CENTRIFUGAL FAN AND NOISE REDUCTION METHOD IN CENTRIFUGAL FAN
A centrifugal fan having a sound reduction effect for noises in a wide frequency range is provided. The centrifugal fan comprises a motor to which an impeller is connected, a casing which surrounds the impeller and which has a bell-mouth-like suction port, and a bell-mouth-like orifice which has a suction port being concentric with the suction port of the casing and having a diameter as large as that of the suction port of the casing, in an outer shell, providing a plurality of protrusions in a resonant space surrounded by the orifice, the casing, and the outer shell, and providing depressions which are formed so as to be interposed between the protrusions.
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The present invention relates to a centrifugal fan for use in ventilation fan equipment or the like and a centrifugal fan noise reduction method of reducing noises caused by operation of the centrifugal fan.
BACKGROUND ARTConventionally, a centrifugal fan of this type has been known that is used in a centrifugal fan or the like and that has an orifice, separate from a suction casing having a bell-mouth-like suction port, on an opening on one face of an outer shell thereof (see Patent Literature 1, for instance).
Hereinbelow, the conventional centrifugal fan 100 will be described with reference to
As shown in
In such a configuration of the conventional centrifugal fan 100, the rotation of the impeller 103 causes sucked air to pass through the grill 113 and the suction hole 108 of the orifice 109, to enter the impeller 103 via the suction port 106 of the suction casing 107, to undergo a pressure increase through agency of the impeller 103, to pass through inside of the scroll casing 105, and to be discharged through the discharge port 114. In this process, acoustic waves of rotation noises caused with the pressure increase in the impeller 103, turbulent flow noises caused by vortices that are produced by the passage through the scroll casing 105, noises produced in the scroll casing 105, and the like are radiated from the suction port 106, and a portion of the acoustic waves is incident on the resonant space 112 from the inlet 115 having the gap i. In the acoustic waves of the incident noises, acoustic waves of the noises having frequencies specified by a capacity, a shape and the like of the resonant space 112 undergo air column resonance in the resonant space 112, reduction in acoustic wave level, and resonance silencing.
Patent Literature 1: JP 3279834 B
DISCLOSURE OF INVENTION Problems to be Solved by the InventionSuch a conventional centrifugal fan is capable of reducing noises having comparatively low frequencies not higher than about 1 kHz by the resonance silencing effect, whereas such a fan is poor in effect of reducing noises having comparatively high frequencies not lower than about 1 kHz, such as noises caused by turbulent flow. Accordingly, there is an issue in that a quantity of reduction of noises is decreased on condition that noises having high frequencies are dominant therein, e.g., on condition that a large quantity of blow is attained by the centrifugal fan. In centrifugal fans, therefore, it is demanded to increase an effect of reducing noises in a high frequency band and to reduce noises in a wide frequency range from low frequency to high frequency.
The invention resolves such conventional issues, and an object of the invention is increase the effect of reducing noises in the high frequency band in a centrifugal fan and to provide a centrifugal fan that is capable of reducing noises in a wide frequency range from low frequency to high frequency.
Means to Solving the IssueIn order to achieve the object, the invention is configured as follows.
According to a first aspect of the present invention, there is provided a centrifugal fan comprising:
an outer shell having an opening portion,
an impeller that is supported rotatably in the outer shell,
a motor for driving and rotating the impeller,
a casing that has a first suction port and that is placed in the outer shell so as to surround the impeller, and
a bell-mouth-like orifice that is placed on the opening portion of the outer shell so as to have a gap between the orifice and the first suction port of the casing and that has a second suction port providing communication between the opening portion of the outer shell and the first suction port of the casing, wherein
a resonant space that communicates with the first suction port through the gap between the first suction port and the second suction port and that effects resonance silencing against noises emitted from the first suction port is defined by the orifice, the casing and the outer shell that serve as definition walls, and wherein a plurality of protruding portions are formed on the definition walls for the resonant space.
According to a second aspect of the present invention, there is provided a centrifugal fan as defined in the first aspect, wherein
the plurality of protruding portions comprise sloped surfaces sloping relative to a surface of the definition walls for the resonant space in positions where the protruding portions are formed, and wherein
the sloped surface of one protruding portion and the sloped surface of another protruding portion adjacent to the one protruding portion are connected to each other so that a recessed part is formed by the sloped surfaces between both the protruding portions.
