An aircraft APU inlet duct sound source simulation device and simulation method

Abstract

The application discloses an aircraft APU air inlet sound source simulation device and a simulation method, and belongs to the technical field of aircraft noise testing. The aircraft APU air inlet sound source simulation device comprises a loudspeaker, a waveguide tube, a fixed connection assembly, a measurement microphone and an electrical and signal control assembly, the measurement microphone and the waveguide tube are fixed on the fixed connection assembly, the loudspeaker is fixed on the waveguide tube, one end of the electrical and signal control assembly is connected to the measurement microphone, and the other end of the electrical and signal control assembly is connected to the loudspeaker, the aircraft APU air inlet sound source simulation method comprises a method for simulating a sound mode sound source and a method for simulating wideband noise / single-frequency noise. The application is aimed at a sound mode generating device in a rectangular pipe of an APU air inlet, and the equation group formed by a response function of a control method part has great innovation.

Description

Technical Field

[0001] This invention belongs to the technical field of aircraft noise testing, and relates to a sound source device required in the laboratory testing stage of the research and development test of the sound liner of the aircraft APU inlet. More specifically, it relates to an aircraft APU inlet sound source simulation device and simulation method. Background Technology

[0002] The aircraft's APU (Auxiliary Power Unit) begins operating during passenger boarding and disembarking at the airport and is a major source of noise on the tarmac. Similar to aircraft engines, noise reduction can be achieved by installing acoustic liners in its air intakes. APU air intake noise propagates outwards in the form of duct acoustic modes. The development and testing of APU air intake acoustic liners requires a sound source device capable of generating the APU's acoustic modes. Unlike the nacelle air intake, the APU air intake duct has a rectangular cross-sectional shape.

[0003] Existing technology 1 addresses acoustic mode generation devices for annular pipes, such as... Figure 1 As shown, multiple ring-shaped loudspeaker arrays are arranged along the axial direction of the modal excitation pipe. Each ring-shaped loudspeaker array includes multiple loudspeakers arranged circumferentially along the modal excitation pipe. In the control method, the contribution of each loudspeaker to the acoustic mode is determined according to the installation position of the loudspeakers, a set of equations of sound source and modal coefficients is constructed, the sound source information is obtained by solving the equations, and then the loudspeakers are controlled to emit sound to form a specific acoustic mode.

[0004] Prior art 2 describes the NASA Curved Duct Test Rig (CDTR) device (such as...) Figure 2 This system can generate acoustic modes within a rectangular pipe with a cross-section of 0.152m × 0.381m. It uses 16 loudspeakers, has a maximum controllable frequency of 2500Hz, and controllable acoustic mode orders of 5 on the long side and 2 on the short side. The control method for the acoustic modes employs the filtered-X LMS algorithm. First, the response of a single loudspeaker to an array of 31 microphones on the pipe wall is measured, forming a transfer function matrix. The sound pressure level of the target acoustic mode at the microphone positions is calculated. Based on the measured sound pressure level, the input value at the loudspeaker end is corrected using the transfer function matrix until the desired target acoustic mode is obtained.

[0005] Existing technology 1 is designed for circular / annular ducts and cannot simulate sound sources within rectangular ducts like APU intake ducts. NASA's CDTR device employs a measurement-feedback control algorithm. It first measures the sound pressure level of a microphone array within the duct and compares it to the expected sound pressure level, then uses a computer program to provide feedback until the target acoustic mode is controlled. Its main drawback is that this feedback mechanism requires a certain amount of time, especially with arrays consisting of multiple speakers, where the efficiency requirements for the feedback algorithm are extremely high, and convergence cannot be guaranteed. In extensive testing under various operating conditions, a considerable testing time is required to complete the tests. Summary of the Invention

[0006] To address the above problems, this invention provides a device and method for simulating the acoustic source of an aircraft APU inlet. Compared with existing technologies, this invention targets the acoustic mode generation device within the rectangular duct of the APU inlet, and its control method features a highly innovative system of equations formed by the response function. Furthermore, this invention directly establishes the transfer function relationship between the loudspeaker input voltage and the acoustic mode through a combination of theoretical derivation and measurement. Based on the amplitude of the target acoustic mode, the loudspeaker input voltage is directly calculated, and the corresponding value is then directly input into the measurement and control software to obtain the desired acoustic mode. Compared to measurement-feedback control algorithms, the process of obtaining the target acoustic mode is much faster.

