JPH06137297A - Fan wing structure - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a fan blade structure capable of effectively preventing the generation of noise caused by the air flow flowing from the blade pressure surface to the suction surface. In an axial flow fan in which the outer peripheral end of a blade 13 is a free end, a rough surface 14 is formed on a positive pressure surface 13a on the outer peripheral side of the blade over a certain range to separate airflow along the centrifugal direction. The radius of the wing 13 is Rtip and the radius of the hub 12 is Rhu
When b is set, the length l of the rough surface forming region extending from the blade tip side toward the center side is set in the range of 0.01 <l / (Rtip-Rhub) <0.3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blade structure for an axial flow fan applied to an air conditioner or the like.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 5, a fan 1 of this type includes a hub 2 having a constant radius from a rotation center O, and a hub 2.
And the blade 3 is continuously provided on the outer peripheral side of the blade 3 is a free end.

In such a fan 1, it is recognized that when the airflow flowing along the centrifugal direction on the pressure surface 3a of the blade 3 during rotation crosses the suction surface 3b, a large noise is generated. ing.

Therefore, conventionally, for example, as shown in FIGS. 6A to 6D, the cross-sectional shape of the outer peripheral side edge of the blade 3 is variously devised so that the blade 3 rotates from the positive pressure surface 3a to the negative pressure surface. The airflow a flowing to the 3b side is suppressed.

FIG. 6 (A) shows the outer peripheral edge of the blade 3 having a smooth cross-sectional shape, and FIG. 6 (B) shows the outer peripheral positive pressure surface 3a of the blade 3 as a curved surface and the negative pressure surface 3b as a flat surface. On the contrary, in the figure (C), the outer peripheral side positive pressure surface 3a of the blade 3 is a flat surface,
The negative pressure surface 3b is a curved surface, and in the same figure (D), the outer peripheral edge of the blade 3 is bent to the positive pressure surface 3a side.

[0006]

However, conventionally, even in the blade structure shown in FIGS. 6A to 6D, since the entire surface of the blade 3 is a smooth surface, the outer peripheral end of the blade 3 is formed. There is a problem that the airflow a flowing from the pressure surface 3a side to the suction surface 3b side at the edge becomes a laminar flow, the boundary layer of the airflow becomes thin, and noise with a large specific frequency (see arrow b) easily occurs. It was

The present invention has been made in view of the above circumstances, and an object thereof is to provide a fan blade structure capable of effectively preventing the generation of noise due to the air flow flowing from the blade pressure surface to the suction surface. To do.

[0008]

In order to achieve the above-mentioned object, the present invention is directed to an axial flow fan whose outer peripheral edge is a free end over a certain range on the positive pressure surface on the outer peripheral side of the blade, in the centrifugal direction. It is characterized in that a rough surface is formed to separate the air flow along the surface.

In the present invention, it is desirable that the blade radius be Rti.
Let p be the hub radius and Rhub be the length l of the rough surface forming region from the blade tip side to the center side,

## EQU2 ## Set within the range of 0.01 <l / (Rtip-Rhub) <0.3.

[0010]

According to the present invention having such a structure, the air flow along the centrifugal direction is separated by the rough surface formed on the pressure surface of the blade, which increases the thickness of the boundary layer and flows toward the suction surface side. Noise of a specific frequency is less likely to be generated in the air flow.

In particular, the radial length of the rough surface forming region of the blade pressure surface is

[Equation 3] When the range of 0.01 <l / (Rtip-Rhub) <0.3 is set, the noise prevention effect is effectively exhibited.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a schematic cross-sectional view showing a propeller fan according to this embodiment, and FIGS. 2A to 2D are views schematically showing various blade cross-sectional shapes and airflow conditions during their operation, FIG. 3 and FIG. 4 is a graph showing the characteristics of this embodiment.

In this embodiment, as shown in FIG.
1 is a hub 12 having a constant radius from the center of rotation O, and this hub 1
2 and the blades 13 arranged in series, and the outer peripheral side of the blades 13 is a free end.

The pressure surface 13a on the outer peripheral side of the blade 13
In addition, a rough surface 14 composed of a large number of minute convex portions is formed over a certain region along the outer peripheral edge. The height of the convex portion of the rough surface 14 is in the range of 0.01t to 0.5t (t is the maximum wall thickness of the blade 13) and 0.01 to 10 mm.

