Noise reducing fairing and method of designing same

Abstract

The application discloses a noise reduction fairing, which comprises a plurality of double-neck sound elimination units, each of which comprises a first neck cavity, an acoustic cavity and a second neck cavity; the first neck cavity is communicated with the second neck cavity through the acoustic cavity; the cross-sectional area of the first neck cavity and the second neck cavity is smaller than that of the acoustic cavity; the first neck cavity and the second neck cavity are communicated with the atmosphere; and the sound elimination frequencies of the double-neck sound elimination units are different. The double-neck sound elimination units are arranged in the noise reduction fairing, so that a part of sound energy is converted into heat energy under the action of thermal viscosity when sound waves pass through, and the sound elimination effect is enhanced compared with the existing perforated plate; meanwhile, the sound elimination frequencies of the double-neck sound elimination units are different, so that the sound elimination frequencies of the double-neck sound elimination units are coupled with each other to achieve the effect of wideband noise reduction, and the noise reduction effect is better compared with the existing perforated plate. The application further discloses a design method for the noise reduction fairing, which can enhance the noise reduction effect and realize wideband noise reduction.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sound attenuation device, more particularly, to a noise reduction fairing and a design method of the noise reduction fairing. BACKGROUND

[0002] Fan is a traditional fluid machinery, which is widely used in various aspects of engineering field, such as energy, automobile, aviation, etc. While the fan realizes the function of heat dissipation, it also causes high aerodynamic noise due to the pressure fluctuation of surrounding medium caused by high-speed rotation. In the prior art, in order to reduce the aerodynamic noise of the fan, a perforated plate is usually arranged on the fan fairing, but the perforated plate is limited by its own aperture and perforation rate, and the width of the sound absorption frequency band is narrow, so it is difficult to achieve wideband noise reduction.

[0003] Therefore, how to optimize the structure of the fairing in order to achieve wideband noise reduction is a problem to be solved by those skilled in the art. SUMMARY

[0004] Therefore, the present application provides a noise reduction fairing, which is provided with double-neck sound attenuation units, so that sound waves promote the conversion of a part of sound energy to heat energy under the action of thermal viscosity, thereby enhancing the sound attenuation effect. Meanwhile, the sound attenuation frequencies of the double-neck sound attenuation units are different, so that the sound attenuation frequencies of the multiple double-neck sound attenuation units are coupled with each other to achieve the effect of wideband noise reduction. The present application also provides a design method of the above-mentioned noise reduction fairing, which can enhance the noise reduction effect and achieve wideband noise reduction.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0006] A noise reduction fairing comprises multiple double-neck sound attenuation units, wherein each double-neck sound attenuation unit comprises a first neck cavity, an acoustic cavity and a second neck cavity; the first neck cavity is communicated with the second neck cavity through the acoustic cavity; the cross-sectional areas of the first neck cavity and the second neck cavity are smaller than the cross-sectional area of the acoustic cavity; the first neck cavity and the second neck cavity are respectively communicated with the atmosphere.

[0007] The sound attenuation frequencies of the double-neck sound attenuation units are different.

[0008] Preferably, in the above-mentioned noise reduction fairing, the first neck cavity and the second neck cavity of the double-neck sound attenuation unit are located on the same side of the acoustic cavity or on the opposite sides of the acoustic cavity.

[0009] Preferably, in the above-mentioned noise reduction fairing, the noise reduction fairing comprises a cover plate and a shell; the shell comprises an annular side wall and a bottom plate enclosed at one end of the annular side wall; the cover plate is fixed to the other end of the annular side wall; the shell and the cover plate enclose an internal space.

[0010] The acoustic cavities of the double-neck muffler units are arranged in the internal space respectively; the cover plate is provided with a through hole communicating with the acoustic cavity, which is a first neck cavity; the bottom plate is provided with a through hole communicating with the acoustic cavity, which is a second neck cavity; the acoustic cavity corresponds to the first neck cavity and the second neck cavity respectively.

