Aircraft noise load suppression superstructure design method under high-speed environment

Abstract

This invention discloses a superstructure design method for suppressing noise loads in aircraft under high-speed environments, relating to the field of aircraft design. The method includes: obtaining characteristic noise frequencies through simulation using a typical cavity model; introducing various designable structures such as micro-perforated plates, Helmholtz resonators, and porous materials to construct acoustic superstructures capable of suppressing or phase-shifting noise loads at these frequencies; and solidifying the acoustic superstructure assembly style through ground tests or wind tunnel tests to facilitate its physical realization. This invention addresses the problem that commonly used cavity noise reduction methods cannot be applied to high-speed cavity structures by designing and optimizing various acoustic superstructure assemblies capable of suppressing or phase-shifting noise loads to achieve optimized suppression of noise loads in aircraft cavities under high-speed environments.

Description

Technical Field

[0001] This invention relates to the field of aircraft design. More specifically, this invention relates to a superstructure design method for suppressing noise loads in aircraft under high-speed environments. Background Technology

[0002] Domestic research on the layout design of various cavity structures of aircraft, fluid-structure-acoustic coupling research and structural safety assessment mainly focuses on Mach numbers below 2.0. There is a lack of systematic research on typical high-speed cavity flow and fluid-structure-acoustic coupling problems above Mach number 2.0.

[0003] However, when commonly used cavity noise reduction methods such as front and rear edge shaping are applied to high-speed cavity structures, they often fail to achieve satisfactory results, and in some cases, they may even lead to a more severe noise environment inside the cavity. Therefore, it is necessary to introduce new high-speed cavity noise suppression methods. Summary of the Invention

[0004] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0005] To achieve these objectives and other advantages of the present invention, a superstructure design method for suppressing aircraft noise loads in high-speed environments is provided, comprising:

[0006] S1. Based on the design method of various cavity structures of the aircraft in the wind tunnel test model, the noise spectrum of the cavity model is predicted to obtain the corresponding noise characteristic frequency band;

[0007] S2. For the noise characteristic frequency band obtained from S1, based on the design theory and parametric modeling method of acoustic superstructure, and relying on the database that is compatible with acoustic superstructure, construct at least three acoustic superstructure combinations that have characteristic noise load suppression or phase transfer and conform to the subwavelength scale.

[0008] S3. Verify the acoustic superstructure assembly through ground tests or wind tunnel tests. If the verification is successful, materialize the acoustic superstructure with the optimal parameters; otherwise, return to S2.

[0009] In S2, the database includes: a phonon crystal database, a metamaterial unit cell parameter database, and a characteristic frequency matching database.

[0010] Preferably, in S2, when performing parametric modeling, it is necessary to select core design parameters from various databases that are compatible with the acoustic superstructure design;

[0011] The core design parameters include: unit cell geometry, material properties, and array arrangement.

[0012] Preferably, in S2, the construction of the acoustic superstructure assembly depends on the matching analysis of the noise characteristic frequency band and the superstructure bandgap.

[0013] Preferably, in S2, the acoustic superstructure assembly is a broadband design of multiple superstructures for the noise characteristic frequency band obtained from S1, resulting in a structure including a micro-perforated array + tortuous propagation path as structure one, a Helmholtz resonator with an extended neck as structure two, and a Helmholtz resonator with an extended neck + porous material as structure three.

[0014] Preferably, the structure constructs a tortuous propagation path in space through multiple internally cavity-shaped sound-absorbing units;

[0015] Each sound-absorbing unit is provided with at least one micro-perforation, so that the sound absorption frequency of the corresponding sound-absorbing unit can be adjusted by adjusting the diameter d and the number n of each micro-perforation, thereby achieving broadband sound absorption through non-local resonance between the sound-absorbing units.

[0016] Preferably, the second structure includes multiple non-uniform but similar Helmholtz resonators;

[0017] In particular, the extended necks of each Helmholtz resonator are all set in an embedded manner, so that the side length of the extended neck unit is within the set length. d A half of the cavity is long r c , Increase neck wall thickness t With 1 remaining unchanged, adjust the neck diameter d a Neck length l a and cavity depth l c This allows each Helmholtz resonator to achieve broadband sound absorption through nonlocal resonance.

[0018] Preferably, in the third structure, based on the second structure, the cavity below each Helmholtz resonator is filled with melamine foam of a predetermined thickness.

[0019] Preferably, in S3, the verification of the acoustic superstructure assembly is achieved using a static impedance tube testing system, which includes: a rectangular impedance tube, a signal generator, a microphone, a data acquisition unit, and a computer.

