Method and system for on-line testing of aerodynamic acoustic performance of a material

Abstract

The application discloses a kind of material aerodynamic acoustic performance online testing method and system, it is related to wind tunnel aerodynamic acoustic performance test field, the application is set in wind tunnel sound-transparent solid wall test section, to be measured acoustic material is installed in its middle part;First, second acoustic sensor is sequentially arranged on the wall surface upstream of material, third, fourth acoustic sensor is sequentially arranged on the wall surface downstream;Respectively collect the sound pressure data of four acoustic sensors under the running state and static state of wind tunnel;Transfer matrix equation set is constructed, and the sound pressure data of running state and static state are substituted into equation set and simultaneously solved, to obtain sound pressure transfer function;According to sound pressure transfer function, the noise reduction of material under current airflow environment is calculated.The application realizes online testing by the synergistic effect of sound-transparent solid wall, four sensor arrangement, double-state acquisition and simultaneous solution of transfer matrix, effectively eliminates wall reflection and wind tunnel background noise interference while testing, and the test result is accurate and reliable.

Description

Technical Field

[0001] This invention relates to the field of wind tunnel aeroacoustic performance testing, specifically to an online testing method and system for the aeroacoustic performance of materials. Background Technology

[0002] Wind tunnels are core equipment for conducting aeroacoustic research. They inherently possess various sources of aerodynamic noise, including unstable flow noise generated when airflow passes through models or ducts, noise from the operation of fans and motors in the power section, and stimulated radiation noise from structural components. Strong aerodynamic noise has several adverse effects on wind tunnel experiments: First, it can mask weak signals generated by the model, leading to distortion of pressure and vibration data and affecting the acquisition of key data such as boundary layer transition and buffeting; second, it may induce resonance, causing fatigue damage to the model, sensors, or wind tunnel structure; and third, long-term exposure to strong noise environments can damage the hearing of participants.

[0003] The most direct method to control aerodynamic noise is to use acoustic materials for absorption, converting sound wave energy into the material's internal energy. Acoustic materials typically have porous characteristics, enabling them to efficiently dissipate sound energy. Current technologies primarily employ the following two methods to test the performance of acoustic materials:

[0004] (a) Static testing methods: The sound absorption performance of materials is measured in the laboratory using the reverberation chamber method or impedance tube method. These methods measure the sound absorption performance of materials under still air conditions and cannot reflect the influence of airflow on the acoustic performance of materials. In practical wind tunnel applications, due to the high flow velocity of the medium, improper use may even amplify the noise intensity propagating along the wind tunnel loop.

[0005] (ii) Testing methods in flowing pipes: To avoid the limitations of static testing, some studies have attempted to conduct tests in flowing pipes. However, in common flowing pipes, wall reflections are significant, making it impossible to accurately measure local noise levels, and the flow velocity is difficult to control precisely, resulting in insufficient reliability of the test results.

[0006] In summary, existing technologies lack an online testing method that can accurately measure the acoustic properties of acoustic materials in an airflow environment while effectively eliminating wind tunnel background noise and wall reflection interference. Summary of the Invention

[0007] The purpose of this invention is to provide an online testing method for the aeroacoustic properties of materials, addressing the following technical problems in existing technologies: static testing methods cannot reflect the influence of airflow on the acoustic properties of materials; traditional flow-through pipe testing methods suffer from problems such as large wall reflections, inaccurate noise intensity measurement, and difficulty in flow velocity control; existing testing methods cannot effectively separate the aerodynamic noise of the wind tunnel itself from the acoustic characteristics of the material itself. Specifically, the purpose of this invention is to provide a material aeroacoustic performance testing method that can, while the wind tunnel is in operation, online separate the upstream and downstream sound fields of the acoustic material and simultaneously eliminate interference from wall reflections and wind tunnel background noise.

[0008] To achieve the above-mentioned objective, this invention provides an online testing method for the aeroacoustic properties of materials, the method comprising:

[0009] Step S1: Set up a sound-permeable solid wall test section in the wind tunnel, install the acoustic material to be tested in the middle of the sound-permeable solid wall test section, so that the airflow is constrained in the sound-permeable solid wall test section and flows through the acoustic material axially.

[0010] Step S2: On the wall surface of the sound-permeable solid wall test section upstream of the acoustic material, a first acoustic sensor and a second acoustic sensor are sequentially installed along the airflow direction; on the wall surface of the sound-permeable solid wall test section downstream of the acoustic material, a third acoustic sensor and a fourth acoustic sensor are sequentially installed along the airflow direction.

