Blisk structure blade mistuning frequency rapid test identification method

Abstract

The invention discloses a quick test identification method for the detuning frequency of a blade of a blisk structure, and the method comprises the steps: adding the same detuning mass at the same positions of all non-test blades except a current to-be-tested blade, so as to greatly weaken the vibration coupling effect between the blade and an adjacent blade; then, vibration of a single blade is isolated from the blisk through a double-blade solution harmonic vibration test, and the influence of the residual inter-blade vibration coupling effect of the blisk on an independent blade vibration frequency test result is evaluated, so that the completely decoupled blade vibration frequency is obtained; and differential distribution of vibration frequencies of all the blades is further obtained, and rapid test identification of blade detuning is realized. The method has the advantages of high test efficiency, strong operability and high blade mistuning frequency identification accuracy, and is suitable for popularization and application in engineering practice.

Description

Technical Field

[0001] The present invention relates to a method for quickly testing and identifying the blade mistuning frequency of an integrated blisk structure of an axial compressor of an aero-engine, belonging to the field of aerospace technology. Background Art

[0002] The integrated blisk with integrated design eliminates the tenon connection structure and locking device in the traditional split blisk design, and is the core technology for the structural design of the axial compressor / fan component of an advanced aero-engine to develop towards lightweight and integration. In an ideal integrated blisk structure, each blade has exactly the same geometric / physical properties, which is called a harmonically tuned integrated blisk. However, in the physical structure of the integrated blisk, factors such as the dispersion of blade manufacturing and operation wear result in inevitable small differences in the geometric / physical properties among individual blades, namely random blade mistuning, which is reflected in their vibration frequencies. Random blade mistuning has a significant impact on the dynamic characteristics of the integrated blisk. On the one hand, random blade mistuning destroys the cyclic symmetry of the ideal integrated blisk structure, causing its vibration energy to be no longer evenly distributed among all blades, but may concentrate and flow to a few blades, forming the phenomenon of vibration mode localization and the "amplitude amplification effect". Coupled with its low structural damping level, the integrated blisk usually has a higher vibration level and a higher risk of high-cycle fatigue failure than the split blisk structure under the same conditions.

[0003] In engineering practice, engineers often adopt special vibration testing and identification methods to obtain the random mistuning distribution of blades in the physical structure of the integrated blisk where the blades cannot be disassembled. This link is called blade mistuning identification. Traditional blade mistuning identification methods are generally based on the reduced-order dynamic model of the mistuned integrated blisk. Taking the modal test data of the physical structure of the integrated blisk (including the overall disk modal frequency and vibration mode) as input, the differential distribution of "independent" blade frequencies or blade model elastic modulus parameters is obtained through mathematical back-calculation. The traditional blade mistuning identification method based on the modal test of the integrated blisk belongs to the category of inverse vibration problems. In practical applications, the blade mistuning identification results are easily affected by the errors of the input overall disk modal vibration mode data. In addition, a large amount of test time and professional testing skills are required to obtain high-quality overall disk modal test data to ensure the effectiveness of the blade mistuning identification results. However, the integrated blisk itself has the characteristic of dense modal distribution. At the same time, the heavy modal separation caused by blade mistuning further exacerbates this phenomenon. This makes it usually difficult for standard single-input modal tests to effectively excite all modal vibrations of the mistuned integrated blisk, and there are also technical difficulties in identifying the modal parameters of the mistuned integrated blisk. Generally speaking, the traditional blade mistuning identification problem based on the modal test of the integrated blisk and the reduced-order dynamic model is extremely difficult and challenging in terms of physical essence.

