Fan and air conditioner

Abstract

An axial flow fan (30) is provided with a plurality of blades (33) that rotate around a prescribed rotation axis (A1). The blade has: a leading edge part (38) that includes a leading edge (36); and a porous part (46) that is positioned further to the rear side in the rotation direction (D1) than the leading edge part and forms a positive pressure surface (40). In a blade cross section in a direction along a blade chord line (CLa) of the blade, a curved raised portion (49) is formed on a positive pressure surface of the leading edge part, where the absolute value of the angle between the tangent line (TLa) of the positive pressure surface and the blade chord line decreases from the leading edge towards a trailing edge in the rotation direction, then increases after passing through zero, and reaches a turning point (Pc) where the rate of change of the absolute value begins to decrease.

Description

Fans and air conditioners

[0001] The present disclosure relates to a fan and an air conditioning apparatus.

[0002] Patent Document 1 discloses an axial flow fan in which each of a plurality of blades includes a porous portion. The porous portion is provided to suppress noise generated by the rotation of the axial flow fan.

[0003] JP 2023-151184 A

[0004] In an axial flow fan, the faster the blades rotate, the greater the volume of air generated by the fan. This increases the flow velocity of the air passing over the pressure surface of the blade, causing significant development of turbulence on the pressure surface. The inventors of the present application discovered that in an axial flow fan with porous portions on the blades, as in Patent Document 1, the noise reduction effect of the porous portions is impaired when the turbulence on the pressure surface of the blades develops and becomes large.

[0005] An object of the present disclosure is to preferably obtain the noise reduction effect of the porous portion in a fan having porous portions in its blades.

[0006] A first aspect of the present disclosure is directed to a fan (30, 50). The fan (30, 50) of the first aspect includes a blade (33, 56) that rotates around a predetermined rotation axis (A1, A2). The blade (33, 56) has a leading edge portion (38, 68) that includes a leading edge (36, 57) that is a leading edge in a rotation direction (D1, D2), and a porous portion (46, 66) that is located rearward of the leading edge portion (38, 68) in the rotation direction (D1, D2) and forms a pressure side (40, 60) of the blade (33, 56). In a blade cross section along the chord line (CLa, CLb) of the blade (33, 56), a curved portion (49, 69) is formed on the pressure surface (40, 60) of the leading edge portion (38, 68), where the absolute value of the angle between the tangent (TLa, TLb) of the pressure surface (40, 60) and the chord line (CLa, CLb) decreases from the leading edge (36, 57) toward the rear in the direction of rotation (D1, D2), passes through 0, and then increases, reaching a change point (Pc) at which the rate of change of the absolute value starts to decrease.

[0007] In the first aspect, in a blade cross section along the chord line (CLa, CLb) of the blade (33, 56), a curved portion (49, 69) is formed on the pressure surface (40, 60) of the leading edge (38, 68) of the blade (33, 56), in which the absolute value of the angle between the tangent (TLa, TLb) of the pressure surface (40, 60) and the chord line (CLa, CLb) gradually changes to form a mountain-like curve. Such a curved portion (49, 69) constitutes a raised portion (49, 69) that is raised on the pressure side of the blade (33, 56). When the raised portion (49, 69) is provided on the pressure surface (40, 60) of the leading edge (38, 68), the area of ​​the leading edge (38, 68) against which the airflow collides during rotation of the blade (33, 56) is increased. Therefore, when an airflow collides with the leading edge portion (38, 68) of the blade (33, 56), an airflow (F1) containing minute vortices (Vt) is generated on the pressure surface (40, 60) side of the blade (33, 56). The airflow (F1) containing the minute vortices (Vt) is unlikely to separate from the curved raised portion (49, 69) and flows along the pressure surface (40, 60) while suppressing turbulence. This makes it possible to suppress the development of turbulence flowing over the pressure surface (40, 60) formed by the porous portion (46, 66). As a result, the noise reduction effect of the porous portion (46, 66) can be favorably obtained.

[0008] A second aspect of the present disclosure is the fan (30, 50) of the first aspect, wherein the leading edge (38, 68) has a first portion (38a, 68a) on which the curved portion (49, 69) is formed. In the blade cross section including the first portion (38a, 68a), a first distance H1 that is the maximum distance from a camber line (SLa, SLb) of the leading edge (38, 68) to the pressure surface (40, 60) and a second distance H2 that is the maximum distance from the camber line (SLa, SLb) of a portion rearward of the leading edge (38, 68) in the direction of rotation (D1, D2) to the pressure surface (40, 60) satisfy the relationship H1 > H2.

[0009] In the second aspect, in a blade cross section along the chord line (CLa, CLb) of the blade (33, 56) including the first portion (38a, 68a), a first distance H1, which is the maximum distance from the camber line (SLa, SLb) of the leading edge (38, 68) to the pressure surface (40, 60), is longer than a second distance H2, which is the maximum distance from the camber line (SLa, SLb) of the leading edge (38, 68) to the suction surface (41, 61) in a portion rearward of the leading edge (38, 68) in the direction of rotation (D1, D2) (H1 > H2). The shape of the blade (33, 56) that satisfies this relationship prevents the blade thickness from becoming excessively large in the portion rearward of the leading edge (38, 68), thereby enabling the weight of the blade (33, 56) to be reduced. This is advantageous for improving the energy efficiency of the fan (30, 50).

[0010] A third aspect of the present disclosure is the fan (30, 50) of the first or second aspect, wherein the leading edge (38, 68) has a first portion (38a, 68a) on which the curved portion (49, 69) is formed. In the blade cross section including the first portion (38a, 68a), the pressure surface (40, 60) of the blade (33, 56) is connected such that a tangent (TLa, TLb) of the pressure surface (40, 60) is continuous from the leading edge (38, 68) to a portion rearward of the leading edge (38, 68) in the direction of rotation.

[0011] In the third aspect, in a blade cross section along the chord line (CLa, CLb) of the blade (33, 56) including the first portion (38a, 68a), the pressure surface (40, 60) of the blade (33, 56) is connected from the leading edge (38, 68) to its aft portion so that the tangent (TLa, TLb) is continuous. When the pressure surface (40, 60) of the blade (33, 56) is smoothly connected from the leading edge (38, 68) including the raised portion (49, 69) to its aft portion, the airflow (F1) including minute vortices (Vt) generated by the airflow impinging on the leading edge (38, 68) can flow from the leading edge (38, 68) to the aft portion along the pressure surface (40, 60). This is advantageous in suppressing the development of turbulence flowing over the pressure surface (40, 60).

[0012] A fourth aspect of the present disclosure is the fan (30, 50) of any one of the first to third aspects, wherein the leading edge (38, 68) has a first portion (38a, 68a) on which the curved portion (49, 69) is formed. When a maximum value of a distance from the chord line (CLa, CLb) of the leading edge (38, 68) to the pressure surface (40, 60) in the aerofoil cross section including the first portion (38a, 68a) is defined as a third distance H3, a length L1 between a first position (P1) where the distance to the pressure surface (40, 60) on the chord line (CLa, CLb) is the third distance H3 and a second position (P2) corresponding to the change point (Pc), and the third distance H3, satisfy the relationship H3<L1.

[0013] In the fourth aspect, in a blade cross section of the blade (33, 56) including the first portion (38a, 68a) in a direction along the chord line (CLa, CLb), a length L1 between a first position (P1) and a second position (P2) on the chord line (CLa, CLb) is longer than a third distance H3 (H3<L1). The first position (P1) is a position at which the distance from the chord line (CLa, CLb) to the pressure surface (40, 60) is longest in the raised portion (49, 69) of the leading edge (38, 68), and the second position (P2) is a position corresponding to a change point (Pc) in the curved shape of the raised portion (49, 69). When the shape of the raised portion (49, 69) is relatively long rearward from the position where the third distance H3 is taken, i.e., the position where the distance from the chord line (CLa, CLb) to the pressure surface (40, 60) is greatest, the shape of the pressure surface (40, 60) of the leading edge portion (38, 68) becomes gentler. This makes it possible to suppress separation of the airflow (F1), including minute vortices (Vt) generated by the airflow collision with the leading edge portion (38, 68), from the pressure surface (40, 60) as it flows rearward from the leading edge portion (38, 68).

[0014] A fifth aspect of the present disclosure is the fan (30, 50) of any one of the first to fourth aspects, wherein the leading edge (38, 68) has a first portion (38a, 68a) on which the curved portion (49, 69) is formed. In the aerofoil cross section including the first portion (38a, 68a), if the maximum value of the distance from the chord line (CLa, CLb) of the leading edge portion (38, 68) to the pressure surface (40, 60) is defined as a third distance H3, then a length L1 between a first position (P1) where the distance to the pressure surface (40, 60) on the chord line (CLa, CLb) is the third distance H3 and a second position (P2) corresponding to the change point (Pc), and a length L2 between the leading edge (38, 68) and the first position (P1) on the chord line (CLa, CLb) satisfy the relationship L2<L1.