[0011] Step S3: Collect the first operating sound pressure and the first stationary sound pressure using the first acoustic sensor; collect the second operating sound pressure and the second stationary sound pressure using the second acoustic sensor; collect the third operating sound pressure and the third stationary sound pressure using the third acoustic sensor; and collect the fourth operating sound pressure and the fourth stationary sound pressure using the fourth acoustic sensor; wherein, the first operating sound pressure, the second operating sound pressure, the third operating sound pressure, and the fourth operating sound pressure are sound pressures collected when the wind tunnel is in operation, and the first stationary sound pressure, the second stationary sound pressure, the third stationary sound pressure, and the fourth stationary sound pressure are sound pressures collected when the wind tunnel is stationary;

[0012] Step S4: Construct a system of transfer matrix equations for the acoustic material. Substitute the first operating sound pressure, second operating sound pressure, third operating sound pressure, and fourth operating sound pressure with the first stationary sound pressure, second stationary sound pressure, third stationary sound pressure, and fourth stationary sound pressure into the system of transfer matrix equations, and solve the system simultaneously to obtain the transfer matrix. The transfer matrix includes the sound pressure transfer function. Sound pressure-velocity transfer function Vibration velocity-sound pressure transfer function and vibrational velocity transfer function ;

[0013] Step S5: Based on the sound pressure transfer function Calculate the noise reduction of the acoustic material under the current airflow environment.

[0014] To address the problem that existing technologies cannot separate the acoustic properties of materials from wind tunnel background noise and wall reflection interference online in an airflow environment, this method employs a sound-permeable solid wall test section, a four-sound sensor arrangement, dual-state acquisition, and simultaneous solution of the transfer matrix to achieve online testing, simultaneously eliminate background noise and wall reflection interference, and accurately obtain the material noise reduction amount.

[0015] Preferably, the axial distance between the first and second acoustic sensors, and the axial distance between the third and fourth acoustic sensors, are both no less than 10 times the diameter of the respective acoustic sensors. Too close a spacing between acoustic sensors can cause mutual interference of measurement signals, affecting the accuracy of sound pressure acquisition. Ensuring that the sound pressure signals acquired by each sensor are independent avoids near-field interference and improves measurement accuracy.

[0016] Preferably, the axial distance between the second acoustic sensor and the upstream end face of the acoustic material, and the axial distance between the third acoustic sensor and the downstream end face of the acoustic material, are both not less than 1 / 4 of the wavelength of the measured sound wave. If the sensor is too close to the acoustic material, the sound field will not fully expand; if it is too far, interference from other noise sources in the pipeline may be introduced. This ensures that the sound wave propagates stably between the sensor and the material, satisfying the boundary conditions of the transfer matrix model.

[0017] Preferably, the transfer matrix equations of the acoustic material are as follows:

[0018] ;

[0019] in, The density of air. The speed of sound in air; These are respectively the first operating sound pressure level, the second operating sound pressure level, the third operating sound pressure level, and the fourth operating sound pressure level; These are the first, second, third, and fourth static sound pressure levels, respectively. They form a closed, solvable system of equations, providing the mathematical basis for the simultaneous solution of the four transfer functions.

[0020] Preferably, according to the sound pressure transfer function The formula for calculating the noise reduction is:

[0021] ;

[0022] in, This refers to the noise reduction measure. The complex transfer function is transformed into a commonly used engineering metric for noise reduction, facilitating evaluation and application.

[0023] To achieve the above-mentioned objectives, the present invention also provides an online testing system for the aeroacoustic properties of materials, the system comprising:

[0024] The acoustically permeable solid-wall test section is set up in a wind tunnel to constrain airflow and form a definable sound propagation path;

[0025] An acoustic material mounting structure is provided in the middle of the sound-permeable solid wall test section to fix the acoustic material to be tested.

[0026] The first acoustic sensor and the second acoustic sensor are sequentially disposed on the wall surface of the sound-permeable solid wall test section upstream of the acoustic material along the airflow direction;

[0027] The third and fourth acoustic sensors are sequentially disposed on the wall surface of the sound-permeable solid wall test section downstream of the acoustic material along the airflow direction;

[0028] The noise acquisition module is electrically connected to the first acoustic sensor, the second acoustic sensor, the third acoustic sensor and the fourth acoustic sensor respectively, and is used to acquire the sound pressure signals output by each acoustic sensor when the wind tunnel is in operation and when it is stationary.

