A method of designing a radial diffuser vane and a radial diffuser

Abstract

The application provides a radial diffuser blade design method and a radial diffuser. The method comprises the following steps: obtaining each order natural frequency corresponding to a diffuser blade; obtaining the relationship between a gap length and each order natural frequency; determining a minimum gap length based on an excitation frequency, the relationship between the gap length and each order natural frequency; and performing a cutting angle operation on the diffuser design blade according to the minimum gap length to complete the design. The frequency-controllable radial diffuser blade can effectively avoid the problem that the airflow of the upstream rotor resonates with the downstream diffuser blade; and on the basis of considering the constraint state change of the contact surface between the radial diffuser blade and the bleed air casing, the excitation frequency of the upstream rotor is combined to effectively avoid the high-cycle fatigue failure of the radial diffuser blade caused by the uncertain blade tip constraint state, and the service life of the diffuser blade is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of diffusers, and in particular relates to a radial diffuser blade design method and a radial diffuser. Background Art

[0002] The radial diffuser is fixed to the bleed air casing by long bolts passing through the radial diffuser blades. The top surface of the radial diffuser blades fits the end surface of the bleed air casing. Figure 1 During operation, the radial diffuser blades are affected by aerodynamic loads, temperature loads, or a decrease in bolt preload, and the deformation of the contact surface between the blade tip and the bleed air casing is inconsistent. At the same time, the contact surface may wear under the action of vibration and aerodynamic loads, resulting in a blade tip gap, which makes the radial diffuser blade tip constraint state uncertain, and the blade frequency changes with the contact surface constraint state.

[0003] However, under the overall requirements of light weight and high performance, the radial diffuser blades are often made of aluminum alloy. Structurally, the air inlet end is designed to be thin, and the blades have low resistance to high-cycle fatigue. At the same time, the centrifugal impeller located upstream of the radial diffuser blades inside the radial diffuser forms an airflow related to the number of centrifugal impeller blades after the airflow passes through the centrifugal impeller, causing the radial diffuser to be subjected to wake excitation from the centrifugal impeller. Once the frequency of the wake excitation is consistent with the frequency of the diffuser blades, the radial diffuser blades will fracture due to high-cycle fatigue caused by resonance, which directly reduces the service life of the diffuser.

[0004] In view of this, overcoming the defects of the above-mentioned prior art is an urgent problem to be solved in this technical field. Summary of the Invention

[0005] In view of the above problems, the present invention proposes a radial diffuser blade design method, comprising:

[0006] Obtain aerodynamic parameters and structural design requirements and build a 3D model of the diffuser blades;

[0007] Obtain the temperature load of the diffuser blades, calculate and analyze the vibration characteristics of the diffuser blades using a three-dimensional model, and obtain the corresponding natural frequencies of each order of the diffuser blades;

[0008] Obtaining blade parameters of the upstream rotor and determining the excitation frequency, and determining that a diffuser blade having a margin between each order natural frequency and the excitation frequency greater than a predetermined margin is a designed diffuser blade;

[0009] Taking the gap length between the blade tip and the mating surface of the bleed air casing as a variable, modal analysis of the diffuser blades with different gap lengths was performed to obtain the relationship between the gap length and each order of natural frequency.

[0010] Determine the minimum gap length based on the relationship between the excitation frequency, gap length and each order natural frequency;

[0011] The diffuser blade design is cut according to the minimum gap length, and the diffuser blade design with the cut angle completed is obtained to complete the design.

[0012] Furthermore, in the step of obtaining the blade parameters of the upstream rotor and determining the excitation frequency:

[0013] The blade parameters of the upstream rotor include: the number of centrifugal impeller blades and the number of centrifugal impeller blade pairs;

[0014] The excitation frequency includes: the excitation frequency of the centrifugal impeller blades which is several times the rotor excitation frequency; the excitation frequency of the centrifugal impeller blades which is several times the rotor excitation frequency.

[0015] Furthermore, the specific steps of determining the minimum gap length based on the relationship between the excitation frequency, the gap length and the natural frequencies of each order are:

[0016] According to the relationship between the gap length and each order natural frequency, the gap length value corresponding to the change amplitude of each order natural frequency value is less than a predetermined amplitude is selected as the steady-state length;

[0017] Determine the frequency value corresponding to each steady-state length as the steady-state frequency, and determine that the steady-state length whose margin between the steady-state frequency and the excitation frequency is greater than a predetermined margin is a qualified steady-state length;

[0018] The qualified steady-state length with the smallest value is selected as the minimum gap length.

