A method for designing structural parameters of an aircraft APU inlet duct muffler

Abstract

The application belongs to the technical field of aircraft APU noise reduction design, and particularly relates to a kind of aircraft APU air inlet noise eliminator structure parameter design method, through the spectrum characteristic analysis of APU air inlet sound source, according to the matching requirement of noise eliminator and sound source, acoustic expression is established, and parameter optimization algorithm is constructed, the forward design of air inlet noise eliminator is realized, it is efficient and convenient, and can meet the needs of rapid iteration design of APU air inlet noise eliminator in practice.

Description

Technical Field

[0001] The present application belongs to the technical field of aircraft APU silencer and noise reduction design, and specifically relates to a method for designing structural parameters of an aircraft APU inlet silencer. Background Art

[0002] Large and medium-sized aircraft all use auxiliary power units (APUs) to provide emergency energy in sudden situations. APUs have become a major source of noise when aircraft are docked for maintenance on the ground.

[0003] The inlet noise in the APU noise propagates forward, seriously affecting the ground work area environment. To address this problem, China's Civil Aviation Airworthiness Standard CCAR-36 specifically limits apron noise.

[0004] Installing a muffler in the APU inlet duct can effectively reduce the inlet noise. Currently, the design of APU inlet muffler mainly relies on experimental feedback design, which is time-consuming and labor-intensive, and cannot meet the needs of rapid iterative design of APU inlet muffler in practice.

[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 designing structural parameters of an aircraft APU inlet muffler to overcome or alleviate at least one of the existing technical deficiencies.

[0007] The technical solution of this application is:

[0008] A structural parameter design method for an aircraft APU air intake muffler includes:

[0009] Step 1: Determine the time domain sound field of the inlet

[0010] Step 2: Calculate the frequency domain sound field of the intake duct

[0011] Step 3: Calculate the APU compressor passing frequency f n ;

[0012] Step 4: Analyze the main frequency f of the intake sound source m ;

[0013] Determine the frequency domain sound field of the air intake The main diffusion frequency f and the APU compressor pass frequency f n If not, return to step 1 and re-determine the time domain sound field of the intake duct. The frequency that has the greatest impact on the total sound pressure level is selected as the main frequency f of the intake sound source m ;

[0014] Step 5: Select the intake muffler configuration;

[0015] Step 6: Using the structural parameters of the intake muffler, establish an expression for the acoustic impedance z of the intake muffler;

[0016] Step 7: Using the acoustic impedance z expression of the intake muffler, establish the frequency domain sound field p of the intake duct with the muffler installed 消 'expression;

[0017] Step 8: Using the sound pressure P, establish an expression for the total sound pressure level SPL(P) of the intake duct;

[0018] Step 9: Combine the frequency domain sound field of the air intake And the frequency domain sound field of the inlet duct with the muffler installed 消 ', the expression of the total sound pressure level SPL (P) of the intake duct, and the expression of the muffler insertion loss TL related to the structural parameters of the intake duct muffler;

[0019] Step 10: Select two intake duct muffler structural parameters as independent variables, calculate the muffler insertion loss within a feasible range using the muffler insertion loss TL expression, and select the independent variable combination that maximizes the muffler insertion loss TL as the optimal value of the intake duct muffler structural parameters;

[0020] Step 11: Determine whether the optimal values ​​of the intake duct muffler structural parameters meet the muffler insertion loss requirements. If not, return to step 10 and reselect two intake duct muffler structural parameters as independent variables.

[0021] According to at least one embodiment of the present application, in the above-mentioned aircraft APU inlet muffler structural parameter design method, step 1 is specifically as follows:

[0022] The time domain sound field of the air intake is obtained by fitting the experimental test

[0023] According to at least one embodiment of the present application, in the above-mentioned aircraft APU inlet muffler structural parameter design method,

[0024] Step 1 is as follows:

[0025] The time domain sound field of the intake duct is calculated based on the intake duct acoustic model

[0026]

[0027] in:

[0028] is the incident sound field of the inlet;

[0029] is the scattered sound field of the inlet;

[0030] s is the discrete micro-unit area in the intake duct;

[0031] is the air density in the intake duct;

[0032] V n ' is the flow-following vibration velocity of the sound source surface in the inlet;

[0033] G is the Green’s function in the flow inlet;

[0034] U is the axial flow velocity in the inlet duct.

[0035] According to at least one embodiment of the present application, in the above-mentioned aircraft APU inlet muffler structural parameter design method, step 2 is specifically as follows:

[0036] Through Fourier transform, the time domain sound field of the intake duct is transformed Transformed into the frequency domain sound field of the air intake

[0037] According to at least one embodiment of the present application, in the above-mentioned aircraft APU inlet muffler structural parameter design method, step three is specifically as follows:

[0038] f n =nBf s ;

[0039] in:

[0040] n is a positive integer of 1, 2, 3, ..., indicating the order of frequency;

[0041] B is the number of APU compressors;

[0042] f s is the APU axis frequency.

