Design method of low-axial-force multi-layer pressurization axial flow impeller

Abstract

The design method comprises the steps that the structure of the axial flow impeller is determined, the axial flow impeller comprises an inner wheel column and an outer wheel column, a plurality of inner-layer blades are arranged between the inner wheel column and the outer wheel column in the circumferential direction, and a plurality of outer-layer blades are arranged on the outer side of the outer wheel column in the circumferential direction; the inner-layer blades and the outer-layer blades are bent in the axial direction; the set lift H and flow Q of an axial flow impeller and the rotating speed n of a pump shaft in the operation process of the axial flow impeller are given, the number i of inner-layer blades and outer-layer blades is determined according to the structural scheme, and the outer diameter D1 of the inner-layer blades, the diameter dh1 of an inner wheel column, the diameter dh2 of an outer wheel column and the diameter D2 of the outer-layer blades are preliminarily calculated in sequence; the lift H2 of a single outer-layer blade and the lift H1 of a single inner-layer blade are calculated and corrected; after the three-dimensional model is established, the gravity of a rotor formed after the axial flow impeller and the rotating shaft are assembled, the buoyancy of the rotor and the thrust of the shaft end are calculated, and then correction is conducted again till the total axial force is close to zero.

Description

Technical Field

[0001] The invention relates to the field of axial flow pumps, and in particular to a design method for a low axial force multi-layer pressurized axial flow impeller. Background Art

[0002] An axial flow pump is a special type of pump that works by pushing the liquid along the axis through the rotation of the impeller. The axial flow pump is mainly composed of a drive device, a housing, a suction chamber, a discharge chamber, an impeller, a guide vane (also called a stator) and a pump shaft. The output end of the drive device is connected to the pump shaft through a coupling. The impeller is sleeved on the pump shaft and together with the pump shaft constitutes a rotor. The impeller is the core component of the axial flow pump. It consists of multiple blades that are installed around a central axis. When the impeller rotates, the blades push the liquid to move in the direction of the axis. The guide vane is located after the impeller. Its function is to guide the fluid coming out of the impeller in the correct direction, and to help reduce turbulence and improve the efficiency of the pump.

[0003] The existing axial flow pump impeller is mainly composed of an impeller hub and a plurality of blades circumferentially arranged on the outer side of the impeller hub. The blades are arc-shaped and arranged in the same direction clockwise or counterclockwise. In order to increase the head of this axial flow impeller, it is mainly achieved by increasing the number of axial flow impellers in the axial direction of the rotating shaft, which leads to a large axial force of the axial flow pump and unstable operation. Based on this, the applicant intends to design an impeller with double-layer blades, which can increase the head of the axial flow pump while reducing its axial length, reducing its axial force and improving its stability. The impeller structure is as follows: Figure 1 As shown, it includes an inner wheel column and a plurality of inner blades arranged circumferentially on the outer side of the inner wheel column, an outer wheel column connected to the outer end of the inner blade is arranged on the outer side of the inner wheel column, and a plurality of outer blades are arranged circumferentially on the outer side of the outer wheel column; the first blade and the outer blade are both arc-shaped and face opposite directions. However, the axial flow pump rotor will generate axial force during operation, and after adopting a double-layer structure, how to ensure the axial force balance between the impeller and the pump shaft during operation, how to determine the number of impellers and the radial length of the inner and outer blades are urgent problems to be solved. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a design method for a low-axial-force multi-layer boosted axial flow impeller, so as to solve the problem that the existing impeller has a single structure, a relatively single method of increasing the head, and a large axial force generated after application, resulting in the axial flow pump running unsmoothly.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A design method for a low axial force multi-layer supercharging axial flow impeller comprises the following steps:

[0007] S1, determining an axial flow impeller structure, wherein the axial flow impeller comprises an inner wheel column and an outer wheel column which are arranged concentrically, a plurality of inner blades are arranged circumferentially between the inner wheel column and the outer wheel column, and a plurality of outer blades are arranged circumferentially outside the outer wheel column; the inner blades and the outer blades are both bent in the axial direction, and the bending directions are opposite;