[0004] In summary, the vibration problem of the blisk is highly sensitive to random blade mistuning. How to achieve more efficient and reliable identification of random blade mistuning and then accurately predict the dangerous blade vibration of the blisk solid structure is one of the long-standing problems that have troubled the structural dynamics of the blisk and the design against high cycle fatigue. Summary of the Invention

[0005] To solve the problem of identifying random blade mistuning in the blisk structure of an axial compressor, the present invention provides a rapid experimental identification method for blade mistuning frequencies based on double blade detuning vibration tests. The specific steps are as follows:

[0006] Step 1: Obtain the modal vibration modes and modal kinetic energy distributions of the blade finite element model of the blisk under clamped boundary conditions.

[0007] Step 2: Select detuning masses and attach them to the same positions of all non-test blades except the current blade j to be measured, completing the detuning mass layout.

[0008] Step 3: For the current blade j to be measured, conduct the first blade detuning vibration test to obtain the first detuning vibration test frequency response function of a single measurement point of the current blade j to be measured.

[0009] Step 4: For the first detuning vibration test frequency response function obtained in Step 3, extract the first isolated peak frequency and denote it as ;

[0010] Step 5: On the basis of the detuning mass layout scheme in Step 2, add an additional set of detuning masses identical to those selected in Step 2 at the same positions of all non-test blades except the current blade j to be measured.

[0011] Step 6: For the current blade j to be measured, conduct the second blade detuning vibration test to obtain the second detuning vibration test frequency response function of the same measurement point of the current blade j to be measured.

[0012] Step 7: For the second detuning vibration test frequency response function obtained in Step 6, extract the second isolated peak frequency and denote it as ;

[0013] Step 8: Compare the first isolated peak frequency extracted in Step 4 and the second isolated peak frequency . If and If the difference is less than the set threshold, it is considered that the current blade j to be measured reaches the ideal vibration decoupling state in the two blade detuning vibration tests, and the second isolated peak frequency is regarded as the detuning frequency of the current blade j to be measured; otherwise, return to step 2 to re-perform the detuning mass layout until the current blade to be measured reaches the ideal vibration decoupling state in the two blade detuning vibration tests;

[0014] Step 9. For all blades ( ), repeat steps 2 to 8 to obtain the detuning frequencies of each blade, and complete the rapid experimental identification of the detuning frequencies of the blades of the overall blisk structure, where N is the total number of blades.

[0015] The present invention also provides a device for rapid experimental identification of the detuning frequencies of the blades of an overall blisk structure, including a soft pad and an overall blisk structure horizontally placed thereon, tuning masses arranged at the same positions of all non-test blades except the current blade to be measured, a force hammer, a non-contact Doppler laser vibrometer, and a data acquisition system;

[0016] Use the force hammer to apply excitation to the current blade to be measured at the set position, and at the same time use the non-contact Doppler laser vibrometer to pick up vibration at the tip of the current blade to be measured;

[0017] The data acquisition system obtains the test results of the two blade detuning vibration tests of all blades based on the above method, and completes the rapid experimental identification of the detuning frequencies of the blades of the overall blisk structure.

[0018] Compared with the prior art by adopting the above technical solutions, the present invention has the following technical effects:

[0019] 1. The present invention proposes a method for rapid experimental identification of the detuning frequencies of the blades of an overall blisk based on blade detuning vibration tests, which can directly and rapidly measure the vibration frequencies of each blade that are approximately completely "independent" and obtain the random detuning frequency distribution of the blades at a relatively low experimental economic and time cost. Compared with the traditional blade detuning identification method based on the overall blisk modal test and the reduced-order dynamic model, it has the advantages of high test efficiency, strong operability, and simple data post-processing, and is more suitable for application in engineering practice.

