Propeller fan and refrigeration cycle device

A propeller fan includes a boss and a blade. The boss rotates about an axis. The blade is provided at an outer periphery of the boss. The blade has a first region in a radial direction. In the first region, a blade chord center line shifts downstream toward an outer peripheral side. In a cylindrical cross section about an axis, a cross-sectional shape of the blade at least in the first region is an airfoil shape. When a cross section taken along the blade chord center line and projected onto a plane including the axis is viewed, the blade chord center line is a curve having a convex on a downstream side in an entire region in the radial direction.

CROSS REFERENCE TO RELATED APPLICATION

This application is a U.S. national stage application of PCT/JP2016/084249 filed on Nov. 18, 2016, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a propeller fan that is used in a refrigeration cycle device, such as an air-conditioning device and a ventilation device, and a refrigeration cycle device including the propeller fan.

BACKGROUND ART

A low-noise propeller fan (axial-flow air-sending device) has been desired. For this reason, various propeller fans designed to reduce noise by the shape of each blade have been proposed.

For example, Patent Literature 1 describes an axial-flow air-sending device. The axial-flow air-sending device includes an electric motor and an air-sending fan. The air-sending fan has a hub and a plurality of blades. The hub is connected to the electric motor. A plurality of blades is provided radially on the hub. Each of the blades has a suction surface and a pressure surface. The suction surface at a leading edge of each blade has a plurality of triangular protrusions having vertices along the leading edge. The pressure surface at the leading edge of each blade has a smooth continuous surface having no triangular protrusions.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the technique described in Patent Literature 1, although the cross section of each blade has an airfoil shape, it is not a sufficient blade shape design made with consideration given to flow of a blade tip vortex that is generated at the blade outer peripheral end. Therefore, there is a problem that fluctuations in the blade tip vortex are increased and, as a result, noise is not reduced.

The present invention has been made to solve the above problem, and an object thereof is to provide a propeller fan that reduces noise by employing a blade shape with consideration given to flow of a blade tip vortex that is generated at a blade outer peripheral end, and a refrigeration cycle device including the propeller fan.

Solution to Problem

A propeller fan of one embodiment of the present invention includes a boss and a blade. The boss rotates about an axis. The blade is provided at an outer periphery of the boss. The blade has a first region in a radial direction. In the first region, a blade chord center line shifts downstream toward an outer peripheral side. In a cylindrical cross section about the axis, a cross-sectional shape of the blade at least in the first region is an airfoil shape. When viewing a cross section taken along the blade chord center line and projected onto a plane including the axis, the blade chord center line is a curve having a convex on a downstream side in an entire region in the radial direction.

A refrigeration cycle device of another embodiment of the present invention includes a refrigerant circuit in which a compressor, a first heat exchanger, an expansion device, and a second heat exchanger are connected by pipes. The above-described propeller fan is installed in a cooling unit in conjunction with the first heat exchanger, and supplies air to the first heat exchanger.

Advantageous Effects of Invention

With the propeller fan of one embodiment of the present invention, the propeller fan includes the blade configured such that, in the cylindrical cross section about the axis, the cross-sectional shape is an airfoil shape at least in the region in which the blade chord center line shifts downstream toward the outer peripheral side (first region) and, when viewing the cross section taken along the blade chord center line and projected onto the plane including the axis, the blade chord center line is a curve having a convex on a downstream side in the entire region in the radial direction. Therefore, air flow blowing out from the blade spreads in the radial direction. This reduces stagnation of flow downstream of the boss to reduce a boss downstream vortex, and an outer peripheral end of the blade has a shape along flow causing a blade tip vortex. For this reason, with the propeller fan of one embodiment of the present invention, it is possible to reduce fluctuations in vortex by stabilizing the blade tip vortex, and exercise the effect of reducing turbulence resulting from the airfoil shape in the cross section of the blade, so noise is reduced.

With the refrigeration cycle device of another embodiment of the present invention, since the above-described propeller fan is provided in the cooling unit in conjunction with the first heat exchanger, noise is reduced.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings includingFIG. 1, the magnitude relations among components can be different from the actual ones. In the following drawings includingFIG. 1, the same reference signs denote the same or corresponding components, and this applies to the entire text of the specification. The modes of elements described in the entire text of the specification are only illustrative, and hence should not be construed as limiting the scope of the invention.

