A method for acoustic mode analysis of a rotary acoustic test harrow pipe

Abstract

This application provides a method for analyzing the acoustic modes of a rotating acoustic rake pipeline, belonging to the field of aero-engine technology. The method includes: calibrating the wirelessly transmitted acoustic signal collected by the acoustic rake based on a standard acoustic signal to obtain the amplitude difference of the acoustic signal collected by the acoustic rake before and after wireless transmission, and the acoustic rake's fidelity transmission signal under wireless transmission conditions; conducting acoustic mode testing based on the acoustic rake parameters, microphone parameters, and typical parameters of the fan pipeline test piece under engineering conditions to obtain the acoustic signal characteristics of the acoustic rake's fidelity signal after wireless transmission, and obtaining the acoustic mode sound pressure amplitude and mode frequency within the pipeline based on mode decomposition theory; correcting the acoustic mode amplitude within the pipeline based on the acoustic signal amplitude difference to obtain the amplitude-corrected acoustic mode sound pressure amplitude; performing mode frequency correction under the Doppler effect based on the rotation speed of the acoustic rake to obtain the frequency-corrected mode frequency deviation; and finally obtaining the pipeline acoustic mode propagation characteristics.

Description

Technical Field

[0001] This application belongs to the field of aero-engine testing technology, and specifically relates to a method for acoustic modal analysis of a rotating acoustic test rake pipe. Background Technology

[0002] Front-transmission noise from the fan in aero-engines is a major noise source for high-bypass-ratio aero-engines. To address the need for high-order acoustic mode identification of the fan, a rotating acoustic test rake is typically used to test the acoustic modes of the fan duct. Compared to other existing acoustic mode testing methods, the rotating acoustic test rake can obtain all modal information at once, offering advantages such as high testing efficiency, fewer microphone measurement points, and reliable accuracy.

[0003] The rotary acoustic test rake performs unified signal conditioning on noise, vibration, and concentricity test signals to ensure a consistent measurement range and unified transmission of the acoustic test rake test signals. The acquisition module collects different parameter signals and performs A / D (analog-to-digital) conversion. The converted digital signals are transmitted to the control module. The signals collected by the acoustic test rake need to be wirelessly transmitted to the local acquisition terminal to obtain the internal noise of the pipeline and the operating status parameters of the acoustic test rake. The local rotational speed signal of the test piece and the frequency converter control signal of the acoustic test rake are connected to the local acquisition terminal via wired transmission. Based on the local data acquisition unit, the operating and test parameters of the acoustic test rake and the test piece are obtained.

[0004] To achieve quantitative identification of high-order acoustic modal parameters of fans, it is necessary to ensure that the wireless transmission data has high reliability and fidelity. Due to the characteristics of fan noise bandwidth and high sampling rate requirements, the existing high sampling rate data will cause distortion of noise signal transmission during signal transmission. Furthermore, the acoustic test rake will generate Doppler effect during relative rotation, causing frequency shift of the noise analysis signal, which in turn affects the accuracy of high-order acoustic modal analysis. Summary of the Invention

[0005] The purpose of this application is to provide a method for analyzing the acoustic modes of a rotating acoustic test rake pipe, in order to solve or mitigate at least one of the problems in the prior art.

[0006] The technical solution of this application is: a method for modal analysis of a rotating acoustic test rake pipeline, comprising:

[0007] Step S10: The acoustic signal of wireless transmission collected by the acoustic rake is calibrated based on the standard acoustic signal to obtain the amplitude difference of the acoustic signal collected by the acoustic rake before and after wireless transmission. The acoustic signal of the acoustic rake after wireless transmission is corrected according to the amplitude difference of the acoustic signal to obtain the acoustic rake fidelity transmission signal under wireless transmission conditions.

[0008] Step S20: Based on the installation position of the acoustic rake, the rotation speed of the acoustic rake, the number of measurement points of the microphone, and the typical parameters of the fan duct test piece under engineering conditions, conduct acoustic modal testing, obtain the acoustic signal characteristics of the acoustic rake fidelity signal after wireless transmission, and obtain the acoustic modal sound pressure amplitude and modal frequency in the duct based on modal decomposition theory.

[0009] Step S30: Correct the acoustic mode amplitude in the pipe based on the difference in acoustic signal amplitude, and then obtain the acoustic mode sound pressure amplitude after amplitude correction;

[0010] Modal frequency correction under the Doppler effect is carried out based on the rotation speed of the acoustic rake to obtain the frequency-corrected modal frequency deviation.