[0020] The rectangular impedance tube has a cutoff frequency of 2500 Hz, and the data acquisition unit is a four-channel acquisition unit with a maximum sampling frequency of 204.8 kHz.

[0021] Preferably, in S1, the noise characteristic frequency band is obtained in the following way:

[0022] S10. Perform acoustic-fluid coupling finite element simulation of various cavity structures of the aircraft using multiphysics simulation software, and design at least two monitoring points in the simulated cavity structure.

[0023] S11. The calculation results of the flow field in the simulated cavity structure are interpolated into the sound field mesh by coupling the multiphysics field with the aeroacoustic flow source.

[0024] S11. The time-domain solution in the sound field grid is converted into the frequency-domain solution through Fourier transform, so as to calculate the spectrum of the cavity structure through pressure acoustics;

[0025] S12. The sound pressure level changes with frequency by using the spectrum of the monitoring points, thereby determining the noise characteristic frequency band of the simulated cavity structure.

[0026] This invention offers at least the following advantages: Addressing the problem that commonly used cavity noise reduction methods cannot be applied to high-speed cavity structures, this invention constructs a superstructure design method for suppressing noise loads in aircraft cavities under high-speed environments. Characteristic noise frequencies are obtained through simulation using a typical cavity model. For these frequencies, various designable structures, such as micro-perforated plates, Helmholtz resonators, and porous materials, are introduced to construct acoustic superstructures capable of suppressing or phase-shifting noise loads. These characteristic superstructures are then solidified through ground tests or wind tunnel tests, enabling the optimization of noise load suppression in aircraft cavities under high-speed environments.

[0027] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the acoustic field of the finite element calculation model of the cavity structure, a typical feature of the aircraft of this invention.

[0029] Figure 2 This is a simulation calculation spectrum of the cavity structure, a typical feature of the aircraft of this invention.

[0030] Figure 3 This is a schematic diagram of a micro-perforated plate + tortuous cavity type sound-absorbing unit in structure one of the present invention;

[0031] Figure 4 This is a schematic diagram of a Helmholtz resonator based on an embedded extended neck in structure two of the present invention;

[0032] Figure 5 for Figure 4 A schematic diagram of the structure with an embedded extended neck;

[0033] Figure 6 This is a schematic diagram of structure three of the present invention, based on a Helmholtz resonator with an embedded extended neck and porous material;

[0034] Figure 7 This is a schematic diagram comparing the experimental sound absorption coefficients of the three superstructures of this invention;

[0035] Figure 8 This is a schematic diagram of the noise load suppression feature superstructure of the present invention after additive manufacturing. Detailed Implementation

[0036] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0037] Step 1: Based on the design methods of various cavity structures and wind tunnel test models of aircraft, perform multi-physics simulation and noise spectrum prediction on the cavity model, including noise, vibration, and structure.

[0038] This step mainly involves using the design methods of various cavity structures and wind tunnel test models of aircraft to predict the noise spectrum of the cavity model. The cavity model needs to be standardized and the noise characteristic frequency band of the monitoring point is obtained through simulation software for this configuration.

[0039] To determine the design frequency band of the acoustic superstructure, COMSOL Multiphysics simulation software was used to perform acoustic-fluid coupled finite element simulations on a typical characteristic cavity structure of an aircraft. First, flow field calculations were performed using the LES-RBVM physics field for transient flow field calculations. Symmetrical boundary conditions were used to simplify the calculations. After the calculations, the velocity and pressure distributions of the flow field were obtained. The flow field calculation results were interpolated into the acoustic field mesh using multiphysics-aeroacoustic flow source coupling in the software, and the time-domain solution was converted to the frequency-domain solution using Fourier transform. Finally, the spectrum of the standard cavity was solved using pressure acoustics. Two monitoring points were selected in the model, namely monitoring point 1 and monitoring point 2, as follows... Figure 1 As shown, the sound pressure level at two points changes with frequency. In this implementation, the basic cavity structure was 200mm × 33.3mm × 66.7mm, and the final calculation results are as follows. Figure 2 As shown in the spectrum, the noise at the two monitoring points is mainly concentrated in the 1000Hz-1500Hz frequency band.

[0040] Step 2: Construct various acoustic superstructures with characteristic noise load suppression or phase shift for the obtained cavity model noise characteristic frequency band.