[0015] In the fifth aspect, in a blade cross section in a direction along the chord line (CLa, CLb) of the blade (33, 56) including the first portion (38a, 68a), a length L1 between a first position (P1) and a second position (P2) on the chord line (CLa, CLb) is longer than a length L2 between the leading edge (36, 57) on the chord line (CLa, CLb) of the blade (33, 56) and the first position (P1) (L2<L1). The first position (P1) is a position at a raised portion (49, 69) of the leading edge (38, 68) where the distance from the chord line (CLa, CLb) to the pressure surface (40, 60) is maximum, and the second position (P2) is a position corresponding to a change point (Pc) of the curved shape of the raised portion (49, 69). When the shape of the raised portion (49, 69) is relatively long rearward from the position where the third distance H3 is taken, i.e., the position where the distance from the chord line (CLa, CLb) to the pressure surface (40, 60) is greatest, the shape of the pressure surface (40, 60) of the leading edge portion (38, 68) becomes gentler. This makes it possible to suppress separation of the airflow (F1), including minute vortices (Vt) generated by the airflow collision with the leading edge portion (38, 68), from the pressure surface (40, 60) as it flows rearward from the leading edge portion (38, 68).

[0016] A sixth aspect of the present disclosure is the fan (30, 50) of any one of the first to fifth aspects, wherein the leading edge (38, 68) has a first portion (38a, 68a) on which the curved portion (49, 69) is formed. In the blade cross section including the first portion (38a, 68a), a first distance H1 that is the maximum distance from a camber line (SLa, SLb) of the leading edge (38, 68) to the pressure surface (40, 60) and a second distance H2 that is the maximum distance from the camber line (SLa, SLb) of a portion rearward of the leading edge (38, 68) in the direction of rotation (D1, D2) to the pressure surface (40, 60) satisfy the relationship H1≦H2×3.

[0017] In the sixth aspect, in a blade cross section along the chord line (CLa, CLb) of the blade (33, 56) including the first portion (38a, 68a), the first distance H1 at the leading edge (38, 68) is smaller than three times the second distance H2 at the portion rearward of the leading edge (38, 68) (H1≦H2×3). This makes it possible to increase the area of ​​the leading edge (38, 68) with which the airflow collides when the blade (33, 56) rotates, while preventing the blade thickness of the leading edge (38, 68) from becoming excessive.

[0018] A seventh aspect of the present disclosure is the fan (30) according to any one of the first to sixth aspects, further comprising a hub (31) rotatable about the rotation axis (A1). The vanes (33) are provided in plurality at intervals in the circumferential direction of the hub (31), and extend radially outward from the hub (31).

[0019] In a seventh aspect, a plurality of blades (33) are provided at intervals in the circumferential direction of the hub (31). Each blade (33) extends radially outward from the hub (31). In such an axial flow fan (30), the noise reduction effect of the porous portion (46) can be suitably obtained, and therefore the technology of the present disclosure is effective.

[0020] An eighth aspect of the present disclosure is the fan (30) of the seventh aspect, wherein the leading edge (38) has a first portion (38a) on which the curved portion (49) is formed. In the blade cross section including the first portion (38a), a third distance H3 which is the maximum distance from the chord line (CLa) of the leading edge (38) to the pressure surface (40) of the blade (33) and a fourth distance H4 from the chord line (CLa) of the leading edge (38) to the suction surface (41) of the blade (33) satisfy the relationship H4<H3.

[0021] In the eighth aspect, in a blade cross section along the chord line (CLa) of the blade (33) including the first portion (38a), a third distance H3 from the chord line (CLa) of the leading edge (38) to the pressure surface (40) is greater than a fourth distance H4 from the chord line (CLa) to the suction surface (41) (H4<H3). This effectively increases the area of ​​the leading edge (38) against which the airflow collides during rotation of the blade (33), while allowing the airflow (F1) including minute vortices (Vt) generated by the airflow colliding with the leading edge (38) to flow along the pressure surface (40) of the blade (33). As a result, the porous portion (46) effectively reduces noise.

[0022] A ninth aspect of the present disclosure is the fan (30) of the eighth aspect, wherein the third distance H3 of the first portion (38a) decreases from the inner side to the outer side of the blade (33) at the leading edge portion (38).

[0023] In the ninth aspect, the third distance H3 of the first portion (38a) decreases from the inner circumferential side to the outer circumferential side of the blade (33) at the leading edge portion (38). Providing the first portion (38a) only on a portion of the leading edge portion (38) located upstream of the airflow (F1) flowing on the positive pressure surface (40) formed by the porous portion (46) reduces the noise reduction effect of the porous portion (46) with minimal modification of the shape of the blade (33). Furthermore, providing the first portion (38a) on the leading edge portion (38) of the blade (33) can suppress a decrease in the static pressure characteristics of the fan (30).

[0024] A tenth aspect of the present disclosure is the fan (30) of any one of the seventh to ninth aspects, wherein the leading edge (38) has a first portion (38a) on which the curved portion is formed. The first portion (38a) is provided on the inner circumferential side of the leading edge (38). The porous portion (46) is provided outward of the first portion (38a) in the direction of the rotation radius of the blades (33).

[0025] In a tenth aspect, the first portion (38a) is provided on the inner circumferential side of the leading edge portion (38) of the blade (33), and the porous portion (46) is provided radially outward of the blade (33) relative to the first portion (38a). In an axial flow fan (30), as the air volume increases, the airflow (F1) on the pressure surface (40) of the blade (33) tends to flow toward the outer periphery due to centrifugal force. Therefore, the airflow (F1) including minute vortices (Vt) generated by the airflow impinging on the leading edge portion (38) including the first portion (38a) can flow on the pressure surface (40) defined by the porous portion (46). This allows the porous portion (46) to effectively reduce noise.

[0026] An eleventh aspect of the present disclosure is the fan (50) of any one of the first to sixth aspects, further comprising: a plate-shaped member (51) rotatable about the rotation shaft (A2); and a shroud (53) disposed at a distance from the plate-shaped member (51) in the axial direction of the rotation shaft (A2). A plurality of the blades (56) are provided between the plate-shaped member (51) and the shroud (53) at intervals in the rotation direction (D2) such that the leading edges (57) are located on the inner circumferential side and trailing edges (58), which are rear edges in the rotation direction (D2), are located on the outer circumferential side.

[0027] In an eleventh aspect, a plurality of blades (56) are provided between the plate-like member (51) and the shroud (53) at intervals in the rotation direction (D2). Each blade (56) is oriented such that its leading edge (57) is located on the inner circumferential side and its trailing edge (58) is located on the outer circumferential side. In such a turbofan (50), the noise reduction effect of the porous portion (66) can be suitably obtained, and therefore the technology of the present disclosure is effective.

[0028] A twelfth aspect of the present disclosure is directed to an air conditioner (1). The air conditioner (1) of the twelfth aspect includes the fan (30, 50) of any one of the first to eleventh aspects.

[0029] In the twelfth aspect, the air conditioner (1) includes a fan (30, 50). The fan (30, 50) can effectively achieve the noise reduction effect of the porous portion (46, 66). Therefore, the noise caused by the rotation of the fan (30, 50) can be reduced, and quietness can be improved in the air conditioner (1).

[0030] FIG. 1 is a schematic diagram of an air conditioning apparatus according to a first embodiment. FIG. 2 is a plan view illustrating an axial fan according to the first embodiment. FIG. 3 is an enlarged plan view of a blade of the axial fan. FIG. 4 is a cross-sectional perspective view illustrating a main portion of a blade of the axial fan. FIG. 5 is a cross-sectional view of the axial fan blade taken along line V-V in FIG. 2. FIG. 6 is a graph showing the relationship between the distance from the leading edge of the leading edge in the blade cross section along the chord line of the blade and the absolute value of the angle between the tangent to the pressure surface and the chord line. FIG. 7 is a conceptual diagram illustrating the airflow on the pressure surface of the blade during operation of the propeller fan according to the first embodiment. FIG. 8 is a conceptual diagram illustrating the airflow on the pressure surface of the blade during operation of the axial fan of the comparative example. FIG. 9 is a graph showing the relationship between airflow volume and static pressure for the axial fan of the example and the axial fans of comparative examples 1 and 2. FIG. 10 is a graph showing the relationship between airflow volume and specific noise level for the axial fan of the example and the axial fans of comparative examples 1 and 2. Fig. 11 is a perspective view illustrating a turbofan according to embodiment 2. Fig. 12 is a plan view of the turbofan. Fig. 13 is a cross-sectional view of a blade of the turbofan.