[0011] Based on the amplitude-corrected modal sound pressure amplitude and the frequency-corrected modal frequency deviation, the pipe acoustic mode propagation characteristics under real conditions of the fan pipe test specimen during wireless transmission are obtained.

[0012] In at least one embodiment of this application, step S10 specifically includes the following process:

[0013] Step S11: Under the static condition of the acoustic rake, the acoustic horn is used as the sound source of the standard acoustic signal for signal excitation, and the acoustic signal collected by the acoustic rake before wireless transmission and the acoustic signal received by the local device after wireless transmission are obtained.

[0014] Step S12: Compare the noise spectrum characteristics of the acoustic signal collected by the acoustic rake before wireless transmission with the acoustic signal received by the local device after wireless transmission in 1 / 3 octave band, and obtain the amplitude difference of the acoustic signal collected by the acoustic rake before and after wireless transmission.

[0015] Step S13: Determine whether the difference in acoustic signal amplitude exceeds a threshold. If it does not exceed the threshold, the acoustic signal received by the local device after wireless transmission is the acoustic signal with high fidelity transmission under wireless transmission conditions. If it exceeds the threshold, the acoustic signal received by the local device after wireless transmission is corrected.

[0016] Step S14: When the acoustic signal received by the local device after wireless transmission needs to be corrected, a numerical fitting method is used to fit the amplitude difference of the acoustic signal within a predetermined frequency range to obtain an amplitude difference curve. Based on the amplitude difference curve, the acoustic signal received by the local device after wireless transmission is processed to obtain an acoustic high-fidelity transmission signal under wireless transmission conditions.

[0017] In at least one embodiment of this application, it further includes:

[0018] Step S15: Under the dynamic rotation state of the acoustic rake, repeat steps S11 to S14 to obtain the noise spectrum of the acoustic rake at the same position under the actual working speed. Compare the noise spectrum under the rotation state of the acoustic rake with the noise spectrum after wireless transmission of the acoustic rake to verify and optimize the developed noise broadband amplitude correction, thereby completing the optimization of the high-fidelity transmission signal of the acoustic rake.

[0019] In at least one embodiment of this application, the threshold for the difference in acoustic signal amplitude is 0.2 dB.

[0020] In at least one embodiment of this application, the predetermined frequency range is 160Hz to 10kHz.

[0021] In at least one embodiment of this application, the amplitude of the modal sound pressure p after amplitude correction satisfies:

[0022]

[0023] Where θ is the spatial angular position of the fixed pressure measuring point. , Let t be the rotational speed of the acoustic rake, and t be the time.

[0024] ω is the angular velocity of the rotating acoustic mode.

[0025] m is the number of circumferential modes. s is the harmonic number, B is the number of rotor blades, k is the speed-related parameter, and V is the number of stator blades;

[0026] M is the modal order. Let be the amplitude of the acoustic mode, e be the natural constant, and i be the imaginary part.

[0027] In at least one embodiment of this application, the modal frequency deviation f m for: .

[0028] The rotary acoustic test rake pipeline acoustic modal analysis method provided in this application can eliminate signal deviation caused by wireless transmission by performing high-fidelity data transmission correction of the acoustic test rake, and realize high-precision signal transmission and acquisition; by performing Doppler frequency shift correction of the fan noise source, the acoustic modal correction can be realized to identify the modal frequency of the acoustic rake in the rotating state. Attached Figure Description

[0029] To more clearly illustrate the technical solutions provided in this application, the accompanying drawings will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application.

[0030] Figure 1 This is a schematic diagram of a rotating acoustic test rake and a fan duct test piece.

[0031] Figure 2 This is a schematic diagram showing the location of the microphone inside the acoustic rake.

[0032] Figure 3 This is a schematic diagram of the rotary acoustic test rake pipe acoustic modal analysis method of this application. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings.

