JPH09126190A - Centrifugal type blower - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce noise in frequencies of a wide band by providing a plurality of ribs for each of a plurality of vanes over its pressure surface subjected to positive pressure in a place close to its end part in the outer side in the radial direction wherein the ribs are arranged in parallel at prescribed intervals while each one is prescribed in thickness, length and height, and is lengthwise directed in the flow direction. SOLUTION: A plurality of ribs 7 are provided at prescribed intervals in parallel with the length L direction of each vane 4 at its rear peripheral part for a plurality of the vanes 4 provided for an impeller. Each rib 7 may be provided only for the positive pressure side, or in order to effectively suppress noise, each rib may be provided for both the positive and negative pressure sides of each vane 4. Since vortexes as noise sources in a wide range are mainly developed within the velocity boundary layer of each vane 4, the height of each rib it to be basically determined based on the velocity boundary layer, and it is normally equal to or more than 2mm but less than 3mm. In addition, the spanwisw length of each rib 7, that is, each interval between the adjacent ribs 7 in the width H direction of each vane 4 is to be equal to or more than 10mm but less than 20mm, and its length is nearly equal to an interval between the ribs.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a centrifugal blower used for air conditioning equipment and the like, and more particularly to a centrifugal blower designed to reduce broadband frequency noise by improving its blade shape.

[0002]

2. Description of the Related Art A conventional centrifugal blower used for a heat exchanger of an air conditioning equipment has an impeller 1 as shown in FIGS. This impeller 1 includes a circular main plate 2 having a boss 2a in the center and a main plate 2
Between the main plate 2 and the sub-plate 3 so as to stand upright at a right angle to the main plate 2 in the vicinity of the outer periphery of the main plate 2 and the sub-plate 3 provided to face above the main plate 2 and facing each other. And a plurality of blade-shaped blades 4 arranged radially. As the impeller 1 rotates in the direction of arrow A in FIG. 5A, an air flow in the direction of arrow B is generated.

As shown in FIG. 6 (a), the impeller 1 is housed in a spiral case 4 having a bell mouth 5a which constitutes an air suction port, and one end of which is fixed to a boss 2a. When the impeller 1 is rotationally driven by (not shown), the air flowing in from the direction of the arrow C through the filter 6 flows through the impeller 1 in the direction of the arrow D and further flows in the case 5 in the circumferential direction. Is blown out in the direction of arrow C.

In such a conventional centrifugal blower, after air is sucked into the case 5 from the bell mouth 5a, a vortex is generated in a corner portion of the case 5 and the sub plate 3 and the case 5 are separated from each other. In the meantime, a backflow was generated, resulting in a decrease in the efficiency of the blower and an increase in noise.

As a conventional technique aiming at solving the above-mentioned problems of the conventional centrifugal blower, for example, in Japanese Patent Laid-Open No. 5-332293, a sub blade is formed on the sub plate 3. It is disclosed to eliminate the generation of swirl and backflow.

Further, Japanese Patent Laid-Open No. 5-126093 discloses that
By providing three-dimensionally convex portions extending in the width direction of the blade on the surface of the blade on which the wind blows when the impeller of the centrifugal blower rotates, the air discharged along the front and back surfaces of the outer edge of the blade A technique for suppressing noise by preventing merging is disclosed, and Japanese Patent Application Laid-Open No. 5-126351 discloses a heat exchange unit in which air discharged from a centrifugal blower is introduced to a heat exchanger. A technique is disclosed in which a control plate extending toward the centrifugal blower side is attached to the suction side of the linear portion to suppress the generation of vortex flow on the suction side of the heat exchanger to prevent the generation of noise.

In addition, various techniques for reducing noise by improving the shape of a bell mouth have been proposed.

[0008]

As described above, the noise reduction of the centrifugal blower used for the air conditioning equipment is being promoted, but especially for the indoor blower used for the indoor unit of the packaged air conditioner or the like. Broadband frequency noise remains a problem for turbofans, and further noise reduction is an issue.

In view of the above conventional problems, it is an object of the present invention to further improve the noise reduction of a centrifugal blower by reducing wide band frequency noise.

[0010]

The centrifugal blower of the present invention which achieves the above object has blade-shaped blades arranged substantially radially along the direction of the circumference centered on the rotation axis, and is rotated in the centrifugal direction. A centrifugal blower that generates an air flow in
Each of the plurality of blades has a predetermined thickness near the radially outer end only on the pressure surface that receives positive pressure or on both the pressure surface and the suction surface behind the pressure surface, It is characterized in that it has a length and a height, and the length direction includes a plurality of ribs which are arranged at predetermined intervals in parallel with each other in the direction of the air flow, that is, the length direction of the blade.

