Fan with silencer, and silencer

Abstract

Provided are a fan with a silencer and a silencer, with which a reduction in silencing performance on the low-frequency side can be suppressed, and the silencer is capable of silencing in a wide band even when a resonance-type silencer is brought close to the fan, which is the sound source.　This fan with a silencer comprises: a fan; and a silencer that silences, by resonance, sound generated by rotation of the fan, the silencer being provided with a wall with an opening, in which a silencer-side opening is provided, and a back space partitioned by the wall with the opening and continuous with the silencer-side opening, the distance between the end of the fan located on the silencer side and the end of the silencer-side opening located on the fan side being the distance at which Fano resonance occurs for the silencer and the sound generated by rotation of the fan, and a conversion mechanism that converts sound energy into thermal energy being provided in at least one of the silencer-side opening and the back space.

Description

Silencer-equipped fans and silencers

[0001] The present invention relates to a fan with a silencer, and a silencer that silences noise generated by the rotation of a fan through resonance.

[0002] It is important that a silencer that can efficiently reduce noise generated by the rotation of a fan can do so without reducing the airflow. Therefore, in conventional silencer-equipped fans, a resonance-type silencer that has a high ability to absorb sound in an open space is sometimes placed on the outside of the housing, specifically near an intake or exhaust hole in the housing, so as not to block the air path. An example of a silencer-equipped fan with such a configuration is the fan described in Patent Document 1.

[0003] The silencer-equipped fan described in Patent Document 1 includes a resonant silencer disposed at a position connected to a space where a sound source (specifically, a fan inside a housing) is located. Furthermore, when the resonant wavelength of the resonant silencer alone is λ, the distance from the sound source to the resonant silencer is less than λ / 2. Furthermore, the fundamental resonant frequency of the resonant silencer is equal to or less than the upper acoustic frequency limit determined by the size of the housing. This configuration makes it possible to muffle low-frequency sounds generated by the fan inside the housing over a wide frequency range.

[0004] International Publication No. 2021 / 171710

[0005] When a resonance type silencer is arranged to silence noise over a wide frequency range, as in the silencer-equipped fan described in Patent Document 1, it is conceivable to place the silencer close to the fan, which is the sound source, in order to effectively silence the noise by arranging the silencer near the sound source. However, the inventors discovered that when a resonance type silencer is arranged close to the fan in an open space, the amount of silencing decreases near the silencing peak on the low frequency side.

[0006] The present invention has been made in consideration of the above circumstances, and aims to solve the problems of the prior art described above, and to provide a fan with a silencer, and a silencer that can suppress a decrease in noise silencing performance on the low frequency side even when a resonance type silencer is placed close to the fan, which is the sound source, and can silence noise over a wide frequency range.

[0007] As a result of intensive research into achieving the above object, the inventors have found that the above object can be achieved by the following configuration: [1] A fan with a silencer, including a fan and a silencer that silences sound generated by fan rotation through resonance, the silencer having an opening wall with a silencer-side opening and a back space that is separated by the opening wall and is continuous with the silencer-side opening, the distance between the end of the fan facing the silencer and the end of the silencer-side opening facing the fan is a distance at which Fano resonance occurs between the sound generated by fan rotation and the silencer, and a conversion mechanism that converts sound energy into thermal energy is provided in at least one of the silencer-side opening and the back space. [2] The fan with a silencer according to [1], wherein the conversion mechanism converts sound energy in the specific frequency band into thermal energy when the amount of silencing due to silencer resonance is minimized in a specific frequency band in the silencing spectrum when Fano resonance occurs. [3] The silencer-equipped fan according to [1] or [2], wherein the ratio of the total area of ​​the silencer-side openings provided in the opening-equipped wall to the sum of the area of ​​the surface of the opening-equipped wall on the side opposite to the rear space is 30% or more. [4] The silencer-equipped fan according to any of [1] to [3], wherein the fan is housed in a housing provided with an opening, and the rear space is in communication with the opening through the silencer-side opening. [5] The silencer-equipped fan according to [4], wherein the side wall of the housing has a communication hole that connects the inside of the housing with the space outside the housing. [6] The fan with a silencer according to [5], wherein the housing includes a first wall forming one end of the housing in the axial direction of the rotation shaft of the fan, a second wall forming the other end of the housing in the axial direction, a first intake hole formed in the first wall, and an exhaust hole as an opening formed in the second wall, a side wall is disposed between the first and second walls in the axial direction, the communication hole is the second intake hole, and the fan takes in gas from an outer space through the first intake hole and the second intake hole and exhausts the gas through the exhaust hole. [7] The fan with a silencer according to any of [4] to [6], wherein the silencer has a vent part through which gas that has passed through the opening flows, and an air-permeable member that collides with the gas that has passed through the vent part is provided at an end of the silencer opposite to the opening in the axial direction of the rotation shaft of the fan.[8] The silencer-equipped fan according to [7], wherein the silencer is further provided with a suppression member that suppresses gas that has passed through the opening from entering the back space through the silencer-side opening. [9] The silencer-equipped fan according to [7] or [8], wherein the shape of the ventilation part when viewed from the axial direction of the fan's rotation shaft is a polygon with six or more angles, a circle, or an ellipse.

[10] The silencer-equipped fan according to any of [1] to [9], wherein the silencer has an outer peripheral wall that separates the back space on the side opposite to the wall with the opening, and a through-hole is provided in a lower end of the outer peripheral wall.

[11] The silencer-equipped fan according to any of [1] to

[10] , wherein the fan is a fan for an outdoor unit of an air conditioning system.

[12] A silencer that silences sound generated by the rotation of a fan through resonance, the silencer comprising: a wall with an opening in which a silencer-side opening is provided; and a back space that is separated by the wall with an opening and is continuous with the silencer-side opening; the distance between the end of the fan that is located on the silencer side and the end of the silencer-side opening that is located on the fan side is the distance at which Fano resonance occurs between the sound generated by the rotation of the fan and the silencer; and a conversion mechanism that converts sound energy into thermal energy is provided in at least one of the silencer-side opening and the back space.

[0008] According to the present invention, it is possible to provide a fan with a silencer and a silencer that can silence noise over a wide frequency range while suppressing a decrease in the amount of silencing at low frequencies, even when the resonance type silencer is placed close to the fan, which is the sound source.

[0009] 1 is an explanatory diagram illustrating noise that is silenced by a silencer according to an embodiment of the present invention, showing a noise spectrum.

[0023] FIG. 1 is a perspective view of a silencer-equipped fan according to an embodiment of the present invention.

[0024] FIG. 2 is a schematic diagram showing the I-I cross section of FIG. 2.

[0025] FIG. 3 is a diagram illustrating a first modified example of the position of the grill.

[0026] FIG. 4 is a diagram relating to the influence of the position of the grill on the silencing effect.

[0027] FIG. 5 is a diagram illustrating a second modified example of the position of the grill.

[0028] FIG. 6 is a diagram illustrating the internal structure of the silencer, showing the J-J cross section of FIG. 3.

[0029] FIG. 7 is a diagram illustrating the dependence of the silencing volume of a silencer on the aperture ratio.

[0030] FIG. 8 is a diagram illustrating sound re-radiation in a resonator.

[0031] FIG. 9 is a diagram illustrating sound pressure at each frequency of incident sound.

[0032] FIG. 10 is a diagram illustrating the waveform of a re-radiated wave in a resonator.

[0033] FIG. 11 is a diagram illustrating a transmission loss spectrum when Fano resonance occurs.

[0034] FIG. 12 is a diagram illustrating the measurement results of Measurement Test 1 (Part 1).

[0035] FIG. 13 is a diagram illustrating the measurement results of Measurement Test 1 (Part 2).

[0036] FIG. 14 is a diagram illustrating the measurement results of Measurement Test 1 (Part 3).

