Patent Publication Number: US-2022221214-A1

Title: Axial flow fan, air-sending device, and refrigeration cycle apparatus

Description:
TECHNICAL FIELD 
     The present disclosure relates to an axial flow fan including a plurality of blade each having a trailing edge having an indentation, an air-sending device including the axial flow fan, and a refrigeration cycle apparatus including the air-sending device. 
     BACKGROUND ART 
     A conventional axial flow fan includes a plurality of blades along a circumferential surface of a cylindrical boss, and is configured to convey a fluid with the blades rotating with a rotative force applied to the boss. Rotation of the blades of the axial flow fan causes a portion of the fluid that is present between the blades to collide with blade surfaces. The surfaces with which the fluid collides are subjected to raised pressures, and the fluid is moved by being pressed in a direction of an axis of rotation serving as a central axis on which the blades rotate. 
     Among such axial flow fans, there has been proposed an axial flow fan provided with a serration portion having serrated projections by providing a trailing edge with a plurality of triangular indentations, the projections each having a central portion that is thick in a radial longitudinal section and an edge portion that is thin in the radial longitudinal section (see, for example, Patent Literature 1). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Application Publication No. 11-210691 
     SUMMARY OF INVENTION 
     Technical Problem 
     The axial flow fan of Patent Literature 1 is supposed to reduce noise generation by generating only small vortices by causing airflows flowing along an outer surface of a blade to smoothly merge at the serration portion of the trailing edge. However, the axial flow fan of Patent Literature 1 has a risk that when a centrifugal force entailed by rotation of the blade causes an airflow to be released at a place off an edge portion at which an airflow is thin, a strong blade tip vortex may be generated by a slipstream generated at an edge portion at which an airflow is thick. 
     The present disclosure is intended to solve such a problem, and has as an object to provide an axial flow fan configured to inhibit the growth of a blade tip vortex at an edge portion, especially at a trailing edge, an air-sending device including the axial flow fan, and a refrigeration cycle apparatus including the air-sending device. 
     Solution to Problem 
     An axial flow fan according to an embodiment of the present disclosure includes a hub driven to rotate and configured to serve as a rotation axis of the axial flow fan and a blade connected to the hub. The blade has a leading edge and a trailing edge. The trailing edge has an indentation indenting toward the leading edge. The indentation narrows from the trailing edge to the leading edge, and has an apex being a point closest to the leading edge from among the points constituting the indentation. The blade has, at the indentation, a maximum thickness portion at which a thickness of the blade is maximum, and which is positioned radially inside of the apex. 
     An air-sending device according to an embodiment of the present disclosure includes the axial flow fan thus configured, a drive source configured to apply a drive force to the axial flow fan, and a casing configured to house the axial flow fan and the drive source. 
     A refrigeration cycle apparatus according to an embodiment of the present disclosure includes the air-sending device thus configured and a refrigerant circuit having a condenser and an evaporator. The air-sending device is configured to send air to at least either the condenser or the evaporator. 
     Advantageous Effects of Invention 
     According to the embodiment of the present disclosure, the axial flow fan is configured such that a thickness of a portion of the blade that is positioned inside of the apex is a maximum thickness. The axial flow fan can reduce a speed difference in a slipstream generated and inhibit the growth of a blade tip vortex, as the apex, at which a wind velocity is high, is smaller in blade thickness than the maximum thickness portion. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view schematically showing a configuration of an axial flow fan according to Embodiment 1. 
         FIG. 2  is a plan view of a blade shown in  FIG. 1  as seen from an angle parallel with an axial direction of a rotation axis. 
         FIG. 3  is a side view conceptually showing an example of a distribution of blade thickness of a trailing edge shown in  FIG. 2 . 
         FIG. 4  is a diagram showing a blade surface distribution of the trailing edge of the axial flow fan according to Embodiment 1. 
         FIG. 5  is another plan view of a blade shown in  FIG. 1  as seen from an angle parallel with the axial direction of the rotation axis. 
         FIG. 6  is a diagram conceptually showing a shape of a cross-section of the trailing edge of the blade shown in  FIG. 5  as taken along line M-M. 
         FIG. 7  is a diagram conceptually showing a shape of another cross-section of the trailing edge of the blade shown in  FIG. 5  as taken along line M-M. 
         FIG. 8  is a diagram conceptually showing a shape of another cross-section of the trailing edge of the blade shown in  FIG. 5  as taken along line M-M. 
         FIG. 9  is a plan view of an axial flow fan according to a comparative example as seen from an angle parallel with an axial direction of a rotation axis. 
         FIG. 10  is a side view conceptually showing a distribution of blade thickness of a trailing edge of a blade shown in  FIG. 9 . 
         FIG. 11  is a diagram showing a blade surface distribution of the trailing edge of the axial flow fan according to the comparative example. 
         FIG. 12  is a schematic view showing a relationship between the blade of the axial flow fan according to Embodiment 1 and airflows. 
         FIG. 13  is a plan view of an axial flow fan according to Embodiment 2 as seen from an angle parallel with an axial direction of a rotation axis. 
         FIG. 14  is a side view conceptually showing an example of a distribution of blade thickness of a trailing edge of a blade shown in  FIG. 13 . 
         FIG. 15  is a diagram showing a blade surface distribution of the trailing edge of the axial flow fan according to Embodiment 2. 
         FIG. 16  is a plan view of an axial flow fan according to Embodiment 3 as seen from an angle parallel with an axial direction of a rotation axis. 
         FIG. 17  is a side view conceptually showing an example of a distribution of blade thickness of a trailing edge of a blade shown in  FIG. 16 . 
         FIG. 18  is a diagram showing a blade surface distribution of the trailing edge of the axial flow fan according to Embodiment 3. 
         FIG. 19  is a plan view of an axial flow fan according to Embodiment 4 as seen from an angle parallel with an axial direction of a rotation axis. 
         FIG. 20  is a side view conceptually showing an example of a distribution of blade thickness of a trailing edge of a blade shown in  FIG. 19 . 
         FIG. 21  is a diagram showing a blade surface distribution of the trailing edge of the axial flow fan according to Embodiment 4. 
         FIG. 22  is a plan view of an axial flow fan according to Embodiment 5 as seen from an angle parallel with an axial direction of a rotation axis. 
         FIG. 23  is an enlarged view conceptually showing blade tip indentations shown in  FIG. 22 . 
         FIG. 24  is a plan view of an axial flow fan according to Embodiment 6 as seen from an angle parallel with an axial direction of a rotation axis. 
         FIG. 25  is a plan view of an axial flow fan according to Embodiment 7 as seen from an angle parallel with an axial direction of a rotation axis. 
         FIG. 26  is a schematic view of a refrigeration cycle apparatus according to Embodiment 8. 
         FIG. 27  is a perspective view of an outdoor unit serving as an air-sending device as seen from an air outlet side. 
