A device for simulating the acoustic modes of fan ducts under incoming flow conditions

Abstract

A fan duct acoustic modal simulation device under incoming flow conditions includes a simplified engine model, a loudspeaker, an acoustic liner installation area, a fairing, a microphone, a nacelle shell, an airfoil support, an airfoil support sheet, a sound control system and a PXi acquisition system. The simplified engine model is connected to the nacelle shell through the airfoil support sheet. In front of the airfoil support sheet, a plurality of loudspeakers are installed at certain intervals along the circumference of the nacelle shell. In front of the loudspeaker, an acoustic liner installation area is provided in the nacelle shell for installing a noise-absorbing acoustic liner test sample. Near the lip of the nacelle shell, a plurality of microphones are fixedly installed at equal distances along the inner wall of the nacelle shell. The present invention uses an electroacoustic source signal to simulate fan noise, thereby meeting the fan forward noise measurement requirements under incoming flow conditions and measuring the noise reduction performance of the acoustic liner under different wind speeds. Compared with the traditional flow tube test method, it is closer to practical application and improves test efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of noise measurement, and in particular relates to a fan duct acoustic mode simulation device under an incoming flow condition. Background Art

[0002] When studying the noise reduction of aircraft engine fan noise, it is crucial to study how to measure the fan noise mode transmitted from the front of the engine. At present, most of the common devices for measuring duct sound modes at home and abroad are based on acoustic theory research in the state of no incoming flow, and most of them adopt cylindrical duct structures, lacking comprehensive consideration of aerodynamics and acoustics.

[0003] In the prior art, the method for measuring the acoustic mode of the engine duct generally adopts the method of arranging an annular duct device at the inlet and outlet of the engine duct, conducting an anechoic chamber test facing the center of the engine, or using a motor-driven engine model in the anechoic chamber to perform scanning rake sensor measurement. For the above methods, when testing under the condition of incoming flow, there is interference flow influence, or unnecessary noise sources are added. Therefore, a technical solution is needed that can be applied to wind tunnel tests to measure the acoustic mode parameters of the nacelle structure duct. Summary of the invention

[0004] In view of the above shortcomings, the present invention provides a fan duct acoustic mode simulation device under incoming flow conditions, which utilizes electroacoustic source signals to simulate fan noise, thereby meeting the fan forward noise measurement requirements under incoming flow conditions and measuring the noise reduction performance of the sound lining under different wind speeds.

[0005] The technical solution adopted by the present invention is: a fan duct acoustic modal simulation device under incoming flow conditions, including a simplified engine model, a speaker, an acoustic liner installation area, a fairing, a microphone, a nacelle shell, an airfoil support, an airfoil support sheet, a sound control system and a PXi acquisition system.

[0006] The simplified engine model is connected to the nacelle shell through an airfoil support piece, and the nacelle shell is connected to the acoustic wind tunnel airfoil support device through an airfoil support. The airfoil support is used to support and fix the entire nacelle model and reduce the impact of aerodynamic noise caused by interference with incoming flow. The airfoil support is vertically fixedly connected to the wind tunnel test bench, so that the strength of the nacelle model is stable during the wind tunnel test. The airfoil support piece adopts an airfoil structure to reduce the impact of aerodynamic noise inside the nacelle model on airflow interference.

[0007] In front of the airfoil support sheet, a plurality of loudspeakers are installed at regular intervals along the circumference of the nacelle shell, and the phase and amplitude of the loudspeakers are controlled by a sound control system to synthesize and simulate the circumferential sound mode generated by the fan, thereby simulating the sound mode of the duct;

[0008] In front of the speaker, a sound liner installation area is provided in the nacelle shell for installing the anechoic liner test sample. The sound absorption hole of the sound liner is flush with the inner wall surface of the nacelle shell. When measuring without the sound liner, it is sealed with a cover plate. The sound absorption hole of the anechoic liner test sample is flush with the inner wall surface of the nacelle shell.