The plurality of blades are provided with a main plate having a circular outer periphery centered on a boss portion to which the rotational driving force is transmitted, and a circular sub-element disposed so as to face the main plate and having an air intake opening in the center. Near the outer periphery of the plate and between the main plate and the sub plate, they are arranged and fixed in a substantially radial pattern so as to stand up at a right angle to the main plate.

According to the structure of the present invention, by having the plurality of ribs arranged in parallel to each other, the turbulence of the air flow near the trailing edge of the blade, that is, near the outer peripheral end of the blade is rectified,
Since the eddy interference in the span direction of the blade at the blade trailing edge that causes wideband frequency noise is reduced, the wideband frequency noise can be suppressed.

Each of the plurality of ribs has a height of 2 mm or more and 3
mm or less, the thickness is 1 mm or more and 2 mm or less, the distance between adjacent ribs is set to 10 mm or more and 20 mm or less, and each of the plurality of ribs has the same length or more as the distance between the adjacent ribs. Preferably has a length of.

The height of the rib is set to 2 mm or more and 3 mm or less because the vortex which is a broadband sound source is generated in the velocity boundary layer of the blade surface, and the height is about the same as the velocity boundary layer thickness. This is because it is appropriate. The distance between adjacent ribs is 10 mm or more and 20 mm.
The reason is as follows. That is, generally, the equivalent correlation length in the span direction of the vortex correlation is 5 to 10 times the plate thickness in the case of a flat plate, and the maximum value of the blade thickness is approximately 10 mm in the centrifugal blower to which the present invention is applied. Since the thickness of the trailing edge of the blade that radiates the vortex is about 2 mm, 1
This is based on the consideration that an interval of about 0 to 20 mm is optimal.

The thickness of the rib is preferably thinner in view of the performance of the centrifugal blower, but is set to 1 mm or more and 2 mm or less in consideration of strength and ease of manufacturing. As for the rib length, too long length causes a problem that air resistance increases, so shorter length is desirable, but in order to achieve the purpose of reducing broadband noise, the rib length must be at least the span direction. It is desirable that the distance is equal to or larger than the interval.

From the viewpoint of suppressing broadband noise, it is basically desirable to provide ribs on both sides of the pressure surface of the blade and the suction surface on the back side thereof. If the radiation is extremely large, that is, if separation occurs due to an inverse pressure gradient near the trailing edge, it is not necessary to provide it on both the front and back sides of the blade, and installing it only on the pressure side of the blade will result in sufficient broadband noise. Suppressed.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. Since the structure of the impeller 1 and the case 5 of the centrifugal blower to which the present invention is applied are not particularly different from the conventional ones described with reference to FIGS. 5 and 6, detailed description thereof will be omitted. . In one embodiment of the present invention, each of the blades 4 provided in the impeller 1 has a structure as shown in FIGS.
As shown in FIG. 7, a plurality of ribs 7 are provided in parallel at the trailing edge portion in the direction of the length L of the blade 4 at a predetermined interval. Although the number of ribs 7 is four in FIG. 1, the number of ribs 7 may be increased or decreased as necessary.

The rib 7 may be provided only on the positive pressure side indicated by the arrow F in FIG. 2A, or on both the positive pressure side of the blade 7 and the negative pressure side indicated by the arrow E as shown in FIG. 2B. May be provided. In order to reduce the broadband frequency noise more effectively, it is preferable to provide it on both the positive pressure side and the negative pressure side of the blade 7 as shown in FIG. 2 (b), but due to the configuration of the blade 7, near the trailing edge. When separation occurs due to a reverse pressure gradient or the like, the sound radiation from the positive pressure side of the blade 7 may be extremely large. In such a case, as shown in FIG. The object of the present invention can be sufficiently achieved by providing only on the positive pressure surface side.

Next, the preferable shape and arrangement of the rib 7 will be considered. As the shape of the rib 7, a partial circular shape as shown in FIG. 3A or a rectangular parallelepiped shape as shown in FIG. 3B can be used, and the optimum value of the shape dimension will be considered. The dimension parameters for the height h, the thickness t, the length c, and the adjacent ribs 7, 7 are
The interval b between them becomes a problem. These dimensional parameters can be considered to be substantially equivalent in any of the rib shapes shown in FIGS. 3 (a) and 3 (b).

First, the rib height h is considered as follows. The vortex that is a broadband sound source is mainly generated in the velocity boundary layer (the area indicated by reference numeral 8 in FIG. 4) on the surface of the blade 4. The thickness of the velocity boundary layer 8 (dimension δ shown in FIG. 4) is determined by the flow velocity U of the main flow, the viscosity ν of air, and the distance x from the leading edge of the blade 8, and δ = f (U, ν,
It can be represented as x). From the general specifications of the centrifugal blower to which the present invention is applied, U = 10 m / s, x
(= L) = 110 mm, ν = 0.154 × 10 ⁻⁴ m ² /
Therefore, the thickness δ of the velocity boundary layer is about 2.5 mm. From this, it is considered appropriate that the height h of the rib is about 2 to 3 mm.