         FIG. 28  is a diagram for explaining a configuration of the outdoor unit from the top. 
         FIG. 29  is a diagram showing a state in which a fan grille has been removed from the outdoor unit. 
         FIG. 30  is a diagram showing an internal configuration of the outdoor unit with the fan grille, a front panel, or other components removed from the outdoor unit. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following, an axial flow fan, an air-sending device, and a refrigeration cycle apparatus according to embodiments are described with reference to the drawings. In the following drawings including  FIG. 1 , relative relationships in dimension between constituent elements, the shapes of the constituent elements, or other features of the constituent elements may be different from actual ones. Further, constituent elements given identical reference signs in the following drawings are identical or equivalent to each other, and these reference signs are adhered to throughout the full text of the description. Further, the directive terms (such as “upper”, “lower”, “right”, “left”, “front”, and “back”) used as appropriate for ease of comprehension are merely so written for convenience of explanation, and are not intended to limit the placement or orientation of a device or a component. 
     Embodiment 1 
     [Axial Flow Fan  100 ] 
       FIG. 1  is a perspective view schematically showing a configuration of an axial flow fan  100  according to Embodiment 1. The direction of rotation DR indicated by an arrow in  FIG. 1  indicates the direction of rotation DR of the axial flow fan  100 . In  FIG. 1 , the solid-white arrow F indicates the direction F in which an airflow flows. In the direction F in which an airflow flows, a Z1 side of the axial flow fan  100  is an upstream side of the airflow with respect to the axial flow fan  100 , and a Z2 side of the axial flow fan  100  is a downstream side of the airflow with respect to the axial flow fan  100 . That is, the Z1 side is a suction side of air with respect to the axial flow fan  100 , and the Z2 side is a blowout side of air with respect to the axial flow fan  100 . Further, the Y axis represents the direction of the radius of the axial flow fan  100  with respect to the rotation axis RS. A Y2 side of the axial flow fan  100  is an inner peripheral side of the axial flow fan  100 , and a Y1 side of the axial flow fan  100  is an outer peripheral side of the axial flow fan  100 . 
     The axial flow fan according to Embodiment 1 is described with reference to  FIG. 1 . The axial flow fan  100  is used, for example, in an air-conditioning apparatus, a ventilating apparatus, or other apparatuses. As shown in  FIG. 1 , the axial flow fan  100  includes a hub  10  provided on the rotation axis RS and a plurality of blades  20  connected to the hub  10 . 
     (Hub  10 ) 
     The hub  10  is driven to rotate and configured to serve as a rotation axis RS of the axial flow fan  100 . The hub  10  rotates on the rotation axis RS. The direction of rotation DR of the axial flow fan  100  is a counterclockwise direction indicated by an arrow in  FIG. 1 . Note, however, that the direction of rotation DR of the axial flow fan  100  is not limited to a counterclockwise direction. For example, by varying the angle of mounting of the blades  20  or the orientation of the blades  20 , the axial flow fan  100  may be configured to rotate in a clockwise direction. The hub  10  is connected to a rotation shaft of a drive source such as a motor (not illustrated). The hub  10  may be configured in the shape of a cylinder or may be configured in the shape of a plate. The hub  10  is not limited to any particular shape, provided the hub  10  is connected to the rotation shaft of the drive source as mentioned above. 
     (Blade  20 ) 
     The plurality of blades  20  are configured to radially extend radially outward from the hub  10 . The plurality of blades  20  are circumferentially placed at spacings from each other. While Embodiment 1 illustrates an aspect in which three blades  20  are provided, any number of blades  20  may be provided. 
     Each of the blades  20  has a leading edge  21 , a trailing edge  22 , an outer peripheral edge  23 , and an inner peripheral edge  24 . The leading edge  21  is placed upstream (Z1 side) in an airflow generated, and is furthest forward in the direction of rotation DR in the blade  20 . That is, the leading edge  21  is placed in front of the trailing edge  22  in the direction of rotation DR. The trailing edge  22  is placed downstream (Z2 side) in the airflow generated, and is furthest rearward in the direction of rotation DR in the blade  20 . That is, the trailing edge  22  is placed behind the leading edge  21  in the direction of rotation DR. The axial flow fan  100  has the leading edge  21  as a blade tip portion facing in the direction of rotation DR of the axial flow fan  100 , and has the trailing edge  22  as a blade tip portion opposite to the leading edge  21  in the direction of rotation DR. 
     The outer peripheral edge  23  is a portion extending back and forth and in an arc to connect an outermost peripheral portion of the leading edge  21  and an outermost peripheral portion of the trailing edge  22 . The outer peripheral edge  23  is placed at an end portion of the axial flow fan  100  in the direction of the radius (i.e. a Y-axis direction). The inner peripheral edge  24  is a portion extending back and forth and in an arc between an innermost peripheral portion of the leading edge  21  and an innermost peripheral portion of the trailing edge  22 . The blades  20  have their inner peripheral edges  24  connected to the outer periphery of the hub  10 . 
     The blades  20  are at a predetermined angle of inclination with respect to the rotation axis RS. The blades  20  convey a fluid by pressing gas present between the blades  20  with blade surfaces as the axial flow fan  100  rotates. A surface of each of these blade surfaces that is subjected to a pressure raised by pressing the fluid serves as a pressure surface  25 , and a surface behind the pressure surface  25  that is subjected to a pressure drop serves as a suction surface  26 . A surface of each of the blades  20  situated upstream (Z1 side) of the blade  20  with respect to the direction in which the airflow flows serves as a suction surface  26 , and a surface of each of the blades  20  situated downstream in a Z2 direction) serves as a pressure surface  25 . In  FIG. 1 , a surface of each of the blades  20  facing toward a viewer who looks at  FIG. 1  serves as a pressure surface  25 , and a surface of each of the blades  20  facing away from the viewer serves as a suction surface  26 . 
       FIG. 2  is a plan view of a blade  20  shown in  FIG. 1  as seen from an angle parallel with an axial direction of the rotation axis RS. In other words,  FIG. 2  is a diagram of the blade  20  as seen in a plane perpendicular to the rotation axis RS. As shown in  FIG. 2 , the trailing edge  22  of the blade  20  has one indentation  30 . The indentation  30  is near a radially central portion of the trailing edge  22 . The indentation  30  is a first indentation with respect to the after-mentioned second indentation. 
     The indentation  30 , which is the first indentation, is a portion at which a wall constituting the trailing edge  22  indents toward the leading edge  21 . Alternatively, the indentation  30  is a portion at which the wall constituting the trailing edge  22  indents in the direction of rotation DR. In other words, the indentation  30  indents in a direction opposite to the direction of rotation DR, and is open in a direction opposite to the direction of rotation DR. 