[0008] S2, given the set head H, flow Q parameters of the axial flow impeller and the speed n of the pump shaft during the operation of the axial flow impeller, determine the number i of inner blades and outer blades according to the structural scheme, and preliminarily calculate the outer diameter D1 of the inner blade and the inner wheel column diameter d h1 , outer wheel column diameter d h2 , outer blade diameter D2;

[0009] S3, according to the impeller parameters calculated in S2, set the total axial force F Z is zero, assuming that the reaction force FZ1 of the inner blades on the fluid is equal to the reaction force FZ1 of the outer blades on the fluid, then If k1=k2, then This formula can be used to calculate the lift H2 of a single outer blade and the lift H1 of a single inner blade;

[0010] S4, correct the parameters of the head H2 of a single outer blade and the head H1 of a single inner blade, and determine k1 and k2; when correcting, first calculate the specific speed n of the inner and outer impellers according to H1 and H2 calculated in S3 s1 、n s2 , then calculate the corresponding k1, k2, and substitute the calculated k1, k2 into Recalculate H1 and H2 and compare them with the H1 and H2 obtained by the initial calculation. If the absolute error between the recalculated value and the initial calculated value is not greater than 0.01m, there is no need to recalculate H1 and H2. If the absolute error between the recalculated value and the initial calculated value is greater than 0.01m, make fine adjustments on the initially calculated H1 and H2 until the error between the calculated H1 and H2 and the H1 and H2 obtained by checking k1 and k2 is not greater than 0.01m.

[0011] S5, designing the hydraulic dimensions of the inner blades and the outer blades in the axial flow impeller according to the corrected parameters of the head H2 of the single outer blade and the head H1 of the single inner blade in S4, and the determined values ​​of k1 and k2;

[0012] S6, establish a three-dimensional model of the rotor composed of the axial flow impeller and the pump shaft, calculate the rotor's deadweight G, the buoyancy F acting on the rotor F , shaft end thrust F T , and the calculated G, F F 、F T Substitute into formula F z =iFZ1 +iF Z2 +G+F T +F F , where F Z1 is the reaction force of the fluid on the inner layer, F Z2 The outer blades are subjected to the reaction of the fluid, and the internal and external heads H1 and H2 are recalculated. Finally, the calculated H1 and H2 are iteratively calculated according to the method of S4 until the total axial force F z =iF Z1 +iF Z2 +G+F T +F F The calculated value of is equal to or close to 0.

[0013] Further, when calculating the inner blade diameter D1, according to the formula Calculate the inner impeller specific speed n' s1 , determine the inner wheel column ratio Determine the inner impeller axial speed according to CC Rudnev formula According to the continuity condition of liquid flow, ignoring the displacement of liquid flow by blades, the axial velocity in the impeller area is:

[0014]

[0015] but:

[0016] Further, according to the calculated inner wheel column ratio And the calculated D1 value, calculate the inner wheel column diameter d h1 .

[0017] Further, in S2, the outer wheel column diameter d is calculated h2 =D1+a, where a is the thickness value required to increase the structural strength; when calculating the outer blade diameter D2, first define the height of the outer blade as half of the difference between the outer impeller diameter and the hub diameter, that is, The inner and outer impeller heights should satisfy A2 = bA1, that is: (D2-d h2 )=b(D1-d h1 ), D2=b(D1-d h1 )+d h2 =b(D1-d h1 )+D1+a=(b+1)D1-bd h1 +a, wherein b is a coefficient, and the value of b is 0.6-0.7.

