A method for designing structural parameters of an exhaust muffler of an auxiliary power unit of an aircraft

Abstract

The application belongs to the technical field of aircraft auxiliary power unit noise reduction design, and particularly relates to a structure parameter design method of an aircraft auxiliary power unit exhaust passage muffler, which realizes forward design of the exhaust passage muffler through analysis of frequency spectrum characteristics of an auxiliary power unit exhaust sound source, determination of a muffler configuration, establishment of an acoustic expression, and construction of a parameter optimization algorithm, is efficient and convenient, and can meet the needs of rapid iterative design of an auxiliary power unit exhaust passage muffler in practice.

Description

Technical Field

[0001] The present application belongs to the technical field of aircraft auxiliary power unit noise reduction design, and specifically relates to a method for designing structural parameters of an aircraft auxiliary power unit exhaust duct muffler. Background Art

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

[0003] The exhaust duct noise in the auxiliary power unit noise propagates backward, seriously affecting the ground work area environment. To address this problem, China Civil Aviation Airworthiness Standard CCAR-36 specifically limits apron noise.

[0004] Installing a muffler in the exhaust duct of the auxiliary power unit can effectively reduce the exhaust duct noise. Currently, the design of the exhaust duct muffler of the auxiliary power unit mainly relies on feedback design through experiments, which is time-consuming and labor-intensive, and cannot meet the needs of rapid iterative design of the exhaust duct muffler of the auxiliary power unit 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 auxiliary power unit exhaust muffler to overcome or alleviate at least one of the existing technical deficiencies.

[0007] The technical solution of this application is:

[0008] A method for designing structural parameters of an aircraft auxiliary power unit exhaust muffler, characterized by comprising:

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

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

[0011] Step 3: Analyze the main frequency band f of the exhaust sound source;

[0012] Step 4: Select the exhaust muffler configuration;

[0013] Step 5: Based on the structural parameters of the exhaust muffler, establish the acoustic impedance z expression of the exhaust muffler perforated plate, and establish the sound field p inside the exhaust muffler cavity. c 'expression;

[0014] Step 6: Take the acoustic impedance z of the exhaust muffler perforated plate and the sound field p inside the cavity as the c'Expression, establish the frequency domain sound field p of the exhaust duct with added muffler 消 'expression;

[0015] Step 7: Using the sound pressure P, establish the expression of the total sound pressure level SPL(P) of the exhaust duct;

[0016] Step 8: Combine the frequency domain sound field of the exhaust duct And the frequency domain sound field of the exhaust duct with the muffler installed 消 ', the expression of the total sound pressure level SPL (P) of the exhaust duct, and the expression of the muffler insertion loss TL related to the structural parameters of the exhaust duct muffler;

[0017] Step 9: Select an exhaust duct muffler structural parameter as an independent variable, calculate the muffler insertion loss within a feasible range using the muffler insertion loss TL expression, and take the independent variable with the largest muffler insertion loss TL as the preferred value of the exhaust duct muffler structural parameter;

[0018] Step 10: Determine whether the optimal value of the exhaust duct muffler structural parameter meets the muffler insertion loss requirement. If not, return to step 9 and reselect an exhaust duct muffler structural parameter as the independent variable.

[0019] Optionally, in the above-mentioned aircraft auxiliary power unit exhaust duct muffler structural parameter design method, step 1 is specifically as follows:

[0020] The exhaust duct time domain sound field is obtained based on the experimental test fitting

[0021] Optionally, in the above-mentioned aircraft auxiliary power unit exhaust duct muffler structural parameter design method, step 1 is specifically as follows:

[0022] The exhaust duct time domain sound field is calculated based on the exhaust duct acoustic model

[0023]

[0024] in:

[0025] is the incident sound field of the exhaust duct;

[0026] The scattered sound field of the exhaust duct;

[0027] s is the discrete micro-unit area in the exhaust duct;

[0028] is the air density in the exhaust duct;

[0029] V n ' is the flow-following vibration velocity of the sound source surface in the exhaust duct;

[0030] G is the Green’s function in the flow exhaust duct;

[0031] U is the axial flow velocity in the exhaust duct.

[0032] Optionally, in the above-mentioned aircraft auxiliary power unit exhaust duct muffler structural parameter design method, step 2 is specifically as follows:

[0033] Through Fourier transform, the exhaust duct time domain sound field Transformed into the exhaust duct frequency domain sound field

[0034] Optionally, in the above-mentioned aircraft auxiliary power unit exhaust duct muffler structural parameter design method, in step three, the frequency that has the greatest impact on the total sound pressure level is selected as the main frequency band f of the exhaust sound source.