[0009] In front of the acoustic liner installation area, near the lip of the nacelle shell, a plurality of microphones are fixedly installed at equal intervals along the inner wall of the nacelle shell;

[0010] A fairing is provided outside the nacelle shell, including the protruding parts of the speaker and the microphone, to prevent the speaker and the sensor from being exposed to the flow field. The connecting cables are all gathered in the fairing and passed through the airfoil support to be respectively connected to the external sound control system and the PXi acquisition system electrical signal;

[0011] The sound control system is installed with an acoustic mode simulation control program for setting the amplitude and phase of each speaker. Finally, the speaker emits a high-intensity plane wave, which synthesizes the fan sound mode axially in the nacelle shell and transmits it to the downstream of the flow field. The PXi acquisition system collects time domain signals through multiple microphones, and measures the sound pressure fluctuation amount of the measurement point in the state without sound lining and in the state with sound lining. After decomposition by the spatial Fourier method, the main mode amplitude and circumferential mode order are obtained, and the sound absorption effect of the sound lining under a specific mode is obtained by comparison.

[0012] In order to make the sound pressure level meet the test standards, a through hole is designed on the surface of the nacelle shell to form a waveguide with equal cross-section. Since the sound generation capacity of the speaker is concentrated at the throat, the size of the waveguide is consistent with the throat diameter of the speaker. The sound amplitude of each speaker is consistent, and the phase difference of adjacent speakers is the same, so that the sound generation requirements of the simulated fan duct sound mode can be met.

[0013] Beneficial effects and advantages of the present invention: The present invention uses an electroacoustic source signal to simulate fan noise, thereby meeting the requirements for measuring fan forward noise under incoming flow conditions, and measuring the noise reduction performance of the acoustic liner under different wind speeds. The device can be used to test the sound absorption effect of the acoustic liner on engine fan noise under incoming flow conditions, which is closer to practical application than the traditional flow tube test method, and also avoids the problem of low efficiency of the acoustic liner test when the real engine is installed, thus improving the test efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 4 is a cross-sectional view of a fan duct acoustic mode simulation device under an incoming flow condition according to an embodiment of the present invention.

[0015] Figure 2 yes Figure 1 Cross-sectional view of the speaker location at section A.

[0016] Figure 3 It is a schematic diagram of the principle of controlling the sound of a loudspeaker by a sound source simulation device.

[0017] Figure 4 It is the flow chart of the fan duct acoustic modal simulation control program. DETAILED DESCRIPTION

[0018] The present invention is further described below with reference to the accompanying drawings:

[0019] Example 1

[0020] like Figure 1-2 As shown, a fan duct acoustic mode simulation device under incoming flow conditions includes an engine simplified model 1, a speaker 2, an acoustic liner installation area 3, a fairing 4, a microphone 5, a nacelle shell 6, an airfoil support 7, an airfoil support sheet 8, a sound control system and a PXi acquisition system. The engine simplified model 1 is connected to the nacelle shell 6 through the airfoil support sheet 8, and the nacelle shell 6 is connected to the acoustic wind tunnel airfoil support device through the airfoil support 7; in front of the airfoil support sheet 8, a plurality of speakers 2 are installed on the nacelle shell 6 along the circumference at a certain interval, and the phase and amplitude thereof are controlled by the sound control system to synthesize and simulate the circumferential acoustic mode generated by the fan, so as to realize the simulation of the duct acoustic mode;

[0021] A sound liner installation area 3 is provided in the nacelle shell 6 in front of the loudspeaker 2 in the axial direction, and is used to install a sound liner test sample to measure the noise reduction performance of the sound liner under different wind speeds; when measuring a sound liner test sample without a sound liner, it is sealed with a cover plate;

[0022] The nacelle shell is divided into two sections at the acoustic liner installation section to facilitate the installation of the acoustic liner, and is connected by rivets. The nacelle shell is connected to the fairing by threads.