FIG. 1is a perspective view of a propeller fan100A according to Embodiment 1 of the present invention.FIG. 2is a cross-sectional view of the propeller fan100A, taken along the line I-I inFIG. 1.FIG. 3is a projection view obtained by projecting a cross section of the propeller fan100A, taken along the line II-II inFIG. 1, onto a plane including an axis of the propeller fan100A. The propeller fan100A will be described with reference toFIG. 1toFIG. 3. The cross section taken along the line II-II depicts a cross section of the propeller fan100A, taken along a blade chord center line27.

As for reference signs of a plurality of portions, such as blades2A of the propeller fan100A, only one representative portion is indicated by a reference sign. Portions indicated by reference signs will be mainly described, and the description of portions not indicated by reference signs is omitted.FIG. 1shows the propeller fan100A having the five blades2A as an example; however, the number of the blades2A is not limited to the number shown in the drawing.

The propeller fan100A includes a boss1and the plurality of blades2A. The boss1rotates about an axis RC. The plurality of blades2A is provided at an outer periphery of the boss1. Each blade2A is surrounded by an inner peripheral end21, an outer peripheral end22, a leading edge23, and a trailing edge24. A cross-sectional shape in the entire region of the blade2A in a cylindrical cross section about the axis RC is an airfoil shape as shown inFIG. 2as the cross section taken along the line I-I.

As shown inFIG. 2, a midpoint of a straight line connecting the leading edge23and trailing edge24of a camber line25of the blade2A in the cylindrical cross section about the axis RC is defined as blade chord center point26. As shown inFIG. 3, a curve connecting the blade chord center points26from the inner peripheral end21to the outer peripheral end22is defined as blade chord center line27. Each blade2A of the propeller fan100A is configured such that, when viewing a cross section of the blade2A, which is taken along the blade chord center line27and projected onto a plane including the axis, the blade chord center line27is a curve having a convex on a downstream side in the entire region in a radial direction.

The operation of the propeller fan100A will be simply described.

As a motor (not shown) connected to the boss1is driven to rotate, the blades2A having the three-dimensional shape shown inFIG. 1rotate in an arrow A direction about the axis RC together with the boss1. Air flow (air-sending flow) from the upper side toward the lower side in the drawing is generated by the rotation of the blades2A. An upstream of each blade2A serves as a suction surface, and a downstream of each blade2A serves as a pressure surface.

Advantageous effects of the propeller fan100A will be described with reference toFIG. 4andFIG. 5.FIG. 4is a projection view that schematically shows flow of air caused by an existing propeller fan100X, and that is obtained by projecting a cross section of the propeller fan100X, taken along a blade chord center line27X, onto a plane including an axis of the propeller fan100X.FIG. 5is a projection view that schematically shows flow of air caused by the propeller fan100A, and that is obtained by projecting the cross section of the propeller fan100A, taken along the blade chord center line27, onto the plane including the axis of the propeller fan100A.FIG. 4shows the existing propeller fan100X with “X” being suffixed to reference signs.

As shown inFIG. 4, the propeller fan100X has the blade chord center line27X that is not a curve having a convex on a downstream side, and air flow S1blowing out from each blade2X is linear. This leads to stagnation of flow downstream of the boss1X, thereby to develop a boss downstream vortex V1, and also develop a blade tip vortex V2at an outer peripheral end22X of the blade2X. For this reason, the propeller fan100X causes large fluctuations in flow, and eliminates the effect of reducing turbulence resulting from the airfoil shape in the cross section of the blade2X. That is, the propeller fan100X not only cannot achieve efficient noise reduction but also reduces fan efficiency.

In contrast, as shown inFIG. 5, the blade chord center line27of the propeller fan100A is a curve having a convex on a downstream side in the entire region in the radial direction, so air flow S2blowing out from each blade2A spreads in the radial direction. This reduces stagnation of flow downstream of the boss1to reduce the boss downstream vortex V1, and the outer peripheral end22of the blade2A has a shape along flow causing the blade tip vortex V2. For this reason, the propeller fan100A reduces fluctuations in vortex by stabilizing the blade tip vortex V2, and maximizes the effect of reducing turbulence resulting from the airfoil shape in the cross section of each blade2A, so noise is reduced.

