Fan and air conditioner

Abstract

An axial fan (30) includes a plurality of blades (33) configured to rotate about a predetermined axis (A1). Each blade has a leading edge portion (38) including a leading edge (36) and a porous portion (46) that is located behind the leading edge portion in a rotation direction (D1) and forms a positive pressure surface (40). In a blade cross section taken along a chord line (CLa) of the blade, the positive pressure surface of the leading edge portion has a raised portion (49) in which an absolute value of an angle formed by a tangent (TLa) to the positive pressure surface and the chord line decreases to zero with increasing distance from the leading edge toward a rear side in the rotation direction, and then increases to reach a change point (Pc) at which a rate of change of the absolute value starts to decrease.

Description

TECHNICAL FIELD

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

[0002] Patent Document 1 discloses an axial fan. This axial fan includes a plurality of blades each having a porous portion. The porous portion is provided to reduce noise generated by the rotation of the axial fan.CITATION LISTPATENT DOCUMENT

[0003] Patent Document 1: Japanese Unexamined Patent Publication No. 2023-151184SUMMARY OF THE INVENTIONTECHNICAL PROBLEM

[0004] The faster the blades rotate, the greater the volume of air the axial fan generates. The flow velocity of the air passing over a positive pressure surface of each blade increases, and a turbulent flow of the air remarkably develops on the positive pressure surface. The inventors of the present application have found that an axial fan having blades each having a porous portion as disclosed by Patent Document 1 impairs the effect of noise reduction by the porous portion when the turbulent flow develops and becomes larger on the positive pressure surface of the blades.

[0005] An object of the present disclosure is to obtain a suitable noise reduction effect for a fan having blades each provided with a porous portion by means of the porous portion.SOLUTION TO THE PROBLEM

[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) configured to rotate about a predetermined axis (A1, A2). The blade (33, 56) has: a leading edge portion (38, 68) including a leading edge (36, 57) which is a front edge in a rotation direction (D1, D2); and a porous portion (46, 66) which is located behind the leading edge portion (38, 68) in the rotation direction (D1, D2) and forms a positive pressure surface (40, 60) of the blade (33, 56). In a blade cross section taken along a chord line (CLa, CLb) of the blade (33, 56), the positive pressure surface (40, 60) of the leading edge portion (38, 68) has a curved portion (49, 69) in which an absolute value of an angle formed by a tangent (TLa, TLb) to the positive pressure surface (40, 60) and the chord line (CLa, CLb) decreases to zero with increasing distance from the leading edge (36, 57) toward a rear side in the rotation direction (D1, D2), and then increases to reach a change point (Pc) at which a rate of change of the absolute value starts to decrease.

[0007] According to the first aspect, in the blade cross section taken along the chord line (CLa, CLb) of the blade (33, 56), the positive pressure surface (40, 60) of the leading edge portion (38, 68) of the blade (33, 56) has a curved portion (49, 69) in which an absolute value of an angle formed by a tangent (TLa, TLb) to the positive pressure surface (40, 60) and the chord line (CLa, CLb) gradually changes in a mountain-shaped curve. Such a curved portion (49, 69) forms a raised portion (49, 69) raised on the positive pressure surface of the blade (33, 56). The raised portion (49, 69) provided on the positive pressure surface (40, 60) of the leading edge portion (38, 68) increases the area of the leading edge portion (38, 68) with which the airflow collides during the rotation of the blade (33, 56). Thus, when the airflow collides with the leading edge portion (38, 68) of the blade (33, 56), an airflow (F1) including minute vortices (Vt) is generated on the positive pressure surface (40, 60) of the blade (33, 56). The airflow (F1) including the minute vortices (Vt) is less likely to be separated from the curved raised portion (49, 69) and flows along the positive pressure surface (40, 60) with reduced generation of the turbulent flow. This can reduce the development of the turbulent flow on the positive pressure surface (40, 60) formed by the porous portion (46, 66). As a result, a suitable noise reduction effect can be achieved by the porous portion (46, 66).

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

[0009] According to the second aspect, in the blade cross section taken along the chord line (CLa, CLb) of the blade (33, 56) including the first portion (38a, 68a), the first distance H1 which is the maximum distance from the camber line (SLa, SLb) in the leading edge portion (38, 68) to the positive pressure surface (40, 60) is greater than the second distance H2 which is the maximum distance from the camber line (SLa, SLb) in the portion behind the leading edge portion (38, 68) in the rotation direction (D1, D2) to the negative pressure surface (41, 61) (H1 > H2) The shape of the blade (33, 56) that satisfies this relationship does not make the portion of the blade (33, 56) behind the leading edge portion (38, 68) excessively thick, reducing the weight of the blade (33, 56). This is advantageous in making the fan (30, 50) more energy efficient.

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

[0011] According to the third aspect, in the blade cross section taken along the chord line (CLa, CLb) of the blade (33, 56) including the first portion (38a, 68a), the positive pressure surface (40, 60) of the blade (33, 56) is shaped such that the tangent (TLa, TLb) is continuous from the leading edge portion (38, 68) to the portion behind the leading edge portion (38, 68). When the positive pressure surface (40, 60) of the blade (33, 56) is smooth and continuous from the leading edge portion (38, 68) including the raised portion (49, 69) to the portion behind the leading edge portion (38, 68) in this manner, an airflow (F1) including minute vortices (Vt) generated upon collision of an airflow with the leading edge portion (38, 68) can move rearward from the leading edge portion (38, 68) along the positive pressure surface (40, 60). This is advantageous in reducing the development of the turbulent flow on the positive 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, in which the leading edge portion (38, 68) has a first portion (38a, 68a) provided with the curved portion (49, 69). In the blade cross section including the first portion (38a, 68a), a relationship of H3 < L1 is satisfied, where H3 represents a third distance H3 which is a maximum distance from the chord line (CLa, CLb) of the leading edge portion (38, 68) to the positive pressure surface (40, 60), and L1 represents a length L1 between a first point (P1) on the chord line (CLa, CLb) at which a distance to the positive pressure surface (40, 60) is the third distance H3, and a second point (P2) corresponding to the change point (Pc).

[0013] According to the fourth aspect, in the blade cross section taken along the chord line (CLa, CLb) of the blade (33, 56) including the first portion (38a, 68a), the length L1 between the first point (P1) and the second point (P2) on the chord line (CLa, CLb) is greater than the third distance H3 (H3 < L1). The first point (P1) is a point where the distance from the chord line (CLa, CLb) to the positive pressure surface (40, 60) in the raised portion (49, 69) of the leading edge portion (38, 68) is the maximum, and the second point (P2) is a point corresponding to the change point (Pc) of the curved shape of the raised portion (49, 69). When the raised portion (49, 69) has a shape that is relatively long in a portion behind the point at the third distance H3, that is, the point where the distance from the chord line (CLa, CLb) to the positive pressure surface (40, 60) is the maximum, the positive pressure surface (40, 60) of the leading edge portion (38, 68) has a gently sloping shape. This can reduce the separation of the airflow (F1) including the minute vortices (Vt) generated upon collision of the airflow with the leading edge portion (38, 68) from the positive pressure surface (40, 60) while the airflow is moving 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, in which the leading edge portion (38, 68) has a first portion (38a, 68a) provided with the curved portion (49, 69). In the blade cross section including the first portion (38a, 68a), a relationship of L2 < L1 is satisfied, where L1 represents a length L1 between a first point (P1) on the chord line (CLa, CLb) at which a distance to the positive pressure surface (40, 60) is a third distance H3, and a second point (P2) corresponding to the change point (Pc), the third distance H3 being a maximum distance from the chord line (CLa, CLb) of the leading edge portion (38, 68) to the positive pressure surface (40, 60), and L2 represents a length L2 between the leading edge (38, 68) and the first point (P1) on the chord line (CLa, CLb).