[0031] Exemplary embodiments will be described in detail below with reference to the drawings. In the following embodiments, examples will be given in which a fan according to the present disclosure is applied to an axial fan and a turbofan. Note that the drawings are intended to conceptually explain the technology of the present disclosure. Therefore, in the drawings, dimensions, ratios, or numbers may be exaggerated or simplified to facilitate understanding of the technology of the present disclosure.

[0032] First Embodiment In this first embodiment, an axial fan (30) will be described as a fan according to the present disclosure. The axial fan (30) is used in an air conditioner (1). In other words, the air conditioner (1) includes the axial fan (30).

[0033] -Air Conditioning Apparatus- The air conditioning apparatus (1) is an apparatus that adjusts the temperature of air in a target space. In this example, the target space is an indoor space. As shown in FIG. 1, the air conditioning apparatus (1) is a pair-type air conditioning apparatus, and includes one indoor unit (3) and one outdoor unit (5). The indoor unit (3) is installed indoors. The outdoor unit (5) is installed outdoors. The indoor unit (3) and the outdoor unit (5) are connected to each other via a liquid connecting pipe (7) and a gas connecting pipe (9).

[0034] The indoor unit (3), the outdoor unit (5), the liquid connecting pipe (7), and the gas connecting pipe (9) constitute a refrigerant circuit (11). The refrigerant circuit (11) is filled with refrigerant. The refrigerant circuit (11) mainly includes a compressor (13), an outdoor heat exchanger (15), an expansion valve (17), a switching mechanism (19), and an indoor heat exchanger (21). The compressor (13), the outdoor heat exchanger (15), the expansion valve (17), and the indoor heat exchanger (21) are connected by piping.

[0035] The compressor (13), the outdoor heat exchanger (15), the expansion valve (17), and the switching mechanism (19) are included in the outdoor unit (5). That is, the outdoor unit (5) includes the compressor (13), the outdoor heat exchanger (15), the expansion valve (17), and the switching mechanism (19). The outdoor unit (5) further includes an outdoor fan (23). A first fan motor (25) is connected to the outdoor fan (23). The outdoor fan (23) is rotated by being driven by the first fan motor (25). The axial fan (30) of this embodiment is used as the outdoor fan (23).

[0036] The compressor (13) draws in and compresses low-pressure gas refrigerant and discharges the compressed refrigerant. The outdoor fan (23) transports outdoor air to pass through the outdoor heat exchanger (15). The outdoor heat exchanger (15) exchanges heat between the outdoor air transported by the outdoor fan (23) and the refrigerant flowing therethrough. The outdoor heat exchanger (15) is configured, for example, as a fin-and-tube type. The expansion valve (17) reduces the pressure of the refrigerant.

[0037] The switching mechanism (19) switches the circulation direction of the refrigerant in the refrigerant circuit (11). The switching mechanism (19) is, for example, a four-way switching valve. The switching mechanism (19) has a first port (19a), a second port (19b), a third port (19c), and a fourth port (19d). The first port (19a) is connected to the discharge side of the compressor (13). The second port (19b) is connected to the suction side of the compressor (13). The third port (19c) is connected to the outdoor heat exchanger (15). The fourth port (19d) is connected to the gas connection pipe (9).

[0038] The switching mechanism (19) is switchable between a first state (a state indicated by a solid line in FIG. 1 ) and a second state (a state indicated by a dashed line in FIG. 1 ). When the switching mechanism (19) is in the first state, it connects the first port (19a) to the third port (19c) and also connects the second port (19b) to the fourth port (19d). When the switching mechanism (19) is in the second state, it connects the first port (19a) to the fourth port (19d) and also connects the second port (19b) to the third port (19c).

[0039] The indoor heat exchanger (21) is included in the indoor unit (3). That is, the indoor unit (3) includes the indoor heat exchanger (21). The indoor unit (3) further includes an indoor fan (27). For example, a cross-flow fan or a turbo fan is used as the indoor fan (27). The indoor fan (27) may be a fan of another type, such as a sirocco fan.

[0040] A second fan motor (29) is connected to the indoor fan (27). The indoor fan (27) is rotated by the driving of the second fan motor (29) and transports indoor air to pass through the indoor heat exchanger (21). The indoor heat exchanger (21) exchanges heat between the indoor air transported by the indoor fan (27) and the refrigerant flowing therein. The indoor heat exchanger (21) is configured, for example, as a fin-and-tube type.

[0041] The air conditioner (1) performs cooling operation and heating operation.

[0042] The cooling operation is an operation for cooling the air in the indoor space. In the cooling operation, the switching mechanism (19) is set to the first state, and the compressor (13), the outdoor fan (23), and the indoor fan (27) are operated. As a result, the refrigerant in the refrigerant circuit (11) flows in the direction of the solid arrow in FIG. 1, and the outdoor heat exchanger (15) functions as a radiator and the indoor heat exchanger (21) functions as an evaporator. In the cooling operation, the air transported by the indoor fan (27) is cooled by the indoor heat exchanger (21) and supplied to the indoor space.

[0043] The heating operation is an operation for heating the air in the indoor space. In the heating operation, the switching mechanism (19) is set to the second state, and the compressor (13), the outdoor fan (23), and the indoor fan (27) are operated. As a result, the refrigerant in the refrigerant circuit (11) flows in the direction of the dashed arrow in FIG. 1, and the outdoor heat exchanger (15) functions as an evaporator, and the indoor heat exchanger (21) functions as a radiator. In the heating operation, the air transported by the indoor fan (27) is heated by the indoor heat exchanger (21) and supplied to the indoor space.

[0044] - Axial flow fan - The axial flow fan (30) is a propeller-type fan. As shown in Fig. 2, the axial flow fan (30) includes one hub (31) and a plurality of blades (33). The hub (31) and the plurality of blades (33) are integrally formed. The axial flow fan (30) of this example has three blades (33). The number of blades (33) may be two, four or more.

[0045] The hub (31) is formed in a cylindrical shape. The hub (31) is a rotation shaft of the axial fan (30) and is located at the center of the axial fan (30). A shaft hole (32) is formed in the center of the hub (31). The drive shaft of the first fan motor (25) is attached to the hub (31) through the shaft hole (32). When the first fan motor (25) is driven, the hub (31) rotates about a predetermined rotation axis (A1). The central axis of the hub (31) coincides with the rotation axis (A1) of the axial fan (30).

[0046] The plurality of blades (33) are provided at intervals in the circumferential direction of the hub (31). Each blade (33) extends radially outward from the outer peripheral surface of the hub (31). The plurality of blades (33) spread radially outward from the hub (31) in the direction of the rotation radius of the axial flow fan (30). Adjacent blades (33) do not overlap with each other in a front or rear view. The plurality of blades (33) have the same shape.

[0047] Each blade (33) has a so-called forward-swept blade shape. Each blade (33) is formed in a smoothly curved plate shape with a slight convex shape on one blade surface side (the suction surface (41) side) along the rotation radius direction and the rotation direction (D1). Each blade (33) has a base (34), a tip (35), a leading edge (36), and a trailing edge (37). The base (34), the tip (35), the leading edge (36), and the trailing edge (37) form the outer periphery of the blade (33) in a plan view.

[0048] The blade base (34) is the end of the blade (33) on the radially central side of the axial fan (30), i.e., the inner end of the blade (33) in the direction of the rotation radius. The blade tip (35) is the end of the blade (33) on the radially outer side of the axial fan (30), i.e., the outer end of the blade (33) in the direction of the rotation radius. The blade base (34) and the blade tip (35) of each blade (33) each extend along the rotation direction (D1) of the axial fan (30).

[0049] The base (34) of each blade (33) is connected to the hub (31). The distance from the rotation axis (A1) of the axial fan (30) to the base (34) is substantially constant over the entire length of the base (34). The tip (35) of each blade (33) is curved so as to form a convex shape toward the outer periphery of the axial fan (30). The distance from the rotation axis (A1) of the axial fan (30) to the tip (35) is substantially constant over the entire length of the tip (35). The length of the tip (35) is longer than the length of the base (34).

[0050] The leading edge (36) is the front edge of the blade (33) in the rotation direction (D1). The trailing edge (37) is the rear edge of the blade (33) in the rotation direction (D1). The leading edge (36) and the trailing edge (37) of each blade (33) extend from the hub (31) side toward the outer periphery of the axial flow fan (30). The leading edge (36) and the trailing edge (37) each have an arc-shaped portion and extend from the blade root (34) toward the blade tip (35) so as to be spaced apart from each other.

[0051] The leading edge (36) of each blade (33) extends from the blade base (34) toward the blade tip (35) so as to protrude forward in the direction of rotation (D1). The leading edge (36) curves so as to be concave toward the rear side in the direction of rotation (D1) of the blade (33). The trailing edge (37) extends from the blade base (34) toward the blade tip (35) so as to protrude slightly rearward in the direction of rotation (D1). The leading edge (36) curves slightly so as to be concave toward the front side in the direction of rotation (D1) of the blade (33).