[0007] According to a first aspect of the present invention, an aircraft APU inlet sound source simulation device is provided, the simulation device comprising: a loudspeaker, a waveguide, a fixed connection assembly, a measuring microphone, and electrical and signal control components.

[0008] The measuring microphone and the waveguide are fixed to the fixed connection assembly;

[0009] The loudspeaker is fixed to the waveguide.

[0010] The electrical and signal control component is connected at one end to the measuring microphone and at the other end to the speaker.

[0011] Furthermore, the fixed connection assembly includes: a first silencing terminal, a transition section pipe, a main pipe for the acoustic mode generator, a first microphone array mounting pipe, an APU intake duct test pipe or acoustic liner, a second microphone array mounting pipe, and a second silencing terminal connected in sequence.

[0012] Furthermore, the first / second silencing terminal includes a first / second silencing terminal pipe and a first / second sound-absorbing sponge respectively located on the first / second silencing terminal pipe.

[0013] Furthermore, the waveguide is fixed in the main pipe of the acoustic mode generator.

[0014] Furthermore, the measuring microphone is inserted into the mounting hole of the first / second microphone array mounting pipe, allowing for direct insertion and removal.

[0015] Furthermore, the electrical and signal control components include: a measurement and control computer and a power amplifier connected to each other, wherein the measurement and control computer includes a processor unit and a data acquisition card and a signal generation card connected to the processor unit.

[0016] Furthermore, the microphone is connected to the data acquisition card via a signal cable, and the signal generation card is connected to the power amplifier via a signal cable.

[0017] Furthermore, the power amplifier is connected to the speaker via a cable.

[0018] Furthermore, the data acquisition card and signal generation card are fixed in the card slot of the measurement and control computer.

[0019] Furthermore, the measurement and control program transmits signals to the data acquisition card and signal generator through the computer's internal circuitry.

[0020] It should be noted that, unless otherwise specified, all signals transmitted between the parts are voltage signals.

[0021] According to a second aspect of the present invention, a method for simulating the sound source of an aircraft APU inlet is provided, the simulation method being operated based on a simulation device according to any of the preceding aspects, the simulation method comprising method 1 for simulating a modal sound source and method 2 for simulating broadband noise / single-frequency noise.

[0022] Furthermore, method 1 for simulating acoustic modal sound sources includes:

[0023] Step 11: Based on the target acoustic modal amplitude, modal order, and frequency, use the loudspeaker input voltage signal calculation method to calculate the required voltage signal amplitude and phase for each loudspeaker;

[0024] Step 12: Based on the amplitude and phase of the voltage signal, input the measurement and control program and start it. The voltage signal is generated by the signal generator card, amplified by the power amplifier, and drives the speaker to emit sound. The array of speakers works together to generate the sound mode at the set frequency.

[0025] Step 13: Use the measurement and control program and data acquisition card to collect the noise signal of the array of microphones, use the acoustic mode decomposition program to calculate the acoustic mode in the pipe, and confirm whether the required acoustic mode is generated;

[0026] Step 14: Repeat steps 11-13 for the next set of test targets.

[0027] Furthermore, in step 11, the method for calculating the speaker input voltage is as follows:

[0028] Step 111: Based on the propagation theory of vibration sound sources in pipes, establish the response function relationship between the vibration velocity of sound particles on the outlet end face of the waveguide and the sound pressure at any point in the pipe;

[0029] Step 112: Determine the acoustic modal distribution function and the order of the propagable acoustic modes within the pipe;

[0030] Step 113: Establish the control equation set Ax = b for the generation of acoustic modes, where A is the coefficient matrix of the equation set and b is the column vector of the target control acoustic modes;

[0031] Step 114: Calculate the coefficient matrix A of the control equations for the generation of acoustic modes, where the number of rows M is the total number of propagating acoustic modes at a set frequency, and the number of columns N is the number of loudspeakers. According to the solution condition of the current equation set, M≤N;

[0032] Step 115: Based on the target acoustic modes, construct a target acoustic mode column vector with M rows;

[0033] Step 116: Solve the linear equation system Ax=b to obtain the column vector x of acoustic particle velocity at the end face of the waveguide, the number of rows of which corresponds to the number of loudspeakers N;

[0034] Step 117: Using calibration test methods, determine the response relationship between the input voltage of each loudspeaker and the velocity of acoustic particles at the waveguide outlet end face at different frequencies;

[0035] Step 118: Using the response relationship determined in step 117, calculate the input voltage value of each loudspeaker, including amplitude and phase.

