JP2002221195A - Moving blade of axial fan - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform an extensive cost reduction while maintaining the same performance as of a conventional one without limitation of minimizing a clearance between the blade head end of a moving blade and a casing inner surface by making it hard to generate noise and vibration. SOLUTION: Lift in the blade height direction is made to show an elliptic distribution 9 so that the lift is not generated on both blade ends in the blade height direction of the moving blade, and the lift on an intermediate part becomes the maximum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an axial fan, and more particularly to a blade of a low-pressure axial fan.

[0002]

2. Description of the Related Art Low-pressure axial fans have been widely used as various blowers from business use to home use. Such a low-pressure axial fan usually includes a moving blade and a stationary blade provided inside a cylindrical casing. or,
Some do not have stationary blades and only have moving blades.

FIG. 7 shows an example of a conventional low-pressure axial fan. In the example of FIG. 7, a boss 2 coaxial with the casing 1 and a boss 2
And a plurality of (four in the cross direction in the figure) moving blades 3 fixed to the outer periphery of the low pressure axial flow fan 4.

When designing the moving blade 3 of such a low-pressure axial flow fan 4, a general moving blade 3 has a larger blade height (radial length) than a chord length, that is, an aspect ratio. Because of its large size, the blade base end 3A (R
OOT section) and both wing tips 3A of wing tip 3B (TIP section),
Except for the vicinity of 3B, the flow state at most points in the blade height direction is the same, and it has been considered that a two-dimensional flow is preferable. Even when the aspect ratio is not so large, a partition plate of a required size (not shown) is integrally fixed to both wing ends 3A and 3B to suppress the flow in the radial direction. Is considered to be in a two-dimensional flow state over the entire area of.

[0005] In such a two-dimensional flow field, all stream lines are in a cross section orthogonal to the axis of the moving blade 3, and the cross section has the same flow pattern in any cross section. Therefore, when considering the fluid characteristics of the rotor blade 3, the handling of a blade having a unit width of a two-dimensional flow field is still the mainstream even today, and its lift distribution is called a free vortex distribution, and is indicated by a broken line in FIG. The blade shape is determined so that the lift distribution in the blade height direction from the blade base end 3A to the blade tip 3B becomes a constant value 5 as shown by.

In FIG. 7, a pitch angle P is obtained by adding an attack angle β of the moving blade 3 to a non-lift angle α that does not generate a lift with respect to a combined velocity of the axial flow and the rotational flow of the fluid.

At this time, the pitch angle P from the blade base end 3A to the blade tip 3B changes linearly as shown in FIG. 8, and the conventional moving blade 3 has a blade height as shown in FIG. When the blades are cut at a plurality of points (radius R) in the direction perpendicular to the axis X of the moving blade 3 and the blade cross sections are stacked, the shape is as shown in the stacking conceptual diagram of FIG.

[0008]

However, the following problem arises with the moving blade 3 of the conventional low-pressure axial flow fan 4 described above.

Conventionally, it has been considered good to generate a constant lift (linear change 6) over the entire blade height direction of the moving blade 3, so that the lift is applied to the blade base end 3A and the blade tip 3B. Therefore, the lift is suddenly lost at both wing ends 3A and 3B close to the casing 1 and the boss portion 2, so that a fluid separation phenomenon occurs, and noise or vibration is generated due to the separation phenomenon. Had the problem of occurring.

Further, in order to generate a constant lift up to the blade tip 3B of the moving blade 3, it is required to make the clearance between the blade tip 3B of the moving blade 3 and the inner surface of the casing 1 as small as possible. That is, when the clearance is increased, there is a problem that the lift at the blade tip 3B of the bucket 3 is rapidly reduced.

