Radial diffuser blade design method and radial diffuser

Abstract

The invention provides a radial diffuser blade design method and a radial diffuser. The method comprises the following steps: acquiring inherent frequency of each order corresponding to the diffuser blade; obtaining the relationship between the gap length and the inherent frequency of each order; determining the minimum gap length based on the relationship among the excitation frequency, the gap length and the inherent frequency of each order; and according to the minimum gap length, corner cutting operation of the designed blade of the diffuser is conducted, and design is completed. According to the frequency-controllable radial diffuser blade, the problem that air flow passing through an upstream rotor resonates with a downstream diffuser blade is effectively solved; and on the basis of considering the constraint state change of the contact surface of the radial diffuser blade and the air entraining casing, the excitation frequency of an upstream rotor is combined, so that the high-cycle fatigue fault of the radial diffuser blade caused by the uncertain constraint state of the blade top is effectively avoided, and the service life of the diffuser blade is guaranteed.

Description

Technical Field

[0001] The 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 blade fits with 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 not coordinated. 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] In order to meet the overall requirements of light weight and high performance, 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 withstand the 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 the field of this technology. 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 establish a three-dimensional model of the diffuser blades;

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

[0008] Obtaining blade parameters of the upstream rotor and determining the excitation frequency, and determining that the diffuser blades whose margins between each order of natural frequency and the excitation frequency are greater than a predetermined margin are the diffuser design blades;

[0009] Taking the gap length between the blade tip of the diffuser design blade and the matching surface of the bleed air casing as a variable, the modal analysis of the diffuser design blades with different gap lengths was carried out to obtain the relationship between the gap length and the natural frequencies of each order;

[0010] Based on the relationship between the excitation frequency, gap length and each order of natural frequency, the minimum gap length is determined;

[0011] The diffuser design blades are cut according to the minimum gap length, the diffuser design blades with the cut angles completed are obtained, and the design is completed.

[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 each order of natural frequency are:

[0016] According to the relationship between the gap length and each order of natural frequency, the gap length value corresponding to the change amplitude of each order of 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, it also includes obtaining the diffuser blade length b of the three-dimensional model, and the gap length between the blade tip of the diffuser design blade and the matching surface of the bleed air casing has a value range of: 0-b.

[0020] Furthermore, in the step of performing an angle cutting operation on the diffuser blade design according to the minimum gap length, the length of the angle cutting 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 the step of obtaining the diffuser design blade with the cut 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 of natural frequency and the excitation frequency is determined by the following calculation formula:

[0027]

[0028] 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.

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

[0030] The present invention also provides a radial diffuser, which includes the radial diffuser blades mentioned 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 then 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 passing 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 matching surface of the bleed air casing, the cut angle 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 uncertain 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 partly become obvious from the description, or be understood by implementing 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 briefly introduces 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 creative work.

[0035] Figure 1A schematic diagram of assembling 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] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution 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. 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.

[0043] In response to the above-mentioned key existing problems, 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 exciting 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 cut angle length of the diffuser blade is controlled based on the above-mentioned exciting frequency, thereby realizing a radial diffuser blade design with controllable blade frequency. The present invention effectively avoids high-cycle fatigue failures of radial diffuser blades caused by uncertain blade tip constraint states, based on the consideration of changes in the constraint state of the contact surface between the radial diffuser blades and the bleed air casing, combined with the exciting frequency of the upstream rotor.

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

[0045] S101, obtaining aerodynamic parameters and structural design requirements, and establishing a three-dimensional model of diffuser blades;

[0046] Among them, the aerodynamic parameters include: the number of diffuser blades, the projection and position of the blade meridian interface, the diffuser flow channel, and the 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 blades, and calculating and analyzing the vibration characteristics of the diffuser blades in combination with the three-dimensional model to obtain the natural frequencies of each order corresponding to the diffuser blades;

[0049] Generally, a single radial diffuser blade is selected for calculation. A single radial diffuser blade model is cut out in the CAD software. The single blade model is pre-processed by finite element using commercial finite element software: finite element mesh is divided, temperature field and constraint boundary conditions are applied. In this analysis process, the blade tip is in an unconstrained state (the blade tip of the designed diffuser blade does not form a fit with the matching surface of the bleed air casing), and then the natural frequency corresponding to the diffuser blade is obtained;

[0050] It should be noted that in the analysis process, the natural frequency of the radial diffuser is infinite, so it can also be said that Figure 4 The 1st-order frequency and the 2nd-order frequency are inherent characteristics of the radial diffuser. Similarly, the inherent frequencies can be defined as 1st-order frequency, 2nd-order frequency, 3rd-order frequency, etc. from small to large. In this embodiment, the 1st-order frequency and the 2nd-order frequency are used as examples for explanation, but this does not mean that the number of inherent frequencies is limited.