     In a plan view of the blade  20  shown in  FIG. 1  as seen from an angle parallel with the axial direction of the rotation axis RS, the indentation  30  is a portion at which a blade plate of the blade  20  serving as the trailing edge  22  is notched into a U shape or a V shape. That is, the indentation  30  narrows from the trailing edge  22  to the leading edge  21 . The U shape or the V shape is an example of the shape of the indentation  30  in a plan view, and the shape of the indentation  30  in a plan view is not limited to the U shape or the V shape. 
     The indentation  30  is defined as a portion of the trailing edge  22  that has a concave shape and extends further forward in the direction of rotation DR than a first straight line L 1  connecting a basal portion  22   b  of the trailing edge  22  and a trailing edge end portion  32  of the trailing edge  22 . The basal portion  22   b  is a portion at which the hub  10  and the trailing edge  22  intersect. The trailing edge end portion  32  is the outermost peripheral end portion of the trailing edge  22 . Alternatively, the trailing edge end portion  32  is a portion of the trailing edge  22  that is close to the outer peripheral edge  23  and projects in a direction opposite to the direction of rotation of the axial flow fan  100 . The trailing edge end portion  32  is positioned outside of than the after-mentioned apex  33 . In a plan view of the blade  20  as seen from an angle parallel with the axial direction of the rotation axis RS, the straight line L 1  intersects the trailing edge  22  at at least one point between the basal portion  22   b  and the trailing edge end portion  32 . 
     An intersection portion  31  is a point of intersection at which the first straight line L 1  and the trailing edge  22  intersect, and is further inward than the trailing edge end portion  32 . The trailing edge end portion  32  is further outward than the intersection portion  31 . The intersection portion  31  is an inner peripheral end portion of the indentation  30 , and the trailing edge end portion  32  is an outer peripheral end portion of the indentation  30 . The indentation  30  is a portion of the trailing edge portion  22  that is between the intersection portion  31 , which is the inner peripheral end portion of the indentation  30 , and the trailing edge end portion  32 , which is the outer peripheral end portion of the indentation  30 . 
     A relationship of each position of the indentation  30  in the direction of rotation DR is discussed here in terms of a relationship between a point of intersection of a second straight line M 1  radially extending from the rotation axis RS and the indentation  30  and an angle of rotation of the second straight line M 1  in a plan view as seen from an angle parallel with the axial direction of the rotation axis RS. Moreover, a point of intersection of the second straight line M 1  and the indentation  30  in a part of the indentation  30  that is furthest forward in the direction of rotation DR is defined as an apex  33  of the indentation  30 . In a case in which the amount by which the indentation  30  indents in the direction of rotation DR is expressed as “depth”, the apex  33  is closest to the leading edge  21  from among the points constituting the indentation  30 , and constitutes a deep part of the indentation  30 . The apex  33  is between the intersection portion  31  of the trailing edge  22  and the trailing edge end portion  32 . That is, the indentation  30  is formed such that the intersection portion  31 , the apex  33 , and the trailing edge end portion  32  are arranged in this order from the inner periphery toward the outer periphery of the trailing edge  22 . The indentation  30  is open in a direction opposite to the direction of rotation DR, and a part of the indentation  30  that is close to the apex  33  is narrower than a part of the indentation  30  that is between the intersection portion  31  and the trailing edge end portion  32 . 
       FIG. 3  is a side view conceptually showing an example of a distribution of blade thickness of the trailing edge  22  shown in  FIG. 2 .  FIG. 4  is a diagram showing a blade surface distribution of the trailing edge  22  of the axial flow fan  100  according to Embodiment 1.  FIG. 3  is a conceptual diagram showing the blade thickness of the blade  20  and the blade thickness of the trailing edge  22  as seen from an angle indicated by an arrow SW in  FIG. 2 . In  FIG. 3 , a pressure surface  25   a  indicates a portion of the pressure surface  25  of the blade  20  that is further forward in the direction of rotation DR than the trailing edge  22 , and a pressure surface  25   e  represents the pressure surface  25  of the trailing edge  22 . Further, in  FIG. 3 , a suction surface  26   a  indicates a portion of the suction surface  26  of the blade  20  that is further forward in the direction of rotation DR than the trailing edge  22 , and a suction surface  26   e  represents the suction surface  26  of the trailing edge  22 .  FIG. 4  plots radial distance in abscissa and axial distance in ordinate, and conceptually represents an axial change in blade surface of the trailing edge in a radial direction. The blade surface shown in  FIG. 4  is the pressure surface  25  or the suction surface  26 . Next, the blade thickness of the trailing edge  22  is described with reference to  FIGS. 3 and 4 . 
     The blade thickness of the blade  20  is defined as a distance between a part of the pressure surface  25  and a part of the suction surface  26  that are at the same radial distance from the rotation axis RS. Moreover, the blade thickness of the trailing edge  22  is defined as a distance between a part of the pressure surface  25  of the trailing edge  22  and a part of the suction surface  26  of the trailing edge  22  that are at the same radial distance from the rotation axis RS. For example, as shown in  FIG. 3 , the blade thickness of the blade  20  at the intersection portion  31  is a blade thickness T 1 . Further, the blade thickness of the blade  20  at the apex  33  is a blade thickness T 3 . Furthermore, the blade thickness of the blade  20  at the trailing edge end portion  32  is a blade thickness T 2 . The blade thickness of the blade  20  may be defined as a distance in the axial direction of the rotation axis RS between a part of the pressure surface  25  of the trailing edge  22  and a part of the suction surface  26  of the trailing edge  22  that are at the same radial distance from the rotation axis RS. Moreover, the blade thickness of the trailing edge  22  may be defined as a distance in the axial direction of the rotation axis RS between a part of the pressure surface  25  of the trailing edge  22  and a part of the suction surface  26  of the trailing edge  22  that are at the same radial distance from the rotation axis RS. 
       FIG. 5  is another plan view of a blade  20  shown in  FIG. 1  as seen from an angle parallel with the axial direction of the rotation axis RS.  FIG. 6  is a diagram conceptually showing a shape of a cross-section of the trailing edge  22  of the blade  20  shown in  FIG. 5  as taken along line M-M.  FIG. 7  is a diagram conceptually showing a shape of another cross-section of the trailing edge  22  of the blade  20  shown in  FIG. 5  as taken along line M-M.  FIG. 8  is a diagram conceptually showing a shape of another cross-section of the trailing edge  22  of the blade  20  shown in  FIG. 5  as taken along line M-M. As shown in  FIG. 6 , in a case in which the trailing edge  22  is rectangular, the blade thickness is defined as that of a portion of the trailing edge  22  at the blade tip. Further, as shown in  FIG. 7 , in a case in which the trailing edge  22  has a round shape, the blade thickness is defined as that of a portion of the trailing edge  22  at a starting point of the round shape. Further, as shown in  FIG. 8 , in a case in which the trailing edge  22  has a pointed end, the blade thickness is defined as that of a portion of the trailing edge  22  at a starting point of the pointed end. The blade thickness of the trailing edge  22  shown in  FIGS. 6 to 8  is shown as the blade thickness T in  FIGS. 6 to 8 . 