[0011] Preferably, in the noise reduction fairing, the acoustic cavities are annularly distributed in the internal space and arranged in one or more circles.

[0012] Preferably, in the noise reduction fairing, the internal space is divided into a plurality of spaces not connected to each other by a partition plate, and each space is the acoustic cavity.

[0013] Preferably, in the noise reduction fairing, the partition plate includes an annular partition plate and a flat partition plate, the annular partition plate is located in the annular side wall, and the flat partition plate extends from one end of the annular side wall to the other end and passes through the annular partition plate.

[0014] Preferably, in the noise reduction fairing, the annular partition plate is a plurality of and is sleeved one by one, or the flat partition plate is one, or the flat partition plate is a plurality of and intersects with each other in the innermost annular partition plate.

[0015] Preferably, in the noise reduction fairing, the noise reduction fairing is used for a fan, and the double-neck muffler unit is located on one side of the fan in the axial direction or arranged on the outer periphery of the fan.

[0016] Preferably, in the noise reduction fairing, the noise reduction fairing is an acoustic metamaterial fairing.

[0017] A design method of a noise reduction fairing, for the noise reduction fairing in any one of the above technical solutions, comprising:

[0018] (1) determining the target noise reduction frequency band of the noise reduction fairing;

[0019] (2) determining the target frequency of each double-neck muffler unit according to the target noise reduction frequency band, the number of double-neck muffler units;

[0020] (3) determining the preset structure size parameters of the double-neck muffler unit and the initial value of the end coefficient in the resonance frequency design formula of the double-neck muffler unit; using the preset structure size parameters and the target frequency, the end coefficient in the resonance frequency design formula of the double-neck muffler unit is corrected by iteration, and the to-be-determined structure size parameters of the double-neck muffler unit are calculated by the resonance frequency design formula of the double-neck muffler unit;

[0021] (4) repeating the step (3) until all the structure size parameters of the double-neck muffler unit are determined.

[0022] Preferably, in the design method, the step (3) comprises:

[0023] (31) determining the specific value of the preset structure size parameter of the double-neck muffler unit, and setting the initial value of the end coefficient in the resonance frequency design formula of the double-neck muffler unit to 0.8;

[0024] (32) calculating the structure size parameter to be determined according to the target frequency, the preset structure size parameter and the initial value of the end coefficient through the resonance frequency design formula of the double-neck muffler unit;

[0025] (33) establishing a finite element model to calculate the transmission loss, searching for the resonance frequency corresponding to the peak value of the transmission loss, and if the resonance frequency deviates from the target frequency, substituting the resonance frequency obtained by simulation into the resonance frequency design formula of the double-neck muffler unit to calculate a new end coefficient;

[0026] (34) adjusting the structure size parameter to be determined of the double-neck muffler unit according to the new end coefficient, and establishing a three-dimensional structure model to verify whether the peak value of the transmission loss curve is located at the target frequency through simulation, if not, returning to step (33) until the transmission loss resonance peak value is exactly at the target frequency; if yes, entering step (4).

[0027] Preferably, in the design method, the preset structure size parameter comprises six of the length, cross-sectional area, diameter of the first neck cavity, the length, cross-sectional area, diameter of the second neck cavity and the volume of the acoustic cavity; and the structure size parameter to be determined is one of the seven.

[0028] Preferably, in the design method, the "determining the target noise reduction frequency band of the noise reduction fairing" comprises:

[0029] obtaining the A-weighted spectrum of the preset measurement point of the noise source radiation sound field through experiment, obtaining the frequency band where the higher peak value is located, and recording the frequency band as the target noise reduction frequency band; or

[0030] obtaining the target noise reduction frequency band according to the discrete noise frequency formula of the fan.

