Impeller design method for improving cavitation resistance of high-rotating-speed axial flow pump

Abstract

The invention belongs to the technical field of fluid machinery, and particularly relates to an impeller design method for improving anti-cavitation performance of a high-rotating-speed axial flow pump, which comprises the following steps of: determining working condition parameters which at least comprise flow, device net positive suction head, rotating speed, theoretical lift and theoretical suction specific rotating speed, and obtaining the diameter of an inlet rim according to the inner diameter of an inlet pipeline; determining impeller parameters, wherein the impeller parameters at least comprise an inlet hub diameter, an outlet hub diameter, an outlet rim diameter, a rim airfoil profile setting angle and a hub setting angle; determining blade parameters, wherein the blade parameters at least comprise the blade number, the hub axial length, the rim axial length, the hub wrap angle, the inlet rounding radius and the blade thickness; obtaining rim wrap angle data according to the proportional relation of the rim axial length, the outlet rim diameter and the rim airfoil profile setting angle; obtaining designed lift data and designed suction ratio rotating speed data; and determining that requirements are met when the design lift data are greater than the theoretical lift data and the theoretical suction ratio rotating speed data are greater than the design suction ratio rotating speed data.

Description

Technical Field

[0001] The invention belongs to the technical field of fluid machinery, and in particular relates to an impeller design method for improving the anti-cavitation performance of a high-speed axial flow pump. Background Art

[0002] Axial flow pumps are suitable for large flow conveying applications such as irrigation, ships, and flood emergency rescue. Their speed is generally between 500 and 1500 r / min. In applications with high head requirements and speeds greater than 3000 r / min, higher requirements are placed on their anti-cavitation performance.

[0003] The high-speed axial flow pump produces large-area cavitation on the suction surface of the blade, which, on the one hand, causes a decrease in head and cannot provide sufficient lift; on the other hand, the frequent action of cavitation bubbles causes cavitation erosion of the blades, seriously affecting the service life of the pump.

[0004] Therefore, we provide an impeller design method for improving the anti-cavitation performance of a high-speed axial flow pump to improve the anti-cavitation performance of the impeller of a high-speed axial flow pump. Summary of the invention

[0005] The purpose of the present invention is to provide an impeller design method for improving the anti-cavitation performance of a high-speed axial flow pump, so as to solve the above-mentioned problem.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] An impeller design method for improving the anti-cavitation performance of a high-speed axial flow pump comprises the following steps:

[0008] Determine the operating parameters, including at least the flow rate, NPSH, speed, theoretical head and theoretical suction specific speed, and obtain the inlet rim diameter based on the inlet pipe inner diameter;

[0009] Determine the impeller parameters, including at least the inlet hub diameter, the outlet hub diameter, the outlet rim diameter, the rim airfoil placement angle, and the hub placement angle;

[0010] Determine blade parameters, including at least the number of blades, hub axis length, rim axis length, hub wrap angle, inlet rounding radius and blade thickness;

[0011] The wheel rim angle data is obtained according to the proportional relationship among the wheel rim axial length, the outlet wheel rim diameter and the wheel rim airfoil placement angle;

[0012] Obtain design head data and design suction specific speed data;

[0013] The requirement is met when it is determined that the designed head data is greater than the theoretical head data, and the theoretical suction specific speed data is greater than the designed suction specific speed data.

[0014] Optionally, the wheel rim angle The calculation formula is:

[0015]

[0016] Among them, D t2 Expressed as the outlet rim diameter, β t Expressed as the rim airfoil placement angle, l t Expressed as the axial length of the rim.

[0017] Optionally, the axial length of the wheel rim is t The calculation formula is:

[0018]

[0019] Among them, S t Expressed as the rim blade density, D t1 It is represented by the inlet rim diameter and Z is represented by the number of blades.

[0020] Optionally, the wheel rim blade density S t The value range is 1.5-3.0.

[0021] Optionally, the rim airfoil placement angle β t The calculation formula is:

[0022]

[0023] Among them, β t1 Expressed as the flange inlet placement angle, β t2 It is expressed as the rim outlet placement angle. Optionally, the calculation formula of the design head Hi is:

[0024]

[0025] Among them, NPSH i is the NPSH margin of the designed pump, u2 is the peripheral speed of the effective diameter of the pump outlet, and NPSHr is the NPSH margin required by the pump design.

[0026] Optionally, the designed pump NPSH i The calculation formula is:

[0027] Among them, Q represents the flow rate, C′ ind It is expressed as the design suction speed ratio, n is expressed as the design pump speed, unit is r / min.

[0028] Optional, wheel hub angle The calculation formula is:

[0029]

[0030] in, Round the corners for import.

[0031] Optionally, the inlet is rounded The value range is 60°-180°.

[0032] An impeller for improving the anti-cavitation performance of a high-speed axial flow pump is manufactured by the above-mentioned impeller design method for improving the anti-cavitation performance of a high-speed axial flow pump.