[0052] In the blade cross section in the rotation direction (D1) of the blade (33), the line segment connecting the leading edge (36) and the trailing edge (37) of the blade (33) is the chord line (CLa). An example of the chord line (CLa) is shown in FIG. 2. In the axial flow fan (30), the blade cross section in the direction along the chord line (CLa) of the blade (33) corresponds to the blade cross section in the rotation direction (D1) of the blade (33), and is referred to as the "symmetric blade cross section" in this embodiment. The length of the chord line (CLa) is the chord length L1. The chord length L1 increases with increasing distance from the root (34) in the rotation radius direction of the blade (33), and is maximum at the tip (35).

[0053] Each blade (33) is inclined so as to intersect with a plane perpendicular to the rotation axis (A1) of the axial fan (30). A leading edge (36) of each blade (33) is located on the rear side (negative pressure side) of the axial fan (30) and extends from a position near one end (the end on the air inflow side) of the hub (31) toward the upstream side of the air being transported. A trailing edge (37) of each blade (33) is located on the front side (positive pressure side) of the axial fan (30) and near the other end (the end on the air outflow side) of the hub (31).

[0054] 4 and 5, each blade (33) further has a positive pressure surface (40) and a negative pressure surface (41). The positive pressure surface (40) is a blade surface that becomes a positive pressure side due to the flow of air carried when the axial flow fan (30) rotates, and constitutes a surface facing the front side of the axial flow fan (30) from which air flows out. The negative pressure surface (41) is a blade surface that becomes a negative pressure side due to the flow of air carried when the axial flow fan (30) rotates, and constitutes a surface facing the rear side of the axial flow fan (30) from which air flows in.

[0055] As shown in Figure 2, the outer edge portion along the blade tip (35) of each blade (33) constitutes a winglet portion (42). The winglet portion (42) is slightly bent toward the suction surface (41) relative to the rest of the blade (33). The winglet portion (42) is provided so that its width gradually increases from the leading edge (36) toward the trailing edge (37). The winglet portion (42) serves to straighten the airflow near the blade tip (35). The provision of the winglet portion (42) is advantageous in suppressing the generation of a blade tip vortex.

[0056] The plurality of blades (33) rotate integrally with the hub (31) around the rotation axis (A1). When the axial fan (30) rotates around the rotation axis (A1), the positive pressure surface (40) of each blade (33) pushes out air. As a result, as the plurality of blades (33) rotate, air flows from the inlet side at the rear of the axial fan (30) to the outlet side at the front. At this time, pressure increases on the positive pressure surface (40) of each blade (33) to push out the air. On the other hand, pressure relatively decreases on the negative pressure surface (41) of each blade (33).

[0057] During rotation of the axial flow fan (30), when the air flowing over the pressure surface (40) of the blade (33) reaches the blade tip (35) and leaves the pressure surface (40), it forms a flow that is drawn from the pressure surface (40) to the suction surface (41), forming a vortex. The vortex generated on the blade tip (35) side is called a blade tip vortex. The blade tip vortex develops rearward as the blade (33) rotates, and becomes a wake vortex that flows rearward in the direction of rotation (D1) from the trailing edge (37) of the blade (33). The higher the energy of the blade tip vortex and the wake vortex, the louder the noise generated during operation of the axial flow fan (30).

[0058] Noise generated during operation of the axial fan (30) is also caused by pressure fluctuations on the blade surfaces of the blades (33). As a countermeasure against noise caused by pressure fluctuations on the blade surfaces of the blades (33), a portion of each blade (33) of the axial fan (30) is formed from a porous material. The non-porous material is a material that is not porous, such as a non-foamed synthetic resin. Each blade (33) has a blade body (44) and a porous portion (46).

[0059] As shown in FIG. 3 , the blade body (44) forms the blade root (34), blade tip (35), leading edge (36), and trailing edge (37). The blade body (44) is made of a non-porous material. The blade body (44) is made of the same synthetic resin as the hub (31). The blade body (44) is integrally molded with the hub (31) by, for example, injection molding. The blade body (44) forms the majority of the blade (33). In other words, the majority of the blade (33) is made of a non-porous material. The porous portion (46) is fixed to the blade body (44) by fitting, bonding, welding, or the like.

[0060] The porous portion (46) is provided in a region surrounded by the base (34), tip (35), leading edge (36), and trailing edge (37). In this example, the porous portion (46) is located near the tip (35) midway in the rotation direction (D1) of the blade (33) and is surrounded by the blade body (44). The porous portion (46) functions to suppress pressure fluctuations on the blade surface of the blade (33) and reduce noise generated by the rotation of the axial flow fan (30). The noise reduction effect of the porous portion (46) varies depending on the position and area of ​​the porous portion (46) on the blade (33).

[0061] The porous portion (46) is provided in, for example, a quadrilateral shape (more specifically, a quadrilateral shape with a curved corner). The porous portion (46) may be provided in another shape, such as a triangular shape or an oval shape. The porous portion (46) constitutes the entire blade (33) in the thickness direction. The porous portion (46) is exposed on both the pressure surface (40) and the suction surface (41) of the blade (33), and forms part of the pressure surface (40) and part of the suction surface (41).

[0062] The porous portion (46) is made of a porous material having a plurality of continuous fine pores. The plurality of fine pores in the porous material communicate with the pressure surface (40) and the suction surface (41) of the blade (33). The average diameter of the pores (voids) in the porous portion (46) is, for example, in the range of 15 μm to 300 μm. The porosity of the porous portion (46) (= void volume / total volume of the porous portion) is, for example, in the range of 35% to 90%.

[0063] The porous material may be a synthetic resin, ceramic, metal, or the like. For example, synthetic resin, ceramic, or metal may be used as a porous sintered body. The porous sintered body is formed by heating a powder material in an accumulated state to partially fuse the powder together. The synthetic resin may be a foamed resin containing open cells. The strength of the porous portion (46) made of such a porous material is lower than the strength of the blade body (44).

[0064] The position of the porous portion (46) on the blade (33) is expressed by the chord ratio (Lb / La) and radius ratio (Rb / Ra) of the center (C1) of the porous portion (46). The center (C1) of the porous portion (46) refers to the central position of the blade (33) in the radial direction and the rotational direction (D1). The chord ratio (Lb / La) is the ratio of the distance Lb from the leading edge (36) to the chord length La in the symmetrical blade cross section of the blade (33). The radius ratio (Rb / Ra) is the ratio of the distance Rb from the root (34) to the distance Ra from the root (34) to the tip (35) in the radial direction of the blade (33).

[0065] The center (C1) of the porous portion (46) is located such that the chord ratio (Lb / La) is in the range of 0.4 to 0.8 and the radius ratio (Rb / Ra) is in the range of 0.6 to 0.8. The porous portion (46) is provided radially outward of the blade (33) from a raised portion (49) of the leading edge portion (38) described below. The area of ​​the porous portion (46) is set within a range that can achieve a noise reduction effect (silencing effect). In this example, the area of ​​the porous portion (46) is 30% or less of the entire area of ​​the pressure surface (40).

[0066] When the axial flow fan (30) rotates, air forms air flows (F1, F2) from the leading edge (36) of the blade (33) toward the pressure surface (40) and the suction surface (41) (see FIG. 7 ). As the axial flow fan (30) rotates, these air flows (F1, F2) along the blade surfaces (the pressure surface (40) and the suction surface (41)) and exit from the trailing edge (37). At this time, pressure fluctuations occur on the blade surfaces due to various factors, such as pressure fluctuations at the boundary surfaces of the air flows (F1, F2) and pressure fluctuations occurring when the flow transitions from laminar to turbulent. These pressure fluctuations on the blade surfaces are a factor that increases the noise (blowing noise) generated when the axial flow fan (30) rotates.

[0067] In the porous portion (46), air flows in and out between the positive pressure surface (40) and the negative pressure surface (41) through a plurality of minute pores in response to pressure fluctuations on the blade surface. When the pressure of the air on the positive pressure surface (40) side increases, the air passes through the porous portion (46) and leaks slightly to the negative pressure surface (41) side. When the pressure on the negative pressure surface (41) side increases, the air passes through the porous portion (46) and leaks slightly to the positive pressure surface (40) side. As a result, the porous portion (46) suppresses pressure fluctuations on the blade surface. This is advantageous in reducing noise during rotation of the axial flow fan (30).

[0068] In a conventional axial flow fan having blades (33) as shown in Fig. 8, the faster the blades (33) rotate, the greater the air volume and the greater the flow velocity of the air passing over the pressure surfaces (40) of the blades (33), resulting in significant development of turbulent air flow on the pressure surfaces (40). When the turbulent air flow on the pressure surfaces (40) of the blades develops and becomes larger, the noise reduction effect of the porous portions (46) is impaired. Therefore, in the axial flow fan (30) of this embodiment, the shape of the leading edge portions (38) of the blades (33) is devised to suitably obtain the noise reduction effect of the porous portions (46) on the high air volume side.