[0037] FIG. 15 is a diagram illustrating the measurement results of Measurement Test 1 (Part 4).

[0038] FIG. 16 is a diagram illustrating the measurement results of Measurement Test 1 (Part 5).

[0039] FIG. 17 is a diagram illustrating the measurement 1 is an explanatory diagram illustrating a method for implementing measurement test 1. FIG. 2 is an explanatory diagram illustrating a method for implementing measurement test 2. FIG. 3 is an explanatory diagram illustrating a method for implementing measurement test 3. FIG. 4 is a diagram illustrating an asymmetric sound deadening spectrum when Fano resonance occurs, and a sound deadening spectrum when Fano resonance does not occur. FIG. 5 is a diagram illustrating the arrangement positions of each device in Example 1. FIG. 6 is a graph illustrating sound pressure levels measured for each of Example 1 and Comparative Example 1. FIG. 7 is a diagram illustrating sound deadening spectra for each of Example 1 and Comparative Example 1. FIG. 8 is a diagram illustrating the difference between the sound deadening spectrum of Example 1 and the sound deadening spectrum of Comparative Example 1. FIG. 9 is a diagram illustrating the sound deadening volume measured while changing the distance between the silencer and the outdoor unit fan for Example 1 and Comparative Example 1. FIG. 10 is a diagram illustrating sound deadening spectra for Comparative Example 1 when the distance between the silencer and the outdoor unit fan is 4.5 cm, 14.5 cm, and 24.5 cm.

[0010] The present invention will now be described in detail with reference to preferred embodiments shown in the accompanying drawings. The following embodiments are merely examples provided to facilitate understanding of the present invention and are not intended to limit the scope of the present invention. In other words, the configuration of the present invention may be modified or improved from the following embodiments without departing from the spirit of the present invention. Furthermore, unless otherwise specified, the materials and shapes of each component used to implement the present invention may be arbitrarily set depending on the intended use of the present invention and the state of the art at the time of implementing the present invention. Furthermore, the present invention includes equivalents thereof.

[0011] Furthermore, in this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. Furthermore, in this specification, "orthogonal," "vertical," and "parallel" are intended to include the range of error acceptable in the technical field to which the present invention belongs. For example, "orthogonal," "vertical," and "parallel" in this specification mean that they are within a range of less than ±10° from the strict "orthogonal," "vertical," and "parallel." Note that the error from the strict "orthogonal," "vertical," and "parallel" is preferably 5° or less, and more preferably 3° or less. Furthermore, in this specification, the meanings of "same" and "identical" may include the range of error generally acceptable in the technical field to which the present invention belongs. Furthermore, in this specification, "100%" includes 100% in the strict sense, as well as a state in which, although it does not actually reach 100% due to structural constraints, it also includes a state that is as close to 100% as possible.

[0012] In addition, "sound deadening" in the present invention means reducing sound, and is a concept that includes both sound insulation and sound absorption. Sound insulation also includes sound reflection and sound cancellation.

[0013] <<Outline of Silencer-Equipped Fan of the Present Invention>> The silencer-equipped fan of the present invention includes a fan and a silencer that silences noise generated by fan rotation through resonance. The noise generated by fan rotation is primarily turbulent noise such as wind noise, and is sound in the range of 400 to 2000 Hz. Note that turbulent noise is distinguished from rotational noise, which has peaks around and below 100 Hz in its noise spectrum, as shown in Figure 1 .

[0014] The silencer is used in an open space, such as an outdoor space, rather than a closed space like a duct. Here, the open space means a space in which sound propagates three-dimensionally. The silencer includes an opening wall in which a silencer-side opening is provided, and a back space that is separated by the opening wall and is continuous with the silencer-side opening. The silencer-side opening and the back space form a resonance structure, specifically an air column resonance structure or a Helmholtz resonance structure.

[0015] Furthermore, the distance between the fan, which is the sound source, and the silencer-side opening is set to a distance that causes Fano resonance between the sound generated by the rotation of the fan and the silencer. Fano resonance will be described in detail later. The distance between the fan and the silencer-side opening is the distance between the end of the fan located on the silencer side and the end of the silencer-side opening located on the fan side. The end of the fan located on the silencer side corresponds to the point closest to the silencer (more specifically, the silencer-side opening) in the path that the tip of the rotor of the fan follows during rotation.

[0016] Furthermore, a conversion mechanism that converts sound energy into thermal energy is provided in at least one of the silencer-side opening and the back space. By providing this conversion mechanism, even if the distance between the fan and the silencer-side opening is λ / 4 or less, it is possible to suppress a decrease in noise silencing performance on the low frequency side and to silence noise over a wide band. Note that examples of the conversion mechanism include the viscosity of the fluid near the wall surface of the silencer, the unevenness (surface roughness) of the wall surface of the silencer, or a sound-absorbing material.

[0017] <<Configuration Example of Silencer-Equipped Fan According to One Embodiment of the Present Invention>> A configuration example of a silencer-equipped fan according to one embodiment of the present invention (hereinafter referred to as this embodiment) will be described with reference to Figures 2 to 9. In the following description, the position, orientation, posture, state, etc. of each device and member represent the position, orientation, posture, and state when the silencer-equipped fan is in its normal usage position, unless otherwise specified.

[0018] The silencer-equipped fan according to this embodiment (hereinafter referred to as the silencer-equipped fan 10) has the appearance shown in Fig. 2 and is used, for example, in the outdoor unit of an air conditioning system (specifically, a building air conditioner). That is, the silencer-equipped fan 10 is used in an open space, specifically, an outdoor space. However, the use of the silencer-equipped fan 10 is not particularly limited, and it may be used for purposes other than the outdoor unit of a building air conditioner, such as car air conditioners, air purifiers, ventilation fans, electric fans, circulators, dehumidifiers, humidifiers, jet engines, air-cooling devices for computers and copiers, and other air-cooling devices.

[0019] 2 and 3, the silencer-equipped fan 10 includes a fan 12, a housing 20, a heat exchanger 40, a shroud 42, a grill 44, and a silencer 50. Each of these components will be described below.

[0020] (Fan) The fan 12 is a blower fan, and in this embodiment, it is a fan that blows air in the axial direction of the rotation shaft (hereinafter simply referred to as the axial direction). In this embodiment, as described above, the fan 12 is a fan for an outdoor unit of an air conditioning system, and blows air by expelling gas that has entered the housing 20, more specifically, air, to the outside of the housing 20. Here, wind refers to an artificial flow of air and gas (airflow). The composition of the air or gas that constitutes the wind and the ratio of each gas component are not particularly limited.

[0021] In the following description, the fan 12 is assumed to be an axial fan that blows normal air. However, the fan 12 may be a fan other than an axial fan, such as a centrifugal fan, a backward-curved fan (turbo fan), a blade fan, a radial fan, a paddle fan, a multi-blade fan (sirocco fan), a tubular centrifugal fan, a mixed-flow fan, an axial fan, a vane-axial fan, a tube-axial fan, a propeller fan, a counter-rotating axial fan, a line flow fan (registered trademark), a cross-flow fan, or a vortex fan.

[0022] The structure of the fan 12 is the same as that of a known axial flow fan. As shown in FIG. 3 , a plurality of rotor blades 16 extend radially from the outer periphery of a cylindrical central portion 14 (hereinafter simply referred to as the radial direction). A rotor shaft 18 is disposed within the central portion 14 with its axial direction oriented horizontally. The rotor shaft 18 rotates using the torque of a motor (not shown), causing the central portion 14 and the rotor blades 16 to rotate integrally with the rotor shaft 18. As a result, air flows from upwind of the fan 12 to downwind of the fan 12 in the axial direction. Note that, hereinafter, the downwind side of the fan 12 in the axial direction will also be referred to as the "front side," and the upwind side will also be referred to as the "rear side" or "back side."