[0031] The application provides a noise reduction fairing, comprising a plurality of double-neck sound absorption units, each double-neck sound absorption unit comprising a first neck cavity, an acoustic cavity and a second neck cavity; the first neck cavity is communicated with the second neck cavity through the acoustic cavity; the cross-sectional area of the first neck cavity and the second neck cavity is smaller than that of the acoustic cavity; the first neck cavity and the second neck cavity are communicated with the atmosphere; the sound absorption frequency of each double-neck sound absorption unit is different.

[0032] The double-neck sound absorption unit is arranged in the noise reduction fairing, so that a part of sound energy is converted into heat energy under the action of thermal viscosity when the sound wave passes through, and the sound absorption effect is enhanced compared with the existing perforated plate; meanwhile, each double-neck sound absorption unit has two neck cavities, and has two basic resonance sound absorption frequencies compared with the sound absorption unit having only one neck cavity, and the sound absorption frequencies of the double-neck sound absorption units are different, so that the noise reduction fairing has more sound absorption frequencies, and the sound absorption frequencies of the double-neck sound absorption units arranged in the limited space are coupled to achieve the effect of wideband noise reduction, and the sound absorption frequency band is wider and the noise reduction effect is better compared with the existing perforated plate.

[0033] The application also provides a design method for the noise reduction fairing, so that the double-neck sound absorption unit has two basic resonance sound absorption frequencies, and the double-neck sound absorption units arranged in the limited space have more sound absorption frequencies, and the design method makes the sound absorption frequencies of the double-neck sound absorption units different, and the sound absorption frequencies of all the double-neck sound absorption units are coupled to achieve the effect of wideband noise reduction.

[0034] In addition, the end coefficient in the resonance frequency design formula of the double-neck sound absorption unit is repeatedly corrected through iteration in the design method, so that the sound absorption frequency of the designed double-neck sound absorption unit is more accurate, and the noise reduction fairing can achieve accurate noise reduction. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only some embodiments of the application, and for those skilled in the art, other drawings can be obtained without creative labor on the basis of these drawings.

[0036] Figure 1 The structure diagram of the double-neck sound absorption unit provided by the embodiments of the application is shown in the following figure.

[0037] Figure 2 The exploded view of the noise reduction fairing provided by the embodiments of the application is shown in the following figure.

[0038] Figure 3 The front view of the noise reduction fairing provided by the embodiments of the application is shown in the following figure.

[0039] Figure 4 A sectional view of the noise reduction fairing provided by the embodiment of the present application;

[0040] Figure 5 A perspective structural schematic view of the noise reduction fairing provided by the embodiment of the present application;

[0041] Figure 6 An assembly view of the noise reduction fairing and the fan provided by the embodiment of the present application;

[0042] Figure 7 A flow chart of the design method of the noise reduction fairing provided by the embodiment of the present application;

[0043] Wherein, Figures 1-6 The present application provides a noise reduction fairing, comprising a plurality of double-neck sound elimination units 101, wherein each double-neck sound elimination unit 101 comprises a first neck cavity 111, an acoustic cavity 113 and a second neck cavity 112; the first neck cavity 111 is communicated with the second neck cavity 112 through the acoustic cavity 113; the cross-sectional area of the first neck cavity 111 and the second neck cavity 112 is smaller than the cross-sectional area of the acoustic cavity 113 respectively; the first neck cavity 111 and the second neck cavity 112 are communicated with the atmosphere respectively; the sound elimination frequency of each double-neck sound elimination unit 101 is different.

[0044] Double-neck sound elimination unit 101; first neck cavity 111; second neck cavity 112; acoustic cavity 113; cover plate 102; partition plate 103; annular partition plate 131; flat partition plate 132; shell 104; bottom plate 141; annular side wall 142; connecting plate 105; connecting ring 106; fan 201; air conveying pipeline 202. DETAILED DESCRIPTION

[0045] The embodiment of the present application discloses a noise reduction fairing, which is provided with double-neck sound elimination units, so that sound waves promote a part of sound energy to be converted into heat energy under the action of thermal viscosity, the sound elimination effect is enhanced, meanwhile, the sound elimination frequencies of the double-neck sound elimination units are different, the sound elimination frequencies of the multiple double-neck sound elimination units are coupled with each other to achieve the effect of wideband noise reduction. The embodiment of the present application also discloses a design method of the noise reduction fairing, which can enhance the noise reduction effect and realize wideband noise reduction.