[0029] The data processing module, electrically connected to the noise acquisition module, is used to receive the sound pressure signal and perform the following operations:

[0030] The first operating sound pressure, the second operating sound pressure, the third operating sound pressure, and the fourth operating sound pressure, as well as the first stationary sound pressure, the second stationary sound pressure, the third stationary sound pressure, and the fourth stationary sound pressure, are obtained based on the sound pressure signal.

[0031] Construct a system of transfer matrix equations for the acoustic material. Substitute the first operating sound pressure, second operating sound pressure, third operating sound pressure, and fourth operating sound pressure with the first stationary sound pressure, second stationary sound pressure, third stationary sound pressure, and fourth stationary sound pressure into the system of transfer matrix equations, and solve the system of equations simultaneously to obtain the transfer matrix. The transfer matrix includes the sound pressure transfer function. Sound pressure-velocity transfer function Vibration velocity-sound pressure transfer function and vibrational velocity transfer function ;

[0032] According to the sound pressure transfer function Calculate the noise reduction of the acoustic material under the current airflow environment.

[0033] One or more technical solutions provided by this invention have at least the following technical effects or advantages:

[0034] Enables online testing: Acoustic performance can be measured directly under wind tunnel operating conditions without removing the material from the wind tunnel, and the test results are closer to actual use conditions.

[0035] Eliminating background noise interference: By acquiring and solving the dual-state data in both the running and stationary states, the aerodynamic noise of the wind tunnel system itself is effectively separated, thus avoiding its impact on the test results of the material's acoustic performance.

[0036] Eliminating wall reflection interference: The use of a sound-permeable solid wall test section effectively avoids sound reflection and ensures that no standing waves are generated inside the pipeline, creating ideal conditions for accurate sound pressure measurement.

[0037] Improved testing accuracy: By arranging four acoustic sensors and solving the transfer matrix simultaneously, a complete description of the upstream and downstream sound fields of the material can be achieved, resulting in accurate and reliable test results.

[0038] Wide range of applications: It is not limited by airflow velocity and can be used for material acoustic performance testing under different flow velocity conditions. Attached Figure Description

[0039] The accompanying drawings, which are provided to further illustrate embodiments of the invention and constitute a part of this invention, are not intended to limit the scope of the invention.

[0040] Figure 1 This is a schematic diagram of a traditional acoustic test section;

[0041] Figure 2 This is a schematic diagram of the sound-permeable solid wall test section;

[0042] Figure 3 This is a schematic diagram showing the arrangement of the test specimen and microphone;

[0043] Figure 4 This is a flowchart illustrating an online testing method for the aeroacoustic properties of materials. Detailed Implementation

[0044] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, where there is no conflict, the embodiments of the present invention and the features thereof can be combined with each other.

[0045] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0046] Those skilled in the art should understand that, in the disclosure of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting this invention.

[0047] It is understood that the term "a" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple, and the term "a" should not be understood as a limitation on the number.

[0048] Example 1;

[0049] Please refer to Figure 4 , Figure 4 This invention provides a method for online testing of the aeroacoustic properties of materials, comprising:

[0050] Step S1: Set up a sound-permeable solid wall test section in the wind tunnel, install the acoustic material to be tested in the middle of the sound-permeable solid wall test section, so that the airflow is constrained in the sound-permeable solid wall test section and flows through the acoustic material axially.

[0051] Step S2: On the wall surface of the sound-permeable solid wall test section upstream of the acoustic material, a first acoustic sensor and a second acoustic sensor are sequentially installed along the airflow direction; on the wall surface of the sound-permeable solid wall test section downstream of the acoustic material, a third acoustic sensor and a fourth acoustic sensor are sequentially installed along the airflow direction.

[0052] Step S3: Collect the first operating sound pressure and the first stationary sound pressure using the first acoustic sensor; collect the second operating sound pressure and the second stationary sound pressure using the second acoustic sensor; collect the third operating sound pressure and the third stationary sound pressure using the third acoustic sensor; and collect the fourth operating sound pressure and the fourth stationary sound pressure using the fourth acoustic sensor; wherein, the first operating sound pressure, the second operating sound pressure, the third operating sound pressure, and the fourth operating sound pressure are sound pressures collected when the wind tunnel is in operation, and the first stationary sound pressure, the second stationary sound pressure, the third stationary sound pressure, and the fourth stationary sound pressure are sound pressures collected when the wind tunnel is stationary;

[0053] Step S4: Construct a system of transfer matrix equations for the acoustic material. Substitute the first operating sound pressure, second operating sound pressure, third operating sound pressure, and fourth operating sound pressure with the first stationary sound pressure, second stationary sound pressure, third stationary sound pressure, and fourth stationary sound pressure into the system of transfer matrix equations, and solve the system simultaneously to obtain the transfer matrix. The transfer matrix includes the sound pressure transfer function. Sound pressure-velocity transfer function Vibration velocity-sound pressure transfer function and vibrational velocity transfer function ;

[0054] Step S5: Based on the sound pressure transfer function Calculate the noise reduction of the acoustic material under the current airflow environment.

