A ventilation duct muffler based on a coiled-back cavity Helmholtz resonator

Abstract

The present invention provides a ventilation duct silencer based on a coiled back cavity Helmholtz resonance cavity, belonging to the field of noise control. It solves the problem that the existing ventilation type silencer has a high sound insulation peak frequency, a low sound insulation in the low frequency range, and is limited by size. It includes a cylindrical silencer body and a neck tube; a central cylindrical ventilation hole is opened at the central axis of the cylindrical silencer body, the outer wall of the silencer, the inner wall of the silencer, the upper cover plate and the lower cover plate are combined to form a Helmholtz resonance cavity, the Helmholtz resonance cavity is connected to the ventilation duct through two neck tubes, and the Helmholtz resonance cavity is divided into two cavities of the same volume by two partition plates, and a plurality of partitions are arranged inside the Helmholtz resonance cavity, wherein there are a plurality of uniformly distributed inner partitions fixed on the inner wall of the silencer, and a plurality of uniformly distributed outer partitions fixed on the outer wall of the silencer, and the inner partitions and the plurality of outer partitions are staggered to form a coiled back cavity. The present invention is suitable for sound elimination.

Description

Technical Field

[0001] The present invention belongs to the field of noise control, and particularly relates to a ventilation duct muffler based on a coiled-back cavity Helmholtz resonator. Background Art

[0002] Sound insulation is one of the main technical measures in noise control. The common sound insulation method is to place a shield to change the noise propagation on the propagation path from the sound source to the receiver. Usually, obstacles need to be set to reflect or absorb sound energy to achieve the purpose of sound insulation. For duct noise reduction, it is necessary to reduce noise under the premise of meeting the ventilation conditions. The traditional methods have little effect, which makes people urgently need an excellent ventilation duct sound insulation method. At present, the main methods for controlling duct noise propagation include installing elastic joints, muffler elbows, perforated plates, and duct mufflers. Among the above methods, installing a duct muffler is the most widely used and effective method at present. However, the existing duct mufflers have a good noise reduction effect on high-frequency noise, but are not satisfactory for low-frequency noise and are difficult to meet the medium and low-frequency control requirements of duct system noise. The Helmholtz resonator muffler can suppress noise propagation at low frequencies, has a simple structure, is easy to process, and its acoustic performance is easy to control, with good sound insulation performance, so it is widely used in practical engineering to reduce noise in the corresponding frequency band. However, because its resonance frequency depends on the geometric dimensions of the cavity and the connecting pipe, it is usually strictly restricted by the spatial geometric dimensions. To meet the demand for further reducing the sound insulation frequency in practical applications, it is necessary to increase the cavity volume or the length of the connecting pipe. However, in some practical application scenarios such as the internal ventilation pipeline system of ships and the intake and exhaust system of internal combustion engines, the space layout is very compact, and the control of the equipment external dimensions is very strict. The feasibility of reducing the sound insulation frequency by increasing the size of the resonator is very low. Based on the idea of metamaterial subwavelength control, the back cavity of the Helmholtz resonator is placed by coiling and folding to extend the sound wave propagation path. A single classical Helmholtz resonator needs to ensure a sufficiently large cavity volume to achieve low-frequency sound insulation, and its practicability is poor due to the limitation of spatial geometric dimensions. Therefore, it is necessary to design a new muffler to solve the above problems. Summary of the Invention

[0003] In view of this, the present invention aims to propose a ventilation duct muffler based on a coiled-back cavity Helmholtz resonator to solve the problems that the sound insulation peak frequency of the existing ventilation muffler is relatively high, the sound insulation amount in the low-frequency range is relatively low, and it is limited by size.