[0023] Axially, in front of the acoustic liner installation area, near the lip of the nacelle shell 6, a plurality of microphones 5 are fixedly installed at equal intervals along the inner wall of the nacelle shell 6;

[0024] A fairing 4 is provided outside the nacelle shell 6, including the protruding parts of the speaker 2 and the microphone 5. The connecting cables are all gathered in the fairing 4 and pass through the airfoil support 7 to be connected to the external sound control system and the PXi acquisition system electrical signal respectively;

[0025] The sound control system is installed with an acoustic mode simulation control program, which is used to set the amplitude and phase of each speaker 2. Finally, the speaker 2 emits a high-intensity plane wave, which synthesizes the fan sound mode axially in the nacelle shell and transmits it to the downstream of the flow field; the PXi acquisition system collects time domain signals through multiple microphones, and measures the sound pressure fluctuation amount of the measurement point in the state without sound lining and in the state with sound lining respectively. After decomposition by the spatial Fourier method, the main mode amplitude and circumferential mode order are obtained, and the sound absorption effect of the sound lining under a specific mode is obtained by comparison.

[0026] A plurality of through holes are opened on the surface of the nacelle shell 6 , and the through holes serve as a waveguide 10 of uniform cross-section, and the size of the waveguide is consistent with the throat diameter 9 of the speaker 2 .

[0027] The sound absorption holes of the silencing liner test sample are flush with the inner wall surface of the nacelle shell 6 .

[0028] The fairing is annular and slightly larger than the outer diameter of the nacelle shell, so that the speaker and sensor can be wrapped inside. By arranging the speaker near the airfoil support piece and using the principle of fan duct acoustic modal synthesis, the sound source of the simulated fan forward noise can be controlled; by arranging the sensor near the lip, the principle of spatial Fourier decomposition can be used to detect the circumferential acoustic modal order and sound pressure level of the fan forward noise after being absorbed by the acoustic liner.

[0029] Figure 3 This is a schematic diagram of controlling the sound of the speaker. The sound control system uses an industrial computer to control the sound card 13 to output a voltage signal to the driver audio processor 12. The driver audio processor controls four power amplifiers 11, and each power amplifier 11 controls four speakers 2 to sound. The sound waves emitted by each speaker 2 are regarded as plane waves. Each speaker 2 has two frequency division lines to control the sound, and can emit medium and low frequency sound waves. The entire cabinet is placed outside the wind tunnel flow field.

[0030] Figure 4 This is a flow chart of the fan duct acoustic modal simulation control program. This program is developed using the Labview graphical programming language and has a GUI interface. It can input the circumferential modal order m, select the corresponding signal output channel, sample the clock and determine the sampling frequency and maximum voltage amplitude, determine the specific drive signal for each speaker, and calibrate and compensate the amplitude and phase of the speakers one by one. This program should be used in conjunction with NI data controllers, power amplifiers, speakers and other hardware devices. The program is divided into four modules according to its function:

[0031] Module 1: Signal parameter setting. In this module, the corresponding signal output channel, sampling clock, sampling frequency and maximum voltage amplitude are selected.

[0032] Module 2: Synthetic mode setting. In this module, the order m, frequency and corresponding intensity of the synthetic circumferential mode need to be specified. The total number of speakers is set. The signal phase difference between two adjacent speakers can be determined by the modal order entered here. Then, according to the set signal frequency and signal amplitude, the specific driving signal of each speaker can be determined. It passes through the power amplifier to drive the speaker to sound.

[0033] Module 3: Speaker calibration parameter input. Since there are differences between speakers, they cannot perfectly respond to driving signals, so the amplitude and phase difference of the speaker array cannot be guaranteed to be completely consistent, so calibration and compensation may be required. If the speaker quality is good, the amplitude and phase difference generally have little effect on the quality of the final synthesized mode, and no calibration is required. In this case, the corresponding supplementary constant can be set to zero.

[0034] Module 4: Signal display output. This mode is used to display the final output signal, making it easier for users to view and confirm the signal status and troubleshoot possible faults.

[0035] The acoustic modal simulation control program is used to input the circumferential modal order m, select the corresponding signal output channel, sample the clock and determine the sampling frequency and maximum voltage amplitude, determine the specific driving signal for each speaker, and calibrate and compensate the amplitude and phase of each speaker one by one.

[0036] The PXi acquisition system collects time domain signals through a microphone, and obtains the main mode amplitude and circumferential mode order after decomposition using the spatial Fourier method.

