Design method of low axial force multistage booster axial impeller

Abstract

The application discloses a design method of a low-axial-force multilayer pressure-boosting axial impeller, which comprises the following steps: determining the structure of the axial impeller, wherein the axial impeller comprises an inner wheel column, an outer wheel column, a plurality of inner layer blades arranged circumferentially between the inner wheel column and the outer wheel column, and a plurality of outer layer blades arranged circumferentially outside the outer wheel column; the inner layer blades and the outer layer blades are arranged to be curved in the axial direction; given the set head H, the flow Q and the rotating speed n of the pump shaft during the operation of the axial impeller, the number i of the inner layer blades and the outer layer blades is determined according to the structural scheme; the outer diameter D1 of the inner layer blades, the diameter d h1 of the inner wheel column, the diameter d h2 of the outer wheel column and the diameter D2 of the outer layer blades are sequentially calculated initially; the head H2 of a single outer layer blade and the head H1 of a single inner layer blade are calculated and corrected; after a three-dimensional model is established, the gravity of the rotor formed after the assembly of the axial impeller and the rotating shaft, the buoyancy of the rotor and the axial end thrust are calculated, and then the correction is performed again until the total axial force is close to zero.

Description

Technical Field

[0001] This invention relates to the field of axial flow pumps, and more specifically to a design method for a low axial force multi-layer booster axial flow impeller. Background Technology

[0002] An axial flow pump is a special type of pump that works by using the rotation of an impeller to propel liquid along its axis. An axial flow pump mainly consists of a drive unit, casing, suction chamber, discharge chamber, impeller, guide vanes (also called stator), and pump shaft. The output end of the drive unit is connected to the pump shaft via a coupling. The impeller is mounted on the pump shaft, forming the rotor together. The impeller is the core component of the axial flow pump; it consists of multiple blades mounted around a central axis. When the impeller rotates, the blades propel the liquid along the axis. The guide vanes, located behind the impeller, guide the fluid exiting the impeller in the correct direction and help reduce turbulence, thus improving pump efficiency.

[0003] Existing axial flow pump impellers mainly consist of an impeller hub and multiple blades circumferentially arranged on the outer side of the impeller hub. These blades are arc-shaped and arranged in the same clockwise or counterclockwise direction. To increase the head of such axial flow impellers, the number of impellers is increased along the axial direction of the shaft, resulting in a large axial force and unstable operation. Therefore, the applicant intends to design an impeller with double-layered blades that increases the head of the axial flow pump while reducing its axial length, lowering its axial force, and improving its stability. The impeller structure is as follows: Figure 1 As shown, the impeller includes an inner impeller column and multiple inner blades circumferentially positioned outside the inner impeller column. An outer impeller column, connected to the outer ends of the inner blades, is located outside the inner blades, and multiple outer blades are circumferentially positioned outside the outer impeller column. Both the first blade and the outer blades are arc-shaped and face opposite directions. However, axial flow pump rotors generate axial forces during operation. With a double-layer structure, ensuring axial force balance between the impeller and pump shaft during operation, and determining the number of impellers and the radial lengths of the inner and outer blades, are pressing issues that need to be addressed. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the existing technology, the purpose of this invention is to provide a design method for a low axial force multi-layer booster axial flow impeller, which solves the problems of the existing impeller structure being simple, the method of increasing head being relatively simple, and the large axial force generated after application, resulting in unstable operation of the axial flow pump.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A design method for a low axial force multilayer booster axial flow impeller includes the following steps:

[0007] S1, Determine the axial flow impeller structure. The axial flow impeller includes an inner impeller and an outer impeller arranged concentrically. Multiple inner blades are arranged circumferentially between the inner and outer impellers, and multiple outer blades are arranged circumferentially on the outer side of the outer impeller. Both the inner and outer blades are bent in the axial direction, and the bending directions are opposite.

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

[0009] S3, based on the impeller parameters calculated in S2, sets the total axial force F. Z The value is zero. Assuming 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... Let k1 = k2, then The head H2 of a single outer blade and the head H1 of a single inner blade can be calculated using this formula.

[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; during correction, based on H1 and H2 calculated in S3, first verify the specific speed n of the inner and outer impellers. s1 n s2 Then calculate the corresponding k1 and k2, and substitute the calculated k1 and k2 into the... Recalculate H1 and H2, and compare them with the initially calculated H1 and H2. If the absolute error between the recalculated values ​​and the initially calculated values ​​is no greater than 0.01m, then there is no need to recalculate H1 and H2. If the absolute error between the recalculated values ​​and the initially calculated values ​​is greater than 0.01m, then make fine adjustments to the initially calculated H1 and H2 until the error between the calculated H1 and H2 and the H1 and H2 obtained by checking through k1 and k2 is no greater than 0.01m.