[0004] To achieve the above object, the technical solution of the present invention is realized as follows:

[0005] A ventilation duct muffler based on a coiled-back cavity Helmholtz resonator, comprising a cylindrical muffler body, a neck tube (6), and several partitions fixed inside the muffler; a central cylindrical ventilation hole (1) is provided on the central axis of the cylindrical muffler body. The cylindrical muffler body includes a muffler outer wall (2), a muffler inner wall (5), an upper cover plate (3), and a lower cover plate (4). The muffler outer wall (2), the muffler inner wall (5), the upper cover plate (3), and the lower cover plate (4) enclose a Helmholtz resonator cavity. The Helmholtz resonator cavity is connected to the central cylindrical ventilation hole (1) through two neck tubes (6). The Helmholtz resonator cavity is divided into two parts of cavities with the same volume by two partition plates (7). Several partitions are provided inside the Helmholtz resonator cavity, including several inner partitions (8) evenly distributed and fixed on the muffler inner wall, and several outer partitions (9) evenly distributed and fixed on the muffler outer wall. Each inner partition and outer partition are arranged radially along the cylindrical muffler body and have the same thickness. The several inner partitions (8) and several outer partitions (9) inside each part of the cavity are staggered to form a coiled-back cavity (10).

[0006] When sound waves propagate along the axial direction of the muffler, they will enter the interior of the muffler through the narrow neck tube (6) and propagate along the coiled-back cavity (10). Intense resonance occurs between the air in the neck and the internal space, dissipating sound energy.

[0007] Furthermore, the resonance frequency formula of the Helmholtz resonator cavity is as follows:

[0008]

[0009] In the formula, c is the speed of sound, S k is the cross-sectional area of the neck tube, V is the volume of the back cavity, l′ n is the effective length of the neck tube;

[0010] The calculation formula for the coiled-back cavity composite Helmholtz resonator is:

[0011]

[0012] Among them, R1 is the radius of the central cylindrical ventilation hole circle, R2 is the radius of the muffler inner wall circle, R3 is the radius of the top circle of the outer partition, R4 is the radius of the top circle of the inner partition, R5 is the radius of the muffler back cavity circle, R6 is the radius of the muffler outer wall circle, l is the length of the back cavity, t1 is the width of the neck tube, and t2 is the thickness of the partition.

[0013] Further, the radius R1 of the central cylindrical ventilation hole is 15 mm, the radius R2 of the inner wall of the muffler is 20 mm, the radius R6 of the outer wall of the muffler is 37 mm, the radius R3 of the top of the outer partition is 23.75 mm, the radius R4 of the top of the inner partition is 31.25 mm, the radius R5 of the back cavity of the muffler is 35 mm, the width t1 of the neck tube is 1.5 mm, the length l of the back cavity is 90 mm, the thickness t2 of the partition is 2 mm, and the width t1 of the neck tube is 1.5 mm.

[0014] Further, inner partitions are arranged on both sides of each partition plate (7).

[0015] Further, ten evenly distributed outer partition plates (9) fixed to the outer wall (2) of the muffler are provided, and twelve evenly distributed inner partition plates (8) fixed to the inner wall (5) of the muffler are provided.

[0016] Further, the angle α between each neck tube and its nearest inner partition is 15°, and the angle β between two adjacent inner and outer partition plates is 30°.

[0017] Further, the two partition plates (7) are arranged close to the neck tubes on the corresponding sides.

[0018] Further, the upper cover plate (3) and the lower cover plate (4) have the same thickness of 2 mm.

[0019] Further, the neck tubes (6) are opened on the inner wall (5) of the muffler, and the neck tubes (6) penetrate through the thickness direction of the inner wall (5) of the muffler.

[0020] Further, two neck tubes (6) are symmetrically arranged.

[0021] Compared with the prior art, the beneficial effects of the ventilation duct muffler based on the coiled-back cavity Helmholtz resonator of the present invention are as follows:

[0022] (1) For the ventilation duct muffler based on the coiled-back cavity Helmholtz resonator of the present invention, partition plates are added to form a coiled-back cavity structure, and on the premise of ensuring the same volume size, the sound insulation peak frequency is greatly reduced.

[0023] (2) For the ventilation duct muffler based on the coiled-back cavity Helmholtz resonator of the present invention, compared with the traditional resonator, on the premise of the same volume, the sound insulation peak frequency of the structure can be reduced from 665 Hz to around 381 Hz, a reduction of about 42%, and a certain bandwidth can be maintained, enabling effective low-frequency sound insulation.