According to a third aspect of the present invention, there is provided a centrifugal fan as defined in the second aspect, wherein connected parts of the sloped surfaces in each recessed part form an acute angle.
According to a fourth aspect of the present invention, there is provided a centrifugal fan as defined in the second aspect, wherein the protruding portions each have a flat surface on a top part thereof.
According to a fifth aspect of the present invention, there is provided a centrifugal fan as defined in the second aspect, wherein the protruding portions each have a shape such that a depth thereof is longer than a height and a width thereof.
According to a sixth aspect of the present invention, there is provided a centrifugal fan as defined in the fifth aspect, wherein a plurality of protruding portion groups in each of which a plurality of protruding portions are arranged with depthwise directions thereof being parallel to one another are arranged so that depthwise directions of adjacent protruding portion groups intersect with each other.
According to a seventh aspect of the present invention, there is provided a centrifugal fan as defined in claim 5, wherein a plurality of protruding portion groups in each of which a plurality of protruding portions are arranged with depthwise directions thereof being parallel to one another are arranged so as to have different depthwise directions.
According to an eighth aspect of the present invention, there is provided a centrifugal fan as defined in the fifth aspect, wherein the plurality of recessed parts formed between the plurality of protruding portions are formed so as to extend along the surfaces of the definition walls and are arranged so that directions in which the recessed parts extend are different from at least one of radial directions, a circumferential direction and an axial direction of the impeller.
According to a ninth aspect of the present invention, there is provided a centrifugal fan as defined in any one of the first through eighth aspects, wherein the plurality of protruding portions have the same shape and wherein the plurality of recessed parts formed between the plurality of protruding portions have the same shape.
According to a tenth aspect of the present invention, there is provided a centrifugal fan as defined in any one of the first through eighth aspects, wherein the protruding portions have a plurality of different shapes and wherein the recessed parts formed between the plurality of protruding portions have a plurality of different shapes.
According to an eleventh aspect of the present invention, there is provided a centrifugal fan as defined in any one of the first through eighth aspects, wherein the plurality of protruding portions are provided on the orifice in the resonant space.
According to a twelfth aspect of the present invention, there is provided a centrifugal fan as defined in any one of the first through eighth aspects, wherein the plurality of protruding portions are formed integrally with the definition walls of the orifice, the casing and the outer shell.
According to a 13th aspect of the present invention, there is provided a centrifugal fan as defined in any one of the first through eighth aspects, wherein the protruding portions are detachably provided on the definition walls.
According to a 14th aspect of the present invention, there is provided a centrifugal fan as defined in the 13th, wherein the protruding portions are formed of sound absorbing material.
According to a 15th aspect of the present invention, there is provided a centrifugal fan as defined in any one of the first through eighth aspects, wherein the protruding portions are formed so as to have cavities inside and wherein holes that provide communication between the cavities and the resonant space are formed on the protruding portions.
According to a 16th aspect of the present invention, there is provided a noise reduction method in a centrifugal fan comprising an outer shell having an opening portion, an impeller that is supported rotatably in the outer shell, a casing that has a first suction port and that is placed in the outer shell so as to surround the impeller, and a bell-mouth-like orifice that is placed on the opening portion of the outer shell so as to have a gap between the orifice and the first suction port of the casing and that has a second suction port providing communication between the opening portion of the outer shell and the first suction port of the casing, the method comprising:
making acoustic waves of noises occurring in the casing with rotational drive of the impeller incident, through the gap between the first suction port and the second suction port, on a resonant space that communicates with the first suction port through the gap between the first suction port and the second suction port and that is defined by the orifice, the casing and the outer shell that serve as definition walls, and
reducing acoustic wave levels of the noises incident on the resonant space by air column resonance, and reducing acoustic wave levels of the noises by diffused reflection of the acoustic waves of the noises in the resonant space.