[0023] When the fan 12 rotates within the housing 20, turbulent noise, including wind noise, is generated. That is, the rotor blades 16 of the fan 12 correspond to the noise source. The noise generated by the rotation of the fan 12 travels within the housing 20 and passes through the exhaust holes 34 together with the wind.

[0024] As shown in FIG. 3 , in this embodiment, a small silencer for the fan 12 (hereinafter referred to as a fan silencer 70) is attached to the front end of the central portion 14 in the axial direction. The fan silencer 70 may be a resonance-type silencer or a silencer made of sound-absorbing material. Resonance-type silencers that can be used include membrane-type resonators, air column resonators, Helmholtz resonators, and resonators made of perforated plates. The fan silencer 70 is preferably positioned so as not to overlap with the rotor blades 16 when viewed from the axial direction, i.e., so as not to affect the airflow rate of the fan 12, and is preferably fixed to the front end face of the central portion 14 with adhesive or fasteners such as screws.

[0025] (Housing) The housing 20 is a hollow body having a box or cylindrical shape, and houses the fan 12. The material of the housing 20 is not particularly limited, and examples of materials that can be used include metal materials, wood, resin materials including reinforced plastic materials, and carbon fiber.

[0026] 2 and 3 , the housing 20 has a first wall 22, a second wall 24, and a side wall 26. The first wall 22 is one end of the housing 20 in the axial direction, more specifically, a wall (rear wall) forming the rear end, and a first intake hole 30 is provided in the first wall 22. The second wall 24 is the other end of the housing 20 in the axial direction, more specifically, a wall (front wall) forming the front end, and an exhaust hole 34 is provided in the second wall 24. The exhaust hole 34 corresponds to an opening of the housing 20 in this embodiment.

[0027] The shapes of the first intake holes 30 and the exhaust holes 34 (more specifically, the shape of the outer edge of each hole) are not particularly limited, and may be circular, elliptical, square, rectangular, other quadrilaterals, polygonal shapes other than quadrilaterals, or irregular shapes. Furthermore, the sizes of the first intake holes 30 and the exhaust holes 34 (more specifically, the areas of the holes when viewed in the axial direction) are not particularly limited, and may be the same or different between the first intake holes 30 and the exhaust holes 34. In this embodiment, the rectangular first intake holes 30 are provided over a wide area in the first wall 22, and the circular exhaust hole 34 is provided in the center of the second wall 24.

[0028] The side wall 26 is a generally rectangular cylindrical wall located between the first wall 22 and the second wall 24 in the axial direction. As shown in Figures 2 and 3, the side wall 26 forms the top, bottom, right, and left walls of the housing 20. As shown in Figure 3, one end of the side wall 26 in the lateral width direction of the housing 20 (hereinafter simply referred to as the lateral width direction), specifically the left or right end of the side wall 26, corresponds to the third wall 28. Here, the lateral width direction refers to a direction that intersects both the up-down direction and the axial direction of the silencer-equipped fan 10, or more precisely, a direction that is perpendicular to these directions.

[0029] 3, a second air intake hole 32 is provided in the third wall 28. This second air intake hole 32 corresponds to a communication hole that connects the interior of the housing 20 with the space outside the housing 20. In other words, the side wall 26 of the housing 20 in this embodiment does not have a completely closed cross-sectional structure, and the portion of the third wall 28 where the second air intake hole 32 is provided is missing.

[0030] The shape of the second air intake holes 32 (more specifically, the shape of the outer edge of the second air intake holes 32) is not particularly limited, and may be circular, elliptical, square, rectangular, other quadrilaterals, polygonal shapes other than quadrilaterals, or an irregular shape. Furthermore, the size of the second air intake holes 32, i.e., the opening area (more specifically, the area of ​​the second air intake holes 32 when viewed from a direction penetrating the third wall 28), is not particularly limited. In this embodiment, the rectangular second air intake holes 32 are provided over a wide area in the third wall 28. More specifically, the rear end of the third wall 28 and the rear end of the second air intake holes 32 are located at approximately the same position in the axial direction, and the front end of the second air intake holes 32 is located closer to the front end of the third wall 28 than to the axial center of the third wall 28.

[0031] The second air intake holes 32 also function as side air intakes, and when the fan 12 is rotating, air enters the housing 20 not only through the first air intake holes 30 but also through the second air intake holes 32. In other words, the fan 12 takes in air from the space outside the housing 20 through the first air intake holes 30 and the second air intake holes 32 and expels the air (wind) through the exhaust holes 34. In other words, within the housing 20, there is an air passage through which air that has passed through the first air intake holes 30 flows, and an air passage through which air that has passed through the second air intake holes 32 flows, and these two air passages meet behind the fan 12 in the axial direction within the housing 20.

[0032] 3, in the present embodiment, the range in the width direction in which the first air intake holes 30 are provided overlaps at least a part of the range in which the exhaust holes 34 are provided. On the other hand, the second air intake holes 32 are arranged in a position in the width direction that is different from the first air intake holes 30 and the exhaust holes 34, more specifically, in a position that does not overlap with these holes.

[0033] As shown in Fig. 3, a machine chamber 36 is provided inside the housing 20 and is adjacent to the space housing the fan 12 in the width direction, and a compressor (not shown) is disposed in the machine chamber 36. As such, the interior of the housing 20 is divided into an air passage space in which the fan 12 is disposed and which forms a flow path (air passage) for air passing through the fan 12, and the machine chamber 36, and these two spaces are separated by a partition wall 38, as shown in Fig. 3. The first intake hole 30, the second intake hole 32, and the exhaust hole 34 are all continuous with the above-mentioned air passage space. Hereinafter, unless otherwise specified, the internal space of the housing 20 will refer to the above-mentioned air passage space.

[0034] (Heat Exchanger) The heat exchanger 40 is disposed inside the housing 20, behind (rearward of) the fan 12, and is disposed within the first air intake vent 30 in the axial direction, as shown in FIG. 3 . The heat exchanger 40 is disposed within the first air intake vent 30 so that its rear end (the end opposite the fan 12) is flush with the rear end surface of the housing 20 in the axial direction. In this embodiment, as shown in FIG. 3 , a heat exchanger 40 is also disposed within the second air intake vent 32. The heat exchanger 40 is formed, for example, of a fin coil, a fin tube, or a heat exchange plate, and exchanges heat with air entering the housing 20 through the first air intake vent 30 to heat or cool the air. In other words, the air entering the housing 20 through the first air intake vent 30 passes through the heat exchanger 40 on its way to the fan 12. In other words, the heat exchanger 40 corresponds to a resistance member that provides resistance to air flowing toward the fan 12.

[0035] (Shroud) As shown in Fig. 3 , the shroud 42 is a cylindrical member that is disposed within the housing 20 and adjusts the airflow (i.e., the wind direction) from the fan 12 toward the exhaust holes 34 inside the housing 20. The shroud 42 extends in the axial direction, and most of the shroud 42 is disposed axially between the fan 12 and the exhaust holes 34. The air from the fan 12 passes through the inside of the shroud 42 toward the exhaust holes 34 and is discharged from the exhaust holes 34. In other words, the shroud 42 defines an air passage through which the air from the fan 12 flows.

[0036] Furthermore, the area of ​​the air passage within the shroud 42 is smaller than the area of ​​the air passage located behind the shroud 42 (on the first air intake hole 30 side) inside the housing 20. The area of ​​the air passage is the area when the air passage is viewed in the axial direction, and is the area through which the air passes, i.e., the flow path area.

[0037] 3, in the present embodiment, the rear end of the shroud 42 approaches the area in which the fan 12 is provided in the axial direction. In other words, the rear end of the shroud 42 is located rearward of the front end of the fan 12 in the axial direction (i.e., closer to the first air intake holes 30). In addition, the shroud 42 may approach the area in which the second air intake holes 32 are provided in the axial direction, or may be located forward of the second air intake holes 32 (downstream in the air blowing direction).