[0046] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0047] Please refer to Figures 1-6 The present application provides a noise reduction fairing, comprising a plurality of double-neck sound elimination units 101, wherein each double-neck sound elimination unit 101 comprises a first neck cavity 111, an acoustic cavity 113 and a second neck cavity 112; the first neck cavity 111 is communicated with the second neck cavity 112 through the acoustic cavity 113; the cross-sectional area of the first neck cavity 111 and the second neck cavity 112 is smaller than the cross-sectional area of the acoustic cavity 113 respectively; the first neck cavity 111 and the second neck cavity 112 are communicated with the atmosphere respectively; the sound elimination frequency of each double-neck sound elimination unit 101 is different.

[0048] The double-neck sound elimination unit 101 is arranged in the above-mentioned noise reduction fairing, so that when sound waves pass through, a part of sound energy can be converted into heat energy under the action of thermal viscosity, thereby enhancing the sound elimination effect compared with the existing perforated plate. Meanwhile, each double-neck sound elimination unit has two neck cavities, and compared with the sound elimination unit having only one neck cavity, it has two basic resonance sound elimination frequencies, and the sound elimination frequencies of the double-neck sound elimination units 101 are different, so that the entire noise reduction fairing has more sound elimination frequencies, and the sound elimination frequencies of multiple double-neck sound elimination units 101 can be coupled with each other in a limited space to achieve the effect of wideband noise reduction. Compared with the existing perforated plate, the sound elimination frequency band is wider, and the noise reduction effect is better.

[0049] The structure size parameters of each double-neck sound elimination unit 101 are different, thereby making the sound elimination frequencies of each double-neck sound elimination unit 101 different. The "structure size parameters of each double-neck sound elimination unit 101 are different" means that at least one of all the structure size parameters of different double-neck sound elimination units 101 is different.

[0050] The two neck cavities in the double-neck sound elimination unit 101 are cylindrical cavities; the structure size parameters of the double-neck sound elimination unit 101 include the cross-sectional area s1, the length l1, and the diameter d1 of the first neck cavity 111, the cross-sectional area s2, the length l2, and the diameter d2 of the second neck cavity 112, and the volume V of the acoustic cavity 113.

[0051] In the double-neck sound elimination unit 101, the first neck cavity 111 and the second neck cavity 112 can be arranged on the same side of the acoustic cavity 113. Preferably, in the double-neck sound elimination unit 101, the two neck cavities are arranged on opposite sides of the acoustic cavity 113, so that the double-neck sound elimination unit 101 can have certain ventilation and rectification functions. At this time, the two neck cavities can be arranged coaxially or the axes of the two neck cavities do not coincide, which is not limited in the embodiment.

[0052] When the above-mentioned noise reduction fairing is applied, if the double-neck sound elimination unit 101 is arranged circumferentially on the outer periphery of the fan 201, the local resonance of the two neck cavities can be used to reduce the aerodynamic noise generated by the rotation of the fan 201; if the double-neck sound elimination unit 101 is directly opposite the fan 201 in the axial direction, and the two neck cavities are located on the side of the acoustic cavity 113 facing the fan 201, the double-neck sound elimination unit 101 can also have the effect of resonance sound elimination, and can also inhibit the noise of the fan 201 from propagating in the axial direction to a certain extent; if the double-neck sound elimination unit 101 is directly opposite the fan 201 in the axial direction, and the two neck cavities are located on the side of the acoustic cavity 113 facing the fan 201 and the side of the acoustic cavity 113 facing away from the fan 201, respectively, the double-neck sound elimination unit 101 can have the effects of resonance sound elimination and rectification noise reduction.