[0034] like Figure 1 and Figure 2 The diagram shows a rotary acoustic test rake. The fan duct test piece 1 includes a pipe 11 and a lip 12. The pipe 11 is a circular tube structure, simulating the internal flow channel of a fan. The lip 12 is located at the front end of the pipe 11, simulating the fan inlet. The rotary acoustic test rake 2 includes a rotary drive mechanism 21 and an acoustic rake 22. The rotary drive mechanism 21 is located at the front end of the pipe 11 and drives the acoustic rake 22 to rotate circumferentially. The acoustic rake 22 has an arc-shaped portion adapted to the lip 12. Multiple radially arranged microphones 221 (also called microphones) are located at the end of this arc-shaped portion facing the pipe 11, used to acquire sound pressure signals within the fan duct test piece 1. During the pipe acoustic modal testing process, the rotary drive mechanism 21 drives the acoustic rake 22 to rotate, and the sensors 221 on the acoustic rake 22 collect the acoustic modal characteristics of the fan duct test piece 1. However, since the acoustic rake 22 is rotating, the acoustic modal characteristic parameters it collects need to be transmitted wirelessly to a local acquisition device for quantitative analysis of the high-order acoustic modes of the fan pipe based on the rotating acoustic test rake. Existing high-sampling-rate signal data can lead to distortion in noise signal transmission during wireless transmission, and the Doppler effect generated by the relative rotation of the acoustic test rake causes frequency shifts in the noise analysis signal.

[0035] Therefore, in order to ensure the high-fidelity transmission of data collected by the acoustic rake during wireless transmission, and to address the impact of the Doppler effect generated by the fan noise source on the accuracy of high-order acoustic modal analysis of pipelines, this application provides a method for acoustic modal analysis of pipelines using a rotating acoustic test rake.

[0036] like Figure 3 As shown, the phase-locked data transmission method for rotary acoustic test rakes provided in this application includes the following process:

[0037] Step S10: The acoustic signal of wireless transmission collected by the acoustic rake 22 is calibrated based on the standard acoustic signal to obtain the amplitude difference of the acoustic signal collected by the acoustic rake before and after wireless transmission. The acoustic signal of the acoustic rake after wireless transmission is corrected according to the amplitude difference of the acoustic signal, so as to obtain the acoustic rake high-fidelity transmission signal under wireless transmission conditions.

[0038] A standard acoustic signal is a standardized sound signal with defined frequency, amplitude, waveform, or time characteristics. It can be emitted through an acoustic speaker and used to calibrate the sound signal collected by the acoustic rake 22. For example, the frequency of the standard acoustic signal can be 10Hz, 100Hz, 250Hz, 1kHz, etc.

[0039] The signals acquired by the acoustic rake 22 can be calibrated and corrected using standard acoustic signals. The specific steps include:

[0040] Step S11: Under the static condition of the acoustic rake 22, the acoustic horn is used as the sound source of the standard acoustic signal to excite the signal, and the acoustic signal collected by the acoustic rake 22 before wireless transmission and the acoustic signal received by the local device after wireless transmission are obtained. The acoustic signal is the acoustic signal of the acoustic rake 22 after wireless transmission.

[0041] In a preferred embodiment of this application, when an acoustic horn is used as the excitation sound source, by controlling the sound emission state of the excitation sound source, the noise signal collected by the acoustic rake 22 under noise excitation within a predetermined frequency range and the acoustic signal after wireless transmission can be recorded. For example, the predetermined frequency range can be 160Hz to 10kHz.

[0042] Step S12: Compare the acoustic signal collected by the acoustic rake 22 before wireless transmission and the acoustic signal received by the local device after wireless transmission using a noise spectrum feature analysis at 1 / 3 octave band to obtain the amplitude difference of the acoustic signal collected by the acoustic rake 22 before and after wireless transmission.

[0043] Step S13: Determine whether the difference in acoustic signal amplitude obtained in step S12 exceeds a threshold. If it does not exceed the threshold, the acoustic signal received by the local device after wireless transmission does not need to be corrected, and the acoustic signal received by the local device is the acoustic signal with high fidelity transmission under wireless transmission conditions. If it exceeds the threshold, the acoustic signal received by the local device after wireless transmission needs to be corrected.

[0044] In some embodiments of this application, the threshold for the difference in acoustic signal amplitude can be 0.2dB. If the amplitude difference is within 0.2dB, it can be considered that the acoustic signal after wireless transmission is in good fidelity with the acoustic signal collected by the acoustic rake 22. If the amplitude difference exceeds 0.2dB, it is considered that the acoustic signal after wireless output is not in good fidelity with the acoustic signal collected by the acoustic rake 22, and the acoustic signal after wireless transmission needs to be corrected.

[0045] Step S14: When the acoustic signal received by the local device after wireless transmission needs to be corrected, the amplitude difference of the acoustic signal in the frequency range of 160Hz to 10kHz is fitted by a numerical fitting method to obtain an amplitude difference curve. Based on the amplitude difference curve, the acoustic signal received by the local device after wireless transmission is processed to obtain the acoustic rake 22 high-fidelity transmission signal under wireless transmission conditions.

