A rotor blade modal testing method based on variable speed conditions

Abstract

This invention belongs to the field of aero-engine strength testing technology and provides a method for modal testing of rotor blades under variable speed conditions. The method includes: installing the rotor under test on a test platform, configuring a Doppler laser vibration measurement system and a speed sensor, and aligning the laser beam with multiple measurement points on the blade; increasing the speed at a constant rate of change, collecting vibration response signals and speed-time data at each measurement point to obtain a uniform speed reference signal set; increasing the speed at a non-constant rate of change along the same speed range, collecting variable speed vibration response signals and speed-time data at the measurement points; using the speed-time data under uniform speed conditions as a time-frequency reference, resampling and aligning the phase of the variable speed vibration signal to generate a steady-state signal; constructing a modal matrix and identifying modal parameters. This invention requires no external excitation or instantaneous speed reconstruction, has strong anti-interference capabilities, and can obtain modes under real variable speed conditions, making it suitable for dynamic characteristic testing of high-end rotating machinery such as aero-engines.

Description

Technical Field

[0001] This invention belongs to the field of aero-engine strength testing technology, and relates to rotating machinery vibration testing and structural dynamics analysis technology. Specifically, it relates to a rotor blade modal testing method based on variable speed conditions, which is applicable to the dynamic characteristic evaluation and health monitoring of blades in high-speed rotating machinery such as aero-engines, gas turbines, steam turbines, and wind turbines. Background Technology

[0002] With the rapid development of aero-engine equipment, the development cycle of aero-engines is constantly shortening, and the testing and evaluation requirements for their key structural components are becoming increasingly stringent. Currently, structural strength testing not only needs to cover a wider range of operating conditions but also requires testing environments that more closely resemble real-world operating conditions, with particular emphasis on high-precision characterization of dynamic characteristics. Against this backdrop, advanced measurement technology has become a core support for ensuring the accuracy of test data and the reliability of designs.

[0003] As a critical rotating component of aero-engines, the dynamic characteristics of rotor blades (such as modal frequencies, mode shapes, and damping) directly affect the vibration stability and structural safety of the entire engine. Traditional modal testing is mostly conducted under static or constant speed conditions, which makes it difficult to reflect the true dynamic response under actual variable speed conditions such as start-stop and acceleration. Furthermore, the vibration signals generated by the blades during speed changes are highly non-stationary, making conventional modal analysis methods difficult to apply directly. Consequently, existing testing methods cannot effectively obtain the modal parameters under actual operating conditions.

[0004] In recent years, modal testing of rotor blades in rotating conditions has become an important emerging direction in engine structural strength testing. Utilizing Doppler laser vibration measurement systems, high-precision vibration measurements can be achieved without added mass and under non-contact conditions, providing a technological possibility for variable-speed modal testing. However, how to effectively process non-stationary signals and accurately extract modal parameters under variable-speed conditions remains a key technical challenge that urgently needs to be overcome in the development of aero-engines. Therefore, developing a rotor blade modal testing method that is suitable for variable-speed conditions, highly accurate, and engineering-implementable has significant engineering application value. Summary of the Invention

[0005] To address the technical challenges in existing technologies, such as the inability to directly use non-stationary vibration signals for modal analysis, the difficulty in applying external excitations, and the ease with which order tracking can be lost, and to achieve high-precision identification of the modal parameters of rotor blades under real variable speed conditions, this invention discloses a rotor blade modal testing method based on variable speed conditions.