[0036] Furthermore, in step 111, the relationship between the vibration velocity of the acoustic particles on the waveguide outlet end face and the sound pressure response function at any point inside the pipe is as follows:

[0037]

[0038] Where: ρ—air density; ω—circular frequency, = 2πf; f—test frequency; S—cross-sectional area of ​​the main pipe; m, n—modal order of the sound, representing the long and short sides respectively; Q S —Volume velocity of sound particle vibration; W S —The area of ​​the waveguide outlet end face; Ψ mn —Modal shape function; Λ mn —Echo mode normalization coefficient; k mn — Acoustic mode wavenumber; x, y, z — Coordinates of any point in the main pipe; F sm F sn FsL —The sound source coefficient at the waveguide exit section is related to the acoustic mode order m, n, and the waveguide cross-sectional dimension L (z-coordinate direction); j—imaginary unit, z s —The z-coordinate of the geometric center of the waveguide outlet end face.

[0039] For an array of multiple loudspeakers, the sound pressure at any point inside its duct is as follows:

[0040]

[0041] Where: P—total number of loudspeakers; Q si —Volume velocity of the acoustic particles at the outlet face of the i-th waveguide; W si —The area of ​​the outlet end face of the i-th waveguide, F sm，i F sn，i F sL，i —These are the sound source coefficients of the i-th waveguide outlet end face, respectively.

[0042] Furthermore, in step 112, the acoustic mode distribution function inside the pipe is:

[0043]

[0044] in, —Amplitude of the incident wave mode; —Amplitude of the reflected wave mode; e is the natural exponent.

[0045] For a propagable mode of a certain order, its cutoff frequency f co for:

[0046]

[0047] Where B is the long side dimension of the main pipe of the acoustic mode generator; D is the short side dimension of the main pipe of the acoustic mode generator; and c0 is the velocity of sound.

[0048] If m and n are taken from 0, then all acoustic modes with a cutoff frequency less than the test frequency f can propagate in the pipe. The maximum modal order that can propagate in the long side of the rectangular pipe is denoted as M, and the maximum modal order that can propagate in the short side of the rectangular pipe is denoted as N.

[0049] Further, in step 113, the coefficient matrix A of the system of equations is:

[0050] The coefficient matrix is ​​as follows:

[0051]

[0052] The variable matrix to be determined is x, which represents the average acoustic particle vibration velocity at the waveguide outlet end face:

[0053]

[0054] The matrix composed of the target control acoustic modal matrix:

[0055]

[0056] Furthermore, method 2 for simulating broadband noise / single-frequency noise includes:

[0057] Step 21: Use a signal generator card to generate a white noise signal or a sine wave signal at a single frequency with a specified amplitude and frequency range, and then use a power amplifier to drive a speaker array to generate a sound source.

[0058] Step 22: Use the measurement and control program and data acquisition card to collect the noise signal of the array of microphones, measure the sound pressure level at different locations in the pipe, further calculate the sound power level in the pipe, and determine the insertion loss and transmission loss of the measured noise reduction component as evaluation indicators of the noise reduction amount.

[0059] Step 23: Repeat steps 21-22 for the next set of test targets.

[0060] The beneficial effects of this invention are:

[0061] The main technical improvements of this invention are as follows: For the simulation of a single acoustic mode source, the structure of the entire device was designed, particularly the internal shape of the waveguide and the silencing terminal of the loudspeaker. The design of the waveguide's internal shape aims to ensure that only plane waves are generated at the waveguide's outlet face within the controllable frequency range of the acoustic mode. The silencing terminal design needs to meet the acoustic non-reflection condition, i.e., a reflection coefficient of less than 0.3 within the test frequency range. These two points are prerequisites for the acoustic mode control principle and method used in the device of this invention. For the device of this invention, the acoustic mode control method within the pipe was improved, proposing a method to directly determine the calculation of the loudspeaker array input signal voltage. By inputting the required input voltage (with different amplitudes and phases) for each loudspeaker into the measurement and control program, a sine wave signal is generated by the signal generator card and amplified by a power amplifier to drive the loudspeakers, thus generating the target acoustic mode within the rectangular pipe. The number of loudspeakers in the device of this invention is twice that of the NASA CDTR device, and the controllable frequency of the acoustic mode is 1000Hz higher.