[0015] According to the fifth aspect, in the blade cross section taken along the chord line (CLa, CLb) of the blade (33, 56) including the first portion (38a, 68a), the length L1 between the first point (P1) and the second point (P2) on the chord line (CLa, CLb) is greater than the length L2 between the leading edge (36, 57) and the first point (P1) on the chord line (CLa, CLb) of the blade (33, 56) (L2 < L1). The first point (P1) is a point where the distance from the chord line (CLa, CLb) to the positive pressure surface (40, 60) in the raised portion (49, 69) of the leading edge portion (38, 68) is the maximum, and the second point (P2) is a point corresponding to the change point (Pc) of the curved shape of the raised portion (49, 69). When the raised portion (49, 69) has a shape that is relatively long in a portion behind the point at the third distance H3, that is, the point where the distance from the chord line (CLa, CLb) to the positive pressure surface (40, 60) is the maximum, the positive pressure surface (40, 60) of the leading edge portion (38, 68) has a gently sloping shape. This can reduce the separation of the airflow (F1) including the minute vortices (Vt) generated upon collision of the airflow with the leading edge portion (38, 68) from the positive pressure surface (40, 60) while the airflow is moving 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, in which the leading edge portion (38, 68) has a first portion (38a, 68a) provided with the curved portion (49, 69). In the blade cross section including the first portion (38a, 68a), a relationship of H1 ≤ H2 ×3 is satisfied, where H1 represents a first distance H1 which is a maximum distance from a camber line (SLa, SLb) in the leading edge portion (38, 68) to the positive pressure surface (40, 60), and H2 represents a second distance H2 which is a maximum distance from the camber line (SLa, SLb) in a portion behind the leading edge portion (38, 68) in the rotation direction (D1, D2) to the positive pressure surface (40, 60).

[0017] According to the sixth aspect, in the blade cross section taken along the chord line (CLa, CLb) of the blade (33, 56) including the first portion (38a, 68a), the first distance H1 in the leading edge portion (38, 68) is smaller than three times the second distance H2 in the portion behind the leading edge portion (38, 68) (H1 < H2 × 3). This can increase the area of the leading edge portion (38, 68) with which the airflow collides during the rotation of the blade (33, 56), without excessively increasing the thickness of the leading edge portion (38, 68).

[0018] A seventh aspect of the present disclosure is the fan (30) of any one of the first to sixth aspects, in which the fan (30) further includes a hub (31) rotatable about the axis (A1). Multiple blades (33), each being identical to the blade (33), are arranged at intervals from each other in a circumferential direction of the hub (31), each of the multiple blades (33) extending radially outward from the hub (31).

[0019] According to the seventh aspect, the blades (33) are arranged at intervals from each other in the circumferential direction of the hub (31). Each blade (33) extends radially outward from the hub (31). The present disclosure is effective for such an axial fan (30) because a suitable noise reduction effect can be achieved by the porous portion (46).

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

[0021] According to the eighth aspect, in the blade cross section taken along the chord line (CLa) of the blade (33) including the first portion (38a), the third distance H3 from the chord line (CLa) in the leading edge portion (38) to the positive pressure surface (40) is greater than the fourth distance H4 from the chord line (CLa) to the negative pressure surface (41) (H4 < H3). This can effectively increase the area of the leading edge portion (38) of the axial fan (30) with which the airflow collides during the rotation of the blade (33), and the airflow (F1) including the minute vortices (Vt) generated upon collision of an airflow with the leading edge portion (38) can move along the positive pressure surface (40) of the blade (33). As a result, a suitable noise reduction effect can be achieved by the porous portion (46).

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

[0023] According to the ninth aspect, the third distance H3 in the first portion (38a) decreases from the inner periphery to the outer periphery of the blade (33) in the leading edge portion (38). When the first portion (38a) is provided only in part of the leading edge portion (38) on the upstream side of the airflow (F1) on the positive pressure surface (40) formed by the porous portion (46), the blade (33) does not require much change in shape to achieve the suitable noise reduction effect by the porous portion (46). The provision of the first portion (38a) in the leading edge portion (38) of the blade (33) can reduce the likelihood of a decrease in the static pressure characteristic 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, in which the leading edge portion (38) includes a first portion (38a) provided with the curved portion. The first portion (38a) is provided on an inner peripheral side of the leading edge portion (38). The porous portion (46) is provided outside of the first portion (38a) in a direction of radius of rotation of the blade (33).

[0025] According to the tenth aspect, the first portion (38a) is provided on the inner peripheral side of the leading edge portion (38) of the blade (33), and the porous portion (46) is provided outside of the first portion (38a) in the radial direction of the blade (33). As the air volume of the axial fan (30) increases, the airflow (F1) on the positive pressure surface (40) of the blade (33) tends to move radially outward due to centrifugal force. Thus, the airflow (F1) including the minute vortices (Vt) generated upon collision of the airflow with the leading edge portion (38) including the first portion (38a) can move on the positive pressure surface (40) formed by the porous portion (46). As a result, a suitable noise reduction effect can be achieved by the porous portion (46).

[0026] An eleventh aspect of the present disclosure is the fan (50) of any one of the first to sixth aspects, in which the fan (50) further includes: a plate-shaped member (51) rotatable about the axis (A2); and a shroud (53) spaced from the plate-shaped member (51) in an axial direction of the axis (A2). Multiple blades (56), each being identical to the blade (56), are arranged at intervals from each other in the rotation direction (D2) between the plate-shaped member (51) and the shroud (53), with the leading edge (57) positioned inward and a trailing edge (58) positioned outward, the trailing edge (58) being a rear edge in the rotation direction (D2).

[0027] According to the eleventh aspect, the blades (56) are arranged at intervals from each other in the rotation direction (D2) between the plate-shaped member (51) and the shroud (53). Each blade (56) is oriented so that the leading edge (57) is positioned inward and the trailing edge (58) is positioned outward. The present disclosure is effective for such a turbo fan (50) because a suitable noise reduction effect can be achieved by the porous portion (66).

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

[0029] According to the twelfth aspect, the air conditioning apparatus (1) includes the fan (30, 50). The fan (30, 50) can achieve a suitable noise reduction effect by the porous portion (46, 66). This can reduce noise caused by the rotation of the fan (30, 50) of the air conditioning apparatus (1), improving quietness.BRIEF DESCRIPTION OF THE DRAWINGS

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

[0031] Exemplary embodiments will be described in detail below with reference to the drawings. In the following embodiments, an axial fan and a turbo fan to which a fan of the present disclosure is applied will be described as examples. The drawings are used for conceptual description of the present disclosure. In the drawings, dimensions, ratios, or numbers may be exaggerated or simplified for easy understanding of the present disclosure.«First Embodiment»

[0032] A first embodiment is directed to an axial fan (30) as a fan according to the present disclosure. The axial fan (30) is used for an air conditioning apparatus (1). In other words, the air conditioning apparatus (1) includes the axial fan (30).-Air Conditioning Apparatus-

[0033] The air conditioning apparatus (1) is an apparatus that controls the temperature of air in a target space. The target space of this example is an indoor space. As illustrated in FIG. 1, the air conditioning apparatus (1) is a pair-type air conditioning apparatus, and includes a single indoor unit (3) and a single outdoor unit (5). The indoor unit (3) is placed inside. The outdoor unit (5) is placed outside. The indoor unit (3) and the outdoor unit (5) are connected to each other by a liquid connection pipe (7) and a gas connection pipe (9).