[0035] Optionally, in the above-mentioned aircraft auxiliary power unit exhaust muffler structural parameter design method,

[0036] In step 4, based on the main frequency band f of the exhaust sound source, the canceller configuration is selected with the principle of maximizing the sound energy absorption.

[0037] Optionally, in the above-mentioned aircraft auxiliary power unit exhaust duct muffler structural parameter design method, in step four, a non-local reactive sound liner is selected as the muffler design configuration.

[0038] Optionally, in the above-mentioned aircraft auxiliary power unit exhaust duct muffler structural parameter design method, in step five, the structural parameters of the exhaust duct muffler include the perforated plate thickness t0, the perforation aperture d, the perforation rate σ, the cavity layer thickness L, and the cavity layer area s0.

[0039] Optionally, in the above-mentioned aircraft auxiliary power unit exhaust muffler structural parameter design method, in step 5, an expression for the acoustic impedance z of the exhaust muffler perforated plate is established, specifically:

[0040] z=r+iχ;

[0041]

[0042]

[0043] ω=2πf;

[0044] in:

[0045] r is the acoustic resistance of the perforated plate;

[0046] i is the imaginary part

[0047] χ is the acoustic reactance of the perforated plate;

[0048] v is the viscosity coefficient of the exhaust gas;

[0049] ω is the angular frequency of the exhaust sound source;

[0050] c is the exhaust duct sound velocity;

[0051] V g is the mainstream velocity in the exhaust duct;

[0052] V0 is the velocity of the sound particle in the small hole;

[0053] δ is the hole end correction coefficient.

[0054] Optionally, in the above-mentioned aircraft auxiliary power unit exhaust muffler structural parameter design method, in step 5, the internal sound field p of the exhaust muffler cavity is established. c 'Expression, specifically:

[0055]

[0056]

[0057] in:

[0058] k is the wave number;

[0059] is the normal particle motion velocity of the muffler sound liner.

[0060] Optionally, in the above-mentioned aircraft auxiliary power unit exhaust duct muffler structural parameter design method, step six is ​​specifically as follows:

[0061]

[0062] Optionally, in the above-mentioned aircraft auxiliary power unit exhaust duct muffler structural parameter design method, step seven is specifically as follows:

[0063]

[0064] in:

[0065] P0 is the reference sound pressure.

[0066] Optionally, in the above-mentioned aircraft auxiliary power unit exhaust duct muffler structural parameter design method, in step seven, the reference sound pressure P0 is taken as 2×10-5.

[0067] Optionally, in the above-mentioned aircraft auxiliary power unit exhaust duct muffler structural parameter design method, step eight is specifically as follows:

[0068] Expressed as TL=F(t0,d,σ,L,s0).

[0069] Optionally, in the above-mentioned aircraft auxiliary power unit exhaust duct muffler structural parameter design method, in step nine, the change step size of the independent variable is 1%, and the cavity layer thickness L and the cavity layer area s0 are preferentially selected as independent variables, and then the perforated plate thickness t0, perforation aperture d, and perforation rate σ are considered as independent variables.

[0070] This application has at least the following beneficial technical effects:

[0071] This paper provides a structural parameter design method for the exhaust duct muffler of an aircraft auxiliary power unit. By analyzing the spectral characteristics of the exhaust sound source of the auxiliary power unit, the muffler configuration is determined, an acoustic expression is established, and a parameter optimization algorithm is constructed to achieve forward design of the exhaust duct muffler. This method is efficient and convenient, and can meet the needs of rapid iterative design of the exhaust duct muffler of the auxiliary power unit in practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 It is a schematic diagram of the structural parameter design method of the aircraft auxiliary power unit exhaust duct muffler provided in an embodiment of the present application.

[0073] 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

[0074] 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.

[0075] 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.

[0076] 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.

[0077] A structural parameter design method for the exhaust muffler of an aircraft auxiliary power unit, such as Figure 1 shown.

[0078] Step 1: Determine the time domain sound field of the exhaust duct

[0079] The exhaust duct time domain sound field can be obtained based on the experimental test fitting The exhaust duct time domain sound field can also be calculated based on the exhaust duct acoustic model

[0080] In the exhaust duct acoustic model, the central axis of the exhaust 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 exhaust duct time domain sound field. The details are as follows:

[0081]

[0082] in:

[0083] is the incident sound field of the exhaust duct;

[0084] The scattered sound field of the exhaust duct;

[0085] s is the discrete micro-unit area in the exhaust duct;

[0086] is the air density in the exhaust duct;

[0087] V n ' is the flow-following vibration velocity of the sound source surface in the exhaust duct;

[0088] G is the Green’s function in the flow exhaust duct;

[0089] U is the axial flow velocity in the exhaust duct.