[0019] Furthermore, the method further includes obtaining the diffuser blade length b of the three-dimensional model, and the gap length between the blade tip of the designed diffuser blade and the matching surface of the bleed air casing has a value range of 0-b.

[0020] Furthermore, in the step of performing the angle chopping operation on the diffuser blades according to the minimum gap length, the length of the angle chopping operation is less than or equal to b and greater than or equal to the minimum gap length.

[0021] Furthermore, in the step of performing an angle cutting operation on the diffuser blades according to the minimum gap length, the angle of the angle cutting operation is less than or equal to 3°.

[0022] Furthermore, after obtaining the diffuser blade design with the chamfered angle completed, the method further includes:

[0023] Perform vibration characteristic calculation and analysis on the designed diffuser blades after cutting to obtain the frequencies of each order of the designed diffuser blades after cutting;

[0024] And calculate the margin between each order frequency and the excitation frequency;

[0025] After determining that the margin is greater than the predetermined margin, the design is completed.

[0026] Furthermore, the margin between each order natural frequency and the excitation frequency is determined by the following calculation formula:

[0027]

[0028] Where Y represents the margin, which is the absolute value of the calculation formula; H1 represents the natural frequency of the diffuser blade; and H2 represents the excitation frequency.

[0029] The present invention also provides a radial diffuser blade obtained by using the above-mentioned radial diffuser blade design method.

[0030] The present invention also provides a radial diffuser, which includes the radial diffuser blades described above.

[0031] Compared with the prior art, the embodiments of the present invention have at least the following advantages:

[0032] The frequency-controllable diffuser blades of the present invention are preliminarily designed based on aerodynamic parameters and structural design requirements, and the vibration characteristics of the preliminarily designed diffuser blades are calculated and analyzed, and then compared with the excitation frequency of the upstream rotor blades to effectively avoid the problem of resonance between the airflow through the upstream rotor and the downstream diffuser blades; and by continuously adjusting the gap length between the blade tip of the designed diffuser blade and the mating surface of the bleed air casing, the tangent length of the diffuser blade is controlled on the basis of the above-mentioned excitation frequency, thereby realizing the design of radial diffuser blades with controllable blade frequency. On the basis of considering the change of the constraint state of the contact surface between the radial diffuser blade and the bleed air casing, combined with the excitation frequency of the upstream rotor, the high-cycle fatigue failure of the radial diffuser blade caused by the uncertainty of the blade tip constraint state is effectively avoided, thereby ensuring the service life of the diffuser blades.

[0033] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1A schematic diagram of the assembly of a conventional diffuser blade and a diffuser casing is shown;

[0036] Figure 2 A schematic diagram of a radial diffuser blade in an embodiment of the present invention is shown;

[0037] Figure 3 A schematic flow chart of a radial diffuser blade design method according to an embodiment of the present invention is shown;

[0038] Figure 4 The relationship between the gap length and the natural frequency of each order in the embodiment of the present invention is shown in FIG. Figure 1 ;

[0039] Figure 5 The relationship between the gap length and the natural frequency of each order in the embodiment of the present invention is shown in FIG. Figure 2 ;

[0040] Figure 6 The schematic diagram of the assembly of the radial diffuser blades and the casing in the embodiment of the present invention is shown. Figure 1 ;

[0041] Figure 7 The schematic diagram of the assembly of the radial diffuser blades and the casing in the embodiment of the present invention is shown. Figure 2 . DETAILED DESCRIPTION

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings 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 making creative efforts shall fall within the scope of protection of the present invention.

[0043] In response to the above-mentioned key issues, the present invention calculates and analyzes the vibration characteristics of the preliminary designed diffuser blades based on the preliminary design of the diffuser blades according to the aerodynamic parameters and structural design requirements, and then compares and calculates with the excitation frequency of the upstream rotor blades to effectively avoid the problem of resonance between the airflow passing through the upstream rotor and the downstream diffuser blades; further, by continuously adjusting the gap length between the blade tip of the designed diffuser blade and the matching surface of the bleed air casing, the tangential length of the diffuser blade is controlled based on the above-mentioned excitation frequency, thereby realizing a radial diffuser blade design with controllable blade frequency. Based on the consideration of the change in the constraint state of the contact surface between the radial diffuser blade and the bleed air casing, the present invention combines the excitation frequency of the upstream rotor to effectively avoid the high-cycle fatigue failure of the radial diffuser blade caused by the uncertainty of the blade tip constraint state.