[0034] The indoor unit (3), the outdoor unit (5), the liquid connection pipe (7), and the gas connection pipe (9) constitute a refrigerant circuit (11). The refrigerant circuit (11) is filled with a refrigerant. The refrigerant circuit (11) includes, as main components, 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 pipes.

[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 coupled to the outdoor fan (23). The first fan motor (25) drives the outdoor fan (23) to rotate. The axial fan (30) of the present embodiment is used as the outdoor fan (23).

[0036] The compressor (13) sucks and compresses a low-pressure gas refrigerant and discharges the compressed refrigerant. The outdoor fan (23) transfers outdoor air so that the outdoor air passes through the outdoor heat exchanger (15). The outdoor heat exchanger (15) allows the outdoor air transferred by the outdoor fan (23) and the refrigerant flowing inside the outdoor heat exchanger (15) to exchange heat. The outdoor heat exchanger (15) is, for example, a fin-and-tube heat exchanger. The expansion valve (17) decompresses the refrigerant.

[0037] The switching mechanism (19) changes the direction of circulation 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 a discharge side of the compressor (13). The second port (19b) is connected to a 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 switched between a first state (a state indicated by solid curves in FIG. 1) and a second state (a state indicated by broken curves in FIG. 1). The switching mechanism (19) in the first state allows the first port (19a) and the third port (19c) to communicate with each other, and allows the second port (19b) and the fourth port (19d) to communicate with each other. The switching mechanism (19) in the second state allows the first port (19a) and the fourth port (19d) to communicate with each other, and allows the second port (19b) and the third port (19c) to communicate with each other.

[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). As the indoor fan (27), a cross-flow fan or a turbo fan may be used for example. The indoor fan (27) may be another type of fan such as a sirocco fan.

[0040] A second fan motor (29) is connected to the indoor fan (27). The indoor fan (27) is driven to rotate by the second fan motor (29), and transfers indoor air so that the indoor air passes through the indoor heat exchanger (21). The indoor heat exchanger (21) allows the indoor air transferred by the indoor fan (27) and the refrigerant flowing in the indoor heat exchanger (21) to exchange heat. The indoor heat exchanger (21) is, for example, a fin-and-tube heat exchanger.

[0041] The air conditioning apparatus (1) performs a cooling operation and a heating operation.

[0042] The cooling operation is an operation of 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. This allows the refrigerant in the refrigerant circuit (11) to flow in the direction of solid arrows shown in FIG. 1, and causes the outdoor heat exchanger (15) to function as a radiator, and the indoor heat exchanger (21) to function as an evaporator. In the cooling operation, the air transferred 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 of 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. This allows the refrigerant in the refrigerant circuit (11) to flow in the direction of broken arrows shown in FIG. 1, and causes the outdoor heat exchanger (15) to function as an evaporator, and the indoor heat exchanger (21) to function as a radiator. In the heating operation, the air transferred by the indoor fan (27) is heated by the indoor heat exchanger (21) and supplied to the indoor space.-Axial fan-

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

[0045] The hub (31) is formed into a cylindrical shape. The hub (31) is a 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). A 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 axis (A1). The center axis of the hub (31) coincides with the axis (A1) of the axial fan (30).

[0046] The blades (33) are arranged at intervals from each other in the circumferential direction of the hub (31). Each blade (33) extends radially outward from an outer peripheral surface of the hub (31). The blades (33) extend radially outward from the hub (31) in the direction of radius of rotation of the axial fan (30). The blades (33) adjacent to each other do not overlap each other when viewed from the front or the back. The blades (33) have the same shape.

[0047] Each blade (33) employs a so-called forward swept wing shape. Each blade (33) is formed in the shape of a smoothly curved plate that is slightly convex on one of blade surfaces (a negative pressure surface (41)) along the direction of radius of rotation and the rotation direction (D1). Each blade (33) has a blade root (34), a blade tip (35), a leading edge (36), and a trailing edge (37). The blade root (34), the blade tip (35), the leading edge (36), and the trailing edge (37) constitute an outer periphery of the blade (33) in plan view.

[0048] The blade root (34) is an end of the blade (33) at the center in the radial direction of the axial fan (30), that is, an inner end of the blade (33) in the direction of radius of rotation. The blade tip (35) is an outer peripheral end of the blade (33) in the radial direction of the axial fan (30), that is, an outer end of the blade (33) in the direction of radius of rotation. The blade root (34) and the blade tip (35) of the blade (33) extend in the rotation direction (D1) of the axial fan (30).

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

[0050] The leading edge (36) is a front edge of the blade (33) in the rotation direction (D1). The trailing edge (37) is a rear edge of the blade (33) in the rotation direction (D1). The leading edge (36) and the trailing edge (37) of the blade (33) extend from the hub (31) toward the outer periphery of the axial fan (30). The leading edge (36) and the trailing edge (37), each forming an arc, extend from the blade root (34) to the blade tip (35) to be apart from each other.

[0051] The leading edge (36) of the blade (33) extends such that it protrudes forward in the rotation direction (D1) as it approaches the blade tip (35) from the blade root (34). The leading edge (36) is curved toward the rear side in the rotation direction (D1) of the blade (33). The trailing edge (37) extends such that it protrudes slightly rearward in the rotation direction (D1) as it approaches the blade tip (35) from the blade root (34). The leading edge (36) is slightly curved toward the front side in the rotation direction (D1) of the blade (33).

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

[0053] Each blade (33) is inclined to intersect with a plane orthogonal to the axis (A1) of the axial fan (30). The leading edge (36) of the blade (33) is on the back side (negative pressure side) of the axial fan (30), and extends from a point near one end (an air inlet end) of the hub (31) toward the upstream side of the air to be transferred. The trailing edge (37) of the blade (33) is on the front side (positive pressure side) of the axial fan (30) and is located closer to the other end (an air outlet end) of the hub (31).

[0054] As illustrated in FIGS. 4 and 5, each blade (33) further includes a positive pressure surface (40) and a negative pressure surface (41). The positive pressure surface (40) is a blade surface where a positive pressure is generated by the flow of the air transferred during the rotation of the axial fan (30), and constitutes a surface facing the front side of the axial fan (30) from which the air flows out. The negative pressure surface (41) is a blade surface where a negative pressure is generated by the flow of the air transferred during the rotation of the axial fan (30), and constitutes a surface facing the back side of the axial fan (30) from which the air flows in.

[0055] As illustrated in FIG. 2, an outer edge portion extending along the blade tip (35) of each blade (33) constitutes a winglet portion (42). The winglet portion (42) is slightly bent toward the negative pressure surface (41) with respect to the other portion of the blade (33). The winglet portion (42) is provided to be gradually widened from the leading edge (36) toward the trailing edge (37). The winglet portion (42) functions to rectify the flow of the air around the blade tip (35). The provision of the winglet portion (42) is advantageous in reducing the generation of blade tip vortices.

[0056] The blades (33) rotate about the axis (A1) together with the hub (31). When the axial fan (30) rotates about the axis (A1), the axial fan (30) pushes out the air with the positive pressure surface (40) of each blade (33). Thus, as the blades (33) rotate, the air flows from the inlet side, which is the back side of the axial fan (30), to the outlet side, which is the front side. At this time, the pressure increases on the positive pressure surface (40) of each blade (33) to push the air out. On the other hand, the pressure is relatively low on the negative pressure surface (41) of the blade (33).