[0041] For the characteristic noise frequency obtained in step one, this step breaks through the performance limitations of traditional single noise reduction structures and adopts the design concept of "wideband adaptation + structural innovation + functional synergy" to construct a combination of acoustic superstructures with different noise reduction mechanisms, so as to achieve precise suppression and phase control of characteristic noise.

[0042] Specifically, this step, based on acoustic superstructure design theory and parametric modeling methods, utilizes phonon crystal databases, metamaterial unit cell parameter libraries, and characteristic frequency matching databases to optimize core design parameters of acoustic superstructures, including unit cell geometry, material properties, and array arrangement. Multiple acoustic superstructure assemblies with characteristic noise load suppression or phase transfer functions are constructed using noise characteristic frequency bands. The noise spectrum obtained from step one shows that the noise at the two monitoring points is mainly concentrated in the 1000 Hz-1500 Hz frequency band. Therefore, this acoustic superstructure assembly will employ broadband designs for various superstructures within the 1000 Hz-1500 Hz range, including a micro-perforated plate + tortuous cavity type (Structure 1), a Helmholtz resonator based on an extended neck (Structure 2), and a Helmholtz resonator based on an extended neck + porous material (Structure 3).

[0043] (1) Structure 1: Micro-perforated plate + tortuous cavity type

[0044] Micro-perforated cavity structures offer advantages such as good low-frequency performance and light weight; however, traditional micro-perforated cavity structures often have large geometric dimensions, limiting their practical engineering applications. To address this, an innovative composite configuration of "micro-perforated array + tortuous propagation path" is adopted. Compared to traditional cavity structures, this results in… Figure 3 As shown, the improved micro-perforated cavity system combines a micro-perforated plate with a tortuous cavity structure, allowing sound waves to propagate within the curved structure. This increases the propagation path for the same thickness, thus delaying the incident wave phase. Different phase delays can be achieved by changing the geometric parameters of the structure, resulting in a superstructure material where the phase continuously varies with length from 0 to 2π.

[0045] For the design frequency band of 1000 Hz-1500 Hz, this design uses 16 (4×4) sound-absorbing units, keeping the tortuous cavity structure parameters unchanged. The side length of the sound-absorbing unit cavity is a=12 mm, the width of the tortuous channel in the tortuous cavity is w=2 mm, the depth of the tortuous cavity is h=15 mm, the thickness of the wall in the tortuous cavity is b=1 mm, and the thickness of the perforated plate is t=3 mm. By controlling the diameter d and the number n of the micro-perforations, the sound absorption frequency is adjusted to create non-local resonance between the sound-absorbing units, thus achieving a wideband sound absorption effect. The final micro-perforation parameters and theoretical sound absorption coefficients of each unit are shown in Table 1. The total structural thickness is 20 mm.

[0046] Table 1: Structural parameters and theoretical sound absorption coefficients of each sound-absorbing unit in Structure 1 - Tortuous Cavity

[0047]

[0048] (2) Structure 2: Helmholtz resonator based on extended neck

[0049] The Helmholtz resonator is an important acoustic structure, widely used in the design of a range of novel acoustic devices due to its ability to manipulate low-frequency sound waves at subwavelength structural dimensions. The Helmholtz resonator has a narrow, high absorption peak, exhibiting good acoustic performance at low frequencies. To obtain a Helmholtz resonator with better low-frequency absorption, the back cavity volume and neck length can be increased. Increasing the back cavity thickness and neck length both increase the structural thickness; therefore, methods such as... Figure 4 The embedded extended neck design shown allows for the creation of a lower-frequency, more efficient Helmholtz resonator without altering its size or thickness (specific parameters of the embedded extended neck are shown in the figure). Figure 5 (as shown), and the acoustic performance of the sound absorber can be modulated by extending the neck to prolong the sound wave path and enhance the energy dissipation characteristics.

[0050] In this implementation, a combination of multiple non-uniform Helmholtz resonators was used in the design. Sixteen (4×4) Helmholtz resonators with similar absorption coefficients were selected, while maintaining the unit side length of the extended neck. d A =12mm, half the length of the cavity r c =5mm, wall thickness of the extended neck t 1 = 1mm remains unchanged, change the neck diameter d a Neck length l a and cavity depth l c This allows each Helmholtz resonator sound-absorbing unit to achieve non-local resonance, thus achieving a broadband sound absorption effect. The final parameters and theoretical sound absorption coefficients of each unit are shown in Table 2, and the total thickness of the structure is 20mm.