[0043] According to at least one embodiment of the present application, in the above-mentioned aircraft APU inlet muffler structural parameter design method, in step 3, the value of n does not exceed 5.

[0044] According to at least one embodiment of the present application, in the above-mentioned aircraft APU inlet muffler structural parameter design method, in step 4, , return to step 1.

[0045] According to at least one embodiment of the present application, in the above-mentioned aircraft APU inlet muffler structural parameter design method, in step 5, according to the main frequency f of the inlet sound source m , and the reflection principle of the air inlet cross section, with the principle of maximizing the amount of sound energy absorption, the canceller configuration is selected.

[0046] According to at least one embodiment of the present application, in the above-mentioned aircraft APU inlet muffler structural parameter design method, in step six, the structural parameters of the inlet muffler include the perforated plate thickness t0, the perforation aperture d, the cavity layer thickness L, and the perforation rate σ.

[0047] According to at least one embodiment of the present application, in the above-mentioned aircraft APU inlet muffler structural parameter design method, in step 6, the expression for the acoustic impedance z of the inlet muffler is established as:

[0048] z=r+iχ;

[0049]

[0050]

[0051] ω=2πf m ;

[0052] in:

[0053] r is the acoustic resistance of the intake muffler;

[0054] i is the imaginary part

[0055] χ is the intake muffler acoustic reactance;

[0056] v is the viscosity coefficient of the inlet gas;

[0057] ω is the angular frequency of the intake sound source;

[0058] c is the speed of sound at the inlet;

[0059] V g is the mainstream velocity in the inlet;

[0060] δ is the hole end correction coefficient.

[0061] According to at least one embodiment of the present application, in the above-mentioned aircraft APU inlet muffler structural parameter design method, step seven is specifically as follows:

[0062]

[0063] in:

[0064] is the normal particle motion velocity of the intake muffler sound liner.

[0065] According to at least one embodiment of the present application, in the above-mentioned aircraft APU inlet muffler structural parameter design method, step eight is specifically as follows:

[0066]

[0067] in:

[0068] P0 is the reference sound pressure.

[0069] According to at least one embodiment of the present application, in the above-mentioned aircraft APU inlet muffler structural parameter design method, in step eight, the reference sound pressure P0 is set to 2×10-5.

[0070] According to at least one embodiment of the present application, in the above-mentioned aircraft APU inlet muffler structural parameter design method, step nine is specifically as follows:

[0071] Expressed as TL=F(t0,d,σ,L).

[0072] According to at least one embodiment of the present application, in the above-mentioned aircraft APU inlet muffler structural parameter design method, in step ten, the change step size of the independent variable is 1%.

[0073] This application has at least the following beneficial technical effects:

[0074] This paper provides a structural parameter design method for aircraft APU inlet muffler. By analyzing the spectral characteristics of the APU intake sound source and establishing an acoustic expression based on the matching requirements between the muffler and the sound source, a parameter optimization algorithm is constructed to achieve forward design of the inlet muffler. This method is efficient and convenient, and can meet the needs of rapid iterative design of APU inlet mufflers in practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 Schematic diagram of the aircraft APU inlet muffler structural parameter design method provided in an embodiment of the present application.

[0076] 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

[0077] 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.

[0078] 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.

[0079] 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.

[0080] A structural parameter design method for aircraft APU inlet muffler, such as Figure 1 shown.

[0081] Step 1: Determine the time domain sound field of the inlet

[0082] The time domain sound field of the inlet can be obtained based on the experimental test fitting The time domain sound field of the intake duct can also be calculated based on the intake duct acoustic model.

[0083] In the intake duct acoustic model, the central axis of the intake duct is the X direction, the circular cross section is the Y direction, and the Z direction is determined according to the right-hand rule to calculate the time domain sound field of the intake duct. The details are as follows:

[0084]

[0085] in:

[0086] is the incident sound field of the inlet;

[0087] is the scattered sound field of the inlet;

[0088] s is the discrete micro-unit area in the intake duct;

[0089] is the air density in the intake duct;

[0090] V n ' is the flow-following vibration velocity of the sound source surface in the inlet;

[0091] G is the Green’s function in the flow inlet;

[0092] U is the axial flow velocity in the inlet duct.

[0093] Step 2: Calculate the frequency domain sound field of the intake duct

[0094] Through Fourier transform, the time domain sound field of the intake duct is transformed Transformed into the frequency domain sound field of the air intake

[0095] Step 3: Calculate the APU compressor passing frequency f n .