[0062] For simulating single-frequency noise and wideband noise, the measurement and control program selects a sinusoidal signal at a specified frequency and a white noise signal within a specified frequency range, respectively. Given an input signal voltage value, a signal generator is used to generate a signal, which is then amplified by a power amplifier to drive a speaker array, thus producing the desired sound source type within the device. Unlike acoustic modal control, in this speaker array, all speakers have the same input signal.

[0063] In the device of the present invention, based on the sound source and structural characteristics of the aircraft APU air intake, a sound source simulation function is realized in a rectangular pipe, which can generate three types of sound sources: acoustic modality, single-frequency noise and broadband random noise, which can meet the needs of conducting acoustic tests in the laboratory during the research and development stage of the aircraft APU air intake acoustic liner.

[0064] Compared with the prior art, in this invention, the loudspeaker is arranged along the axial and circumferential directions of the modal excitation channel. By using the channel high-order acoustic mode control method, considering the circumferential and axial positions of the loudspeaker, the excitation of circumferential and radial modes can be realized. Multiple acoustic modes can be excited and controlled simultaneously, which has a wider range of applications and the target acoustic mode obtained is dominant in the sound field. Attached Figure Description

[0065] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0066] Figure 1 This illustrates a prior art annular pipe acoustic modal device;

[0067] Figure 2 This illustrates the NASA CDTR device in a wind tunnel in the prior art;

[0068] Figure 3 A diagram of an APU intake duct acoustic mode generator according to an embodiment of the present invention is shown;

[0069] Figure 4 A diagram showing the electrical and signal control components of a device according to an embodiment of the present invention is provided.

[0070] Figure 5 A schematic flowchart of a speaker input voltage signal calculation method according to an embodiment of the present invention is shown;

[0071] Figure 6 A waveguide structure diagram according to an embodiment of the present invention is shown;

[0072] Figure 7The coordinate system of the main pipeline according to an embodiment of the present invention is shown;

[0073] Figure 8 A schematic diagram illustrating the calculation of sound pressure and acoustic particle velocity response function at the outlet end face of the waveguide according to an embodiment of the present invention is shown.

[0074] Figure 9 Numerical verification of acoustic modal control according to an embodiment of the present invention is shown;

[0075] Figure 10 The results of acoustic mode decomposition propagating in the air intake duct according to an embodiment of the present invention are shown.

[0076] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0077] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this disclosure as detailed in the appended claims.

[0078] The terms "first," "second," etc., used in this disclosure are for distinguishing similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that the embodiments of this disclosure described herein can be implemented, for example, in orders other than those illustrated or described herein.

[0079] Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, such that a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or apparatus.

[0080] Multiple, including two or more.

[0081] And / or, it should be understood that, for the purposes of this disclosure, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone.

[0082] This invention provides an APU inlet sound source simulation device that can simulate three types of sound sources in an aircraft APU inlet: modal acoustics, single-frequency noise, and broadband random noise. The mechanical components of the device are as follows: Figure 3 As shown, it includes: 1-speaker; 2-waveguide; 3-main duct of acoustic mode generator; 4-transition section duct; 5-silencing terminal duct; 6-sound-absorbing sponge; 7-microphone array mounting duct; 8-APU intake duct test duct or acoustic liner; 9-measuring microphone.

[0083] The electrical and signal control components of the device are as follows: Figure 4 As shown, it includes: 10-Control computer; 11-Control program; 12-Data acquisition card; 13-Signal generator card; 14-Power amplifier. The connection relationships of each part are as follows:

[0084] Speaker 1 is fixed to waveguide 2. Waveguide 2 is fixed to the main pipe 3 of the acoustic mode generator. Pipes 3, 4, 5, 6, 7, and 8 are connected as a whole using a fixed connection method, with 3, 4, 5, 7, and 8 connected by bolts and nuts, and 6 fixed to pipe 5 by adhesive bonding. Pipes 5 and 6 together form a silencing terminal. Microphone 9 is inserted into the mounting hole of pipe 7 and can be directly plugged in and removed.

[0085] Microphone 9 is connected to data acquisition card 12 via a signal cable. Signal generator card 13 is connected to power amplifier 14 via a signal cable. Power amplifier 14 is connected to speaker 1 via a cable. Data acquisition card 12 and signal generator card 13 are fixed in the card slots of measurement and control computer 10. The processor unit containing measurement and control program 11 transmits signals to data acquisition card 12 and signal generator through internal computer circuitry. Unless otherwise stated, all signals transmitted between these components are voltage signals.

