Patent Application
20190293091
The present invention relates to a propeller fan which is provided with blades including notches formed in trailing edges of the blades.
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.
Patent Literature 1: Japanese Unexamined Patent Application Publication No. 8-189497
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.
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 P1 is the width of the at least one notch in the first area, P2 is the width of the at least one notch in the second area, and P3 is the width of the at least one notch in each of the third areas.
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.
A propeller fan according to embodiment 1 of the present invention will be described.
As illustrated in
Each of the blades 2 has a leading edge 23, a trailing edge 24, an outer circumferential edge 21 and an inner circumferential edge 22. The leading edge 23 is an edge which is located at a front portion of the blade 2 when the boss 1 and the blade 2 are rotated. The trailing edge 24 is an edge which is located at a rear portion of the blade 2 when the boss 1 and the blade 2 are rotated. The outer circumferential edge 21 is an edge which is located on an outer circumferential side of the blade 2 and extends between an outer peripheral end of the leading edge 23 and an outer peripheral end of the trailing edge 24. The inner circumferential edge 22 is an edge which is located on an inner circumferential side of the blade 2, and extends between an inner peripheral end of the leading edge 23 and an inner peripheral end of the trailing edge 24. The inner circumferential edge 22 is connected to an outer circumferential surface of the boss 1.
The blade 2 has a first area 51, a second area 52 and third areas 53 arranged in a radial direction of the propeller fan 100 (which may be hereinafter simply referred to as “radial direction”). The first area 51 is located relatively close to the outer circumferential side of the blade 2. For example, the first area 51 is located outward of an intermediate portion between the outer circumferential edge 21 and the inner circumferential edge 22, that is, an intermediate portion of the blade 2 in the radial direction. The second area 52 is located inward of the first area 51. The third areas 53 are located outward of the second area 52, and are located inward and outward of the first area 51, with the first area 51 interposed between the third areas 53. To be more specific, the third areas 53 include a first sub-area 53-1 located outward of the first area 52 and inward of the second area 51, and a second sub-area 53-2 located outward of the first area 51. The first sub-area 53-1 is adjacent to an outer circumferential side of the second area 52 and an inner circumferential side of the first area 51. The second sub-area 53-2 is adjacent to an outer circumferential side of the first area 51. The first area 51, the second area 52, and the first sub-area 53-1 and second sub-area 53-2 of the blade 2 extend in the circumferential direction of the propeller fan 100.
In the trailing edge 24 of the blade 2, a plurality of notches are formed. To be more specific, each of the first area 51, the second area 52 and the third areas 53 includes at least one notch formed in the trailing edge 24. As described later, the notches of the first area 51, the second area 52 and the third areas 53 are 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 portion 252 is formed. The width of each of the notches is defined as the distance between adjacent two crest portions 252 located 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 portions 252 located 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 edge 24.
The first area 51 includes a single notch 25a formed in the trailing edge 24. The second area 52 includes a plurality of notches 25b formed in the trailing edge 24. For example, all the notches 25b are formed to have the same width. Since the notches 25b are continuously formed along the trailing edge 24, the pitch at which corresponding points on the notches 25b are located is equal to the width of each of the notches 25b. In the third areas 53, the first sub-area 53-1 includes a plurality of notches 25c formed in the trailing edge 24; and the second sub-area 53-2 includes a plurality of notches 25d formed in the trailing edge 24. For example, all the notches 25c and the notches 25d are formed to have the same width. Since the notches 25c are continuously formed along the trailing edge 24, the pitch at which corresponding points on the notches 25c are located is equal to the width of each of the notches 25c. Furthermore, since the notches 25d are continuously formed along the trailing edge 24, the pitch at which corresponding points on the notches 25d are located is equal to the width of each of the notches 25d. The above notches satisfy the relationship “P1>P2 >P3”, where P1 is the width of the notch 25a, P2 is the width of each of the notches 25b, and P3 is the width of each of the notches 25c and 25d.
In embodiment 1, P1 is 0.32R, P2 is 0.072R, and P3 is 0.019R, where R is the distance between the rotation axis RC and the outer circumferential edge 21, that is, R is the radius of the outer circumferential edge 21. However, P1, P2 and P3 are not limited to the above values.
Furthermore, in embodiment 1, the relationship “n1<n2<n3” is satisfied, where n1 is the number of notches 25a in the first area 51, n2 is the number of notches 25b in the second area 52, and n3 is the total number of notches 25c and 25d in the third areas 53.