FIG. 6is a perspective view of a propeller fan1006according to Embodiment 2 of the present invention.FIG. 7is a cross-sectional view of the propeller fan1006, taken along the line III-III inFIG. 6.FIG. 8is a projection view obtained by projecting a cross section of the propeller fan100B, taken along the line II-II inFIG. 6, onto a plane including an axis of the propeller fan100B. The propeller fan100B will be described with reference toFIG. 6toFIG. 8. The cross section taken along the line II-II depicts a cross section of the propeller fan100B, taken along the blade chord center line27.

In Embodiment 2, a difference from Embodiment 1 will be mainly described, the same reference signs denote the same portions as those of Embodiment 1, and the description thereof is omitted.

In Embodiment 2, each blade2B of the propeller fan100B differs from each blade2A of the propeller fan100A in Embodiment 1.

As for reference signs of a plurality of portions, such as the blades2B of the propeller fan100B, only one representative portion is indicated by a reference sign. Portions indicated by reference signs will be mainly described, and the description of portions not indicated by reference signs is omitted.FIG. 6shows the propeller fan100B having the five blades2B as an example; however, the number of the blades2B is not limited to the number shown in the drawing.

A region in which the blade chord center line27shifts downstream toward the outer peripheral end22is defined as first region R1, and a region in which the blade chord center line27shifts upstream toward the outer peripheral end22is defined as second region R2. In the first region R1, a cross-sectional shape of each blade2B in a cylindrical cross section about the axis RC is an airfoil shape as shown inFIG. 2and described in Embodiment 1. On the other hand, in the second region R2, a cross-sectional shape of each blade2B in the cylindrical cross section about the axis RC is a circular arc shape having substantially constant thickness from the leading edge23toward the trailing edge24as shown inFIG. 7as the cross section taken along the line III-III. The first region R1and the second region R2smoothly connect with each other. The boundary between the first region R1and the second region R2just needs to fall within a predetermined range including a middle portion of the blade2B, and does not need to be specifically set.

Advantageous effects of the propeller fan100B will be described with reference toFIG. 9.FIG. 9is a schematic view that schematically shows flow of air caused by the propeller fan100B.

As shown inFIG. 9, the blade tip vortex V2develops along the outer peripheral end22of each blade2B from the leading edge23of the blade2B to the trailing edge24of the blade2B. In the propeller fan100B, the cross-sectional shape of each blade2B in the cylindrical cross section about the axis RC is a circular arc shape having a substantially constant thickness from the leading edge23to the trailing edge24in the second region R2. This reduces fluctuations in the blade tip vortex V2in process of developing from the leading edge23to the trailing edge24, so noise reduction is achieved.

FIG. 10is a projection view that is obtained by projecting a cross section of a propeller fan100C according to Embodiment 3 of the present invention, taken along the blade chord center line27, onto a plane including an axis of the propeller fan100C. The propeller fan100C will be described with reference toFIG. 10.FIG. 10corresponds to a projection view that is obtained by projecting the cross section of the propeller fan, shown inFIG. 3, or the cross section of the propeller fan, shown inFIG. 8, taken along the line II-II, onto the plane including the axis.

In Embodiment 3, a difference from Embodiment 1 or Embodiment 2 will be mainly described, the same reference signs denote the same portions as those in Embodiment 1 or Embodiment 2, and the description thereof is omitted.

In Embodiment 3, each blade2C of the propeller fan100C differs from each blade2A of the propeller fan100A in Embodiment 1 or each blade2B of the propeller fan100B in Embodiment 2.

As for reference signs of a plurality of portions, such as the blades2C of the propeller fan100C, only one representative portion is indicated by a reference sign. Portions indicated by reference signs will be mainly described, and the description of portions not indicated by reference signs is omitted.

As shown inFIG. 10, each blade2C has a rounded portion28provided at a downstream end of the blade2C at a side closer to the outer peripheral end22. That is, each blade2C has a shape that is further effectively formed along flow causing the outer peripheral end22of the blade2C to generate a blade tip vortex V2. For this reason, the propeller fan100C reduces fluctuations in vortex by further stabilizing the blade tip vortex V2and maximally exercises the effect of reducing turbulence resulting from the airfoil shape in the cross section of the blade2C, so noise is reduced.