[0020] 2. The double blade detuning vibration test method proposed by the present invention evaluates the influence of the residual inter-blade vibration coupling effect of the overall blisk on the test results of the "independent" blade vibration frequencies through experiments. On the one hand, it provides a simple and efficient technical approach for evaluating the effectiveness of the blade detuning vibration test (i.e., the vibration decoupling degree of a "single" blade); on the other hand, it can also improve the accuracy of the identification results of the random detuning frequencies of the blades. Description of the Drawings

[0021] Figure 1Schematic diagram of the rapid test identification device for the blade mistuning frequency of the blisk structure

[0022] Figure 2 Frequency response function of the conventional vibration test of Blade No. 1 when there is no additional mistuning mass on the blisk

[0023] Figure 3 Comparison diagram of the frequency response function of the mistuning vibration test of Blade No. 1 in the first blade mistuning vibration test of the blisk

[0024] Figure 4 Schematic diagram of the second blade mistuning vibration test of the blisk

[0025] Figure 5 Comparison diagram of the frequency response function of the mistuning vibration test of Blade No. 1 in the second blade mistuning vibration test of the blisk Specific implementation manner

[0026] Next, taking the Figure 1 axial-flow compressor blisk structure as an example, the blade mistuning vibration test device and the rapid test identification method for blade mistuning frequency involved in the present invention will be described

[0027] As Figure 1 shown in the rapid test identification device for the blade mistuning frequency of the blisk structure, where the blisk structure is horizontally placed on a soft pad, and tuning masses are respectively arranged at the same positions of all non-test blades except the currently tested blade. A force hammer is used to apply excitation to the currently tested blade at the set position, and at the same time, a non-contact Doppler laser vibrometer is used to pick up vibrations at the tip of the currently tested blade. The data acquisition system obtains the frequency response function of the mistuning vibration test of the currently tested blade in two blade mistuning vibration tests based on the excitation signal applied by the force hammer and the velocity response signal obtained by the non-contact Doppler laser vibrometer, and completes the rapid test identification of the blade mistuning frequency of the blisk structure. It should be noted that the rapid test identification method for blade mistuning frequency proposed by the present invention is also applicable to the blisk structure in the installed state

[0028] For the blade mistuning vibration test, the same tuning masses need to be added at the same positions of all non-test blades except the currently tested blade to completely destroy the cyclic symmetry characteristics of the blisk structure and achieve the purpose of weakening the inter-blade vibration coupling effect. The size, magnitude of the tuning mass and its position on the blade determine the success of the blade mistuning vibration test. The selection and arrangement criteria for the tuning mass are as follows: the size of the tuning mass should cover the region with the maximum kinetic energy density in the target order modal vibration of the blade, so that the modal vibration frequency of the "single" blade after adding the tuning mass can reach the maximum change range as much as possible. The weight (g) of the tuning mass is not strictly required and can be reasonably adjusted according to the subsequent test results of the blade mistuning vibration

[0029] To illustrate the necessity of blade detuning vibration testing, first, for the integral bladed disk without any detuning mass added, the above test device and the impact method are used to obtain the frequency response function of the conventional vibration test of the blade. Figure 2 The measured frequency response function of blade No. 1 within the frequency range of the first bending mode family of the integral bladed disk is shown. It can be seen from this figure that there is a vibration coupling effect between adjacent blades of the integral bladed disk, making it exhibit the characteristic of modal dense distribution. Superimposing the heavy mode separation effect caused by blade mistuning, the frequency response function of the conventional vibration test of the blade shows multiple peaks. Obviously, the vibration frequency of the "independent" blade cannot be identified through the frequency response function of the conventional impact vibration test of the blade.

[0030] To further illustrate the technical solution of the present invention, the detuning mass composed of two identical disc-shaped magnets is taken as an example below. As Figure 1 shown, the two identical disc-shaped magnets are attached to a certain fixed position of the blade by mutual attraction. The essence of the blade detuning vibration test is to use the impact method to obtain the test frequency response function of a single measurement point of the blade to be measured without added detuning mass, so as to quickly measure the vibration frequency of the approximately "independent" blade. As Figure 1 shown, a small impact hammer can be used to apply excitation to the blade at a suitable position, and at the same time, a non-contact Doppler laser vibrometer is used to pick up the vibration at the tip of the blade. The impact hammer excitation signal and the velocity response signal of the laser vibrometer are input into the data acquisition system, and the frequency response function of the detuning vibration test corresponding to the blade can be obtained after signal processing.

