Propeller fan

A propeller fan includes a boss on a rotation axis, and a blade at an outer circumferential portion of the boss. The blade includes a leading edge and a trailing edge. The blade includes a first area, a second area inward of the first area, and third areas outward of the second area. The third areas are located inward and outward of the first area, with the first area interposed between the third areas. The first area, the second area and the third areas each include at least one notch in the trailing edge. The notches satisfy the relationship “P1>P2>P3”, where P1 is the width of the notch in the first area, P2 is the width of the notch in the second area, and P3 is the width of the notch in each of the third areas.

CROSS REFERENCE TO RELATED APPLICATION

This application is a U.S. national stage application of PCT/JP2016/069670 filed on Jul. 1, 2016, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a propeller fan which is provided with blades including notches formed in trailing edges of the blades.

BACKGROUND ART

Patent literature 1 describes a propeller fan including a plurality of vanes. In the propeller fan, each of the vanes includes a trailing edge into which serrations are cut. Thereby, wind at a suction surface of each vane and wind at a pressure surface thereof gradually join each other, and the velocity loss in the vicinity of the trailing edge is therefore small. As a result, the velocity gradient is reduced as compared with those of conventional propeller fans, thus reducing the frequency of occurrence of turbulence, and also reducing noise.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 8-189497

SUMMARY OF INVENTION

Technical Problem

However, in the propeller fan described in patent literature 1, the pitch and the widths of the serrations are determined without sufficiently considering the difference between flow areas of the vane which are located at different positions in the radial direction. Thus, it is not possible to reduce the maximum wind velocity or divide an eddy, which is a source of noise. Therefore, it is not possible to sufficiently reduce noise.

The present invention was made to solve the above problems, and an object of the invention is to provide a propeller fan which can more greatly reduce noise.

Solution to Problem

A propeller fan according to an embodiment of the present invention includes a boss provided on a rotation axis and a blade provided on an outer circumferential portion of the boss. The blade includes a leading edge and a trailing edge. The blade includes a first area, a second area located inward of the first area, and third areas located outward of the second area. The third areas are located inward and outward of the first area, with the first area interposed between the third areas. Each of the first area, the second area and the third areas includes at least one notch formed in the trailing edge. The notches satisfy the relationship “P1>P2>P3”, where P1is the width of the at least one notch in the first area, P2is the width of the at least one notch in the second area, and P3is the width of the at least one notch in each of the third areas.

Advantageous Effects of Invention

According to an embodiment of the present invention, each of the notches at the trailing edge of the blade has a width determined in accordance with its position in the radial direction of the propeller fan. Thereby, noise made by the propeller fan can be more greatly reduced.

DESCRIPTION OF EMBODIMENTS

A propeller fan according to embodiment 1 of the present invention will be described.FIG. 1is a perspective view schematically illustrating a configuration of a propeller fan100according to embodiment 1.FIG. 2is a front view illustrating a configuration of a boss1and one of blades2of the propeller fan100according to embodiment 1. The propeller fan100is used in, for example, an air-conditioning apparatus or a ventilator. In figures referred to below, which includeFIGS. 1 and 2, for example, the relative dimensions of structural elements or the shapes thereof may differ from those of an actual propeller fan.

As illustrated inFIGS. 1 and 2, the propeller fan100includes a boss1and a plurality of blades2(one of which is illustrated inFIG. 2) provided at an outer circumferential portion of the boss1. The boss1is located on a rotation axis RC of the propeller fan100. The boss1is rotated about the rotation axis RC by a driving force of a motor (not illustrated) in a rotation direction indicated by a bold arrow inFIG. 2. The blades2are arranged at regular intervals, for example, in a circumferential direction. The blades2have, for example, the same configuration. Referring toFIG. 1, the number of blades2is three, but it is not limited to three.

Each of the blades2has a leading edge23, a trailing edge24, an outer circumferential edge21and an inner circumferential edge22. The leading edge23is an edge which is located at a front portion of the blade2when the boss1and the blade2are rotated. The trailing edge24is an edge which is located at a rear portion of the blade2when the boss1and the blade2are rotated. The outer circumferential edge21is an edge which is located on an outer circumferential side of the blade2and extends between an outer peripheral end of the leading edge23and an outer peripheral end of the trailing edge24. The inner circumferential edge22is an edge which is located on an inner circumferential side of the blade2, and extends between an inner peripheral end of the leading edge23and an inner peripheral end of the trailing edge24. The inner circumferential edge22is connected to an outer circumferential surface of the boss1.

The blade2has a first area51, a second area52and third areas53arranged in a radial direction of the propeller fan100(which may be hereinafter simply referred to as “radial direction”). The first area51is located relatively close to the outer circumferential side of the blade2. For example, the first area51is located outward of an intermediate portion between the outer circumferential edge21and the inner circumferential edge22, that is, an intermediate portion of the blade2in the radial direction. The second area52is located inward of the first area51. The third areas53are located outward of the second area52, and are located inward and outward of the first area51, with the first area51interposed between the third areas53. To be more specific, the third areas53include a first sub-area53-1located outward of the first area52and inward of the second area51, and a second sub-area53-2located outward of the first area51. The first sub-area53-1is adjacent to an outer circumferential side of the second area52and an inner circumferential side of the first area51. The second sub-area53-2is adjacent to an outer circumferential side of the first area51. The first area51, the second area52, and the first sub-area53-1and second sub-area53-2of the blade2extend in the circumferential direction of the propeller fan100.