[0057] During the rotation of the axial fan (30), the air flowing on the positive pressure surface (40) of the blade (33) separates from the positive pressure surface (40) when it reaches the blade tip (35), and then is dragged from the positive pressure surface (40) to the negative pressure surface (41) to form a vortex. The vortex generated at the blade tip (35) is called a blade tip vortex. The blade tip vortex develops rearward with the rotation of the blade (33) and becomes a trailing vortex flowing rearward in the rotation direction (D1) from the trailing edge (37) of the blade (33). The higher the energy of the blade tip vortex and the trailing vortex is, the louder the noise becomes during the operation of the axial fan (30).

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

[0059] As also illustrated in FIG. 3, the blade body (44) has the blade root (34), the blade tip (35), the leading edge (36), and the 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 formed integrally with the hub (31) by, for example, injection molding. The blade body (44) constitutes most of the blade (33). That is, most of the blade (33) is made of the non-porous material. The porous portion (46) is fixed to the blade body (44) by fitting, bonding, or welding.

[0060] The porous portion (46) is provided in a region surrounded by the blade root (34), the blade tip (35), the leading edge (36), and the trailing edge (37). The porous portion (46) of this example is arranged near the blade tip (35) in a substantially middle region of the blade (33) in the rotation direction (D1), and is surrounded by the material forming the blade body (44). The porous portion (46) has a function of reducing noise generated by the rotation of the axial fan (30) by reducing the pressure fluctuations on the blade surfaces of the blade (33). The silencing effect of the porous portion (46) varies depending on the position and area of the porous portion (46) in the blade (33).

[0061] The porous portion (46) is provided in, for example, a quadrangular shape (specifically, a quadrangular shape with four rounded corners). The porous portion (46) may have other shapes such as a triangular shape and an oval shape. The porous portion (46) extends over the entire thickness of the blade (33). The porous portion (46) is exposed on the positive pressure surface (40) and the negative pressure surface (41) of the blade (33) and constitutes part of the positive pressure surface (40) and part of the negative pressure surface (41).

[0062] The porous portion (46) is made of a porous material having a plurality of fine pores connected to each other. The fine pores in the porous material communicate with the positive pressure surface (40) and the negative pressure surface (41) of the blade (33). The average diameter of the pores (air gaps) of the porous portion (46) is, for example, in a range of 15 µm to 300 µm. The porosity of the porous portion (46) (= the volume of the air gaps / the entire volume of the porous portion) is, for example, in a range of 35% to 90%.

[0063] The porous material is a synthetic resin, ceramics, metal, or the like. For example, the synthetic resin, the ceramics, or the metal is used as a sintered porous body. The sintered porous body is formed by heating accumulated powder particles to partially weld them. 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) in the blade (33) is represented by a chord ratio (Lb / La) and a radius ratio (Rb / Ra) at the center (C1) of the porous portion (46). The center (C1) of the porous portion (46) refers to the center position in the radial direction and the rotation direction (D1) of the blade (33). The chord ratio (Lb / La) is a ratio of a distance Lb from the leading edge (36) to an arbitrary portion to a chord length La in the target blade cross section of the blade (33). The radius ratio (Rb / Ra) is a ratio of a distance Rb from the blade root (34) to the arbitrary portion to a distance Ra from the blade root (34) to the blade tip (35) in the radial direction of the blade (33).

[0065] The center (C1) of the porous portion (46) is located at a position in which 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 located outside a raised portion (49) of the leading edge portion (38), which will be described later, in the radial direction of the blade (33). The area of the porous portion (46) is set within a range in which the noise reduction effect (silencing effect) can be exhibited. In this example, the area of the porous portion (46) is 30% or less of the area of the entire positive pressure surface (40).

[0066] When the axial fan (30) rotates, the air forms airflows (F1, F2) from the leading edge (36) of the blade (33) toward the positive pressure surface (40) and the negative pressure surface (41) (see FIG. 7). The airflows (F1, F2) move along the blade surfaces (the positive pressure surface (40) and the negative pressure surface (41)) as the axial fan (30) rotates, and leave the blade surfaces at the trailing edge (37). At this time, pressure fluctuations occur on the blade surfaces due to various factors, such as pressure fluctuations at a boundary surface between the airflows (F1, F2) and pressure fluctuations upon transition from a laminar flow to a turbulent flow. Such pressure fluctuations on the blade surfaces are one of causes that increase the noise (blowing sound) during the rotation of the axial fan (30).

[0067] The air flows between the positive pressure surface (40) and the negative pressure surface (41) through the fine pores in the porous portion (46) in accordance with the pressure fluctuations on the blade surfaces. When the pressure of the air on the positive pressure surface (40) rises, the air slightly leaks to the negative pressure surface (41) through the porous portion (46). When the pressure of the air on the negative pressure surface (41) rises, the air slightly leaks to the positive pressure surface (40) through the porous portion (46). As a result, the pressure fluctuations on the blade surface are reduced in the porous portion (46). This is advantageous in reducing the noise during the rotation of the axial fan (30).

[0068] In a usual axial fan having the blades (33) as illustrated in FIG. 8, the air volume increases with the increase in rotation speed of the blades (33), and the flow velocity of the air passing on the positive pressure surfaces (40) of the blades (33) increases, significantly developing the turbulent flow of the air on the positive pressure surfaces (40). When the turbulent flow of the air on the positive pressure surfaces (40) of the blades grows large, the noise reduction effect by the porous portion (46) is impaired. In the axial fan (30) of the present embodiment, the shape of the leading edge portion (38) of each blade (33) is devised to achieve a suitable noise reduction effect by the porous portion (46) on the higher air volume side.

[0069] Specifically, as illustrated in FIGS. 4 and 5, the raised portion (49) is provided on the positive pressure surface (40) of the leading edge portion (38) of the blade (33). Here, the leading edge portion (38) is a portion that includes the leading edge (36) of the blade (33) and takes 10% of the chord length L1 from the leading edge (36). The raised portion (49) is a curved portion raised toward the positive pressure side of the blade (33). The raised portion (49) is provided on the inner peripheral side of the leading edge portion (38) of the blade (33). The raised portion (49) of this example extends from the blade root (34) to a point where the radius ratio (R2 / R1) is 0.4 to 0.7.

[0070] In FIG. 4, the surface shape of the raised portion (49) is indicated by a two-dot-dash line for convenience. In the target blade cross section of the blade (33), the surface of the raised portion (49) is curved. The curved shape of the raised portion (49) is represented by an angle formed by a tangent (TLa) to the positive pressure surface (40) and the chord line (CLa), distances (first distance H1 and second distance H2) from a camber line (SLa) to the positive pressure surface (40), a distance (third distance H3) from the chord line (CLa) to the positive pressure surface (40), and a distance (fourth distance H3) from the chord line (CLa) to the negative pressure surface (41).

[0071] As illustrated in FIG. 6, in the target blade cross section of the blade (33), the curved shape of the raised portion (49) is designed such that an absolute value of the angle formed by the tangent (TLa) to the positive pressure surface (40) and the chord line (CLa) decreases to zero with increasing distance from the leading edge (36) toward the rear side in the rotation direction (D1) of the blade (33), and then increases to reach a change point (Pc) at which the rate of change of the absolute value starts to decrease. The tangent (TLa) to the positive pressure surface (40) formed by the raised portion (49) is partially shown in FIG. 5. In the target blade cross section of the blade (33) including a first portion (38a), the positive pressure surface (40) of the blade (33) is shaped such that the tangent (TLa) to the positive pressure surface (40) is continuous from the leading edge portion (38) to a portion behind the leading edge portion (38) in the rotation direction (D1).

