US20200240430A1

US20200240430A1 - Propeller fan and axial flow blower

Info

Publication number: US20200240430A1
Application number: US16/643,647
Authority: US
Inventors: Toshikatsu Arai; Hitoshi Kikuchi; Chikage Kadoi
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2017-10-03
Filing date: 2017-10-03
Publication date: 2020-07-30
Also published as: TWI658215B; TW201915341A; JPWO2019069374A1; WO2019069374A1; JP6811873B2; CN111133201B; CN111133201A

Abstract

A stagger angle of a rotor blade has a first stagger angle distribution having a local minimum value in a region from an inner circumferential edge to a first boundary position, and has a second stagger angle distribution that increases toward an outer circumferential edge and follows an n-dimensional function using the radius of the rotor blade as a parameter in a region from the first boundary position to the outer circumferential edge, where n is a value ranging from 1 to 2 and exclusive of 1. This can limit the height of the outer circumferential portion, and can achieve a reduced noise level and higher efficiency.

Description

FIELD

The present invention relates to a propeller fan and to an axial flow blower for use in a ventilation fan, an air conditioner, and the like.

BACKGROUND

To achieve a reduced noise level, a rotor blade of a propeller fan of an axial flow blower has been improved to be swept forward in the rotation direction and to be inclined toward the upstream side of an airflow. In recent years, to achieve a further reduced noise level, it has been proposed that an outer circumferential part of a rotor blade be bent toward the upstream side of an airflow to reduce interference caused by blade tip vortex.
Patent Literature 1 describes that rotor blades are each inclined toward the upstream side at a certain first forward tilt angle in an inner circumferential portion of the rotor blade, while the rotor blades are each inclined toward the upstream side at a second forward tilt angle greater than the first forward tilt angle in an outer circumferential portion.
Patent Literature 2 describes that a stagger angle of the blade is linearly increased from the inner circumferential edge to the outer circumferential edge. Patent Literature 2 also describes that the stagger angle in an inner circumferential portion side has a distribution having a local minimum value, and the stagger angle in an outer circumferential portion side has a distribution having a local maximum value.
Patent Literature 3 describes that an angle of advance in an inner circumferential portion side of a rotor blade has a distribution of a quadratic function, while an angle of advance in an outer circumferential portion side thereof has a linear distribution.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Patent No. 4680840
Patent Literature 2: Japanese Patent No. 6005256
Patent Literature 3: Re-publication of PCT International Publication No. WO 2015/125306 A1

SUMMARY

Technical Problem

Setting of geometry parameters as described in Patent Literatures 1 to 3 enables a reduced noise level to be achieved and fan efficiency to be improved. Nevertheless, there has been a demand to change a geometry parameter based on which further improvement in performance can be achieved.
The present invention has been made in view of the foregoing circumstances, and it is an object of the present invention to provide a propeller fan and an axial flow blower that can further reduce the noise level and further improve the fan efficiency.

Solution to Problem

In order to solve the above-mentioned problems and achieve the object, the present invention provides a propeller fan including a boss portion that is driven rotationally, and more than one rotor blade radially attached to the boss portion to generate an airflow in a rotational axis direction, wherein a radial cross section of the rotor blade on an inner circumferential portion side of the rotor blade has a shape convex against a direction of the airflow, and a radial cross section of the rotor blade on an outer circumferential portion side of the rotor blade has a shape concave along the direction of the airflow, the radial cross section of the rotor blade is inclined toward an upstream side of the airflow in a leading edge side region with an inclination angle increasing toward a leading edge, and is inclined toward a downstream side of the airflow in a trailing edge side region with the inclination angle increasing toward a trailing edge, and a stagger angle of the rotor blade has a first stagger angle distribution having a local minimum value in a region from an inner circumferential edge to a first boundary position, and has a second stagger angle distribution that increases toward an outer circumferential edge and follows an n-dimensional function using a radius of the rotor blade as a parameter in a region from the first boundary position to the outer circumferential edge, where n is a value ranging from 1 to 2 and exclusive of 1.

Advantageous Effects of Invention

The present invention enables a rotor blade to have a shape suitable for an airflow over a region from an inner circumferential edge to an outer circumferential edge, and can thus reduce noise possibly caused by a blade tip vortex and improve fan efficiency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view illustrating an example of an axial flow blower.

FIG. 2 is a perspective view illustrating an example of a propeller fan.

FIG. 3 is a schematic view illustrating generation of a blade tip vortex.

FIG. 4 is a cross-sectional view of a rotor blade of the present embodiment, taken along a radial direction of the blade.

FIGS. 5A-5D are diagrams schematically illustrating a cross-sectional shape of a rotor blade of the present embodiment, a blade tip vortex, and a radial flow at a number of cross-sectional positions.

FIG. 6 is a diagram illustrating different cross-sectional positions.

FIG. 7 is a diagram illustrating a positional relationship between a rotor blade and a half bell mouth.

FIG. 8 is a diagram illustrating a positional relationship between a rotor blade and a full bell mouth.

FIG. 9 is a diagram illustrating a state of airflow to a rotor blade when a half bell mouth is used.

FIG. 10 is a diagram illustrating a state of airflow to a rotor blade when a full bell mouth is used.

FIG. 11 is a diagram for describing a definition of a stagger angle.

FIG. 12 is a diagram illustrating an example of a distribution of the stagger angle of a rotor blade of the present embodiment.

FIG. 13 is a diagram illustrating distributions of stagger angles of the rotor blades in Comparative Example 1 and Comparative Example 2.

FIG. 14 is a developed sectional view illustrating comparison between the stagger angle in Comparative Example 1 and the stagger angle in Comparative Example 2 in a first region.

FIG. 15 is a developed sectional view illustrating comparison between the stagger angle in Comparative Example 1 and the stagger angle in Comparative Example 2 in a second region.

FIG. 16 is a schematic view illustrating a rotor blade of Comparative Example 1.

FIG. 17 is a schematic view illustrating a rotor blade of Comparative Example 2.

FIG. 18 is a diagram for describing a definition of an angle of advance.

FIG. 19 is a graph illustrating an example of a distribution of an angle of advance of the rotor blade of the present embodiment.

FIG. 20 is a plan view illustrating a blade shape of Comparative Example 3 when an increase rate in the angle of advance is lower.

FIG. 21 is a plan view illustrating a blade shape of Comparative Example 3 when an increase rate in the angle of advance is higher.

FIG. 22 is a plan view illustrating a rotor blade of the present embodiment.

FIG. 23 is a diagram for describing a definition of a forward tilt angle.

FIG. 24 is a diagram illustrating a chord center line of a rotor blade of the present embodiment.