[0096] f n =nBf s ;

[0097] in:

[0098] n is a positive integer such as 1, 2, 3, etc., which indicates the frequency order and usually does not exceed 5;

[0099] B is the number of APU compressors;

[0100] f s is the APU axis frequency.

[0101] Step 4: Analyze the main frequency f of the intake sound source m .

[0102] Determine the frequency domain sound field of the air intake The main diffusion frequency f and the APU compressor pass frequency f n Is it consistent? If not, return to step 1 and design the specific When , return to step 1 to determine the time domain sound field of the intake duct The frequency that has the greatest impact on the total sound pressure level is selected as the main frequency f of the intake sound source m .

[0103] Step 5: Select the intake muffler configuration.

[0104] According to the main frequency f of the intake sound source m , and the reflection principle of the air inlet cross section, with the principle of maximizing the sound energy absorption, the muffler configuration is selected. Usually, the local reaction sound liner can be selected as the muffler design configuration. The local reaction sound liner is mainly composed of a perforated plate and a honeycomb structure cavity layer.

[0105] Step 6: Based on the structural parameters of the intake muffler, establish the expression of the acoustic impedance z of the intake muffler.

[0106] The structural parameters of the intake muffler include the perforated plate thickness t0, the perforation aperture d, the cavity layer thickness L, and the perforation rate σ.

[0107] The expression of the acoustic impedance z of the intake muffler is as follows:

[0108] z=r+iχ;

[0109]

[0110]

[0111] ω=2πf m ;

[0112] in:

[0113] r is the acoustic resistance of the intake muffler;

[0114] i is the imaginary part

[0115] χ is the intake muffler acoustic reactance;

[0116] v is the viscosity coefficient of the inlet gas;

[0117] ω is the angular frequency of the intake sound source;

[0118] c is the speed of sound at the inlet;

[0119] V g is the mainstream velocity in the inlet;

[0120] δ is the hole end correction coefficient.

[0121] Step 7: Use the acoustic impedance z expression of the intake muffler to establish the installation of the muffler

[0122] Frequency domain sound field of the intake duct p 消 ' expression.

[0123]

[0124] in:

[0125] is the normal particle motion velocity of the intake muffler sound liner.

[0126]

[0127] Step 8: Using the sound pressure P, establish the expression for the total sound pressure level SPL(P) of the intake duct.

[0128]

[0129] in:

[0130] P0 is the reference sound pressure, which is 2×10-5.

[0131] Step 9: Combine the frequency domain sound field of the air intake And the frequency domain sound field of the inlet duct with the muffler installed 消 ', the expression of the total sound pressure level SPL(P) of the intake duct, and the expression of the muffler insertion loss TL related to the structural parameters of the intake duct muffler are established.

[0132]

[0133] The muffler insertion loss TL is a function of the structural parameters of the intake muffler and can be expressed as TL = F(t0, d, σ, L), which serves as an optimization function for the intake muffler design.

[0134] Step 10: Select two intake duct muffler structural parameters as independent variables, calculate the muffler insertion loss within a feasible range using the muffler insertion loss TL expression, and take the independent variable combination that maximizes the muffler insertion loss TL as the preferred value of the intake duct muffler structural parameters.

[0135] The change step of the independent variable can be 1%, and the other intake muffler structural parameters are fixed.

[0136] The feasible range of the independent variables is determined by considering the requirements of processing technology, weight and space constraints.

[0137] The two independent variables can be used as the horizontal and vertical coordinates to draw a contour map of the muffler insertion loss TL, from which the optimal values ​​of the intake muffler structural parameters can be selected.

[0138] Step 11: Determine whether the optimal values ​​of the intake duct muffler structural parameters meet the muffler insertion loss requirements. If not, return to step 10 and reselect two intake duct muffler structural parameters as independent variables.

[0139] The aircraft APU inlet muffler structural parameter design method disclosed in the above embodiment analyzes the spectral characteristics of the APU inlet sound source, establishes an acoustic expression based on the matching requirements between the muffler and the sound source, and constructs a parameter optimization algorithm to achieve forward design of the inlet muffler. This method is efficient and convenient, and can meet the needs of rapid iterative design of APU inlet mufflers in practice. Ground tests have shown that a muffler with an insertion loss of 5dB or more can be designed.