[0053] Specifically, the noise reduction fairing comprises a cover plate 102 and a shell 104; the shell 104 comprises a ring-shaped side wall 142 and a bottom plate 141 enclosed at one end of the ring-shaped side wall 142; the cover plate 102 is fixed at the other end of the ring-shaped side wall 142; the shell 104 and the cover plate 102 enclose an internal space; the acoustic cavities 113 of the double-neck muffler units 101 are arranged in the internal space respectively; the cover plate 102 is provided with through holes in communication with the acoustic cavities 113, which are the first neck cavities 111; the bottom plate 141 is provided with through holes in communication with the acoustic cavities 113, which are the second neck cavities 112; the acoustic cavities 113 correspond to the first neck cavities 111 one by one, and the acoustic cavities 113 correspond to the second neck cavities 112 one by one. The ring-shaped side wall 142 and the bottom plate 141 cooperate to form a barrel-shaped structure.

[0054] In the noise reduction fairing provided by the embodiment, the two neck cavities of the double-neck muffler unit 101 are arranged in the bottom plate 141 and the cover plate 102 respectively, so that the first neck cavities 111 and the second neck cavities 112 are distributed on both sides of the acoustic cavities 113, and the perforation rate of the fairing (i.e. the ratio of the cross-sectional area of the first neck cavity 111 to the area of the cover plate 102) can be adjusted according to actual conditions. When the perforation rate is large, the ventilation amount of the noise reduction fairing is larger, which can achieve certain rectification and ventilation effect.

[0055] The cross section of the ring-shaped side wall 142 can be circular, rectangular, trapezoidal, etc., which is not limited in the embodiment.

[0056] The acoustic cavities 113 of all the double-neck muffler units 101 are distributed in a ring shape in the internal space of the noise reduction fairing and arranged in one or more circles. In the embodiment, the acoustic cavities 113 are arranged in a circumferential array, and in addition, the acoustic cavities 113 can be arranged in a rectangular array or randomly in the internal space of the noise reduction fairing, which is not limited in the embodiment.

[0057] Specifically, the internal space of the noise reduction fairing is divided into multiple spaces not connected to each other by a partition plate 103, and each space is an acoustic cavity 113. As shown in Figure 2 , 4 The partition plate 103 comprises a ring-shaped partition plate 131 and a flat partition plate 132, the ring-shaped partition plate 131 is located in the ring-shaped side wall 142, and the flat partition plate 132 extends from one end of the ring-shaped side wall 142 to the other end and passes through the ring-shaped partition plate 131. The shape of the ring-shaped partition plate 131 is preferably the same as that of the ring-shaped side wall 142.

[0058] The ring-shaped partition plate 131 can be one or multiple and be sleeved one by one, as shown in Figure 2 , 4 The flat partition plate 132 is one or multiple and crosses each other in the innermost ring-shaped partition plate 131, as shown inFigure 2 、 4 as shown.

[0059] The above noise reduction fairing is used for the fan 201; the double-neck noise reduction unit 101 is located on the axial side of the fan 201, or the double-neck noise reduction unit 101 is arranged on the outer periphery of the fan 201. Of course, the above noise reduction fairing can also be applied to other noise sources, not limited to the fan 201.

[0060] As shown in Figure 6 , the above noise reduction fairing further comprises a connecting ring 106 connected with the shell 104 through a connecting plate 105; the connecting ring 106 is connected with the air conveying pipeline 202 of the fan 201 through a fixing piece, so that the noise reduction fairing is installed.

[0061] Preferably, the connecting ring 106, the connecting plate 105 and the shell 104 are preferably provided as an integrated structure, and the partition plate 103 and the shell are an integrated structure.

[0062] Further, the above noise reduction fairing is provided as an acoustic metamaterial fairing (i.e. the shell 104 is an acoustic metamaterial shell, and the cover plate 102 is an acoustic metamaterial cover plate), which has a subwavelength size, and compared with the structure size in the prior art, a limited number of perforated plates are arranged in a limited space, so that more double-neck noise reduction units 101 can be arranged in the limited space, which is beneficial to realize a broadband noise reduction effect. At the same time, the noise reduction fairing structure provided by the embodiment has a smaller size and a wider application scenario.