FIG. 25 is a graph illustrating an example of a distribution of a forward tilt angle of a rotor blade of the present embodiment.

FIGS. 26A-26C are diagrams illustrating a fan efficiency characteristic, a specific noise characteristic, and a static pressure characteristic of a rotor blade of Example 1, Example 2, and Comparative Example 5 in a case of use of a half bell mouth.

FIGS. 27A-27C are diagrams illustrating a fan efficiency characteristic, a specific noise characteristic, and a static pressure characteristic of a rotor blade of Example 1, Example 2, and Comparative Example 5 in a case of use of a full bell mouth.

FIGS. 28A-28C are diagrams illustrating a fan efficiency characteristic, a specific noise characteristic, and a static pressure characteristic of a rotor blade of Example 1, Example 3, and Comparative Example 5 in a case of use of a half bell mouth.

FIGS. 29A-29C are diagrams illustrating a fan efficiency characteristic, a specific noise characteristic, and a static pressure characteristic of a rotor blade of Example 1, Example 3, and Comparative Example 5 in a case of use of a full bell mouth.

FIG. 30 is a graph illustrating relationships between the degree of the forward tilt angle distribution function and the specific noise level in Example 1 and Comparative Example 5 in a case of use of a half bell mouth.

FIG. 31 is a graph illustrating relationships between the degree of the forward tilt angle distribution function and the fan efficiency in Example 1 and Comparative Example 5 in a case of use of a half bell mouth.

FIG. 32 is a graph illustrating relationships between the degree of the forward tilt angle distribution function and the minimum specific noise level in Example 1 and Comparative Example 5 in a case of use of a half bell mouth.

FIG. 33 is a graph illustrating relationships between the degree of the forward tilt angle distribution function and the maximum fan efficiency in Example 1 and Comparative Example 5 in a case of use of a half bell mouth.

FIG. 34 is a graph illustrating relationships between the degree of the forward tilt angle distribution function and the specific noise level in Example 1 and Comparative Example 5 in a case of use of a full bell mouth.

FIG. 35 is a graph illustrating relationships between the degree of the forward tilt angle distribution function and the fan efficiency in Example 1 and Comparative Example 5 in a case of use of a full bell mouth.

FIG. 36 is a graph illustrating relationships between the degree of the forward tilt angle distribution function and the minimum specific noise level in Example 1 and Comparative Example 5 in a case of use of a full bell mouth.

FIG. 37 is a graph illustrating relationships between the degree of the forward tilt angle distribution function and the maximum fan efficiency in Example 1 and Comparative Example 5 in a case of use of a full bell mouth.