[0024] (3) For the ventilation duct muffler based on the coiled-back cavity Helmholtz resonator of the present invention, there is no specific requirement for the material, and it can be achieved only with a solid rigid structure. Brief Description of the Drawings

[0025] The drawings forming a part of this invention are used to provide a further understanding of the invention. The schematic embodiments and descriptions thereof of the invention are used to explain the invention and do not unduly limit the invention. In the drawings:

[0026] Figure 1 is an external view of a ventilation duct muffler based on a coiled-back cavity Helmholtz resonator according to an embodiment of the invention;

[0027] Figure 2 is a perspective view of a ventilation duct muffler based on a coiled-back cavity Helmholtz resonator according to an embodiment of the invention;

[0028] Figure 3 is a cross-sectional schematic view of a ventilation duct muffler based on a coiled-back cavity Helmholtz resonator according to an embodiment of the invention;

[0029] Figure 4 is a schematic view of the dimensions of each part of a ventilation duct muffler based on a coiled-back cavity Helmholtz resonator according to an embodiment of the invention;

[0030] Figure 5 is a schematic view of the outer wall thickness dimension of a ventilation duct muffler based on a coiled-back cavity Helmholtz resonator according to an embodiment of the invention;

[0031] Figure 6 is a comparison chart of the transmission loss between a ventilation duct muffler based on a coiled-back cavity Helmholtz resonator and a classical resonator of the same volume.

[0032] Description of the Reference Numerals:

[0033] 1. Central cylindrical ventilation hole; 2. Muffler outer wall; 3. Upper cover plate; 4. Lower cover plate; 5. Muffler inner wall; 6. Neck tube; 7. Partition plate; 8. Inner partition plate; 9. Outer partition plate; 10. Coiled-back cavity. Detailed Embodiments

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0035] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0036] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0037] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0038] like Figures 1 - 5 As shown, a ventilation duct muffler based on a coiled back cavity Helmholtz resonance cavity comprises a cylindrical muffler body, a neck tube 6 and a plurality of partitions fixed inside the muffler; a central cylindrical ventilation hole 1 is opened at the central axis of the cylindrical muffler body, the cylindrical muffler body comprises a muffler outer wall 2, a muffler inner wall 5, an upper cover plate 3 and a lower cover plate 4, the muffler outer wall 2, the muffler inner wall 5, the upper cover plate 3 and the lower cover plate 4 together form a Helmholtz resonance cavity, and the Helmholtz resonance cavity is connected to the central cylindrical ventilation hole 1 through two neck tubes 6 The Helmholtz resonance cavity is divided into two cavities of equal volume by two partition plates 7. A plurality of partition plates are arranged inside the Helmholtz resonance cavity, including a plurality of evenly distributed inner partition plates 8 fixed on the inner wall of the muffler, and a plurality of evenly distributed outer partition plates 9 fixed on the outer wall of the muffler. Each inner partition plate and outer partition plate are arranged radially along the cylindrical muffler body and have the same thickness. The plurality of inner partition plates 8 and the plurality of outer partition plates 9 inside each cavity are staggered to form a coiled back cavity 10. The thickness of the partition plate 7 is the same as that of the inner and outer partition plates.

[0039] When the sound wave propagates along the axial direction of the muffler, it enters the interior of the muffler through the narrow neck tube 6 and propagates along the coiled back cavity 10, generating a violent resonance between the air in the neck and the internal space, which consumes the sound energy.

[0040] The resonance frequency formula of the Helmholtz resonator is as follows:

[0041]

[0042] In the formula, c is the speed of sound, S k is the cross-sectional area of the neck tube, V is the volume of the back cavity, and l′ n is the effective length of the neck tube;

[0043] The calculation formula for the coiled-back cavity composite Helmholtz resonator is:

[0044]

[0045] Among them, R1 is the radius of the central cylindrical ventilation hole circle, R2 is the radius of the inner wall circle of the muffler, R3 is the radius of the top circle of the outer partition, R4 is the radius of the top circle of the inner partition, R5 is the radius of the back cavity circle of the muffler, R6 is the radius of the outer wall circle of the muffler, l is the length of the back cavity, t1 is the width of the neck tube, and t2 is the thickness of the partition.