[0063] As shown in Figure 7 , the embodiment of the application further provides a design method of a noise reduction fairing, which is used for the noise reduction fairing provided in the above embodiment, and comprises the following steps:

[0064] (1) determining a target noise reduction frequency band of the noise reduction fairing;

[0065] (2) determining a target frequency f0 of each double-neck noise reduction unit 101 and the number N of the double-neck noise reduction units 101 according to the target noise reduction frequency band;

[0066] (3) determining a preset structure size parameter of the double-neck noise reduction unit 101 and an initial value of an end coefficient x in a resonance frequency design formula of the double-neck noise reduction unit 101; using the preset structure size parameter and the target frequency f0, the value of the end coefficient x in the resonance frequency design formula of the double-neck noise reduction unit 101 is corrected through iteration, and then the to-be-determined structure size parameter of the double-neck noise reduction unit 101 is calculated through the resonance frequency design formula of the double-neck noise reduction unit 101;

[0067] (4) repeating step (3) until the structure size parameters of all the double-neck noise reduction units 101 are determined.

[0068] The structural size parameters of the double-neck muffler unit 101 include the cross-sectional area s1, the length l1, and the diameter d1 of the first neck cavity 111, the cross-sectional area s2, the length l2, and the diameter d2 of the second neck cavity 112, and the volume V of the acoustic cavity 113; the preset structural size parameters include six of the above seven parameters, and the to-be-determined structural size parameter is one structural size parameter other than the preset structural size parameters.

[0069] The step (3) includes:

[0070] (31) determining the specific value of the preset structural size parameter of the double-neck muffler unit 101, and setting the initial value of the end coefficient x in the resonance frequency design formula of the double-neck muffler unit 101 to 0.8;

[0071] (32) calculating the to-be-determined structural size parameter according to the target frequency f0, the preset structural size parameter, and the initial value of the end coefficient x through the resonance frequency design formula of the double-neck muffler unit 101;

[0072] The resonance frequency design formula of the double-neck muffler unit 101 is:

[0073]

[0074] Wherein:

[0075] c0 is the speed of sound in air;

[0076] S1 and S2 are the cross-sectional areas of the first neck cavity 111 and the second neck cavity 112, respectively;

[0077] l1 and l2 are the lengths of the first neck cavity 111 and the second neck cavity 112, respectively (the length refers to the axial dimension of the neck cavity);

[0078] d1 and d2 are the diameters of the first neck cavity 111 and the second neck cavity 112, respectively;

[0079] V is the volume of the acoustic cavity 113;

[0080] x is the end coefficient;

[0081] (33) establishing a finite element model to calculate the transmission loss, searching for the resonance frequency f1 corresponding to the peak value of the transmission loss (the resonance frequency f1 is the actual resonance frequency of the double-neck muffler unit 101), and if the resonance frequency f1 deviates from the target frequency f0 (i.e. f0≠f1), the resonance frequency f1 obtained by simulation is substituted into the resonance frequency design formula of the double-neck muffler unit 101 to calculate a new end coefficient x1;

[0082] In this step, the finite element model refers to the air domain inside and around the noise reduction fairing, including the inlet face and the outlet face, the inlet face is defined as a plane wave incidence, and the outlet face is defined as a full absorption boundary, and the inlet sound power w in and the outlet sound power w out are obtained through simulation, and the transmission loss curve is further obtained, and the actual resonance frequency f1 corresponding to the peak value of the curve is obtained; the transmission loss formula is:

[0083]

[0084] (34) According to the new correction coefficient x1, the to-be-determined structure size parameter of the double-neck muffler unit 101 is adjusted, and a three-dimensional structure model is established to verify whether the peak value of the transmission loss curve is located at the target frequency f0, if not, return to step (33) until the transmission loss resonance peak value is exactly at the target frequency f0; if yes, go to step (4).

