Method for determining acoustic impedance of silencing acoustic liner of turbofan engine

Abstract

The invention belongs to the technical field of turbofan engine silencing acoustic liner design, and particularly relates to a turbofan engine silencing acoustic liner acoustic impedance determination method comprising the following steps: 1, calculating silencing acoustic liner acoustic resistance rn influenced by high sound intensity; 2, calculating the acoustic resistance rg of the silencing acoustic liner influenced by the tangential flow; 3, considering the influence of high sound intensity and tangential flow, and according to the relative magnitude of the sound particle speed amplitude Vo and the main flow speed Vg in the small hole, calculating the sound resistance r of the sound reduction acoustic liner in a segmented manner; 4, calculating a noise reduction acoustic liner tail end correction coefficient delta under the comprehensive influence of tangential flow and high sound intensity; step 5, considering the comprehensive influence of tangential flow and high sound intensity, and calculating the acoustic reactance x of the silencing acoustic liner; and step 6, integrating the acoustic resistance r and the acoustic resistance x of the silencing acoustic liner, and calculating the acoustic resistance z of the silencing acoustic liner.

Description

Technical Field

[0001] The present application belongs to the technical field of turbofan engine silencer liner design, and specifically relates to a method for determining the acoustic impedance of a turbofan engine silencer liner. Background Art

[0002] In order to reduce the noise of the turbofan engine, a sound-absorbing liner is installed on the wall of the nacelle, and a perforated plate liner is used to absorb and reduce noise.

[0003] Accurately determining the acoustic impedance of the turbofan engine muffler liner is of great significance to the design and improvement of the muffler liner.

[0004] At present, the acoustic impedance of the muffler liner of a turbofan engine is mostly determined through a semi-empirical and semi-theoretical method, which is extremely dependent on the experience level of the designers, is time-consuming and labor-intensive, and it is difficult to obtain accurate results, making it difficult to guide the design and improvement of the muffler liner.

[0005] This application is proposed in view of the above-mentioned technical defects. Summary of the invention

[0006] The purpose of this application is to provide a method for determining the acoustic impedance of a turbofan engine muffler liner to overcome or alleviate at least one of the known technical deficiencies.

[0001] The technical solution of this application is:

[0007] A method for determining the acoustic impedance of a turbofan engine silencing liner, comprising:

[0008] Step 1: Calculate the acoustic resistance r of the anechoic lining affected by high sound intensity n ;

[0009] Step 2: Calculate the acoustic resistance r of the absorbing liner affected by the tangential flow g ;

[0010] Step 3: Consider the high sound intensity and tangential flow, and calculate the velocity amplitude V of the sound particle in the small hole. o , mainstream speed V g The relative size of the sound insulation is calculated in sections.

[0011] Step 4: Calculate the correction coefficient δ of the end of the anechoic liner due to the combined effects of tangential flow and high sound intensity;

[0012] Step 5: Considering the combined effects of tangential flow and high sound intensity, calculate the acoustic impedance of the anechoic lining χ;

[0013] Step 6: Calculate the acoustic impedance z of the silencing liner by comprehensively considering the acoustic resistance r and acoustic reactance χ of the silencing liner.

[0014] According to at least one embodiment of the present application, in the above-mentioned method for determining the acoustic impedance of the sound absorbing liner of a turbofan engine, step 1 is specifically as follows:

[0015]

[0016] in:

[0017] k n is the proportionality coefficient;

[0018] V o is the velocity amplitude of the sound particle in the small hole;

[0019] σ is the perforation rate;

[0020] c is the speed of sound.

[0021] According to at least one embodiment of the present application, in the above-mentioned method for determining the acoustic impedance of the muffler liner of a turbofan engine, in step 1, k n =1.1.

[0022] According to at least one embodiment of the present application, in the above-mentioned method for determining the acoustic impedance of the sound absorbing liner of a turbofan engine, step 2 is specifically as follows:

[0023]

[0024] in:

[0025] V g Mainstream speed;

[0026] f is the sound frequency;

[0027] d is the aperture diameter.