[0038] (Grill) The grill 44 corresponds to a breathable member with which the air (wind) discharged from the exhaust hole 34 and passing through the ventilation section 52 of the silencer 50 collides. The grill 44 is formed, for example, of a lattice panel, and the wind passes through the open parts of the grill 44 while colliding with the non-open parts (more specifically, the linear parts) of the grill 44. Note that the grill 44 is not limited to the grill 44, and may be any device that can collide with the wind discharged from the exhaust hole 34 and is breathable, for example, a device for adjusting the amount of airflow, such as a louver.

[0039] In this embodiment, as shown in Fig. 3, the grille 44 is disposed at the front end of the silencer 50 in the axial direction (the end opposite the exhaust hole 34). With this configuration, the noise absorbing effect of the silencer 50, particularly the noise absorbing effect on the high frequency side, is improved compared to a configuration in which the grille 44 is disposed between the exhaust hole 34 and the silencer 50 as shown in Fig. 4.

[0040] More specifically, wind noise is generated when wind impinges on the non-opening portion of the grille 44. On the other hand, by locating the grille 44 at the downstream end of the ventilation section 52, the flow speed of the wind decreases as it passes through the ventilation section 52. Then, because the wind impinges on the non-opening portion of the grille 44 at the downstream end of the ventilation section 52, the range through which the wind flows increases, further decreasing the wind speed. As a result, wind noise is reduced, and the amount of silencing of the silencer 50 on the high frequency side increases, as shown in Figure 5. In Figure 5, the solid line shows the silencing spectrum when the grille 44 is located at the position shown in Figure 3, and the dashed line shows the silencing spectrum when the grille 44 is located at the position shown in Figure 4.

[0041] The position of the grill 44 is not limited to the position shown in Fig. 3, and may be the position shown in Fig. 4. Furthermore, as shown in Fig. 6, the grill 44 may be disposed at the rear end portion (the end portion on the exhaust hole 34 side) of the silencer 50 in the axial direction. Furthermore, as shown in Fig. 7, the grill 44 may extend into the rear end portion (the end portion on the exhaust hole 34 side) of a ventilation portion 52 provided in the silencer 50. However, from the viewpoint of reducing wind noise and improving the silencing effect on the high frequency side, it is more preferable to dispose the grill 44 at the position shown in Fig. 3.

[0042] (Muffler) The silencer 50 is disposed adjacent to the housing 20 on the front side thereof, and uses resonance to muffle noise generated by the rotation of the fan 12 housed in the housing 20, primarily turbulent noise. The silencer 50 muffles noise by resonating with the sound to be silenced in an open space, rather than in a closed space such as the inside of a duct. As shown in FIG. 3 , the silencer 50 has a ventilation section 52, an opening-equipped wall 56 having a silencer-side opening 54, a back space 60 partitioned by the opening-equipped wall 56 and an outer peripheral wall 62, and a conversion mechanism 66.

[0043] The ventilation section 52 is a hollow portion that communicates with the exhaust hole 34 (the opening of the housing 20), and in this embodiment, is adjacent to and continuous with the exhaust hole 34 in the axial direction. Air that has passed through the exhaust hole 34, i.e., the wind from the fan 12, flows through the ventilation section 52. In other words, the ventilation section 52 forms an air passage in the silencer 50.

[0044] Furthermore, the shape of the ventilation portion 52 when viewed in the axial direction (more specifically, the shape of the outer edge of the space surrounded by the inner circumferential surface 58 of the opening wall 56) is a polygon with six or more angles, a circle, or an ellipse. In this embodiment, as shown in FIG. 8 , the shape of the ventilation portion 52 when viewed in the axial direction is a regular hexadecagon, but in practice, it may be a circle. This allows for good communication between the exhaust hole 34 and the ventilation portion 52, allowing the silencer 50 to be appropriately positioned with respect to the fan 12 and the housing 20 so as not to reduce the airflow rate of the silencer-equipped fan 10. The size (opening area) of the ventilation portion 52 is not particularly limited, and may be the same as or different from the size of the exhaust hole 34.

[0045] Furthermore, in this embodiment, the center of the ventilation section 52 and the center of the exhaust hole 34 are arranged on the same straight line, so that the air (wind) that has passed through the exhaust hole 34 smoothly enters the ventilation section 52 and flows inside the ventilation section 52. However, this is not limiting, and the center of the ventilation section 52 and the center of the exhaust hole 34 may not be on the same straight line but may be slightly offset.

[0046] The opening wall 56 is an annular wall surrounding the ventilation section 52, and more specifically, is a hollow wall having a regular hexagonal shape when viewed from the axial direction. The material of the opening wall 56 is not particularly limited, and examples that can be used include metal materials, wood, resin materials including reinforced plastic materials, and carbon fiber.

[0047] 3 and 8 , the opening wall 56 is provided with a plurality of silencer-side openings 54. Each of the plurality of silencer-side openings 54 is a hole that penetrates the opening wall 56, with one end contacting the ventilation section 52 and the other end contacting the rear space 60. In other words, by providing each silencer-side opening 54, the ventilation section 52 and the rear space 60 communicate with each other. In other words, the rear space 60 is continuous with each silencer-side opening 54.

[0048] The multiple silencer-side openings 54 are provided at equal intervals in the circumferential direction of the opening-equipped wall 56 (hereinafter simply referred to as the circumferential direction), and in the configuration shown in Fig. 8, four silencer-side openings 54 are provided at 90-degree intervals. However, the number of silencer-side openings 54 provided in the opening-equipped wall 56 and the interval (pitch) at which the silencer-side openings 54 are provided in the circumferential direction are not particularly limited and can be determined arbitrarily.

[0049] The shape of each silencer-side opening 54 is not particularly limited, and may be, for example, a polygon, a circle, an ellipse, or an irregular shape. The size of each silencer-side opening 54 is also not particularly limited.

[0050] In the present embodiment, the ratio of the silencer-side openings 54 in the opening-equipped wall 56 (hereinafter referred to as the opening ratio) is 30% or more. The opening ratio is the ratio of the total area of ​​all the silencer-side openings 54 provided in the opening-equipped wall 56 to the sum of the area of ​​the inner circumferential surface 58 of the opening-equipped wall 56 on the ventilation section 52 side (in other words, the side opposite to the rear space 60).

[0051] The aperture ratio may be set to any value as long as it is 30% or more, but it is preferable to set it within a suitable range in the following case. In the following case, the frequency at which the sound pressure of the noise to be silenced (specifically, turbulent noise) reaches its peak is set as f ０ If the silencer 50 has an opening rate of 100%, the silencing peak frequency is f １ The silencing peak frequency of the silencer 50, whose aperture ratio is set to a certain value, is f ｘ Let (f ０ ≧f １ The aperture ratio is preferably 40% or more, and more preferably 60% or more. ０ <f １ (case where f ０ = f ｘ The aperture ratio is D ０ In this case, the aperture ratio is 30% or more, and D ０ The reason why the preferable range of the aperture ratio is as described above is that in a situation where Fano resonance, which will be described later, occurs, ０ <f１ When f is set, there is a risk that the silencing performance of the silencer will be reduced. ０ ≧f １ It should be noted that a decrease in the silencing performance of the silencer means that the sound pressure peak of the noise is amplified in a band (more specifically, a specific frequency band) where the silencing volume due to the resonance is minimized in the silencing spectrum when Fano resonance occurs.

