A method for determining the acoustic impedance of a sound absorbing lining of a turbofan engine

Abstract

The present application belongs to the technical field of turbofan engine muffler liner design, and specifically relates to a method for determining the acoustic impedance of a turbofan engine muffler liner, comprising: step 1, calculating the acoustic impedance r of the muffler liner affected by high sound intensity. n ; Step 2: Calculate the acoustic resistance r of the muffler lining affected by tangential flow g ; Step 3, considering the influence of high sound intensity and tangential flow, according to 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 used to calculate the acoustic resistance r of the sound insulation lining in sections; Step 4, calculate the correction coefficient δ of the sound insulation lining end due to the combined influence of tangential flow and high sound intensity; Step 5, consider the combined influence of tangential flow and high sound intensity to calculate the acoustic reactance χ of the sound insulation lining; Step 6, comprehensively consider the acoustic resistance r and acoustic reactance χ of the sound insulation lining to calculate the acoustic impedance z of the sound insulation lining.

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 lining is installed on the wall of its nacelle, and a perforated plate lining is used to absorb and reduce noise.

[0003] Accurately determining the acoustic impedance of the turbofan engine's 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 designer, 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.

[0007] The technical solution of this application is:

[0008] A method for determining the acoustic impedance of a turbofan engine muffler liner comprises:

[0009] Step 1: Calculate the acoustic resistance r of the anechoic lining affected by high sound intensity n ;

[0010] Step 2: Calculate the acoustic resistance r of the muffler lining affected by tangential flow g ;

[0011] 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 silencing lining is calculated segment by segment;

[0012] 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;

[0013] Step 5: Considering the combined effects of tangential flow and high sound intensity, calculate the noise resistance of the anechoic lining;

[0014] Step 6: Calculate the acoustic impedance z of the silencing lining by comprehensively considering the acoustic resistance r and acoustic reactance χ of the silencing lining.

[0015] 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 1 is specifically as follows:

[0016]

[0017] in:

[0018] k n is the proportionality coefficient;

[0019] V o is the velocity amplitude of the sound particle in the small hole;

[0020] σ is the perforation rate;

[0021] c is the speed of sound.

[0022] 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.

[0023] 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 2 is specifically as follows:

[0024]

[0025] in:

[0026] V g For mainstream speed;

[0027] f is the sound frequency;

[0028] d is the aperture diameter.

[0029] According to at least one embodiment of the present application, in the above-mentioned method for determining the acoustic impedance of the muffler lining of a turbofan engine, in step 2, when V g When <8fd, r g =0.

[0030] According to at least one embodiment of the present application, in the above-mentioned method for determining the acoustic impedance of the muffler lining 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 silencing lining in sections.

[0031] According to at least one embodiment of the present application, in the above-mentioned method for determining the acoustic impedance of the muffler lining of a turbofan engine, in step 3, V0 / V g When ≤0.15:

[0032] in,

[0033] v is the gas viscosity coefficient;

[0034] ω is the angular frequency of the sound source.

[0035] According to at least one embodiment of the present application, in the above-mentioned method for determining the acoustic impedance of the muffler lining of a turbofan engine, in step 3, V0 / V g >0.15:

[0036] 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 three, ω=2πf.

[0037] 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 four is specifically as follows:

[0038] V0 / V g When ≤0.15:

[0039]

[0040] V0 / V g >0.15:

[0041]

[0042] in:

[0043] t is the thickness of the perforated plate.

[0044] 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 five is specifically as follows:

[0045]

[0046] in,

[0047] L is the cell depth.

[0048] 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:

[0049] z=r+iχ

[0050] in:

[0051] i is the imaginary part.

[0052] This application has at least the following beneficial technical effects:

[0053] A method for determining the acoustic impedance of a turbofan engine muffler liner is provided. The method considers the influence of the acoustic environment on the acoustic impedance of the turbofan engine muffler liner, modifies the purely 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

[0054] Figure 1 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;

[0055] Figure 2 Schematic diagram of the effect of the acoustic environment on the acoustic impedance of the muffler lining of a turbofan engine provided by an embodiment of the present application;

[0056] Figure 3 It is a schematic diagram of the method for determining the acoustic impedance of the sound absorbing liner of a turbofan engine provided in an embodiment of the present application.

[0057] In order to better illustrate this embodiment, some contents of the drawings may be omitted. They are only used for illustrative purposes and should not be construed as limiting the present application. DETAILED DESCRIPTION

[0058] To make the technical solution and its advantages of this application more clear, the technical solution of this application will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described here are only some of the embodiments of this application and are only used to explain this application, not to limit this application. It should be noted that for ease of description, only the parts relevant to this application are shown in the accompanying drawings, and other relevant parts can refer to the general design.