[0055] The core technical principles of this invention include the following four aspects:

[0056] (I) Sound-permeable solid-wall test section—Constructing a definable sound propagation path:

[0057] In traditional open acoustic test sections, the airflow boundary extends, the sound field diffuses, and the upstream and downstream boundaries are not clearly defined, resulting in an uncertain sound propagation path. This invention employs a sound-permeable solid-wall test section, using sound-permeable materials to confine the airflow within the test area. This ensures airflow uniformity within the test section and effectively avoids sound reflection, ensuring no standing waves are generated within any cross-section of the pipe. This creates a definable sound propagation path for accurate measurement of airflow noise in the test section. It provides a test environment with clearly defined geometric boundaries and a single sound propagation path for establishing the transfer matrix model.

[0058] (II) Four acoustic sensor arrangement—to achieve sound field separation and bidirectional measurement, and to realize a complete description of the upstream and downstream sound fields:

[0059] A single acoustic sensor can only measure the total local sound pressure and cannot distinguish between incident and reflected waves. First and second acoustic sensors are sequentially installed along the airflow direction on the upstream wall of the acoustic material, and third and fourth acoustic sensors are sequentially installed on the downstream wall. The upstream dual sensors separate incident and reflected waves within the upstream pipe, while the downstream dual sensors separate transmitted and reflected waves within the downstream pipe. The coordinated arrangement of the four sensors allows the system to simultaneously acquire sound pressure information from both sides of the material, providing input for establishing the transfer matrix model. Through spacing design (no less than 10 times the sensor diameter and no less than 1 / 4 of the measured sound wave wavelength), it is ensured that there is no near-field coupling interference between the sensors, and that they are located in the stable sound wave propagation region, satisfying the plane wave assumption. The upstream dual sensors can separate incident and reflected waves within the upstream pipe, and the downstream dual sensors can separate transmitted and reflected sound waves, providing complete boundary conditions for the transfer matrix.

[0060] (III) Dual-state acquisition—eliminating wind tunnel background noise:

[0061] Sound pressure data from four acoustic sensors were collected under both operating and stationary conditions in the wind tunnel. Data collected during operation included the coupling information between wind tunnel background noise and the acoustic properties of the materials; data collected under stationary conditions reflected only the noise transmission characteristics of the wind tunnel system itself. The sound pressure data collected during operation included both the background noise generated by the wind tunnel system and the sound wave transmission / reflection characteristics of the acoustic materials; the sound pressure data collected under stationary conditions included only the background noise of the wind tunnel system itself (without airflow excitation). Substituting both sets of data into the transfer matrix equations and solving the four equations simultaneously, the influence of background noise was mathematically eliminated, retaining only the intrinsic transmission characteristics of the materials, thus achieving effective separation of wind tunnel background noise from the acoustic properties of the materials.

[0062] (iv) Solving the transfer matrix simultaneously—obtaining the intrinsic acoustic parameters of the material and the noise reduction amount of the material:

[0063] A system of four linear transfer matrix equations for acoustic materials is constructed. Sound pressure data from both operational and static states are substituted into the equations, and the four transfer functions of the transfer matrix are obtained by solving the system simultaneously. , , and .in, The sound pressure transfer function reflects the transmission relationship between sound pressure upstream and downstream of the acoustic material. Since the four transfer functions are coupled in the system of equations, they must be solved simultaneously for accurate results. Finally, based on... The noise reduction of the material under the current airflow environment was calculated.

[0064] This invention utilizes a sound-permeable solid-wall test section to construct a definable sound propagation path. The test section wall is constructed using sound-permeable materials (such as micro-perforated plates or sound-permeable fabrics), confining airflow within fixed geometric boundaries. In traditional open test sections, the airflow boundary is diffused, the sound wave propagation path is uncertain, and a clear upstream and downstream interface cannot be defined, resulting in a lack of benchmark for sound field measurement. The sound-permeable solid-wall test section constrains airflow through physical boundaries, forming a defined sound propagation channel. The characteristic impedance of the sound-permeable material is close to that of air, resulting in minimal reflection of sound waves passing through the wall and avoiding the standing wave phenomenon caused by rigid walls. This provides a test environment with clearly defined geometric boundaries and a single sound propagation path for subsequent acoustic modeling, making the establishment of a transfer matrix model possible.