[0052] The plots in Figure 9 show the measured sound silencing volume for mufflers with opening ratios of 20%, 40%, 60%, and 100%. In the test, a muffler measuring 530 mm high, 537 mm wide, and 10 mm thick was placed adjacent to the exhaust port of an air conditioner outdoor unit (Model R22ZES7, manufactured by Daikin Industries, Ltd.), and the outdoor unit fan was operated at 1,000 rpm. The outdoor unit compressor was not operated during the test. The opening shape of the muffler's ventilation section was a regular hexagon, with an opening width of 457 mm. The opening ratio of the muffler was adjusted by changing the perimeter of the wall panel surrounding the ventilation section (the wall corresponding to the opening wall 56). The sound silencing volume was measured using the sound silencing measurement method described below.

[0053] Furthermore, as described above, because one end of each silencer-side opening 54 is in contact with the ventilation section 52, there is a possibility that the air (wind) flowing through the ventilation section 52 may enter the rear space 60 through the silencer-side opening 54. In this case, the amount of air passing through the ventilation section 52, i.e., the amount of air blown by the silencer-equipped fan 10, will be reduced by the amount of wind that enters the rear space 60. For this reason, as shown in FIG. 8 , the silencer 50 may further be provided with a suppression member 64 that suppresses the air (wind) flowing through the ventilation section 52 from entering through the silencer-side opening 54.

[0054] The damping member 64 is a flow resistor that resists wind flow while allowing sound to pass through. It is made of, for example, fabric, more specifically, nonwoven fabric, woven fabric, knitted fabric, etc. Examples of nonwoven fabrics that make up the damping member 64 include polymer fibers (e.g., felt, particularly sound-absorbing felt made of various fibers such as polyester, polypropylene, and polyethylene terephthalate, as well as 3M's Thinsulate®, which is made of polypropylene and polyester), metal fibers (e.g., Unix's Poal, which is made of aluminum, and Tomoegawa Paper's Tommyfirec SS, which is made of stainless steel), and nonwoven fabrics made of paper fibers. Examples of woven fabrics that make up the damping member 64 include broadcloth (plain woven fabric), non-flammable cloth (e.g., Istflon, manufactured by IST Corporation), metal woven fabric, and metal-polymer composite fiber cloth (e.g., conductive cloth, manufactured by Seiren Co., Ltd.). Examples of fibers that can be used for the fabric constituting the suppression member 64 include fibers made of resin materials such as aramid fibers, glass fibers, cellulose fibers, nylon fibers, vinylon fibers, polyester fibers, polyethylene fibers, polypropylene fibers, polyolefin fibers, rayon fibers, low-density polyethylene resin fibers, ethylene vinyl acetate resin fibers, synthetic rubber fibers, copolymer polyamide resin fibers, and copolymer polyester resin fibers; fibers made of metal materials such as stainless steel fibers; fibers of carbon materials; fibers of carbon-containing materials; and fibers of glass materials.

[0055] The material constituting the suppression member 64 may be a material other than cloth, as long as it can suppress the air (wind) flowing through the ventilation section 52 from entering the rear space 60 through the silencer-side opening 54. For example, a finely perforated plate such as a relatively thin expanded metal or punched metal may be used, or a thin porous sheet (film) may be used.

[0056] Furthermore, each of the multiple silencer-side openings 54 is provided in a position close to the fan 12 in the axial direction, specifically, at a position that is a distance of λ / 4 or less from the fan 12. Here, λ is a wavelength corresponding to the resonant frequency of the silencer 50, and the resonant frequency of the silencer 50 is determined depending on the shape, structure, and size (dimensions) of the silencer 50 and the material of each part of the silencer 50.

[0057] As described above, the distance between the fan 12 and the silencer-side opening 54 is the distance between the end of the fan 12 that is located on the silencer 50 side and the end of the silencer-side opening 54 that is located on the fan 12 side. The end of the fan 12 that is located on the silencer 50 side is the point that is located closest to the silencer 50 side (more specifically, on the silencer-side opening 54 side) of the path that the tips of the rotor blades 16 of the fan 12 follow when the fan 12 rotates. In addition, it is preferable that the distance between the fan 12 and the silencer-side opening 54 be as short as possible, taking into account the effective silencing of turbulent noise.

[0058] The rear space 60 is a space formed outside the opening wall 56. The outer peripheral wall 62 is a wall body in the shape of a circular ring or a square frame that separates the rear space 60 on the side opposite the opening wall 56. The material of the outer peripheral wall 62 is not particularly limited, and examples that can be used include metal materials, wood, resin materials including reinforced plastic materials, and carbon fiber.

[0059] The back space 60 forms a resonance structure together with the silencer-side opening 54, and more specifically, forms an air column resonator or a Helmholtz resonator. In other words, the silencer 50 silences turbulent noise generated when the fan 12 rotates by resonance of the resonance structure formed by the silencer-side opening 54 and the back space 60.

[0060] Furthermore, rainwater or the like may enter the rear space 60 through the ventilation portion 52 and the silencer-side opening 54. In consideration of this, it is preferable that a through-hole 68 for draining water is provided at the lower end of the outer peripheral wall 62, as shown in FIG.

[0061] Furthermore, the length of the opening wall 56 and the outer peripheral wall 62 in the axial direction, i.e., the thickness of the silencer 50, is not particularly limited, but from the viewpoint of making the silencer 50 compact and space-saving, it is preferable that it be, for example, 10 cm to 20 cm.

[0062] The conversion mechanism 66 is a mechanism for silencing sound, converting sound energy into thermal energy, and as described above, is constituted by the viscosity of the fluid in the vicinity of the wall surface of the silencer 50, the unevenness (surface roughness) of the wall surface of the silencer 50, or a sound-absorbing material. Below, a case where the conversion mechanism 66 is constituted by a sound-absorbing material will be described.

[0063] Examples of sound-absorbing materials constituting the conversion mechanism 66 include open-cell foam sound-absorbing materials and fiber-based sound-absorbing materials. Examples of foam-based sound-absorbing materials include urethane foam, such as Calmflex (registered trademark) from Inoac Corporation and urethane foam from Hikarisha, soft urethane foam, ceramic particle sintered material, phenolic foam, melamine foam, insulation board, and polyamide foam. Examples of fiber-based sound-absorbing materials include microfiber nonwoven fabrics such as 3M Thinsulate, polyester nonwoven fabrics such as White Quon (registered trademark) from Tokyo Bouon Co., Ltd. and QonPET (registered trademark) from Bridgestone KBG, plastic nonwoven fabrics such as acrylic fiber nonwoven fabrics, natural fiber nonwoven fabrics such as wool and felt, meltblown nonwoven fabrics, metal nonwoven fabrics, glass nonwoven fabrics, floor mats, and carpets. The polyester nonwoven fabrics mentioned above include two-layer products having a high-density, thin nonwoven fabric on the front side and a low-density nonwoven fabric on the back side. Other sound-absorbing materials that can be used include various sound-absorbing materials made of materials containing minute air particles, such as glass wool, rock wool, gypsum board, wood wool cement board, and sound-absorbing materials made of nanofiber fibers, etc. Examples of nanofiber fibers include silica nanofibers and acrylic nanofibers such as XAI manufactured by Mitsubishi Chemical Corporation.

[0064] The conversion mechanism 66 is disposed in at least one of the silencer-side opening 54 and the rear space 60, and in the configuration shown in Fig. 8, it is disposed in the rear space 60. However, without being limited to this, the conversion mechanism 66 may be disposed in the silencer-side opening 54, or may be disposed in both the silencer-side opening 54 and the rear space 60. When the conversion mechanism 66 is disposed in the silencer-side opening 54, it is preferable to dispose the conversion mechanism 66 in the silencer-side opening 54 instead of the suppression member 64 described above, or together with the suppression member 64.

[0065] In this embodiment, the silencer 50 is provided with the conversion mechanism 66, so that it is possible to muffle noise over a wide frequency range even if the silencer 50 (more specifically, the silencer-side opening 54 that forms the resonant structure) is placed close to the fan 12. This point will be described in more detail with reference to FIGS.