     As shown in  FIGS. 3 and 4 , the indentation  30  of the trailing edge  22  increases in blade thickness outward from the intersection point  31  and reaches a maximum blade thickness inside of the apex  33 . The blade  20  has, at the indentation  30 , a maximum thickness portion  36  at which a thickness of the blade  20  is maximum, and which is positioned radially inside of the apex  33 . Thus, the indentation  30  of the blade  20  has the maximum thickness portion  36  in an area between the apex  33  and the intersection portion  31 . The area between the apex  33  and the intersection portion  31  is referred to as “inner peripheral area  38 ”. Accordingly, the indentation  30  of the blade  20  has the maximum thickness portion  36  in the inner peripheral area  38 . As shown in  FIG. 3 , the blade thickness TL of the maximum thickness portion  36  is greatest of the thicknesses at the indentation  30 . The blade thickness of the indentation  30  of the trailing edge  22  is partially greater radially inside of the apex  33  than the blade thickness of the apex  33 , which is the deepest part of the indentation  30  in the direction of rotation DR. Accordingly, at the indentation  30  of the trailing edge  22 , the blade thickness T 1  of the intersection portion  31 , which is the inner peripheral end portion of the indentation  30 , and the blade thickness T 3  of the apex  33  are smaller than the blade thickness TL of the maximum thickness portion  36 . 
       FIG. 3  shows an example of the trailing edge  22 . Accordingly, the configuration of the blade thickness of the indentation  30  at the trailing edge  22  needs only be formed as indicated below, and the configuration of the pressure surface  25  and the configuration of the suction surface  26  do not need to be identical. Therefore, for example, either the pressure surface  25  or the suction surface  26  may be constituted by a curved surface, and the other blade surface may be constituted by a flat surface. Alternatively, the pressure surface  25  and the suction surface  26  may be constituted by different curved surfaces. 
     It is desirable that as shown in  FIG. 3 , the maximum thickness portion  36  be between the intersection portion  31 , which is the inner peripheral end portion of the indentation  30 , and the apex  33  and be closer to the apex  33  than a center  37  between the intersection portion  31 , which is the inner peripheral end portion of the indentation  30 , and the apex  33 . 
     [Operation of Axial Flow Fan  100 ] 
     When the axial flow fan  100  rotates in the direction of rotation DR shown in  FIG. 1 , each blade  20  presses ambient air with the pressure surface  25  to generate an airflow in the direction F shown in  FIG. 1 . Further, the rotation of the axial flow fan  100  produces a pressure difference between the pressure surface  25  and the suction surface  26  in an area around each blade  20 . Specifically, the suction surface  26  is subjected to a lower pressure than the pressure surface  25 . 
     [Effects of Axial Flow Fan  100 ] 
       FIG. 9  is a plan view of an axial flow fan  100 L according to a comparative example as seen from an angle parallel with an axial direction of a rotation axis RS.  FIG. 10  is a side view conceptually showing a distribution of blade thickness of a trailing edge  22  of a blade  20 L shown in  FIG. 9 .  FIG. 11  is a diagram showing a blade surface distribution of the trailing edge  22  of the axial flow fan  100 L according to the comparative example. In general, an axial flow fan is configured such that an air flow having flowed in through the leading edge of a blade is caused by a centrifugal force to flow radially outward. In the axial flow fan  100 L according to the comparative example, an airflow flowing radially inward from the apex  33  passes through the indentation  30  in the process of moving radially outward in the axial flow fan  100 L. Therefore, in the axial flow fan  100 L, airflows flowing in radially inside of the apex  33  concentrate near the apex  33 , so that a wind velocity is high near the apex  33 . 
     As shown in  FIGS. 10 and 11 , the axial flow fan  100 L according to the comparative example is configured such that the maximum thickness portion  36  is positioned at the apex  33 . The axial flow fan  100 L according to the comparative example is configured such that the blade thickness TE of the maximum thickness portion  36 , which is positioned at the apex  33 , is greatest of the blade thicknesses at the indentation  30 . That is, as shown in  FIGS. 10 and 11 , the axial flow fan  100 L according to the comparative example is configured such that the apex  33 , which is close to the middle of the length of the blade as seen on identical radii, is greatest in blade thickness. In general, at a place at which a blade tip is thick, separation of an airflow from the blade produces a slipstream with a great difference in velocity between the pressure surface and the suction surface, so that a blade tip vortex is generated. In the axial flow fan  100 L, in which the apex  33 , at which a wind velocity is high, is greatest in blade thickness, separation of an airflow from the blade produces a slipstream with a great difference in velocity between the pressure surface and the suction surface, so that a blade tip vortex is easily generated. Meanwhile, the indentation needs a portion with an increased thickness for the securing of strength against a centrifugal force that is applied to the blade. 
       FIG. 12  is a schematic view showing a relationship between the blade  20  of the axial flow fan  100  according to Embodiment 1 and airflows. The relationship between the blade  20  of the axial flow fan  100  according to Embodiment 1 and airflows is described with reference to  FIG. 12 . As compared with the axial flow fan  100 L according to the comparative example, the axial flow fan  100  according to Embodiment 1 is configured such that the blade  20  has, at the indentation  30 , a maximum thickness portion  36  at which a thickness of the blade  20  is maximum, and which is positioned radially inside of the apex  33 . Since the axial flow fan  100  is configured such that a thickness of a portion of the blade that is positioned inside of the apex  33  is a maximum thickness, the axial flow fan  100  can make the difference in velocity between the pressure surface and the suction surface of a slipstream produced at the apex  33 , at which a wind velocity is high, smaller than the axial flow fan  100 L, and can inhibit blade tip vortices WV. 
     The inner peripheral area  38  in which the maximum thickness portion  36  is provided, and which is positioned inside (Y2 side) of the apex  33 , produces a comparatively weak slipstream and hardly forms blade tip vortices WV, as an air flow FL 2  reaching the blade tip is small in amount and low in velocity. Note, however, that the inner peripheral area  38  can secure strength against a centrifugal force by having the maximum thickness portion  36 . That is, the inner peripheral area  38  prioritizes the strength of the blade  20  over the inhibition of blade tip vortices WV. 
     In an outer peripheral area  39  positioned outside (Y1 side) of the apex  33 , an airflow reaching the blade tip of the trailing edge  22  is large in amount and high in velocity, as an airflow FL 1  having flowed in through the leading edge  21  of the blade  20  is caused by a centrifugal force to flow radially outward. The outer peripheral area  39  is an area between the apex  33  and the trailing edge end portion  32 , which is the outer peripheral end portion of the indentation  30 . However, in the outer peripheral area  39 , which is thinner in blade thickness than the inner peripheral area  38  and shorter in distance between the pressure surface  25  and the suction surface  26  than the inner peripheral area  38 , blade tip vortices WV formed downstream of the blade tip, if any, are small and weak. That is, by prioritizing the flow of gas over the strength of the blade  20 , the outer peripheral area  39  prioritizes the inhibition of blade tip vortices WV that are formed downstream of the blade tip. 