The rounded portion28may be applied to each blade2B of the propeller fan100B in Embodiment 2.

FIG. 11is a perspective view of a propeller fan100D according to Embodiment 4 of the present invention.FIG. 12is a cross-sectional view of the propeller fan100D, taken along the line III-III inFIG. 11. The propeller fan100D will be described with reference toFIG. 11andFIG. 12.

In Embodiment 4, a difference from Embodiment 1, Embodiment 2, or Embodiment 3 will be mainly described, like reference signs denote the same portions as those in Embodiment 1, Embodiment 2, or Embodiment 3, and the description thereof is omitted.

In Embodiment 4, each blade2D of the propeller fan100D differs from each blade2A of the propeller fan100A in Embodiment 1, each blade2B of the propeller fan100B in Embodiment 2, or each blade2C of the propeller fan100C in Embodiment 3.

As for reference signs of a plurality of portions, such as the blades2D of the propeller fan100D, only one representative portion is indicated by a reference sign. Portions indicated by reference signs will be mainly described, and the description of portions not indicated by reference signs is omitted.FIG. 11shows the propeller fan100D having the five blades2D as an example; however, the number of the blades2D is not limited to the number shown in the drawing.

As shown inFIG. 12, each blade2D has a thin-walled portion29formed by thinning the trailing edge24of the blade2D in the second region. That is, each blade2D has a locally thinned portion at the trailing edge24in the second region. The thin-walled portion29smoothly connects with the other portion, and gradually reduces its weight toward the trailing edge24. For this reason, the propeller fan100D reduces fluctuations in blade tip vortex V2because of constant blade thickness near the leading edge23of each blade2D, and reduces generation of a trailing edge release vortex V3because of the provision of the thin-walled portion29near the trailing edge24of each blade2D. Therefore, the propeller fan100D reduces interference between the blade tip vortex V2and the trailing edge release vortex V3. Thus, the propeller fan100D reduces fluctuations in vortex by further stabilizing the blade tip vortex V2, so noise reduction can be achieved.

The rounded portion28described in Embodiment 3 may be applied to each blade2D.

In Embodiment 1 to Embodiment 4, an example in which the blade chord center line27is a curve having a convex on a downstream side in the entire region in the radial direction and each of the blades2A to blades2D themselves is formed in a curve having a convex on a downstream side in the entire region in the radial direction is shown. Even when the blade chord center line27is a curve having a convex on a downstream side in the entire region in the radial direction, each of the blades2A to blades2D themselves is not always formed in a curve having a convex on a downstream side in the entire region in the radial direction. In this case as well, advantageous effects of the present invention can be obtained.

FIG. 13is a circuit configuration diagram that schematically shows a refrigerant circuit configuration of a refrigeration cycle device200according to Embodiment 5 of the present invention.FIG. 14is a schematic perspective view that schematically shows an example of the configuration of a cooling unit210that is a part of the refrigeration cycle device200(hereinafter, referred to as cooling unit210A).FIG. 15is a cross-sectional view of the cooling unit210A, taken along the line IV-IV inFIG. 14.FIG. 16is a schematic configuration diagram that schematically shows another example of the configuration of a cooling unit210that is a part of the refrigeration cycle device200(hereinafter, referred to as cooling unit210B). The refrigeration cycle device200will be described with reference toFIG. 13toFIG. 16.

<Refrigerant Circuit Configuration of Refrigeration Cycle Device200>

The refrigeration cycle device200is used to operate a vapor compression refrigeration cycle. The refrigeration cycle device200is configured such that the propeller fan according to Embodiment 1, Embodiment 2, Embodiment 3, or Embodiment 4 is provided in the cooling unit210(the cooling unit210A or the cooling unit210B). In Embodiment 5, the case where the propeller fan100A according to Embodiment 1 is provided will be described as an example.

The refrigeration cycle device200includes a compressor211, a first heat exchanger205, an expansion device213, and a second heat exchanger221.

In the refrigeration cycle device200, a refrigerant circuit is formed by connecting the compressor211, the first heat exchanger205, the expansion device213, and the second heat exchanger221by refrigerant pipes216.

The compressor211compresses refrigerant into high temperature and high pressure, and discharges the refrigerant. The compressor211may be, for example, an inverter compressor, or other compressors. For example, a rotary compressor, a scroll compressor, a screw compressor, a reciprocating compressor, or another compressor, may be employed as the compressor211.