[0072] Thus, the positive pressure surface (40) of the leading edge portion (38), including the raised portion (49), changes smoothly in shape. The leading edge portion (38) of the blade (33) has a first portion (38a) and a second portion (38b). The first portion (38a) is a portion provided with the raised portion (49). The second portion (38b) is a portion without the raised portion (49). In the target blade cross section of the blade (33), a line connecting the midpoints of the positive pressure surface (40) and the negative pressure surface (41) is a camber line (SLa). The camber line (SLa) in the first portion (38a) is curved in a convex manner toward the positive pressure surface (40) in accordance with the shape of the raised portion (49), and is smoothly connected to the camber line (SLa) behind the first portion (38a).

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

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

[0075] In the target blade cross section of the blade (33), the maximum distance from the chord line (CLa) in the leading edge portion (38) to the positive pressure surface (40) of the blade (33) is defined as a third distance H3. In the target blade cross section of the blade (33), the maximum distance from the chord line (CLa) in the leading edge portion (38) to the negative pressure surface (41) of the blade (33) is defined as a fourth distance H4. In FIG. 5, the third distance H3 and the fourth distance H4 are intentionally shifted from the first point (P1) for convenience.

[0076] In the target blade cross section of the blade (33) including the first portion (38a), the third distance H3 and the fourth distance H4 satisfy the relationship of H4 < H3. This relationship means that the raised portion (49) is provided in the leading edge portion (38) while keeping the blade (33) being curved in a convex shape toward the negative pressure surface (41) in the rotation direction (D1). In the target blade cross section of the blade (33) including the second portion (38b), the third distance H3 and the fourth distance H4 satisfy the relationship of H4 ≥ H3.

[0077] The third distance H3 in the first portion (38a) decreases from the inner periphery to the outer periphery of the blade (33) in the leading edge portion (38) (see FIG. 4). In other words, the third distance H3 in the first portion (38a) increases from the end of the first portion (38a) closer to the blade tip (35) to the blade root (34), and is the maximum at the blade root (34). The height of the raised portion (49) varies to correspond to the third distance H3 in the first portion (38a).

[0078] The height of the raised portion (49) is a distance from a change point (Pc) of the raised portion (49) to a raised end (Pe), which is an end on the positive pressure surface (40), in a direction orthogonal to the chord line (CLa) of the blade (33). The height of the raised portion (49) decreases with increasing distance from the blade root (34) of the leading edge portion (38). The raised end (Pe) is located near the leading edge (36) of the raised portion (49), that is, closer to the leading edge (36) relative to the entire length of the raised portion (49) in the target blade cross section of the blade (33).

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

[0080] A length L1 between the first point (P1) and the second point (P2) and the third distance H3 satisfy the relationship of H3 < L1. The length L1 between the first point (P1) and the second point (P2) and a length L2 between the leading edge (36) and the first point (P1) on the chord line (CLa) satisfy the relationship of L2 < L1. These relationships mean that the raised portion (49) has a shape extending relatively long from the raised end (Pe) toward the rear side in the rotation direction (D1) of the blade (33).-Silence Performance of Axial fan-

[0081] An air volume-static pressure characteristic (P-Q curve) and an air volume-specific noise level characteristic of the axial fan (30) of Example will be described below in comparison with those of axial fans of Comparative Examples 1 and 2. The axial fan (30) of Example has the same configuration as that of the first embodiment described above. The axial fan of Comparative Example 1 is similar to the axial fan (30) of Example except that each blade (33) does not have the porous portion (46) and the raised portion (49). The axial fan of Comparative Example 2 is similar to the axial fan (30) of Example except that each blade (33) has no raised portion (49).

[0082] FIG. 9 shows the air volume-static pressure characteristics (P-Q curves) of the axial fan (30) of Example and the axial fans of Comparative Examples 1 and 2. In FIG. 9, the solid line represents the air volume-static pressure characteristic (P-Q curve) of the axial fan (30) of Example; the broken line represents the air volume-static pressure characteristic (P-Q curve) of the axial fan of Comparative Example 1; and the dash dotted line represents the air volume-static pressure characteristic (P-Q characteristic) of the axial fan of Comparative Example 2. As shown in FIG. 9, the line representing the air volume-static pressure characteristic (P-Q curve) of the axial fan (30) of Example and the lines representing the air volume-static pressure characteristics (P-Q curves) of the axial fans of Comparative Examples 1 and 2 overlap each other and almost coincide with each other. Thus, the axial fan (30) of Example has substantially the same air volume-static pressure characteristic as those of the axial fans of Comparative Examples 1 and 2.

[0083] FIG. 10 shows the air volume-specific noise level characteristics of the axial fan (30) of Example and the axial fans of Comparative Examples 1 and 2. In FIG. 10, the solid line represents the air volume-specific noise level characteristic of the axial fan (30) of Example; the broken line represents the air volume-specific noise level characteristic of the axial fan of Comparative Example 1; and the dash dotted line represents the air volume-specific noise level characteristic of the axial fan of Comparative Example 2. As shown in FIG. 10, the axial fan (30) of Example has a lower specific noise level on the higher air volume side compared to the axial fans of Comparative Examples 1 and 2 at the same air volume. As can be seen from the above, the axial fan (30) of Example can reduce noise during the operation on the higher air volume side, while maintaining the air volume-static pressure characteristic, compared with the axial fans of Comparative Examples 1 and 2.-Features of First Embodiment-

[0084] In the target blade cross section of the blade (33) of the axial fan (30) of the first embodiment, the positive pressure surface (40) of the leading edge portion (38) of the blade (33) is provided with the curved raised portion (49) in which the absolute value of the angle formed between the tangent (TLa) to the positive pressure surface (40) and the chord line (CLa) gradually changes in a mountain-shaped curve. Such a curved raised portion (49) provided on the positive pressure surface (40) of the leading edge portion (38) increases the area of the leading edge portion (38), with which the airflow collides during the rotation of the blade (33), in the first portion (38a) including the raised portion (49). Thus, as illustrated in FIG. 7, when the airflow collides with the leading edge portion (38) of the blade (33), the airflow (F1) including minute vortices (Vt) is generated on the positive pressure surface (40) of the blade (33). The airflow (F1) including the minute vortices (Vt) is less separated from the curved portion, and flows along the positive pressure surface (40) with reduced generation of the turbulent flow. This can reduce the development of the turbulent flow on the positive pressure surface (40) formed by the porous portion (46). As a result, a suitable noise reduction effect can be achieved by the porous portion (46).

[0085] In the axial fan (30) of the first embodiment, in the target blade cross section of the blade (33) including the first portion (38a), the first distance H1 which is the maximum distance from the camber line (SLa) in the leading edge portion (38) to the positive pressure surface (40) is greater than the second distance H2 which is the maximum distance from the camber line (SLa) in the portion behind the leading edge portion (38) in the rotation direction (D1) to the negative pressure surface (41) (H1 > H2). The shape of the blade (33) that satisfies this relationship does not make the portion of the blade (33) behind the leading edge portion (38) excessively thick, reducing the weight of the blade (33). This is advantageous in making the axial fan (30) more energy efficient.

[0086] In the axial fan (30) of the first embodiment, in the target blade cross section of the blade (33) including the first portion (38a), the positive pressure surface (40) of the blade (33) is shaped such that the tangent (TLa) is continuous from the leading edge portion (38) to the portion behind the leading edge portion (38). When the positive pressure surface (40) of the blade (33) is smooth and continuous from the leading edge portion (38) including the raised portion (49) to the portion behind the leading edge portion (38) in this manner, the airflow including the minute vortices (Vt) generated upon collision of the airflow with the leading edge portion (38) can move rearward from the leading edge portion (38) along the positive pressure surface (40). This is advantageous in reducing the development of the turbulent flow on the positive pressure surface (40).