DESCRIPTION OF EMBODIMENT

A propeller fan and an axial flow blower according to an embodiment of the present invention will be described in detail below with reference to the drawings. Note that this embodiment is not intended to necessarily limit the scope of this invention.
Embodiment.
FIG. 1 is a perspective view illustrating an example of an axial flow blower 100 according to an embodiment. FIG. 2 is a perspective view illustrating an example of a propeller fan 10 according to the embodiment. The axial flow blower 100 includes the propeller fan 10, a body 20, a bell mouth 30, a motor (not illustrated), and a motor fixing member (not illustrated). The propeller fan 10 and the motor are disposed inside the bell mouth 30. The propeller fan 10 includes a boss portion 2 having a cylindrical shape, and multiple rotor blades 1 having equal three-dimensional shapes.
The boss portion 2 is rotationally driven by the motor to rotate about a rotational axis O in a direction of an arrow W. Each of the rotor blades 1 is radially attached to an outer periphery of the boss portion 2. The rotor blade 1 includes: a leading edge 1 a that is a front edge portion in the rotation direction W; a trailing edge 1 b that is a rear edge portion in the rotation direction W; an inner circumferential edge 1 c that is an edge portion on the inner circumferential side (nearer to the boss portion 2); and an outer circumferential edge 1 d that is an edge portion on the outer circumferential side. Rotation of the propeller fan 10 causes the rotor blades 1 to generate an airflow in a direction of an arrow A. FIG. 1 illustrates five of the rotor blades 1, and FIG. 2 illustrates three of the rotor blades 1. As the number of rotor blades 1, any other number can also be adopted.
FIG. 3 illustrates one of the impeller blades 1 of the propeller fan 10. When an airflow in the arrow A direction is generated by rotation of the propeller fan 10, a pressure difference is caused between the blade pressure surface and the blade negative pressure surface of the rotor blade 1. As illustrated in FIG. 3, this leads to a leakage vortex from the blade pressure surface subject to a higher pressure to the blade negative pressure surface subject to a lower pressure, in an outer circumferential portion of the rotor blade 1. This vortex is referred to as a blade tip vortex 5. As illustrated in FIG. 4, the upstream blade surface is a negative pressure surface if subject to the lower pressure, and the downstream surface is a pressure surface 1 g subject to a higher pressure with respect to the airflow direction A. Note that in the following description, the rotational axis O is designated Z-axis, and two axes perpendicular to the Z-axis are designated X-axis and Y-axis.
FIG. 4 is a cross-sectional view illustrating the shape, along the radial direction, of the rotor blade 1 according to the embodiment. The rotor blade 1 has a radial cross section that is convex against the airflow direction A near the boss portion 2, and is concave in the airflow direction A in an outer circumferential portion. In other words, the rotor blade 1 has a vertex portion m1 having a convex shape on an inner circumferential portion side, and a vertex portion m2 having a concave shape on an outer circumferential portion side. Thus, a cross section of the rotor blade 1 has an S-shape that is convex with respect to the airflow in an inner circumferential portion, and is concave with respect to the airflow in an outer circumferential portion.
The rotor blade 1 also has a radial cross-sectional shape changing over the region from the leading edge 1 a to the trailing edge 1 b. Specifically, in a leading edge region, the rotor blade 1 is inclined toward upstream of the airflow direction A so that an inclination angle θ increases toward the leading edge 1 a. In a trailing edge region, the rotor blade 1 is inclined toward downstream of the airflow direction A so that the inclination angle θ increases toward the trailing edge 1 b. FIGS. 5A to 5D are diagrams schematically illustrating the blade shape, a blade tip vortex, and a radial flow in the radial cross section of the rotor blade 1 according to the embodiment. FIG. 5A illustrates the cross-sectional shape taken along a line O-D1 in FIG. 6. FIG. 5B illustrates the cross-sectional shape taken along a line O-D2 in FIG. 6. FIG. 5C illustrates the cross-sectional shape taken along line O-D3 in FIG. 6. FIG. 5D illustrates the cross-sectional shape taken along line O-D4 in FIG. 6. Note that, in FIG. 6, the line O-D 1 is a line resulting from extending a line connecting the rotational axis O and a rear end Fr of the leading edge 1 a to the outer circumferential edge 1 d; and the line O-D 4 is a line connecting the rotational axis O and a front end Rf of the trailing edge 1 b.
As illustrated in the O-D 1 cross section and in the O-D 2 cross section, a leading edge region of the rotor blade 1, which is an area nearer to the leading edge 1 a than a blade center C, is inclined toward upstream of the airflow A, and the inclination angle θ(O-D1) in the O-D 1 cross section is greater than the inclination angle θ(O-D2) in the O-D 2 cross section. In other words, in the leading edge region, the inclination angle θ increases toward the leading edge 1 a. The blade center C corresponds to a bisector of an angle formed between the lines O-D1 and O-D 4. Note that FIGS. 5A-5D illustrate the inclination angle θ as an angle formed between a line segment connecting the inner circumferential edge 1 c and the vertex portion m2 on the outer circumferential side, and the XY-plane. The leading edge region of the rotor blade 1 has a shape adaptable to the blade tip vortex 5 and to a lateral sink flow 9 toward the blade outer circumferential portion.
As illustrated in the O-D 3 cross section and in the O-D 4 cross section, a trailing edge region of the rotor blade 1, which is a region nearer to the trailing edge 1 b than the blade center C, is inclined toward downstream of the airflow A, and the inclination angle θ(O-D4) in the O-D 4 cross section is greater than the inclination angle θ(O-D3) in the O-D 3 cross section. In other words, in the trailing edge region, the inclination angle θ increases toward the trailing edge 1 b. As described above, the trailing edge region of the rotor blade 1 has a shape such that the blade tip vortex 5 is controlled, and also a centrifugal component 14 of a flow on the inner circumferential portion side, which has been subject to a raised pressure, is prevented from leaking, thereby preventing reduction in efficiency.
In addition, in the rotor blade 1 according to the embodiment, a curvature radius value R2 in an outer concave portion that is a region from the vertex portion m2 in the outer circumferential portion to the outer circumferential edge 1 d has a distribution that gradually decreases from the leading edge 1 a toward the trailing edge 1 b. In other words, a relationship of R2(O-D1)>R2(O-D2)>R2(O-D3)>R2(O-D4) holds. In addition, the curvature radius value R2 gradually decreases at a rate that decreases toward the trailing edge 1 b.
As described above, the rotor blade 1 according to the embodiment illustrated in FIGS. 4 and 5 has a shape that allows the blade tip vortex 5 generated in an outer circumferential portion to smoothly leave from the blade surface, and allows the blade tip vortex 5 to be dispersed without concentration. In this way, the rotor blade 1 reduces turbulence caused by the blade tip vortex 5, thereby making it possible to curb generation of noise.
The propeller fan 10 is disposed in an inner part of the bell mouth 30, which surrounds the propeller fan to pressurize and regulate the airflow. FIG. 7 is a schematic cross-sectional view of an axial flow blower that uses the rotor blade 1 and a half bell mouth 30 a. The half bell mouth 30 a surrounds the rotor blades 1 with allowing a region including the leading edge 1 a to be open. FIG. 8 is a schematic cross-sectional view of an axial flow blower that uses the rotor blade 1 and a full bell mouth 30 b. The full bell mouth 30 b surrounds the rotor blades 1 circumferentially to entirely cover a side face of the rotor blade 1. The half bell mouth 30 a and the full bell mouth 30 b both have an inlet curved surface Rin, a straight part ST having a cylindrical shape, and an outlet curved surface Rout.
FIG. 9 is a diagram illustrating a distribution of an airflow of the axial flow blower that uses the rotor blade 1 and the half bell mouth 30 a. The axial flow blower including the half bell mouth 30 a is configured such that the region including the leading edge 1 a of the rotor blade 1 is widely open. This allows the lateral sink flow 9 and a passing-through-blade flow 11 directed from the leading edge 1 a toward the trailing edge 1 b to flow onto the rotor blade 1. For this reason, the blade tip vortex 5 grows large from the leading edge 1 a side of the rotor blade 1. In addition, a condition of the passing-through-blade flow 11 is changed from the leading edge 1 a to the trailing edge 1 b, so that the blade tip vortex 5 is subjected to significantly different conditions depending on the axial positions.
