A Helmholtz silencer structure with an acoustic black hole as its neck

Abstract

This invention relates to a Helmholtz silencer structure using an acoustic black hole as its neck. It includes an array of annular thin plates, a cylindrical cavity, a tubular neck, and a back cavity. The annular thin plate array comprises several annular thin plates with different inner diameters, which are parallel and uniformly fixed to the cylindrical cavity. The outer diameter of each annular thin plate is equal to the inner diameter of the cylindrical cavity. The annular thin plate with the largest and smallest inner diameters are located at one end and the other end of the cylindrical cavity, respectively. The inner diameter of the annular thin plates gradually decreases from one end of the cylindrical cavity along the other end in a linear function. The acoustic black hole and the back cavity are connected to the tubular neck via the annular thin plate with the smallest inner diameter. This invention has a simple structure, low cost, and exhibits low-frequency, broadband sound absorption performance.

Description

Technical Field

[0001] This invention relates to a low-frequency, broadband sound-absorbing structure designed using acoustic black holes and Helmholtz silencers, specifically a Helmholtz silencer structure with an acoustic black hole as its neck. Background Technology

[0002] The term "acoustic black hole structure" initially referred to a structure whose thickness gradually decreases to zero according to a power function. With further research, two-dimensional acoustic black holes and acoustic black hole conduit structures have been proposed, where the speed of sound waves propagating within the structure gradually decreases to zero. Due to their simplicity and wideband sound absorption effect, acoustic black hole structures are widely used in noise control. For example, patent application number 202110973436.9 proposes a spiral two-dimensional acoustic black hole vibration isolation and noise reduction structure. Patent application number 202110976044.8 proposes a low-frequency ultra-wideband acoustic black hole acoustic material structure, achieving low-frequency broadband noise control through the combination of a micro-perforated plate and an acoustic black hole.

[0003] The air inside the neck and back cavity of a Helmholtz muffler can be considered as an elastic system. When the frequency of the incident sound wave is the same as the natural frequency of the structure, the sound wave resonates with the elastic system, increasing the friction between the air and the neck wall, thus producing a significant noise reduction effect. Due to its simple structure and significant noise reduction effect, the Helmholtz muffler is commonly used in automotive intake systems, air conditioning compressor noise reduction, acoustic-to-electric conversion equipment, and aero-engines. For example, Chen Xing et al. (Design and Verification of Compressor Exhaust Muffler. Proceedings of the 2014 China Household Appliance Technology Conference. 2014: 526-531) conducted noise tests on indoor units operating at low fan speed before and after installing a Helmholtz muffler. The results showed that the noise of the indoor unit operating at low fan speed was reduced by 2.8 dB across the entire frequency range. Patent application number 201710150786.9 proposes a pump-jet propulsion model with a Helmholtz resonant cavity and its design method to suppress low-frequency line spectrum noise of the pump jet and reduce overall noise.

[0004] As can be seen from the sound absorption principle of Helmholtz silencers, their natural frequency can be changed by altering the dimensions of the silencer structure. To overcome the drawback of having a single sound absorption frequency, an acoustic black hole structure is connected to its neck, thereby combining the broadband sound absorption characteristics of the acoustic black hole to achieve low-frequency, wideband sound absorption. Summary of the Invention

[0005] This invention addresses the issue of Helmholtz silencers with only a single absorption peak and acoustic black hole structures with wideband sound absorption but whose absorption frequency band is mainly concentrated in the mid-to-high frequencies. It proposes a Helmholtz silencer structure with an acoustic black hole as its neck. This structure not only exhibits good sound absorption at certain low frequencies but also demonstrates excellent broadband sound absorption in the mid-to-high frequencies.

[0006] The present invention is achieved through the following technical solution.