[0066] The noise source for noise generated when the fan 12 rotates, primarily turbulent noise, is the fan 12, particularly the tips of the rotor blades 16. In light of this, in order to silence noise over a wide frequency range using a resonance structure such as the silencer 50 of this embodiment, it is conceivable to bring the resonance structure of the silencer, specifically the silencer-side opening 54, closer to the tips of the rotor blades 16 of the fan 12, which are the noise source.

[0067] On the other hand, in a closed space such as a duct, when noise having a broadband spectrum that is the target of sound attenuation is incident on a resonator, part of the incident sound travels toward the resonator, and the rest passes through the resonator as transmitted waves, as shown in Fig. 10. In this case, the spectrum of the incident sound (incident wave) is continuous in the frequency domain (see Fig. 11A), whereas the spectrum of the resonator is discrete in the frequency domain.

[0068] Furthermore, when incident sound reaches the resonator, a portion of the sound is re-radiated from the resonator, and as shown in FIG. 10 , a portion of this re-radiated wave interferes with the transmitted wave. At this time, the phase of the re-radiated wave changes by π (180 degrees) at the boundary of the resonance frequency, as shown in FIG. 11B . Therefore, the interference between the re-radiated wave and the transmitted wave may become asymmetric at the boundary of the resonance frequency. Specifically, as shown in FIG. 11C , on the higher frequency side of the resonance frequency, the re-radiated wave and the transmitted wave weaken each other, whereas on the lower frequency side of the resonance frequency, the re-radiated wave and the transmitted wave strengthen each other. This phenomenon is called Fano resonance. In Fano resonance, as shown in FIG. 11C , the silencing spectrum due to the resonance of the resonator becomes asymmetric. A frequency band where the silencing amount due to resonance is maximized and a frequency band where the silencing amount is minimized exist near the resonance frequency. Here, the frequency band where the silencing amount is maximized refers to the silencing peak in the silencing spectrum. The frequency band where the amount of silencing is minimized means the minimum peak (in other words, the noise deterioration peak) in the silencing spectrum.

[0069] To explain Fano resonance in more detail, it was first proposed by U. Fano in 1961 to explain a phenomenon in the field of atomic physics (specifically, the energy spectrum of electrons in materials such as atoms and molecules). Subsequently, manifestations of Fano resonance have also been reported in optics (plasmons), elasticity, and acoustics.

[0070] In acoustics (acoustic metamaterials), Fano resonance has attracted attention since a paper (Nature Materials, 5, p. 452 (2006)) reported a "Fano-like asymmetric peak." In particular, research has been reported on reflective sound cancellation using Fano resonance as a method of silencing sound in one-dimensional systems, such as sound propagation inside a duct, without blocking the duct cross section. However, this method achieves high ventilation sound cancellation by changing the direction of the sound wave, i.e., by reflection. In other words, this method propagates sound in the opposite direction to the incident direction, so it does not reduce the total energy of the generated sound.

[0071] On the other hand, in systems where sound waves propagate in three dimensions, such as in free space outdoors, changing the direction of the sound often does not solve the noise problem, and a method to reduce the total noise energy in three-dimensional systems is desired. However, Fano resonance in three-dimensional systems is difficult to understand because the interference conditions depend on the direction of propagation and are complex, and there have been few research reports to date.

[0072] The inventors of the present invention discovered a phenomenon in which the total energy of noise changes due to Fano resonance in an open space (i.e., a system in which sound waves propagate in three-dimensional space), and developed a method for reducing the total energy of noise by controlling this phenomenon.

[0073] 12A to 14 obtained in Measurement Tests 1 to 3 below, the inventors have clarified that Fano resonance occurs in an open space depending on the distance between the sound source and the resonator. Specifically, when the wavelength of the incident sound is λ, it has been revealed that Fano resonance occurs when the distance between the sound source and the resonator is λ / 4 or less. On the other hand, when the distance exceeds λ / 4, Fano resonance does not occur, and the silencing spectrum due to resonance becomes symmetrical.

[0074] (Measurement Test 1 and Its Measurement Results) In Measurement Test 1, as shown in FIG. 15 , a speaker Sp was installed as a sound source in a test room whose walls and ceiling were covered with sound-absorbing material, and the distance between the speaker Sp and a resonator K (hereinafter simply referred to as the distance) was changed to 4.5 cm, 9.5 cm, 14.5 cm, 19.5 cm, and 24.5 cm. The resonator K was an air column resonator, which is the simplest resonator. Specifically, a cylindrical resonator with a diameter of 8 cm and a resonant frequency of 540 Hz was used. The sound deadening volume was measured at each distance using the following measurement method. Note that if the wavelength corresponding to the resonant frequency of the resonator K is λ, 15.9 cm corresponds to λ / 4.

[0075] [Method for Measuring the Level of Attenuation] To measure the level of attenuation, a microphone M was installed in a test room to measure the sound pressure level in each of a case where the resonator K was installed and a case (reference) where the resonator K was not installed. The difference in sound pressure between the two cases was then calculated as the level of attenuation. More specifically, as shown in FIG. 15 , one microphone M was installed at 45-degree intervals around the speaker Sp, which is the sound source, at a distance of 1 m or more (specifically, 1.14 m) from the speaker Sp. The average value of the sound pressure levels measured by the eight microphones M was then calculated for each of the two cases, and the difference in the average sound pressure levels was taken as the level of attenuation.

[0076] Measurement Test 1 was performed as described above, and the measurement results shown in Figures 12A to 12E were obtained. As can be seen from these measurement results, when the distance was 4.5 cm, Fano resonance occurred for the sound from speaker Sp and resonator K, and the silencing spectrum of resonator K became an asymmetric spectrum. On the other hand, when the distance exceeded λ / 4 (i.e., when the distance was 24.5 cm), Fano resonance did not occur. Note that Figure 12A shows the measurement result when the distance was 4.5 cm, Figure 12B shows the measurement result when the distance was 9.5 cm, Figure 12C shows the measurement result when the distance was 14.5 cm, Figure 12D shows the measurement result when the distance was 19.5 cm, and Figure 12E shows the measurement result when the distance was 24.5 cm.

[0077] (Measurement Test 2 and Its Measurement Results) In Measurement Test 2, as shown in FIG. 16 , a speaker Sp was installed as a sound source in a test room whose walls and ceiling were covered with sound-absorbing material, and the distance between the speaker Sp and the resonator K was set to approximately 0 cm. Furthermore, microphones M were installed at 45-degree intervals around the speaker Sp, one at a time, at a predetermined distance (specifically, 1.14 m) from the speaker Sp. Each microphone M was positioned at a height of 1 m from the floor. Then, sound pressure levels were measured using each of the eight microphones M for both a case where the resonator K was installed and a case where the resonator K was not installed (reference), and the difference from the sound pressure level in the reference was calculated for each microphone M as the silencing volume. In FIG. 16 , the solid arrows indicate the emitted sound (incident wave) from the speaker Sp, and the dashed arrows indicate the re-radiated wave from the resonator K.

[0078] Measurement Test 2 was performed in the above manner, and the measurement results shown in FIG. 13 were obtained. As can be seen from FIG. 13 , Fano resonance occurred at all of the eight measurement points in the azimuth directions (i.e., the positions of the microphones M), and the sound deadening spectrum of resonator K became an asymmetric spectrum. This is because the phase difference between the sound emitted from speaker Sp and the re-radiated wave from resonator K was the same at each measurement point in the azimuth direction. In other words, at each measurement point, the re-radiated wave had a waveform with its phase inverted across the resonance frequency, and the interference between the sound emitted from speaker Sp and the re-radiated wave was similar at all measurement points. Therefore, even when the sound deadening spectra at the measurement points in the eight azimuth directions are averaged, an asymmetric spectrum results. In this case, sound wave emission is suppressed on the high-frequency side and increased on the low-frequency side across the resonance frequency, and the total amount of sound energy (acoustic energy) in a specific frequency band changes. This is because interference between resonator K and the noise source changes the efficiency of sound energy extraction from the noise source.