EFFECT OF THE INVENTIONThe centrifugal fan of the invention employs the configuration including the resonant space communicating with the first suction port of the casing and the plurality of protruding portions in the resonant space. With the employment of such a configuration, acoustic wave levels of acoustic waves of noises incident on the resonant space can be reduced by the air column resonance and can be reduced by occurrence of the diffused reflection caused by the plurality of protruding portions. Therefore, the two functions of the air column resonance and the diffused reflection increase the sound reduction effect in the high frequency band for noises caused by operation of the centrifugal fan and ensure reduction of noises in a wide frequency range from low frequency to high frequency.
According to the noise reduction method for the centrifugal fan in accordance with the invention, noises caused by operation of the centrifugal fan are made incident on the resonant space communicating with the first suction port of the casing of the centrifugal fan, and acoustic wave levels of the noises incident on the resonant space can be reduced by the air column resonance. In addition, the acoustic wave levels can be reduced by the diffused reflection of the acoustic waves of the noises in the resonant space. Therefore, the two functions of the air column resonance and the diffused reflection increase the sound reduction effect in the high frequency band for the noises caused by the operation of the centrifugal fan and ensure reduction of noises in a wide frequency range from low frequency to high frequency.
These aspects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which:
Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings.
Hereinbelow, embodiments of the invention will be described in detail with reference to the drawings.
First EmbodimentOn the opening 2 of the outer shell 3 is provided an orifice 18 having a bell-mouth-like suction port 17 (second suction port) concentric with the suction port 7 of the casing 10. That is, the opening 2 of the outer shell 3 communicates with the suction port 7 of the casing 10 through the suction port 17 of the orifice 18. As shown in
On an outer circumference of the orifice 18 is formed a resonant space 19 surrounded and defined by the orifice 18, the casing 10 and the outer shell 3, which serve as definition walls. The resonant space 19 communicates with the suction port 7 of the casing 10 through the gap part 21 between the orifice 18 and the casing 10.
A plurality of protrusions (protruding portions) 22 are formed on the definition walls in the resonant space 19, and depressions (recessed parts) 23 are formed between adjacent protrusions 22.
Hereinbelow will be described a function of reducing noises caused by the rotational drive of the impeller 5 through agency of the resonant space 19 and the plurality of protrusions 22 provided in the resonant space 19 in the centrifugal fan 1 having such a configuration. In the centrifugal fan 1, the rotation of the impeller 5 effected by the motor 6 causes sucked air to pass through the main body opening 2 and the suction port 17 of the orifice 18, to enter the impeller 5 via the suction port 7 of the casing 10, to undergo a pressure increase through agency of the impeller 5, to pass through inside of the casing 10, and to be discharged through the discharge adapter 12 into the duct 16 and then to outdoors.
In this process, acoustic waves of rotation noises caused with the pressure increase in the impeller 5, turbulent flow noises caused by vortices that are produced by the passage through the casing 10, noises amplified by resonance in the casing 10, and the like are radiated downward from the suction port 7. A portion of the acoustic waves of the noises radiated from the suction port of the casing 10 is incident on the resonant space 19 through the gap part 21 formed between the end 20 of the orifice 18 and the casing 10. A portion of the incident acoustic waves is made into of antiphase acoustic waves and is returned to the gap part 21 by fixed end reflection on wall surfaces (definition wall surfaces) in the resonant space 19. Thus there occurs such resonance silencing resulting from air column resonance as cancels out a portion of the acoustic waves radiated from the suction port 7, so that acoustic wave levels of the noises can be reduced. A frequency of the acoustic waves that are cancelled out is determined by a distance of a path of the acoustic waves from the gap part 21 to a position where the reflection occurs. The existence of a large number of protrusions 22 in the resonant space 19 facilitates reflection on the large number of protrusions 22 of the acoustic waves incident on the resonant space 19, and a variety of distances between the gap part 21 and the protrusions 22 make it possible to reduce noises having various frequencies.
A portion of the acoustic waves having collided with the protrusions 22 may travel toward adjacent protrusions 22 after the reflection, depending on angles of incidence thereof, and may gradually be reduced in energy in the depressions 23 by diffused reflection with subsequent repetition of reflection, so that the noises can be reduced.