[0069] Specifically, as shown in Figures 4 and 5, a raised portion (49) is provided on the pressure surface (40) of the leading edge (38) of the blade (33). Here, the leading edge (38) refers to a portion including the leading edge (36) of the blade (33) and 10% of the blade chord length L1 from the leading edge (36). The raised portion (49) is a curved portion that rises toward the pressure side of the blade (33). The raised portion (49) is provided on the inner circumferential side of the leading edge (38) of the blade (33). In this example, the raised portion (49) extends from the blade root (34) to a position where the radius ratio (R2 / R1) is 0.4 to 0.7.

[0070] For convenience, the surface shape of the raised portion (49) is shown by a two-dot chain line in Figure 4. In the target aerofoil cross section of the blade (33), the surface of the raised portion (49) is formed in a curved shape. The curved shape of the raised portion (49) is represented by the angle between the tangent (TLa) of the pressure surface (40) and the chord line (CLa), the distance from the camber line (SLa) to the pressure surface (40) (first distance H1, second distance H2), and the distance from the chord line (CLa) to the pressure surface (40) and the suction surface (41) (third distance H3, fourth distance H3).

[0071] As shown in Fig. 6 , the curved shape of the raised portion (49) is such that, in a target aerofoil cross section of the blade (33), the absolute value of the angle between a tangent (TLa) to the pressure surface (40) and a chord line (CLa) decreases from the leading edge (36) toward the rear in the direction of rotation (D1) of the blade (33), passes through zero, increases, and reaches a transition point (Pc) at which the rate of change of the absolute value starts to decrease. A portion of the tangent (TLa) to the pressure surface (40) formed by the raised portion (49) is shown in Fig. 5 . In a target aerofoil cross section of the blade (33) including the first portion (38a), the pressure surface (40) of the blade (33) is connected such that the tangent (TLa) to the pressure surface (40) is continuous from the leading edge (38) to a portion rearward of the leading edge (38) in the direction of rotation (D1).

[0072] In this manner, the pressure surface (40) of the leading edge (38) smoothly changes, including the raised portion (49). The leading edge (38) of the blade (33) has a first portion (38a) and a second portion (38b). The first portion (38a) is the portion where the raised portion (49) is formed. The second portion (38b) is the portion where the raised portion (49) is not formed. In the symmetrical blade cross section of the blade (33), the line connecting the midpoints of the pressure surface (40) and the suction surface (41) is the camber line (SLa). In the first portion (38a), the camber line (SLa) has a shape that protrudes convexly toward the pressure surface (40) in accordance with the surface shape of the raised portion (49), and smoothly connects to the rear side of the first portion (38a).

[0073] In the target aerofoil section of the blade (33), the maximum value of the distance from the camber line (SLa) of the leading edge (38) to the pressure surface (40) is defined as a first distance H1. In addition, in the target aerofoil section of the blade (33), the maximum value of the distance from the camber line (SLa) aft of the leading edge (38) in the direction of rotation (D1) to the pressure surface (40) is defined as a second distance H2.

[0074] In the target aerofoil section of the blade (33) including the first portion (38a), the first distance H1 and the second distance H2 satisfy the relationship H1 > H2. This relationship means that in the target aerofoil section of the blade (33), the raised portion (49) protrudes most toward the pressure side at the leading edge (38). In the target aerofoil section of the blade (33), the first distance H1 and the second distance H2 satisfy the relationship H1 ≦ H2 × 3. On the other hand, in the target aerofoil section of the blade (33) including the second portion (38b), the first distance H1 and the second distance H2 satisfy the relationship H1 ≦ H2.

[0075] In the target aerofoil section of the blade (33), the maximum value of the distance from the chord line (CLa) of the leading edge (38) to the pressure surface (40) of the blade (33) is defined as a third distance H3. In addition, in the target aerofoil section of the blade (33), the maximum value of the distance from the chord line (CLa) of the leading edge (38) to the suction surface (41) of the blade (33) is defined as a fourth distance H4. Note that in Figure 5, for convenience, the positions of the third distance H3 and the fourth distance H4 are shown shifted from the first position (P1).

[0076] In the symmetric blade cross section of the blade (33) including the first portion (38a), the third distance H3 and the fourth distance H4 satisfy the relationship H4<H3. This relationship means that the blade (33) has a curved shape convex toward the suction surface (41) in the direction of rotation (D1), and the raised portion (49) is provided at the leading edge (38). On the other hand, in the symmetric blade cross section of the blade (33) including the second portion (38b), the third distance H3 and the fourth distance H4 satisfy the relationship H4≧H3.

[0077] The third distance H3 of the first portion (38a) decreases from the inner circumferential side toward the outer circumferential side of the blade (33) at the leading edge (38) (see FIG. 4 ). In other words, the third distance H3 of the first portion (38a) increases from the end of the first portion (38a) on the blade tip (35) side toward the blade base (34), and reaches a maximum at the blade base (34). The height of the raised portion (49) changes corresponding to the third distance H3 of the first portion (38a).

[0078] The height of the raised portion (49) is the distance from the transition point (Pc) of the raised portion (49) in a direction perpendicular to the chord line (CLa) of the wing (33) to the raised tip (Pe), which is the end of the raised portion (49) on the pressure surface (40) side. The height of the raised portion (49) decreases the further away from the root (34) of the leading edge (38) is. The raised tip (Pe) is located on the leading edge (36) side of the raised portion (49), i.e., closer to the leading edge (36) with respect to the total length of the raised portion (49) in the target aerofoil cross section of the wing (33).

[0079] In the target aerofoil section of the blade (33) including the first portion (38a), a position on the chord line (CLa) at which the distance to the pressure surface (40) is a third distance H3 is defined as a first position (P1). Also, in the target aerofoil section of the blade (33) including the first portion (38a), a position on the chord line (CLa) corresponding to the change point (Pc) of the raised portion (49) is defined as a second position (P2).

[0080] The length L1 between the first position (P1) and the second position (P2) and the third distance H3 satisfy the relationship H3<L1. Furthermore, the length L1 between the first position (P1) and the second position (P2) and the length L2 between the leading edge (36) on the chord line (CLa) and the first position (P1) satisfy the relationship L2<L1. These relationships mean that the raised portion (49) has a shape that extends relatively far from the raised tip (Pe) to the rear side in the rotation direction (D1) of the blade (33).

[0081] --Quietness Performance of Axial Fan-- The air volume-static pressure characteristics (P-Q curve) and air volume-specific noise characteristics of the axial flow fan (30) of the example will be explained in comparison with the axial flow fans of Comparative Examples 1 and 2. The configuration of the axial flow fan (30) of the example is the same as that of the above-described first embodiment. The axial flow fan of Comparative Example 1 is a fan similar to the axial flow fan (30) of the example, except that the blades (33) do not have the porous portion (46) or the raised portion (49). The axial flow fan of Comparative Example 2 is a fan similar to the axial flow fan (30) of the example, except that the blades (33) do not have the raised portion (49).

[0082] FIG. 9 shows the air volume-static pressure characteristics (P-Q curves) of the axial flow fan (30) of the example and the axial flow fans of Comparative Examples 1 and 2. In FIG. 9, the air volume-static pressure characteristics (P-Q curve) of the axial flow fan (30) of the example are shown by a solid line, the air volume-static pressure characteristics (P-Q curve) of the axial flow fan of Comparative Example 1 are shown by a dashed line, and the air volume-static pressure characteristics (P-Q curve) of the axial flow fan of Comparative Example 2 are shown by a dashed line. As shown in FIG. 9, the line showing the air volume-static pressure characteristics (P-Q curve) of the axial flow fan (30) of the example and the line showing the air volume-static pressure characteristics (P-Q curves) of the axial flow fans of Comparative Examples 1 and 2 overlap almost in agreement. Thus, the axial flow fan (30) of the example has substantially the same air volume-static pressure characteristics as the axial flow fans of Comparative Examples 1 and 2.

[0083] FIG. 10 shows the air volume-specific noise characteristics of the axial fan (30) of the example and the axial fans of Comparative Examples 1 and 2. In FIG. 10, the air volume-specific noise characteristics of the axial fan (30) of the example are shown by a solid line, the air volume-specific noise characteristics of the axial fan of Comparative Example 1 are shown by a dashed line, and the air volume-specific noise characteristics of the axial fan of Comparative Example 2 are shown by a dashed line. As shown in FIG. 10, the axial fan (30) of the example has a reduced specific noise at the same air volume on the high air volume side compared to the axial fans of Comparative Examples 1 and 2. As can be seen from the above, the axial fan (30) of the example can reduce noise during operation on the high air volume side while maintaining the air volume-static pressure characteristics compared to the axial fans of Comparative Examples 1 and 2.