[0059] In addition, unless otherwise defined, the technical terms or scientific terms used in the description of this application should have the usual meanings understood by those skilled in the art in the field to which this application belongs. The words indicating orientation used in the description of this application 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 means 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.

[0060] In addition, it should be noted that, unless otherwise clearly stipulated 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.

[0061] According to experience and relevant theoretical formulas, the factors affecting the acoustic impedance of the muffler lining of a turbofan engine can be divided into two aspects: structural parameters and acoustic environment. Among them, structural parameters include small hole diameter, perforated plate thickness, perforation rate, honeycomb depth, etc.; acoustic environment includes tangential flow, high sound intensity, gas viscosity, radiation effect, etc.

[0062] Analyze the effect 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 impact on the acoustic resistance of the muffler liner of the turbofan engine, while the effects of gas viscosity and radiation effect on the acoustic resistance of the muffler liner of the turbofan engine can be ignored.

[0063] 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 greater impact 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.

[0064] Based on the above, the embodiment of the present application provides a method for determining the acoustic impedance of the muffler liner of a turbofan engine, such as Figure 1 shown.

[0065] Step 1: Calculate the acoustic resistance r of the anechoic lining affected by high sound intensity n .

[0066] At high sound intensity, the nonlinear acoustic resistance is proportional to the particle velocity in the small hole, and so:

[0067]

[0068] in:

[0069] k n is the proportional coefficient, considering the effect of harmonics caused by nonlinear odd changes, k n =1.1;

[0070] V o is the velocity amplitude of the sound particle in the small hole;

[0071] σ is the perforation rate;

[0072] c is the speed of sound.

[0073] Step 2: Calculate the acoustic resistance r of the muffler lining affected by tangential flow g .

[0074] Considering the tangential flow effect, based on the geometry and flow conditions, a mainstream velocity-type acoustic resistance empirical model can be constructed, which is:

[0075]

[0076] in:

[0077] V g For mainstream speed;

[0078] f is the sound frequency;

[0079] d is the aperture diameter.

[0080] When V g When <8fd, r g =0.

[0081] 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 insulation is calculated in sections, and the sound resistance r of the sound insulation is calculated in sections.

[0082] V0 / V g When ≤0.15:

[0083]

[0084] V0 / V g >0.15:

[0085]

[0086] in,

[0087] v is the gas viscosity coefficient;

[0088] ω is the angular frequency of the sound source.

[0089] ω=2πf。

[0090] 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.

[0091] 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 reactance can be established:

[0092] V0 / V g When ≤0.15:

[0093]

[0094] V0 / V g >0.15:

[0095]

[0096] in:

[0097] t is the thickness of the perforated plate.

[0098] Step 5. Considering the combined effects of tangential flow and high sound intensity, calculate the sound resistance of the silencing lining χ.

[0099]

[0100] in,

[0101] L is the cell depth.

[0102] Step 6: Calculate the acoustic impedance z of the silencing lining by comprehensively considering the acoustic resistance r and acoustic reactance χ of the silencing lining.

[0103] z=r+iχ

[0104] in:

[0105] i is the imaginary part.

[0106] The method for determining the acoustic impedance of the muffler liner of a turbofan engine disclosed in the above embodiment is based on existing experience, experimental data and semi-empirical models, takes into account the influence of the acoustic environment on the acoustic impedance of the muffler liner of the turbofan engine, modifies the pure theoretical model, and determines the acoustic impedance of the muffler liner of the 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 the turbofan engine can be obtained quickly and accurately, and can effectively guide the design improvement of the muffler liner.

[0107] 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 replacements to the relevant technical features, and the technical solutions after these changes or replacements 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 muffler lining affected by tangential flow g ; Step 3: Consider the influence of high sound intensity and tangential flow, according to the velocity amplitude V of the sound particle in the small hole o , mainstream speed V g The relative size of the silencing lining is calculated segment by segment; 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; 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 anechoic lining by comprehensively considering the acoustic resistance r and the acoustic reactance χ of the anechoic lining; 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; Step 2 is as follows: in: V g For mainstream speed; f is the sound frequency; d is the aperture of the small hole; In step 3, according to V0 / V g ≤0.15, V0 / V g >0.15, calculate the acoustic resistance r of the anechoic lining in sections; V0 / V g When ≤0.15: in, v is the gas viscosity coefficient; ω is the angular frequency of the sound source; V0 / V g >0.15: Step 4 is as follows: V0 / V g When ≤0.15: V0 / V g >0.15: in: t is the thickness of the perforated plate; Step 5 is as follows: in, L is the cell depth.

2. 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.

3. 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.

4. 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.

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

Images