[0085] In the resonance frequency design formula of the double-neck muffler unit 101 described above, due to the influence of high-order modal dissipation waves, the length l of the neck cavity needs to be corrected to obtain the equivalent length L of the neck cavity (i.e. 1+xd), and then the theoretical resonance frequency of the double-neck muffler unit 101 is closer to the actual value. The equivalent length L is usually obtained by taking the end coefficient x as an empirical value of 0.8, however, the resonance frequency of the double-neck muffler unit 101 designed by the empirical value of 0.8 will have a large deviation from the actual resonance frequency. The design method provided in the embodiment iteratively corrects x to obtain the equivalent length L of the neck cavity, which makes the resonance frequency of the designed double-neck muffler unit 101 closer to the actual resonance frequency, so that the designed noise reduction fairing can achieve precise noise reduction effect in actual application.

[0086] In the above design method, the "determining the target noise reduction frequency band of the noise reduction fairing" includes: obtaining the A-weighted frequency spectrum of the noise source radiation sound field at the preset measurement point, obtaining the frequency band with a higher peak value, and recording the frequency band as the target noise reduction frequency band; or when the noise source is a fan, the above "determining the target noise reduction frequency band of the noise reduction fairing" can be set to include: obtaining the target noise reduction frequency band according to the discrete noise frequency formula of the fan; the discrete noise frequency formula of the fan is:

[0087]

[0088] Wherein, i represents the order, which is 1, 2, 3,...

[0089] n is the fan speed, the unit is rpm;

[0090] z is the number of blades of the fan.

[0091] In the design method, step (1) further comprises determining the structural form of the noise reduction fairing, the structural form comprising an arrangement manner of the plurality of acoustic cavities 113 inside the noise reduction fairing, and arrangement positions of the two neck cavities and the acoustic cavities in the double-neck muffler unit 101; correspondingly, the design method further comprises step (5): adjusting the structural form of the noise reduction fairing according to the determined structural size parameters of each double-neck muffler unit 101, and finally determining the structure of the noise reduction fairing. In step (31), the specific values of the preset structural size parameters of the double-neck muffler unit 101 are designed according to the structural form of the noise reduction fairing determined in step (1), and the size of the installation position of the noise reduction fairing reserved at the noise source.

[0092] Step (2) further comprises determining the sound attenuation frequency interval Δf between adjacent double-neck muffler units 101 (referring to two double-neck muffler units with similar sound attenuation frequencies). In this step, the total number of sound attenuation units under the target sound attenuation frequency band and the frequency interval are determined, so as to better couple the frequencies of the plurality of double-neck muffler units 101 and achieve wideband sound attenuation.

[0093] The design method of the noise reduction fairing provided by the embodiments of the present application can ensure the accurate design of the resonance frequency of the double-neck muffler unit 101 through repeated search and calculation of the transmission loss peak frequency and the end coefficient.

[0094] Each embodiment in the specification is described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The same or similar parts between the embodiments can be referred to each other.

[0095] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A noise reduction fairing applied to a fan, characterized in that, The double-neck muffler unit is located on one axial side of the fan, and comprises a first neck cavity, an acoustic cavity and a second neck cavity. The first neck cavity is communicated with the second neck cavity through the acoustic cavity; the cross-sectional areas of the first neck cavity and the second neck cavity are smaller than the cross-sectional area of the acoustic cavity respectively; The first neck cavity and the second neck cavity are respectively communicated with the atmosphere; the first neck cavity and the second neck cavity are located on opposite sides of the acoustic cavity in the double-neck muffler unit, and the conversion of acoustic energy into heat energy is realized through the thermal viscous effect to enhance the noise reduction effect; The noise reduction frequency of each double-neck muffler unit is different; The noise reduction fairing comprises a cover plate and a shell; the shell comprises an annular side wall and a bottom plate enclosed at one end of the annular side wall; the cover plate is fixed to the other end of the annular side wall; the shell and the cover plate enclose an internal space; The acoustic cavities of the double-neck muffler units are respectively arranged in the internal space; the cover plate is provided with a through hole communicated with the acoustic cavities, which is the first neck cavity; the bottom plate is provided with a through hole communicated with the acoustic cavities, which is the second neck cavity; the acoustic cavities and the first neck cavities and the second neck cavities are one-to-one corresponding respectively; The internal space is divided into a plurality of spaces not communicated with each other by a partition plate; each space is the acoustic cavity; the partition plate comprises an annular partition plate and a flat partition plate; the annular partition plate is located in the annular side wall; the flat partition plate extends from one end of the annular side wall to the other end and passes through the annular partition plate.