FIG. 10 is a diagram illustrating a distribution of an airflow of the axial flow blower that uses the rotor blade 1 and the full bell mouth 30 b. The axial flow blower having the full bell mouth 30 b is configured such that the region including the leading edge 1 a is open to a very limited extent, thereby almost eliminating the lateral sink flow 9. Thus, almost only the passing-through-blade flow 11 flows toward the rotor blade 1. Accordingly, the blade tip vortex 5 does not start to be generated from the leading edge 1 a, but starts to be generated from a point where the pressurization has been initiated to some extent.
As described above, even if the same rotor blades 1 are used, a location of the blade tip vortex 5 is changed depending on the shape of a bell mouth used therefor.
The two types of bell mouths, i.e., the half bell mouth 30 a and the full bell mouth 30 b may be used in one and the same product. In this case, if a rotor blade is designed specifically for each of the types, the cost for the rotor blades is doubled. In the circumstances, the same type of rotor blades are used even with different bell mouth types, and therefore, what is required is a rotor blade that can achieve a low noise level and high efficiency blowing even with different bell mouth types.
In response, the present embodiment defines a stagger angle, an angle of advance, and a forward tilt angle among the geometry parameters for forming the rotor blade 1 for each of a first region that is an inner circumferential region and a second region that is an outer circumferential region, which are obtained by division of a region from the inner circumferential edge 1 c to the outer circumferential edge 1 d of the rotor blade 1, to propose a shape of the first region and a shape of the second region that can achieve a reduced noise level and improvement in fan efficiency.
First of all, a stagger angle ξ of the present embodiment will be described. FIG. 11 is a developed sectional view of the rotor blade 1 taken along an arc 6-6′ having an arbitrary radius illustrated in FIG. 6, in which the cylindrical surface along the arc 6-6′ is developed on a plane. The stagger angle ξ is an angle formed between a chord line 41 and a line segment 42. The chord line 41 is a line connecting the leading edge 1 a on a cross-sectional surface 40 of the rotor blade 1 and the trailing edge 1 b on the said cross-sectional surface 40. The line segment 42 is a line that is parallel with the said rotational axis O and intersects the leading edge 1 a.
FIG. 12 is a diagram illustrating an example of a distribution of the stagger angle ξ of the present embodiment. In FIG. 12, the horizontal axis corresponds to a radius R of the rotor blade 1, and the vertical axis represents the stagger angle ξ. In FIG. 12, the solid line Ls represents the distribution of the stagger angle ξ in the present embodiment, while the broken line Lv1 represents the distribution of the stagger angle ξ in Comparative Example 1. The left end of the line segment Ls represents a stagger angle ξc at a radial position Rc of the inner circumferential edge 1 c connected to the boss portion 2, and the right end of the line segment Ls represents a stagger angle ξd at a radial position Rd of the outer circumferential edge 1 d. The stagger angle ξ of the present embodiment has a first stagger angle distribution Ls1 in a first region AR1 from the radial position Rc to a boundary position Re1, and has a second stagger angle distribution Ls2 different from the first stagger angle distribution Ls1 in a second region AR2 from the boundary position Re1 to the radial position Rd.
The first stagger angle distribution Ls1 has a local minimum value ξmin at a position Rmin near the boundary position Re1. The position Rmin is between the midpoint of the first region AR1 and the boundary position Re1. The first stagger angle distribution Ls1 has a distribution such that the stagger angle ξ gradually decreases from the radial position Rc toward the radial position Rmin and the stagger angle ξ gradually increases from the radial position Rmin toward the boundary position Re1. The second stagger angle distribution Ls2 has a distribution such that the stagger angle ξ gradually increases so that the distribution Ls2 smoothly connects with the first stagger angle distribution Ls1. The second stagger angle distribution Ls2 has a distribution defined by a linear to quadratic function using the radius R as a parameter. Note that the second stagger angle distribution Ls2 does not cover a linear function. The second stagger angle distribution Ls2 is defined as a function that is convex downward. The second stagger angle distribution Ls2 illustrated in FIG. 12 follows a 1.2-dimensional function. Setting is made such that the second stagger angle distribution Ls2 has a higher absolute value of an increase rate than that of the decrease rate of the first stagger angle distribution Ls1.
FIG. 13 is a diagram illustrating the distribution Lv1 of the stagger angle ξ in Comparative Example 1 and the distribution Lv2 of the stagger angle ξ in Comparative Example 2. Comparative Example 1 and Comparative Example 2 are described in Patent Literature 2. The distribution Lv1 is such that the stagger angle ξ increases linearly (in a manner of a linear function) at a constant increase rate. The distribution Lv2 has, similarly to the stagger angle ξ of the present embodiment, a distribution in a first region AR1′ from the radial position Rc of the inner circumferential edge 1 c to a boundary position Re′, and a distribution in a second region AR2′ from the boundary position Re′ to the radial position Rd of the outer circumferential edge 1 d. In the first region AR1′, the stagger angle ξ gradually decreases in the form of a curved line from the radial position Rc to the radial position Re′, and has a local minimum value at the radial position Re′. The stagger angle ξ at the radial position Rc has the maximum value of the stagger angle ξ over the entire range of the rotor blade 1. In the second region AR2′, the stagger angle ξ gradually increases from the boundary position Re′ and reaches a local maximum value, and gradually decreases from the radial position of the local maximum value toward the radial position Rd.
FIG. 14 is a developed sectional view illustrating comparison between the stagger angle in Comparative Example 1 and the stagger angle in Comparative Example 2 in the first region AR1′. FIG. 14 is a view of the rotor blades of Comparative Example 1 and Comparative Example 2 taken at the radius R1′ illustrated in FIG. 13, in which a cylindrical surface on the cross section is developed on a plane. The broken line 43 corresponds to Comparative Example 1, and the bold solid line 44 corresponds to Comparative Example 2. The reference character ξ_R11represents the stagger angle at the radius R1′ in Comparative Example 1, and the reference character ξ_R12represents the stagger angle at the radius R1′ in Comparative Example 2. FIG. 14 shows that in the first region AR1′, the blade is less inclined in Comparative Example 2 than in Comparative Example 1.
FIG. 15 is a developed sectional view illustrating comparison between the stagger angle in Comparative Example 1 and the stagger angle in Comparative Example 2 in the second region AR2′. FIG. 15 is a view of the rotor blades of Comparative Example 1 and Comparative Example 2 taken at the radius R2′ illustrated in FIG. 13, in which the cylindrical surface on the cross section is developed on a plane. The broken line 45 corresponds to Comparative Example 1, and the bold solid line 46 corresponds to Comparative Example 2. The reference character ξ_R21represents the stagger angle at the radius R2′ in Comparative Example 1, and the reference character ξ_R22represents the stagger angle at the radius R2′ in Comparative Example 2. FIG. 15 shows that in the second region AR2′, the blade is more inclined in Comparative Example 2 than in Comparative Example 1.
FIG. 16 is a schematic view illustrating the rotor blade of Comparative Example 1. FIG. 17 is a schematic view illustrating the rotor blade of Comparative Example 2. As illustrated in FIGS. 16 and 17, a blade height H2 of Comparative Example 2 is greater than a blade height H1 of Comparative Example 1 at the outer circumferential edge.
As described above, by use of the stagger angle distribution as in Comparative Example 2, the blade angle is set to an appropriate value for a flow in each of a high flow rate region and a low flow rate region, thereby resulting in a reduced noise level and higher efficiency. However, as illustrated in FIG. 17, the blade height is larger in an outer circumferential portion. This will present no problem with a product having enough margin space in the height direction, but when a further reduced height is required, it will be difficult to use a stagger angle distribution as shown in Comparative Example 2.