In the trailing edge24of the blade2, a plurality of notches are formed. To be more specific, each of the first area51, the second area52and the third areas53includes at least one notch formed in the trailing edge24. As described later, the notches of the first area51, the second area52and the third areas53are different from each other in size (at least in width). The notches are each formed in the shape of a triangle having a rounded root portion. Between any adjacent two of the notches, a crest portion252is formed. The width of each of the notches is defined as the distance between adjacent two crest portions252located on the both sides of each notch. The depth of each notch is defined as the distance between the root portion of thereof and a straight line connecting the adjacent two crest portions252located on the both sides of each notch. In embodiment 1, all the notches are the same as each other in ratio between width and depth. All the notches may be similar to each other in shape. Furthermore, in embodiment 1, the notches are continuously formed along the trailing edge24.

The first area51includes a single notch25aformed in the trailing edge24. The second area52includes a plurality of notches25bformed in the trailing edge24. For example, all the notches25bare formed to have the same width. Since the notches25bare continuously formed along the trailing edge24, the pitch at which corresponding points on the notches25bare located is equal to the width of each of the notches25b. In the third areas53, the first sub-area53-1includes a plurality of notches25cformed in the trailing edge24; and the second sub-area53-2includes a plurality of notches25dformed in the trailing edge24. For example, all the notches25cand the notches25dare formed to have the same width. Since the notches25care continuously formed along the trailing edge24, the pitch at which corresponding points on the notches25care located is equal to the width of each of the notches25c. Furthermore, since the notches25dare continuously formed along the trailing edge24, the pitch at which corresponding points on the notches25dare located is equal to the width of each of the notches25d. The above notches satisfy the relationship “P1>P2>P3”, where P1is the width of the notch25a, P2is the width of each of the notches25b, and P3is the width of each of the notches25cand25d.

In embodiment 1, P1is 0.32R, P2is 0.072R, and P3is 0.019R, where R is the distance between the rotation axis RC and the outer circumferential edge21, that is, R is the radius of the outer circumferential edge21. However, P1, P2and P3are not limited to the above values.

Furthermore, in embodiment 1, the relationship “n1<n2<n3” is satisfied, where n1is the number of notches25ain the first area51, n2is the number of notches25bin the second area52, and n3is the total number of notches25cand25din the third areas53.

As described above, the propeller fan100according to embodiment 1 includes the boss1provided on the rotation axis RC and the blades2which are located at the outer circumferential portion of the boss1, and each of which includes the leading edge23and the trailing edge24. Each blade2has the first area51, the second area52located inward of the first area51, and the third areas53which are located outward of the second area52, and which are also located inward and outward of the first area51, with the first area51interposed between the third areas53. Each of the first area51, the second area52and the third areas53includes at least one notch formed in the trailing edge24. The above notches satisfy the relationship “P1>P2>P3”, where P1is the width of the notch25ain the first area51, P2is the width of the notch25bin the second area52, and P3is the width of each of the notches25cand25din the third areas53.

The advantages obtained by the propeller fan100according to embodiment 1 will be described with reference toFIG. 3.FIG. 3is a view illustrating an example of the winds at the propeller fan100according to embodiment 1, and corresponds toFIG. 2. As illustrated inFIG. 3, since the first area51is located on the outer circumferential side of the blade2, the moving velocity of the first area51of the blade2is relatively high. Thus, at the surface of the blade2, the velocity V1of wind at the first area51is, for example, the maximum wind velocity. Part of the trailing edge24which is located in the first area51includes a large notch, that is, the notch25ahaving a width P1. By virtue of this configuration, the wind having the velocity V1can be roughly divided into wind which flows to the first sub-area53-1located on the inner circumferential side and wind which flows to the second sub-area53-2located on the outer circumferential side. It is therefore possible to reduce the velocity of wind passing the trailing edge24, which greatly contributes to generation of noise.

The second area52is located inward of the first area51. Thus, when the blade2is moved, the moving velocity of the second area52is lower than that of the first area51. Therefore, at the surface of the blade2, the velocity V2of wind at the second area52is lower than the velocity V1. Thus, at the second area52, a trailing-edge eddy Wa which is generated from the trailing edge24when the wind passes the trailing edge24is a dominant source of noise. Part of the trailing edge24which is located in the second area52includes the notches25beach having the width P2, which is smaller than that of the notch25ain the first area51, and can thus divide the trailing-edge eddy Wa, which is a smaller stream phenomenon than that generated at the first area51.