However, as described above, the blade tip 3 of the rotor blade 3
In order to make the clearance between B and the inner surface of the casing 1 as small as possible, it is necessary to accurately center the rotation axis of the boss portion 2 and to precisely adjust the height and shape of the blade tip 3B of each blade 3. It is necessary to manufacture them so that they match, and it is also necessary to finish the inner surface of the casing 1 with high accuracy. For this reason, high precision is required for the production of the low-pressure axial flow fan 4, and there is a problem that the production takes time and the production cost increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the conventional apparatus, and it is difficult to generate noise or vibration, and it is possible to eliminate the restriction of reducing the clearance between the tip of the rotor blade and the inner surface of the casing. It is an object of the present invention to provide an axial flow fan blade capable of achieving a significant cost reduction while maintaining the same performance as the conventional one.

[0013]

According to the present invention, the lift in the blade height direction has an elliptical distribution so that lift is not generated at both ends of the blade in the blade height direction and the lift in the middle portion is maximized. A rotor blade of an axial fan.

[0014] In the above means, the pitch angle at both blade tips in the blade height direction of the moving blade is small, and the pitch angle at the middle portion is large.

In the present invention, the lift distribution in the blade height direction in the blade height direction is made elliptical, so that lift is not generated between the blade base end and the blade tip of the blade. In this case, the fluid separation phenomenon does not occur at both wing ends near the casing and the boss portion, and noise and vibration due to the separation phenomenon can be prevented.

Further, by preventing the above problem, it is possible to eliminate the restriction that the clearance between the tip of the blade and the inner surface of the casing is made as small as possible. The manufacturing process can be remarkably simplified by eliminating the conventionally troublesome work of precisely matching the height and shape of the blade tips and finishing the inner surface of the casing with high accuracy. Therefore, the manufacturing time can be shortened and the manufacturing cost can be significantly reduced.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 shows an example of a moving blade 7 of a low-pressure axial flow fan embodying the present invention. The moving blade 7 has a plurality of blades in the blade height direction (radius R) similarly to FIG. When cut in a direction perpendicular to the axis X at a point and the blade cross sections are stacked, the blade has the shape shown in the conceptual stacking diagram of FIG.

As shown in FIG. 2, the blade 7 shown in FIG. 4 has a pitch angle distribution 8 in which the pitch angle between the blade tip 7A and the blade tip 7B of the blade 7 is small and the pitch angle in the middle portion is large. ing. The pitch angle distribution 8 has a curve that forms an ellipse or a part of a parabola as shown in FIG. 3, and the straight line change 6 in the case of the conventional blade shown by a broken line for comparison. Are significantly different.

As shown by the solid line in FIG. 1, no lift is generated at the blade base end 7A and the blade tip 7B of the rotor blade 7, and the lift in the middle portion is maximized, thereby increasing the lift in the blade height direction. The pitch angle distribution 8 is determined so that the distribution becomes an elliptical distribution 9.

The above-mentioned rotor blade 7 generates a total lift represented by the area inside the elliptical distribution 9 shown by the solid line in FIG. 1, and this area is equal to the conventional lift distribution of the constant value 5 shown by the broken line. If it is set to be equal to the area inside, the same performance as that of the conventional moving blade will be exhibited.

FIG. 5 is a flow chart showing an example of a design method when a low-pressure axial fan is manufactured using the moving blades 7.

In producing a low-pressure axial fan,
First, in step A, the required air volume, the number of revolutions and the diameter of the low-pressure axial fan, and the like are determined. Subsequently, in step B, the required lift of the bucket 7 is determined. Next, in step C, NAC
Select a wing type such as A type. Subsequently, in step D, the contour of the moving blade 7 (chord tension at each radial position) is set. next,
In step E, the lift at each radial position is set so that the lift distribution on the wing surface becomes elliptical. Next, in step F, an angle of attack for producing a lift at each radial position is set. next,
In the process G, the blade characteristic diagram is examined. Next, in step H, it is determined whether the stall is not caused at the set angle of attack or the drag is small.

At this time, the angle of attack and the drag are determined using the relationship diagram between the angle of attack curve 10 and the drag curve 11 shown in FIG. In FIG. 6, reference numeral 12 denotes a preferred range of the angle of attack at which the drag is minimized.

In the above step H, if the angle of attack causes a stall or the drag is large, the process returns to the step D to start over from the setting of the contour of the moving blade 7.