[0084] Features of First Embodiment In the axial flow fan (30) of the first embodiment, a curved raised portion (49) is formed on the pressure surface (40) of the leading edge (38) of the blade (33) in a symmetrical blade cross section. The absolute value of the angle between the tangent (TLa) of the pressure surface (40) and the chord line (CLa) of the pressure surface (40) gradually changes to form a mountain-like curve. When such a curved raised portion (49) is provided on the pressure surface (40) of the leading edge (38), the area of ​​the leading edge (38) against which the airflow collides during rotation of the blade (33) increases in the first portion (38a) including the raised portion (49). Therefore, as shown in FIG. 7 , when the airflow collides with the leading edge (38) of the blade (33), an airflow (F1) including a minute vortex (Vt) is generated on the pressure surface (40) side of the blade (33). The airflow (F1) including the minute vortices (Vt) is unlikely to separate from the curved portion and flows along the pressure surface (40) while suppressing turbulence. This makes it possible to suppress the development of turbulence flowing on the pressure surface (40) formed by the porous portion (46). As a result, the noise reduction effect of the porous portion (46) can be favorably obtained.

[0085] In the axial fan (30) of this first embodiment, in a symmetrical blade cross section of the blade (33) including the first portion (38a), a first distance H1, which is the maximum distance from the camber line (SLa) of the leading edge (38) to the pressure surface (40), is longer than a second distance H2, which is the maximum distance from the camber line (SLa) of the portion rearward of the leading edge (38) in the direction of rotation (D1) to the suction surface (41) (H1>H2). A blade (33) shape that satisfies this relationship prevents the blade thickness from becoming excessively large in the portion rearward of the leading edge (38), thereby enabling the blade (33) to be made lighter. This is advantageous for improving the energy efficiency of the axial fan (30).

[0086] In the axial flow fan (30) of this first embodiment, in the symmetrical blade cross section of the blade (33) including the first portion (38a), the pressure surface (40) of the blade (33) is connected so that the tangent line (TLa) is continuous from the leading edge (38) to the rear portion thereof. When the pressure surface (40) of the blade (33) is smoothly connected from the leading edge (38) including the raised portion (49) to the rear portion thereof, the airflow including minute vortices (Vt) generated by the collision of the airflow with the leading edge (38) can flow from the leading edge (38) to the rear portion along the pressure surface (40). This is advantageous in suppressing the development of turbulence flowing over the pressure surface (40).

[0087] In the axial flow fan (30) of this first embodiment, in a symmetrical blade cross section of the blade (33) including the first portion (38a), the length L1 between the first position (P1) and the second position (P2) on the chord line (CLa) is longer than the third distance H3 (H3<L1). The first position (P1) is the position where the distance from the chord line (CLa) to the pressure surface (40) is maximum in the raised portion (49) of the leading edge (38), and the second position (P2) is the position corresponding to the change point (Pc) of the curved shape of the raised portion (49). When the shape of the raised portion (49) is relatively long from the position where the third distance H3 is taken, i.e., the position where the distance from the chord line (CLa) to the pressure surface (40) is maximum, toward the rear, the shape of the pressure surface (40) of the leading edge (38) becomes gentler. This makes it possible to prevent the airflow, which includes minute vortices (Vt) generated by the collision of the airflow with the leading edge portion (38), from separating from the positive pressure surface (40) while flowing from the leading edge portion (38) to the rear side.

[0088] In the axial flow fan (30) of this first embodiment, in a target blade cross section of the blade (33) including the first portion (38a), a length L1 between a first position (P1) and a second position (P2) on the chord line (CLa) is longer than a length L2 between the leading edge (36) of the blade (33) on the chord line (CLa) and the first position (P1) (L2<L1). The first position (P1) is a position at which the distance from the chord line (CLa) to the pressure surface (40) is greatest on the raised portion (49) of the leading edge (38), and the second position (P2) is a position corresponding to a change point (Pc) in the curved shape of the raised portion (49). When the shape of the raised portion (49) is relatively long rearward from the position where the third distance H3 is taken, i.e., the position where the distance from the chord line (CLa) to the pressure surface (40) is greatest, the shape of the pressure surface (40) of the leading edge portion (38) becomes gentler. This makes it possible to prevent the airflow, which includes minute vortices (Vt) generated by the collision of the airflow with the leading edge portion (38), from separating from the pressure surface (40) as it flows rearward from the leading edge portion (38).

[0089] In the axial flow fan (30) of this first embodiment, in a symmetrical blade cross section of the blade (33) including the first portion (38a), the first distance H1 at the leading edge (38) is smaller than three times the second distance H2 at the portion rearward of the leading edge (38) (H1≦H2×3). This makes it possible to increase the area of ​​the leading edge (38) with which the airflow collides when the blade (33) rotates, while preventing the blade thickness of the leading edge (38) from becoming excessive.

[0090] In the axial flow fan (30) of this embodiment, a plurality of blades (33) are provided at intervals in the circumferential direction of the hub (31). Each blade (33) extends radially outward from the hub (31). In such an axial flow fan (30), the technique of the present disclosure is effective because it is possible to preferably obtain the noise reduction effect of the porous portion (46).

[0091] In the axial fan (30) of this first embodiment, in a symmetrical blade cross section of the blade (33) including the first portion (38a), a third distance H3 from the chord line (CLa) of the leading edge (38) to the pressure surface (40) is greater than a fourth distance H4 from the chord line (CLa) to the suction surface (41) (H4<H3). This effectively increases the area of ​​the leading edge (38) against which the airflow collides when the blade (33) rotates, while allowing the airflow (F1) including minute vortices (Vt) generated by the airflow colliding with the leading edge (38) to flow along the pressure surface (40) of the blade (33). As a result, the porous portion (46) effectively reduces noise.

[0092] In the axial fan (30) of this first embodiment, the first portion (38a) is provided on the inner circumferential side of the leading edge (38) of the blade (33), and the porous portion (46) is provided outward of the first portion (38a) in the direction of the rotation radius of the blade (33). In the axial fan (30), as the airflow increases, the airflow on the pressure surface (40) of the blade (33) tends to flow outward due to centrifugal force. Therefore, the airflow (F1) including minute vortices (Vt) generated by the airflow impinging on the leading edge (38) including the first portion (38a) can flow on the pressure surface (40) defined by the porous portion (46). This allows the porous portion (46) to effectively reduce noise.

[0093] In the axial fan (30) of this first embodiment, the third distance H3 of the first portion (38a) decreases from the inner periphery to the outer periphery of the blade (33) at the leading edge (38). Providing the first portion (38a) only on a portion of the leading edge (38) located upstream of the airflow (F1) flowing on the positive pressure surface (40) formed by the porous portion (46) reduces the noise reduction effect of the porous portion (46) with minimal modification to the shape of the blade (33). Furthermore, providing the first portion (38a) on the leading edge (38) of the blade (33) can suppress a decrease in the static pressure characteristics of the axial fan (30).

[0094] The air conditioner (1) of this first embodiment includes an axial fan (30). The axial fan (30) can effectively achieve the noise reduction effect of the porous portion (46). Therefore, the noise caused by the rotational operation of the axial fan (30) can be reduced, and quietness can be improved in the air conditioner (1).

[0095] Second Embodiment In the second embodiment, a turbofan (50) will be described as a fan according to the present disclosure. The turbofan (50) is used in the air conditioner (1) described in the first embodiment. In other words, the air conditioner (1) includes the turbofan (50). The turbofan (50) is used as an indoor fan (27) in the indoor unit (3) of the air conditioner (1). The indoor unit (3) is configured as a so-called ceiling-mounted type.

[0096] 11 and 12, the turbofan (50) includes one plate-like member (51), one shroud (53), and a plurality of blades (56). The turbofan (50) of this example has seven blades (56). The number of blades (56) may be six or less, or eight or more.

[0097] The plate-shaped member (51) is a disk-shaped member with a recessed center. The plate-shaped member (51) is a hub of the turbofan (50) and is disposed substantially coaxially with the drive shaft of the second fan motor (29). A shaft hole (52) is formed in the center of the plate-shaped member (51). The drive shaft of the second fan motor (29) is attached to the plate-shaped member (51) through the shaft hole (52). When the second fan motor (29) is driven, the plate-shaped member (51) rotates about a predetermined rotation axis (A2). The central axis of the plate-shaped member (51) coincides with the rotation axis (A2) of the turbofan (50).

[0098] The shroud (53) is an annular member. The shroud (53) is disposed facing the plate-shaped member (51) at a distance from the plate-shaped member (51) in the axial direction of the rotation shaft (A2). The shroud (53) is disposed substantially coaxially with the plate-shaped member (51). The outer diameter of the shroud (53) is approximately equal to the outer diameter of the plate-shaped member (51). The inner peripheral edge of the shroud (53) protrudes away from the plate-shaped member (51). In the turbofan (50), the inner peripheral edge of the shroud (53) forms an inlet (54), and the outer peripheral edges of the plate-shaped member (51) and the shroud (53) form an outlet (55).