Adjacent protrusions 22 are continuously arranged so that each depression 23 has the section generally in shape of the letter V, and the depressions 23 are provided so as to have a small width. Thus the acoustic waves incident on the depressions 23 are reflected a larger number of times, and the resultant diffused reflection strengthens the sound reduction effect, thereby reducing the noises. The protrusion height ho and the width b of the depression openings preferably have a relation ho b, for instance.
Each protrusion 22 has the trapezoidal shape in the section perpendicular to the direction of the depth of the protrusion 22, so that the depressions 23 formed by the protrusions 22 gradually narrow with respect to the downward direction. Therefore, acoustic waves incident on the depressions 23 undergo diffused reflection. The lower the acoustic waves travel in the depressions 23, the shorter time intervals of occurrence of the reflection become. This results in an increase in the number of times of the reflection, strengthened action of the sound reduction effect, and reduction of the noises. In the trapezoidal section of each protrusion 22, the protrusion height ho and the width c of the sloped surfaces 32 preferably have a relation ho≧c, for instance.
With use of protrusions 22 having triangular sections, similar effects can be expected. With use of the protrusions 22 having the trapezoidal sections, however, capacities of the depressions 23 can be adjusted by adjustment in a width a of the top flat surfaces 31 of the protrusions 22 while the angle of the sloped surfaces 32 is kept at an optimum angle. Achievement of the resonance silencing based on air column resonance requires optimum setting of a capacity of the resonant space 19, and the optimization of the capacity requires the adjustment in the capacities of the depressions 23. Accordingly, the protrusions 22 having the trapezoidal sections facilitate the adjustment for the optimization of the capacity of the resonant space 19. The sloped surfaces of the protrusions forming the depressions 23 are not limited to flat surfaces, and similar effects can be expected with use of the sloped surfaces formed of curved surfaces.
The depression angle α of the depressions 23 that is set as an acute angle facilitates diffused reflection of acoustic waves having shallow angles of incidence on the depressions 23 and obtainment of the sound reduction effect, resulting in effective reduction of noises.
The protrusions 22 have the shape such that the depth thereof is longer than the height and width thereof, and thus the depressions 23 formed by the protrusions 22 are shaped like slits. Thus diffused reflection can be effected even for acoustic waves having shallow (small) angles of incidence with respect to the direction (i.e., the Y-direction (see
On condition that the shapes of the protrusions 22 are identical and that the shapes of the depressions 23 formed by the protrusions 22 are identical, the sound reduction effect strongly acts on a specified frequency and the relevant noises can be reduced because frequencies of the acoustic waves that undergo sound reduction caused by diffused reflection on the depressions 23 depend on the shapes of the depressions 23.
The acoustic waves that come into the resonant space 19 through the gap part 21 tend to be diffracted toward the orifice 18 in the resonant space 19 by the end 20 of the orifice 18 (see
As shown in
With the employment of the configuration in which the plurality of protrusion groups 30 each composed of the set of three protrusions 22 are arranged alternately lengthwise and breadthwise, at maximum four slit-like depressions 23 arranged in parallel can be formed in one protrusion group 30. There is a characteristic in that an incidence of the diffused reflection on the depressions 23 is the higher for acoustic waves in a direction the closer to a direction perpendicular to a longitudinal direction of the slit-like depressions 23, and provision of, e.g., four or more protrusions 22 as one set strengthens the characteristic. Though the incidence of the diffused reflection is comparatively low for acoustic waves nearly parallel to the longitudinal direction of the slit-like depressions 23, the alternately lengthwise and breadthwise arrangement on the orifice 18 of the protrusion groups 30 each forming the set of four protrusions 22 can compensate for the low incidence with regard to the adjoining sets. Therefore, the diffused reflection on the depressions 23 can effectively be brought about so that the sound reduction effect can be obtained.
As shown in
Though the configuration of the centrifugal fan 1 of
The first embodiment provides the centrifugal fan that is capable of increasing the effect of reducing sound in a high frequency band and reducing noises in a wide frequency range from low frequency to high frequency, by use in combination of the sound reduction effect resulting from air column resonance and the sound reduction effect resulting from diffused reflection.
Second EmbodimentHereinbelow will be described a centrifugal fan in accordance with a second embodiment of the invention. In the following description, the same component members as those of the first embodiment are designated by the same reference numerals, and description thereof is omitted.