(First Heat Exchanger205) The first heat exchanger205performs the function of a condenser (radiator). The first heat exchanger205condenses refrigerant, discharged from the compressor211, into high-pressure liquid refrigerant. The upstream of the first heat exchanger205is connected to the compressor211, and the downstream of the first heat exchanger205is connected to the expansion device213. The first heat exchanger205may be, for example, a fin and tube heat exchanger, or other heat exchangers. The propeller fan100A is provided together with the first heat exchanger205. The propeller fan100A supplies air to the first heat exchanger205.

(Expansion Device213) The expansion device213expands refrigerant passing through the first heat exchanger205to decompress the refrigerant. The expansion device213is preferably, for example, an electric expansion valve that is adjustable in opening degree and that is able to adjust the flow rate of refrigerant, or other valves. The expansion device213is not limited to the electric expansion valve. A mechanical expansion valve that employs a diaphragm for a pressure receiving portion, a capillary tube, or other devices, may be applied as the expansion device213. The upstream of the expansion device213is connected to the first heat exchanger205, and the downstream of the expansion device213is connected to the second heat exchanger221.

(Second Heat Exchanger221) The second heat exchanger221performs the function of an evaporator. The second heat exchanger221evaporates refrigerant, decompressed by the expansion device213, into gaseous refrigerant. The upstream of the second heat exchanger221is connected to the expansion device213, and the downstream of the second heat exchanger221is connected to the compressor211. The second heat exchanger221may be, for example, a fin and tube heat exchanger, or other heat exchangers. A fan222, such as a propeller fan, is provided together with the second heat exchanger221. The fan222supplies air to the second heat exchanger221.

(Cooling Unit210) The compressor211, the first heat exchanger205, and the propeller fan100A are installed in the cooling unit210.

(Use-side Unit220) The expansion device213, the second heat exchanger221, and the fan222are installed in a use-side unit220. The expansion device213may be installed not in the use-side unit220but in the cooling unit210.

(Others) By providing a flow passage switching device for switching a refrigerant flow passage at a discharge side of the compressor211, the first heat exchanger205may be configured to perform the function of an evaporator and the second heat exchanger221may be configured to perform the function of a condenser.

The flow passage switching device may be, for example, a four-way valve, a combination of two two-way valves, or a combination of two three-way valves.

<Operation of Refrigeration Cycle Device200>

Next, the operation of the refrigeration cycle device200will be described in conjunction with flow of refrigerant.

By driving the compressor211, high-temperature high-pressure gaseous refrigerant is discharged from the compressor211. The high-temperature high-pressure gaseous refrigerant discharged from the compressor211flows into the first heat exchanger205. In the first heat exchanger205, heat is exchanged between the high-temperature high-pressure gaseous refrigerant flowed into the first heat exchanger205and air that is supplied by the propeller fan100A, and the high-temperature high-pressure gaseous refrigerant condenses into high-pressure liquid refrigerant.

The high-pressure liquid refrigerant sent out from the first heat exchanger205becomes two-phase refrigerant, that is, low-pressure gaseous refrigerant and liquid refrigerant, by the expansion device213. The two-phase refrigerant flows into the second heat exchanger221. In the second heat exchanger221, heat is exchanged between the two-phase refrigerant flowed into the second heat exchanger221and air that is supplied by the fan222, and the liquid refrigerant within the two-phase refrigerant evaporates into low-pressure gaseous refrigerant. The low-pressure gaseous refrigerant sent from the second heat exchanger221flows into the compressor211, the low-pressure gaseous refrigerant is compressed into high-temperature high-pressure gaseous refrigerant, and then the high-temperature high-pressure gaseous refrigerant is discharged from the compressor211. After that, this cycle is repeated.

As shown inFIG. 14andFIG. 15, the cooling unit210A is intended to be mounted on a vehicle, such as an electric train. The cooling unit210A includes a base201, the propeller fan100A, a casing204A, a motor206, and the first heat exchangers205.

The base201constitutes the bottom (surface for installing the motor206) and sides of the cooling unit210A.

The casing204A is provided on the base201so as to surround at least the propeller fan100A. The casing204A has a discharge portion202and suction portions203.