     In response to an airflow FL, the axial flow fan  100  can secure the strength of the indentation  30  in the inner peripheral area  38 , through which a small amount of airflow passes, and, at the same time, can inhibit the generation of blade tip vortices WV, which are a cause of an energy loss, downstream of the blade tip of the trailing edge  22  in the outer peripheral area  39 , through which a large amount of airflow passes. As a result, the axial flow fan  100  can achieve an energy-saving and low-noise air-sending device. In general, since the volume of air that passes is large on the outer periphery of a blade, the length of the blade tends to be great on the outer periphery. In the axial flow fan  100  according to Embodiment 1, the volume of the blade  20  is reduced by reducing the thickness of a portion of the blade  20  that is positioned outside of the apex  33 . This makes it possible to reduce the weights of the blade  20  and the axial flow fan  100 . 
     Further, the axial flow fan  100  is configured such that the maximum thickness portion  36  is between the intersection portion  31 , which is the inner peripheral end portion of the indentation  30 , and the apex  33  and is closer to the apex  33  than a center  37  between the intersection portion  31  which is the inner peripheral end portion of the indentation  30 , and the apex  33 . Since the apex  33  is subjected to a high load by a centrifugal force, the strength of the blade  20  can be secured by positioning the maximum thickness portion  36  closer to the apex  33  than the center  37 . 
     Embodiment 2 
       FIG. 13  is a plan view of an axial flow fan  100 A according to Embodiment 2 as seen from an angle parallel with an axial direction of a rotation axis RS.  FIG. 14  is a side view conceptually showing an example of a distribution of blade thickness of a trailing edge  22  of a blade  20 A shown in  FIG. 13 .  FIG. 15  is a diagram showing a blade surface distribution of the trailing edge  22  of the axial flow fan  100 A according to Embodiment 2.  FIG. 14  shows an example of the trailing edge  22 , and as indicated by the blade surface of  FIG. 15 , the blade thickness of the blade  20 A may be specified by either the pressure surface  25  or the suction surface  26 . The axial flow fan  100 A according to Embodiment 2 is intended to specify the configuration of a portion between the apex  33  and the trailing edge end portion  32 , which is the outer peripheral end portion of the indentation  30 . Components identical to those of the axial flow fan  100  or other axial flow fans of  FIGS. 1 to 12  are given identical reference signs, and a description of such components is omitted. 
     The axial flow fan  100 A according to Embodiment 2 is configured such that the blade  20 A has, at the indentation  30 , a minimum thickness portion  34  at which a thickness of the blade  20 A is minimum, and which is positioned radially outside of the apex  33 . The axial flow fan  100 A according to Embodiment 2 is configured such that the blade  20 A has, at the indentation  30 , a minimum thickness portion  34  at which a thickness of the blade  20 A is minimum, and which is positioned between the apex  33  and the trailing edge end portion  32 , which is the outer peripheral end portion of the indentation  30 . That is, the axial flow fan  100 A according to Embodiment 2 has the minimum thickness portion  34  in the outer peripheral area  39 . As shown in  FIG. 14 , the blade thickness TS of the maximum thickness portion  34  is smallest of the thicknesses at the indentation  30 . That is, the indentation  30  of the trailing edge  22  decreases in blade thickness outward from the apex  33  and is smallest in blade thickness inside of the trailing edge end portion  32 , which is the outer peripheral end portion of the indentation  30 . The blade thickness of the indentation  30  of the trailing edge  22  is partially smaller radially outside of the apex  33  than the blade thickness of the apex  33 , which is the deepest part of the indentation  30  in the direction of rotation DR. Accordingly, at the indentation  30  of the trailing edge  22 , the blade thickness T 2  of the trailing edge end portion  32 , which is the outer peripheral end portion of the indentation  30 , and the blade thickness T 3  of the apex  33  are greater than the blade thickness TS of the minimum thickness portion  34 . 
     As shown in  FIGS. 14 and 15 , the indentation  30  of the trailing edge  22  increases in blade thickness outward from the intersection point  31  and reaches a maximum blade thickness inside of the apex  33 . Moreover, the indentation  30  of the trailing edge decreases in thickness of the blade outward from the maximum thickness portion  36 , at which the thickness of the blade  20 A is maximum, and is smallest in blade thickness at the minimum thickness portion  34 , which is positioned between the apex  33  and the trailing edge end portion  32 . Moreover, the indentation  30  of the trailing edge increases in blade thickness from the minimum thickness portion  34  toward the trailing edge end portion  32 . 
     [Effects of Axial Flow Fan  100 A] 
     The axial flow fan  100 A according to Embodiment 2 is configured such that the blade  20 A has, at the indentation  30 , a minimum thickness portion  34  at which a thickness of the blade  20 A is minimum, and which is positioned radially outside of the apex  33 . The axial flow fan  100 A according to Embodiment 2 is configured such that the blade  20 A has, at the indentation  30 , a minimum thickness portion  34  at which a thickness of the blade  20 A is minimum, and which is positioned between the apex  33  and the trailing edge end portion  32 , which is the outer peripheral end portion of the indentation  30 . An airflow flowing along a blade surface is subjected to a centrifugal force to flow radially outward from the apex  33  of the indentation  30 . In the axial flow fan  100 A, a thickness of a portion of the blade that is positioned radially outside is reduced at the indentation  30 , at which airflows concentrate. This makes it hard for an airflow separated from the blade tips of the pressure surface and the suction surface to be sucked in behind the blade tips, and makes it possible to reduce blade tip vortices WV that are generated downstream of the blade tips. As a result, the axial flow fan  100 A reduces an energy loss attributed to the blade tip vortices WV and reduces disturbances of air flow, thereby making it possible to achieve energy conservation and reduce noise. Further, in the axial flow fan  100 A, in which a thickness of a portion of the blade that is positioned radially outside is reduced, a reduced force is applied to the indentation  30  by a centrifugal force. This makes it possible to secure the strength of the axial flow fan  100 A. 
     Embodiment 3 
       FIG. 16  is a plan view of an axial flow fan  100 B according to Embodiment 3 as seen from an angle parallel with an axial direction of a rotation axis RS.  FIG. 17  is a side view conceptually showing an example of a distribution of blade thickness of a trailing edge  22  of a blade  20 B shown in  FIG. 16 .  FIG. 18  is a diagram showing a blade surface distribution of the trailing edge  22  of the axial flow fan  100 B according to Embodiment 3.  FIG. 16  shows an example of the trailing edge  22 , and as indicated by the blade surface of  FIG. 18 , the blade thickness of the blade  20 B may be specified by either the pressure surface  25  or the suction surface  26 . The axial flow fan  100 B according to Embodiment 3 is intended to specify the configuration of a portion between the apex  33  and the trailing edge end portion  32 , which is the outer peripheral end portion of the indentation  30 . Components identical to those of the axial flow fan  100  or other axial flow fans of  FIGS. 1 to 15  are given identical reference signs, and a description of such components is omitted. 