At the third areas53, divided winds separated by the notch25ain the first area51flow while having a velocity V3. Since they are winds into which the wind having the velocity V1is divided, the velocity V3is lower than the velocity V1. Furthermore, since the third areas53are located outward of the second area52, the velocity V3is higher than the velocity V2. That is, the relationship between the velocities V1, V2and V3satisfies V1>V3>V2. Also, at the third areas53, trailing-edge eddies Wb generated from the trailing edge24when wind passes the trailing edge24are dominant sources of noise. Since the velocity V3of the wind at each of the third areas53is higher than the velocity V2of the wind at the second area52, the scale of each of the trailing-edge eddies Wb is far smaller than that of the trailing-edge eddy Wa. Since at the trailing edge24, the third areas53have notches25cand25deach having the width P3, which is smaller than that of the notch25bin the second area52, they can divide trailing-edge eddies Wb, which are smaller in scale than that in the second area52.

As described above, in embodiment 1, the widths of the notches25a,25b,25c, and25dformed in the trailing edge24of the blade2are appropriately determined in accordance with the positions of these notches in the radial direction. It is therefore possible to more greatly reduce noise generated by the propeller fan100, and also further reduce the power input to the propeller fan100.

A propeller fan according to embodiment 2 of the present invention will be described.FIG. 4is a front view illustrating a configuration of the boss1and one of the blade2of the propeller fan100according to embodiment 2. With respect to embodiment 2, structural elements having the same functions and operations as those in embodiment 1 will be denoted by the same reference signs as in embodiment 1, and their explanations will thus be omitted.

As illustrated inFIG. 4, the widths of the first area51, the second area52, the first sub-area53-1and the second sub-area53-2in the radial direction are R1, R2, R31, and R32, respectively. The total width of the third areas53in the radial direction is the sum of the width R31of the first sub-area53-1and the width R32of the second sub-area53-2. In embodiment 2, the total of the widths R31and R32of the third areas53is equal to the width R1of the first area51(R31+R32=R1). In the present specification, the word “equal” covers not only “exactly equal” but “substantially equal” in the case where things can be considered substantially equal to each other in view of common knowledge in technique.

The advantages obtained by the propeller fan100according to embodiment 2 will be described. As illustrated inFIG. 3, the winds at the third areas53are divided winds separated by the notch25ain the first area51. In embodiment 2, since the total of the widths R31and R32of the third areas53is equal to the width R1of the first area51, the width of wind not yet divided and the width of divided winds can be made equal to each other. Thus, the trailing-edge eddies Wb generated at the third areas53can be further effectively divided, and noise generated by the propeller fan100can thus be further reduced.

In embodiment 2, although the total of the widths R31and R32of the third areas53is equal to the width R1of the first area51, even if the total of the widths R31and R32of the third areas53is set greater than the width R1of the first area51(R31+R32>R1), the same advantage as described above can be obtained.

A propeller fan according to embodiment 3 of the invention will be described.FIG. 5is a front view illustrating a configuration of the boss1and one of the blades2of the propeller fan100according to embodiment 3. With respect to embodiment 3, structural elements having the same functions and operations as those of embodiment 1 will be denoted by the same reference signs as in embodiment 1, and their descriptions will thus be omitted.

As illustrated inFIG. 5, in embodiment 3, notches25a,25b,25cand25dare all triangularly formed. Thereby, a root portion251of each of the notches25a,25b,25c, and25dhas an acute angle.

In the first area51, since the root portion251of the notch25ahas an acute angle, wind having the velocity V1can be effectively divided into wind flows to the first sub-area53-1located on the inner circumferential side and wind which flows to the second sub-area53-2located on the outer circumferential side. As a result, the velocity of wind passing the trailing edge24, which greatly contributes to generation of noise, can be further reduced. In the second area52and the third areas53, the root portions251of the notches25b,25cand25dhave an acute angle, and the trailing-edge eddies Wa and Wb can thus be effectively disposed. It is therefore possible to further greatly reduce noise generated by the propeller fan100.

A propeller fan according to embodiment 4 of the invention will be described with reference toFIG. 5referred to above. In embodiment 4, the width and the depth of each of the notches are equal to each other. Specifically, the width P1and depth H1of the notch25aare equal to each other (P1=H1), the width P2and depth H2of the notch25bare equal to each other (P2=H2), and the width P3and depth H3of each of the notches25cand25dare equal to each other (P3=H3). As described above, the depth of each of the notches is defined as a distance between a straight line connecting two crest portions252located on both sides of each notch and the root portion251thereof. In this specification, the term “equal” covers not only “exactly equal” but “substantially equal” in the case where things can be considered substantially equal to each other in view of common knowledge in technique.

By virtue of the above configuration, in the first area51, the angle of the root portion251of the notch25ais set to enable the notch25ato most effectively divide wind having the wind velocity V1into wind which flows to the first sub-area53-1located on the inner circumferential side and wind which flows to the second sub-area53-2located on the outer circumferential side. It is therefore possible to further greatly reduce the velocity of wind passing the trailing edge24, which greatly contributes to generation of noise. In the second area52and the third areas53, the angles of the root portions251of the notches25b,25cand25dare set to enable the notches25b,25cand25dto most effectively divide the trailing-edge eddies Wa and Wb. It is therefore possible to further greatly reduce noise of the propeller fan100.

The above embodiments can be put to practical use in combination.