Where a z-axis is set such that an upward side in the direction of the normal to the base201is positive and an x-axis is set in a direction perpendicular to the z-axis, the discharge portion202is provided within a z-axis plane under the condition that z>0. That is, an opening above the propeller fan100A performs the function of the discharge portion202that is an air outlet port.

The suction portions203are provided on the base201so as to be opposed to each other in the x-axis direction. That is, openings in positions in which the first heat exchangers205are located perform the function of the suction portions203that are air inlet ports.

The first heat exchangers205exchange heat between refrigerant flowing through the refrigerant pipes (not shown) and air that is supplied by the propeller fan100A. The pair of first heat exchangers205is provided on the casing204A in proximity to the suction portions203.

The propeller fan100A is located upstream of the discharge portion202in the casing204A on the z-axis such that air flow is discharged toward the positive side of the z-axis. Specifically, the propeller fan100A is preferably provided directly below the discharge portion202. The propeller fan100A takes air into the casing204A via the suction portions203, and discharges air from the inside of the casing204A to the outside via the discharge portion202.

The motor206supports the propeller fan100A, and drives the propeller fan100A.

As shown inFIG. 15, in the cooling unit210A, an angle (an angle α shown inFIG. 15) formed by the normal to a discharge plane (a discharge plane A1shown inFIG. 15) of the discharge portion202and the normal to any one of suction planes (suction planes A2shown inFIG. 15) of the suction portions203is an acute angle. Therefore, in the cooling unit210A, flow of air inside the base201forms a substantially V shape (a substantially V shape or a substantially U shape) (air flow S3indicated by the arrows inFIG. 15). The discharge plane A1and the suction planes A2are imaginary planes.

In the thus configured cooling unit210A, since flow of air in an air passage inside the casing204A forms a substantially V shape (a substantially V shape or a substantially U shape), flow of air is complex, and turbulence of flow increases. For this reason, the effect of reducing turbulence resulting from the airfoil shape in the cross section of each blade2A of the propeller fan100A is remarkably obtained.

That is, as shown inFIG. 5of Embodiment 1, since the blade chord center line27is a curve having a convex on a downstream side in the entire region in the radial direction, air flow S2blowing out from each blade2A spreads in the radial direction. This reduces stagnation of flow downstream of the boss1to reduce the boss downstream vortex V1, and the outer peripheral end22of each blade2A has a shape along flow causing the blade tip vortex V2, so it is possible to reduce fluctuations in vortex by stabilizing the blade tip vortex V2. Thus, the effect of reducing turbulence resulting from the airfoil shape in the cross-sectional shape of each blade2A is maximally exercised further remarkably, so noise is reduced.

As shown inFIG. 16, a cooling unit210B is intended to be used as a heat source-side unit (outdoor unit). The cooling unit210B includes a casing204B, the propeller fan100A, the motor206, the first heat exchanger205, the compressor211shown inFIG. 13, and other devices. The casing204B constitutes an outer housing. The propeller fan100A is installed inside the casing204B. The motor206is installed inside the casing204B. The first heat exchanger205is installed inside the casing204B.

The casing204B is formed into a box shape, and air inlets are provided at at least two faces (for example, a side face and a back face). A separator250is provided inside the casing204B. An air-sending device chamber252in which the propeller fan100A is installed and a machine chamber251in which the compressor211, and other devices, are installed are partitioned by the separator250.

The first heat exchanger205is formed in an L shape in top plan view so as to be located on the side face and back face corresponding to the air inlets of the casing2046.

An opening through which air flows is perforated at a front face of the casing2046.

The propeller fan100A is driven for rotation by the motor206that is installed inside the casing204B.

With the thus configured cooling unit210B as well, as shown inFIG. 5of Embodiment 1, since the blade chord center line27is a downstream convex curve in the entire region in the radial direction, air flow S2blowing out from each blade2A spreads in the radial direction. This reduces stagnation of flow downstream of the boss1to reduce the boss downstream vortex V1, and the outer peripheral end22of each blade2A has a shape along flow causing the blade tip vortex V2, so it is possible to reduce fluctuations in vortex by stabilizing the blade tip vortex V2. Thus, the effect of reducing turbulence resulting from the airfoil shape in the cross-sectional shape of each blade2A is maximally exercised further remarkably, so noise can be reduced.

REFERENCE SIGNS LIST