[0051] Table 2: Structural parameters and theoretical absorption coefficients of each Helmholtz resonator - extended neck

[0052]

[0053] (3) Structure 3: Helmholtz resonator with extended neck + porous material

[0054] Porous materials are widely used in various fields due to their excellent acoustic properties, exhibiting good noise reduction effects. However, the excellent sound absorption performance of porous materials is mainly manifested in the high-frequency range, with less noticeable absorption of mid- and low-frequency sound waves, or requiring the use of thicker and larger quantities of material, resulting in a significant increase in the overall structure's volume and weight. Therefore, this implementation process, based on a Helmholtz resonator with an extended neck, fills the cavity with porous material to enhance the noise reduction performance of the superstructure. Among porous materials, porous sound-absorbing materials are divided into two main categories based on their physical properties and appearance characteristics: foam materials and fiber materials.

[0055] This implementation process adopted a synergistic design scheme of "resonance noise reduction + porous sound absorption," utilizing melamine foam as a porous material for sound-absorbing superstructure design, such as... Figure 6 As shown ( Figure 6 In this design, A represents the Helmholtz resonator, B represents the melamine foam layer, and h represents the thickness of the melamine foam layer. Based on the combined structure II, this design fills the bottom of the cavity with 5mm thick melamine foam. The parameters of the melamine foam used are shown in Table 3. Porosity As a tortuosity factor, For flow resistance, The viscous characteristic length, The thermal characteristic length is given. The theoretical average sound absorption coefficient is 0.92 in the 1000 Hz-1500 Hz range, and the total structural thickness is 20 mm.

[0056] Table 3: Melamine foam parameters in Structure 3

[0057]

[0058] All three types of acoustic superstructure assemblies are designed based on subwavelength scales. Through precise control of structural parameters and arrayed layout, they achieve an optimized balance between noise load suppression performance and structural compactness. Furthermore, each structure is designable and combinable, providing diverse technical solutions for subsequent experimental optimization. This overcomes the technical limitations of traditional noise reduction structures, such as poor adaptability in high-speed environments and narrow noise reduction frequency bands.

[0059] In this step, each acoustic superstructure assembly combines traditional materials with a pre-designed structure, controlling material dimensions at the subwavelength scale. Through rational and orderly structural design, extraordinary functions exceeding the inherent properties of nature can be achieved. This can effectively assist in suppressing noise loads on the cavity walls of high-speed aircraft, possessing significant scientific and engineering value.

[0060] Step 3: Through ground tests or wind tunnel tests, the acoustic superstructure assembly is optimized and finally solidified into a feature superstructure design method for use in aircraft cavity models.

[0061] This step primarily involves using a static impedance tube (SIT) testing system to optimize the acoustic superstructure assembly and compare test results from various superstructure assemblies to determine the best option. Specifically, the SIT testing system includes: a static impedance tube, a signal generator, microphones, a data acquisition unit, and a computer. A rectangular impedance tube with a cutoff frequency of 2500 Hz is used. Other hardware components utilize a VibPilot four-channel acquisition unit (maximum sampling frequency 204.8 kHz) and a PA100 dual-channel power amplifier from m+p, along with a Danish GRAS 46BD 1 / 4 pressure field microphone. In practical applications, the sample under test is mounted at the end of the SIT, with two GRAS46BD microphones mounted on it, spaced 5 cm apart. The m+p equipment serves as the signal generation and acquisition device, connected to the speaker and microphones, and simultaneously connected to the computer via a network cable, completing the hardware connection of the testing system. The procedure for testing sound absorption using a static impedance tube is existing technology and will not be described further here.

[0062] like Figure 7 As shown, comparing the static impedance tube test results of the three designed acoustic superstructure assemblies, their average sound absorption coefficients are 0.84, 0.91, and 0.90, respectively. It can be seen that structures two and three both have high average sound absorption coefficients. However, the sound absorption coefficient of structure three drops rapidly in the 1400 Hz-1500 Hz frequency range, reaching only 0.66 at 1500 Hz. Compared to structure two, structure three shows a certain gap in sound absorption performance across the entire 1000 Hz-1500 Hz frequency range. Therefore, structure two, namely the Helmholtz resonator structure based on the extended neck, has a relatively better sound absorption effect in the 1000 Hz-1500 Hz frequency range. Based on the above analysis, the optimal acoustic superstructure assembly selected in this implementation is the Helmholtz resonator structure based on the extended neck.

[0063] Step 4: Materialize the noise load suppression feature superstructure through additive manufacturing and other methods.