[0018] Furthermore, in S3, F Z1 =F Z2 , Where ρ is the density of the conveying fluid, in kg / m 3 , g is the acceleration due to gravity; from the above changes we can get:

[0019] First consider k1=k2, then:

[0020] H=i(H1+H2), when the total head H is known, d h1 ,d h2 , D1, and D2 have been calculated, and the number of impellers i is determined according to the structure. Therefore, the head of a single inner impeller H1 and the head of a single outer impeller H2 can be calculated. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the cross-sectional structure of the axial flow impeller in the embodiment;

[0022] Figure 2 is a flow chart of the axial flow impeller design method in the embodiment;

[0023] Figure 3 A schematic diagram of the installation structure of a conventional axial flow impeller and an axial flow impeller designed using the method of this embodiment in an axial flow pump of the same level;

[0024] Figure 4 1. is a performance curve comparison diagram of an axial flow pump multi-stage axial flow pump having an axial flow impeller in this embodiment and a conventional axial flow impeller;

[0025] Figure 5 It is a curve comparison diagram of the total axial force of the axial flow pump of the axial flow impeller in this embodiment and the conventional axial flow impeller. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0027] It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. In the description of the present invention, it should be noted that the orientation or position relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the invention product is usually placed when used, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance. In addition, the terms "horizontal", "vertical", etc. do not mean that the components are absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted. In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] The design method of the low axial force multi-layer supercharging axial flow impeller provided in this embodiment includes the following steps:

[0029] S1, determine the axial flow impeller structure (such as Figure 1 As shown), the axial flow impeller comprises an inner wheel column 1 and an outer wheel column 3 which are arranged concentrically, a plurality of inner blades 2 are circumferentially arranged between the inner wheel column 1 and the outer wheel column 3, and a plurality of outer blades 4 are circumferentially arranged outside the outer wheel column 3; the inner blades 2 and the outer blades 4 are both bent in the axial direction, and the bending directions are opposite;

[0030] S2, given the set head H, flow Q parameters of the axial flow impeller and the speed n of the pump shaft during the operation of the axial flow impeller, determine the number i of the inner blades 2 and the outer blades 4 according to the structural scheme, and preliminarily calculate the outer diameter D1 of the inner blade 2 and the diameter d of the inner wheel column 1 in turn. h1 、Outer wheel column 3 diameter d h2 , the outer blade 4 has a diameter D2;

[0031] S3, according to the impeller parameters calculated in S2, set the total axial force F Zis zero, assuming that the inner blade 2 is affected by the fluid

[0032] H1=k2(D2-d h2 )'s reaction force FZ1 = the reaction force FZ1 of the fluid on the outer blade 4, then H2 k1(D1-d h1 ), set k1 = k2, then

[0033] H1=(D2-d h2 )

[0034] H2(D1-d h1 ); From this formula, the lift H2 of a single outer blade 2 and the lift H1 of a single inner blade 2 can be calculated;

[0035] S4, correct the parameters of the head H2 of a single outer blade 4 and the head H1 of a single inner blade 4, and determine k1 and k2; when correcting, first calculate the inner and outer impeller specific speed n according to H1 and H2 calculated in S3 s1 、n s2 , then calculate the corresponding k1, k2, and substitute the calculated k1, k2 into Recalculate H1 and H2 and compare them with the H1 and H2 obtained by the initial calculation. If the absolute error between the recalculated value and the initial calculated value is not greater than 0.01m, there is no need to recalculate H1 and H2. If the absolute error between the recalculated value and the initial calculated value is greater than 0.01m, make fine adjustments on the initially calculated H1 and H2 until the error between the calculated H1 and H2 and the H1 and H2 obtained by checking k1 and k2 is not greater than 0.01m.

[0036] S5, designing the hydraulic dimensions of the inner blade 2 and the outer blade 4 in the axial flow impeller according to the corrected parameters of the head H2 of the single outer blade and the head H1 of the single inner blade 4 in S4, and the determined values ​​of k1 and k2;

[0037] S6, establish a three-dimensional model of the rotor composed of the axial flow impeller and the pump shaft, calculate the rotor's deadweight G, the buoyancy F acting on the rotor F , shaft end thrust F T , and the calculated G, F F 、F T Substitute into formula F z =iF Z1 +iF Z2 +G+F T +F F , where F Z1 is the reaction force of the fluid on the inner layer, F Z2The outer blade 4 is subjected to the reaction of the fluid, and the internal and external heads H1 and H2 are recalculated. Finally, the calculated H1 and H2 are iteratively calculated according to the method of S4 until the total axial force F z =iF Z1 +iF Z2 +G+F T +F F The calculated value of is equal to or close to 0, completing the design of the axial flow impeller.