[0028] According to at least one embodiment of the present application, in the above-mentioned method for determining the acoustic impedance of the sound lining of a turbofan engine, in step 2, when V g When <8fd, r g =0.

[0029] According to at least one embodiment of the present application, in the above-mentioned method for determining the acoustic impedance of the muffler liner of a turbofan engine, in step 3, according to V0 / V g ≤0.15, V0 / V g >0.15, calculate the acoustic resistance r of the sound insulation in sections.

[0030] According to at least one embodiment of the present application, in the above-mentioned method for determining the acoustic impedance of the silencing liner of a turbofan engine, in step 3, V0 / V g ≤0.15:

[0031] in,

[0032] v is the gas viscosity coefficient;

[0033] ω is the angular frequency of the sound source.

[0034] According to at least one embodiment of the present application, in the above-mentioned method for determining the acoustic impedance of the silencing liner of a turbofan engine, in step 3, V0 / V g >0.15:

[0035] According to at least one embodiment of the present application, in the above-mentioned method for determining the acoustic impedance of the sound absorbing liner of a turbofan engine, in step three, ω=2πf.

[0036] According to at least one embodiment of the present application, in the above-mentioned method for determining the acoustic impedance of the sound absorbing liner of a turbofan engine, step 4 is specifically as follows:

[0037] V0 / V g ≤0.15:

[0038]

[0039] V0 / V g >0.15:

[0040]

[0041] in:

[0042] t is the thickness of the perforated plate.

[0043] According to at least one embodiment of the present application, in the above-mentioned method for determining the acoustic impedance of the sound absorbing liner of a turbofan engine, step five is specifically as follows:

[0044]

[0045] in,

[0046] L is the cell depth.

[0047] According to at least one embodiment of the present application, in the above-mentioned method for determining the acoustic impedance of the muffler liner of a turbofan engine, step six is ​​specifically as follows:

[0048] z=r+iχ

[0049] in:

[0050] i is the imaginary part.

[0051] This application has at least the following beneficial technical effects:

[0052] A method for determining the acoustic impedance of a turbofan engine muffler liner is provided. The method takes into account the influence of the acoustic environment on the acoustic impedance of the turbofan engine muffler liner, modifies the pure theoretical model, and determines the acoustic impedance of the turbofan engine muffler liner. The method is efficient, convenient, and has high accuracy, and can effectively guide the design improvement of the muffler liner. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a schematic diagram of the effect of the acoustic environment on the acoustic resistance of the muffler liner of a turbofan engine provided by an embodiment of the present application;

[0054] Figure 2 It is a schematic diagram of the effect of the acoustic environment on the acoustic impedance of the muffler liner of a turbofan engine provided by an embodiment of the present application;

[0055] Figure 3 It is a schematic diagram of a method for determining the acoustic impedance of a noise-absorbing liner of a turbofan engine provided in an embodiment of the present application.

[0056] In order to better illustrate the present embodiment, some contents of the drawings may be omitted, which is only used for illustrative purposes and should not be construed as limiting the present application. DETAILED DESCRIPTION

[0057] In order to make the technical solution and advantages of the present application clearer, the technical solution of the present application will be described in further detail in detail and in detail with reference to the accompanying drawings. It can be understood that the specific embodiments described here are only partial embodiments of the present application, which are only used to explain the present application, not to limit the present application. It should be noted that, for the convenience of description, only the parts related to the present application are shown in the accompanying drawings, and other related parts can refer to the general design.

[0058] In addition, unless otherwise defined, the technical terms or scientific terms used in the description of this application shall have the usual meanings understood by those of ordinary skill in the art to which this application belongs. The words used in the description of this application to indicate orientation are only used to indicate relative directions or positional relationships. When the absolute position of the described object changes, its relative positional relationship may also change accordingly. The word "include" used in the description of this application indicates that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, but does not exclude other elements or objects.