[0044] The present invention provides a radial diffuser blade design method. Figure 3 FIG. 1 is a flow chart showing a method for designing radial diffuser blades according to an embodiment of the present invention. Figure 3 In the present invention, the radial diffuser blade design method includes the following steps:

[0045] S101. Obtain aerodynamic parameters and structural design requirements, and establish a three-dimensional model of the diffuser blade;

[0046] Among them, aerodynamic parameters include: number of diffuser blades, blade meridian interface projection and position, diffuser flow channel, and blade profile data;

[0047] The structural design requirements include: ambient temperature limits, weight requirements, sealing requirements, connection methods of adjacent parts and interface requirements.

[0048] S102, obtaining the temperature load of the diffuser blade, performing calculation and analysis on the vibration characteristics of the diffuser blade using a three-dimensional model, and obtaining the natural frequencies of each order corresponding to the diffuser blade;

[0049] Generally, a single radial diffuser blade is selected for calculation. A single radial diffuser blade model is cut out in CAD software and finite element pre-processing is performed on the single blade model using commercial finite element software: finite element meshing, temperature field application, and constraint boundary conditions are applied. During this analysis, the blade tip is in an unconstrained state (the blade tip of the designed diffuser blade does not form a fit with the mating surface of the bleed air casing), and the corresponding natural frequency of the diffuser blade is then obtained.

[0050] It should be noted that during the analysis, the natural frequency of the radial diffuser is infinite, so it can also be said that Figure 4 The first-order frequency and the second-order frequency are inherent characteristics of the radial diffuser. Similarly, the natural frequencies can be defined as the first-order frequency, the second-order frequency, the third-order frequency, and so on, from small to large. In this embodiment, the first-order frequency and the second-order frequency are used as examples for illustration, but this does not limit the number of natural frequencies.

[0051] S103, obtaining blade parameters of the upstream rotor and determining the excitation frequency, and determining that the diffuser blades whose margins between each order natural frequency and the excitation frequency are greater than a predetermined margin are the designed diffuser blades;

[0052] When considering the upstream rotor, the upstream rotor conventionally adopts a centrifugal impeller, which is usually designed with large and small blades. After the airflow passes through the centrifugal impeller, an airflow related to the number of centrifugal impeller blades and the logarithm of the large and small blades of the centrifugal impeller is formed, causing the radial diffuser to withstand the wake excitation from the centrifugal impeller.

[0053] Correspondingly, the blade parameters of the upstream rotor include: the number of centrifugal impeller blades and the number of centrifugal impeller blade pairs;

[0054] The excitation frequency includes: the excitation frequency of the centrifugal impeller blades is several times the rotor excitation frequency; the excitation frequency of the centrifugal impeller blades is several times the rotor excitation frequency.

[0055] In this embodiment, the margins between the natural frequencies of each order and the excitation frequency are determined by the following calculation formula:

[0056]

[0057] Among them, Y represents the margin, which is the absolute value of the calculation formula; H1 represents the natural frequency of the diffuser blade; H2 represents the excitation frequency; and in this application, the frequency margin is taken into account calculation and actual processing errors and material dispersion, and the frequency margin of each order of the radial diffuser blade is required to meet certain requirements, usually 8%; that is, when the margin values ​​between each order of natural frequency and the excitation frequency are greater than 8%, the corresponding diffuser blade meets the design requirements and can be used as the diffuser design blade.

[0058] exist Figure 4 In the example shown, the centrifugal impeller blade number excitation zone represents the number of centrifugal impeller blades times the rotor excitation frequency, and the centrifugal impeller blade size logarithmic excitation zone represents the centrifugal impeller blade size logarithmic multiple of the rotor excitation frequency; correspondingly, only when the margin values ​​between each order natural frequency and the centrifugal impeller blade number rotor excitation frequency and the centrifugal impeller blade size logarithmic multiple of the rotor excitation frequency are greater than 8%, the corresponding diffuser blade meets the design requirements and can be used as the diffuser design blade.

[0059] S104. Using the gap length between the blade tip of the designed diffuser blade and the mating surface of the bleed air casing as a variable, perform modal analysis on the designed diffuser blades with different gap lengths to obtain the relationship between the gap length and each order of natural frequency;

[0060] The diffuser blade length b of the three-dimensional model is obtained, and the gap length between the blade tip of the diffuser design blade and the matching surface of the bleed air casing is in the range of 0-b; the relationship between the gap length and the natural frequency of each order can be Figure 2 expressed in the form of .