[0065] This invention utilizes a four-sound-sensor arrangement to achieve a complete description of the upstream and downstream sound fields. The first and second acoustic sensors are sequentially positioned on the upstream wall of the acoustic material, and the third and fourth acoustic sensors are sequentially positioned on the downstream wall, with a defined spacing constraint (≥10 times the diameter, ≥1 / 4 wavelength). A single acoustic sensor can only measure the local total sound pressure and cannot distinguish between incident and reflected waves. The upstream dual sensors, through spacing design, can separate incident and reflected sound waves within the upstream pipe based on a dual-microphone method. Similarly, the downstream dual sensors can separate transmitted and reflected sound waves. The spacing constraint (≥10 times the diameter) ensures no near-field coupling interference between the sensors. The spacing constraint with the material end face (≥1 / 4 wavelength) ensures that the sensors are located in the stable sound wave propagation region, satisfying the plane wave assumption. This decomposes the complex sound field on both sides of the material into clearly oriented wave components, providing complete boundary conditions for the transfer matrix.

[0066] This invention eliminates wind tunnel background noise through dual-state data acquisition and simultaneous solution. Sound pressure data from four acoustic sensors are collected in both the wind tunnel's operating and stationary states, and then substituted into a set of transfer matrix equations for simultaneous solution. The sound pressure collected in the operating state comprises two parts: the background noise generated by the wind tunnel system itself, and the acoustic material's transmission / reflection characteristics. The sound pressure collected in the stationary state only includes the background noise of the wind tunnel system itself (without airflow excitation). Substituting both sets of data into the transfer matrix equations simultaneously, the unknowns in the equations represent the material's acoustic transmission characteristics, independent of the wind tunnel background noise. By solving the four equations simultaneously, the influence of background noise is mathematically eliminated, retaining only the material's intrinsic transmission characteristics. This achieves effective separation of wind tunnel background noise from the material's acoustic properties, something that existing technologies cannot do.

[0067] In this invention, the noise reduction amount of the material is obtained by simultaneously solving the transfer matrix, constructing a system of four linear equations, and simultaneously solving four transfer functions. Ultimately, only the following methods are used: Calculate the noise reduction amount. The transfer matrix fully describes the linear relationship between the sound pressure upstream and downstream of the material and the particle velocity, mathematically ensuring the accurate extraction of the material's acoustic properties and avoiding errors caused by simplified models.

[0068] This invention employs a synergistic combination of four technical components: a sound-permeable solid-wall test section, a four-acoustic sensor arrangement, dual-state data acquisition, and simultaneous solution of the transfer matrix. These four components are interdependent: the sound-permeable solid-wall test section provides a definable sound propagation path for the transfer matrix model; the four-acoustic sensor arrangement provides complete boundary conditions for the transfer matrix; dual-state data acquisition enables the mathematical elimination of wind tunnel background noise; and simultaneous solution of the transfer matrix ensures the accurate extraction of the material's acoustic properties. Through the combined action of these four components, the simultaneous separation of the material's acoustic properties from wind tunnel background noise and wall reflections under flowing conditions is achieved for the first time.

[0069] Example 2;

[0070] Based on Embodiment 1, Embodiment 2 of the present invention provides a detailed description of the method:

[0071] Traditional acoustic test sections of wind tunnels, such as Figure 1 As shown, the stable airflow converges again into the wind tunnel loop after passing through the open area, thus completing the interaction between the airflow and the model. Aeroacoustic measurements are carried out in this open area. To prevent interference from the testing instruments, the microphone is required to be placed outside the airflow for far-field measurements. Due to the lack of necessary constraints in the test section area, the airflow boundary exhibits a gradually expanding shape.

[0072] This invention employs a different type of wind tunnel test section, utilizing sound-permeable material to confine airflow within the test area. This ensures uniform airflow within the test area while effectively preventing sound reflection and ensuring no standing waves are generated within any cross-section of the pipe, thus creating conditions for accurate measurement of airflow noise in the test section. The sound-permeable material is selected from one or more of the following: Kevlar fiber cloth, glass fiber cloth, micro-perforated plate, or a composite structure of sound-permeable felt and perforated plate. Its sound wave transmission loss is no greater than 3dB within the target frequency band and it can withstand the aerodynamic loads under wind tunnel operating conditions.