[0059] In addition, it should be noted that, unless otherwise clearly specified and limited, the words "installation", "connection" and similar terms used in the description of this application should be understood in a broad sense. For example, the connection can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. Technical personnel in the field can understand its specific meaning in this application according to the specific circumstances.

[0060] According to experience and relevant theoretical formulas, the factors affecting the acoustic impedance of the muffler liner of a turbofan engine can be divided into two aspects: structural parameters and acoustic environment. The structural parameters include the aperture of the small hole, the thickness of the perforated plate, the perforation rate, the honeycomb depth, etc.; the acoustic environment includes tangential flow, high sound intensity, gas viscosity, radiation effect, etc.

[0061] Analyze the influence of acoustic environment on the acoustic resistance of the turbofan engine muffler liner, such as Figure 1 As shown in the figure, tangential flow and high sound intensity have a greater influence on the acoustic resistance of the muffler liner of the turbofan engine, while the influence of gas viscosity and radiation effect on the acoustic resistance of the muffler liner of the turbofan engine can be ignored.

[0062] Ignoring the radiation effect, the influence of the acoustic environment on the acoustic impedance of the turbofan engine muffler liner is analyzed, such as Figure 1 As shown in the figure, the tangential flow and high sound intensity have a great influence on the acoustic impedance of the muffler liner of the turbofan engine, while the effect of gas viscosity on the acoustic impedance of the muffler liner of the turbofan engine can be ignored.

[0063] Based on the above, the embodiment of the present application provides a method for determining the acoustic impedance of a turbofan engine muffler liner, such as Figure 1 shown.

[0064] Step 1: Calculate the acoustic resistance r of the anechoic lining affected by high sound intensity n .

[0065] Under high sound intensity, the nonlinear acoustic resistance is proportional to the particle velocity in the small hole, and we have:

[0066]

[0067] in:

[0068] k n is the proportionality coefficient, considering the effect of harmonics caused by nonlinear odd changes, k n =1.1;

[0069] V o is the velocity amplitude of the sound particle in the small hole;

[0070] σ is the perforation rate;

[0071] c is the speed of sound.

[0072] Step 2: Calculate the acoustic resistance r of the absorbing liner affected by the tangential flow g .

[0073] Considering the tangential flow effect, according to the geometry and flow conditions, the mainstream velocity type acoustic resistance empirical model can be constructed:

[0074]

[0075] in:

[0076] V g Mainstream speed;

[0077] f is the sound frequency;

[0078] d is the aperture diameter.

[0079] When V g When <8fd, r g =0.

[0080] Step 3: Consider the influence of high sound intensity and tangential flow, and calculate the velocity amplitude V of the sound particle in the small hole. o , mainstream speed V g The relative size of the sound resistance r of the sound-absorbing lining is calculated segmentally.

[0081] V0 / V g ≤0.15:

[0082]

[0083] V0 / V g >0.15:

[0084]

[0085] in,

[0086] v is the gas viscosity coefficient;

[0087] ω is the angular frequency of the sound source.

[0088] ω=2πf.

[0089] Step 4: Calculate the correction coefficient δ at the end of the anechoic liner due to the combined effects of tangential flow and high sound intensity.

[0090] By measuring the effect of tangential flow on the terminal correction with the mainstream velocity and considering the interference between small holes, an empirical model related to acoustic impedance can be established:

[0091] V0 / V g ≤0.15:

[0092]

[0093] V0 / V g >0.15:

[0094]

[0095] in:

[0096] t is the thickness of the perforated plate.

[0097] Step 5. Considering the combined effects of tangential flow and high sound intensity, calculate the acoustic impedance χ of the sound insulation.

[0098]

[0099] in,

[0100] L is the cell depth.

[0101] Step 6: Calculate the acoustic impedance z of the silencing liner by comprehensively considering the acoustic resistance r and acoustic reactance χ of the silencing liner.