[0006] Specifically, the method includes the following steps:

[0007] S100. Install the rotor to be tested on the test platform and configure a Doppler laser vibration measurement system and a speed sensor, so that the laser beam of the Doppler laser vibration measurement system is aligned with multiple measurement points on the rotor blades of the rotor to be tested. S200: Control the rotor under test to accelerate at a constant speed change rate, and synchronously collect the vibration response signals and corresponding speed-time data of each measuring point to obtain a reference signal set under uniform speed conditions; S300: Control the rotor under test to increase its speed along the same speed range at a non-constant speed change rate, and synchronously collect the vibration response signal and corresponding speed-time data of each measuring point to obtain the test signal set under variable speed conditions, wherein the position of the collected measuring point corresponds completely to the position of the measuring point under uniform speed conditions. S400. For each measuring point, the rotational speed-time data of the measuring point under uniform speed conditions is used as the time-frequency reference. The vibration response signal of the measuring point under variable speed conditions is resampled and phase-aligned to generate a steady-state signal with the same phase and length. S500. Based on the steady-state signals from all measuring points, construct a modal matrix and perform modal parameter identification on the modal matrix to obtain the modal frequencies, mode shapes, and damping parameters of the rotor blades under variable speed conditions.

[0008] Furthermore, in step S100, the test platform is a T-slot cast iron base platform, the rotor to be tested is fixedly installed on the test platform by a support structure and bolts, and the speed sensor is a high-precision photoelectric encoder.

[0009] Furthermore, in step S100, the Doppler laser vibration measurement system is synchronized with the rotational motion of the rotor under test, and the synchronization accuracy of the two rotational speeds is less than 0.5°.

[0010] Furthermore, in step S100, the number of measurement points on the rotor blade is not less than (2N)², where N is the modal order to be identified.

[0011] Furthermore, in steps S200 and S300, the acceleration process under uniform speed conditions and variable speed conditions has the same starting speed and ending speed, and only the vibration response signal and the corresponding speed-time data of the acceleration stage are collected.

[0012] Furthermore, in step S200, the rotational speed-time data under uniform speed conditions constitute a monotonically increasing and reversible function, which is used to establish a unique mapping relationship between the vibration response signal under variable speed conditions and the uniform speed time axis.

[0013] Furthermore, in step S400, the resampling methods include: For any moment of the vibration response signal under variable speed conditions Find the moment in the speed-time data under uniform speed conditions where the instantaneous speeds are equal. The vibration response signal under the variable speed condition is in The amplitude at that point is mapped to Place.

[0014] Furthermore, in step S400, phase alignment uses the moment when the rotor under test passes through a preset mechanical angle mark as a global trigger reference to perform time zero-point correction on the signals of all measuring points.

[0015] Furthermore, step S400 also includes: performing a stationarity test on the stabilized signal; if the standard deviation of its short-time Fourier transform spectrum is less than a preset threshold, then the signal reconstruction is deemed valid.

[0016] Furthermore, the testing process of this invention requires no external excitation; the vibration response is generated by self-excited vibration caused by rotor imbalance force or pneumatic excitation. The acceleration process is executed by a servo motor drive system according to a preset speed curve. The speed control device supports setting parameters such as starting speed, ending speed, speed change rate, and running time, and can display the current speed in real time.

[0017] The rotor blade modal testing method of the present invention is based on the testing principle of uniform speed reference and variable speed reconstruction: by carrying out uniform speed increase and variable speed increase tests at the same measuring point, the stable speed-time relationship obtained in the uniform speed process is used as a high-precision time-frequency reference. The non-stationary vibration signal collected under variable speed conditions is time-axis mapped, resampled and phase-aligned to generate a steady-state signal set that can be used for standard modal analysis. Finally, the modal parameters (including natural frequency, mode shape and damping ratio) of the rotor blade under real variable speed conditions are identified with high precision.