[0033] Compared with the prior art, the present invention has the following advantages and technical effects:

[0034] This scheme increases the wheel rim angle by selecting a larger wheel rim blade density and draws on the design concept of the inducer to design the axial flow pump, which greatly improves the anti-cavitation performance of the high-speed and large-lift axial flow pump. It has the characteristics of simple processing and manufacturing and stable operation, and has broad application prospects in the design process of improving the anti-cavitation performance of the axial flow pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative labor:

[0036] Figure 1 Flowchart for the impeller design of the present invention;

[0037] Figure 2 It is a schematic diagram of the structure of the present invention;

[0038] Figure 3 This is a structural diagram of the impeller of the present invention;

[0039] Figure 4 This is a schematic diagram of the blade rim wrap angle of the present invention;

[0040] Figure 5 This is a schematic diagram of the blade rim wrap angle commonly used in axial flow pumps;

[0041] Figure 6 This is a cloud diagram of the steam volume fraction when the cavitation number is 0.097 according to the present invention;

[0042] Figure 7 This is a cloud diagram of the steam volume fraction when the cavitation number is 0.097 for a common design of an axial flow pump.

[0043] Among them, 1. impeller; 2. guide vane; 101. blade top; 102. blade suction surface; 103. blade pressure surface; 104. trailing edge; 105. leading edge; 106. hub. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0046] Reference Figures 1 to 7 The present invention discloses an impeller design method for improving the anti-cavitation performance of a high-speed axial flow pump, comprising the following steps:

[0047] Determine the operating parameters, including at least the flow rate Q, the NPSHa of the device, the speed n, the theoretical head Ht and the theoretical suction specific speed C ind , and the inlet rim diameter D is obtained according to the inner diameter of the inlet pipe t1 ;

[0048] Determine the impeller parameters, including at least the inlet hub diameter Dh1, outlet hub diameter Dh2, outlet rim diameter D t2 、Flange airfoil placement angle β t , wheel hub placement angle;

[0049] Determine the blade parameters, including at least the number of blades Z, hub axis length lh, rim axis length l t 、Wheel hub angle 、Rim angle , inlet rounding radius R and blade thickness, where the rim angle The calculation formula is:

[0050]

[0051] Design lift Hi and design suction specific speed C′ ind Verification, Hi>Ht and C′ ind <C ind When the requirements are met.

[0052] Theoretical suction specific speed C ind The calculation formula is:

[0053]

[0054] This scheme increases the wheel rim angle by selecting a larger wheel rim blade density and draws on the design concept of the inducer to design the axial flow pump, which greatly improves the anti-cavitation performance of the high-speed and large-lift axial flow pump. It has the characteristics of simple processing and manufacturing and stable operation, and has broad application prospects in the design process of improving the anti-cavitation performance of the axial flow pump.

[0055] As an additional implementation method, the calculation formula of the design head Hi is:

[0056]

[0057] Among them, U2 is the outlet average effective diameter circumferential speed, and the calculation formula of the outlet average effective diameter circumferential speed U2 is:

[0058]

[0059] v m2 is the outlet axial velocity, the outlet axial velocity v m2 The calculation formula is:

[0060]

[0061] The number of blades Z is usually selected from 2 to 5, and in this embodiment, 4 blades are preferred.

[0062] As an additional implementation, the hub shaft length l h The calculation formula is:

[0063]

[0064] Among them, the diameter of the imported hub is D h1 =ξ1D t1 , where the inlet hub ratio ξ1 = (0.2-0.4), the outlet hub diameter D h2 =ξ2D t2 , where the outlet hub ratio ξ2 is determined based on the designed hub end face being conical at 8-12°.

[0065] As an additional implementation method, the calculation formula of the inlet rounding radius R is:

[0066]

[0067] As an optional embodiment, the axial length of the wheel rim is l t The calculation formula is:

[0068]

[0069] Among them, S t Expressed as the rim blade density.

[0070] As an optional embodiment, the wheel rim blade density S t The value range is 1.5-3.0.

[0071] The design of the axial flow pump installation angle often adopts two design methods: forced vortex and free vortex.

[0072] As an optional embodiment, the rim airfoil placement angle β t The calculation formula is:

[0073]

[0074] Among them, β t1 Expressed as the flange inlet placement angle, β t2 It is expressed as the rim outlet placement angle;

[0075] in:

[0076]

[0077] v t1 =0.7m / s

[0078]

[0079] As an optional implementation, the calculation formula for the design lift Hi is:

[0080]

[0081] Among them, NPSH i To design the cavitation margin of the pump, u2 is the circumferential speed of the effective diameter of the pump outlet.

[0082] As an optional implementation, the pump NPSH is designed i The calculation formula is:

[0083]

[0084] NPSHr is the cavitation margin required by the pump design, which is generally 0.95NPSHa.

[0085] As an additional implementation method, the suction specific speed C' is designed ind The calculation formula is:

[0086]

[0087] As an optional embodiment, the hub angle The calculation formula is:

[0088]

[0089] in, Round the corners for import.

[0090] As an optional implementation, the import rounding corners The value range is 60°-180°.