[0087] In the axial fan (30) of the first embodiment, in the target blade cross section of the blade (33) including the first portion (38a), the length L1 between the first point (P1) and the second point (P2) on the chord line (CLa) is greater than the third distance H3 (H3 < L1). The first point (P1) is a point where the distance from the chord line (CLa) to the positive pressure surface (40) in the raised portion (49) of the leading edge portion (38) is the maximum, and the second point (P2) is a point corresponding to the change point (Pc) of the curved shape of the raised portion (49). When the raised portion (49) has a shape that is relatively long in a portion behind the point at the third distance H3, that is, the point where the distance from the chord line (CLa) to the positive pressure surface (40) is the maximum, the positive pressure surface (40) of the leading edge portion (38) has a gently sloping shape. This can reduce the separation of the airflow including the minute vortices (Vt) generated upon collision of the airflow with the leading edge portion (38) from the positive pressure surface (40) while the airflow is moving rearward from the leading edge portion (38).

[0088] In the axial fan (30) of the first embodiment, in the target blade cross section of the blade (33) including the first portion (38a), the length L1 between the first point (P1) and the second point (P2) on the chord line (CLa) is greater than the length L2 between the leading edge (36) and the first point (P1) on the chord line (CLa) of the blade (33) (L2 < L1). The first point (P1) is a point where the distance from the chord line (CLa) to the positive pressure surface (40) in the raised portion (49) of the leading edge portion (38) is the maximum, and the second point (P2) is a point corresponding to the change point (Pc) of the curved shape of the raised portion (49). When the raised portion (49) has a shape that is relatively long in a portion behind the point at the third distance H3, that is, the point where the distance from the chord line (CLa) to the positive pressure surface (40) is the maximum, the positive pressure surface (40) of the leading edge portion (38) has a gently sloping shape. This can reduce the separation of the airflow including the minute vortices (Vt) generated upon collision of the airflow with the leading edge portion (38) from the positive pressure surface (40) while the airflow is moving rearward from the leading edge portion (38).

[0089] In the axial fan (30) of the first embodiment, in the target blade cross section of the blade (33) including the first portion (38a), the first distance H1 in the leading edge portion (38) is smaller than three times the second distance H2 in the portion behind the leading edge portion (38) (H1 ≤ H2 × 3). This can increase the area of the leading edge portion (38) with which the airflow collides during the rotation of the blade (33), without excessively increasing the thickness of the leading edge portion (38).

[0090] In the axial fan (30) of the first embodiment, the blades (33) are arranged at intervals from each other in the circumferential direction of the hub (31). Each blade (33) extends radially outward from the hub (31). The present disclosure is effective for such an axial fan (30) because a suitable noise reduction effect can be achieved by the porous portion (46).

[0091] In the axial fan (30) of the first embodiment, in the target blade cross section of the blade (33) including the first portion (38a), the third distance H3 from the chord line (CLa) in the leading edge portion (38) to the positive pressure surface (40) is greater than the fourth distance H4 from the chord line (CLa) to the negative pressure surface (41) (H4 < H3). This can effectively increase the area of the leading edge portion (38) of the axial fan (30) with which the airflow collides during the rotation of the blade (33), and the airflow (F1) including the minute vortices (Vt) generated upon collision of an airflow with the leading edge portion (38) can move along the positive pressure surface (40) of the blade (33). As a result, a suitable noise reduction effect can be achieved by the porous portion (46).

[0092] In the axial fan (30) of the first embodiment, the first portion (38a) is provided on the inner peripheral side of the leading edge portion (38) of the blade (33), and the porous portion (46) is provided outside of the first portion (38a) in the direction of radius of rotation of the blade (33). As the air volume of the axial fan (30) increases, the airflow on the positive pressure surface (40) of the blade (33) tends to move radially outward due to centrifugal force. Thus, the airflow (F1) including the minute vortices (Vt) generated upon collision of the airflow with the leading edge portion (38) including the first portion (38a) can move on the positive pressure surface (40) formed by the porous portion (46). As a result, a suitable noise reduction effect can be achieved by the porous portion (46).

[0093] In the axial fan (30) of the first embodiment, the third distance H3 in the first portion (38a) decreases from the inner periphery to the outer periphery of the blade (33) in the leading edge portion (38). When the first portion (38a) is provided only in part of the leading edge portion (38) on the upstream side of the airflow (F1) on the positive pressure surface (40) formed by the porous portion (46), the blade (33) does not require much change in shape to achieve the suitable noise reduction effect by the porous portion (46). The provision of the first portion (38a) in the leading edge portion (38) of the blade (33) can reduce the likelihood of a decrease in the static pressure characteristic of the axial fan (30).

[0094] The air conditioning apparatus (1) of the first embodiment includes the axial fan (30). The axial fan (30) can achieve a suitable noise reduction effect by the porous portion (46). This can reduce noise caused by the rotation of the axial fan (30) of the air conditioning apparatus (1), improving quietness.«Second Embodiment»

[0095] A second embodiment is directed to a turbo fan (50) as a fan according to the present disclosure. The turbo fan (50) is used in the air conditioning apparatus (1) described in the first embodiment. In other words, the air conditioning apparatus (1) includes the turbo fan (50). The turbo fan (50) is used as the indoor fan (27) of the indoor unit (3) of the air conditioning apparatus (1). The indoor unit (3) is a so-called ceiling embedded indoor unit.

[0096] As illustrated in FIGS. 11 and 12, the turbo fan (50) includes a single plate-shaped member (51), a single shroud (53), and a plurality of blades (56). The turbo fan (50) of this example has seven blades (56). The number of the blades (56) may be six or less, or eight or more.

[0097] The plate-shaped member (51) is a disc-shaped member having a hollow center. The plate-shaped member (51) is a hub of the turbo fan (50), and is substantially coaxial with the drive shaft of the second fan motor (29). A shaft hole (52) is formed in a center portion 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 axis (A2). The center axis of the plate-shaped member (51) coincides with the axis (A2) of the turbo fan (50).

[0098] The shroud (53) is an annular member. The shroud (53) is arranged to face the plate-shaped member (51) and spaced from the plate-shaped member (51) in the axial direction of the axis (A2). The shroud (53) is substantially coaxial with the plate-shaped member (51). The outer diameter of the shroud (53) is substantially equal to the outer diameter of the plate-shaped member (51). The shroud (53) has an inner peripheral edge protruding away from the plate-shaped member (51). In the turbo fan (50), the inner peripheral edge of the shroud (53) forms an inlet (54), and outer peripheral edges of the plate-shaped member (51) and the shroud (53) form an outlet (55).

[0099] The blades (56) are provided between the plate-shaped member (51) and the shroud (53). The blades (56) are arranged at intervals from each other in the circumferential direction of the plate-shaped member (51) and the shroud (53), that is, in a rotation direction (D2) of the turbo fan (50). Each blade (56) is located close to the outer peripheral edge of the plate-shaped member (51). Each blade (56) stands in a direction in which the plate-shaped member (51) and the shroud (53) face each other, with a leading edge (57) positioned inward and trailing edge (58) positioned outward. Each blade (56) has one end fixed to the plate-shaped member (51) and the other end fixed to the shroud (53).

[0100] Each blade (56) has the leading edge (57), the trailing edge (58), a positive pressure surface (60), and a negative pressure surface (61). The leading edge (57) is a front edge in the rotation direction (D2) of the blade (56). The trailing edge (58) is a rear edge in the rotation direction (D2) of the blade (56). The positive pressure surface (60) is a blade surface where a positive pressure is generated by the flow of the air transferred during the rotation of the turbo fan (50), and constitutes a surface facing the outer peripheral side of the turbo fan (50) from which the air flows out. The negative pressure surface (61) is a blade surface where a negative pressure is generated by the flow of the air transferred during the rotation of the turbo fan (50), and constitutes a surface facing the inner peripheral side of the turbo fan (50) from which the air flows in.