[0018] Compared with the prior art, the present invention has at least the following advantages: 1. Traditional frequency domain modal analysis methods require stable signals. This invention converts non-stationary variable speed response into an equivalent steady-state signal through signal reconstruction, fundamentally solving the problem of mode identification failure under variable speed conditions. 2. Existing order tracking methods rely heavily on high-precision instantaneous speed estimation, which is prone to loss of lock when speed fluctuations are large or signal-to-noise ratio is low, easily leading to signal distortion. This invention uses the measured uniform speed curve as a benchmark, eliminating the need for complex speed reconstruction, resulting in stronger anti-interference capabilities and higher signal fidelity. 3. No external excitation is required; it is based entirely on rotor self-excited vibration (such as pneumatic excitation or unbalanced force), avoiding the installation difficulties of contact excitation devices in high temperature and high speed environments, and more closely reflecting the actual operating state of the engine. 4. This invention combines Doppler laser non-contact measurement, which has no additional mass influence, low testing cost and high accuracy. The obtained modal parameters can be directly used for rotor dynamics modeling, resonance margin assessment and structural optimization design, significantly improving the authenticity of structural strength tests and engineering guidance value.

[0019] In summary, this invention provides a reliable, efficient, and high-precision new method for variable speed modal testing of high-end rotating machinery such as aero-engines and gas turbines, filling the gap in existing testing technologies for characterizing real dynamic operating conditions. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the rotor blade modal testing system based on variable speed conditions. Figure 2 The flowchart shows a method for modal testing of rotor blades under variable speed conditions. The components include: 1. T-slot cast iron foundation platform; 2. Rotor to be tested; 3. Support bearing; 6. Doppler laser vibration measurement system; 7. Signal acquisition and processing device; and 8. Modal analysis software. Detailed Implementation

[0022] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0023] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features of the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] This invention discloses a method for testing the modal characteristics of rotor blades under variable speed conditions. This method is achieved by constructing a test principle based on the synergy of uniform speed reference and variable speed reconstruction. Specifically, uniform speed-increase and variable speed-increase tests are carried out at the same measuring point. The stable speed-time relationship obtained during the uniform speed process is used as a high-precision time-frequency reference. The non-stationary vibration signals collected under variable speed conditions are time-axis mapped, resampled, and phase-aligned to generate a steady-state signal set that can be used for standard modal analysis. Finally, high-precision identification of the modal parameters (including natural frequency, mode shape, and damping ratio) of rotor blades under real variable speed conditions is achieved.

[0025] Before performing modal testing on the rotor blades, a setup is constructed as follows: Figure 1 The test system shown includes: a T-slot cast iron base platform 1, a rotor under test 2, a support bearing 3, a servo motor drive system, a high-precision photoelectric encoder (sampling frequency 10 kHz), a Doppler laser vibration measurement system 6, a signal acquisition and processing device 7, and modal analysis software 8.

[0026] Specifically, see Figure 1 As shown, the method includes the following steps: S100. Install the rotor to be tested on the test platform and configure a Doppler laser vibration measurement system and a speed sensor, so that the laser beam of the Doppler laser vibration measurement system is aligned with multiple measurement points on the rotor blades of the rotor to be tested. S200: Control the rotor under test to accelerate at a constant speed change rate, and synchronously collect the vibration response signals and corresponding speed-time data of each measuring point to obtain a reference signal set under uniform speed conditions; S300: Control the rotor under test to increase its speed along the same speed range at a non-constant speed change rate, and synchronously collect the vibration response signal and corresponding speed-time data of each measuring point to obtain the test signal set under variable speed conditions, wherein the position of the collected measuring point corresponds completely to the position of the measuring point under uniform speed conditions. S400. For each measuring point, the rotational speed-time data of the measuring point under uniform speed conditions is used as the time-frequency reference. The vibration response signal of the measuring point under variable speed conditions is resampled and phase-aligned to generate a steady-state signal with the same phase and length. S500. Based on the steady-state signals from all measuring points, construct a modal matrix and perform modal parameter identification on the modal matrix to obtain the modal frequencies, mode shapes, and damping parameters of the rotor blades under variable speed conditions.