[0086] The working steps of this invention for simulating acoustic modal sound sources are as follows:

[0087] Step 1: Based on the target acoustic mode amplitude, modal order, and frequency, use the loudspeaker input voltage signal calculation method of the acoustic mode generator involved in this invention to calculate the voltage signal amplitude and phase required for each loudspeaker.

[0088] Step 2: Based on the pre-calculated voltage signal amplitude and phase, input the measurement and control program and start it. The voltage signal is generated by the signal generator card, amplified by the power amplifier, and drives the speaker 1 to produce sound. The array of speakers 1 works together to produce the sound mode at the set frequency.

[0089] Step 3: Use the measurement and control program and data acquisition card to collect the noise signal from the array of microphones 9, and use the acoustic mode decomposition program to calculate the acoustic modes in the pipe to confirm whether the required acoustic modes are generated. The measurement and control program and acoustic mode decomposition program used in this step are existing methods and programs and are not included in the scope of this invention.

[0090] Step 4: Repeat steps 1-3 for the next set of test targets.

[0091] This invention also includes a method for controlling the acoustic modes in the APU intake duct and a method for calculating the speaker input voltage, as shown in the flowchart below. Figure 5 As shown.

[0092] Explanation of speaker input voltage calculation method:

[0093] Step 1: Based on the propagation theory of vibration sound sources in pipes, establish the relationship between the vibration velocity of sound particles on the waveguide outlet end face (the face flush with the main pipe wall 3) and the sound pressure at any point in the pipe.

[0094] Step 2: Determine the acoustic mode distribution function and the order of the propagable acoustic modes within the pipeline.

[0095] Step 3: Establish the control equation set Ax = b for acoustic mode generation. Where A is the coefficient matrix of the equation set, and b is the column vector of the target control acoustic modes.

[0096] Step 4: Calculate the coefficient matrix A of the governing equations for acoustic mode generation, where the number of rows M represents the total number of propagable acoustic modes at a given frequency, and the number of columns N represents the number of loudspeakers. According to the condition that the current equations have a solution, M ≤ N.

[0097] Step 5: Based on the target acoustic modes, construct a target acoustic mode column vector with M rows.

[0098] Step 6: Solve the linear equation system Ax=b to obtain the column vector x of acoustic particle velocity at the end face of the waveguide, and the number of rows corresponds to the number of loudspeakers N.

[0099] Step 7: Using calibration testing methods, determine the response relationship between the input voltage of each loudspeaker and the velocity of acoustic particles at the waveguide outlet face at different frequencies. This step can also be completed before step 1.

[0100] Step 8: Using the response relationship determined in Step 7, calculate the input voltage value of each loudspeaker, including amplitude and phase.

[0101] For different acoustic modal testing conditions, repeat steps 4-6 and step 8.

[0102] The working steps of this invention for simulating broadband noise / single-frequency noise are as follows:

[0103] Step 1: Use a signal generator card to generate a white noise signal or a sine wave signal at a single frequency with a specified amplitude and frequency range, and then use a power amplifier to drive a speaker array to generate a sound source.

[0104] Step 2: Use the measurement and control program and data acquisition card to collect the noise signal of the array composed of microphones 9, measure the sound pressure level at different locations in the pipe, further calculate the sound power level in the pipe, and determine the noise reduction indicators such as insertion loss and transmission loss of the tested noise reduction component.

[0105] Step 3: Repeat steps 1-2 for the next set of test targets.

[0106] The core component of the device in this invention is an acoustic mode generator. Loudspeakers generate sound wave vibrations, which are guided into the main duct through a waveguide. The waveguide requires special design so that only plane waves are guided into the main duct at the test frequency. By controlling the input voltage and phase of multiple loudspeakers, multiple sound waves with different phases are superimposed and canceled out within the main duct, ultimately achieving control of the target acoustic mode.

[0107] The waveguide design is as follows: Figure 6 As shown. The upper end is a cylindrical section with a diameter matching the speaker's microphone head diameter. The speaker is connected and fixed to the upper end of the waveguide, and sealing measures are taken to prevent sound leakage. Figure 6 Position 1. The middle part of the waveguide is a cylindrical throat. Figure 6 At position 2, the throat diameter is smaller than the upper diameter, which cuts off higher-order acoustic modes, allowing only plane waves to pass. The lower end is a gradually expanding conical surface. To reduce interference with adjacent waveguides, both ends are cut flat, resulting in an approximately rectangular outlet face. Figure 6 Position 3 in the middle.