[0101] In the turbo fan (50), of a space between the plate-shaped member (51) and the shroud (53), a portion where the blades (56) are arranged constitutes an air flow path (62). The air flow path (62) is an annular flow path continuous with the outlet (55). The air passing through the turbo fan (50) flows from the inside to the outside of the air flow path (62) in the radial direction. Each blade (56) increases the pressure of the air by a change in speed of the airflow in the rotation direction (D2) from the leading edge (57) to the trailing edge (58) and a difference in circumferential velocity between the leading edge (57) and the trailing edge (58). The turbo fan (50) increases the pressure of the air sucked through the inlet (54) and then blows out the air through the outlet (55).

[0102] Each blade (56) is curved in a convex shape toward the outer peripheral side of the turbo fan (50). As illustrated in FIG. 13, in a cross section of the blade (56) in the direction of radius of rotation (a blade cross section in a plane orthogonal to the rotational 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 turbo fan (50), a blade cross section taken along the chord line (CLb) of the blade (56) corresponds to a blade cross section taken along the direction of radius of rotation of the blade (56), and will be referred to as a "target blade cross section" in the present embodiment. In the target blade cross section of the blade (56), a line connecting the midpoints of the positive pressure surface (60) and the negative pressure surface (61) is a camber line (SLb).

[0103] Each blade (56) includes 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 most of the blade (56). That is, most of the blade (56) is made of the non-porous material. The porous portion (66) is fixed to the blade body (64) by fitting, bonding, or welding. The shape, material, average pore diameter, and porosity of the porous portion (66) of this example are the same as those of the porous portion (46) of the first embodiment.

[0104] The porous portion (66) is arranged near the trailing edge (58) in a substantially middle region of the blade (56) in its width direction, and is surrounded by the material forming the blade body (64). The porous portion (66) has a function of reducing noise generated by the rotation of the turbo fan (50) by reducing the pressure fluctuations on the blade surfaces of the blade (56). The porous portion (66) extends over the entire thickness of the blade (56). The porous portion (66) is exposed on the positive pressure surface (60) and the negative pressure surface (61) of the blade (56) and constitutes part of the positive pressure surface (60) and part of the negative pressure surface (61).

[0105] In the turbo fan (50) of the present embodiment, the shape of the leading edge portion (68) of each blade (56) is devised to achieve a suitable noise reduction effect by the porous portion (66) on the higher air volume side. Specifically, a raised portion (69) is provided on the positive pressure surface (60) of the leading edge portion (68) of the blade (56). Here, the leading edge portion (68) is a portion that includes the leading edge (57) of the blade (56) and takes 10% of the chord length L1 from the leading edge (57). The raised portion (69) is a curved portion raised toward the positive pressure surface (60) of the blade (56). The raised portion (69) of this example is provided over the entire length of the leading edge portion (68).

[0106] In the target blade cross section of the blade (56), the surface of the raised portion (69) is curved. The curved shape of the raised portion (69) is designed, similarly to the shape of the raised portion (69) of the blade (33) of the axial fan (30) of the first embodiment, such that an absolute value of the angle formed by the tangent (TLb) to the positive pressure surface (60) and the chord line (CLb) decreases to zero with increasing distance from the leading edge (57) toward the rear side in the rotation direction (D2) of the blade (56), and then increases to reach a change point (Pc) at which the rate of change of the absolute value starts to decrease (see FIG. 6). The tangent (TLb) to the positive pressure surface (60) formed by the raised portion (69) is partially shown in FIG. 13.

[0107] In the target blade cross section of the blade (56), the positive pressure surface (60) of the blade (56) is shaped such that the tangent (TLb) to the positive pressure surface (60) is continuous from the leading edge portion (68) to the portion behind the leading edge portion (68) in the rotation direction (D2). The positive pressure surface (60) of the leading edge portion (68), including the raised portion (69), changes smoothly in shape. The leading edge portion (68) of the blade (56) constitutes a first portion (68a). The first portion (68a) is a portion provided with the raised portion (69). The camber line (SLb) in the first portion (68a) is curved in a convex shape toward the positive pressure surface (60) in accordance with the shape of the raised portion (69), and is smoothly connected to the camber line (SLb) behind the first portion (68a).

[0108] In the target blade cross section of the blade (56), the maximum distance from the camber line (SLb) in the leading edge portion (68) to the positive pressure surface (60) is defined as a first distance H1. In the target blade cross section of the blade (56), the maximum distance from the camber line (SLb) in the portion behind the leading edge portion (68) in the rotation direction (D2) to the positive pressure surface (60) is defined as a second distance H2. In the same manner as in the first embodiment, in the target blade cross section of the blade (56), the first distance H1 and the second distance H2 satisfy the relationship of H1 > H2 and H1 ≤ H2 × 3.

[0109] In the target blade cross section of the blade (56), the maximum distance from the chord line (CLb) in the leading edge portion (68) to the positive pressure surface (60) of the blade (56) is defined as a third distance H3. In the target blade cross section of the blade (56), the maximum distance from the chord line (CLb) in the leading edge portion (68) to the negative pressure surface (61) of the blade (56) is defined as a fourth distance H4. In FIG. 13, the third distance H3 and the fourth distance H4 are intentionally shifted from the first point (P1) for convenience. In the target blade cross section of the blade (56), the third distance H3 and the fourth distance H4 satisfy the relationship of H4 < H3.

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

[0111] In the target blade cross section of the blade (56), the turbo fan (50) of the second embodiment also has the curved raised portion (69) formed on the positive pressure surface (60) of the leading edge portion (68) of the blade (56), thereby increasing the area of the leading edge portion (68) with which the airflow collides during the rotation of the blade (56). Thus, when the airflow collides with the leading edge portion (68) of the blade (56), the airflow including minute vortices flowing on the positive pressure surface (60) of the blade (56) is generated, which makes it possible to reduce the development of the turbulent flow on the positive pressure surface (60) formed by the porous portion (66), and as a result, makes it possible to achieve a suitable noise reduction effect by the porous portion (66).

[0112] In the turbo fan (50) of the second embodiment, the blades (56) are arranged at intervals from each other in the rotation direction between the plate-shaped member (51) and the shroud (53). Each blade (56) is oriented so that the leading edge (57) is positioned inward and the trailing edge (58) is positioned outward. The present disclosure is effective for such a turbo fan (50) because a suitable noise reduction effect can be achieved by the porous portion (66). The same effects as those of the first embodiment can be obtained by the shape of the surface of the raised portion (69) represented by the first to fourth distances H1, H2, H3, and H4.«Other Embodiments»

[0113] 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 portion (38). That is, the entire length of the leading edge portion (38) may form the first portion (38a). The raised portion (49) of the blade (33) may be provided only on the outer peripheral side of the leading edge portion (38). In the turbo fan (50) of the second embodiment, the raised portion (69) of the blade (56) may be provided only in part of the leading edge portion (68). In short, it is only necessary that the curved raised portion (49, 69) is formed on the positive pressure surface (40, 60) of the leading edge portion (38, 68) of the blade (33, 56).