[0027] Further, in step S100, the test platform is a T-slot cast iron base platform, the rotor to be tested is fixedly installed on the test platform by a support structure and bolts, and the speed sensor is a high-precision photoelectric encoder, wherein the sampling frequency of the speed sensor is not less than 10 kHz, and it is used to generate speed-time data with a time resolution better than 0.1 ms.

[0028] The acceleration process is executed by the servo motor drive system according to the preset speed curve. The speed control device supports setting the starting speed, ending speed, speed change rate and running time parameters, and can display the current speed in real time.

[0029] Furthermore, in step S100, the Doppler laser vibration measurement system is synchronized with the rotational motion of the rotor under test, and the synchronization accuracy of the two rotational speeds is less than 0.5°.

[0030] Furthermore, in step S100, the number of measurement points on the rotor blade is not less than (2N)², where N is the modal order to be identified.

[0031] Furthermore, in steps S200 and S300, the acceleration process under uniform speed conditions and variable speed conditions has the same starting speed and ending speed, and only the vibration response signal and the corresponding speed-time data of the acceleration stage are collected.

[0032] Furthermore, in step S200, the rotational speed-time data under uniform speed conditions constitute a monotonically increasing and reversible function, which is used to establish a unique mapping relationship between the vibration response signal under variable speed conditions and the uniform speed time axis.

[0033] Furthermore, in step S400, the resampling methods include: For any moment of the vibration response signal under variable speed conditions Find the moment in the speed-time data under uniform speed conditions where the instantaneous speeds are equal. The vibration response signal under the variable speed condition is in The amplitude at that point is mapped to Place.

[0034] Furthermore, in step S400, phase alignment uses the moment when the rotor under test passes through a preset mechanical angle mark as a global trigger reference to perform time zero-point correction on the signals of all measuring points.

[0035] Furthermore, step S400 also includes: performing a stationarity test on the stabilized signal; if the standard deviation of its short-time Fourier transform spectrum is less than a preset threshold, then the signal reconstruction is deemed valid.

[0036] Furthermore, no external excitation is required during the testing process of this invention; the vibration response is generated by self-excited vibration caused by rotor imbalance force or pneumatic excitation.

[0037] This invention provides a detailed explanation of the rotor blade modal testing method based on variable speed conditions, using the example of setting 36 measuring points on the rotor blade: Step 1: Conduct a test under uniform velocity conditions The servo motor is set to accelerate from 3000 rpm to 9000 rpm at a constant rate (e.g., 100 rpm / s). Vibration response signals from each measuring point are collected simultaneously. and the angular displacement signal output by the encoder Rotation speed-time data are obtained through differential processing. Repeat the process 36 times, collecting data at one measurement point each time, to obtain a uniform velocity reference signal set.

[0038] Step 2: Perform a gear shift condition test The servo motor is programmed to accelerate within a preset nonlinear curve (e.g., initially fast then slow) over the same speed range (3000–9000 rpm). Vibration response signals from six identical measuring points are simultaneously acquired. and speed-time data , thus obtaining the variable speed test signal set.

[0039] Step 3: Reconstruct the vibration response signal of the measuring point under variable speed conditions. For each measurement point i, perform the following operation: 1) Through Construct a monotonically invertible function; 2) For any moment of the vibration response signal under variable speed conditions Solve , making = ) 3) Mapped to Generate steady-state signal ; 4) Using the moment when the rotor passes the 0° reflective mark as the trigger reference, for all... Time zero-point correction is performed, and data segments of equal length are extracted to form a steady-state signal set.

[0040] Step 4: Perform modality recognition The steady-state signal set was input into the LMS Test.Lab software, and the mode matrix was constructed and solved using the PolyMAX frequency domain method. The frequencies of the first three modes were obtained as follows: Order 1: 285 Hz (mode shape: bending); Order 2: 892 Hz (mode shape: torsion); Order 3: 1420 Hz (mode shape: composite); The damping ratios are all between 0.8% and 1.2%.

[0041] Verification has shown that the method of this invention improves recognition accuracy by 8% compared to traditional order tracking methods.