[0038] In the specific implementation, after the axial flow impeller structure is determined, the axial flow impeller and the rotating shaft are fixed, and the force analysis of the rotor formed shows that the inner and outer impellers do work on the fluid, and the fluid reacts to the axial water thrust on the inner and outer impellers. Since the axial flow directions of the fluid when flowing through the inner and outer layers are opposite, the force directions of the two are opposite. Rotor buoyancy F F =ρgV2≈ρgV1. Since one end of the rotor is immersed in the liquid and is subject to the internal fluid pressure, and the other end is subject to the atmospheric pressure, the resulting pressure difference will cause the rotor to be subjected to an axial force, which is the shaft end thrust, which can be calculated as follows:

[0039] Where d is the shaft diameter at the mechanical seal (or packing seal), m; the size is determined by the shaft structure; p1 is the absolute pressure at the outlet of the last stage guide vane, pa; p is the inlet absolute pressure p0 plus the total inlet and outlet pressure difference of the pump: p a is the absolute pressure of the ambient atmosphere.

[0040] Further, when calculating the inner blade diameter D1, according to the formula Calculate the inner impeller specific speed n' s1 , determine the inner wheel column ratio Determine the inner impeller axial speed according to CC Rudnev formula According to the continuity condition of liquid flow, ignoring the displacement of liquid flow by blades, the axial velocity of the impeller area is:

[0041]

[0042] but:

[0043] Further, according to the calculated inner wheel column ratio And the calculated D1 value, calculate the inner wheel column diameter d h1 .

[0044] Further, in S2, the outer wheel column diameter d is calculated h2 =D1+a, where a is the thickness value required to be increased according to the structural strength; when calculating the outer blade diameter D2, first define the height of the outer blade 4 as half of the difference between the outer impeller diameter and the hub diameter, that is, The inner and outer impeller heights should satisfy A2 = bA1, that is: (D2-d h2 )=b(D1-d h1 ), D2=b(D1-d h1 )+d h2 =b(D1-d h1 )+D1+a=(b+1)D1-bd h1 +a, wherein the coefficient b is 0.7, and the value of b is 0.6-0.7.

[0045] Furthermore, in S3, F Z1 =F Z2 , Where ρ is the density of the conveying fluid, in kg / m 3 , g is the acceleration due to gravity; from the above changes we can get:

[0046] First consider k1=k2, then:

[0047] H=i(H1+H2), when the total head H is known, dh1, dh2, D1, and D2 have been calculated, and the number of impellers i is determined according to the structure, the head of a single inner blade H1 and the head of a single outer impeller H2 can be calculated.

[0048] Take the design of a double-layer axial flow pump with a flow rate of 1200 cubic meters, a total head of 20m, a speed of 1000rpm, and an ambient pressure of 101325pa as an example (designed as 4-level hydraulic).

[0049] 1.1 Calculate the outer diameter D1 of the inner blade:

[0050] 1.1.1 Preliminary calculation of the inner impeller specific speed n' s1 :

[0051]

[0052] 1.1.2 Determine the inner wheel column ratio According to the relationship curve between inner wheel column ratio and specific speed,

[0053] 1.1.3 Determine the outer diameter D1 of the inner blade and the hub diameter d h1 :

[0054]

[0055] Take D1 = 0.35m;

[0056] Calculate d h1 =0.1855m, take d h1 =0.185m.

[0057] 1.2. Outer wheel column diameter d h2 :

[0058] Take a=0.03, then:

[0059] d h2 =D1+a=0.35+0.03=0.38m. (3)

[0060] 1.3. Calculate the outer diameter D2 of the outer impeller:

[0061] D2=(b+1)D1-bd h1 +a=(0.7+1)×0.35-0.7×0.185+0.03=0.4955m (4)

[0062] Among them, the value of b is 0.7, and D2 is rounded to D2=495mm.

