this shape circumferentially on the inner surface of the front cover plate, and that's it.

[0013] The characteristics of the present invention also lie in that

[0014] In Step 1, the radius of the auxiliary circle is 16d, where d is the tip clearance, and the center M of the auxiliary circle is at 2 / 3H.

[0015] In Step 3, the radius of circle M1 is Md; in Step 4, the radius of circle F2 is 4d.

[0016] In Step 6, specifically: Stretch circle M1 along the straight line ME to obtain an annular ring G, which intersects with the inner surface of the front cover plate at curves L1 and L2. Create circular surfaces H and H1 through circle M1 and E1 respectively, and they intersect with the front cover plate at curves L3 and L4.

[0017] In Step 7, the removal process is specifically: Remove the parts of the annular ring surface G that exceed the inner surface of the front cover plate along the intersection lines L1 and L2, and remove the parts of circular surfaces H and H1 that exceed the front cover plate along the intersection lines L3 and L4 respectively.

[0018] In Step 7, the number of arc seams is 25.

[0019] The beneficial effects of the present invention are: The present invention arranges arc seams on the front cover plate, with a simple structure and easy implementation. By using the high-energy fluid impact of the arc seams on the inlet recirculation, the blockage at the inlet is improved, the inlet flow pattern is optimized, thereby suppressing the inlet recirculation and improving the stability of the centrifugal pump. Description of the Drawings

[0020] Figure 1 It is the axial projection view of the front cover plate of the semi-open impeller centrifugal pump of the present invention;

[0021] Figure 2 It is the distribution diagram of each point on the front cover plate of the semi-open impeller centrifugal pump of the present invention;

[0022] Figure 3 It is the structural diagram of the circular ring on the front cover plate of the semi-open impeller centrifugal pump of the present invention;

[0023] Figure 4 It is the shape diagram of the arc seam on the front cover plate of the semi-open impeller centrifugal pump of the present invention;

[0024] Figure 5 It is the solid structure diagram of the arc seam on the front cover plate of the semi-open impeller centrifugal pump of the present invention;

[0025] Figure 6 It is the axial velocity distribution diagram of the inlet section of the semi-open impeller centrifugal pump at Q d ;

[0026] Figure 7 It is the axial velocity distribution diagram of the inlet section of the semi-open impeller centrifugal pump at 0.8Q d ;

[0027] Figure 8 It is the axial velocity distribution diagram of the inlet section of the semi-open impeller centrifugal pump at 0.6Q d ;

[0028] Figure 9 It is the axial velocity distribution diagram along the circumference at different radii of the inlet section of the original semi-open impeller centrifugal pump at Q d ;

[0029] Figure 10 It is the axial velocity distribution diagram along the circumference at different radii of the inlet section of the semi-open impeller centrifugal pump improved by the method of the present invention at Q d ;

[0030] Figure 11 It is the axial velocity distribution diagram along the circumference at different radii of the inlet section of the original semi-open impeller centrifugal pump at 0.8Q d ;

[0031] Figure 12 It is the axial velocity distribution diagram along the circumference at different radii of the inlet section of the semi-open impeller centrifugal pump improved by the method of the present invention at 0.8Q d ;

[0032] Figure 13 It is the axial velocity distribution diagram along the circumference at different radii of the inlet section of the original semi-open impeller centrifugal pump at 0.6Q d ;

[0033] Figure 14 It is the axial velocity distribution diagram along the circumference at different radii of the inlet section of the semi-open impeller centrifugal pump improved by the method of the present invention at 0.6Q d ; Specific embodiments

[0034] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0035] A method for end wall treatment to suppress the inlet reflux of a centrifugal pump according to the present invention is specifically implemented according to the following steps:

[0036] Step 1: Establish a geometric model of a semi-open impeller centrifugal pump. Define the axial length of the front cover plate of the semi-open impeller centrifugal pump as H. Make a longitudinal perpendicular line at 2 / 3H on the axial section of the front cover plate, which intersects with the inner surface bus of the front cover plate at point M. Then make an auxiliary circle with point M as the center, and the radius of the auxiliary circle is 16d, where d is the tip clearance, as Figure 1 shown by the dashed circle in the axial plane projection diagram;

[0037] Step 2: The auxiliary circle intersects with the inner surface bus of the front cover plate at two points A and B, as Figure 2 shown. Connect points A and B to form a straight line. Take the midpoint C of the straight line, connect point M with the midpoint C and extend it to intersect with the auxiliary circle at point D to obtain the MD straight line;