[0042] Obviously, those skilled in the art should understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Various modifications and variations of the embodiments of the present invention are possible for those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for modal testing of rotor blades based on variable speed conditions, characterized in that, include: The rotor to be tested is installed on the test platform, and a Doppler laser vibration measurement system and a speed sensor are configured so that the laser beam of the Doppler laser vibration measurement system is aligned with multiple measurement points on the rotor blades of the rotor to be tested. The rotor under test is controlled to accelerate at a constant rate of change of speed, and the vibration response signals and corresponding speed-time data of each measuring point are collected simultaneously to obtain a reference signal set under uniform speed conditions. The rotor under test is controlled to increase its speed along the same speed range at a non-constant speed change rate. Vibration response signals and corresponding speed-time data of each measuring point are collected simultaneously to obtain a set of test signals under variable speed conditions. The positions of the collected measuring points correspond completely to the positions of the measuring points under uniform speed conditions. For each measuring point, the rotational speed-time data of the measuring point under uniform speed conditions is used as the time-frequency reference. The vibration response signal of the measuring point under variable speed conditions is resampled and phase-aligned to generate a steady-state signal with the same phase and length. Based on the steady-state signals from all measurement points, a modal matrix is ​​constructed, and modal parameters are identified on the modal matrix to obtain the modal frequencies, mode shapes, and damping parameters of the rotor blades under variable speed conditions.

2. The rotor blade modal testing method based on variable speed conditions according to claim 1, characterized in that, The test platform is a T-slot cast iron base platform. The rotor to be tested is fixedly installed on the test platform by a support structure and bolts. The speed sensor is a high-precision photoelectric encoder.

3. The rotor blade modal testing method based on variable speed conditions according to claim 1, characterized in that, The Doppler laser vibration measurement system is synchronized with the rotational motion of the rotor under test, and the synchronization accuracy of the two speeds is less than 0.5°.

4. The rotor blade modal testing method based on variable speed conditions according to claim 1, characterized in that, The number of measurement points on the rotor blades is not less than (2N)², where N is the modal order to be identified.

5. The rotor blade modal testing method based on variable speed conditions according to claim 1, characterized in that, The acceleration process under both uniform and variable speed conditions has the same starting and ending speeds, and only the vibration response signal and corresponding speed-time data are collected during the acceleration phase.

6. The rotor blade modal testing method based on variable speed conditions according to claim 1, characterized in that, The rotational speed-time data under uniform speed conditions constitute a monotonically increasing and reversible function, which is used to establish a unique mapping relationship between the vibration response signal under variable speed conditions and the uniform speed time axis.

7. The rotor blade modal testing method based on variable speed conditions according to claim 1, characterized in that, Resampling methods include: For any moment of the vibration response signal under variable speed conditions Find the moment in the speed-time data under uniform speed conditions where the instantaneous speeds are equal. The vibration response signal under the variable speed condition is in The amplitude at that point is mapped to Place.

8. The rotor blade modal testing method based on variable speed conditions according to claim 1, characterized in that, Phase alignment uses the moment when the rotor under test passes through a preset mechanical angle mark as the global trigger reference to perform time zero-point correction on the signals of all measurement points.

9. The rotor blade modal testing method based on variable speed conditions according to claim 1, characterized in that, Also includes: The stationarity of the stabilized signal is tested. If the standard deviation of its short-time Fourier transform spectrum is less than a preset threshold, the signal reconstruction is deemed valid.

10. The rotor blade modal testing method based on variable speed conditions according to claim 1, characterized in that, No external excitation is required during the test; the vibration response is generated by the self-excited vibration caused by rotor imbalance force or aerodynamic excitation. The acceleration process is executed by the servo motor drive system according to the preset speed curve. The speed control device supports setting the starting speed, ending speed, speed change rate and running time parameters, and can display the current speed in real time.

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