[0102] z=r+iχ

[0103] in:

[0104] i is the imaginary part.

[0105] The method for determining the acoustic impedance of the muffler liner of a turbofan engine disclosed in the above-mentioned embodiment is based on existing experience, test data and semi-empirical models, takes into account the influence of the acoustic environment on the acoustic impedance of the muffler liner of a turbofan engine, corrects the pure theoretical model, and determines the acoustic impedance of the muffler liner of a turbofan engine. The method is efficient, convenient, and has high accuracy, and can improve the insertion loss by more than 2dB compared with the pure theoretical method. The acoustic impedance of the muffler liner of a turbofan engine can be obtained quickly and accurately, and can effectively guide the design improvement of the muffler liner.

[0106] So far, the technical solution of the present application has been described in conjunction with the preferred embodiments shown in the accompanying drawings. Those skilled in the art should understand that the scope of protection of the present application is obviously not limited to these specific embodiments. Without departing from the principles of the present application, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the scope of protection of the present application.

Claims

1. A method for determining the acoustic impedance of a turbofan engine muffler liner, characterized in that: include: Step 1: Calculate the acoustic resistance r of the anechoic lining affected by high sound intensity n ; Step 2: Calculate the acoustic resistance r of the absorbing liner affected by the tangential flow g ; Step 3: Consider the high sound intensity and tangential flow, and calculate the velocity amplitude V of the sound particle in the small hole. o , mainstream speed V g The relative size of the sound insulation is calculated in sections. Step 4: Calculate the correction coefficient δ of the end of the anechoic liner due to the combined effects of tangential flow and high sound intensity; Step 5: Considering the combined effects of tangential flow and high sound intensity, calculate the acoustic impedance of the anechoic lining χ; Step 6: Calculate the acoustic impedance z of the silencing liner by comprehensively considering the acoustic resistance r and acoustic reactance χ of the silencing liner.

2. The method for determining the acoustic impedance of a turbofan engine muffler liner according to claim 1, characterized in that: Step 1 is as follows: in: k n is the proportionality coefficient; V o is the velocity amplitude of the sound particle in the small hole; σ is the perforation rate; c is the speed of sound.

3. The method for determining the acoustic impedance of a turbofan engine muffler liner according to claim 1, characterized in that: In step 1, k n =1.

1.

4. The method for determining the acoustic impedance of a turbofan engine muffler liner according to claim 1, characterized in that: Step 2 is as follows: in: V g Mainstream speed; f is the sound frequency; d is the aperture diameter.

5. The method for determining the acoustic impedance of a turbofan engine muffler liner according to claim 1, characterized in that: In step 2, when V g When <8fd, r g =0.

6. The method for determining the acoustic impedance of a turbofan engine muffler liner according to claim 1, characterized in that: In step 3, according to V0 / V g ≤0.15, V0 / V g >0.15, calculate the acoustic resistance r of the sound insulation in sections.

7. The method for determining the acoustic impedance of a turbofan engine muffler liner according to claim 1, characterized in that: In step 3, V0 / V g ≤0.15: in, v is the gas viscosity coefficient; ω is the angular frequency of the sound source.

8. The method for determining the acoustic impedance of a turbofan engine muffler liner according to claim 1, characterized in that: In step 3, V0 / V g >0.15:

9. The method for determining the acoustic impedance of a turbofan engine muffler liner according to claim 1, characterized in that: In step 3, ω=2πf.

10. The method for determining the acoustic impedance of a turbofan engine muffler liner according to claim 1, characterized in that: Step 4 is as follows: V0 / V g ≤0.15: V0 / V g >0.15: in: t is the thickness of the perforated plate.

11. The method for determining the acoustic impedance of a turbofan engine muffler liner according to claim 1, characterized in that: Step 5 is as follows: in, L is the cell depth.

12. The method for determining the acoustic impedance of a turbofan engine muffler liner according to claim 1, characterized in that: Step 6 is as follows: z=r+iχ in: i is the imaginary part.

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