[0063] 1.4. Calculate the internal and external lift H1 and H2:

[0064]

[0065] H=i(H1+H2) (6)

[0066] Set i=2, k1=k2=1, D1=0.35, d h1 =0.185, D2=0.495, d h2 =0.38 Substitute into (5) and (6) to obtain: H1 = 5.34, H2 = 4.66

[0067] 1.5 Calculate the specific speed and axial force coefficient of the inner and outer layers:

[0068]

[0069]

[0070]

[0071]

[0072] 1.6 Correction of inner and outer impeller lift H1, H2:

[0073] Based on the initial lift calculation, H1 and H2 are iteratively fine-tuned to make the equations H1, H2 and the corresponding k1, k2, and n s1 、n s2 as follows:

[0074] H1=5.27, H2=4.73, k1=1.03, k2=1, n s1=606,n s2 =657.

[0075] 1.7. Impeller blades and guide vanes design

[0076] According to the existing axial flow pump design method, the impeller blades and guide vanes are designed. The final hydraulic dimensions are shown in the following table:

[0077] Table 1. Hydraulic dimensions of double-layer impeller blades

[0078]

[0079] 1.8. Rotor deadweight G, buoyancy F F , shaft end thrust F T Calculation and iterative calculation of lift

[0080] The rotor is modeled in three dimensions and its volume is 0.0202m 3 The rotor material is stainless steel, with a density of 7850kg / m 3 The medium is clean water, with a density of 998.2 kg / m 3 , the shaft diameter at the mechanical seal is 80mm.

[0081] Rotor weight G:

[0082] G=ρ0gV1=7850×9.81×0.0202=1555.6N (11)

[0083] Rotor buoyancy F F :

[0084] FF=ρ1gV2≈ρ1gV1=998.2×9.81×0.0202=197.8N (12)

[0085] Shaft end thrust F T :

[0086]

[0087] Total axial force F Z :

[0088] F z =iF Z1 +iF Z2 +G+F T +F F =-2|F Z1 |+2|F Z2 |+1555.6-197.8+984.4 (14)

[0089] Press F Z =0 and recalculate, then:

[0090] 2|F Z2 |+2342.2=2|F Z1 | (15)

[0091]

[0092] And because:

[0093] H=2(H1+H2) (17)

[0094] Set k1=k2=1, D2=0.495, D1=0.35, d h1 =0.185, d h2 =0.38 is substituted into (16) and combined with (17), and we get:

[0095] H1=6.13m,H2=3.87m

[0096] 1.9. Calculate the specific speed and axial force coefficient of the inner and outer layers:

[0097]

[0098]

[0099]

[0100]

[0101] 1.10. Correction of inner and outer impeller lift H1 and H2:

[0102] Based on the initial lift calculation, H1 and H2 are iteratively fine-tuned to make the equations H1, H2 and the corresponding k1, k2, and n s1 、n s2 as follows:

[0103] H1=5.924, H2=4.076, k1=1.053, k2=0.971, n s1 =554.97, n s2 =734.61

[0104] 1.11. Iterative design of impeller blades and guide vanes: According to the existing axial flow pump design method, the impeller blades and guide vanes are designed. The final impeller hydraulic dimensions are shown in the following table:

[0105] Table 2. Hydraulic dimensions of double-layer impeller blades

[0106]

[0107]

[0108] 1.12. Rotor deadweight G, buoyancy F F , shaft end thrust F T Calculation and iterative calculation of lift

[0109] The rotor is modeled in three dimensions and its volume is 0.0201m 3 The rotor material is stainless steel, with a density of 7850kg / m 3 The medium is clean water, with a density of 998.2 kg / m 3 , the shaft diameter at the mechanical seal is 80mm, then:

[0110] Rotor weight G:

[0111] G=ρ0gV1=7850×9.81×0.0201=1547.9N (50)

[0112] Rotor buoyancy F F :

[0113] FF=ρ1gV2≈ρ1gV1=998.2×9.81×0.0201=196.8N (51)

[0114] Shaft end thrust F T :

[0115]

[0116] Total axial force F Z :

[0117] F z =iF Z1 +iF Z2 +G+F T +F F =-7.2N (53)

[0118] The total axial force is relatively close to 0, and it can be considered that the low axial force design goal has been achieved.

