DESCRIPTION

Title of Invention

AXIAL FLOW FAN

Technical Field

[0001]
The present invention relates to axial flow fans applicable to a wide range of devices such as, for example, air-conditioning devices and ventilation devices.

Background Art

[0002]
Axial flow fans are used in a wide range of air-conditioning devices, ventilation devices, and the like, and reduction of noise of the axial flow fan is demanded. There have been proposed a variety of axial flow fans devised to reduce noise. As such an axial flow fan, there is one disclosed in. which "an axial flow fan comprising a plurality of blades disposed at an outer periphery of a cylindrical boss portion, wherein a shape of each of the blades is defined such that, in any portion of a section of the blade along a given plane radially extending from a rotation centerline through a blade root portion contacting the boss portion, the blade is bent toward an outer peripheral portion side, the outer peripheral portion of the blade is directed in an air sending direction, and a horizontal angle of the blade gradually increases as the blade extends toward the outer peripheral portion side" (for example, see Patent Literature 1).

[0003]
In the axial flow fan described in Patent Literature 1, in addition to the above-described structure, each blade is formed as a swept-forward wing, and a swept-forward angle formed between a line connecting the rotation centerline and the midpoint of the blade root portion and a line connecting the rotation centerline and the midpoint of an outer peripheral edge of the blade is set to an angle in a range from 20° to 40°, thereby reducing noise.

Citation List Patent Literature

[0004]
Patent Literature 1: Japanese Unexamined Patent Application Publication No. 6-229398 (page 5, Fig. 1, etc.) Summary of Invention Technical Problem

[0005]
However, according to such a technique described in Patent Literature 1, since the shape of each blade is defined such that the horizontal angle of the blade gradually increases as the blade extends toward the outer peripheral portion side, air flows that move toward an inner peripheral side of the fan are caused to interfere with one another, thereby generating turbulence and increasing noise. Also according to such a technique described in Patent Literature 1, the pressure difference between a pressure surface and a suction surface is increased near the outer peripheral portion of the blade. Thus, a large and unstable blade tip vortex is generated, and accordingly, noise is increased.

[0006]
The invention is made for solving the problem described above. An object of the invention is to provide an axial flow fan with which effective work of each blade is ensured and a blade tip vortex is suppressed, thereby reducing noise.

Solution to Problem

[0007]
An axial flow fan according to the invention includes a boss that rotates about a shaft center and a plurality of blades disposed in an outer peripheral portion of the boss. In the axial flow fan, the blades are each formed such that a chord centerline connecting chord center points from an inner peripheral end of the blade to an outer peripheral end of the blade is curved so as to protrude toward a downstream side of an air flow in a whole region of the blade in a radial direction.

Advantageous Effects of Invention

[0008]

With the axial flow fan according to the invention, effective work can be ensured by forming flows that move toward the inner peripheral side while turbulence due to interference of air flows with one another and enlargement and destabilization of the blade tip vortex can be suppressed. Thus, noise can be reduced.

Brief Description of Drawings

[0009]
[Fig. 1] Fig. 1 is a perspective view illustrating the structure of an axial flow fan according to Embodiment of the invention.

[Fig. 2] Fig. 2 is a front view illustrating the structure of the axial flow fan according to Embodiment of the invention.

[Fig. 3] Fig. 3 is a plan development view illustrating an l-l section of Fig. 2.

[Fig. 4] Fig. 4 is a projection view, in which a chord centerline and a blade section, which is taken along a curved plane along a rotation axis including the chord centerline, of the axial flow fan according to Embodiment of the invention are projected onto a flat plane including the rotation axis.

[Fig. 5] Fig. 5 includes explanatory views illustrating a flow field of the axial flow fan according to Embodiment of the invention.

[Fig. 6] Fig. 6 is a graph illustrating the relationship between a normalized noise reduction amount and Ro/(Rt - Rb) of the axial flow fan according to Embodiment of the invention.

[Fig. 7] Fig. 7 is a graph illustrating the relationship between the normalized noise reduction amount and Zmax/Rt of the axial flow fan according to Embodiment of the invention.
Description of Embodiments

[0010]
Embodiment of the invention will be described below with reference to the drawings.

Fig. 1 is a perspective view illustrating the structure of an axial flow fan according to Embodiment.

Fig. 2 is a front view illustrating the structure of the axial flow fan according to Embodiment. Fig. 3 is a plan development view illustrating an l-l section of Fig. 2. Fig. 4 is a projection view, in which a chord centerline and a blade section, which is taken along a curved plane along a rotation axis including the chord centerline, of the axial flow fan according to Embodiment of the invention are projected onto a flat plane including the rotation axis. Fig. 5 includes explanatory views illustrating a flow field of the axial flow fan according to Embodiment. Fig. 6 is a graph illustrating the relationship between the normalized noise reduction amount and Ro/(Rt - Rb) of the axial flow fan according to Embodiment. Fig. 7 is a graph illustrating the relationship between the normalized noise reduction amount and Zmax/Rt of the axial flow fan according to Embodiment.

[0011]
The axial flow fan according to Embodiment will be described with reference to Figs. 1 to 7. The axial flow fan according to Embodiment is applicable to a wide range of devices such as, for example, an air-conditioning device and a ventilation device, and has a function of applying pressure so as to send air. In the following drawings including Fig. 1, the dimensional relationships among the components may differ from the actual dimensional relationships among the components. Also in the following drawings including Fig. 1, the same or equivalent components are denoted by the same reference signs, and this is applicable throughout the description. Furthermore, forms of elements described throughout the description are only exemplary. The forms of the elements are not limited to the description herein. For example, although an example of the axial flow fan having three blades is illustrated in the drawings in Embodiment, this does not limit the number of blades.

[0012]
As illustrated in Figs. 1 to 4, the axial flow fan according to Embodiment includes an impeller 1 having a boss 2, which rotates about a shaft center, and a plurality of blades 3, which are disposed at an outer periphery of the boss 2. That is, the blades 3 each having a three-dimensional spatial shape are attached to the outer periphery of the cylindrical boss 2 so as to extend in radial directions. The boss 2 is rotated by a motor (not shown). Rotation of the blades 3 generates air flows. As illustrated in Fig. 1, a surface on an upstream side of each blade 3 is a suction surface 3S and a surface on a downstream side thereof is a pressure surface 3P.

[0013]
As illustrated in Fig. 3, a chord line 33 is defined as a line connecting a leading edge 31 and a trailing edge 32 of each blade 3 in a flat plane, which is a developed plane of a cylindrical section centering around the rotation axis of the impeller 1 (for example, the l-l section of Fig. 2). A midpoint of the chord line 33 is defined as a chord center point 34. As illustrated in Figs. 2 and 4, a chord centerline 37 is defined as a curved line connecting the chord center points 34 of each radius from an inner-peripheral-end chord center point 35 to an outer-peripheral-end chord center point 36.

[0014]
As illustrated in Fig. 4, when Ro is determined so as to satisfy Rb < Ro