[0046] Specifically, it can be: the radius R1 of the central cylindrical ventilation hole circle is 15 mm, the radius R2 of the inner wall circle of the muffler is 20 mm, the radius R6 of the outer wall circle of the muffler is 37 mm, the radius R3 of the top circle of the outer partition is 23.75 mm, the radius R4 of the top circle of the inner partition is 31.25 mm, the radius R5 of the back cavity circle of the muffler is 35 mm, the width t1 of the neck tube is 1.5 mm, the length l of the back cavity is 90 mm, the thickness t2 of all partitions is 2 mm, and the width t1 of the neck tube is 1.5 mm; the thicknesses of the upper cover plate 3 and the lower cover plate 4 are the same and are both 2 mm.

[0047] Inner partitions are arranged on both sides of each partition plate 7. Ten evenly distributed outer partition plates 9 are fixed on the outer wall 2 of the muffler, and twelve evenly distributed inner partition plates 8 are fixed on the inner wall 5 of the muffler. The angle α between each neck tube and its nearest inner partition is 15°, and the angle β between adjacent inner and outer partition plates is 30°. The two partition plates 7 are arranged close to the neck tubes on the corresponding sides.

[0048] The neck tubes 6 are opened on the inner wall 5 of the muffler, and the neck tubes 6 penetrate through the thickness direction of the inner wall 5 of the muffler. The two neck tubes 6 are symmetrically arranged.

[0049] The following gives a specific example:

[0050] The ventilation duct muffler of the coiled-back cavity Helmholtz resonator of the present application is composed of two identical coiled-back cavity Helmholtz resonators placed in rotational symmetry, and is connected to the central ventilation pipe through the neck tubes. The overall geometric dimensions of the composite Helmholtz muffler are defined by 11 parameters, as Figure 4 and Figure 5 shown. The geometric parameters are as follows in the table:

[0051]

[0052] The transmission loss of the designed and completed structure was calculated, and a composite Helmholtz muffler with a coiled back cavity was realized under the dimensions of 74 mm in diameter and 94 mm in length. The sound insulation performance of the composite Helmholtz muffler with a coiled back cavity was verified through simulation calculation. It was obtained that the sound insulation peak frequency of the structure of this application was at 381 Hz. Compared with the traditional resonance cavity, under the condition of equal volume, the sound insulation peak decreased from 665 Hz to 381 Hz. As Figure 6 shown, it decreased by about 42%, and could maintain a certain bandwidth, and could achieve effective low-frequency sound insulation; it shows that the coiled back cavity structure can greatly reduce the sound insulation peak frequency.

[0053] The ventilation duct muffler of the coiled back cavity Helmholtz resonator is determined by the geometric parameters defined in the table; a total of 11 geometric dimensions are jointly used to reduce the sound insulation peak frequency.

[0054] The sound insulation peak frequency dropped to 381 Hz, and the sound insulation peak could reach 33.5 dB; effective low-frequency sound insulation was achieved through the combined structure, and the effect of maintaining a certain bandwidth could still be maintained.

[0055] There are no specific requirements for the materials used in this structure, and any rigid material can be used to achieve ideal results.

[0056] In summary, the coiled back cavity is used to optimize the sound insulation peak frequency of the Helmholtz resonator. By calculating the structure through finite element and simulating the sound insulation effect of the structure, a low-frequency sound insulation muffler can be designed.

[0057] The embodiments of the present invention disclosed above are only used to help explain the present invention. The embodiments do not describe all the details in detail, nor do they limit the present invention to the specific embodiments described. According to the content of this specification, many modifications and changes can be made. These embodiments are selected and specifically described in this specification to better explain the principle and practical application of the present invention, so that those skilled in the art can understand and utilize the present invention well.