[0091] As an additional implementation, the hub placement angle includes the hub inlet placement angle β h1 and hub outlet placement angle β h2 , wheel hub inlet placement angle β h1 and hub outlet placement angle β h2 The calculation formula is:

[0092]

[0093] β2=24.5°

[0094] An impeller for improving the anti-cavitation performance of a high-speed axial flow pump is manufactured by the above-mentioned impeller design method for improving the anti-cavitation performance of a high-speed axial flow pump.

[0095] It includes an impeller 1, which includes a blade suction surface 102, a blade pressure surface 103, a blade top 101, a trailing edge 104, a leading edge 105, and a hub 106, wherein the blade top 101, the blade suction surface 102 and the blade pressure surface 103 intersect each other, and the blade top 101, the blade suction surface 102 and the blade pressure surface 103 constitute the blades of the impeller 1, and the blades are preferably 4.

[0096] As an additional implementation, a guide vane 2 is fixedly connected to the side of the hub 106 of the impeller 1 away from the liquid outlet of the blade, and the number of blades of the guide vane 2 can be designed according to design requirements. The guide vane 2 can be designed using conventional methods in the art.

[0097] A guide vane 2 is added to the liquid outlet side of the impeller 1 to facilitate stable outflow.

[0098] Compared with the prior art, the present invention adopts a structure in which the blade placement angle of the forced vortex and the larger blade wrap angle are designed for the axial flow pump blades and are combined with the rear guide vanes 2 to achieve high-speed and high-lift operating conditions and improve the anti-cavitation capability.

[0099] The numerical calculation shows that the fracture cavitation number calculated by using a larger blade density under the same design parameters is 0.05, while the fracture cavitation number calculated by using the conventional axial flow pump rim blade density is 0.097; therefore, when the cavitation number is 0.097, the cavitation volume on the blade of the two schemes is compared. Figure 6 and 7 As shown, it can be obviously found that the cavitation area on the blade of the present invention is smaller than that of the conventional design.

[0100] In the description of the present invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0101] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for designing an impeller for improving the anti-cavitation performance of a high-speed axial flow pump, characterized in that: The steps include: Determine the operating parameters, including at least the flow rate, NPSH, speed, theoretical head and theoretical suction specific speed, and obtain the inlet rim diameter based on the inlet pipe inner diameter; Determine the impeller parameters, including at least the inlet hub diameter, the outlet hub diameter, the outlet rim diameter, the rim airfoil placement angle, and the hub placement angle; Determine blade parameters, including at least the number of blades, hub axis length, rim axis length, hub wrap angle, inlet rounding radius and blade thickness; Obtaining wheel rim wrap angle data according to the proportional relationship among the wheel rim axial length, the outlet wheel rim diameter and the wheel rim airfoil placement angle; Obtain design head data and design suction specific speed data; The requirement is met when it is determined that the designed head data is greater than the theoretical head data, and the theoretical suction specific speed data is greater than the designed suction specific speed data.

2. The impeller design method for improving the anti-cavitation performance of a high-speed axial flow pump according to claim 1, characterized in that: The wheel rim angle The calculation formula is: Among them, D t2 Expressed as the outlet rim diameter, β t Expressed as the rim airfoil placement angle, l t Expressed as the axial length of the wheel rim.

3. The impeller design method for improving the anti-cavitation performance of a high-speed axial flow pump according to claim 2 is characterized in that: The axial length of the wheel rim is l t The calculation formula is: Among them, S t Expressed as the rim blade density, D t1 It is represented by the inlet rim diameter and Z is represented by the number of blades.

4. The impeller design method for improving the anti-cavitation performance of a high-speed axial flow pump according to claim 3 is characterized in that: The wheel rim blade density S t The value range is 1.5-3.

0.

5. The impeller design method for improving the anti-cavitation performance of a high-speed axial flow pump according to claim 1, characterized in that: The wheel rim airfoil placement angle β t The calculation formula is: Among them, β t1 Expressed as the flange inlet placement angle, β t2 Expressed as the rim exit placement angle.

6. The impeller design method for improving the anti-cavitation performance of a high-speed axial flow pump according to claim 1, characterized in that: The calculation formula of the design head Hi is: Among them, NPSH i is the NPSH margin of the designed pump, u2 is the peripheral speed of the effective diameter of the pump outlet, and NPSHr is the NPSH margin required by the pump design.

7. The impeller design method for improving the anti-cavitation performance of a high-speed axial flow pump according to claim 6, characterized in that: The designed pump NPSH i The calculation formula is: Among them, Q represents the flow rate, C′ ind It is expressed as the design suction speed, n is the design pump speed, unit is r / min 。 8. The impeller design method for improving the anti-cavitation performance of a high-speed axial flow pump according to claim 1, characterized in that: Wheel angle The calculation formula is: in, Round the corners for import.

9. The impeller design method for improving the anti-cavitation performance of a high-speed axial flow pump according to claim 8, characterized in that: The inlet rounding corner The value range is 60°-180°.

10. An impeller for improving the anti-cavitation performance of a high-speed axial flow pump, manufactured by the impeller design method for improving the anti-cavitation performance of a high-speed axial flow pump according to any one of claims 1 to 9.

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