JPH0783198A - Axial fan - Google Patents

Abstract

PURPOSE:To reduce a turbulent vortex due to an effect of a flange so as to reduce noise by cutting the outer peripheral shape of a fan blade by a line connecting a predetermined point at the end in the rotating direction of the blade to another predetermined point inside a radius at the end. CONSTITUTION:A motor 4 is supported at the center of an air duct by a plurality of support legs 2 disposed at the end on an air discharge side of a hollow and cylindrical venturi case 1. A plurality of fan blades 3 planted in a rotor hub of the motor 4 is housed in the air duct. The tip of the fan blade 3 is cut on a straight or arcuate line connecting a point A apart by a length W' of 20-30% of an arcuate length W from the tip in the rotating direction to a point B of 90-95% of a radius at the front edge in the rotating direction, thus obtaining a shape 9. Since a clearance between the inner circumferential surface of the air duct 1 and the tip 13 in the rotating direction of the fan blade 3 is enlarged in a tapered manner, it is possible to restrain a turbulent vortex generated by an air flow toward the air duct 1 so as to reduce noise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an axial flow fan, and more particularly to a small axial flow fan suitable for internal cooling of electronic devices and the like.

[0002]

2. Description of the Related Art FIG. 5 is a front view seen from the suction side of an axial fan that has been conventionally used, and FIG.
FIG. 7 is a sectional view taken along line -X ', and FIG. 7 is a sectional view taken along line YY' in FIG. In FIGS. 5, 6 and 7, the motor 4 is supported at the center of the wind tunnel by the plurality of support legs 2 provided on the end face of the hollow cylindrical venturi case 1 on the air discharge side, and the plurality of rotor legs of the motor 4 support the motor 4. One fan blade 3
Is planted in the wind tunnel. On the air intake side 7 and the discharge side 8 of the wind tunnel, respectively, square mounting flanges 5a,
5b is provided, and mounting holes 6 are provided at the corners of the flange.

In the axial fan shown in FIGS. 5, 6 and 7, when the motor 4 is driven, the fan blade 3 rotates and air flows from the suction side 7 to the discharge side 8 of the wind tunnel as indicated by arrow F. A flow occurs. The axial fan shown in the drawing can be attached to either side of the mounting flanges 5a or 5b in the housing of the electronic device, so that it is possible to select two functions for discharging or sucking air in the housing to the outside. ing.

[0004]

In the axial fan according to the above-mentioned prior art, the flow of the air flowing into the wind tunnel 1 is uniform in the circumferential direction due to the influence of the mounting flange 5a provided on the suction side 7. Notably, especially at the four corners where the mounting flanges 5a are provided, so-called turbulent flow is generated between the inner peripheral surface of the wind tunnel 1 and the outer peripheral side of the fan blade due to uneven flow due to difference in flow velocity, difference in flow direction, and the like. Vortex 12 is generated,
Due to this turbulent vortex, harmonics with high sound pressure level are generated,
It was increasing noise. That is, comparing the cross section (shown in FIG. 6) taken along line XX ′ of FIG. 5 and the cross section (shown in FIG. 7) taken along line YY ′ of FIG. )
And 11 '(Fig. 7) cause turbulent vortices to be generated, which are affected by the turbulent vortices at four corners four times during one rotation of the fan blade 3. ,
There has been a problem that a harmonic having a high sound pressure level is generated at a frequency (fourth rotational frequency: f0 × 4) that is four times the rotational sound frequency (f0) of the fan blade alone, which increases noise. As a countermeasure against this, in the prior art, the roundness of the tip end 13 in the rotational direction of the outer periphery of the fan blade was implemented to be large, but this shape has a limit and a sufficient effect cannot be obtained.

[0005]

In the present invention, the shape of the outer periphery of the fan blade is set to have an arc length of 2 from the tip in the rotational direction.
By cutting it along a straight or chordal line between 0 to 30% on the outer circumference and 90 to 95% of the outer circumference radius at the front edge of the fan blade in the direction of rotation. Solve.