     The axial flow fan  100 B according to Embodiment 3 is configured such that the blade  20 B has, at the indentation  30 , a minimum thickness portion  34  at which a thickness of the blade  20 B is minimum, and which is positioned radially outside of the apex  33 . The axial flow fan  100 B according to Embodiment 3 is configured such that the blade  20 B has, at the indentation  30 , a minimum thickness portion  34  at which a thickness of the blade  20 B is minimum, and which is positioned at the trailing edge end portion  32 , which is the outer peripheral end portion of the indentation  30 . That is, the indentation  30  of the trailing edge  22  decreases in blade thickness outward from the apex  33  and is smallest in blade thickness at the trailing edge end portion  32 , which is the outer peripheral end portion of the indentation  30 . The blade thickness of the indentation  30  of the trailing edge  22  is partially smaller radially outside of the apex  33  than the blade thickness of the apex  33 , which is the deepest part of the indentation  30  in the direction of rotation DR. Accordingly, at the indentation  30  of the trailing edge  22 , the blade thickness T 3  of the apex  33  is greater than the blade thickness TS of the minimum thickness portion  34 . 
     As shown in  FIGS. 14 and 15 , the indentation  30  of the trailing edge  22  increases in blade thickness outward from the intersection point  31  and reaches a maximum blade thickness inside of the apex  33 . Moreover, the indentation  30  of the trailing edge decreases in blade thickness outward from the maximum thickness portion  36 , at which the thickness of the blade  20 B is maximum, toward the apex  33  and then toward the trailing edge end portion  32 . 
     [Effects of Axial Flow Fan  100 B] 
     The axial flow fan  100 B according to Embodiment 3 is configured such that the blade  20 B has, at the indentation  30 , a minimum thickness portion  34  at which a thickness of the blade  20 B is minimum, and which is positioned radially outside of the apex  33 . The axial flow fan  100 A according to Embodiment 2 is configured such that the blade  20 B has, at the indentation  30 , a minimum thickness portion  34  at which a thickness of the blade  20 B is minimum, and which is positioned between the apex  33  and the trailing edge end portion  32 , which is the outer peripheral end portion of the indentation  30 . An airflow flowing along a blade surface is subjected to a centrifugal force to flow radially outward from the apex  33  of the indentation  30 . In the axial flow fan  100 B, a thickness of a portion of the blade that is positioned radially outside is reduced at the indentation  30 , at which airflows concentrate. This makes it possible to reduce blade tip vortices WV that are generated downstream of the blade tips and, by reducing an energy loss and reducing disturbances of airflow, achieve energy conservation and reduced noise. Further, in the axial flow fan  100 B, in which a thickness of a portion of the blade that is positioned radially outside is reduced, a reduced force is applied to the indentation  30  by a centrifugal force. This makes it possible to secure the strength of the axial flow fan  100 B. Further, since the axial flow fan  100 B is configured such that the thickness of the blade  20  gradually changes from the inner periphery toward the outer periphery of the blade  20 , a local stress concentration hardly occurs. This makes it possible to better secure the strength of the axial flow fan  100 B than that of the axial flow fan  100 A. 
     Embodiment 4 
       FIG. 19  is a plan view of an axial flow fan  100 C according to Embodiment 4 as seen from an angle parallel with an axial direction of a rotation axis RS.  FIG. 20  is a side view conceptually showing an example of a distribution of blade thickness of a trailing edge  22  of a blade  20 C shown in  FIG. 19 .  FIG. 21  is a diagram showing a blade surface distribution of the trailing edge  22  of the axial flow fan  100 C according to Embodiment 4.  FIG. 19  shows an example of the trailing edge  22 , and as indicated by the blade surface of  FIG. 21 , the blade thickness of the blade  20 C may be specified by either the pressure surface  25  or the suction surface  26 . The axial flow fan  100 C according to Embodiment 4 is intended to specify the configuration of a portion between the apex  33  and the intersection portion  31 , which is the inner peripheral end portion of the indentation  30 . Components identical to those of the axial flow fan  100  or other axial flow fans of  FIGS. 1 to 18  are given identical reference signs, and a description of such components is omitted. 
     The axial flow fan  100 C according to Embodiment 4 is configured such that the blade  20 C has, at the indentation  30 , a maximum thickness portion  36  at which a thickness of the blade  20 C is maximum, and which is positioned radially inside of the apex  33 . The axial flow fan  100 C according to Embodiment 4 is configured such that the blade  20 C has, at the indentation  30 , a maximum thickness portion  36  at which a thickness of the blade  20 C is maximum, and which is positioned at the intersection portion  31 , which is the inner peripheral end portion of the indentation  30 . That is, the indentation  30  of the trailing edge  22  increases in blade thickness inward from the apex  33  and reaches a maximum blade thickness at the intersection portion  31 , which is the inner peripheral end portion of the indentation  30 . The blade thickness of the indentation  30  of the trailing edge  22  is partially greater radially inside of the apex  33  than the blade thickness of the apex  33 , which is the deepest part of the indentation  30  in the direction of rotation DR. Accordingly, at the indentation  30  of the trailing edge  22 , the blade thickness T 3  of the apex  33  is smaller than the blade thickness TL of the maximum thickness portion  36 . 
     As shown in  FIGS. 20 and 21 , the indentation  30  of the trailing edge  22  decreases in blade thickness outward from the intersection portion  31  having the maximum thickness portion  36 , at which the thickness of the blade  20 B is maximum, toward the apex  33  and then toward the trailing edge end portion  32 . 
     [Effects of Axial Row Fan  100 C] 
     The axial flow fan  100 C according to Embodiment 4 is configured such that the blade  20 C has, at the indentation  30 , a maximum thickness portion  36  at which a thickness of the blade  20 C is maximum, and which is positioned at the intersection portion  31 , which is the inner peripheral end portion of the indentation  30 . The indentation  30  of the axial flow fan  100 C according to Embodiment 4 decreases in blade thickness and mass toward the outer periphery, to which a centrifugal force is applied. This makes it possible to secure the strength of the blade  20 . Further, the indentation  30  of the axial flow fan  100 C according to Embodiment 4 has no abrupt change in blade thickness of the trailing edge  22  in a radial direction. The axial flow fan  100  according to Embodiment 4 reduces changes in strength of vortices that are generated inside and outside of the intersection portion  31 , which is the inner peripheral end portion of the indentation  30 , and reduces disturbances of airflow. 