In the circumstances, the present embodiment uses the stagger angle distribution as illustrated in FIG. 12 to thereby make it possible to limit the height of the outer circumferential portion that can cause increase in height of a product and to also make the stagger angle distribution more appropriate. The blade in the present embodiment has a shape that is similar to the shape in Comparative Example 1 on the outer circumferential portion side and similar to the shape in Comparative Example 2 on the inner circumferential portion side. Therefore, the present embodiment can limit the height of the outer circumferential portion, and match the angle of the blade with the angle of the flow. This can reduce leading edge separation and trailing vortex loss of the blade, and can thus achieve a reduced noise level and higher efficiency. Moreover, the use of a distribution having a local minimum value in the first region AR1 where a flow rate is lower enables the stagger angle in the second region AR2 to be adjusted, and also enables the first region AR1 to smoothly connect with the second region AR2.
Next, an angle of advance δ_θ in the present embodiment will be described. FIG. 18 is a plan view for describing the angle of advance δ_θ. In FIG. 18, the reference character g designates the chord center line. The chord center line g is a line that connects the midpoints between the leading edge 1 a and the trailing edge 1 b at every radial position from the inner circumferential edge 1 c to the outer circumferential edge 1 d. An angle formed between a straight line 51 connecting the rotational axis O and the said midpoint 52 on the inner circumferential edge 1 c, and a straight line 54 connecting an intersection point 53 between an arc on an arbitrary radius and the chord center line g and the rotational axis O is defined as an angle of advance δ_θ.
FIG. 19 is a graph illustrating an example of a distribution of the angle of advance δ_θ in the present embodiment, and a distribution of the angle of advance δ_θ of Comparative Example 3. The solid line corresponds to the present embodiment, and the broken line corresponds to Comparative Example 3. In the case of Comparative Example 3, the angle of advance δ_θ linearly increases from the inner circumferential edge 1 c to the outer circumferential edge 1 d. As illustrated in FIG. 18, use of the distribution of Comparative Example 3 causes the outer circumferential portion to have a delta wing shape. A delta wing shape causes a separation vortex to be generated from the delta wing portion, and the generated separation vortex can reduce or prevent generation of a leading edge separation vortex and a blade tip vortex, thereby making it possible to achieve a reduced noise level.
FIG. 20 is a diagram illustrating the blade shape in Comparative Example 3 when an increase rate of the angle of advance is low. FIG. 21 is a diagram illustrating the blade shape in Comparative Example 3 when an increase rate of the angle of advance is greater than the increase rate of FIG. 20. The length of the inner circumferential edge 1 c in FIG. 20 is the same as the length of the inner circumferential edge 1 c in FIG. 21. In addition, the length of the outer circumferential edge 1 d in FIG. 20 is the same as the length of the outer circumferential edge 1 d in FIG. 21. The angle of advance δ _θ 2 on the outer circumferential edge 1 d in FIG. 21 is greater than the angle of advance δ _θ 1 on the outer circumferential edge 1 d in FIG. 20.
As illustrated in FIG. 21, use of a linear distribution in which an increase rate of the angle of advance δ_θ is higher can achieve a further reduced noise level than the case of FIG. 20, but leads to a problem such as insufficient strength of a root part of the blade, so that a large angle of advance cannot be set for the outer circumferential portion.
As illustrated by the solid line of FIG. 19, the angle of advance of the rotor blade according to the present embodiment has different distributions in the first region AR1 and in the second region AR2. The first region AR1 is an area from the radius Rc corresponding to the inner circumferential edge 1 c to a boundary position Re2. The second region AR2 is an area from the boundary position Re2 to the outer circumferential edge 1 d. The angle of advance δ_θ has, in the first region AR1, a linear distribution that gradually increases from the radial position Rc toward the boundary position Re2. The angle of advance δ_θ has, in the second region AR2, a linear to quadratic function distribution that gradually increases from the boundary position Re2 toward the radial position Rd. In other words, the angle of advance δ_θ in the second region AR2 follows a linear to quadratic function using the radius R as a parameter. Note that the angle of advance δ_θ in the second region AR2 does not cover a linear function. The angle of advance δ_θ in the second region AR2 is defined as a linear to quadratic function that is convex downward. FIG. 19 shows a 1.2-dimensional function as a distribution function in the second region AR2. The linear distribution in the first region AR1 smoothly connects with a distribution of the 1.2-dimensional function in the second region AR2. The distribution of the angle of advance δ_θ in the second region AR2 desirably has an increase rate higher than the increase rate of the distribution of the angle of advance δ_θ in the first region AR1.
FIG. 22 illustrates an example of the shape of the rotor blade in the case of use of the angle-of-advance distribution according to the present embodiment illustrated in FIG. 19. Use of the angle-of-advance distribution according to the present embodiment enables a delta wing shape to be ensured for reducing the noise level in the blade outer circumferential portion, and an area of the blade to be increased in the blade inner circumferential portion thereby to increase the strength of the blade root portion.
Next, a forward tilt angle δz of the present embodiment will be described. FIG. 23 is a diagram for describing a definition of a forward tilt angle δz. FIG. 23 is a revolved projection of a rotor blade having a constant forward tilt angle δz projected onto the plane including the rotational axis O and the X-axis. The forward tilt angle δz is an angle formed between a chord center line g′ and a plane perpendicular to the rotational axis O of the rotor blade 1. A direction toward the upstream side of the flow is defined as positive for the angle δz. FIG. 24 is a diagram illustrating the chord center line g of the rotor blade 1 according to the present embodiment in which the blade outer circumferential portion is bent toward the upstream direction side of the flow, and shows a revolved projection of the rotor blade projected onto the plane including the rotational axis O and the X-axis.
FIG. 25 is a graph illustrating an example of a distribution of the forward tilt angle δz of the present embodiment, and a distribution of the forward tilt angle δz of Comparative Example 4. The solid line corresponds to the present embodiment, and the broken line corresponds to Comparative Example 4. Comparative Example 4 is described in Patent Literature 1. In Comparative Example 4 and in the present embodiment, the forward tilt angle δz has a distribution in the first region AR1 from the radial position Rc of the inner circumferential edge 1 c to a boundary position Re3, and a distribution in the second region AR2 from the boundary position Re3 to the radial position Rd of the outer circumferential edge 1 d.
In Comparative Example 4, the forward tilt angle δz has a constant value δz1 in the first region AR1, and the forward tilt angle δz has a distribution with further inclination toward an upstream side of the flow in the second region AR2 so as to follow an n-dimensional function (1≤n) using the radius R as a parameter. By use of a forward tilt angle distribution as shown in Comparative Example 4, the blade tip vortex generated on the blade outer circumferential portion can be controlled and turbulence caused by the blade tip vortex can be reduced, and thus making it possible to reduce a noise level.
In this regard, in the present embodiment, the forward tilt angle δz has a constant value δz1 in the first region AR1 similarly to Comparative Example 4, while the forward tilt angle δz in the second region AR2 follows a distribution based on a quadratic to quintic function using the radius R as a parameter, thereby achieving a further reduced noise level. In FIG. 25, in the second region AR2, of Comparative Example 4 is shown as following a quadratic function, and the present embodiment is shown as following a cubic function. Of quadratic to quintic functions, quadratic to cubic functions are particularly suitable.