[0006]

[Operation] By changing the shape of the tip of the fan blade as described above, it is possible to reduce turbulent vortices due to the influence of the flange, reduce harmonics with a high sound pressure level, and reduce noise.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of an axial fan according to the present invention will be described with reference to the drawings. 1 is a front view seen from the suction side of an axial fan according to the present invention, FIG. 2 is a partially enlarged view of a fan blade 3 of FIG. 1, and FIG. 3 is a sectional view taken along line XX 'of FIG. FIG. 4 is a cross-sectional view taken along the line YY ′ of FIG. 3, and the point different from the prior art shown in FIGS. 5, 6 and 7 is the tip shape 9 of the fan blade 3. However, there is no difference from the conventional technology. As shown in FIG. 2, the tip shape 9 of the fan blade 3 has a point A of W'which corresponds to 20 to 30% of the arc length W from the tip in the rotational direction and a point of 90 to 95% of the radius at the front edge in the rotational direction. It is cut into a shape that connects with B with a straight line or a chordal line.

In this embodiment, as shown in FIGS. 3 and 4, the gap between the inner peripheral surface of the wind tunnel 1 and the tip end portion 13 of the fan blade 3 in the rotational direction widens in a tapered manner.
The turbulent vortex 12 caused by the difference between the air flows 11 and 11 'to the wind tunnel 1 can be suppressed, which has an effect of reducing noise. FIG. 8 is a test result showing the frequency analysis data of the rotating sound of the axial flow fan according to the present invention and the prior art. The horizontal axis shows the rotating sound frequency (Hz) and the vertical axis shows the sound pressure level (db). . The experimental conditions in FIG. 8 are that the number of fan blades is 5, the number of revolutions is 3180 (rpm), (53rps),
Is. Therefore, the frequency (f0) of the independent rotating sound of the fan blade is 3180 × 5/60 = 265 (Hz). Also, due to the interference of the fan blades, the wind tunnel, and the mounting flange, secondary and tertiary for each multiple of 265 (Hz).
Next, 4th, 5th, ... In FIG. 8, (a) shows the data of the axial flow fan according to the present invention,
(B) shows data of axial fan according to the prior art, respectively, and the peak value of the fourth-order rotational sound frequency (f0 × 4) due to turbulent vortices is 4 to 5 (db) lower in the present invention. And
The overall value had a noise reduction effect of 2 to 3 (db).

[0009]

Since the axial flow fan according to the present invention has the above-mentioned structure, it has an effect of realizing low noise by effectively reducing the level of the fourth harmonic of the rotation sound of the fan blade.

[Brief description of drawings]

FIG. 1 is a front view showing a structure of an axial fan according to the present invention as seen from a suction side.

FIG. 2 is a partially enlarged view of a fan blade of an axial fan according to the present invention.

FIG. 3 is a cross-sectional view taken along line X-X ′ of FIG.

FIG. 4 is a cross-sectional view taken along the line Y-Y ′ of FIG.

FIG. 5 is a front view showing the structure of an axial flow fan according to a conventional technique as seen from the suction side.

6 is a cross-sectional view taken along line X-X 'of FIG.

7 is a cross-sectional view taken along the line Y-Y 'of FIG.

FIG. 8 is frequency analysis data of rotating sounds of the axial fan according to the present invention and the prior art.

[Explanation of symbols]

 1 Cylindrical Wind Tunnel 2 Support Leg 3 Fan Blade 4 Motor 5a, 5b Mounting Flange 6 Mounting Hole 7 Air Suction Side 8 Air Outlet Side 9 Fan Blade Outer Perimeter 10 Rotation Direction 11 Air Flow 12 Turbulent Vortex 13 Rotation Direction Tip

Claims (1)

[Claims] 1. A venturi case in which both ends of a hollow wind tunnel having a cylindrical cross section are provided with mounting flanges, respectively.
A drive motor supported in the wind tunnel by a plurality of support legs provided on the end face of the venturi case on the air discharge side, and a plurality of fan blades are planted on the outer circumference of the rotor hub of the drive motor. In an axial flow fan in which a fan blade is arranged concentrically with the wind tunnel, the outer peripheral shape of the fan blade is 20 to 3 of an outer peripheral arc length from an end portion in the rotational direction of the blade.
0% point and 90 to 9 of the outer radius on the radius of the end
An axial-flow fan characterized by being cut off with a straight line or a line connecting in a chord shape with 5% points.