In
On condition that acoustic waves of noises that have come in through the gap part 21 travel in various directions through agency of diffraction, reflection and/or the like inside the resonant space 19, employment of the arrangement configuration of the protrusions 22 and the depressions 23 of the second embodiment ensures a sound reduction effect and noise reduction for the acoustic waves in the various directions because the depressions 23 are placed so that the longitudinal directions of the slit-like shapes thereof extend in various directions.
The configuration in which the protrusions 22 have the plurality of shapes and in which the depressions formed by the protrusions 22 have the plurality of shapes is employed because frequencies of the acoustic waves that undergo sound reduction caused by diffused reflection on the depressions 23 depend on the shapes of the depressions 23. Such a configuration ensures the sound reduction effect for various frequencies and noise reduction in a wider frequency range in comparison with the configuration of the first embodiment. As long as the longitudinal directions of the protrusions 22 and the depressions 23 are arranged so as to differ from at least any one of the radial directions, a circumferential direction and an axial direction of the impeller 5, the sound reduction effect can be obtained for the acoustic waves in various directions.
The second embodiment provides the centrifugal fan that is capable of increasing the effect of reducing sound in a high frequency band and reducing noises in a wide frequency range from low frequency to high frequency, by use in combination of the sound reduction effect resulting from air column resonance and the sound reduction effect resulting from diffused reflection.
Third EmbodimentHereinbelow will be described a centrifugal fan in accordance with a third embodiment of the invention. In the following description, the same component members as those of the first embodiment are designated by the same reference numerals, and description thereof is omitted.
As shown in
The employment of such a configuration makes it possible to provide arrangement configuration of the units 24 in various manners and to produce various arrangements of the depressions 23 with use of the units 24 having one type of shape. With use of the detachable units 24, frequencies for which sound reduction can be attained can be adjusted by alteration in the arrangement of the depressions 23.
Use of the units 24 made of sound absorbing material such as glass wool furthers gradual decrease in energy caused by diffused reflection on the depressions 23 and thus results in increased action of the sound reduction effect and attainment of noise reduction.
The third embodiment provides the centrifugal fan that is capable of increasing the effect of reducing sound in a high frequency band and reducing noises in a wide frequency range from low frequency to high frequency, by use in combination of the sound reduction effect resulting from air column resonance and the sound reduction effect resulting from diffused reflection, and that allows the adjustment in frequencies of noises that can be reduced.
Fourth EmbodimentHereinbelow will be described a centrifugal fan in accordance with a fourth embodiment of the invention. In the following description, the same component members as those of the first embodiment are designated by the same reference numerals, and description thereof is omitted.
As shown in
In such a configuration of the fourth embodiment, the cavities 25 are formed inside and the holes 27 are formed therein, in addition to the depressions 23 that effect sound reduction. Thus addition of resonance silencing effected by the Helmholtz resonance structure ensures a further sound reduction effect and noise reduction.
Therefore, the fourth embodiment provides the centrifugal fan that is capable of increasing the effect of reducing sound in a high frequency band and reducing noises in a wide frequency range from low frequency to high frequency.
It is to be noted that, by properly combining the arbitrary embodiments of the aforementioned various embodiments, the effects possessed by them can be produced.
The invention provides the centrifugal fans that are capable of increasing the sound reduction effect in a high frequency band and reducing noises in a wide frequency range from low frequency to high frequency, and thus can be applied to air conditioning equipment, ventilation fan equipment and the like.
Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.
The disclosure of specifications, drawings, and claims of Japan Patent Application No. 2008-111032 filed on Apr. 22, 2008 is incorporated herein by reference in its entirety.
Claims
1. A centrifugal fan comprising:
- an outer shell having an opening portion,
- an impeller that is supported rotatably in the outer shell,
- a motor for driving and rotating the impeller,
- a casing that has a first suction port and that is placed in the outer shell so as to surround the impeller, and
- a bell-mouth-like orifice that is placed on the opening portion of the outer shell so as to have a gap between the orifice and the first suction port of the casing and that has a second suction port providing communication between the opening portion of the outer shell and the first suction port of the casing, wherein
- a resonant space that communicates with the first suction port through the gap between the first suction port and the second suction port and that effects resonance silencing against noises emitted from the first suction port is defined by the orifice, the casing and the outer shell that serve as definition walls, and wherein a plurality of protruding portions are formed on the definition walls for the resonant space.