[0046] In this application, the calibration process further includes:

[0047] Step S15: Under the dynamic rotation state of the acoustic rake 22, repeat the above process to obtain the noise spectrum of the acoustic rake 22 at the same position under the actual working speed, compare it with the noise spectrum after wireless transmission of the acoustic rake 22, verify and optimize the developed noise broadband amplitude correction, thereby completing the optimization of the high-fidelity transmission signal of the acoustic rake.

[0048] Step S20: Based on the installation position of the acoustic rake 22, the rotation speed of the acoustic rake 22, the number of measuring points of the microphone 221, and the typical parameters of the fan duct test piece 1 under engineering conditions, acoustic modal testing is carried out to obtain the acoustic signal characteristics of the acoustic rake's high-fidelity transmission signal after wireless transmission, and the acoustic modal sound pressure amplitude and modal frequency in the duct are obtained based on modal decomposition theory.

[0049] Typical parameters for fan duct test piece 1 include the number of rotor and stator blades and fan speed.

[0050] Step S30: Based on the difference in acoustic signal amplitude in step S10, the acoustic mode amplitude in the pipe in step S20 is corrected to obtain the amplitude-corrected acoustic mode sound pressure amplitude; the mode frequency is corrected under the Doppler effect according to the rotation speed of the acoustic rake 22 to obtain the frequency-corrected mode frequency deviation; based on the above amplitude-corrected acoustic mode sound pressure amplitude and frequency-corrected mode frequency deviation, the pipe acoustic mode propagation characteristics under real conditions of the fan pipe test piece 1 during wireless transmission are obtained.

[0051] This application evaluates the Doppler effect of the acoustic rake during the acoustic modal testing of the fan duct using a rotating acoustic test rake 2 by analyzing the mechanism and impact of the Doppler effect of the moving sound source, and provides a method for establishing high-precision data analysis and correction for engineering environments.

[0052] The generation mechanism of the circumferential rotating pressure mode is that the pressure field in the cylindrical tube containing the axial fan consists of rotating modes with different maximum and minimum values, which can be expressed as a superposition of periodic functions: ;

[0053] In the formula, m is the number of circumferential modes, s is the number of harmonics, B is the number of rotor blades, k is a speed-related parameter (e.g., speed ratio, which is a positive integer), and V is the number of stator blades.

[0054] The sound pressure p caused by all acoustic modes at a fixed pressure measuring point in pipe 11 is:

[0055]

[0056] In the formula, M is the modal order. Let θ be the amplitude of the acoustic mode, e be the natural constant, i be the imaginary part, θ be the spatial angular position of the fixed pressure measuring point, ω be the angular velocity of the rotating acoustic mode, and t be the time.

[0057] When the acoustic rake 22 rotates circumferentially, the acoustic modal sound pressure p collected by the acoustic rake 22 inside the pipe satisfies the following:

[0058] ,

[0059] In the formula, The rotational speed of the acoustic rake 22 , where υ is the speed ratio, and the typical value of the speed ratio υ is between 100 and 250.

[0060] The acoustic signal amplitude difference curve obtained in step S14 can be used to analyze the acoustic mode amplitude. Corrections are made, and the amplitude of the corrected acoustic modes is used. Substituting these values ​​into the acoustic modal sound pressure formula yields the amplitude of the acoustic modal sound pressure after amplitude correction.

[0061] Modal frequency deviation f m for: .

[0062] As can be seen from the above formula, the modal frequency is deflected from the fundamental frequency. The amount of deflection is proportional to the circumferential mode number m and inversely proportional to the fan speed ratio υ. It should be noted that when the speed of the acoustic rake 22 is in the same direction as the rotor, the frequency of the mode number (+m) rotating in the same direction decreases, while the frequency of the mode number (-m) rotating in the opposite direction shifts to a higher frequency direction. The plane wave (m=0) falls on the harmonic frequency of the fan.

[0063] The acoustic modal analysis method for rotating acoustic test rake pipelines provided in this application eliminates signal deviations caused by wireless transmission by performing high-fidelity data transmission correction for the acoustic test rake, achieving high-precision signal transmission and acquisition. Furthermore, by applying Doppler frequency shift correction to the fan noise source, the method corrects the identification of modal frequencies during the rotation of the acoustic rake. Based on this application, the method establishes the accuracy of acoustic modal analysis for rotating acoustic test rake pipelines in engineering environments, enabling quantitative assessment of fan-front noise, supporting the verification of integrated aeroacoustic design and noise reduction design for engines, and promoting the development of civil aircraft and transport aircraft models in China.