[0064] This step primarily involves additive manufacturing of a noise load suppression feature superstructure to achieve physical materialization for the specific operating environment of the aircraft. Based on an optimal acoustic metamaterial structure, this step focuses on additive manufacturing of the noise load suppression feature superstructure with specific cavity dimensions (200mm × 33.3mm × 66.7mm), such as... Figure 8As shown, wind tunnel tests have verified that the noise reduction effect of the superstructure lining reaches more than 2dB, thus enabling the design of a superstructure to suppress the noise load of aircraft in high-speed environments.

[0065] The above solution is merely an illustration of a preferred example and is not limited thereto. When implementing this invention, appropriate substitutions and / or modifications can be made according to the user's needs.

[0066] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for the present invention. Other modifications can be readily made by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and examples shown and described herein.

Claims

1. A superstructure design method for suppressing noise loads in aircraft under high-speed environments, characterized in that, include: S1. Based on the design method of various cavity structures of the aircraft in the wind tunnel test model, the noise spectrum of the cavity model is predicted to obtain the corresponding noise characteristic frequency band; S2. For the noise characteristic frequency band obtained from S1, based on the design theory and parametric modeling method of acoustic superstructure, and relying on the database that is compatible with acoustic superstructure, construct at least three acoustic superstructure combinations that have characteristic noise load suppression or phase transfer and conform to the subwavelength scale. S3. Verify the acoustic superstructure assembly through ground tests or wind tunnel tests. If the verification is successful, materialize the acoustic superstructure with the optimal parameters; otherwise, return to S2. In S2, the database includes: a phonon crystal database, a metamaterial unit cell parameter database, and a characteristic frequency matching database; In S2, the acoustic superstructure assembly is a broadband design of multiple superstructures for the noise characteristic frequency band obtained from S1, resulting in a structure including a micro-perforated array + tortuous propagation path as structure one, a Helmholtz resonator with an extended neck as structure two, and a Helmholtz resonator with an extended neck + porous material as structure three. The structure constructs a tortuous propagation path in space through multiple internally cavity-shaped sound-absorbing units; Each sound-absorbing unit is provided with at least one micro-perforation, so that the sound absorption frequency of the corresponding sound-absorbing unit can be adjusted by adjusting the diameter d and the number n of each micro-perforation, thereby achieving broadband sound absorption through non-local resonance between the sound-absorbing units. The second structure includes multiple non-uniform but similar Helmholtz resonators; In particular, the extended necks of each Helmholtz resonator are all set in an embedded manner, so that the side length of the extended neck unit is within the set length. d A half of the cavity is long r c , Increase neck wall thickness t With 1 remaining unchanged, adjust the neck diameter d a Neck length l a and cavity depth l c This allows each Helmholtz resonator to achieve broadband sound absorption through nonlocal resonance; Based on structure two, structure three fills the cavity below each Helmholtz resonator with melamine foam of a predetermined thickness.

2. The superstructure design method for suppressing aircraft noise load in high-speed environments as described in claim 1, characterized in that, In S2, when performing parametric modeling, it is necessary to select core design parameters from various databases that are compatible with the acoustic superstructure design. The core design parameters include: unit cell geometry, material properties, and array arrangement.

3. The superstructure design method for suppressing aircraft noise load in high-speed environments as described in claim 2, characterized in that, In S2, the construction of the acoustic superstructure assembly depends on the matching analysis of the noise characteristic frequency band and the superstructure bandgap.

4. The superstructure design method for suppressing aircraft noise load in high-speed environments as described in claim 1, characterized in that, In S3, the verification of the acoustic superstructure assembly is achieved using a static impedance tube testing system, which includes: a rectangular impedance tube, a signal generator, a microphone, a data acquisition unit, and a computer. The rectangular impedance tube has a cutoff frequency of 2500 Hz, and the data acquisition unit is a four-channel acquisition unit with a maximum sampling frequency of 204.8 kHz.

5. The superstructure design method for suppressing aircraft noise load in high-speed environments as described in claim 1, characterized in that, In S1, the noise characteristic frequency band is obtained as follows: S10. Perform acoustic-fluid coupling finite element simulation of various cavity structures of the aircraft using multiphysics simulation software, and design at least two monitoring points in the simulated cavity structure. S11. The calculation results of the flow field in the simulated cavity structure are interpolated into the sound field mesh by coupling the multiphysics field with the aeroacoustic flow source. S11. The time-domain solution in the sound field grid is converted into the frequency-domain solution through Fourier transform, so as to calculate the spectrum of the cavity structure through pressure acoustics; S12. The sound pressure level changes with frequency by using the spectrum of the monitoring points, thereby determining the noise characteristic frequency band of the simulated cavity structure.

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