[0011] S5. Based on the corrected parameters of the single outer blade head H2 and the single inner blade head H1 in S4, and the determined values ​​of k1 and k2, design the hydraulic dimensions of the inner and outer blades in the axial flow impeller.

[0012] S6. Establish a three-dimensional model of the rotor consisting of the axial impeller and the pump shaft, and calculate the rotor's self-weight G and the buoyancy force F acting on the rotor. F Thrust F at the shaft end T And calculate G and F F F T Substitute into formula F z =iFZ1 +iF Z2 +G+F T +F F In the formula, F Z1 For the inner layer to be subjected to the reaction force of the fluid, F Z2 To account for the reaction force of the fluid on the outer blades, the inner and outer head H1 and H2 are recalculated. Finally, the calculated H1 and H2 are iteratively calculated using the S4 method until the total axial force F is reached. z =iF Z1 +iF Z2 +G+F T +F F The calculated value is equal to or close to 0.

[0013] Furthermore, when calculating the inner blade diameter D1, according to the formula... Calculate the specific speed n' of the inner impeller s1 Determine the inner wheel column ratio Determine the axial velocity of the inner impeller using the C. Ludnev formula. Based on the continuity condition of the fluid flow, and neglecting the displacement of the fluid flow by the blades, the axial velocity in the impeller region is:

[0014]

[0015] but:

[0016] Furthermore, based on the calculated inner wheel column ratio Based on the calculated value of D1, the inner wheel column diameter d is calculated. h1 .

[0017] Furthermore, in S2, the diameter d of the outer wheel column is calculated. h2 = D1 + a, where a is the required increase in thickness based on structural strength; when calculating the outer blade diameter D2, the height of the outer blade is first defined as half the difference between the outer impeller diameter and the hub diameter, i.e. Then the height of the inner impeller and the height of the outer impeller 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, where b is a coefficient, and the value of b is 0.6-0.7.

[0018] Furthermore, in S3, F Z1 =F Z2 , In the formula, ρ is the density of the transported fluid, with units of kg / m³. 3 Where g is the acceleration due to gravity; from the above changes, we can obtain:

[0019] First, consider k1 = k2, then:

[0020] H = i(H1 + H2), where the total head H is known, d h1 d h2 D1 and D2 have been calculated. The number of impellers i is determined according to the structure. Therefore, the head H1 of a single inner impeller and the head H2 of a single outer impeller can be calculated. Attached Figure Description

[0021] Figure 1 This is a schematic cross-sectional view of the axial flow impeller in the embodiment;

[0022] Figure 2 This is a flowchart 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 the same level axial flow pump;

[0024] Figure 4 This is a comparison chart of the performance curves of the multistage axial flow pump with an axial flow impeller and a conventional axial flow impeller in this embodiment;

[0025] Figure 5 This is a curve comparing the total axial force of the axial flow pump with that of the axial flow impeller and the conventional axial flow impeller in this embodiment. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0027] It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the figures, or the orientation or positional relationship commonly used when the product is in use. They are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance. In addition, the terms "horizontal," "vertical," etc., do not indicate that the component is required to be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" simply 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 this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0028] The design method for a low axial force multilayer booster axial flow impeller provided in this embodiment includes the following steps:

[0029] S1, determine the axial flow impeller structure (e.g.) Figure 1 As shown), the axial flow impeller includes an inner impeller column 1 and an outer impeller column 3 arranged concentrically. Multiple inner blades 2 are arranged circumferentially between the inner impeller column 1 and the outer impeller column 3, and multiple outer blades 4 are arranged circumferentially outside the outer impeller 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 and flow rate Q parameters of the axial flow impeller and the pump shaft speed n during the operation of the axial flow impeller, determine the number i of inner blades 2 and outer blades 4 according to the structural scheme, and initially calculate the outer diameter D1 of inner blade 2 and the diameter d of inner impeller 1 in sequence. h1 , outer wheel column 3 diameter d h2 The outer blade has a diameter of D2.

[0031] S3, based on the impeller parameters calculated in S2, sets the total axial force F. ZThe value is zero, assuming the inner blade 2 is subjected to fluid.