[0037] Example 2

[0038] The main test steps of the present invention for measuring the acoustic modes of the fan duct in a wind tunnel include the following:

[0039] Step 1: Open the cover of the acoustic liner installation section and install the acoustic liner test piece to be tested. The acoustic liner test piece is a ring-shaped structure, and the nacelle shell can be split into two sections in the acoustic liner installation area. Split the nacelle shell, and insert the acoustic liner test piece into the groove, and finally connect the two sections of the nacelle shell with rivets.

[0040] Step 2: Connect the nacelle shell with the fairing, airfoil support sheet, simplified engine model, and airfoil support, and move them to the wind tunnel test platform, with the simplified engine model corresponding to the center of the wind tunnel collector.

[0041] Step 3: Connect the fan duct acoustic modal simulation device, connect the cabinet to the speaker cable, and place the cabinet outside the wind tunnel. The main control system controls the 16 speakers to sound, and each speaker has the same amplitude, and the phase difference between adjacent speakers increases. In this way, a sound source mode with a circumferential modal order of 8 can be synthesized.

[0042] Step 4: The synthesized sound source propagates downstream of the nacelle model along the incoming flow direction. The sensor receives the time domain signal and obtains the main mode amplitude and circumferential mode order after spatial Fourier decomposition.

[0043] Step 5: In the state of no sound lining (cover plate installed), repeat the test measurement according to steps 2 to 4, measure the sound pressure amplitude of the measuring point in the state of no sound lining, and compare it with the test conditions of sound lining to obtain the sound absorption effect of the sound lining.

[0044] The above steps are an 8th-order circumferential modal synthesis and acoustic liner test solution. If you need to change the order of the sound source being tested and the acoustic liner sample, you can make corresponding modifications according to the above steps. Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solution of this solution, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that it is still possible to modify the technical solutions described in the aforementioned embodiments, or to make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fan duct acoustic modal simulation device under incoming flow conditions, comprising a simplified engine model (1), a loudspeaker (2), an acoustic liner mounting area (3), a fairing (4), a microphone (5), a nacelle shell (6), an airfoil support (7), an airfoil support sheet (8), a sound control system and a PXi acquisition system, characterized in that: The simplified engine model (1) is connected to the nacelle shell (6) via an airfoil support sheet (8), and the nacelle shell (6) is connected to the acoustic wind tunnel airfoil support device via an airfoil support (7); In front of the airfoil support sheet (8), a plurality of loudspeakers (2) are installed at regular intervals along the circumference of the nacelle shell (6), and the phase and amplitude of the loudspeakers are controlled by a sound control system to synthesize and simulate the circumferential sound mode generated by the fan, thereby simulating the sound mode of the duct; In front of the loudspeaker (2), a sound liner installation area (3) is provided in the nacelle shell (6) for installing a sound liner test sample. When the sound liner test sample is not measured, it is sealed with a cover plate. In front of the sound liner installation area, near the lip of the nacelle shell (6), a plurality of microphones (5) are fixedly installed at equal intervals along the inner wall of the nacelle shell (6); A fairing (4) is provided outside the nacelle shell (6), including protruding parts of a speaker (2) and a microphone (5), and connecting cables are gathered in the fairing (4) and pass through the airfoil support (7) to be respectively connected to an external sound control system and a PXi acquisition system for electrical signals; The sound control system is installed with an acoustic mode simulation control program for setting the amplitude and phase of each loudspeaker (2), and finally the loudspeaker (2) emits a high-intensity plane wave, which is axially synthesized into a fan acoustic mode in the nacelle shell and transmitted to the downstream of the flow field; The PXi acquisition system collects time domain signals through multiple microphones, and measures the sound pressure fluctuations at the measurement points in the state without and with sound lining. After decomposition using the spatial Fourier method, the main mode amplitude and circumferential mode order are obtained, and the sound absorption effect of the sound lining under specific modes is obtained by comparison.

2. The device for simulating fan duct acoustic modes under incoming flow conditions according to claim 1, characterized in that: A plurality of through holes are opened on the surface of the nacelle shell (6), and the through holes serve as a waveguide (10) with a uniform cross-section, and the size of the waveguide is consistent with the throat diameter (9) of the speaker (2).

3. The device for simulating fan duct acoustic modes under incoming flow conditions according to claim 1, characterized in that: The sound absorption holes of the noise-absorbing liner test sample are flush with the inner wall surface of the nacelle shell (6).

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