Claims

1. A ventilation duct muffler based on a coiled-back cavity Helmholtz resonator, characterized in that: It includes a cylindrical muffler body, a neck tube (6), and several partition plates fixed inside the muffler; a central cylindrical ventilation hole (1) is provided on the central axis of the cylindrical muffler body. The cylindrical muffler body includes a muffler outer wall (2), a muffler inner wall (5), an upper cover plate (3), and a lower cover plate (4). The muffler outer wall (2), the muffler inner wall (5), the upper cover plate (3), and the lower cover plate (4) enclose a Helmholtz resonance cavity. The Helmholtz resonance cavity is connected to the central cylindrical ventilation hole (1) through two neck tubes (6). The Helmholtz resonance cavity is divided into two parts of cavities with the same volume by two partition plates (7). Several partition plates are provided inside the Helmholtz resonance cavity, including several inner partition plates (8) evenly distributed and fixed on the muffler inner wall, and several outer partition plates (9) evenly distributed and fixed on the muffler outer wall. Each inner partition plate and outer partition plate are arranged radially along the cylindrical muffler body and have the same thickness. The several inner partition plates (8) and several outer partition plates (9) inside each part of the cavity are staggered to form a coiled back cavity (10). When sound waves propagate along the axial direction of the muffler, they will enter the inside of the muffler through the narrow neck tube (6) and propagate along the coiled back cavity (10). Intense resonance occurs between the air in the neck and the internal space, dissipating the sound energy.

2. The ventilation duct muffler based on a coiled back cavity Helmholtz resonator according to claim 1, wherein: The resonance frequency formula of the Helmholtz resonance cavity is: Where c is the speed of sound, S k is the cross-sectional area of the neck tube, V is the volume of the back cavity, l′ n is the effective length of the neck tube; The calculation formula of the coiled back cavity composite Helmholtz resonance cavity is: Where, R1 is the radius of the central cylindrical ventilation hole circle, R2 is the radius of the muffler inner wall circle, R3 is the radius of the top circle of the outer partition plate, R4 is the radius of the top circle of the inner partition plate, R5 is the radius of the muffler back cavity circle, R6 is the radius of the muffler outer wall circle, l is the length of the back cavity, t1 is the width of the neck tube, and t2 is the thickness of the partition plate.

3. The ventilation duct muffler based on a coiled-back cavity Helmholtz resonator according to claim 2, characterized in that: The radius R1 of the central cylindrical ventilation hole circle is 15 mm, the radius R2 of the muffler inner wall circle is 20 mm, the radius R6 of the muffler outer wall circle is 37 mm, the radius R3 of the top circle of the outer partition plate is 23.75 mm, the radius R4 of the top circle of the inner partition plate is 31.25 mm, the radius R5 of the muffler back cavity circle is 35 mm, the width t1 of the neck tube is 1.5 mm, the length l of the back cavity is 90 mm, the thickness t2 of the partition plate is 2 mm, and the width t1 of the neck tube is 1.5 mm.

4. The ventilation duct muffler based on a coiled-back cavity Helmholtz resonator according to claim 1, wherein: Inner partition plates are arranged on both sides of each partition plate (7).

5. The ventilation duct muffler based on a coiled-back cavity Helmholtz resonator according to claim 1, wherein: Ten evenly distributed outer partition plates (9) are fixed on the muffler outer wall (2), and twelve evenly distributed inner partition plates (8) are fixed on the muffler inner wall (5).

6. The ventilation duct muffler based on a coiled back cavity Helmholtz resonator according to claim 5, wherein: The angle α between each neck tube and its nearest inner partition plate is 15°, and the angle β between adjacent inner and outer partition plates is 30°.

7. The ventilation duct muffler based on a coiled-back cavity Helmholtz resonator according to claim 1, characterized in that: The two partition plates (7) are arranged close to the neck tubes on the corresponding sides.

8. The ventilation duct muffler based on a coiled-back cavity Helmholtz resonator according to claim 3, wherein: The upper cover plate (3) and the lower cover plate (4) have the same thickness of 2 mm.

9. A ventilation duct muffler based on a coiled back cavity Helmholtz resonator according to any one of claims 1-8, characterized in that: The neck tube (6) is opened on the muffler inner wall (5), and the neck tube (6) penetrates through the thickness direction of the muffler inner wall (5).

10. The ventilation duct muffler based on a coiled-back cavity Helmholtz resonator according to claim 9, characterized in that: The two neck tubes (6) are symmetrically arranged.

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