[0032] H1=k2(D2-d h2 The reaction force FZ1 of the outer blade 4 is equal to the reaction force FZ1 of the fluid. Then H2 k1(D1-d) h1 Let k1 = k2, then

[0033] H1=(D2-d h2 )

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

[0035] 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; during correction, based on H1 and H2 calculated in S3, first verify the specific speed n of the inner and outer impellers. s1 n s2 Then calculate the corresponding k1 and k2, and substitute the calculated k1 and k2 into the... Recalculate H1 and H2, and compare them with the initially calculated H1 and H2. If the absolute error between the recalculated values ​​and the initially calculated values ​​is no greater than 0.01m, then there is no need to recalculate H1 and H2. If the absolute error between the recalculated values ​​and the initially calculated values ​​is greater than 0.01m, then make fine adjustments to the initially calculated H1 and H2 until the error between the calculated H1 and H2 and the H1 and H2 obtained by checking through k1 and k2 is no greater than 0.01m.

[0036] S5. Based on the corrected parameters of the head H2 of a single outer blade and the head H1 of a single inner blade 4 in S4, and the determined values ​​of k1 and k2, design the hydraulic dimensions of the inner blade 2 and the outer blade 4 in the axial flow impeller.

[0037] S6. Establish a three-dimensional model of the rotor consisting of the axial impeller and the pump shaft, and calculate the rotor's self-weight G and the buoyancy force F acting on the rotor. F Thrust F at the shaft end T And calculate G and F F F T Substitute into formula F z =iF Z1 +iF Z2 +G+F T +F F In the formula, F Z1 For the inner layer to be subjected to the reaction force of the fluid, F Z2For the outer blade 4 subjected to the reaction force of the fluid, the inner and outer head 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 is reached. z =iF Z1 +iF Z2 +G+F T +F F The calculated value is equal to or close to 0, thus completing the design of the axial flow impeller.

[0038] In practical implementation, after determining the axial flow impeller structure, force analysis of the rotor formed after fixing the axial flow impeller and the shaft reveals that the inner and outer impellers do work on the fluid, and the fluid reacts with axial water thrust on the inner and outer impellers. Since the fluid flows in opposite axial directions through the inner and outer layers, the forces acting on them are opposite. The rotor buoyancy F... F =ρgV2≈ρgV1, Since one end of the rotor is immersed in the liquid and subjected to internal fluid pressure, while the other end is subjected to atmospheric pressure, the resulting pressure difference will cause the rotor to experience an axial force, which is the shaft end thrust, and can be calculated using the following formula:

[0039] In the formula, d is the shaft diameter at the mechanical seal (or packing seal), in meters; its size is determined according to the shaft structure; p1 is the absolute pressure at the outlet of the last stage guide vane, in pa; and p0 is the inlet absolute pressure plus the total inlet and outlet pressure difference of the pump: p a The absolute pressure of the ambient atmosphere.

[0040] Furthermore, when calculating the inner blade diameter D1, according to the formula... Calculate the specific speed n' of the inner impeller s1 Determine the inner wheel column ratio Determine the axial velocity of the inner impeller using the C. Ludnev formula. Based on the continuity condition of the fluid flow, and neglecting the displacement of the fluid flow by the blades, the axial velocity in the impeller region is:

[0041]

[0042] but:

[0043] Furthermore, based on the calculated inner wheel column ratio Based on the calculated value of D1, the inner wheel column diameter d is calculated. h1 .

[0044] Furthermore, in S2, the diameter d of the outer wheel column is calculated. h2 =D1+a, where a is the required increase in thickness based on structural strength; when calculating the outer blade diameter D2, the height of the outer blade 4 is first defined as half the difference between the outer impeller diameter and the hub diameter, i.e. Then the height of the inner impeller and the height of the outer impeller 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, where the coefficient b takes the value 0.7, and the value of b is between 0.6 and 0.7.

[0045] Furthermore, in S3, F Z1 =F Z2 , In the formula, ρ is the density of the transported fluid, with units of kg / m³. 3 Where g is the acceleration due to gravity; from the above changes, we can obtain:

[0046] First, consider k1 = k2, then:

[0047] H = i(H1 + H2). With the total head H known, dh1, dh2, D1, and D2 have been calculated. The number of impellers i is determined by the structure. Therefore, the head H1 of a single inner blade and the head H2 of a single outer impeller 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 20 meters, a speed of 1000 rpm, and an ambient pressure of 101325 Pa as an example (designed as a 4-stage hydraulic pump).

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

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

[0051]

[0052] 1.1.2 Determine the inner wheel column ratio Based on the relationship curve between the inner wheel cylinder ratio and specific speed,

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

[0054]

[0055] Take D1 = 0.35m;

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

[0057] 1.2, outer wheel column diameter d h2 :

[0058] If we 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] Where b is 0.7, and D2 is rounded to D2 = 495mm.