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

[0115] In the axial fan (30) of the first embodiment, the center (C1) of the porous portion (46) may be located outside the region where the chord ratio (Lb / La) is ranging from 0.4 to 0.8, and may be located outside the region where the radius ratio (Rb / Ra) is ranging 0.6 to 0.8. The area of the porous portion (46) may be larger than 30% of the total area of the positive pressure surface (40) as long as the strength of the blade (33) can be ensured. In the turbo fan (50) of the second embodiment, the porous portion (66) may also extend toward the leading edge (57) of the blade (56), or may be divided into two or more portions. In short, it is only necessary that the porous portion (46, 66) is located behind the leading edge portion (38, 68) in the rotation direction to form the positive pressure surface (40, 60) of the blade (33, 56).

[0116] The fan of the present disclosure is also applicable to other types of fans such as a mixed flow fan. The fan of the present disclosure can be used in various other devices that require air blowing, in addition to the air conditioning apparatus (1) that controls the temperature of air in a target space. Examples of the other devices include, for example, humidity controllers that control the humidity of the air in the target space, ventilators that ventilate the target space, and air purifiers that purify the air in the target space.

[0117] While the embodiments and variations thereof have been described above, it will be understood that various changes in form and details may be made without departing from the spirit and scope of the claims. The foregoing embodiments and variations thereof may be combined and replaced with each other without deteriorating the intended functions of the present disclosure.

[0118] The expressions of "first," "second," ... described above are used to distinguish the terms to which these expressions are given, and do not limit the number and order of the terms. In addition, the description "to" in a numerical range means that the range includes numerical values before and after the description. That is, when X and Y are used as the numerical values, the description "X to Y" indicates a range of "X or more and Y or less."INDUSTRIAL APPLICABILITY

[0119] As described above, the present disclosure is useful for a fan and an air conditioning apparatus.DESCRIPTION OF REFERENCE CHARACTERS

[0120] A1, A2Axis CLa, CLbChord Line D1, D2Rotation Direction PcChange Point P1First Point P2Second Point TLa, TLbTangent 1Air Conditioning Apparatus 30Axial Fan (Fan) 31Hub 33Blade 36Leading Edge 38Leading Edge Portion 38aFirst portion 40Positive Pressure Surface 41Negative Pressure Surface 49Raised Portion (Curved Portion) 50Turbo Fan (Fan) 51Plate-shaped Member 53Shroud 56Blade 57Leading Edge 58Trailing Edge 60Positive Pressure Surface 68Leading Edge Portion 68aFirst portion 69Raised Portion (Curved Portion)

Claims

1. A fan comprising: a blade (33, 56) configured to rotate about a predetermined axis (A1, A2), wherein the blade (33, 56) has: a leading edge portion (38, 68) including a leading edge (36, 57) which is a front edge in a rotation direction; and a porous portion (46, 66) which is located behind the leading edge portion (38, 68) in the rotation direction and forms a positive pressure surface (40, 60) of the blade (33, 56), and in a blade cross section taken along a chord line (CLa, CLb) of the blade (33, 56), the positive pressure surface (40, 60) of the leading edge portion (38, 68) has a curved portion (49, 69) in which an absolute value of an angle formed by a tangent (TLa, TLb) to the positive pressure surface (40, 60) and the chord line (CLa, CLb) decreases to zero with increasing distance from the leading edge (36, 57) toward a rear side in the rotation direction (D1, D2), and then increases to reach a change point (Pc) at which a rate of change of the absolute value starts to decrease.

2. The fan of claim 1, wherein the leading edge portion (38, 68) has a first portion (38a, 68a) provided with the curved portion, and in the blade cross section including the first portion (38a, 68a), a relationship of H1 > H2 is satisfied, where H1 represents a first distance H1 which is a maximum distance from a camber line (SLa, SLb) in the leading edge portion (38, 68) to the positive pressure surface (40, 60), and H2 represents a second distance H2 which is a maximum distance from the camber line (SLa, SLb) in a portion behind the leading edge portion (38, 68) in the rotation direction (D1, D2) to the positive pressure surface (40, 60).

3. The fan of claim 1 or 2, wherein the leading edge portion (38, 68) has a first portion (38a, 68a) provided with the curved portion, and in the blade cross section including the first portion (38a 68a), the positive pressure surface (40, 60) of the blade (33, 56) is shaped such that the tangent (TLa, TLb) to the positive pressure surface (40, 60) is continuous from the leading edge portion (38, 68) to the portion behind the leading edge portion (38, 68) in the rotation direction (D1, D2).

4. The fan of any one of claims 1 to 3, wherein the leading edge portion (38, 68) has a first portion (38a, 68a) provided with the curved portion, and in the blade cross section including the first portion (38a, 68a), a relationship of H3 < L1 is satisfied, where H3 represents a third distance H3 which is a maximum distance from the chord line (CLa, CLb) of the leading edge portion (38, 68) to the positive pressure surface (40, 60), and L1 represents a length L1 between a first point (P1) on the chord line (CLa, CLb) at which a distance to the positive pressure surface (40, 60) is the third distance H3, and a second point (P2) corresponding to the change point (Pc).

5. The fan of any one of claims 1 to 4, wherein the leading edge portion (38, 68) has a first portion (38a, 68a) provided with the curved portion, and in the blade cross section including the first portion (38a, 68a), a relationship of L2 < L1 is satisfied, where L1 represents a length L1 between a first point (P1) on the chord line (CLa, CLb) at which a distance to the positive pressure surface (40, 60) is a third distance H3, and a second point (P2) corresponding to the change point (Pc), the third distance H3 being a maximum distance from the chord line (CLa, CLb) of the leading edge portion (38, 68) to the positive pressure surface (40, 60), and L2 represents a length L2 between the leading edge (36, 57) and the first point (P1) on the chord line (CLa, CLb).

6. The fan of any one of claims 1 to 5, wherein the leading edge portion (38, 68) has a first portion (38a, 68a) provided with the curved portion, and in the blade cross section including the first portion (38a, 68a), a relationship of H1 ≤ H2 × 3 is satisfied, where H1 represents a first distance H1 which is a maximum distance from a camber line (SLa, SLb) in the leading edge portion (38, 68) to the positive pressure surface (40, 60), and H2 represents a second distance H2 which is a maximum distance from the camber line (SLa, SLb) in a portion behind the leading edge portion (38, 68) in the rotation direction (D1, D2) to the positive pressure surface (40, 60).

7. The fan of any one of claims 1 to 6, further comprising: a hub (31) rotatable about the axis (A1), wherein multiple blades (33), each being identical to the blade (33), are arranged at intervals from each other in a circumferential direction of the hub (31), each of the multiple blades (33) extending radially outward from the hub (31).

8. The fan of claim 7, wherein the leading edge portion (38) has a first portion (38a) provided with the curved portion, and in the blade cross section including the first portion (38a), a relationship of H4 < H3 is satisfied, where H3 represents a third distance H3 which is a maximum distance from the chord line (CLa) in the leading edge portion (38) to the positive pressure surface (40) of the blade (33), and H4 represents a fourth distance H4 which is a maximum distance from the chord line (CLa) in the leading edge portion (38) to a negative pressure surface (41) of the blade (33).

9. The fan of claim 8, wherein the third distance H3 in the first portion (38a) decreases from an inner periphery to an outer periphery of the blade (33) in the leading edge portion (38).

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

11. The fan of any one of claims 1 to 6, further comprising: a plate-shaped member (51) rotatable about the axis (A2); and a shroud (53) spaced from the plate-shaped member (51) in an axial direction of the axis (A2), wherein multiple blades (56), each being identical to the blade (56), are arranged at intervals from each other in the rotation direction (D2) between the plate-shaped member (51) and the shroud (53), with the leading edge (57) positioned inward and a trailing edge (58) positioned outward, the trailing edge (58) being a rear edge in the rotation direction (D2).

12. An air conditioning apparatus comprising the fan (30, 50) of any one of claims 1 to 11.

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