[0031] Since the detuning mass can weaken but cannot completely eliminate the inter-blade vibration coupling effect of the integral bladed disk. For this reason, the present invention proposes to carry out the second blade detuning vibration test to evaluate the influence of the residual inter-blade vibration coupling effect and improve the accuracy of the blade mistuning frequency identification result. Through the double blade detuning vibration test of the present invention, the vibration of the "single" blade is "isolated" from the integral bladed disk, thereby obtaining the completely decoupled blade vibration frequency, and further obtaining the differential distribution of the vibration frequencies of all blades, realizing the rapid experimental identification of blade mistuning. The implementation process will be described in detail below.

[0032] 1. The first blade detuning vibration test:

[0033] (1) Obtain the finite element model of the blade from the integral bladed disk design model, apply displacement constraints to its root, and carry out simulation calculations in the finite element software to obtain the modal vibration mode and modal kinetic energy distribution of the target order of the fixed blade.

[0034] (2) Use the Figure 1 shown disc-shaped magnets as the detuning mass and attach them to the same position of all non-test blades except the current blade to be measured.

[0035] (3) Conduct the first blade detuning vibration test on the currently measured Blade No. 1, that is, use the hammer impact method to obtain the detuning vibration test frequency response function of a single measurement point on this blade. Note that for different target modal orders of the blade, it is usually necessary to change the force hammer excitation position until a smooth test frequency response function with significant vibration decoupling phenomenon is generated, as shown in Figure 3 . In addition, the frequency response function of the conventional hammer impact vibration test of Blade No. 1 when no detuning mass is added to the integral bladed disk is also shown in Figure 3 for comparison.

[0036] (4) Observe Figure 3 that after adding detuning mass to the non-test blades of the integral bladed disk, the detuning vibration test frequency response function of Blade No. 1 shows a significant isolated peak in the frequency range of the first bending mode family of the integral bladed disk. Extract this peak frequency and denote it as , where the superscript " " represents the first detuning vibration test, and the subscript "1" corresponds to Blade No. 1. This indicates that the presence of the detuning mass significantly weakens the vibration coupling effect between Blade No. 1 and its adjacent blades. When Blade No. 1 is excited by a hammer impact, most of the vibration energy of the integral bladed disk is concentrated on this blade, making it exhibit vibration characteristics similar to an "independent" blade, that is, the so-called vibration decoupling phenomenon.

[0037] However, it must be emphasized that the isolated peak frequency in the detuning vibration test frequency response function of the blade is not strictly the modal vibration frequency of an "independent" blade. In the detuning vibration test, the residual inter-blade vibration coupling effect in the integral bladed disk structure not only depends on the sufficiency of the vibration decoupling effect of the detuning mass, but also is closely related to the strength of the inter-blade vibration coupling effect of different modal families of the integral bladed disk itself, and may still have a non-negligible impact on the measured isolated peak frequency.

[0038] Therefore, the present invention proposes to conduct a second blade detuning vibration test to evaluate the influence of the residual inter-blade vibration coupling effect and improve the accuracy of the blade mistuning frequency identification result.

[0039] 2. Second blade detuning vibration test:

[0040] (1) On the basis of the detuning mass layout scheme in the first blade detuning vibration test, add an additional set of identical circular magnets at the same positions of all non-test blades other than the currently measured blade, so that the detuning mass is (g), as shown in Figure 4 .

[0041] (2) Conduct the second blade detuning vibration test on Blade No. 1 to be measured, that is, use the hammer impact method to obtain the detuning vibration test frequency response function of a single measurement point on this blade.