[0007] A Helmholtz silencer structure with an acoustic black hole as its neck includes an array of annular thin plates, a cylindrical cavity, a tubular neck, and a back cavity. The annular thin plate array comprises several annular thin plates with different inner diameters, which are parallel and uniformly fixed to the cylindrical cavity. The outer diameter of each annular thin plate is equal to the inner diameter of the cylindrical cavity. The annular thin plate with the largest and smallest inner diameters are located at one end and the other end of the cylindrical cavity, respectively. The inner diameter of the annular thin plates gradually decreases from one end of the cylindrical cavity along the other end in a linear function, where the linear function is... r1 represents the radius of the annular plate with the smallest inner diameter, R represents the inner diameter of the cylindrical cavity, L represents the length of the cylindrical cavity, and x represents the distance between any annular plate and the annular plate with the largest inner diameter. The array of annular plates and the cylindrical cavity form an acoustic black hole. The acoustic black hole and the back cavity are connected to a tubular neck via the annular plate with the smallest inner diameter, forming a Helmholtz silencer structure.

[0008] Furthermore, the thickness of the annular thin plate is no more than 2 mm. The annular thin plate is fixed in the cylindrical cavity.

[0009] Furthermore, the annular plate with the smallest inner diameter is tightly connected to the tubular neck. The inner diameter of the tubular neck is equal to the inner diameter of the annular plate with the smallest inner diameter.

[0010] Furthermore, the dorsal cavity is closely connected to the tubular neck, which can extend into the interior of the dorsal cavity.

[0011] Furthermore, the annular thin plate, cylindrical cavity, tubular neck, and back cavity are integrally formed by 3D printing.

[0012] Furthermore, the annular thin plate, cylindrical cavity, tubular neck, and back cavity are connected and fixed using strong adhesive, welding, or bolts.

[0013] Compared with existing sound-absorbing structures, the advantages of the present invention are: the structure of the present invention not only has good sound absorption effect at a certain frequency in the low frequency range, but also has good broadband sound absorption in the mid-to-high frequency range. Attached Figure Description

[0014] Figure 1 This is a cross-sectional view of the present invention;

[0015] Figure 2 This is an isometric side view of the present invention;

[0016] Figure 3 This invention relates to a ring-shaped thin-plate array;

[0017] Figure 4 The cylindrical cavity of this invention;

[0018] Figure 5 The tubular neck of this invention;

[0019] Figure 6 The back cavity of the present invention

[0020] Figure 7 The curve showing the change of the sound absorption coefficient with the incident noise frequency is shown in an embodiment of the Helmholtz silencer structure with an acoustic black hole as the neck of the present invention.

[0021] In the diagram: 1. Annular thin plate, 2. Cylindrical cavity, 3. Tubular neck, 4. Dorsal cavity. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and specific examples, but this should not be construed as limiting the present invention.

[0023] like Figures 1 to 6 As shown, a Helmholtz silencer structure with an acoustic black hole as its neck includes an annular thin plate array, a cylindrical cavity 2, a tubular neck 3, and a back cavity 4. The annular thin plate array includes several annular thin plates 1 with different inner diameters. The annular thin plates 1 are parallel and uniformly fixed on the cylindrical cavity 2. The outer diameter of the annular thin plate 1 is equal to the inner diameter of the cylindrical cavity 2. The annular thin plate 1 with the largest inner diameter and the annular thin plate 1 with the smallest inner diameter are located at one end and the other end of the cylindrical cavity 2, respectively. The inner diameter of the annular thin plate 1 gradually decreases from one end of the cylindrical cavity 2 along the other end in a linear function, where the linear function is... r1 represents the radius of the annular plate 1 with the smallest inner diameter, R represents the inner diameter of the cylindrical cavity 2, L represents the length of the cylindrical cavity 2, and x represents the distance between any annular plate 1 and the annular plate 1 with the largest inner diameter. The annular plate array and the cylindrical cavity 2 form an acoustic black hole. The acoustic black hole and the back cavity 4 are connected to the tubular neck 3 through the annular plate 1 with the smallest inner diameter. The other end of the tubular neck is connected to the back cavity 4 to form a Helmholtz silencer structure.

[0024] Furthermore, the thickness of all annular plates 1 is no greater than 2 mm. The annular plates 1 are fixed in the cylindrical cavity 2.

[0025] Furthermore, the annular thin plate 1 with the smallest inner diameter is tightly connected to the tubular neck 3. The inner diameter of the tubular neck 3 is equal to the inner diameter of the annular thin plate with the smallest inner diameter.