[0108] The core of generating the target acoustic mode lies in determining the input voltage of each loudspeaker, according to... Figure 3 The method shown determines the input voltage. The relationship between the acoustic particle velocity of the plane wave at the waveguide outlet face and the response function of the acoustic pressure at any point inside the main duct is as follows:

[0109]

[0110] Where: ρ—air density; ω—circular frequency, = 2πf; f—frequency; S—cross-sectional area of ​​the main pipe; m, n—mode order of the sound, representing the long and short sides respectively; Q S —Volume velocity; W S —The area of ​​the waveguide outlet end face; Ψ mn —Modal shape function; Λ mn —Echo mode normalization coefficient; k mn— Acoustic mode wavenumber; x, y, z — Coordinates of any point in the main pipe; F sm F sn F sL —The sound source coefficient at the waveguide exit section is related to the acoustic mode order m, n, and the waveguide cross-sectional dimension L (z-coordinate direction); j—imaginary unit, z s —The z-coordinate of the geometric center of the waveguide outlet end face.

[0111] In the above formula, the subscript "s" indicates a quantity related to the position of the outlet end face. The coordinate system in the above formula is defined as follows: Figure 7 As shown.

[0112] right Figure 3 The sound pressure at any point in the array of multiple loudspeakers shown in the diagram has the following relationship:

[0113]

[0114] Where: P—total number of loudspeakers; Q si —Volume velocity of the acoustic particles at the outlet face of the i-th waveguide; W si —The area of ​​the outlet end face of the i-th waveguide, F sm，i F sn，i F sL，i —These are the sound source coefficients of the i-th waveguide outlet end face, respectively.

[0115] The target acoustic mode and the sound pressure distribution at any point in the main duct are as follows:

[0116]

[0117] in, —Amplitude of the incident wave mode; —Amplitude of the reflected wave mode; e is the natural exponent.

[0118] In the main pipe, only the incident sound wave is considered, and the reflected wave is ignored (there is no reflection condition at the outlet of the main pipe). By combining equations (2) and (3) and then decoupling and simplifying them, the system of equations Ax = b is established.

[0119] The coefficient matrix is ​​as follows:

[0120]

[0121] The variable matrix to be determined is x, which represents the average acoustic particle vibration velocity at the waveguide outlet end face:

[0122]

[0123] The matrix composed of the target control acoustic modal matrix:

[0124]

[0125] In this matrix, the amplitude is given for the target acoustic mode, and the amplitude of other non-target acoustic modes is 0. In the equation system Ax = b, MN is the order corresponding to the maximum propagable acoustic mode at the test frequency. The control accuracy of the acoustic modes in the main duct is related to the condition number of the coefficient matrix A, and to the arrangement and number of loudspeakers. The number of rows in the coefficient matrix is ​​equal to the total number of propagable modes in the duct at the test frequency. Assuming that the total number of propagable acoustic modes at 3000Hz is 24, then the number of rows in the coefficient matrix is ​​24. The number of columns in the coefficient matrix is ​​the total number of loudspeakers. According to the condition that the linear equation system has a solution, the number of rows in the coefficient matrix should be less than or equal to the number of columns. And the index of the target acoustic mode is less than the total number of propagable acoustic modes. In other words, in this invention, the index of the maximum controllable acoustic mode in the aircraft APU inlet acoustic mode generator does not exceed the total number of loudspeakers.

[0126] The location of the waveguide exit end face can be obtained by solving the above system of equations. Figure 6 The velocity of the sound particles at position 3 in the middle was calculated. A numerical model was established to calculate the sound pressure at the speaker mounting surface within the waveguide. Figure 6 The response relationship between the sound particle velocity at different frequencies between the middle position (position 1) and the outlet end face position. The relationship between the sound pressure level and the input voltage at the speaker mounting surface position is determined by the characteristics of the speaker. The sound pressure level is measured using a microphone, and the input voltage is measured using a multimeter. The response relationship between the two is established, such as... Figure 8 As shown.

[0127] Based on the above analysis, the target acoustic mode can be generated in the main pipe by controlling the input voltage of each speaker in the speaker array.