[0038] Step 3: Make a parallel line of the AB straight line through point M to obtain the ab straight line. Rotate the MD straight line 45 degrees in the impeller rotation direction with the ab straight line as the axis, that is, radially tilt 45 degrees, to obtain the Md straight line. Let the plane radially tilted 45 degrees be plane S. Make a circle with M as the center and Md as the radius in plane S, and denote it as circle M1;

[0039] Step 4: Make a perpendicular line to the axis through point M, and the foot of the perpendicular is F. At 2 / 3H of the axial section of the front cover plate, make a circle with F as the center and MF as the radius, and denote it as circle F1. Circle F1 is on the inner surface of the front cover plate. Make a circle with M as the center and 4d as the radius at 2 / 3H of the axial section of the front cover plate, and denote it as circle F2, which intersects with circle F1 at point E;

[0040] Step 5: Take point E as an end point and make a parallel line of the Md straight line to obtain the straight line Ed1. The plane where the straight line Ed1 is located is plane S1. Make a circle with E as the center and Ed1 as the radius in plane S1, and denote it as circle E1;

[0041] Step 6: Stretch the circle M1 along the ME straight line to obtain an annular ring G, which intersects with the inner surface of the front cover plate at curves L1 and L2. Create circular surfaces H and H1 through the circle M1 and E1 respectively, which intersect with the front cover plate at curves L3 and L4, as Figure 3 shown;

[0042] Step 7: Remove the part of the annular ring surface G that exceeds the inner surface of the front cover plate along the intersection lines L1 and L2. Similarly, remove the parts of the circular surfaces H and H1 that exceed the front cover plate along the intersection lines L3 and L4 respectively. The final three-dimensional figure obtained is the shape of the arc seam to be processed, as Figure 4As shown, 25 arc-shaped seams of this shape are evenly machined circumferentially on the inner surface of the front cover plate; that is, multiple arc-shaped seams are formed on the front cover plate surface to eliminate or weaken the inlet backflow under small flow conditions, playing a role in improving the inlet flow pattern and reducing energy loss.

[0043] The end wall treatment method of the present invention arranges arc-shaped seams on the front cover plate. By using the high-energy fluid of the arc-shaped seams to impact the inlet backflow, the inlet flow pattern is improved, and the backflow of the centrifugal pump under small flow conditions can be effectively suppressed. This end wall treatment method is simple and easy to implement, only by machining arc-shaped seams on the front cover plate, with low cost and good economy, which is beneficial to improving the stability of the semi-open impeller centrifugal pump under small flow conditions.

[0044] Numerical simulations are carried out on the original semi-open impeller centrifugal pump and the semi-open impeller centrifugal pump improved by the method of the present invention under 3 working conditions respectively for verification. Figure 6 、 Figure 7 、 Figure 8 They are respectively the axial velocity distributions at the inlet section under Q d 、0.8Q d 、0.6Q d (Q d is the design flow rate). Among them, the left figures are all the original semi-open impeller centrifugal pumps, and the right figures are all the semi-open impeller centrifugal pumps improved by the method of the present invention. It can be seen from the figures that the axial velocity of the original centrifugal pump is positive under the design flow rate Q d , that is, no backflow occurs. At 0.8Q d and 0.6Q d , there are regions where the axial velocity becomes negative, indicating that backflow occurs, and the backflow region increases as the flow rate decreases. After adopting the method of the present invention, the axial velocity is always positive at 0.8Q d and 0.6Q d , that is, no backflow occurs, indicating that the present invention effectively suppresses the inlet backflow and improves the inlet flow pattern.

[0045] Figure 9 、 Figure 11 、 Figure 13 are the circumferential distributions of the axial velocity at different radii of the inlet section of the original semi-open impeller centrifugal pump under Q d , 0.8Q d and 0.6Q d ; it can be seen from the figures that the axial velocity shows a periodic distribution near the wall surface, and the number of periods is the same as the number of blades. The axial velocity is negative near the wall surface, fluctuating between 0 and -2 m / s, and the peaks and valleys alternate every 30 degrees, and there are differences between each peak and between each valley, indicating that backflow occurs near the wall surface, and the backflow region is roughly divided into 6 along the circumference, with differences between each; at 0.6R and 0.2R, the axial velocity shows a linear distribution, indicating that the water flow is smooth at the center of the inlet pipe and the flow pattern is good.