[0119] Since a double-layer impeller is equivalent to a two-stage conventional axial flow pump impeller, a four-stage impeller axial flow pump is equivalently designed using the conventional axial flow pump design method. The fluid domain in the pump is as follows: Figure 3 As shown ( Figure 3 The left side is a schematic diagram of the structure of a 4-stage impeller axial flow pump designed by the existing method. Figure 3 The right side is a schematic diagram of the structure of a 4-stage impeller axial flow pump designed using the method in this embodiment). In terms of size, the total axial length of the multi-stage axial flow pump designed using the low axial force design method is approximately 3 / 4 of the total length of a conventional multi-stage axial flow pump, and the radial dimension is slightly larger than a conventional axial flow pump.

[0120] The axial force of the axial flow impeller obtained in this embodiment is compared with the axial force of the impeller designed by the conventional axial flow pump design method. The relationship curve between the axial force and the flow rate is shown in FIG. Figure 4 , Figure 5 As shown. Among them, Figure 4 1. is a performance curve comparison diagram of an axial flow pump multi-stage axial flow pump having an axial flow impeller in this embodiment and a conventional axial flow impeller; Figure 5 It is a curve comparison diagram of the total axial force of the axial flow pump of the axial flow impeller in this embodiment and the conventional axial flow impeller.

[0121] Through CFD simulation, the head and efficiency of the multi-stage axial flow pump designed by conventional methods and low axial force methods are predicted, and the force of the axial fluid acting on the impeller wall is counted as the rotor water thrust, and the total rotor axial force Fz is calculated (the positive and negative axial force values ​​represent the direction, and the absolute value represents the magnitude of the axial force). Performance comparison curve and axial force comparison curve are shown in Figure 2. Figure 4 , Figure 5 As shown in the figure, the lift and efficiency comparison curves show that under rated point conditions, the lift of the multi-stage axial flow pump designed by the low axial force design method can meet the design requirements, and the efficiency is slightly lower than that of the multi-stage axial flow pump designed by the conventional method, but the stability and reliability are higher, and after being installed in the axial flow pump, the axial length installed on the rotating shaft is shorter, which can effectively reduce the axial length of the axial flow pump and reduce the floor space of the axial flow pump.

[0122] It can be seen from the axial force comparison curve that the axial force obtained by the rated point simulation calculation is slightly higher than the designed axial force. Compared with the axial flow pump designed by the conventional design method, the axial force of the axial flow pump rotor designed by the low axial force hydraulic design method is relatively low in the range of 0.2 times the rated operating condition (0.2Qopt, Qopt is the rated operating flow) to 1.4 times the rated operating condition (1.4Qopt). Under the rated operating condition, the axial force of the axial flow pump designed by the low axial force design method is about 1 / 4 of that of the axial flow pump designed by the conventional design method. At the 0.2Qopt operating condition, it is only 1 / 5 of the axial force of the axial flow pump designed by the conventional design method.

[0123] In summary, it can be seen that after adopting the axial flow impeller design method in this embodiment and applying it to a multi-stage axial flow pump, the axial flow impeller in this embodiment receives lower axial force and runs more smoothly. In addition, among axial flow pumps of the same level, the axial length is smaller, the head is similar, and it is easier to transport.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Those skilled in the art should understand that those modifications or equivalent substitutions of the technical solution of the present invention that do not depart from the purpose and scope of the technical solution should be included in the scope of the claims of the present invention.