[0128] For the openings at both ends of the main duct, sound-absorbing terminals are designed to achieve no sound wave reflection and meet the acoustic mode control conditions. The sound-absorbing terminals are designed in accordance with Appendix E of GB / T 17697-2014 / ISO 5136:2003 "Measurement of acoustic power radiated into ducts by duct method for acoustic fans and other ventilation equipment".

[0129] Numerical calculations were performed on the APU intake duct sound source simulation device of this invention using acoustic calculation software to verify its acoustic modal control principle. With a frequency of 3000Hz, a target acoustic modal order of (3, 2), and a sound pressure level of 110dB, the complex sound pressure levels at the installation locations of 32 loudspeakers were calculated using the control method of this invention. The results were obtained through calculation. Figure 9 The acoustic modal cloud diagram shown.

[0130] Further, the sound pressure at the intake duct wall is extracted, and the sound mode decomposition method is used to obtain the actual sound mode decomposition results propagating in the duct, such as... Figure 10 As shown, the main mode and the target acoustic mode are completely identical, with an amplitude of 112.6 dB, which is very close to the amplitude of the target acoustic mode. The verification results show that the acoustic mode generator developed in this invention, which is located in a rectangular duct and is designed for the characteristics of the APU intake duct, is feasible and can produce the desired acoustic mode amplitude and order.

[0131] In the device of the present invention, for the simulation of single-frequency noise and wideband noise, a sine wave signal at a specified frequency and a white noise signal within a specified frequency range are selected in the measurement and control program, respectively. The signal is generated by the signal generation card and amplified by the power amplifier to drive the speaker array to generate the required sound source type in the device.

[0132] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A sound source simulation device within a rectangular duct of an aircraft APU air intake, characterized in that, The sound source simulation device within the rectangular duct of the aircraft APU air intake includes: a loudspeaker, a waveguide, a fixed connection assembly, a measuring microphone, and electrical and signal control components. The measuring microphone and the waveguide are fixed to the fixed connection assembly; The loudspeaker is fixed to the waveguide; The electrical and signal control component is connected at one end to the measuring microphone and at the other end to the speaker; The fixed connection assembly includes: a first silencing terminal, a transition section pipe, a main pipe for a sound mode generator, a first microphone array mounting pipe, an APU intake duct test pipe or acoustic liner, a second microphone array mounting pipe, and a second silencing terminal connected in sequence; the first / second silencing terminal includes a first / second silencing terminal pipe and a first / second sound-absorbing sponge respectively located on the first / second silencing terminal pipe. The upper end of the waveguide is a cylindrical section with a diameter matching the diameter of the speaker head. The speaker is connected to and fixed to the upper end of the waveguide, and sealing measures are taken to prevent sound leakage. The middle part of the waveguide is a cylindrical throat with a diameter smaller than that of the upper end, which cuts off higher-order sound modes, allowing only plane waves to pass through. The lower end of the waveguide is a gradually expanding conical surface. To reduce interference with adjacent waveguides in terms of size, both ends are cut flat, and the outlet end face is approximately rectangular.

2. The sound source simulation device within the rectangular duct of the aircraft APU air intake as described in claim 1, characterized in that, The waveguide is fixed in the main pipe of the acoustic mode generator; the measuring microphone is inserted into the mounting hole of the first / second microphone array mounting pipe and can be directly plugged in and out.

3. A method for simulating the sound source of an aircraft APU inlet, characterized in that, The simulation method is based on a sound source simulation device in a rectangular duct of an aircraft APU intake as described in claim 1 or 2, and the simulation method includes method 1 for simulating acoustic modal sound sources and method 2 for simulating broadband noise / single-frequency noise. Method 1 for simulating acoustic modal sound sources includes: Step 11: Based on the target acoustic modal amplitude, modal order, and frequency, use the loudspeaker input voltage signal calculation method to calculate the required voltage signal amplitude and phase for each loudspeaker; Step 12: Based on the amplitude and phase of the voltage signal, input the measurement and control program and start it. The voltage signal is generated by the signal generator card, amplified by the power amplifier, and drives the speaker to emit sound. The array of speakers works together to generate the sound mode at the set frequency. Step 13: Use the measurement and control program and data acquisition card to collect the noise signal of the array of microphones, use the acoustic mode decomposition program to calculate the acoustic mode in the pipe, and confirm whether the required acoustic mode is generated; Step 14: Repeat steps 11-13 for the next set of test targets; Method 2 for simulating broadband noise / single-frequency noise includes: Step 21: Use a signal generator card to generate a white noise signal or a sine wave signal at a single frequency with a specified amplitude and frequency range, and then use a power amplifier to drive a speaker array to generate a sound source. Step 22: Use the measurement and control program and data acquisition card to collect the noise signal of the array of microphones, measure the sound pressure level at different locations in the pipe, further calculate the sound power level in the pipe, and determine the insertion loss and transmission loss of the measured noise reduction component as evaluation indicators of the noise reduction amount. Step 23: Repeat steps 21-22 for the next set of test targets.