[0140] 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 designing structural parameters of an aircraft APU inlet muffler, characterized in that: include: Step 1: Determine the time domain sound field of the inlet Step 2: Calculate the frequency domain sound field of the intake duct Step 3: Calculate the APU compressor passing frequency f n ; Step 4: Analyze the main frequency f of the intake sound source m ; Determine the frequency domain sound field of the air intake The main diffusion frequency f and the APU compressor pass frequency f n If not, return to step 1 and re-determine the time domain sound field of the intake duct. The frequency that has the greatest impact on the total sound pressure level is selected as the main frequency f of the intake sound source m ; Step 5: Select the intake muffler configuration; Step 6: Using the structural parameters of the intake muffler, establish an expression for the acoustic impedance z of the intake muffler; Step 7: Using the acoustic impedance z expression of the intake muffler, establish the frequency domain sound field p of the intake duct with the muffler installed 消 ′’s expression; Step 8: Using the sound pressure P, establish an expression for the total sound pressure level SPL(P) of the intake duct; Step 9: Combine the frequency domain sound field of the air intake And the frequency domain sound field of the inlet duct with the muffler installed 消 ', the expression of the total sound pressure level SPL (P) of the intake duct, and the expression of the muffler insertion loss TL related to the structural parameters of the intake duct muffler; Step 10: Select two intake duct muffler structural parameters as independent variables, calculate the muffler insertion loss within a feasible range using the muffler insertion loss TL expression, and select the independent variable combination that maximizes the muffler insertion loss TL as the optimal value of the intake duct muffler structural parameters; Step 11: Determine whether the optimal values ​​of the intake duct muffler structural parameters meet the muffler insertion loss requirements. If not, return to step 10 and reselect two intake duct muffler structural parameters as independent variables.

2. The aircraft APU inlet muffler structural parameter design method according to claim 1, characterized in that: Step 1 is as follows: The time domain sound field of the air intake is obtained by fitting the experimental test 3. The aircraft APU inlet muffler structural parameter design method according to claim 2, characterized in that: Step 1 is as follows: The time domain sound field of the intake duct is calculated based on the intake duct acoustic model in: is the incident sound field of the inlet; is the scattered sound field of the inlet; s is the discrete micro-unit area in the intake duct; is the air density in the intake duct; V n ' is the flow-following vibration velocity of the sound source surface in the inlet; G is the Green’s function in the flow inlet; U is the axial flow velocity in the inlet duct.

4. The aircraft APU inlet muffler structural parameter design method according to claim 3, characterized in that: Step 2 is as follows: Through Fourier transform, the time domain sound field of the intake duct is transformed Transformed into the frequency domain sound field of the air intake 5. The aircraft APU inlet muffler structural parameter design method according to claim 4, characterized in that: Step three is as follows: f n =nBf s ; in: n is a positive integer of 1, 2, 3, ..., indicating the order of frequency; B is the number of APU compressors; f s is the APU axis frequency.

6. The aircraft APU inlet muffler structural parameter design method according to claim 5, characterized in that: In step 3, the value of n does not exceed 5.

7. The aircraft APU inlet muffler structural parameter design method according to claim 6, characterized in that: In step 4, , return to step 1.

8. The aircraft APU inlet muffler structural parameter design method according to claim 7, characterized in that: In step 5, according to the main frequency f of the intake sound source m , and the reflection principle of the air inlet cross section, with the principle of maximizing the amount of sound energy absorption, the canceller configuration is selected.

9. The aircraft APU inlet muffler structural parameter design method according to claim 8, characterized in that: In step six, the structural parameters of the intake muffler include the perforated plate thickness t0, the perforation diameter d, the cavity layer thickness L, and the perforation ratio σ.

10. The aircraft APU inlet muffler structural parameter design method according to claim 9, characterized in that: In step 6, the expression of the acoustic impedance z of the intake muffler is established as: z=r+iχ; ω=2πf m ; in: r is the acoustic resistance of the intake muffler; i is the imaginary part χ is the intake muffler acoustic reactance; v is the viscosity coefficient of the inlet gas; ω is the angular frequency of the intake sound source; c is the speed of sound at the inlet; V g is the mainstream velocity in the inlet; δ is the hole end correction coefficient.

11. The aircraft APU inlet muffler structural parameter design method according to claim 10, characterized in that: Step seven is as follows: p 消 '=-V n f ·with; in: V n f is the normal particle motion velocity of the intake muffler sound liner.

12. The aircraft APU inlet muffler structural parameter design method according to claim 11, characterized in that: Step 8 is as follows: in: P0 is the reference sound pressure.

13. The aircraft APU inlet muffler structural parameter design method according to claim 12, characterized in that: In step eight, the reference sound pressure P0 is set to 2×10-5.

14. The aircraft APU inlet muffler structural parameter design method according to claim 13, characterized in that: Step nine is as follows: Expressed as TL=F(t0,d,σ,L).

15. The aircraft APU inlet muffler structural parameter design method according to claim 14, characterized in that: In step 10, the change step size of the independent variable is 1%.

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