[0090] Step 2: Calculate the frequency domain sound field of the exhaust duct

[0091] Through Fourier transform, the exhaust duct time domain sound field Transformed into the exhaust duct frequency domain sound field

[0092] Step 3: Analyze the main frequency band f of the exhaust sound source.

[0093] The frequency that has the greatest impact on the total sound pressure level is selected as the main frequency band f of the exhaust sound source.

[0094] Step 4: Select the exhaust muffler configuration.

[0095] According to the main frequency band f of the exhaust sound source, the canceller configuration is selected with the principle of maximizing the sound energy absorption.

[0096] Non-local reactive sound lining can usually be selected as the muffler design configuration. The non-local reactive sound lining is mainly composed of a perforated panel and a cavity layer, which can broaden the sound absorption band.

[0097] Step 5: Based on the structural parameters of the exhaust muffler, establish the acoustic impedance z expression of the exhaust muffler perforated plate, and establish the sound field p inside the exhaust muffler cavity. c 'expression.

[0098] The structural parameters of the exhaust muffler include the perforated plate thickness t0, the perforation aperture d, the perforation rate σ, the cavity layer thickness L, and the cavity layer area s0.

[0099] The acoustic impedance z expression of the exhaust muffler perforated plate is established as follows:

[0100] z=r+iχ;

[0101]

[0102]

[0103] ω=2πf;

[0104] in:

[0105] r is the acoustic resistance of the perforated plate;

[0106] i is the imaginary part

[0107] χ is the acoustic reactance of the perforated plate;

[0108] v is the viscosity coefficient of the exhaust gas;

[0109] ω is the angular frequency of the exhaust sound source;

[0110] c is the exhaust duct sound velocity;

[0111] V g is the mainstream velocity in the exhaust duct;

[0112] V0 is the velocity of the sound particle in the small hole;

[0113] δ is the hole end correction coefficient.

[0114] Establish the sound field inside the exhaust muffler cavity p c 'The expression is as follows:

[0115]

[0116]

[0117] in:

[0118] k is the wave number;

[0119] is the normal particle motion velocity of the muffler sound liner

[0120] is the normal particle motion velocity of the exhaust muffler sound liner.

[0121]

[0122] Step 6: Take the acoustic impedance z of the exhaust muffler perforated plate and the sound field p inside the cavity as the c 'Expression, establish the frequency domain sound field p of the exhaust duct with added muffler 消 ' expression.

[0123]

[0124] Step 7: Using the sound pressure P, establish the expression for the total sound pressure level SPL(P) of the exhaust duct.

[0125]

[0126] in:

[0127] P0 is the reference sound pressure, which is 2×10-5.

[0128] Step 8: Combine the frequency domain sound field of the exhaust duct And the frequency domain sound field of the exhaust duct with the muffler installed 消 ', the expression of the total sound pressure level SPL (P) of the exhaust duct, and the expression of the muffler insertion loss TL related to the structural parameters of the exhaust duct muffler are established.

[0129]

[0130] The muffler insertion loss TL is a function of the structural parameters of the exhaust muffler and can be expressed as TL=F(t0, d, σ, L, s0), which serves as an optimization function for the exhaust muffler design.

[0131] Step 9. Select an exhaust duct muffler structural parameter as the independent variable, and calculate the muffler insertion loss within the feasible range using the muffler insertion loss TL expression. The independent variable with the largest muffler insertion loss TL is selected as the preferred value of the exhaust duct muffler structural parameter.

[0132] The change step of the independent variable can be 1%, and the other exhaust muffler structural parameters are fixed.

[0133] The feasible range of the independent variables is determined by considering the requirements of processing technology, weight and space constraints.

[0134] The cavity parameters cavity layer thickness L and cavity layer area s0 are preferably selected as independent variables, and then the perforated plate parameters perforated plate thickness t0, perforation aperture d, and perforation rate σ are considered as independent variables.

[0135] The contour map of the muffler insertion loss TL can be drawn, from which the optimal values ​​of the exhaust muffler structural parameters can be selected.

[0136] Step 10: Determine whether the optimal value of the exhaust duct muffler structural parameter meets the muffler insertion loss requirement. If not, return to step 9 and reselect an exhaust duct muffler structural parameter as the independent variable.

[0137] The structural parameter design method for an aircraft auxiliary power unit exhaust duct muffler disclosed in the above embodiment determines the muffler configuration by analyzing the spectral characteristics of the auxiliary power unit exhaust sound source, establishes an acoustic expression, and constructs a parameter optimization algorithm to achieve forward design of the exhaust duct muffler. This method is efficient and convenient, and can meet the needs of rapid iterative design of auxiliary power unit exhaust duct mufflers in practice. Ground tests have shown that a muffler with an insertion loss of more than 3dB can be designed.