[0079] (Measurement Test 3 and Its Measurement Results) In Measurement Test 3, as shown in Fig. 17, the distance between the speaker Sp and the resonator K was set to 15 cm, and the other conditions were the same as those in Measurement Test 2. Here, when the resonant frequency of the resonator K is λ, 15 cm corresponds to λ / 4.2.

[0080] Measurement Test 3 was performed in the above manner, and the measurement results shown in FIG. 14 were obtained. As can be seen from FIG. 14 , the sound deadening spectrum of resonator K changed at the measurement points in the eight azimuth directions (i.e., the positions of each microphone M). Furthermore, there were both measurement points where the sound deadening spectrum was asymmetric and measurement points where the sound deadening spectrum was symmetric. This is because, at each measurement point, the phase difference between the sound emitted from speaker Sp and the re-radiated wave from resonator K changed depending on the azimuth direction of the measurement point. Therefore, even when the sound deadening spectra averaged over the eight measurement points in the eight azimuth directions were averaged, the spectrum was one in which the two waves canceled each other out (canceled out). In this case, there was almost no change in the total amount of sound energy (acoustic energy) in a specific frequency band. This was because the propagation direction of the re-radiated wave from resonator K, which interfered with the sound wave generated by the noise source, changed, and the efficiency of extracting sound energy from the noise source remained unchanged.

[0081] Returning to the explanation of the silencer 50 of this embodiment, the distance between the fan 12 and the silencer-side opening 54 is λ / 4 or less, which is the distance at which the silencing spectrum due to resonance of the silencer 50 becomes asymmetric across the resonance frequency, that is, the distance at which Fano resonance occurs between the sound generated by the rotation of the fan 12 and the silencer 50. Here, the resonance frequency is the resonance frequency of the resonance structure formed by the silencer-side opening 54 and the back space 60, more specifically, the resonance frequency of the air column resonator.

[0082] In the silencing spectrum that becomes asymmetric due to the occurrence of Fano resonance, as shown in Fig. 18 , the silencing volume is improved at the silencing peak frequency, i.e., the resonance frequency due to the resonance structure formed by the silencer-side opening 54 of the silencer 50 and the back space 60. On the other hand, in the above-mentioned asymmetric silencing spectrum, the silencing volume is minimized in the vicinity of the silencing peak frequency and in a frequency band lower than the silencing peak frequency (hereinafter referred to as a specific frequency band), and is significantly reduced compared to when Fano resonance is not occurring. In other words, due to the occurrence of Fano resonance, a silencing volume minimum peak appears in the silencing spectrum in a specific frequency band, as shown in Fig. 18 . Note that Fig. 18 shows the asymmetric silencing spectrum when Fano resonance is occurring with a solid line, and, as comparative data, shows the silencing spectrum when Fano resonance is not occurring with a dashed line. Incidentally, the noise reduction spectrum indicated by the solid line in FIG. 18 is the noise reduction spectrum when the distance between the fan 12 and the silencer-side opening 54 is 4.5 cm (that is, less than λ / 4).

[0083] In this embodiment, taking the above points into consideration, the silencer 50 is provided with a conversion mechanism 66 that converts sound energy in the above-mentioned specific frequency band into thermal energy. Here, converting sound energy in a specific frequency band into thermal energy means effectively converting sound energy in the frequency band of the sound to be silenced, including the specific frequency band, into thermal energy, for example, having a sound absorption peak in the specific frequency band.

[0084] By providing the silencer 50 with the conversion mechanism 66, it is possible to effectively improve the sound absorbing performance of the silencer 50 in an open space. This is because the change in the total amount of sound energy (acoustic energy) due to Fano resonance differs between a closed space such as a duct and an open space such as the present embodiment. To explain in more detail, when Fano resonance occurs in a closed space, changing the phase of the re-radiated wave only changes the ratio of transmitted sound and reflected sound in the incident sound, but does not change the total amount of sound energy.

[0085] In contrast, when Fano resonance occurs in an open space such as the present embodiment, the phase of the re-radiated wave from the silencer 50 is related to the phase of the noise. Here, when the two phases are in phase, the sound (i.e., air vibration) is amplified and the amount of radiation of sound energy increases. Conversely, when the two phases are out of phase, the incident wave and the re-radiated wave cancel each other out, thereby reducing the amount of radiation of sound energy. Thus, in an open space, the total amount of sound energy extracted from the noise source changes depending on the difference between the two phases.

[0086] As described above, when attempting to muffle sound in all directions in an open space where the total amount of sound energy can change due to the occurrence of Fano resonance, simply reflecting the sound to be muffled is not enough; it is necessary to reduce the sound energy. Therefore, in this embodiment, the resonant structure of the silencer 50 reduces sound energy on the high-frequency side above the resonance frequency. Furthermore, low-frequency sounds that are amplified by Fano resonance, i.e., sounds in a specific frequency band, can be efficiently muffled by the action of the conversion mechanism 66.

[0087] Note that the specific frequency band in which the amount of silencing is reduced by Fano resonance can be identified from the asymmetric silencing spectrum obtained when Fano resonance occurs, obtained through experiments or numerical simulations. Furthermore, to realize a conversion mechanism 66 that converts sound energy in a specific frequency band into thermal energy, for example, a sound-absorbing material having a sound absorption peak in a specific frequency band can be selected. Specifically, since the sound absorption peak of a sound-absorbing material can vary depending on the material, shape, structure, size, etc. of the sound-absorbing material, it is advisable to find a sound-absorbing material that can effectively absorb sound (sound components) in a specific frequency band, taking this into consideration.

[0088] As described above, in the silencer-equipped fan 10 according to this embodiment, the silencer 50 includes the conversion mechanism 66, which prevents a decrease in the silencing effect on the low-frequency side (specifically, a specific frequency band) of the resonance frequency. Furthermore, the conversion mechanism 66 also improves the silencing effect on the high-frequency side of the resonance frequency (see FIG. 21 ). As a result, noise generated when the fan 12 rotates can be silenced over a wide frequency band.

[0089] In the above embodiment, the fan 12 is housed in the housing 20, but the present invention is also applicable to a fan with a silencer that does not have a housing 20. That is, when the resonance-type silencer 50 is disposed near a fan that is not housed in a housing 20 having an opening, by providing the conversion mechanism 66 in at least one of the silencer-side opening 54 of the silencer 50 and the back space 60, it is possible to appropriately muffle the frequency band in which the silencing volume is reduced by Fano resonance. As a result, even in a configuration in which the fan is not housed in the housing 20, it is possible to muffle the noise generated when the fan rotates over a wide frequency band.

[0090] The present invention will be explained in more detail below with reference to examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the examples shown below.

[0091] Example 1 In Example 1, an outdoor unit Z equipped with a silencer was placed in the center of a test room, as shown in Fig. 19. The outdoor unit Z was an outdoor unit with model number R22ZES7 manufactured by Daikin Industries, Ltd. During the test, the outdoor unit fan was operated at a rotation speed of 1000 rpm, while the outdoor unit compressor was not operated. The test room had a structure in which at least the walls and ceiling were covered with sound-absorbing material, that is, it was a soundproof room, a semi-anechoic room, or an anechoic room.