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

[0064]

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

[0066] Given i = 2, k1 = k2 = 1, D1 = 0.35, d h1 =0.185, D2=0.495, d h2 Substituting 0.38 into equations (5) and (6), we get: H1 = 5.34, H2 = 4.66

[0067] 1.5 Calculation of specific rotational speed and axial force coefficient of inner and outer layers:

[0068]

[0069]

[0070]

[0071]

[0072] 1.6 Correction of head H1 and H2 for inner and outer impellers:

[0073] Based on the initial head calculation, H1 and H2 are iteratively fine-tuned to make the equations H1, H2, and their corresponding k1, k2, and n hold true. 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 Blade and Guide Vane Design

[0076] Based on existing axial flow pump design methods, the impeller blades and guide vanes are designed. The final hydraulic dimensions are shown in the table below:

[0077] Table 1. Hydraulic Dimensions of Double-Layer Impeller Blades

[0078]

[0079] 1.8 Rotor self-weight G, buoyancy F F Shaft end thrust F T Calculation and head iteration calculation

[0080] A 3D model of the rotor was performed, resulting in a rotor volume of 0.0202 m³. 3 The rotor is made of stainless steel with a density of 7850 kg / m³. 3 The medium is clean water with a density of 998.2 kg / m³. 3 The shaft diameter at the mechanical seal is 80mm.

[0081] Rotor self-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 If the result is 0, recalculate:

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

[0091]

[0092] And because:

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

[0094] Given k1 = k2 = 1, D2 = 0.495, D1 = 0.35, d h1 =0.185, d h2 Substituting 0.38 into (16) and solving (17) simultaneously, 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 head H1 and H2 for inner and outer impellers:

[0102] Based on the initial head calculation, H1 and H2 are iteratively fine-tuned to make the equations H1, H2, and their corresponding k1, k2, and n hold true. 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: Based on existing axial flow pump design methods, the impeller blades and guide vanes were designed. The final impeller hydraulic dimensions are shown in the table below:

[0105] Table 2. Hydraulic Dimensions of Double-Layer Impeller Blades

[0106]

[0107]

[0108] 1.12, Rotor self-weight G, buoyancy F F Shaft end thrust F T Calculation and head iteration calculation

[0109] A 3D model of the rotor was performed, resulting in a rotor volume of 0.0201 m³. 3 The rotor is made of stainless steel with a density of 7850 kg / m³. 3 The medium is clean water with a density of 998.2 kg / m³. 3 If the shaft diameter at the mechanical seal is 80mm, then:

[0110] Rotor self-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 close to 0, which means that the design goal of low axial force has been achieved.

[0119] Since a double-layer impeller is equivalent to a two-stage conventional axial flow pump impeller, a four-stage axial flow pump was designed using conventional axial flow pump design methods. The fluid domain inside the pump is as follows: Figure 3 As shown ( Figure 3 The left side shows a schematic diagram of a 4-stage impeller axial flow pump designed using existing methods. 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 about 3 / 4 of the total length of a conventional multi-stage axial flow pump, and the radial dimension is slightly larger than that of a conventional axial flow pump.

[0120] The axial force of the axial flow impeller obtained in this embodiment is compared with that of the impeller designed by the conventional axial flow pump design method. The relationship curve between axial force and flow rate is shown in the figure below. Figure 4 , Figure 5 As shown. Among them, Figure 4 This is a comparison chart of the performance curves of the multistage axial flow pump with an axial flow impeller and a conventional axial flow impeller in this embodiment; Figure 5 This is a curve comparing the total axial force of the axial flow pump with that of the axial flow impeller and the conventional axial flow impeller in this embodiment.

[0121] CFD simulations were used to predict the head and efficiency of multistage axial flow pumps designed using conventional and low axial force methods. The forces acting on the impeller wall along the axial direction were statistically analyzed as the rotor water thrust, and the total rotor axial force Fz was calculated (the sign of the axial force value represents the direction, and the absolute value represents the magnitude of the axial force). Performance comparison curves and axial force comparison curves are shown below. Figure 4 , Figure 5 As shown in the curves comparing head and efficiency, it can be seen that under rated operating conditions, the head of the multistage axial flow pump designed using the low axial force design method can meet the design requirements. The efficiency is slightly lower than that of the multistage axial flow pump designed using the conventional method, but the stability and reliability are higher. Moreover, after being installed inside 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 footprint of the axial flow pump.