[0138] 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 auxiliary power unit exhaust muffler, characterized in that: include: Step 1: Determine the time domain sound field of the exhaust duct Step 2: Calculate the frequency domain sound field of the exhaust duct Step 3: Analyze the main frequency band f of the exhaust sound source; Step 4: Select the exhaust muffler configuration; Step 5: Based on the structural parameters of the exhaust muffler, establish the acoustic impedance z expression of the exhaust muffler perforated plate, and establish the sound field p inside the exhaust muffler cavity. c 'expression; Step 6: Take the acoustic impedance z of the exhaust muffler perforated plate and the sound field p inside the cavity as the c ′ expression, establish the frequency domain sound field p of the exhaust duct with added muffler 消 ′’s expression; Step 7: Using the sound pressure P, establish the expression of the total sound pressure level SPL(P) of the exhaust duct; Step 8: Combine the frequency domain sound field of the exhaust duct And the frequency domain sound field of the exhaust duct with the muffler installed 消 ', the expression of the total sound pressure level SPL (P) of the exhaust duct, and the expression of the muffler insertion loss TL related to the structural parameters of the exhaust duct muffler; Step 9: Select an exhaust duct muffler structural parameter as an independent variable, calculate the muffler insertion loss within a feasible range using the muffler insertion loss TL expression, and take the independent variable with the largest muffler insertion loss TL as the preferred value of the exhaust duct muffler structural parameter; Step 10: Determine whether the optimal value of the exhaust duct muffler structural parameter meets the muffler insertion loss requirement. If not, return to step 9 and reselect an exhaust duct muffler structural parameter as the independent variable.

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

4. The aircraft auxiliary power unit exhaust muffler structural parameter design method according to claim 3, characterized in that: Step 2 is as follows: Through Fourier transform, the exhaust duct time domain sound field Transformed into the exhaust duct frequency domain sound field 5. The aircraft auxiliary power unit exhaust muffler structural parameter design method according to claim 4, characterized in that: In step 3, the frequency that has the greatest impact on the total sound pressure level is selected as the main frequency band f of the exhaust sound source.

6. The aircraft auxiliary power unit exhaust muffler structural parameter design method according to claim 5, characterized in that: In step 4, based on the main frequency band f of the exhaust sound source, the canceller configuration is selected with the principle of maximizing the sound energy absorption.

7. The aircraft auxiliary power unit exhaust muffler structural parameter design method according to claim 6, characterized in that: In step 4, the non-local reactive sound lining is selected as the muffler design configuration.

8. The aircraft auxiliary power unit exhaust muffler structural parameter design method according to claim 7, characterized in that: In step 5, the structural parameters of the exhaust muffler include the thickness of the perforated plate t0, the perforation diameter d, the perforation ratio σ, the thickness of the cavity layer L, and the area of ​​the cavity layer s0.

9. The aircraft auxiliary power unit exhaust muffler structural parameter design method according to claim 8, characterized in that: In step 5, the acoustic impedance z expression of the exhaust muffler perforated plate is established, specifically: z=r+iχ; ω=2πf; in: r is the acoustic resistance of the perforated plate; i is the imaginary part χ is the acoustic reactance of the perforated plate; v is the viscosity coefficient of the exhaust gas; ω is the angular frequency of the exhaust sound source; c is the exhaust duct sound velocity; V g is the mainstream velocity in the exhaust duct; V0 is the velocity of the sound particle in the small hole; δ is the hole end correction coefficient.

10. The aircraft auxiliary power unit exhaust muffler structural parameter design method according to claim 9, characterized in that: In step 5, the sound field inside the exhaust muffler cavity is established c ' expression, specifically: in: k is the wave number; V n f is the normal particle motion velocity of the muffler sound liner.

11. The aircraft auxiliary power unit exhaust muffler structural parameter design method according to claim 10, characterized in that: Step six is ​​as follows: p 消 '=p c '+ρcV n f With.

12. The aircraft auxiliary power unit exhaust muffler structural parameter design method according to claim 11, characterized in that: Step seven is as follows: in: P0 is the reference sound pressure.

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

14. The aircraft auxiliary power unit exhaust muffler structural parameter design method according to claim 13, characterized in that: Step 8 is as follows: Expressed as TL=F(t0,d,σ,L,s0).

15. The aircraft auxiliary power unit exhaust muffler structural parameter design method according to claim 14, characterized in that: In step nine, the change step of the independent variable is 1%, and the cavity layer thickness L and the cavity layer area s0 are preferentially selected as independent variables, and then the perforated plate thickness t0, the perforation aperture d, and the perforation rate σ are considered as independent variables.

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