     Embodiment 5 
       FIG. 22  is a plan view of an axial flow fan  100 D according to Embodiment 5 as seen from an angle parallel with an axial direction of a rotation axis RS.  FIG. 23  is an enlarged view conceptually showing blade tip indentations  40  shown in  FIG. 22 . Components identical to those of the axial flow fan  100  or other axial flow fans of  FIGS. 1 to 21  are given identical reference signs, and a description of such components is omitted. 
     A blade  20 D has, as a portion of the trailing edge  22  that is close to the outer periphery, a blade tip indentation  40  having a serrated shape. The blade tip indentation  40  is a second indentation of the blade  20 D, and is a portion of at least the indentation  30 . More specifically, the blade tip indentation  40 , which is the second indentation, is positioned between the apex  33  and the trailing edge end portion  32 , which is the outer peripheral end portion of the indentation  30 . That is, the blade tip indentation  40 , which is the second indentation, is positioned at least in the outer peripheral area  39  of the indentation  30 . The blade tip indentation  40 , which is the second indentation, needs only be positioned at least in the outer peripheral area  39  of the indentation  30 , and may be a portion of the trailing edge  22  that is positioned outside of the trailing edge end portion  32 . Accordingly, the indentation  30  has a blade tip indentation  40  having a serrated shape along the trailing edge as a portion of the indentation  30  that is positioned outside of the apex  33 . 
     The blade tip indentation  40 , which is the second indentation, includes a plurality of notches  41  and mountain portions  42  each positioned between one and another of the plurality of notches  41  and projecting in the direction of rotation DR, and is a series of the notches  41  and the mountain portions  42  along the trailing edge  22 . In the example shown in  FIG. 22 , there are provided three notches  41  and two mountain portions  42 . As a result, the portion of the trailing edge  22  that is close to the outer periphery has a serrated shape. Assume that, as shown in  FIG. 23 , a distance between a position  44   a  of an apex  44  and a position  45   a  of a valley portion  45  in the direction of rotation DR is a notch depth TD. The apex  44  is a top of a mountain portion  42  in the direction in which the mountain portion  42  projects, and the valley portion  45  is the position of a valley floor between one mountain portion  42  and another mountain portion  42 . That is, the depth TD is the depth of a notch of the blade tip indentation  40 , and is the difference in height between a mountain and a valley of the blade tip indentation  40 . 
     The blade tip indentation  40  needs only include a plurality of notches  41  and may include any number of notches  41 . Although, in the example shown in  FIGS. 22 and 23 , the notches  41  each has a triangular shape in a plan view of the axial flow fan  100 D as seen from an angle parallel with the axial direction of the rotation axis RS, the shape of each of the notches  41  is not limited to such a shape. Some or all of the notches  41  of the blade tip indentation  40  may have different shapes. 
     Although, in the example shown in  FIGS. 22 and 23 , the mountain portions  42  each has a triangular shape in a plan view of the axial flow fan  100 D as seen from an angle parallel with the axial direction of the rotation axis RS, the shape of each of the mountain portions  42  is not limited to such a shape. Some or all of the mountain portions  42  of the blade tip indentation  40  may have different shapes. 
     [Effects of Axial Flow Fan  100 D] 
     The indentation  30  has a blade tip indentation  40  having a serrated shape along the trailing edge as a portion of the indentation  30  that is positioned outside of the apex  33 . Since the portion of the indentation  30  that is close to the outer periphery is smaller in blade thickness than the apex  33 , blade tip vortices WV that are generated at an end portion of the blade  20 D by an airflow FL are small. By including the serrated blade tip indentation  40  on the outer periphery, at which a wind velocity is high, the axial flow fan  100 D can create small disturbances in advance, further weaken the blade tip vortices WV, and thereby reduce trailing vortices. 
     Embodiment 6 
       FIG. 24  is a plan view of an axial flow fan  100 E according to Embodiment 6 as seen from an angle parallel with an axial direction of a rotation axis RS. Components identical to those of the axial flow fan  100  or other axial flow fans of  FIGS. 1 to 23  are given identical reference signs, and a description of such components is omitted. 
     A blade  20 E has, as a portion of the trailing edge  22  that is close to the inner periphery, a blade tip indentation  40  having a serrated shape. The blade tip indentation  40  is a second indentation of the blade  20 E, and is a portion of at least the indentation  30 . More specifically, the blade tip indentation  40 , which is the second indentation, is positioned between the apex  33  and the intersection portion  31 , which is the inner peripheral end portion of the indentation  30 . That is, the blade tip indentation  40 , which is the second indentation, is positioned at least in the inner peripheral area  38  of the indentation  30 . The blade tip indentation  40 , which is the second indentation, needs only be positioned at least in the inner peripheral area  38  of the indentation  30 , and may be a portion of the trailing edge  22  that is positioned inside of the intersection portion  31 . Accordingly, the indentation  30  has a blade tip indentation  40  having a serrated shape along the trailing edge as a portion of the indentation  30  that is positioned inside of the apex  33 . 
     [Effects of Axial Flow Fan  100 E] 
     The indentation  30  has a blade tip indentation  40  having a serrated shape along the trailing edge as a portion of the indentation  30  that is positioned inside of the apex  33 . By including the serrated blade tip indentation  40  on the inner periphery, at which a thickness of the blade  20  is great, the axial flow fan  100 E can create small disturbances in advance also in a portion in which the strength of the blade  20  is secured, further weaken the blade tip vortices WV, and thereby reduce trailing vortices. 
     Embodiment 7 
       FIG. 25  is a plan view of an axial flow fan  100 F according to Embodiment 7 as seen from an angle parallel with an axial direction of a rotation axis RS. Components identical to those of the axial flow fan  100  or other axial flow fans of  FIGS. 1 to 24  are given identical reference signs, and a description of such components is omitted. 
     The blade  20 F has, as portions of the trailing edge  22  that are close to the outer periphery and the inner periphery, blade tip indentations  40  each having a serrated shape. The blade tip indentations  40  are second indentations of the blade  20 F, and are portions of at least the indentation  30 . More specifically, one of the blade tip indentations  40 , which are the second indentations, is positioned between the apex  33  and the intersection portion  31 , which is the inner peripheral end portion of the indentation  30 , and the other of the blade tip indentations  40 , which are the second indentations, is positioned between the apex  33  and the trailing edge end portion  32 , which is the outer peripheral end portion of the indentation  30 . That is, one of the blade tip indentations  40 , which are the second indentations, is positioned in the inner peripheral area  38  of the indentation  30 , and the other of the blade tip indentations  40 , which are the second indentations, is positioned in the outer peripheral area  39  of the indentation  30 . 
     One of the blade tip indentations  40 , which are the second indentations, needs only be positioned at least in the inner peripheral area  38  of the indentation  30 , and may be a portion of the trailing edge  22  that is positioned inside of the intersection portion  31 . Further, the other of the blade tip indentations  40 , which are the second indentations, needs only be positioned at least in the outer peripheral area  39  of the indentation  30 , and may be a portion of the trailing edge  22  that is positioned outside of the trailing edge end portion  32 . Accordingly, the indentation  30  has blade tip indentations  40  having serrated shapes along the trailing edge as portions of the indentation  30  that are positioned inside and outside of the apex  33 . 