[0061] S105, determining the minimum gap length based on the relationship between the excitation frequency, the gap length, and the natural frequencies of each order;

[0062] Specifically, according to the relationship between the gap length and each order natural frequency, the gap length value corresponding to the change amplitude of each order natural frequency value is less than a predetermined amplitude is selected as the steady-state length;

[0063] For example, the predetermined amplitude is selected as 5% according to actual operation, that is, the gap length value corresponding to the change amplitude of each order natural frequency value is less than 5% is the steady-state length;

[0064] Determine the frequency value corresponding to each steady-state length as the steady-state frequency, and determine that the steady-state length whose margin between the steady-state frequency and the excitation frequency is greater than a predetermined margin is a qualified steady-state length;

[0065] The qualified steady-state length with the smallest value is selected as the minimum gap length.

[0066] S106: Perform angle cutting of the designed diffuser blades according to the minimum gap length, obtain the designed diffuser blades after angle cutting, and complete the design.

[0067] During the angle cutting operation, considering that the angle cutting has a certain impact on the blade frequency or performance, the angle cutting angle α needs to be reduced as much as possible. Therefore, the angle α of the angle cutting operation is set to be less than or equal to 3°. By cutting the angle, a gap is created between the cut angle part of the blade and the air bleed casing, so that the blade frequency is insensitive to the constraint state of the blade tip contact surface of the uncut part.

[0068] In addition, after obtaining the design blades of the diffuser with the cut angle completed, it is necessary to perform vibration characteristic calculation and analysis on the design blades of the diffuser with the cut angle completed to obtain the various order frequencies of the design blades of the diffuser with the cut angle completed;

[0069] And calculate the margin between each order frequency and the excitation frequency;

[0070] Determine whether the margin is greater than the predetermined margin, thereby achieving secondary confirmation of the design and further ensuring that the margin between the designed diffuser blades and the excitation frequency is greater than 8%;

[0071] When the margin is determined to be greater than the predetermined margin, the design is completed.

[0072] refer to Figure 4 To further illustrate this design method, we use the first-order frequency and the second-order frequency as examples. Assume that the length of the diffuser blade is b, in mm, and the gap length between the diffuser blade tip and the mating surface of the bleed air casing is d, in mm.

[0073] For the first-order frequency of the diffuser blade, when the gap length between the tip of the diffuser blade and the mating surface of the bleed air casing is d0, then when d0 is in the range of d1-d2 (mm), the first-order frequency of the diffuser blade coincides with the excitation frequency of the centrifugal impeller blade, indicating that the diffuser blade has resonance caused by the excitation frequency of the upstream centrifugal impeller blade rotor, that is, when the gap length d0 is between d1-d2, the margin between the frequency corresponding to the excitation frequency is less than the predetermined margin, and high-cycle fatigue damage of the blade will occur.

[0074] When the gap length d0 between the tip of the diffuser blade and the mating surface of the bleed air casing is greater than or equal to d3 (mm), the amplitude of the corresponding diffuser blade 1st order frequency is less than 5%, and the margin between the corresponding diffuser blade 1st order frequency and the centrifugal impeller blade several times the rotor excitation frequency and the centrifugal impeller blade several times the rotor excitation frequency is greater than 8%, so d3 is selected as the first qualified steady-state length.

[0075] For the second-order frequency of the diffuser blade, when the gap length d0 between the blade tip of the diffuser blade and the mating surface of the bleed air casing is any value between ob, the corresponding value of the second-order frequency of the diffuser blade and the centrifugal impeller blade multiple rotor excitation frequency and the centrifugal impeller blade multiple rotor excitation frequency are all greater than 8%; based on the amplitude of the second-order frequency being less than 5%, d0 is selected as d4 as the second qualified steady-state length for illustration. Considering that the second-order frequency does not require cutting angle to meet the frequency margin requirement, d3 is selected as the minimum gap length.

[0076] refer to Figure 6 , the diffuser blades are cut with a gap length d0 of d3 and an inclination angle α of 3°.

[0077] It should be noted that the 1st-order frequency, 2nd-order frequency, 3rd-order frequency, 4th-order frequency, etc. increase in sequence. On the basis that the 2nd-order frequency is higher than the maximum excitation frequency and has sufficient margin, the 3rd-order frequency, 4th-order frequency, etc. are no longer considered, thereby reducing the calculation workload and improving design efficiency.

[0078] Reference Figure 5 , Figure 5 The relationship between the gap length and the natural frequency of each order is shown in Figure 2. Figure 2 , which shows the relationship between each frequency order and gap length after the angle cut. It can be seen that the margin between the radial diffuser blade frequency after the angle cut and the excitation frequency is always greater than the predetermined margin, and the overall amplitude of the radial diffuser blade frequency after the angle cut is reduced. In other words, the frequency characteristics of the radial diffuser blade after the angle cut are insensitive to the constraint state of the diffuser blade tip and the bleed air casing mating surface, the frequency variation is small, and there is sufficient safety margin for each excitation zone.