[0073] In practical applications, the acoustic material to be tested can be installed in the middle of the test section. The material size matches the cross-section of the test section (0.5 m × 0.5 m), with a thickness of 50 mm, and is made of polyurethane foam (open area ratio ≥ 90%). The material is fixed to the test section wall via flanges, and the edges are sealed with sealing strips to ensure airtightness.

[0074] The schematic diagram of this invention is as follows Figure 3 As shown, the acoustic material to be tested (the acoustic material being tested, including porous sound-absorbing materials such as fibers, cotton, and sponges, as well as resonant sound-absorbing structures made using the principle of resonance) is placed in the middle of the test section. The acoustic material is installed in the middle of the test section, and its coverage area can be adjusted according to the test requirements, and is not limited to the position shown in the figure. In Embodiment 2 of this invention, the acoustic sensor specifically uses microphones. Microphones 1 and 2 are set on the upstream wall of the acoustic material, and microphones 3 and 4 are set on the downstream wall of the acoustic material. The specific positions of the microphones are explained as follows: the distance between microphones 1 and 2, and between microphones 3 and 4, is not less than 10 times the diameter of the microphones, and the distance between microphones 2 and 3 and the acoustic material is not less than 1 / 4 of the wavelength of the measured sound wave.

[0075] Each acoustic sensor uses a 1 / 4-inch condenser microphone with a sensitivity of 50 mV / Pa and a frequency response range of 20 Hz to 20 kHz. The sensors are installed flush with the wall surface, with the sensor end face flush with the inner wall of the test section to avoid protrusions that would generate additional aerodynamic noise.

[0076] Construct the system of transfer matrix equations:

[0077] ;

[0078] ;

[0079] ;

[0080] ;

[0081] In the formula: This is the sound pressure transfer function, which is the transfer function of sound pressure from downstream to upstream of an acoustic material. This is the sound pressure-velocity transfer function, which is the transfer function of downstream particle velocity to upstream sound pressure in acoustic materials. This is the transfer function of sound pressure downstream to the velocity of upstream particles in an acoustic material, i.e., the velocity-sound pressure transfer function. This is the transfer function of the downstream velocity to the upstream particle velocity in an acoustic material, also known as the vibration velocity transfer function. The density of air. The speed of sound in air; These are the frequency-band noise data collected by microphones 1, 2, 3, and 4 during wind tunnel operation, respectively. These are respectively the first operating sound pressure level, the second operating sound pressure level, the third operating sound pressure level, and the fourth operating sound pressure level; These are the frequency-band noise data collected by microphones 1, 2, 3, and 4 in a stationary state in the wind tunnel, respectively. These are the first static sound pressure level, the second static sound pressure level, the third static sound pressure level, and the fourth static sound pressure level, respectively.

[0082] All data except for the transfer function can be obtained through a noise acquisition system. That is, by substituting the experimental data into the above equation, we obtain a value related to the transfer function. , , and A system of four linear equations in four variables. By solving the system of equations simultaneously, the transfer functions are obtained. , , and The noise reduction of the acoustic material can be calculated using the following formula:

[0083] .

[0084] Where TL is the noise reduction amount, in decibels (dB). is the sound pressure transfer function, which is the first element of the transfer matrix and reflects the sound pressure transfer relationship between the upstream and downstream of the acoustic material; for The modulus represents the transmission ratio of the sound pressure amplitude. The physical meaning of this formula is: the ratio of the downstream transmitted sound power to the upstream incident sound power of an acoustic material is equal to 1 / Taking the logarithm to base 10 and multiplying it by 10 yields the commonly used noise reduction index in engineering. The larger the noise reduction index TL is, the stronger the acoustic material's ability to attenuate sound waves, and the better the material's acoustic performance.

[0085] Example 3;

[0086] Embodiment 3 of the present invention also provides an online testing system for the aeroacoustic properties of materials, the system comprising:

[0087] The acoustically permeable solid-wall test section is set up in a wind tunnel to constrain airflow and form a definable sound propagation path;

[0088] An acoustic material mounting structure is provided in the middle of the sound-permeable solid wall test section to fix the acoustic material to be tested.