As described above, the propeller fan 100 according to embodiment 1 includes the boss 1 provided on the rotation axis RC and the blades 2 which are located at the outer circumferential portion of the boss 1, and each of which includes the leading edge 23 and the trailing edge 24. Each blade 2 has the first area 51, the second area 52 located inward of the first area 51, and the third areas 53 which are located outward of the second area 52, and which are also located inward and outward of the first area 51, with the first area 51 interposed between the third areas 53. Each of the first area 51, the second area 52 and the third areas 53 includes at least one notch formed in the trailing edge 24. The above notches satisfy the relationship “P1>P2>P3”, where P1 is the width of the notch 25a in the first area 51, P2 is the width of the notch 25b in the second area 52, and P3 is the width of each of the notches 25c and 25d in the third areas 53.
The advantages obtained by the propeller fan 100 according to embodiment 1 will be described with reference to
The second area 52 is located inward of the first area 51. Thus, when the blade 2 is moved, the moving velocity of the second area 52 is lower than that of the first area 51. Therefore, at the surface of the blade 2, the velocity V2 of wind at the second area 52 is lower than the velocity V1. Thus, at the second area 52, a trailing-edge eddy Wa which is generated from the trailing edge 24 when the wind passes the trailing edge 24 is a dominant source of noise. Part of the trailing edge 24 which is located in the second area 52 includes the notches 25b each having the width P2, which is smaller than that of the notch 25a in the first area 51, and can thus divide the trailing-edge eddy Wa, which is a smaller stream phenomenon than that generated at the first area 51.
At the third areas 53, divided winds separated by the notch 25a in the first area 51 flow while having a velocity V3. Since they are winds into which the wind having the velocity V1 is divided, the velocity V3 is lower than the velocity V1. Furthermore, since the third areas 53 are located outward of the second area 52, the velocity V3 is higher than the velocity V2. That is, the relationship between the velocities V1, V2 and V3 satisfies V1>V3>V2. Also, at the third areas 53, trailing-edge eddies Wb generated from the trailing edge 24 when wind passes the trailing edge 24 are dominant sources of noise. Since the velocity V3 of the wind at each of the third areas 53 is higher than the velocity V2 of the wind at the second area 52, 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 edge 24, the third areas 53 have notches 25c and 25d each having the width P3, which is smaller than that of the notch 25b in the second area 52, they can divide trailing-edge eddies Wb, which are smaller in scale than that in the second area 52.
As described above, in embodiment 1, the widths of the notches 25a, 25b, 25c, and 25d formed in the trailing edge 24 of the blade 2 are 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 fan 100, and also further reduce the power input to the propeller fan 100.
A propeller fan according to embodiment 2 of the present invention will be described.
As illustrated in
The advantages obtained by the propeller fan 100 according to embodiment 2 will be described. As illustrated in
In embodiment 2, although the total of the widths R31 and R32 of the third areas 53 is equal to the width R1 of the first area 51, even if the total of the widths R31 and R32 of the third areas 53 is set greater than the width R1 of the first area 51 (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.
As illustrated in
In the first area 51, since the root portion 251 of the notch 25a has an acute angle, wind having the velocity V1 can be effectively divided into wind flows to the first sub-area 53-1 located on the inner circumferential side and wind which flows to the second sub-area 53-2 located on the outer circumferential side. As a result, the velocity of wind passing the trailing edge 24, which greatly contributes to generation of noise, can be further reduced. In the second area 52 and the third areas 53, the root portions 251 of the notches 25b, 25c and 25d have 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 fan 100.
A propeller fan according to embodiment 4 of the invention will be described with reference to
By virtue of the above configuration, in the first area 51, the angle of the root portion 251 of the notch 25a is set to enable the notch 25a to most effectively divide wind having the wind velocity V1 into wind which flows to the first sub-area 53-1 located on the inner circumferential side and wind which flows to the second sub-area 53-2 located on the outer circumferential side. It is therefore possible to further greatly reduce the velocity of wind passing the trailing edge 24, which greatly contributes to generation of noise. In the second area 52 and the third areas 53, the angles of the root portions 251 of the notches 25b, 25c and 25d are set to enable the notches 25b, 25c and 25d to most effectively divide the trailing-edge eddies Wa and Wb. It is therefore possible to further greatly reduce noise of the propeller fan 100.
The above embodiments can be put to practical use in combination.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16072210 | Jul 2018 | US |
| Child | 16437190 | US |