[0042] (3) Compare the frequency response functions of the detuned vibration tests of Blade No. 1 in the two detuned vibration tests, as Figure 5 shown. Figure 5 shows the additional detuning mass of the non-tested blades of the integral bladed disk After that, the frequency response function of the detuned vibration test of Blade No. 1 also shows a significant isolated peak in the frequency range of the first bending mode family of the integral bladed disk. The peak frequency has only a slight difference from the peak frequency obtained in the first detuned vibration test and is much smaller than the set threshold value, which can be ignored.

[0043] The above test results show that in the first blade detuned vibration test, the residual interblade vibration coupling effect of the integral bladed disk has been at a very low level, and the detuned vibration decoupling effect of Blade No. 1 has been relatively sufficient. Therefore, when the detuning mass is increased to After that, the peak frequencies obtained from the two detuned vibration tests of the same test blade are basically the same. At this time, it can be considered that in the second blade detuned vibration test, the first bending mode vibration of the "single" blade has been completely "isolated" from the integral bladed disk, and its isolated peak frequency can be regarded as the vibration frequency of complete decoupling of Blade No. 1, that is, the detuning frequency. Thus, the dual blade detuned vibration test proposed by the present invention quickly evaluates the influence of the residual interblade vibration coupling effect through experiments, providing a simple and efficient technical approach for measuring the vibration frequency of approximately completely "independent" blades.

[0044] 3. Referring to the second blade detuned vibration test, sequentially repeat the blade detuned vibration test for all blades to obtain the corresponding isolated peak frequencies of the blade detuned vibration tests , and further calculate the differential distribution of the blade detuning frequencies: , where represents the average value of the isolated peak frequencies of all blade detuned vibration tests.

[0045] The rapid test identification method for the blade mistuning frequencies of the blisk structure proposed by the present invention is used to obtain the vibration frequency distribution of each "independent" blade in the blisk structure of an axial compressor with non-removable blades. The core of the blade mistuning vibration test is to attach the same mistuning mass at the same position of all non-test blades other than the blade to be tested currently, so as to greatly weaken the vibration coupling effect between this blade and its adjacent blades. Thus, the vibration of a single blade can be isolated from the blisk structure, and the vibration frequencies of each blade that are approximately completely "independent" can be directly and rapidly measured at a relatively low test economic and time cost. The dual blade mistuning vibration test aims to evaluate the influence of the residual inter-blade vibration coupling effect of the blisk on the test results of the "independent" blade vibration frequencies through experiments, and further improve the accuracy of the identification results of the blade random mistuning frequencies. This method has the advantages of high test efficiency, strong operability and high accuracy in identifying the blade mistuning frequencies, and is suitable for popularization and application in engineering practice.

[0046] Based on the same technical solution, the present invention also provides an electronic device, comprising:

[0047] a memory for storing a computer program;

[0048] a processor for implementing the steps of the above-mentioned rapid test identification method for the blade mistuning frequencies of the blisk structure when executing the computer program.

[0049] Based on the same technical solution, the present invention also provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the above-mentioned rapid test identification method for the blade mistuning frequencies of the blisk structure are implemented. The computer-readable storage medium may include various media such as USB flash drives, mobile hard disks, read-only memories (ROMs), random access memories (RAMs), magnetic disks or optical discs that can store program codes.