[0089] The first acoustic sensor and the second acoustic sensor are sequentially disposed on the wall surface of the sound-permeable solid wall test section upstream of the acoustic material along the airflow direction;

[0090] The third and fourth acoustic sensors are sequentially disposed on the wall surface of the sound-permeable solid wall test section downstream of the acoustic material along the airflow direction;

[0091] The noise acquisition module is electrically connected to the first acoustic sensor, the second acoustic sensor, the third acoustic sensor and the fourth acoustic sensor respectively, and is used to acquire the sound pressure signals output by each acoustic sensor when the wind tunnel is in operation and when it is stationary.

[0092] The data processing module, electrically connected to the noise acquisition module, is used to receive the sound pressure signal and perform the following operations:

[0093] The first operating sound pressure, the second operating sound pressure, the third operating sound pressure, and the fourth operating sound pressure, as well as the first stationary sound pressure, the second stationary sound pressure, the third stationary sound pressure, and the fourth stationary sound pressure, are obtained based on the sound pressure signal.

[0094] Construct a system of transfer matrix equations for the acoustic material. Substitute the first operating sound pressure, second operating sound pressure, third operating sound pressure, and fourth operating sound pressure with the first stationary sound pressure, second stationary sound pressure, third stationary sound pressure, and fourth stationary sound pressure into the system of transfer matrix equations, and solve the system of equations simultaneously to obtain the transfer matrix. The transfer matrix includes the sound pressure transfer function. Sound pressure-velocity transfer function Vibration velocity-sound pressure transfer function and vibrational velocity transfer function ;

[0095] According to the sound pressure transfer function Calculate the noise reduction of the acoustic material under the current airflow environment.

[0096] In this embodiment of the invention, the axial distance between the first acoustic sensor and the second acoustic sensor, and the axial distance between the third acoustic sensor and the fourth acoustic sensor, are both not less than 10 times the diameter of the corresponding acoustic sensor.

[0097] In this embodiment of the invention, the axial distance between the second acoustic sensor and the upstream end face of the acoustic material, and the axial distance between the third acoustic sensor and the downstream end face of the acoustic material, are both not less than 1 / 4 of the wavelength of the measured sound wave.

[0098] In this embodiment of the invention, the transfer matrix equations of the acoustic material are as follows:

[0099] ;

[0100] in, The density of air. The speed of sound in air; These are respectively the first operating sound pressure level, the second operating sound pressure level, the third operating sound pressure level, and the fourth operating sound pressure level; These are the first static sound pressure level, the second static sound pressure level, the third static sound pressure level, and the fourth static sound pressure level, respectively.

[0101] In this embodiment of the invention, based on the sound pressure transfer function The formula for calculating the noise reduction is:

[0102] ;

[0103] in, This is the noise reduction amount.

[0104] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0105] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for online testing of the aeroacoustic properties of materials, characterized in that, The method includes: Step S1: Set up a sound-permeable solid wall test section in the wind tunnel, install the acoustic material to be tested in the middle of the sound-permeable solid wall test section, so that the airflow is constrained in the sound-permeable solid wall test section and flows through the acoustic material axially. Step S2: On the wall surface of the sound-permeable solid wall test section upstream of the acoustic material, a first acoustic sensor and a second acoustic sensor are sequentially installed along the airflow direction; on the wall surface of the sound-permeable solid wall test section downstream of the acoustic material, a third acoustic sensor and a fourth acoustic sensor are sequentially installed along the airflow direction. Step S3: Collect the first operating sound pressure and the first stationary sound pressure using the first acoustic sensor; collect the second operating sound pressure and the second stationary sound pressure using the second acoustic sensor; collect the third operating sound pressure and the third stationary sound pressure using the third acoustic sensor; and collect the fourth operating sound pressure and the fourth stationary sound pressure using the fourth acoustic sensor; wherein, the first operating sound pressure, the second operating sound pressure, the third operating sound pressure, and the fourth operating sound pressure are sound pressures collected when the wind tunnel is in operation, and the first stationary sound pressure, the second stationary sound pressure, the third stationary sound pressure, and the fourth stationary sound pressure are sound pressures collected when the wind tunnel is stationary; Step S4: Construct a system of transfer matrix equations for the acoustic material. Substitute the first operating sound pressure, second operating sound pressure, third operating sound pressure, and fourth operating sound pressure with the first stationary sound pressure, second stationary sound pressure, third stationary sound pressure, and fourth stationary sound pressure into the system of transfer matrix equations, and solve the system simultaneously to obtain the transfer matrix. The transfer matrix includes the sound pressure transfer function. Sound pressure-velocity transfer function Vibration velocity-sound pressure transfer function and vibrational velocity transfer function ; Step S5: Based on the sound pressure transfer function Calculate the noise reduction of the acoustic material under the current airflow environment.