Next, the optimum value of the span distance b between the ribs, that is, the distance b between adjacent ribs in the width direction (dimension H shown in FIG. 1A) of the blade 4 will be considered. Generally, the equivalent correlation length of the eddy correlation in the span direction is 5 to 1 of the plate thickness in the case of a flat plate.
It is 0 times, and the maximum value of the thickness of the blade 4 is about 10 mm in the centrifugal blower to which the present invention is applied. However, since the thickness of the trailing edge of the blade that radiates the vortex is about 2 mm, the interval b is optimally about 10 to 20 mm.

Next, the thickness t and the length c of the rib 7 will be considered. First, the thickness t is preferably as thin as possible in view of the performance of the centrifugal blower, but considering the strength and the easiness of manufacturing, the thickness t is preferably about 1 to 2 mm. Also, regarding the length c of the rib 7, if the length is too long, the air resistance increases, so it is desirable to be as short as possible from the viewpoint of reducing the air resistance. However, in order to achieve the object of the present invention of reducing broadband noise, it is desirable that the length c be set to be equal to or greater than at least the interval b in the span direction.

The above-described embodiments of the present invention are merely examples for realizing the present invention, and various modifications within the scope equivalent to the configurations described in the claims are also included in the present invention. It goes without saying that it will be done.

[0024]

As described above, according to the present invention, a plurality of ribs each having a predetermined thickness, length and height are arranged parallel to each other in the air flow direction on the surface near the trailing edge of the blade. By arranging them at a predetermined interval, the turbulence of the air flow near the trailing edge of the blade is rectified, and eddy interference in the span direction at the trailing edge of the blade is reduced. As a result, the broadband frequency noise is suppressed and the noise is significantly reduced, so that it is possible to provide a centrifugal blower suitable for an indoor unit of an air conditioning equipment.

[Brief description of the drawings]

1A is a plan view showing a structure of a blade 4 according to an embodiment of the present invention, and FIG. 1B is a perspective view of the blade shown in FIG. 1A.

FIG. 2 (a) shows a rib 7 according to an embodiment of the present invention.
Is a diagram showing a mode in which the blades are provided only on one surface side of the blade 4, that is, only on the pressure surface side, and (b) is a diagram showing an example in which the ribs 7 are provided on both the pressure surface side and the suction surface side of the blade 4.

FIG. 3 is an enlarged perspective view for explaining the definition of dimensional parameters for two types of ribs 7;

FIG. 4 is a diagram for explaining a velocity boundary layer in considering an optimum value of the rib height of the present invention.

5A is a plan view showing an outline of an impeller of a conventional centrifugal blower, and FIG. 5B is a view showing a cross section taken along line VB-VB in FIG. 5A.

FIG. 6A is a partial cross-sectional view of a conventional centrifugal blower,
(B) is a perspective view showing the appearance of a conventional centrifugal blower.

[Explanation of symbols]

 1 Impeller 2 Main plate 2a Boss 3 Sub-plate 3a Air intake opening 4 Wing 5 Case 5a Bell mouth 7 Rib

Claims (3)

[Claims] 1. A centrifugal blower in which blade-shaped blades are arranged in a substantially radial pattern along a circumferential direction around a rotation axis, and an air flow is generated in a centrifugal direction by rotation. Each of the blades has a predetermined thickness and length near the radially outer end only on the pressure surface that receives positive pressure or on both the pressure surface and the suction surface on the back side of the pressure surface. And a plurality of ribs having a height and a length direction facing the direction of the air flow and arranged in parallel with each other at a predetermined interval, and a centrifugal blower. 2. A main plate having a circular outer periphery centering on a boss portion to which a rotational driving force is transmitted, and a circular sub-plate arranged so as to face the main plate and having an air intake opening in the center. An impeller having a plurality of plate-shaped blades that stand up at a right angle to the main plate in the vicinity of the outer periphery of the main plate between the main plate and the sub plate and that are substantially radially arranged, A centrifugal blower having a bell mouth that forms a mouth and a spiral case that houses the impeller, wherein each of the plurality of blades receives a positive pressure in the vicinity of the radially outer end portion. It has a predetermined thickness, length and height only on the pressure surface or on both the pressure surface and the suction surface on the back side of the pressure surface, and the length direction is the length direction of the blade. Facing each other and parallel to each other at a specified interval A plurality of ribs arranged Te provided, centrifugal blower. 3. The height of each of the plurality of ribs is 2 mm.
Has a thickness of 3 mm or less and a thickness of 1 mm or more and 2 mm or less,
The distance between the adjacent ribs is set to 10 mm or more and 20 mm or less, and each of the plurality of ribs has a length equal to or greater than the distance between the adjacent ribs. The centrifugal blower described in 2.