4. The method for simulating the sound source of an aircraft APU inlet according to claim 3, characterized in that, In step 11, the method for calculating the speaker input voltage is as follows: Step 111: Based on the propagation theory of vibration sound sources in pipes, establish the response function relationship between the vibration velocity of sound particles on the outlet end face of the waveguide and the sound pressure at any point in the pipe; Step 112: Determine the acoustic modal distribution function and the order of the propagable acoustic modes within the pipe; Step 113: Establish the control equation set Ax=b for acoustic mode generation, where A is the coefficient matrix of the equation set and b is the column vector composed of the target control acoustic modes; Step 114: Calculate the coefficient matrix A of the control equations for the generation of acoustic modes, where the number of rows M is the total number of propagating acoustic modes at a set frequency, and the number of columns N is the number of loudspeakers. According to the solution condition of the current equation set, M≤N; Step 115: Based on the target acoustic modes, construct a target acoustic mode column vector with M rows; Step 116: Solve the linear equation system Ax=b to obtain the column vector x of acoustic particle velocity at the end face of the waveguide, the number of rows of which corresponds to the number of loudspeakers N; Step 117: Using calibration test methods, determine the response relationship between the input voltage of each loudspeaker and the velocity of acoustic particles at the waveguide outlet end face at different frequencies; Step 118: Using the response relationship determined in step 117, calculate the input voltage value of each loudspeaker, including amplitude and phase.

5. The method for simulating the sound source of an aircraft APU inlet according to claim 4, characterized in that, In step 111, the relationship between the vibration velocity of acoustic particles on the waveguide outlet end face and the sound pressure at any point inside the pipe is as follows: In the formula: —Air density; — Circular frequency, ; —Test frequency; —Cross-sectional area of ​​the main pipeline; —The order of the acoustic mode, with the long side and the short side respectively; —Volume velocity of sound particles; —The area of ​​the waveguide outlet end face; —Modal shape function; —Echo mode normalization coefficients; — Acoustic mode wavenumber; —The coordinates of any point in the main pipeline; —The sound source coefficient at the waveguide exit section is related to the acoustic mode order. and the cross-sectional dimensions of the waveguide in the z-coordinate direction Related; —Imaginary unit, ; —The z-coordinate of the geometric center of the waveguide outlet end face; For an array of multiple loudspeakers, the sound pressure at any point inside its duct is as follows: In the formula: —Total number of speakers; —Volume velocity of acoustic particles at the outlet end face of the i-th waveguide; —The area of ​​the outlet end face of the i-th waveguide. —These are the sound source coefficients of the i-th waveguide outlet end face, respectively.

6. The method for simulating the sound source of an aircraft APU inlet according to claim 4, characterized in that, In step 112, the acoustic mode distribution function inside the pipe is: in, —Amplitude of the incident wave mode; —Amplitude of the reflected wave mode; For natural index; For a propagable mode of a certain order, its cutoff frequency for: in, —Length of the main pipe of the acoustic mode generator; —Short side dimension of the main pipe of the acoustic mode generator; —Speed ​​of sound; If we start taking values ​​from 0, the cutoff frequency will be less than the test frequency. All acoustic modes can propagate within the pipe, and the maximum modal order that can propagate along the long side of the rectangular pipe is denoted as . The maximum modal order that can propagate along the short side of a rectangular pipe is denoted as . .

7. The method for simulating the sound source of an aircraft APU inlet according to claim 4, characterized in that, In step 113, the coefficient matrix A of the system of equations is: The coefficient matrix is ​​as follows: The variable matrix to be determined is x, which represents the average acoustic particle vibration velocity at the waveguide outlet end face: The matrix composed of the target control acoustic modal matrix: 。

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