In step H, when it is determined that the drag is small at the angle of attack without stall, in step I, the pitch angle distribution is determined. If the pitch angle distribution is good, the design ends. On the other hand, if the pitch angle distribution was not good,
Returning to the process C, the process is repeated from the airfoil selection.

As described above, according to the moving blade 7 having the pitch angle distribution 8 determined so that the lift distribution in the blade height direction becomes the elliptical distribution 9 in FIG. 1, the blade base end 7A of the moving blade 7 and the blade Since the lift is not generated between the tip 7B and the tip 7B, when applied to the low-pressure axial flow fan shown in FIG. Therefore, generation of noise and vibration due to the peeling phenomenon can be prevented.

Further, by preventing such a problem, it is possible to eliminate the restriction that the clearance between the blade tip 7B and the inner surface of the casing 1 is made as small as possible. Therefore, the rotation axis of the boss 2 can be accurately centered. To make the height and shape of the blade tip 7B of each rotor blade 7 exactly match, to finish the inner surface of the casing 1 with high accuracy, etc.
The manufacturing process of the low-pressure axial flow fan 4 with high accuracy which has been conventionally required can be remarkably simplified, so that the manufacturing time can be shortened and the manufacturing cost can be greatly reduced.

It should be noted that the present invention is not limited only to the above-described embodiment, but is not limited to the airfoil type, contour, etc. of the moving blade, and may be variously modified without departing from the gist of the present invention. Of course, things like that.

[0030]

According to the present invention, the lift distribution in the blade height direction of the moving blade is made elliptical, so that no lift is generated between the base end and the tip of the moving blade. When applied to a low-pressure axial fan, fluid separation does not occur at both wing ends close to the casing and the boss, and there is an effect that noise and vibration due to the separation can be prevented.

In addition, by preventing the above problem, it is possible to eliminate the restriction that the clearance between the tip of the blade and the inner surface of the casing is made as small as possible. The manufacturing process can be greatly simplified by eliminating the cumbersome work that had conventionally been performed, such as precisely matching the height and shape of the wing tip and finishing the inner surface of the casing with high accuracy, thereby shortening the manufacturing time. This has the effect of significantly reducing the manufacturing cost.

[Brief description of the drawings]

FIG. 1 shows a lift distribution of a rotor blade of a low-pressure axial flow fan according to the present invention;
It is the diagram which showed and compared with the lift distribution of the conventional moving blade.

FIG. 2 is a diagram showing a pitch angle distribution of a rotor blade according to the present invention.

FIG. 3 is a diagram showing a comparison between a pitch angle distribution of a moving blade of the present invention and a pitch angle distribution of a conventional moving blade.

FIG. 4 is a conceptual diagram of lamination in which a rotor blade according to the present invention is cut at a plurality of points in a blade height direction and the blade cross sections are laminated.

FIG. 5 is a flowchart illustrating an example of a design method when a low-pressure axial fan is manufactured using the moving blade of the present invention.

FIG. 6 is a relationship diagram between an attack angle curve and a drag curve.

FIG. 7 is a cut-away side view showing an example of a conventional low-pressure axial flow fan.

FIG. 8 is a diagram showing a pitch angle distribution of a conventional moving blade.

FIG. 9 is an explanatory diagram for explaining a state in which a moving blade is cut at a plurality of points in a height direction.

FIG. 10 is a conceptual diagram of lamination in which a conventional rotor blade is cut at a plurality of points in the blade height direction and the blade cross sections are laminated.

[Explanation of symbols]

 7 Moving blade 7A Blade base 7B Blade tip 8 Pitch angle distribution 9 Elliptic distribution

Claims (2)

[Claims] An axial flow fan characterized in that the lift in the blade height direction has an elliptical distribution so that lift is not generated at both ends of the blade in the blade height direction and the lift in the middle part is maximized. Rotor blades. 2. A moving blade of an axial flow fan according to claim 1, wherein the moving blade has a pitch angle distribution in which the pitch angles of both blade tips in a blade height direction are small and the pitch angle of a middle portion is large. .