[0122] The axial force comparison curves show that the axial force calculated by the simulation at the rated point is slightly higher than the design axial force. Compared with the axial flow pump designed by the conventional design method, the axial force on the rotor of the axial flow pump designed by the low axial force hydraulic design method is lower in the range of 0.2 times the rated operating condition (0.2Qopt, where Qopt is the rated operating flow rate) to 1.4 times the rated operating condition (1.4Qopt). Under the rated operating condition, the axial force on the axial flow pump designed by the low axial force design method is about 1 / 4 of that on the axial flow pump designed by the conventional design method, and at the 0.2Qopt operating condition, it is only 1 / 5 of that on 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, runs more smoothly, and has a smaller axial length and similar head compared to other axial flow pumps of the same stage, making it easier to transport.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method of designing a low axial force multi-stage booster axial flow impeller, characterized in that, Comprising the following steps: S1, determining the structure of the axial flow impeller, the axial flow impeller comprising an inner wheel column and an outer wheel column arranged concentrically, a plurality of inner layer blades being circumferentially arranged between the inner wheel column and the outer wheel column, and a plurality of outer layer blades being circumferentially arranged outside the outer wheel column; the inner layer blades and the outer layer blades are both arranged in a curved manner in the axial direction, and the curved directions are opposite; S2, given the setting head H, flow Q parameters and the axial impeller running process of the pump shaft speed n, according to the structure scheme, determine the number of inner and outer blade i, the outer diameter of the inner layer blade D1, the inner wheel column diameter d h1 , the outer wheel column diameter d h2 , the outer diameter of the outer layer blade D2; S3, based on the parameters of the impeller calculated in S2, set the total axial force F Z = 0, assuming that the inner blade is subjected to the reaction force F Z1 = the reaction force F Z2 , set k1 = k2, then ; from this formula, the single outer blade head H2 and the single inner blade head H1 can be calculated;​ S4, correct the parameters of single outer blade head H2 and single inner blade head H1, and determine k1 and k2; in correction, according to H1 and H2 calculated in S3, first calculate the ratio of speed n of inner and outer impellers s1 , n s2 , then calculate the corresponding k1 and k2, and bring the calculated k1 and k2 into to recalculate H1 and H2, and compare with H1 and H2 obtained by initial calculation; if the absolute error of the recalculated value and the initial calculated value is not greater than 0.01 m, H1 and H2 do not need to be recalculated; if the absolute error of the recalculated value and the initial calculated value is greater than 0.01 m, fine-tune H1 and H2 of the initial calculation until the error of the calculated H1 and H2 and the H1 and H2 checked through k1 and k2 is not greater than 0.01 m; S5, designing the hydraulic size of the inner layer blades and the outer layer blades in the axial flow impeller according to the single outer layer blade head H2, the single inner layer blade head H1 parameters and the determined k1, k2 values after correction in S4; S6, a three-dimensional model of the rotor composed of the axial impeller and the pump shaft is established, and the weight G of the rotor and the buoyancy F of the rotor are calculated F , the thrust F of the shaft end T , and the calculated G, F F , F T are brought into the formula , in which F Z1 is the reaction force of the inner layer of blades on the fluid, and F Z2 is the reaction force of the outer layer of blades on the fluid, the head H1 and H2 are recalculated, and finally the calculated H1 and H2 are iteratively calculated according to the method of S4 until the calculated value of the total axial force 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, characterized in that, The inner layer blade diameter D1 is calculated according to the formula The inner layer impeller specific speed is calculated The inner wheel column ratio is determined The inner layer impeller axial velocity is determined according to the C.C. Rudnev formula According to the continuity condition of the liquid flow, without considering the extrusion of the blade to the liquid flow, the impeller area axial velocity is Then: .

3. The method of designing a low axial thrust multi-stage booster axial impeller as claimed in claim 2 wherein, According to the calculated inner wheel cylinder ratio and the calculated D1 value, the inner wheel cylinder diameter d h1 is calculated.

4. A method of designing a low axial thrust multi-stage booster axial impeller according to claim 1 or 2 or 3, characterized in that, S2, calculating the outer wheel column diameter , a is the thickness value required by structural strength; when calculating the outer layer blade diameter D2, the height of the outer layer blade is defined as half of the difference between the outer layer impeller diameter and the hub diameter, i.e. , the height of the inner layer impeller and the height of the outer layer impeller should satisfy , i.e. , , wherein b is a coefficient, and the value of b is 0.6-0.

7.

5. The method of designing a low axial thrust multi-stage booster axial impeller as claimed in claim 1 or 2 wherein, In S3, F Z1 = F Z2 , , , where p is the density of the fluid being transported, in kg / m3, and g is the acceleration due to gravity; from the above, we have: consider, then:​​ , , in total head H is known, d h1 , d h2 , D1, D2 has been calculated by calculation, the number of impeller i according to the structure is determined, so the single inner layer blade head H1, single outer layer impeller head H2 can be calculated.

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