Referring to FIGS. 26 to 37, results of evaluation of the rotor blade of the present embodiment will be described. FIGS. 26 to 37 illustrate evaluation results when rotor blades having a diameter of 260 (mm) are rotated at a constant rotational speed. The specific noise level Kt with a total pressure as a reference, the specific noise level Ks with a static pressure as a reference, the fan efficiency Et with a total pressure as a reference, and the fan efficiency Es with a static pressure as a reference, which are used in FIGS. 26 to 37 are calculated values defined by the following expressions.
Kt=SPLA−10 Log(Q·PT ^2.5)
Q: airflow rate [m³/min]
PT: total pressure [Pa]
SPLA: noise characteristic (after Correction A) [dB]
Ks=SPLA−10 Log(Q·PS ^2.5)
Q: airflow rate [m³/min]
PS: static pressure [Pa]
SPLA: noise characteristic (after Correction A) [dB]
Et=(PT·Q)/(60·PW)
Q: airflow rate [m³/min]
PT: total pressure [Pa]
PW: shaft power [W]
Es=(PS·Q)/(60·PW)
Q: airflow rate [m³/min]
PS: static pressure [Pa]
PW: shaft power [W]
Note that Correction A refers to correction to reduce the sound level at low frequencies to fit the characteristics of human auditory sense, and corresponds to, for example, correction based on Characteristic A determined in JIS C 1502-1990.
FIGS. 26A to 26C are diagrams illustrating different kinds of characteristics of the rotor blade of Comparative Example 5, the rotor blade of Example 1 in the embodiment, and the rotor blade of Example 2 in the embodiment in the case of use of the half bell mouth 30 a illustrated in FIG. 7. Comparative Example 5 is represented by the broken line. The embodiment's Example 1 is represented by the solid line. The embodiment's Example 2 is represented by the dashed-and-dotted line. FIG. 26A illustrates relationships between the fan efficiency Es and the airflow rate. FIG. 26B illustrates relationships between the specific noise level Kt and the airflow rate. FIG. 26C illustrates relationships between the static pressure PS and the airflow rate. The rotor blade of Comparative Example 5 has the rotor blade shape illustrated in FIGS. 4 and 5, has the stagger angle distribution Lv1 represented by the broken line in FIG. 12, has the angle-of-advance distribution represented by the broken line in FIG. 19, and has the forward tilt angle distribution represented by the broken line in FIG. 25. The rotor blade of the embodiment's Example 1 and the rotor blade of the embodiment's Example 2 each correspond to the rotor blade illustrated in FIGS. 4 and 5, have the stagger angle distribution represented by the solid line in FIG. 12, have the angle-of-advance distribution represented by the solid line in FIG. 19, and have the forward tilt angle distribution represented by the solid line in FIG. 25. The rotor blade of Example 1 has, in the second region AR2, a stagger angle distribution that follows a 1.2-dimensional function being set, has, in the second region AR2, a angle-of-advance distribution that follows a 1.2-dimensional function being set, and has, in the second region AR2, a forward tilt angle distribution that follows a 3-dimensional function being set. The rotor blade of Example 2 has, in the second region AR2, a stagger angle distribution that follows a 2-dimensional function being set, has, in the second region AR2, a angle-of-advance distribution that follows a 2-dimensional function being set, and has, in the second region AR2, a forward tilt angle distribution that follows a 3-dimensional function being set.
In the case of use of the half bell mouth 30 a, the rotor blades of Examples 1 and 2 in the embodiment enable, as illustrated in FIG. 26C, an open airflow rate at the open point corresponding to [static pressure=0] to be improved by +2(%), and the static pressure to be improved by up to +7.8(%) as compared to Comparative Example 5. In addition, as illustrated in FIG. 26A, the fan efficiency Es can be improved by up to +3.5 points. Moreover, as illustrated in FIG. 26B, the specific noise level Kt can be improved by up to −1 (dB).
FIGS. 27A to 27C are diagrams illustrating different kinds of characteristics of the rotor blade of Comparative Example 5 described above, the rotor blade of Example 1 in the embodiment described above, and the rotor blade of Example 2 in the embodiment described above in the case of use of the full bell mouth 30 b illustrated in FIG. 8. Comparative Example 5 is shown by the broken line. The embodiment's Example 1 is shown by the solid line. The embodiment's Example 2 is shown by the dashed-and-dotted line. FIG. 27A illustrates relationships between the fan efficiency Es and the airflow rate. FIG. 27B illustrates relationships between the specific noise level Kt and the airflow rate. FIG. 27C illustrates relationships between the static pressure PS and the airflow rate.
In the case of use of the full bell mouth 30 b, the rotor blades of Examples 1 and 2 in the embodiment enable, as illustrated in FIG. 27C, an open airflow rate to be improved by +3.6(%) and a static pressure to be improved by up to +7.8(%) as compared to Comparative Example 5. In addition, as illustrated in FIG. 27A, the fan efficiency Es can be improved by up to +7 points. Moreover, as illustrated in FIG. 27B, the specific noise level Kt can be improved by up to −1.5 (dB).
The evaluation results of FIGS. 26 and 27 indicate that the rotor blades of Examples 1 and 2 enable the blowing characteristic, the noise characteristic, and the fan efficiency characteristic to be improved irrespective of the form of a bell mouth used therein.
FIGS. 28A to 28C are diagrams illustrating different kinds of characteristics of the rotor blade of Comparative Example 5 described above, the rotor blade of Example 1 in the embodiment described above, and the rotor blade of Example 3 in the embodiment in the case of use of the half bell mouth 30 a illustrated in FIG. 7. Comparative Example 5 is shown by the broken line. The embodiment's Example 1 is shown by the solid line. The embodiment's Example 3 is represented by the dashed-and-dotted line. FIG. 28A illustrates relationships between the fan efficiency Es and the airflow rate. FIG. 28B illustrates relationships between the specific noise level Kt and the airflow rate. FIG. 28C illustrates relationships between the static pressure PS and the airflow rate. Similarly to the rotor blades of Examples 1 and 2 in the embodiment, the rotor blade of Example 3 in the embodiment has a rotor blade shape illustrated in FIGS. 4 and 5, has the stagger angle distribution represented by the solid line in FIG. 12, has the angle-of-advance distribution represented by the solid line in FIG. 19, and has the forward tilt angle distribution represented by the solid line in FIG. 25. The rotor blade of the embodiment's Example 3 has, in the second region AR2, a stagger angle distribution that follows a function to be set having a degree of 1.2, has, in the second region AR2, a angle-of-advance distribution that follows a function to be set having a degree of 1.2, and has, in the second region AR2, a forward tilt angle distribution that follows a function to be set having a degree of 4.
In the case of use of the half bell mouth 30 a, the rotor blade of Example 3 enables, as illustrated in FIG. 28C, the open airflow rate to be improved by +2.2(%) and the static pressure to be improved by up to +5.9(%) as compared to Comparative Example 5. In addition, as illustrated in FIG. 28A, the fan efficiency Es can be improved by up to +4 points. Moreover, as illustrated in FIG. 28B, the specific noise level Kt can be improved by up to −3 (dB).
FIGS. 29A to 29C are diagrams illustrating different kinds of characteristics of the rotor blade of Comparative Example 5 described above, the rotor blade of Example 1 in the embodiment described above, and the rotor blade of Example 3 in the embodiment described above in the case of use of the full bell mouth 30 b illustrated in FIG. 8. Comparative Example 5 is shown by the broken line. The embodiment's Example 1 is shown by the solid line. The embodiment's Example 3 is shown by the dashed-and-dotted line. FIG. 29A illustrates relationships between the fan efficiency Es and the airflow rate. FIG. 29B illustrates relationships between the specific noise level Kt and the airflow rate. FIG. 29C illustrates relationships between the static pressure PS and the airflow rate.
In the case of use of the full bell mouth 30 b, the rotor blade of Example 3 in the embodiment enables, as illustrated in FIG. 29C, the open airflow rate to be improved by +3(%) and the static pressure to be improved by up to +6.9(%) as compared to Comparative Example 5. In addition, as illustrated in FIG. 29A, the fan efficiency Es can be improved by up to +12 points. Moreover, as illustrated in FIG. 29B, the specific noise level Kt can be improved by up to −2 (dB).
The evaluation results of FIGS. 28 and 29 indicate that the rotor blade of Example 3 enables the blowing characteristic, the noise characteristic, and the fan efficiency characteristic to be improved irrespective of the form of a bell mouth used therefor.