[0099] The plurality of blades (56) are provided between the plate-shaped member (51) and the shroud (53). The plurality of blades (56) are arranged at intervals in the circumferential direction of the plate-shaped member (51) and the shroud (53), i.e., in the rotation direction (D2) of the turbofan (50). Each blade (56) is located in an area near the outer periphery of the plate-shaped member (51). Each blade (56) is provided upright in a direction in which the plate-shaped member (51) and the shroud (53) face each other, with its leading edge (57) located on the inner periphery and its trailing edge (58) located on the outer periphery. One edge of each blade (56) is fixed to the plate-shaped member (51), and the other edge of each blade (56) is fixed to the shroud (53).

[0100] Each blade (56) has a leading edge (57), a trailing edge (58), a pressure surface (60), and a suction surface (61). The leading edge (57) is the leading edge in the rotation direction (D2) of the blade (56). The trailing edge (58) is the trailing edge in the rotation direction (D2) of the blade (56). The pressure surface (60) is a blade surface that becomes a positive pressure side due to the flow of air being transported when the turbofan (50) rotates, and constitutes a surface facing the outer periphery of the turbofan (50) from which air flows out. The suction surface (61) is a blade surface that becomes a negative pressure side due to the flow of air being transported when the turbofan (50) rotates, and constitutes a surface facing the inner periphery of the turbofan (50) from which air flows in.

[0101] In the turbofan (50), a portion of the space between the plate-like member (51) and the shroud (53), where the blades (56) are arranged, forms an air flow path (62). The air flow path (62) is an annular flow path that continues to the outlet (55). Air passing through the turbofan (50) flows from the inside to the outside in the radial direction of the air flow path (62). Each blade (56) increases the pressure of the air by changing the speed of the air flow in the rotational direction (D2) from the leading edge (57) to the trailing edge (58) and by the difference in circumferential velocity between the leading edge (57) and the trailing edge (58). The turbofan (50) pressurizes the air drawn in through the inlet (54) and then blows it out through the outlet (55).

[0102] Each blade (56) is curved to form a convex shape toward the outer periphery of the turbofan (50). As shown in FIG. 13 , in a blade cross section in the rotation radius direction of the blade (56) (a blade cross section in a plane perpendicular to the rotation axis (A2)), a line segment connecting the leading edge (57) and the trailing edge (58) of the blade (56) is a chord line (CLb). In the turbofan (50), the blade cross section in the direction along the chord line (CLb) of the blade (56) corresponds to the blade cross section in the rotation radius direction of the blade (56), and is referred to as a "symmetric blade cross section" in this embodiment. In the symmetric blade cross section of the blade (56), a line connecting the midpoints of the pressure surface (60) and the suction surface (61) is a camber line (SLb).

[0103] Each blade (56) has a blade body (64) and a porous portion (66). The blade body (64) is made of a non-porous material such as a non-foamed synthetic resin. The blade body (64) constitutes the majority of the blade (56). In other words, the majority of the blade (56) is made of a non-porous material. The porous portion (66) is fixed to the blade body (64) by fitting, bonding, welding, or the like. The shape, material, average pore diameter, and porosity of the porous portion (66) in this example are the same as those of the porous portion (46) in the first embodiment.

[0104] The porous portion (66) is located midway in the width direction of the blade (56) and closer to the trailing edge (58), and is surrounded by the portion forming the blade main body (64). The porous portion (66) has the function of suppressing pressure fluctuations on the blade surface of the blade (56) and reducing noise generated by rotation of the turbofan (50). The porous portion (66) constitutes the entire blade (56) in the thickness direction. The porous portion (66) is exposed on both the pressure surface (60) and the suction surface (61) of the blade (56), and forms part of the pressure surface (60) and part of the suction surface (61).

[0105] In the turbofan (50) of this embodiment, the shape of the leading edge portion (68) of the blade (56) is devised to suitably obtain the noise reduction effect of the porous portion (66) on the high airflow side. Specifically, a raised portion (69) is provided on the pressure surface (60) of the leading edge portion (68) of the blade (56). Here, the leading edge portion (68) refers to a portion including the leading edge (57) of the blade (56) and extending 10% from the leading edge (57) with respect to the blade chord length L1. The raised portion (69) is a curved portion that is raised toward the pressure surface (60) of the blade (56). In this example, the raised portion (69) is provided over the entire length of the leading edge portion (68).

[0106] In the symmetrical blade cross section of the blade (56), the surface of the raised portion (69) is curved. The curved shape of the raised portion (69), like the raised portion (69) of the blade (33) in the axial fan (30) of the first embodiment, is such that the absolute value of the angle between the tangent (TLb) to the pressure surface (60) and the chord line (CLb) decreases from the leading edge (57) toward the rear in the direction of rotation (D2) of the blade (56), passes through zero, then increases, and reaches a transition point (Pc) where the rate of change of the absolute value starts to decrease (see FIG. 6 ). A portion of the tangent (TLb) to the pressure surface (60) formed by the raised portion (69) is shown in FIG. 13 .

[0107] In the symmetrical blade cross section of the blade (56), the pressure surface (60) of the blade (56) is connected such that a tangent (TLb) of the pressure surface (60) is continuous from the leading edge (68) to a portion rearward of the leading edge (68) in the direction of rotation (D2). The pressure surface (60) at the leading edge (68) smoothly changes, including the raised portion (69). The leading edge (68) of the blade (56) constitutes a first portion (68a). The first portion (68a) is a portion where the raised portion (69) is formed. The camber line (SLb) of the first portion (68a) has a shape that protrudes convexly toward the pressure surface (60) following the surface shape of the raised portion (69), and smoothly connects to the rear side of the first portion (68a).

[0108] In a target aerofoil section of the blade (56), the maximum value of the distance from the camber line (SLb) of the leading edge (68) to the pressure surface (60) is defined as a first distance H1. In addition, in a target aerofoil section of the blade (56), the maximum value of the distance from the camber line (SLb) aft of the leading edge (68) in the direction of rotation (D2) to the pressure surface (60) is defined as a second distance H2. As in the first embodiment, in the target aerofoil section of the blade (56), the first distance H1 and the second distance H2 satisfy the relationship H1 > H2 and also satisfy the relationship H1 ≦ H2 × 3.

[0109] In the target aerofoil section of the blade (56), the maximum distance from the chord line (CLb) of the leading edge (68) to the pressure surface (60) of the blade (56) is defined as a third distance H3. In addition, in the target aerofoil section of the blade (56), the maximum distance from the chord line (CLb) of the leading edge (68) to the suction surface (61) of the blade (56) is defined as a fourth distance H4. For convenience, in FIG. 13 , the positions of the third distance H3 and the fourth distance H4 are shifted from the first position (P1). In the target aerofoil section of the blade (56), the third distance H3 and the fourth distance H4 satisfy the relationship H4<H3.

[0110] In the target aerofoil section of the blade (56), a position on the chord line (CLb) where the distance to the pressure surface (60) is a third distance H3 is defined as a first position (P1). Furthermore, in the target aerofoil section of the blade (56), a position on the chord line (CLb) corresponding to the change point (Pc) of the raised portion (69) is defined as a second position (P2). As in the first embodiment, the length L1 between the first position (P1) and the second position (P2) and the third distance H3 satisfy the relationship H3<L1. Furthermore, the length L1 between the first position (P1) and the second position (P2) and the length L2 between the leading edge (57) on the chord line (CLb) and the first position (P1) satisfy the relationship L2<L1.

[0111] - Features of Embodiment 2 - In the turbofan (50) of Embodiment 2, a curved raised portion (69) is also formed on the pressure surface (60) of the leading edge (68) of the blade (56) in the target blade cross section of the blade (56). This increases the area of ​​the leading edge (68) with which the airflow collides when the blade (56) rotates. When the airflow collides with the leading edge (68) of the blade (56), an airflow containing tiny vortices is generated on the pressure surface (60) side of the blade (56). This makes it possible to suppress the development of turbulence flowing over the pressure surface (60) formed by the porous portion (66), and as a result, the noise reduction effect of the porous portion (66) can be favorably obtained.

[0112] In the turbofan (50) of this second embodiment, a plurality of blades (56) are provided between the plate-like member (51) and the shroud (53) at intervals in the rotational direction. Each blade (56) is oriented such that its leading edge (57) is located on the inner periphery and its trailing edge (58) is located on the outer periphery. In such a turbofan (50), the noise reduction effect of the porous portion (66) can be suitably achieved, and therefore the technology of the present disclosure is effective. Additionally, similar to the first embodiment, the effects associated with the surface shape of the raised portion (69) represented by the first to fourth distances H1, H2, H3, and H4 can be obtained.