[0050] Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be completed by instructing relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above various methods. Among them, any reference to a memory, storage, database, or other medium used in the various embodiments provided in the present application can include non-volatile and / or volatile memories. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and Rambus dynamic RAM (RDRAM), etc.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A rapid test identification method for the mistuning frequency of blades in an integral bladed disk structure, characterized in that The specific steps are as follows: Step 1: Obtain the modal vibration modes and modal kinetic energy distributions of the blade finite element model of the integral bladed disk under clamped boundary conditions; Step 2: Select the detuning mass and attach it to the same positions of all non-test blades except the current blade to be tested to complete the detuning mass layout; Step 3: For the current blade to be tested, conduct the first blade detuning vibration test to obtain the first detuning vibration test frequency response function of a single measurement point of the current blade to be tested; Step 4: Extract the first isolated peak frequency from the first detuning vibration test frequency response function obtained in Step 3; Step 5: Based on the detuning mass layout scheme in Step 2, at the same positions of all non-test blades except the current blade to be tested, additionally add a set of detuning masses identical to the detuning masses selected in Step 2; Step 6: For the current blade to be tested, conduct the second blade detuning vibration test to obtain the second detuning vibration test frequency response function of the same measurement point of the current blade to be tested; Step 7: Extract the second isolated peak frequency from the second detuning vibration test frequency response function obtained in Step 6; Step 8: Compare the first and second isolated peak frequencies extracted in Step 4 and Step 7. If the difference between the first and second isolated peak frequencies is less than the set threshold, it is considered that the current blade to be tested reaches the ideal vibration decoupling state in the two blade detuning vibration tests, and the second isolated peak frequency is regarded as the detuning frequency of the current blade to be tested; otherwise, return to Step 2 to re-conduct the detuning mass layout until the current blade to be tested reaches the ideal vibration decoupling state in the two blade detuning vibration tests; Step 9: Repeat Steps 2 to 8 for all blades to obtain the detuning frequencies of each blade and complete the rapid experimental identification of the blade detuning frequencies of the integral bladed disk structure; 2. The method according to claim 1, characterized in that, Specifically, Step 1 is: Obtain the finite element model of the blade from the integral bladed disk design model, apply displacement constraints to its root, conduct simulation calculations in finite element software, and obtain the modal vibration modes and modal kinetic energy distributions of the target order of the clamped blade; 3. The method according to claim 1, wherein The selection and layout criteria of the detuning mass in Step 2 are: The size of the detuning mass can cover the region with the maximum kinetic energy density in the modal vibration of the target order of the blade; 4. The method according to claim 1, wherein In both Step 3 and Step 6, the hammering method is used to obtain the first and second detuning vibration test frequency response functions of a single measurement point of the current blade to be tested: Use a force hammer to apply excitation to the current blade to be tested at the set position, and at the same time use a non-contact Doppler laser vibrometer to pick up vibrations at the tip of the current blade to be tested; Based on the excitation signal applied by the force hammer and the velocity response signal obtained by the non-contact Doppler laser vibrometer, obtain the detuning vibration test frequency response function of the current blade to be tested; 5. The method according to claim 1, wherein This method further includes: Based on the detuning frequencies of each blade, calculate the frequency detuning amounts of each blade to obtain the differential distribution of blade detuning frequencies; 6. The method according to claim 5, characterized in that The frequency detuning amount of each blade is: ， In the formula, is the frequency detuning amount of blade j, is the detuned frequency of blade j, is the mean value of the detuned frequencies of all blades, and N is the total number of blades.

7. A rapid test identification device for the blade mistuning frequency of an integral bladed disk structure, characterized in that, It includes a soft pad and an integral bladed disk structure horizontally placed thereon, tuning masses set at the same positions of all non-test blades except the current blade to be tested, a force hammer, a non-contact Doppler laser vibrometer, and a data acquisition system; Apply excitation to the current blade under test at the set position using a force hammer, and at the same time, pick up the vibration at the tip of the current blade under test using a non-contact Doppler laser vibrometer. Based on the method described in any one of claims 1 to 6, the data acquisition system obtains the results of two blade detuning vibration tests for all blades, and completes the rapid experimental identification of the blade detuning frequencies of the overall bladed disk structure.

8. The device according to claim 7, characterized in that Each tuned mass consists of two identical magnets, and the two identical magnets are attached to the blade by attracting each other.

9. A computer-readable storage medium, characterized in that, A computer program is stored on the computable readable storage medium, and when the computer program is executed by a processor, the steps of the method described in any one of claims 1 to 6 are implemented.

10. An electronic device, characterized in that, Comprising: A memory for storing a computer program; A processor for implementing the steps of the method described in any one of claims 1 to 6 when executing the computer program.

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