Next, referring to FIGS. 30 to 37, the degree of the forward tilt of the rotor blade of Example 1 in the embodiment will be described. FIG. 30 is a graph illustrating the specific noise characteristics at the open point of the rotor blade of Comparative Example 5 described above and the rotor blade of the embodiment's Example 1 described above in the case of use of the half bell mouth 30 a illustrated in FIG. 7. FIG. 30 illustrates the relationships between the degree of the function used for the forward tilt angle distribution in the second region AR2 and the specific noise level Kt at the open point. The degree has been changed from 1.2 to 5. Note that the forward tilt angle distribution in the second region AR2 for the rotor blade of Comparative Example 5 follows a quadratic function as described above. As illustrated in FIG. 30, the rotor blade of the embodiment's Example 1 exhibits a specific noise level Kt higher than that of Comparative Example 5 when the degree is 1.2, but a specific noise level Kt improved as compared to Comparative Example 5 in the range of degree from 2 to 7.
FIG. 31 is a graph illustrating the fan efficiency characteristics at the open point of the rotor blade of Comparative Example 5 described above and the rotor blade of the embodiment's Example 1 described above in the case of use of the half bell mouth 30 a illustrated in FIG. 7. FIG. 31 illustrates the relationships between the degree of the function used for the forward tilt angle distribution in the second region AR2 and the fan efficiency Et at the open point. The degree has been changed from 1.2 to 5. As illustrated in FIG. 31, the rotor blade of the embodiment's Example 1 exhibits a fan efficiency Et improved as compared to Comparative Example 5 in terms of all the degrees.
FIG. 32 is a graph illustrating the minimum specific noise characteristics at the time of application of static pressure of the rotor blade of Comparative Example 5 described above and the rotor blade of the embodiment Example 1 described above in the case of use of the half bell mouth 30 a illustrated in FIG. 7. FIG. 32 illustrates the relationships between the degree of the function used for the forward tilt angle distribution in the second region AR2 and the minimum specific noise level Ks at the time of application of static pressure. The degree has been changed from 1.2 to 5. As illustrated in FIG. 32, the specific noise level Ks is higher than that of Comparative Example 5 when the degree is 1.2, but the specific noise level Ks is improved as compared to Comparative Example 5 in the range of degree from 2 to 5.
FIG. 33 is a graph illustrating the maximum fan efficiency characteristics of the rotor blade of Comparative Example 5 described above and the rotor blade of the embodiment's Example 1 described above in the case of use of the half bell mouth 30 a illustrated in FIG. 7. FIG. 33 illustrates the relationships between the degree of the function used for the forward tilt angle distribution in the second region AR2 and the maximum fan efficiency Esmax. The degree has been changed from 1.2 to 5. As illustrated in FIG. 33, the maximum fan efficiency Esmax is improved as compared to Comparative Example 5 in terms of all the degrees.
FIG. 34 is a graph illustrating the specific noise characteristics at the open point of the rotor blade of Comparative Example 5 described above and the rotor blade of the embodiment's Example 1 described above in the case of use of the full bell mouth 30 b illustrated in FIG. 8. FIG. 34 illustrates the relationships between the degree of the function used for the forward tilt angle distribution in the second region AR2 and the specific noise level Kt at the open point. The degree has been changed from 1.2 to 5. As illustrated in FIG. 34, the rotor blade of Example 1 in the embodiment exhibits a specific noise level Kt improved as compared to Comparative Example 5 in terms of all the degrees.
FIG. 35 is a graph illustrating the fan efficiency characteristics of the rotor blade of Comparative Example 5 described above and the rotor blade of the embodiment's Example 1 described above at the open point in the case of use of the full bell mouth 30 b illustrated in FIG. 8. FIG. 35 illustrates the relationships between the degree of the function used for the forward tilt angle distribution in the second region AR2 and the fan efficiency Et at the open point. The degree has been changed from 1.2 to 5. As illustrated in FIG. 35, the rotor blade of Example 1 in the embodiment exhibits a fan efficiency Et almost the same as that of Comparative Example 5 when the degree is 1.2. In addition, the rotor blade of the embodiment's Example 1 exhibits a fan efficiency Et degraded with respect to that of Comparative Example 5 when the degree is 5, but a fan efficiency Et improved as compared to Comparative Example 5 over the range of degree from 2 to 4.
FIG. 36 is a graph illustrating the minimum specific noise characteristics at the time of application of static pressure of the rotor blade of Comparative Example 5 described above and the rotor blade of Example 1 in the embodiment described above in the case of use of the full bell mouth 30 b illustrated in FIG. 8. FIG. 36 illustrates the relationships between the degree of the function used for the forward tilt angle distribution in the second region AR2 and the minimum specific noise level Ks at the time of application of static pressure. The degree has been changed from 1.2 to 5. As illustrated in FIG. 36, the rotor blade of the embodiment's Example 1 exhibits a specific noise level Ks improved as compared to Comparative Example 5 in terms of all the degrees.
FIG. 37 is a graph illustrating the maximum fan efficiency characteristics of the rotor blade of Comparative Example 5 described above and the rotor blade of Example 1 in the embodiment described above in the case of use of the full bell mouth 30 b illustrated in FIG. 8. FIG. 37 illustrates the relationships between the degree of the function used for the forward tilt angle distribution in the second region AR2 and the maximum fan efficiency Esmax. The degree has been changed from 1.2 to 5. As illustrated in FIG. 37, the maximum fan efficiency Esmax is improved as compared to Comparative Example 5 over the range of degree from 2 to 5.
As illustrated in FIGS. 30 to 37, the present embodiment enables the blowing characteristic, the noise characteristic, and the fan efficiency characteristic to be improved irrespective of the form of a used bell mouth as long as a distribution of the forward tilt angle δz in the second region follows a quadratic to quintic function.
As described above, according to the present embodiment, the stagger angle ξ of the rotor blade has a first stagger angle distribution having a local minimum value in an area from the inner circumferential edge to the first boundary position Re1, and has a second stagger angle distribution that increases toward the said outer circumferential edge and follows an n-dimensional function using the radius of the said rotor blade as a parameter in an area from the first boundary position Rel to the outer circumferential edge. “n”, which is used in the n-dimensional, is a value ranging from 1 to 2, but exclusive of 1. Thus, the present embodiment can limit the height of the outer circumferential portion, and can also achieve a reduced noise level and higher efficiency.
In addition, in the present embodiment, the angle of advance δ_θ of the rotor blade has a first angle-of-advance distribution that linearly increases in an area from the inner circumferential edge to the second boundary position Re2, and has a second angle-of-advance distribution that increases toward the said outer circumferential edge and follows an m-dimensional function using the radius as a parameter in an area from the second boundary position Re2 to the outer circumferential edge, where m is a value ranging from 1 to 2, but exclusive of 1. Therefore, the present embodiment enables a delta wing shape to be ensured for reducing the noise level in the blade outer circumferential portion, and at the same time, the strength at the blade root portion to be increased.
Moreover, in the present embodiment, the forward tilt angle δz of the rotor blade has a first forward tilt angle distribution having a constant value in an area from the inner circumferential edge to the third boundary position Re3, and has a second forward tilt angle distribution that increases toward the outer circumferential edge and follows a p-dimensional function using the radius as a parameter in an area from the third boundary position Re3 to the outer circumferential edge, where p is a value ranging from 2 to 5. Therefore, the present embodiment can achieve a further reduced noise level.
The configurations described in the foregoing embodiment are merely examples of various aspects of the present invention, and can be combined with other publicly known techniques and partially omitted and/or modified without departing from the spirit of the present invention.

