Aircraft auxiliary power device exhaust passage silencer structure parameter design method

Abstract

The invention belongs to the technical field of silencing and noise reduction design of aircraft auxiliary power devices, and particularly relates to a structural parameter design method of an exhaust passage silencer of an aircraft auxiliary power device, which comprises the following steps of: analyzing the spectral characteristics of an exhaust sound source of the auxiliary power device, determining the configuration of the silencer, establishing an acoustic expression and constructing a parameter optimization algorithm; the forward design of the exhaust passage silencer is achieved, high efficiency and convenience are achieved, and the requirement for rapid iterative design of the exhaust passage silencer of an auxiliary power device in practice can be met.

Description

Technical Field

[0001] The present application belongs to the technical field of aircraft auxiliary power unit silencing and 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 unexpected situations. Auxiliary power units have become an important source of noise when aircraft are docked on the ground for maintenance.

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

[0004] Setting 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 from experiments, which is time-consuming and labor-intensive, and can hardly 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 the present application is to provide a method for designing structural parameters of an exhaust muffler for an aircraft auxiliary power unit, so as to overcome or alleviate at least one aspect of the known technical defects.

[0007] The technical solution of this application is:

[0008] A method for designing structural parameters of an exhaust muffler for an aircraft auxiliary power unit, 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 exhaust duct total sound pressure level SPL (P), establish the expression of muffler insertion loss TL about exhaust duct muffler structural parameters;

[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 an independent variable.

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

[0020] The exhaust duct time domain sound field is obtained by fitting according to the experimental test

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

[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 scattering 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:

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

[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 in order to maximize 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 muffler structural parameter design method, in step 5, the structural parameters of the exhaust muffler include the perforated plate thickness t 0 , perforation diameter d, perforation rate σ, cavity layer thickness L, cavity layer area s 0 .

[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 sound velocity in the exhaust duct;

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

[0052] V 0 is the velocity of the sound particle in the small hole;

[0053] δ is the hole end correction factor.

[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:

[0061]

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

[0063]

[0064] in:

[0065] P 0 is the reference sound pressure.

[0066] Optionally, in the above-mentioned aircraft auxiliary power unit exhaust duct muffler structural parameter design method, in step 7, the reference sound pressure P 0 Take 2×10-5.

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

[0068] Expressed as TL = F(t0 ,d,σ,L,s 0 ).

[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 s are preferably selected. 0 , as the independent variable, and then consider the selection of the perforated plate thickness t 0 , perforation aperture d, and perforation rate σ are used as independent variables.

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

[0071] A structural parameter design method for an aircraft auxiliary power unit exhaust duct muffler is provided. 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 a structural parameter design method for an aircraft auxiliary power unit exhaust duct muffler provided in an embodiment of the present application.

[0073] 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

[0074] 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.

[0075] 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.

[0076] 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.

[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 according to 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 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 scattering 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 frequency domain sound field of the exhaust duct

[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] Usually, non-local reactive sound lining can 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 frequency 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 thickness of the perforated plate t 0 , perforation diameter d, perforation rate σ, cavity layer thickness L, cavity layer area s 0 .

[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 sound velocity in the exhaust duct;

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

[0112] V 0 is the velocity of the sound particle in the small hole;

[0113] δ is the hole end correction factor.

[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 of the total sound pressure level SPL(P) of the exhaust duct.

[0125]

[0126] in:

[0127] P 0 As the reference sound pressure, take 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(t 0 ,d,σ,L,s 0 ), as an optimization function for the exhaust muffler design.

[0131] Step nine, 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, and take the independent variable with the largest muffler insertion loss TL 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 are preferably selected as the cavity layer thickness L and the cavity layer area s 0 , as the independent variable, and then consider the selection of perforated plate parameters perforated plate thickness t 0 , perforation aperture d, and perforation rate σ are used as independent variables.

[0135] The contour map of the muffler insertion loss TL can be drawn, from which the optimal values ​​of the exhaust duct 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 an independent variable.

[0137] The structural parameter design method of the aircraft auxiliary power unit exhaust duct muffler disclosed in the above embodiment determines the muffler configuration, establishes an acoustic expression, and constructs a parameter optimization algorithm by analyzing the spectral characteristics of the exhaust sound source of the auxiliary power unit. The method realizes the forward design of the exhaust duct muffler. The 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. 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 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 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 exhaust duct total sound pressure level SPL (P), establish the expression of muffler insertion loss TL related to exhaust duct muffler structural parameters; 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 an 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 by fitting according to the experimental test 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 scattering 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 frequency domain sound field of the exhaust duct 5. The aircraft auxiliary power unit exhaust muffler structural parameter design method according to claim 4, characterized in that: 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.

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 in order to maximize the amount of 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 liner 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 aperture d, the perforation rate 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 sound velocity in the exhaust duct; 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 factor.

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 p 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 6 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 7 is as follows: in: P0 is the reference sound pressure.

13. The method for designing structural parameters of an aircraft auxiliary power unit exhaust muffler according to claim 12, characterized in that: In step seven, the reference sound pressure P0 is taken as 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 perforated aperture d, and the perforation rate σ are considered as independent variables.

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