2. The centrifugal fan as defined in claim 1, wherein
- the plurality of protruding portions comprise sloped surfaces sloping relative to a surface of the definition walls for the resonant space in positions where the protruding portions are formed, and wherein
- the sloped surface of one protruding portion and the sloped surface of another protruding portion adjacent to the one protruding portion are connected to each other so that a recessed part is formed by the sloped surfaces between both the protruding portions.
3. The centrifugal fan as defined in claim 2, wherein connected parts of the sloped surfaces in each recessed part form an acute angle.
4. The centrifugal fan as defined in claim 2, wherein the protruding portions each have a flat surface on a top part thereof.
5. The centrifugal fan as defined in claim 2, wherein the protruding portions each have a shape such that a depth thereof is longer than a height and a width thereof.
6. The centrifugal fan as defined in claim 5, wherein a plurality of protruding portion groups in each of which a plurality of protruding portions are arranged with depthwise directions thereof being parallel to one another are arranged so that depthwise directions of adjacent protruding portion groups intersect with each other.
7. The centrifugal fan as defined in claim 5, wherein a plurality of protruding portion groups in each of which a plurality of protruding portions are arranged with depthwise directions thereof being parallel to one another are arranged so as to have different depthwise directions.
8. The centrifugal fan as defined in claim 5, wherein the plurality of recessed parts formed between the plurality of protruding portions are formed so as to extend along the surfaces of the definition walls and are arranged so that directions in which the recessed parts extend are different from at least one of radial directions, a circumferential direction and an axial direction of the impeller.
9. The centrifugal fan as defined in claim 1, wherein the plurality of protruding portions have the same shape and wherein the plurality of recessed parts formed between the plurality of protruding portions have the same shape.
10. The centrifugal fan as defined in claim 1, wherein the protruding portions have a plurality of different shapes and wherein the recessed parts formed between the plurality of protruding portions have a plurality of different shapes.
11. The centrifugal fan as defined in claim 1, wherein the plurality of protruding portions are provided on the orifice in the resonant space.
12. The centrifugal fan as defined in claim 1, wherein the plurality of protruding portions are formed integrally with the definition walls of the orifice, the casing and the outer shell.
13. The centrifugal fan as defined in claim 1, wherein the protruding portions are detachably provided on the definition walls.
14. The centrifugal fan as defined in claim 13, wherein the protruding portions are formed of sound absorbing material.
15. The centrifugal fan as defined in claim 1, wherein the protruding portions are formed so as to have cavities inside and wherein holes that provide communication between the cavities and the resonant space are formed on the protruding portions.
16. A noise reduction method in a centrifugal fan comprising an outer shell having an opening portion, an impeller that is supported rotatably in the outer shell, a casing that has a first suction port and that is placed in the outer shell so as to surround the impeller, and a bell-mouth-like orifice that is placed on the opening portion of the outer shell so as to have a gap between the orifice and the first suction port of the casing and that has a second suction port providing communication between the opening portion of the outer shell and the first suction port of the casing, the method comprising:
- making acoustic waves of noises occurring in the casing with rotational drive of the impeller incident, through the gap between the first suction port and the second suction port, on a resonant space that communicates with the first suction port through the gap between the first suction port and the second suction port and that is defined by the orifice, the casing and the outer shell that serve as definition walls, and
- reducing acoustic wave levels of the noises incident on the resonant space by air column resonance, and reducing acoustic wave levels of the noises by diffused reflection of the acoustic waves of the noises in the resonant space.
Type: Application
Filed: Apr 21, 2009
Publication Date: Jan 6, 2011
Applicants: PANASONIC ECOLOGY SYSTEMS GUANGDONG CO., LTD. (Foshan, Guangdong), PANASONIC CORPORATION (Osaka)
Inventors: Dongbin Ma (Foshan), Masamitsu Morioka (Aichi), Seiji Shirahama (Aichi)
Application Number: 12/920,163
International Classification: F04D 29/66 (20060101); F04D 29/44 (20060101);