[0051] S103, obtaining blade parameters of the upstream rotor and determining the excitation frequency, and determining that the diffuser blades whose margins between the natural frequencies of each order 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 size of the centrifugal impeller blades 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 exciting frequencies include: the centrifugal impeller blades are several times the rotor exciting frequency; the centrifugal impeller blade size is several times the rotor exciting 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 the calculation and actual processing errors and material dispersion, etc., and the frequency margins of each order of the radial diffuser blade are 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 times 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 logarithmic times 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, taking the gap length between the blade tip of the designed diffuser blade and the matching surface of the bleed air casing as a variable, performing modal analysis of the designed diffuser blades with different gap lengths, and obtaining 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 to express in the form of .

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

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

[0063] Exemplarily, 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, performing angle cutting of the designed diffuser blade according to the minimum gap length, obtaining the designed diffuser blade after angle cutting, and completing the design.

[0067] In the step of the angle cutting operation, considering that the angle cutting has a certain influence on the blade frequency or performance, it is necessary to reduce the angle cutting angle α 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 angle cutting part of the blade and the air bleed casing, so as to achieve the purpose of making the blade frequency insensitive to the constraint state of the blade tip contact surface of the un-angled part.

[0068] In addition, after the step of obtaining the designed diffuser blades after the cut angle is completed, it is also necessary to perform vibration characteristic calculation and analysis on the designed diffuser blades after the cut angle is completed to obtain the various order frequencies of the designed diffuser blades after the cut angle is 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, realize secondary confirmation of the design, and further ensure that the margin between the designed diffuser blade and the excitation frequency is more than 8%;

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

[0072] refer to Figure 4 In order to further illustrate this design method, the first-order frequency and the second-order frequency are used as examples. The length of the diffuser blade is set to b, in mm, and the gap length between the blade tip of the diffuser blade and the matching surface of the bleed air casing is set to 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 number, indicating that the diffuser blade has resonance caused by the excitation frequency of the upstream centrifugal impeller blade number 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 1st-order frequency of the diffuser blade is less than 5%, and the margins between the corresponding 1st-order frequency of the diffuser blade and the several times rotor excitation frequency of the centrifugal impeller blade and the several times rotor excitation frequency of the centrifugal impeller blade are greater than 8%, so d3 is selected as the first qualified steady-state length.

[0075] For the 2nd 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 2nd order frequency of the diffuser blade and the margin of the centrifugal impeller blade multiple times the rotor excitation frequency and the centrifugal impeller blade multiple times the rotor excitation frequency are both greater than 8%; based on the amplitude of the 2nd order frequency being less than 5%, d0 is selected as d4 as the second qualified steady-state length for illustration, and considering that the 2nd order frequency does not require cutting 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 each order of natural frequency is shown in Figure 2. Figure 2 , which is a schematic diagram showing the relationship between each order frequency and the gap length after the angle cutting is completed. It can be seen that the margin between the radial diffuser blade frequency after the angle cutting and the excitation frequency is always greater than the predetermined margin, and the overall amplitude of the radial diffuser blade frequency after the angle cutting becomes smaller; that is, the frequency characteristics of the radial diffuser blade after the angle cutting are insensitive to the constraint state of the diffuser blade tip and the matching surface of the bleed air casing, the frequency change 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 bleed air casing, that is, the angle cutting length is d0 and the angle cutting angle α is a value between 0-3° on the bleed air casing.

[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 principle of the present invention and the actual application situation, as long as the principle of the present invention can be realized.

[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 clearly specified and limited, the terms "installation", "connection", and "connection" 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, an electrical connection, or mutual communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of multiple components or the interaction relationship of multiple components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to 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 substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions 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 establish a three-dimensional model of the diffuser blades; Obtain the temperature load of the diffuser blades, and calculate and analyze the vibration characteristics of the diffuser blades in combination with the three-dimensional model. In the initial analysis, the blade tip is in an unconstrained state, and the natural frequencies of each order corresponding to the diffuser blades are obtained; Obtaining blade parameters of the upstream rotor and determining the excitation frequency, and determining that the diffuser blades whose margins between each order of natural frequency and the excitation frequency are greater than a predetermined margin are the diffuser design blades; Taking the gap length between the blade tip of the diffuser design blade and the matching surface of the bleed air casing as a variable, the modal analysis of the diffuser design blades with different gap lengths was carried out to obtain the relationship between the gap length and the natural frequencies of each order; Based on the relationship between the excitation frequency, gap length and each order of natural frequency, the minimum gap length is determined; The diffuser design blades are cut according to the minimum gap length, the diffuser design blades with the cut angles completed are obtained, and the design is completed.

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 exciting 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 specific steps of determining the minimum gap length based on the relationship between the excitation frequency, the gap length and each order of natural frequency are as follows: According to the relationship between the gap length and each order of natural frequency, the gap length value corresponding to the change amplitude of each order of 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.

4. The radial diffuser blade design method according to claim 3, 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 diffuser design blade and the matching surface of the bleed air casing has a value range of 0-b.

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

6. The radial diffuser blade design method according to claim 4, 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°.

7. The radial diffuser blade design method according to claim 1, characterized in that: After obtaining the diffuser blade design step with the chamfered blade completed, it also includes: 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.

8. The radial diffuser blade design method according to claim 7, characterized in that: The margin between the natural frequency of each order and the excitation frequency is determined by the following calculation formula: 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.

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

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

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