[0079] refer to Figure 7 According to the radial diffuser blade design method of the present application, according to the same design method, the angle cutting operation can also be performed on the air bleed casing, that is, the angle cutting length d0 and the angle cutting angle α on the air bleed casing are between 0-3°.

[0080] Based on the above excitation frequency, the cutting operation of the air bleed casing is controlled to complete the design of the air bleed casing. Those skilled in the art can comprehensively consider the design principles of the present invention and actual application conditions, as long as the principles of the present invention can be implemented.

[0081] In addition, the present invention also discloses a radial diffuser blade obtained by using the radial diffuser blade design method.

[0082] In addition, the present invention also discloses a radial diffuser, which includes the radial diffuser blades mentioned above.

[0083] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they may refer to fixed, detachable, or integral connections; mechanical, electrical, or intercommunication connections; direct or indirect connections through an intermediary; and may encompass internal connectivity between multiple components or interactions between multiple components. Those skilled in the art will understand the specific meanings of these terms in the present invention based on specific circumstances.

[0084] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A radial diffuser blade design method, characterized in that: include: Obtain aerodynamic parameters and structural design requirements and build a 3D model of the diffuser blades; Obtain the temperature load of the diffuser blades and calculate and analyze the vibration characteristics of the diffuser blades using a three-dimensional model. In the initial analysis, the blade tip is in an unconstrained state, and the corresponding natural frequencies of each order of the diffuser blades are obtained. Obtaining blade parameters of the upstream rotor and determining the excitation frequency, and determining that a diffuser blade having a margin between each order natural frequency and the excitation frequency greater than a predetermined margin is a designed diffuser blade; Taking the gap length between the blade tip and the mating surface of the bleed air casing as a variable, modal analysis of the diffuser blades with different gap lengths was performed to obtain the relationship between the gap length and each order of natural frequency. Determine the minimum gap length based on the relationship between the excitation frequency, gap length and each order natural frequency; Perform angle cutting of the diffuser design blades according to the minimum gap length, obtain the diffuser design blades after angle cutting, and complete the design; The specific steps of determining the minimum gap length are: According to the relationship between the gap length and each order natural frequency, the gap length value corresponding to the change amplitude of each order natural frequency value is less than a predetermined amplitude is selected as the steady-state length; Determine the frequency value corresponding to each steady-state length as the steady-state frequency, and determine that the steady-state length whose margin between the steady-state frequency and the excitation frequency is greater than a predetermined margin is a qualified steady-state length; The qualified steady-state length with the smallest value is selected as the minimum gap length.

2. The radial diffuser blade design method according to claim 1, characterized in that: In the step of obtaining the blade parameters of the upstream rotor and determining the excitation frequency: The blade parameters of the upstream rotor include: the number of centrifugal impeller blades and the number of centrifugal impeller blade pairs; The excitation frequency includes: the excitation frequency of the centrifugal impeller blades which is several times the rotor excitation frequency; the excitation frequency of the centrifugal impeller blades which is several times the rotor excitation frequency.

3. The radial diffuser blade design method according to claim 1, characterized in that: The method also includes obtaining the diffuser blade length b of the three-dimensional model, and the gap length between the blade tip of the designed diffuser blade and the matching surface of the bleed air casing has a value range of: 0-b.

4. The radial diffuser blade design method according to claim 3, characterized in that: In the step of performing the angle chopping operation on the diffuser blades according to the minimum gap length, the length of the angle chopping operation is less than or equal to b and greater than or equal to the minimum gap length.

5. The radial diffuser blade design method according to claim 3, characterized in that: In the step of performing an angle cutting operation on the diffuser blades according to the minimum gap length, the angle of the angle cutting operation is less than or equal to 3°.

6. The radial diffuser blade design method according to claim 1, characterized in that: After obtaining the diffuser blade design with the chamfered blades, the following steps are also included: Perform vibration characteristic calculation and analysis on the designed diffuser blades after cutting to obtain the frequencies of each order of the designed diffuser blades after cutting; And calculate the margin between each order frequency and the excitation frequency; After determining that the margin is greater than the predetermined margin, the design is completed.

7. The radial diffuser blade design method according to claim 6, characterized in that: The margin between the natural frequency of each order and the excitation frequency is determined by the following calculation formula: Where Y represents the margin, which is the absolute value of the calculation formula; H1 represents the natural frequency of the diffuser blade; and H2 represents the excitation frequency.

8. A radial diffuser blade obtained by using the radial diffuser blade design method according to any one of claims 1 to 7.

9. A radial diffuser, characterized in that: The radial diffuser includes the radial diffuser blades according to claim 8.

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