When the radius of the blade 13 is Rtip and the radius of the hub 12 is Rhub, the length l of the rough surface forming region from the tip side of the blade 13 to the center side is:

## EQU4 ## It is set in the range of 0.01 <l / (Rtip-Rhub) <0.3.

Specifically, if the outer peripheral edge of the blade 13 shown in FIG. 6A has a smooth cross-sectional shape, the rough surface 14
Is formed in a certain region of the pressure surface 13a from the outer peripheral edge portion of the blade 13, and the outer pressure surface 1 of the blade 13 shown in FIG.
In the case where 3a is a curved surface and the negative pressure surface 13b is a flat surface, the rough surface 14 is formed in the curved surface portion, and the outer peripheral side positive pressure surface 13a of the blade 13 shown in FIG. 1
In the case where 3b is a curved surface, the rough surface 14 is formed on the flat positive pressure surface 13a of the blade 13, and the outer peripheral edge of the blade 13 shown in FIG. 3D is bent to the positive pressure surface 13a side. In, the rough surface 14 is formed on the bent portion of the blade 13.

According to the structure of this embodiment, the blade 1
3 is rotated, the air flow c along the centrifugal direction is separated by the rough surface 14 formed on the pressure surface 13a, the film thickness of the boundary layer is increased by the turbulent flow d, and when the air flow c crosses the suction surface 13b side, the specific frequency No noise peaks will occur.

According to the result of the experiment, it was confirmed that the noise was reduced by 10 dBA under the same air volume as compared with the case of the conventional structure.

FIG. 3 shows that the sound pressure level of noise is 1 / (Rtip
-Rhub) shows the experimental results for investigating how the value changes. As shown in the figure, from the state where there is no rough surface 14 (l / (Rtip-Rhub) = 0), the rough surface 1
The sound pressure level of the noise gradually decreases as the radial length 1 of 4 increases, and (l / (Rtip-Rhub) = 0.
01) Above, it became almost constant.

When the rough surface 14 is formed by molding, as shown in FIG. 4, the mold cost (cost) is (l / (R
It increases as the value of (tip-Rhub)) is increased, but the most efficient manufacturing method is (l / (Rtip-Rhub).
) = 0.3).

Therefore, (l / (Rtip-Rhub))
The desirable range of the value of

## EQU00005 ## 0.01 <l / (Rtip-Rhub) <0.3.

Although the rough surface 14 is formed also on the outer peripheral side edge of the blade 13 in the above-mentioned embodiment, it is substantially the same as the above when the rough surface 14 is not formed on the outer peripheral side edge portion of the blade 13. The effect of was confirmed. Therefore, the formation of the rough surface 14 may be omitted at the outer peripheral edge of the blade 13.

[0024]

As described above, according to the blade structure of the fan according to the present invention, by forming the rough surface in a certain area of the pressure surface of the blade, the noise caused by the air flow flowing from the blade pressure surface to the suction surface is generated. The excellent effect of effectively preventing the occurrence of

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a fan blade structure according to the present invention.

2A to 2D are enlarged cross-sectional views taken along the line BB of FIG. 1, each illustrating various types of blade structures.

FIG. 3 is a graph showing noise characteristics according to the example.

FIG. 4 is a graph showing cost characteristics according to the example.

FIG. 5 is a schematic view showing a conventional structure.

6A to 6D are enlarged cross-sectional views taken along the line AA of FIG. 5, each illustrating various types of blade structures.

[Explanation of symbols]

 11 Fan 12 Hub 13 Blade 13a Positive Pressure Surface 13b Negative Pressure Surface 14 Rough Surface

Claims (2)

[Claims] 1. An axial flow fan whose outer peripheral edge is a free end, characterized in that a rough surface is formed on a positive pressure surface on the outer peripheral side of the blade over a certain range to separate airflow along the centrifugal direction. And the fan wing structure. 2. When the blade radius is Rtip and the hub radius is Rhub, the length l of the rough surface forming region from the blade tip side toward the center side is expressed by the following formula: 0.0l <l / (Rtip-Rhub ) <0.3 The range of the fan blade according to claim 1, wherein the range is set to <0.3.