REFERENCE SIGNS LIST

1 rotor blade; 1 a leading edge; 1 b trailing edge; 1 c inner circumferential edge; 1 d outer circumferential edge; 2 boss portion; 5 blade tip vortex; 10 propeller fan; 30 bell mouth; 30 a half bell mouth; 30 b full bell mouth; 100 axial flow blower; g chord center line; O rotational axis; W rotation direction; ξ stagger angle; δ_θ angle of advance; δz forward tilt angle.

Claims

1. A propeller fan including a boss portion that is driven rotationally, and more than one rotor blade radially attached to the boss portion to generate an airflow in a rotational axis direction, wherein

a radial cross section of the rotor blade on an inner circumferential portion side of the rotor blade has a shape convex against a direction of the airflow, and a radial cross section of the rotor blade on an outer circumferential portion side of the rotor blade has a shape concave along the direction of the airflow,

the radial cross section of the rotor blade is inclined toward an upstream side of the airflow in a leading edge side region with an inclination angle increasing toward a leading edge, and is inclined toward a downstream side of the airflow in a trailing edge side region with the inclination angle increasing toward a trailing edge, and

a stagger angle of the rotor blade has a first stagger angle distribution having a local minimum value in a region from an inner circumferential edge to a first boundary position, and has a second stagger angle distribution that increases toward an outer circumferential edge and follows an n-dimensional function using a radius of the rotor blade as a parameter in a region from the first boundary position to the outer circumferential edge, where n is a value ranging from 1 to 2 and exclusive of 1.

2. The propeller fan according to claim 1, wherein an angle of advance of the rotor blade has a first angle-of-advance distribution that linearly increases in a region from the inner circumferential edge to a second boundary position, and has a second angle-of-advance distribution that increases toward the outer circumferential edge and follows an m-dimensional function using the radius as a parameter in a region from the second boundary position to the outer circumferential edge, where m is a value ranging from 1 to 2 and exclusive of 1.

3. The propeller fan according to claim 1, wherein a forward tilt angle of the rotor blade has a first forward tilt angle distribution having a constant value in a region from the inner circumferential edge to a third boundary position, and has a second forward tilt angle distribution that increases toward the outer circumferential edge and follows a p-dimensional function using the radius as a parameter in a region from the third boundary position to the outer circumferential edge, where p is a value ranging from 2 to 5.

4. The propeller fan according to claim 1, wherein the second stagger angle distribution changes at a rate higher than a rate of change in the first stagger angle distribution.

5. The propeller fan according to claim 2, wherein the second angle-of-advance distribution increases at a rate higher than a rate of increase in the first angle-of-advance distribution.

6. An axial flow blower comprising:

the propeller fan according to claim 1;

a motor to rotationally drive the boss portion of the propeller fan; and

a body including a bell mouth disposed around the propeller fan.

7. The propeller fan according to claim 2, wherein a forward tilt angle of the rotor blade has a first forward tilt angle distribution having a constant value in a region from the inner circumferential edge to a third boundary position, and has a second forward tilt angle distribution that increases toward the outer circumferential edge and follows a p-dimensional function using the radius as a parameter in a region from the third boundary position to the outer circumferential edge, where p is a value ranging from 2 to 5.

8. The axial flow blower according to claim 6, wherein an angle of advance of the rotor blade has a first angle-of-advance distribution that linearly increases in a region from the inner circumferential edge to a second boundary position, and has a second angle-of-advance distribution that increases toward the outer circumferential edge and follows an m-dimensional function using the radius as a parameter in a region from the second boundary position to the outer circumferential edge, where m is a value ranging from 1 to 2 and exclusive of 1.

9. The axial flow blower according to claim 6, wherein a forward tilt angle of the rotor blade has a first forward tilt angle distribution having a constant value in a region from the inner circumferential edge to a third boundary position, and has a second forward tilt angle distribution that increases toward the outer circumferential edge and follows a p-dimensional function using the radius as a parameter in a region from the third boundary position to the outer circumferential edge, where p is a value ranging from 2 to 5.

10. The axial flow blower according to claim 8, wherein a forward tilt angle of the rotor blade has a first forward tilt angle distribution having a constant value in a region from the inner circumferential edge to a third boundary position, and has a second forward tilt angle distribution that increases toward the outer circumferential edge and follows a p-dimensional function using the radius as a parameter in a region from the third boundary position to the outer circumferential edge, where p is a value ranging from 2 to 5.

11. The axial flow blower according to claim 6, wherein the second stagger angle distribution changes at a rate higher than a rate of change in the first stagger angle distribution.

12. The axial flow blower according to claim 8, wherein the second angle-of-advance distribution increases at a rate higher than a rate of increase in the first angle-of-advance distribution.