[0092] The silencer has substantially the same configuration as the silencer 50 described above, measuring 530 mm high, 537 mm wide, and 10 mm thick, and is disposed adjacent to the exhaust port of the outdoor unit Z. In Example 1, the distance between the silencer (more specifically, the silencer-side opening of the silencer) and the fan of the outdoor unit Z is set to 4.5 cm, a distance at which Fano resonance occurs between the sound generated by the rotation of the fan and the silencer. The aperture ratio of the silencer-side opening of the silencer is set to 60%. A sound-absorbing material with a sound absorption peak in a specific frequency band, i.e., a conversion mechanism that converts sound energy into thermal energy, is disposed in the back space of the silencer.

[0093] Comparative Example 1 In Comparative Example 1, the sound absorbing material (conversion mechanism) was not disposed in the back space of the silencer, and the other conditions were the same as those in Example 1.

[0094] (Regarding Test Results) In Example 1 and Comparative Example 1, the sound pressure level during the test was measured using the same method as the above-described method for measuring the sound deadening volume. Specifically, the average value of the sound pressure levels measured by the eight microphones M was calculated. As a reference, a test was also conducted on the outdoor unit Z alone, without a silencer installed, and the sound pressure level during the test was measured in the same manner as in Example 1 and Comparative Example 1. The measurement results of the sound pressure level in each test are shown in FIG. 20. Furthermore, for Example 1 and Comparative Example 1, the sound deadening spectrum was determined from the above measurement results, and the result is shown in FIG. 21. Furthermore, the difference between the sound deadening spectrum of Example 1 and the sound deadening spectrum of Comparative Example 1 was calculated, and the result is shown in FIG. 22.

[0095] 20 and 21, in Comparative Example 1, due to Fano resonance, the sound pressure is greater than that of the reference in the vicinity of 500 Hz, which is on the lower frequency side of the silencing peak frequency (resonance frequency). That is, in Comparative Example 1, when a specific frequency band is set to 500 Hz, the silencing volume in that band is minimized. In contrast, as can be seen from FIGS. 20 to 22, in Example 1, the effect of the sound-absorbing material (conversion mechanism) provided in the silencer suppresses the sound pressure in a specific frequency band, and it has become clear that the silencing volume in that band is improved compared to Comparative Example 1.

[0096] (Test on Distance Dependence of Noise Reduction Performance) A test on distance dependence of the noise reduction performance of the muffler was conducted for each of Example 1 and Comparative Example 1 described above. Specifically, for each of Example 1 and Comparative Example 1, the distance between the muffler (more specifically, the muffler-side opening of the muffler) and the fan of the outdoor unit Z was changed to 4.5 cm, 9.5 cm, 14.5 cm, 19.5 cm, and 24.5 cm, and the noise reduction volume was measured for each distance. The noise reduction volume was measured using the noise reduction volume measurement method described above. The noise reduction volume measurement results from the test conducted in this manner are shown in FIG. 23. Here, in each of the systems of Example 1 and Comparative Example 1, λ / 4 corresponds to 17.2 cm. Furthermore, for Comparative Example 1, the noise reduction spectra were determined for distances of 4.5 cm, 14.5 cm, and 24.5 cm from the noise reduction volume measured while changing the distance between the muffler and the fan, and the results are shown in FIG. 24.

[0097] As can be seen from Figure 24, in a silencer that does not have a sound-absorbing material as a conversion mechanism, the closer the silencer is to the fan of the outdoor unit Z, the larger the sound-absorbing peak (i.e., the amount of sound absorbing at the resonant frequency), while the decrease in the amount of sound absorbing at a specific frequency that is lower than the peak frequency becomes more pronounced. In contrast, in a silencer that has a sound-absorbing material as a conversion mechanism, as shown in Figure 23, the amount of sound absorbing is greater than that of a silencer that does not have a sound-absorbing material, for all of the distances between the silencer and the fan set in the above test. Furthermore, as is clear from Figure 23, in a silencer that has a sound-absorbing material, the amount of sound absorbing increases as the distance between the silencer and the fan decreases. As described above, the configuration of Example 1 described above falls within the scope of the present invention, and the effects of the present invention are clear from the results of Example 1.

[0098] REFERENCE SIGNS LIST 10 Fan with silencer 12 Fan 14 Central portion 16 Rotor 18 Rotating shaft 20 Housing 22 First wall 24 Second wall 26 Side wall 28 Third wall 30 First air intake hole 32 Second air intake hole 34 Exhaust hole (opening) 36 Machine room 38 Partition wall 40 Heat exchanger 42 Shroud 44 Grill (breathable member) 50 Silencer 52 Ventilation section 54 Silencer-side opening 56 Wall with opening 58 Inner peripheral surface 60 Back space 62 Outer peripheral wall 64 Suppression member 66 Conversion mechanism 68 Through-hole 70 Silencer for fan K Resonator M Microphone Sp Speaker Z Outdoor unit

Claims

1. A fan with a silencer, comprising a fan and a silencer that silences sound generated by rotation of the fan through resonance, wherein the silencer comprises an opening wall having a silencer-side opening, and a back space that is separated by the opening wall and is continuous with the silencer-side opening, the distance between the end of the fan located on the silencer side and the end of the silencer-side opening located on the fan side is the distance at which Fano resonance occurs between the sound generated by rotation of the fan and the silencer, and a conversion mechanism that converts sound energy into thermal energy is provided in at least one of the silencer-side opening and the back space.

2. A fan with a silencer as described in claim 1, wherein when the amount of silencing caused by the resonance of the silencer is minimized in a specific frequency band in the silencing spectrum when the Fano resonance occurs, the conversion mechanism converts sound energy in the specific frequency band into thermal energy.

3. A fan with a silencer as described in claim 1, wherein the ratio of the total area of ​​the silencer-side openings provided in the opening-equipped wall to the sum of the area of ​​the surface of the opening-equipped wall on the side opposite the back space is 30% or more.

4. A fan with a silencer according to claim 1, wherein the fan is housed in a housing having an opening, and the rear space communicates with the opening via the silencer-side opening.

5. A fan with a silencer according to claim 4, wherein the side wall of the housing has a communication hole that connects the inside of the housing with the space outside the housing.

6. A fan with a silencer as described in claim 5, wherein the housing comprises a first wall forming one end of the housing in the axial direction of the rotation axis of the fan, a second wall forming the other end of the housing in the axial direction, a first intake hole formed in the first wall, and an exhaust hole as the opening formed in the second wall, the side wall is arranged between the first wall and the second wall in the axial direction, the communication hole is a second intake hole, and the fan takes in gas from the outer space through the first intake hole and the second intake hole and discharges the gas through the exhaust hole.

7. A fan with a silencer as described in claim 4, wherein the silencer has a ventilation section through which the gas that has passed through the opening flows, and a breathable member that collides with the gas that has passed through the ventilation section is provided at the end of the silencer opposite to the opening in the axial direction of the rotation shaft of the fan.

8. A fan with a silencer as described in claim 7, wherein the silencer is further provided with a suppression member that suppresses gas that has passed through the opening from entering the rear space through the silencer-side opening.

9. A fan with a silencer as described in claim 7 or 8, wherein the shape of the ventilation section when viewed from the axial direction of the rotation shaft of the fan is a polygon with six or more angles, a circle, or an ellipse.

10. A fan with a silencer as described in claim 1, wherein the silencer has an outer peripheral wall that separates the rear space on the side opposite the wall with the opening, and a through hole is provided at the lower end of the outer peripheral wall.

11. The fan with a silencer according to claim 1, wherein the fan is a fan for an outdoor unit of an air conditioning system.

12. A silencer that silences sound generated by the rotation of a fan through resonance, the silencer comprising: an opening wall in which a silencer-side opening is provided; and a back space that is separated by the opening wall and is continuous with the silencer-side opening; the distance between the end of the fan located on the silencer side and the end of the silencer-side opening located on the fan side is the distance at which Fano resonance occurs between the sound generated by the rotation of the fan and the silencer; and a conversion mechanism that converts sound energy into thermal energy is provided in at least one of the silencer-side opening and the back space.

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