[0046] Figure 10 , Figure 12 , Figure 14 are the circumferential distributions of the axial velocities at different radii of the inlet section of the semi-open impeller centrifugal pump improved by the method of the present invention at Q d , 0.8Q d , 0.6Q d . It can be seen from the figure that the axial velocity is always positive near the wall surface and there is no generation of backflow. The axial velocities at all radii fluctuate between 1.0 and 1.5, indicating that the water flow in the inlet pipe is smooth, the proportion of the high-speed area is large, there is no interference of the backflow on the main flow, and the additional hydraulic loss is avoided.

[0047] The above results can show that the end-wall treatment method of the present invention slightly increases the axial velocity near the wall surface of the inlet pipe and slightly decreases the axial velocity at the center under the design conditions, and the overall influence is small.

[0048] In summary, after adopting the present invention, the situation where the axial velocity is negative near the wall surface disappears, that is, there is no generation of backflow. Therefore, the end-wall treatment method of the present invention effectively weakens or even eliminates the inlet backflow.

Claims

1. An end-wall treatment method for suppressing the inlet backflow of a centrifugal pump, characterized in that, it is specifically implemented according to the following steps: Step 1: Define the axial length of the front cover plate of the semi-open impeller centrifugal pump as H. Make a longitudinal vertical line on the axial section of the front cover plate, and it intersects with the inner surface bus of the front cover plate at point M. Make an auxiliary circle with point M as the center; Step 2: The auxiliary circle intersects with the inner surface bus of the front cover plate at points A and B. Connect points A and B to form a straight line. Take the midpoint C of the straight line, connect point M with the midpoint C and extend it to intersect with the auxiliary circle at point D to obtain the MD straight line; Step 3: Make a parallel line of the AB straight line through point M to obtain the ab straight line. Rotate the MD straight line 45 degrees in the impeller rotation direction with the ab straight line as the axis to obtain the Md straight line. Make a circle M1 with M as the center; Step 4: Make a perpendicular line to the axis through point M, and the foot of the perpendicular is F. At 2 / 3H of the axial section of the front cover plate, make a circle F1 with F as the center and MF as the radius; Make a circle F2 with M as the center at 2 / 3H of the axial section of the front cover plate, and it intersects with the circle F1 at point E; Step 5: Take point E as an end point and make a parallel line of the Md straight line to obtain the straight line Ed1. Make a circle E1 with E as the center and Ed1 as the radius; Step 6: Use the straight line ME, the circle M1, and E1 to create a circular ring and a circular surface respectively, and they intersect with the inner surface of the front cover plate at curves L1-L4; Step 7: Remove the part of the circular ring surface that exceeds the inner surface of the front cover plate along the intersection line L1-L4 to obtain the shape of the arc seam to be processed. Then, evenly process multiple arc seams of this shape circumferentially on the inner surface of the front cover plate.

2. An end-wall treatment method for suppressing the inlet backflow of a centrifugal pump according to claim 1, characterized in that, in the said Step 1, the radius of the auxiliary circle is 16d, where d is the tip clearance, and the center M of the auxiliary circle is at 2 / 3H.

3. An end-wall treatment method for suppressing the inlet backflow of a centrifugal pump according to claim 2, characterized in that, in the said Step 3, the radius of the circle M1 is equal to the length of the straight line Md; in the said Step 4, the radius of the circle F2 is 4d.

4. An end-wall treatment method for suppressing the inlet backflow of a centrifugal pump according to claim 1, characterized in that, in the said Step 6, specifically: Stretch the circle M1 along the ME straight line to obtain a circular ring surface G, which intersects with the inner surface of the front cover plate at curves L1 and L2. Create circular surfaces H and H1 through the circle M1 and E1 respectively, and they intersect with the front cover plate at curves L3 and L4.

5. An end-wall treatment method for suppressing the inlet backflow of a centrifugal pump according to claim 4, characterized in that, in the said Step 7, the removal process is specifically: Remove the part of the circular ring surface G that exceeds the inner surface of the front cover plate along the intersection lines L1 and L2, and remove the parts of the circular surfaces H and H1 that exceed the front cover plate along the intersection lines L3 and L4 respectively.

6. An end-wall treatment method for suppressing the inlet backflow of a centrifugal pump according to claim 1, characterized in that, in the said Step 7, the number of arc seams is 25.

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