2. The method for online testing of the aeroacoustic properties of materials according to claim 1, characterized in that, The axial distance between the first acoustic sensor and the second acoustic sensor, and the axial distance between the third acoustic sensor and the fourth acoustic sensor, are both not less than 10 times the diameter of the corresponding acoustic sensor.

3. The method for online testing of the aeroacoustic properties of materials according to claim 1, characterized in that, The axial distance between the second acoustic sensor and the upstream end face of the acoustic material, and the axial distance between the third acoustic sensor and the downstream end face of the acoustic material, are both not less than 1 / 4 of the wavelength of the measured sound wave.

4. The online testing method for the aeroacoustic properties of materials according to claim 1, characterized in that, The transfer matrix equations of the acoustic material are as follows: ； in, The density of air. The speed of sound in air; These are respectively the first operating sound pressure level, the second operating sound pressure level, the third operating sound pressure level, and the fourth operating sound pressure level; These are respectively the first static sound pressure, the second static sound pressure, the third static sound pressure, and the fourth static sound pressure.

5. The method for online testing of the aeroacoustic properties of materials according to claim 1, characterized in that, According to the sound pressure transfer function The formula for calculating the noise reduction is: ； in, This is the noise reduction amount.

6. An online testing system for the aeroacoustic properties of materials, characterized in that, The system includes: The acoustically permeable solid-wall test section is set up in a wind tunnel to constrain airflow and form a definable sound propagation path; An acoustic material mounting structure is provided in the middle of the sound-permeable solid wall test section to fix the acoustic material to be tested. The first acoustic sensor and the second acoustic sensor are sequentially disposed on the wall surface of the sound-permeable solid wall test section upstream of the acoustic material along the airflow direction; The third and fourth acoustic sensors are sequentially disposed on the wall surface of the sound-permeable solid wall test section downstream of the acoustic material along the airflow direction; The noise acquisition module is electrically connected to the first acoustic sensor, the second acoustic sensor, the third acoustic sensor and the fourth acoustic sensor respectively, and is used to acquire the sound pressure signals output by each acoustic sensor when the wind tunnel is in operation and when it is stationary. The data processing module, electrically connected to the noise acquisition module, is used to receive the sound pressure signal and perform the following operations: The first operating sound pressure, the second operating sound pressure, the third operating sound pressure, and the fourth operating sound pressure, as well as the first stationary sound pressure, the second stationary sound pressure, the third stationary sound pressure, and the fourth stationary sound pressure, are obtained based on the sound pressure signal. Construct a system of transfer matrix equations for the acoustic material. Substitute the first operating sound pressure, second operating sound pressure, third operating sound pressure, and fourth operating sound pressure with the first stationary sound pressure, second stationary sound pressure, third stationary sound pressure, and fourth stationary sound pressure into the system of transfer matrix equations, and solve the system of equations simultaneously to obtain the transfer matrix. The transfer matrix includes the sound pressure transfer function. Sound pressure-velocity transfer function Vibration velocity-sound pressure transfer function and vibrational velocity transfer function ; According to the sound pressure transfer function Calculate the noise reduction of the acoustic material under the current airflow environment.

7. The online testing system for the aeroacoustic properties of materials according to claim 6, characterized in that, The axial distance between the first acoustic sensor and the second acoustic sensor, and the axial distance between the third acoustic sensor and the fourth acoustic sensor, are both not less than 10 times the diameter of the corresponding acoustic sensor.

8. The online testing system for the aeroacoustic properties of materials according to claim 6, characterized in that, The axial distance between the second acoustic sensor and the upstream end face of the acoustic material, and the axial distance between the third acoustic sensor and the downstream end face of the acoustic material, are both not less than 1 / 4 of the wavelength of the measured sound wave.

9. The online testing system for the aeroacoustic properties of materials according to claim 6, characterized in that, The transfer matrix equations of the acoustic material are as follows: ； in, The density of air. The speed of sound in air; These are respectively the first operating sound pressure level, the second operating sound pressure level, the third operating sound pressure level, and the fourth operating sound pressure level; These are respectively the first static sound pressure, the second static sound pressure, the third static sound pressure, and the fourth static sound pressure.

10. The online testing system for the aeroacoustic properties of materials according to claim 6, characterized in that, According to the sound pressure transfer function The formula for calculating the noise reduction is: ； in, This is the noise reduction amount.

Images