[0064] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for modal analysis of a rotating acoustic testing rake pipe, characterized in that, include: Step S10: The acoustic signal collected by the acoustic rake for wireless transmission is calibrated based on a standard acoustic signal to obtain the amplitude difference of the acoustic signal collected by the acoustic rake before and after wireless transmission. The acoustic signal of the acoustic rake after wireless transmission is corrected according to the amplitude difference to obtain the acoustic rake's high-fidelity transmission signal under wireless transmission conditions. The specific process includes: Step S11: Under the static condition of the acoustic rake, the acoustic horn is used as the sound source of the standard acoustic signal for signal excitation, and the acoustic signal collected by the acoustic rake before wireless transmission and the acoustic signal received by the local device after wireless transmission are obtained. Step S12: Compare the noise spectrum characteristics of the acoustic signal collected by the acoustic rake before wireless transmission with the acoustic signal received by the local device after wireless transmission in 1 / 3 octave band, and obtain the amplitude difference of the acoustic signal collected by the acoustic rake before and after wireless transmission. Step S13: Determine whether the difference in acoustic signal amplitude exceeds a threshold. If it does not exceed the threshold, the acoustic signal received by the local device after wireless transmission is the acoustic signal with high fidelity transmission under wireless transmission conditions. If it exceeds the threshold, the acoustic signal received by the local device after wireless transmission is corrected. Step S14: When the acoustic signal received by the local device after wireless transmission needs to be corrected, the amplitude difference of the acoustic signal within a predetermined frequency range is fitted using a numerical fitting method to obtain an amplitude difference curve. Based on the amplitude difference curve, the acoustic signal received by the local device after wireless transmission is processed to obtain an acoustic high-fidelity transmission signal under wireless transmission conditions. Step S20: Based on the installation position of the acoustic rake, the rotation speed of the acoustic rake, the number of measurement points of the microphone, and the typical parameters of the fan duct test piece under engineering conditions, conduct acoustic modal testing, obtain the acoustic signal characteristics of the acoustic rake fidelity signal after wireless transmission, and obtain the acoustic modal sound pressure amplitude and modal frequency in the duct based on modal decomposition theory. Step S30: Correct the acoustic mode amplitude in the pipe based on the difference in acoustic signal amplitude, and then obtain the acoustic mode sound pressure amplitude after amplitude correction; Modal frequency correction under the Doppler effect is carried out based on the rotation speed of the acoustic rake to obtain the frequency-corrected modal frequency deviation. Based on the amplitude-corrected acoustic modal sound pressure amplitude and the frequency-corrected modal frequency deviation, the propagation characteristics of the pipe acoustic modes under real conditions of the fan pipe test specimen during wireless transmission are obtained.

2. The method for modal analysis of a rotating acoustic test rake pipe as described in claim 1, characterized in that, Also includes: Step S15: Under the dynamic rotation state of the acoustic rake, repeat steps S11 to S14 to obtain the noise spectrum of the acoustic rake at the same position under the actual working speed. Compare the noise spectrum under the rotation state of the acoustic rake with the noise spectrum after wireless transmission of the acoustic rake to verify and optimize the developed noise broadband amplitude correction, thereby completing the optimization of the high-fidelity transmission signal of the acoustic rake.

3. The method for modal analysis of a rotating acoustic test rake pipe as described in claim 1, characterized in that, The threshold for the difference in acoustic signal amplitude is 0.2 dB.

4. The method for modal analysis of a rotating acoustic test rake pipe as described in claim 1, characterized in that, The predetermined frequency range is 160Hz to 10kHz.

5. The method for modal analysis of a pipe acoustic test rake as described in any one of claims 1 to 4, characterized in that, The amplitude of the modal sound pressure p after amplitude correction satisfies: Where θ is the spatial angular position of the fixed pressure measuring point. , Let t be the rotational speed of the acoustic rake, and t be the time. ω is the angular velocity of the rotating acoustic mode. m is the number of circumferential modes. s is the harmonic number, B is the number of rotor blades, k is the speed-related parameter, and V is the number of stator blades; M is the modal order. Let be the amplitude of the acoustic mode, e be the natural constant, and i be the imaginary part.

6. The method for modal analysis of a pipe acoustic test rake as described in claim 5, characterized in that, The modal frequency deviation f m for: .

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