Claims

1. A design method for a low axial force multi-layer supercharged axial flow impeller, characterized in that: The steps include: S1, determining an axial flow impeller structure, wherein the axial flow impeller comprises an inner wheel column and an outer wheel column which are arranged concentrically, a plurality of inner blades are arranged circumferentially between the inner wheel column and the outer wheel column, and a plurality of outer blades are arranged circumferentially outside the outer wheel column; the inner blades and the outer blades are both bent in the axial direction, and the bending directions are opposite; S2, given the set head H, flow Q parameters of the axial flow impeller and the speed n of the pump shaft during the operation of the axial flow impeller, determine the number i of inner blades and outer blades according to the structural scheme, and preliminarily calculate the outer diameter D1 of the inner blade and the inner wheel column diameter d h1 , outer wheel column diameter d h2 , outer blade diameter D2; S3, according to the impeller parameters calculated in S2, set the total axial force F Z is zero, assuming that the inner blades are subject to the reaction force F of the fluid Z1 = The outer blades are subjected to the reaction of the fluid F Z1 ,but If k1=k2, then This formula can be used to calculate the lift H2 of a single outer blade and the lift H1 of a single inner blade; S4, correct the parameters of the head H2 of a single outer blade and the head H1 of a single inner blade, and determine k1 and k2; when correcting, first calculate the specific speed n of the inner and outer impellers according to H1 and H2 calculated in S3 s1 、n s2 , then calculate the corresponding k1, k2, and substitute the calculated k1, k2 into Recalculate H1 and H2 and compare them with the H1 and H2 obtained by the initial calculation. If the absolute error between the recalculated value and the initial calculated value is not greater than 0.01m, there is no need to recalculate H1 and H2. If the absolute error between the recalculated value and the initial calculated value is greater than 0.01m, make fine adjustments on the initially calculated H1 and H2 until the error between the calculated H1 and H2 and the H1 and H2 obtained by checking k1 and k2 is not greater than 0.01m. S5, designing the hydraulic dimensions of the inner blades and the outer blades in the axial flow impeller according to the corrected parameters of the head H2 of the single outer blade and the head H1 of the single inner blade in S4, and the determined values ​​of k1 and k2; S6, establish a three-dimensional model of the rotor composed of the axial flow impeller and the pump shaft, calculate the rotor's deadweight G, the buoyancy F acting on the rotor F , shaft end thrust F T , and the calculated G, F F 、F T Substitute into formula F z =iF Z1 +iF Z2 +G+F T +F F , where F Z1 is the reaction force of the fluid on the inner blades, F Z2 The outer blades are subjected to the reaction of the fluid, and the internal and external heads H1 and H2 are recalculated. Finally, the calculated H1 and H2 are iteratively calculated according to the method of S4 until the total axial force F z =iF Z1 +iF Z2 +G+F T +F F The calculated value of is equal to or close to 0.

2. The design method of the low axial force multi-layer supercharged axial flow impeller according to claim 1 is characterized in that: When calculating the inner blade diameter D1, according to the formula Calculate the inner impeller specific speed n' s1 Determine the inner wheel column ratio Determine the inner impeller axial speed according to CC Rudnev formula According to the continuity condition of liquid flow, ignoring the displacement of liquid flow by blades, the axial velocity in the impeller area is: but:

3. The design method of the low axial force multi-layer supercharged axial flow impeller according to claim 2 is characterized in that: According to the calculated inner wheel column ratio And the calculated D1 value, calculate the inner wheel column diameter d h1 .

4. The design method of the low axial force multi-layer supercharged axial flow impeller according to claim 1, 2 or 3, characterized in that: In S2, calculate the outer wheel column diameter d h2 =D1+a, where a is the thickness value required to be increased according to the structural strength; when calculating the outer blade diameter D2, first define the height of the outer blade as half of the difference between the outer impeller diameter and the hub diameter, that is, The inner and outer impeller heights should satisfy A2 = bA1, that is: (D2-d h2 )=b(D1-d h1 ), D2=b(D1-d h1 )+d h2 =b(D1-d h1 )+D1+a=(b+1)D1-bd h1 +a, wherein b is a coefficient, and the value of b is 0.6-0.

7.

5. The design method of the low axial force multi-layer supercharged axial flow impeller according to claim 1 or 2, characterized in that: S3, F Z1 =F Z2 , Where ρ is the density of the conveying fluid, in kg / m 3 , g is the acceleration due to gravity; from the above changes we can get: First consider k1=k2, then: H=i(H1+H2), when the total head H is known, d h1 ,d h2 , D1, and D2 have been calculated, and the number of impellers i is determined according to the structure. Therefore, the head of a single inner blade H1 and the head of a single outer impeller H2 can be calculated.

Images