[0026] Furthermore, the dorsal cavity 4 is tightly connected to the tubular neck 3, and the tubular neck 3 can extend into the interior of the dorsal cavity 4.

[0027] Furthermore, the annular thin plate 1, the cylindrical cavity 2, the tubular neck 3, and the back cavity 4 are integrally formed by 3D printing.

[0028] Furthermore, the annular thin plate 1, the cylindrical cavity 2, the tubular neck 3, and the back cavity 4 are connected and fixed by using strong glue, welding, or bolts.

[0029] In this embodiment, an experimental model was obtained using 3D printing. The model consisted of 30 thin plates, each 0.7 mm thick, with a radius of 47.5 mm, a spacing of 3 mm between adjacent plates, a tubular neck with a radius of 4.5 mm and a length of 6 mm, and a cylindrical back cavity with a radius of 47.5 mm and a length of 25 mm. The sound absorption coefficient was experimentally measured using the impedance tube method. The results are as follows: Figure 7 As shown. For comparison, the sound absorption coefficient of a conventional Helmholtz silencer without an acoustic black hole as its neck was also measured. The experimental results show that for the Helmholtz silencer with an acoustic black hole neck, the sound absorption coefficient is 0.99 at 305 Hz, and greater than 0.7 at frequencies above 735 Hz. However, for the conventional Helmholtz silencer, the sound absorption coefficient only reaches 0.99 at 284 Hz, indicating good sound absorption only around 284 Hz. This demonstrates that the acoustic black hole silencing structure described in this invention possesses excellent low-frequency, broadband sound absorption characteristics.

[0030] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A Helmholtz silencer structure with an acoustic black hole as its neck, characterized in that, The system includes an annular thin plate array, a cylindrical cavity (2), a tubular neck (3), and a back cavity (4). The annular thin plate array comprises several annular thin plates (1) with different inner diameters. The annular thin plates (1) are parallel and uniformly fixed on the cylindrical cavity (2). The outer diameter of each annular thin plate (1) is equal to the inner diameter of the cylindrical cavity (2). The annular thin plate (1) with the largest inner diameter and the annular thin plate (1) with the smallest inner diameter are located at one end and the other end of the cylindrical cavity (2), respectively. The inner diameter of each annular thin plate (1) gradually decreases from one end of the cylindrical cavity (2) along the other end in a linear function. r1 represents the radius of the annular thin plate (1) with the smallest inner diameter, R represents the inner diameter of the cylindrical cavity (2), L represents the length of the cylindrical cavity (2), and x represents the distance between any annular thin plate (1) and the annular thin plate (1) with the largest inner diameter; the annular thin plate array and the cylindrical cavity (2) form an acoustic black hole, and the acoustic black hole and the back cavity (4) are connected to the tubular neck (3) through the annular thin plate (1) with the smallest inner diameter to form a Helmholtz silencer structure.

2. The Helmholtz silencer structure with an acoustic black hole as its neck as described in claim 1, characterized in that, The thickness of the annular thin plate (1) is no more than 2 mm, and the annular thin plate (1) is fixed on the cylindrical cavity (2).

3. The Helmholtz silencer structure with an acoustic black hole as its neck as described in claim 1, characterized in that, The annular thin plate (1) with the smallest inner diameter is tightly connected to the tubular neck (3), and the inner diameter of the tubular neck (3) is equal to the inner diameter of the annular thin plate with the smallest inner diameter.

4. The Helmholtz silencer structure with an acoustic black hole as its neck as described in claim 1, characterized in that, The dorsal cavity (4) is closely connected to the tubular neck (3), and the tubular neck (3) can extend into the interior of the dorsal cavity (4).

5. The Helmholtz silencer structure with an acoustic black hole as its neck according to claim 1, characterized in that, The annular thin plate (1), cylindrical cavity (2), tubular neck (3) and back cavity (4) are integrally formed by 3D printing.

6. The Helmholtz silencer structure with an acoustic black hole as its neck according to claim 1, characterized in that, The annular thin plate (1), cylindrical cavity (2), tubular neck (3) and back cavity (4) are connected and fixed by using strong glue, welding or bolts.

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