2. The noise reducing fairing of claim 1, wherein, The acoustic cavities are annularly distributed in the internal space and are arranged in one or more circles.

3. The noise-reducing fairing of claim 1, wherein, The annular partition plates are a plurality of and are sleeved one by one; the flat partition plate is one, or the flat partition plates are a plurality of and are crossed with each other in the innermost annular partition plate.

4. The noise-reducing fairing of claim 1, wherein, The noise reduction fairing is an acoustic metamaterial fairing.

5. A method of designing a noise reducing fairing for use in any one of the noise reducing fairings of claims 1-4, characterized in that, It comprises: (1) determining the target noise reduction frequency band of the noise reduction fairing; (2) determining the target frequency of each double-neck muffler unit according to the target noise reduction frequency band, the number of double-neck muffler units; (3) determining the preset structure size parameter of the double-neck muffler unit and the initial value of the end coefficient in the resonance frequency design formula of the double-neck muffler unit; Using the preset structure size parameter and the target frequency, the end coefficient in the resonance frequency design formula of the double-neck muffler unit is corrected by iteration, and the to-be-determined structure size parameter of the double-neck muffler unit is calculated by the resonance frequency design formula of the double-neck muffler unit; (4) repeating step (3) until the structure size parameters of all double-neck muffler units are determined.

6. The method of designing a noise-reducing fairing of claim 5, wherein, The step (3) comprises: (31) determining the specific value of the preset structure size parameter of the double-neck muffler unit, and setting the initial value of the end coefficient in the resonance frequency design formula of the double-neck muffler unit to 0.8; (32) calculating the to-be-determined structure size parameter of the double-neck sound elimination unit according to the initial value of the end coefficient, the preset structure size parameter, and the target frequency through a resonance frequency design formula of the double-neck sound elimination unit; (33) establishing a finite element model to calculate the transmission loss, searching for a resonance frequency corresponding to a peak value of the transmission loss, and if the resonance frequency deviates from the target frequency, substituting the resonance frequency obtained through simulation into the resonance frequency design formula of the double-neck sound elimination unit to calculate a new end coefficient; (34) adjusting the to-be-determined structure size parameter of the double-neck sound elimination unit according to the new end coefficient, and establishing a three-dimensional structure model to simulate and verify whether a peak value of a transmission loss curve is located at the target frequency, and if not, returning to step (33) until the transmission loss resonance peak value is exactly at the target frequency; and if yes, entering step (4).

7. The design method of a noise-reducing fairing according to claim 5 or 6, characterized in that, The preset structure size parameter includes six of the length, cross-sectional area, and diameter of the first neck cavity, the length, cross-sectional area, and diameter of the second neck cavity, and the volume of the acoustic cavity. The to-be-determined structure size parameter is one of the seven parameters other than the preset structure size parameter.

8. The method of designing a noise-reducing fairing of claim 5, wherein, The "determining the target sound elimination frequency band of the noise reduction fairing" includes: obtaining an A-weighted frequency spectrum of a preset measurement point of a noise source radiation sound field through experiment, obtaining a frequency band with a higher peak value, and recording the frequency band as the target sound elimination frequency band; or obtaining the target sound elimination frequency band according to a discrete noise frequency formula of the fan.

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