[0113] Other Embodiments In the axial fan (30) of the first embodiment, the raised portion (49) of the blade (33) may be provided over the entire length of the leading edge (38). That is, the entire length of the leading edge (38) may constitute the first portion (38a). Furthermore, the raised portion (49) of the blade (33) may be provided only on the outer periphery of the leading edge (38). In the turbofan (50) of the second embodiment, the raised portion (69) of the blade (56) may be provided only on a portion of the leading edge (68). In short, it is sufficient that the curved raised portion (49, 69) is formed on the pressure surface (40, 60) of the leading edge (38, 68) of the blade (33, 56).

[0114] In the axial fan (30) of the first embodiment, the leading edge (38) of the blade (33) may be a portion that is less than 10% of the blade chord length L1 from the leading edge (36). For example, the leading edge (38) may be a portion that is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or 9% of the blade chord length L1 from the leading edge (36). The same applies to the leading edge (68) of the blade (56) in the turbofan (50) of the second embodiment.

[0115] In the axial flow fan (30) of the first embodiment, the center (C1) of the porous portion (46) may be located outside the range of 0.4 to 0.8 for the chord ratio (Lb / La) and outside the range of 0.6 to 0.8 for the radius ratio (Rb / Ra). The area of ​​the porous portion (46) may be greater than 30% of the overall area of ​​the pressure surface (40) as long as the strength of the blade (33) is ensured. In the turbofan (50) of the second embodiment, the porous portion (66) may be provided so as to extend toward the leading edge (57) of the blade (56), or may be provided in multiple portions. In short, the porous portion (46, 66) may be located rearward of the leading edge (38, 68) in the direction of rotation to form the pressure surface (40, 60) of the blade (33, 56).

[0116] The fan according to the present disclosure can also be applied to other types of fans, such as a mixed flow fan. Furthermore, the fan according to the present disclosure can be used in various other devices that require airflow, in addition to the air conditioner (1) that adjusts the temperature of the air in a target space. Examples of other devices include a humidity control device that adjusts the humidity of the air in the target space, a ventilation device that ventilates the target space, and an air purifier that purifies the air in the target space.

[0117] Although the embodiments and modifications have been described above, it will be understood that various modifications in form and details are possible without departing from the spirit and scope of the claims. Furthermore, the above embodiments and modifications may be combined or substituted as appropriate as long as the functionality of the subject matter of the present disclosure is not impaired.

[0118] Note that the above descriptions such as "first," "second," etc. are merely used to distinguish the terms to which these descriptions are attached, and do not limit the number or order of the terms. Furthermore, the description "to" in a numerical range means a range that includes the numerical values ​​before and after it. In other words, if X and Y are used as substitutes for numerical values, then "X to Y" indicates a range of "greater than or equal to X and less than or equal to Y."

[0119] INDUSTRIAL APPLICABILITY As described above, the present disclosure is useful for fans and air conditioners.

[0120] A1, A2 Rotation axis CLa, CLb Chord line D1, D2 Direction of rotation Pc Point of change P1 First position P2 Second position TLa, TLb Tangent 1 Air conditioning unit 30 Axial flow fan (fan) 31 Hub 33 Blade 36 Leading edge 38 Leading edge portion 38a First portion 40 Pressure surface 41 Suction surface 49 Raised portion (curved portion) 50 Turbofan (fan) 51 Plate-like member 53 Shroud 56 Blade 57 Leading edge 58 Trailing edge 60 Pressure surface 68 Leading edge portion 68a First portion 69 Raised portion (curved portion)

Claims

1. A turbine rotor includes a blade (33, 56) that rotates around a predetermined rotation axis (A1, A2), the blade (33, 56) having a leading edge portion (38, 68) including a leading edge (36, 57) that is a leading edge in the direction of rotation, and a porous portion (46, 66) that is located rearward of the leading edge portion (38, 68) in the direction of rotation and forms a pressure surface (40, 60) of the blade (33, 56), a fan, in a blade cross section taken along a chord line (CLa, CLb) of the blade (33, 56), on the pressure surface (40, 60) of the leading edge portion (38, 68), formed with a curved portion (49, 69) in which the absolute value of the angle between a tangent (TLa, TLb) to the pressure surface (40, 60) and the chord line (CLa, CLb) decreases from the leading edge (36, 57) toward the rear in the direction of rotation (D1, D2), passes through zero, then increases, and reaches a change point (Pc) at which the rate of change of the absolute value starts to decrease.

2. A fan according to claim 1, wherein the leading edge (38, 68) has a first portion (38a, 68a) on which the curved portion is formed, and in the blade cross section including the first portion (38a, 68a), a first distance H1 which is the maximum distance from a camber line (SLa, SLb) of the leading edge (38, 68) to the pressure surface (40, 60) and a second distance H2 which is the maximum distance from the camber line (SLa, SLb) of a portion rearward of the leading edge (38, 68) in the direction of rotation (D1, D2) to the pressure surface (40, 60) satisfy the relationship H1 > H2.

3. A fan according to claim 1 or 2, wherein the leading edge (38, 68) has a first portion (38a, 68a) on which the curved portion is formed, and in the blade cross section including the first portion (38a, 68a), the pressure surface (40, 60) of the blade (33, 56) is connected so that a tangent (TLa, TLb) of the pressure surface (40, 60) is continuous from the leading edge (38, 68) to a portion rearward of the leading edge (38, 68) in the direction of rotation (D1, D2).

4. A fan according to any one of claims 1 to 3, wherein the leading edge (38, 68) has a first portion (38a, 68a) on which the curved portion is formed, and when a maximum value of the distance from the chord line (CLa, CLb) of the leading edge (38, 68) to the pressure surface (40, 60) is defined as a third distance H3 in the aerofoil cross section including the first portion (38a, 68a), a length L1 between a first position (P1) where the distance to the pressure surface (40, 60) on the chord line (CLa, CLb) is the third distance H3, and a second position (P2) corresponding to the change point (Pc), and the third distance H3, satisfy the relationship H3<L1.

5. A fan according to any one of claims 1 to 4, wherein the leading edge (38, 68) has a first portion (38a, 68a) on which the curved portion is formed, and wherein, in the aerofoil cross section including the first portion (38a, 68a), when a maximum value of the distance from the chord line (CLa, CLb) of the leading edge (38, 68) to the pressure surface (40, 60) is defined as a third distance H3, a length L1 between a first position (P1) on the chord line (CLa, CLb) where the distance to the pressure surface (40, 60) is the third distance H3 and a second position (P2) corresponding to the change point (Pc), and a length L2 between the leading edge (36, 57) on the chord line (CLa, CLb) and the first position (P1) satisfy the relationship L2<L1.

6. A fan according to any one of claims 1 to 5, wherein the leading edge (38, 68) has a first portion (38a, 68a) on which the curved portion is formed, and in the blade cross section including the first portion (38a, 68a), a first distance H1 which is the maximum distance from a camber line (SLa, SLb) of the leading edge (38, 68) to the pressure surface (40, 60) and a second distance H2 which is the maximum distance from the camber line (SLa, SLb) of a portion rearward of the leading edge (38, 68) in the direction of rotation (D1, D2) to the pressure surface (40, 60) satisfy the relationship H1≦H2×3.

7. A fan according to any one of claims 1 to 6, comprising a hub (31) rotatable around the rotation axis (A1), wherein the blades (33) are provided in a plurality at intervals in the circumferential direction of the hub (31), and each blade extends radially outward from the hub (31).

8. A fan according to claim 7, wherein the leading edge (38) has a first portion (38a) in which the curved portion is formed, and in the blade cross section including the first portion (38a), a third distance H3 which is the maximum distance from the chord line (CLa) of the leading edge (38) to the pressure surface (40) of the blade (33) and a fourth distance H4 which is the maximum distance from the chord line (CLa) of the leading edge (38) to the suction surface (41) of the blade (33) satisfy the relationship H4<H3.

9. A fan according to claim 8, wherein the third distance H3 of the first portion (38a) decreases from the inner circumferential side to the outer circumferential side of the blade (33) at the leading edge portion (38).

10. A fan according to any one of claims 7 to 9, wherein the leading edge (38) has a first portion (38a) on which the curved portion is formed, the first portion (38a) is provided on the inner peripheral side of the leading edge (38), and the porous portion (46) is provided outside the first portion (38a) in the direction of the rotation radius of the blade (33).

11. A fan according to any one of claims 1 to 6, comprising: a plate-like member (51) rotatable about the rotation axis (A2); and a shroud (53) arranged at a distance from the plate-like member (51) in the axial direction of the rotation axis (A2), wherein a plurality of the blades (56) are provided between the plate-like member (51) and the shroud (53) at a distance from each other in the rotation direction (D2) such that the leading edges (57) are located on the inner circumferential side and trailing edges (58), which are the rear edges in the rotation direction (D2), are located on the outer circumferential side.

12. An air conditioning device comprising a fan (30, 50) according to any one of claims 1 to 11.

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