     It is desirable that the axial flow fan  100 F be configured such that a depth TD 1  of any one of the notches of the blade tip indentation  40  positioned inside of the apex  33  is greater than a depth TD 2  of a notch of the blade tip indentation  40  positioned outside of the apex  33 . Further, it is further desirable that a minimum value of the depth TD 1  of each of the plurality of notches of the blade tip indentation  40  positioned inside of the apex  33  be greater than a maximum value of the depth TD 2  of each of the plurality of notches of the blade tip indentation  40  positioned outside of the apex  33 . The depth TD 1  and the depth TD 2  are defined by the depth TD described above. 
     It is desirable that the axial flow fan  100 F be configured such that in the inner peripheral area  38 , a depth TD 1  of any one of notches of the blade tip indentation  40  positioned inside of the maximum thickness portion  36  is greater than a depth TD 3  of a notch of the blade tip indentation  40  positioned outside of the maximum thickness portion  36 . This configuration may be applied to the axial flow fan  100 E described above. The depth TD 3  is defined by the depth TD described above. 
     [Effects of Axial Flow Fan  100 F] 
     The indentation  30  has a blade tip indentation  40  having a serrated shape along the trailing edge as a portion of the indentation  30  that is positioned outside of the apex  33 . Since the portion of the indentation  30  that is close to the outer periphery is smaller in blade thickness than the apex  33 , blade tip vortices WV that are generated at an end portion of the blade  20 D by an airflow FL are small. By including the serrated blade tip indentation  40  on the outer periphery, at which a wind velocity is high, the axial flow fan  100 F can create small disturbances in advance, further weaken the blade tip vortices WV, and thereby reduce trailing vortices. Furthermore, the indentation  30  has a blade tip indentation  40  having a serrated shape along the trailing edge as a portion of the indentation  30  that is positioned inside of the apex  33 . By including the serrated blade tip indentation  40  on the inner periphery, at which a thickness of the blade  20  is great, the axial flow fan  100 F can create small disturbances in advance also in a portion in which the strength of the blade  20  is secured, further weaken the blade tip vortices WV, and thereby reduce trailing vortices. 
     The indentation  30  is configured such that in a direction of rotation DR of the blade  20 , a depth TD 1  of any one of notches of the blade tip indentation  40  positioned inside of the apex  33  is greater than a depth TD 2  of a notch of the blade tip indentation  40  positioned outside of the apex  33 . By having a blade tip indentation  40  positioned on the inner periphery, at which a thickness of the blade  20  is great and a slipstream is easily generated, and formed by notches that are deeper than those of a blade tip portion  40  positioned on the outer periphery, the axial flow fan  100 F can create small disturbances in advance, further weaken the blade tip vortices WV, and thereby reduce trailing vortices. Since the thickness of a portion of the blade  20  that is positioned on the inner periphery is greater than the thickness of a portion of the blade  20  that is positioned on the outer periphery, the axial flow fan  100 F can better secure the strength of the portion of the blade  20  that is positioned on the inner periphery than the strength of the portion of the blade  20  that is positioned on the outer periphery. Therefore, in the axial flow fan  100 F, the depth of a notch of the blade tip indentation  40  positioned on the inner periphery of the blade  20  can be made greater than the depth of a notch of the blade tip indentation  40  positioned on the outer periphery of the blade  20 . 
     The indentation  30  is configured such that in a direction of rotation DR of the blade  20 , a depth TD 1  of any one of notches of the blade tip indentation  40  positioned inside of the maximum thickness portion  36  is greater than a depth TD 3  of a notch of the blade tip indentation  40  positioned outside of the maximum thickness portion  36 . By having a blade tip indentation  40  positioned on the inner periphery, at which a thickness of the blade  20  is great and a slipstream is easily generated, and formed by notches that are deeper than those of a blade tip portion  40  positioned on the outer periphery, the axial flow fan  100 F can create small disturbances in advance, further weaken the blade tip vortices WV, and thereby reduce trailing vortices. Since the thickness of a portion of the blade  20  that is positioned on the inner periphery is greater than the thickness of a portion of the blade  20  that is positioned on the outer periphery, the axial flow fan  100 F can better secure the strength of the portion of the blade  20  that is positioned on the inner periphery than the strength of the portion of the blade  20  that is positioned on the outer periphery. Therefore, in the axial flow fan  100 F, the depth of a notch of the blade tip indentation  40  positioned on the inner periphery of the blade  20  can be made greater than the depth of a notch of the blade tip indentation  40  positioned on the outer periphery of the blade  20 . 
     Embodiment 8 
     Embodiment 8 illustrates a case in which the axial flow fan  100  or other axial flow fans of Embodiments 1 to 7 are applied to an outdoor unit  50  serving as an air-sending device in a refrigeration cycle apparatus  70 . 
       FIG. 26  is a schematic view of the refrigeration cycle apparatus  70  according to Embodiment 8. While the following describes a case in which the refrigeration cycle apparatus  70  is used in air conditioning, the refrigeration cycle apparatus  70  is not limited to use in air conditioning. The refrigeration cycle apparatus  70  is used for example in a refrigerator, a freezer, a self-vending machine, an air-conditioning apparatus, a refrigerating apparatus, or a water heater for a freezing or air-conditioning purpose. 
     As shown in  FIG. 26 , the refrigeration cycle apparatus  70  includes a refrigerant circuit  71  connecting a compressor  64 , a condenser  72 , an expansion valve  74 , and an evaporator  73  in sequence by refrigerant pipes. The condenser  72  is provided with a condenser fan  72   a  configured to send air to the condenser  72  for use in heat exchange. Further, the evaporator  73  is provided with an evaporator fan  73   a  configured to send air to the evaporator  73  for use in heat exchange. At least either the condenser fan  72   a  or the evaporator fan  73   a  is constituted by the axial flow fan  100  or other axial flow fans of Embodiments 1 to 7. By providing the refrigerant circuit  71  with a flow switch device, such as a four-way valve, configured to switch the flow of refrigerant, the refrigeration cycle apparatus  70  may be configured to switch between heating operation and cooling operation. 
       FIG. 27  is a perspective view of the outdoor unit  50 , which is an air-sending device, as seen from an air outlet side.  FIG. 28  is a diagram for explaining a configuration of the outdoor unit  50  from the top.  FIG. 29  is a diagram showing a state in which a fan grille has been removed from the outdoor unit  50 .  FIG. 30  is a diagram showing an internal configuration of the outdoor unit  50  with the fan grille, a front panel, or other components removed from the outdoor unit  50 . 
     As shown in  FIGS. 27 to 30 , an outdoor unit body  51  serving as a casing is configured as a housing having a pair of left and right side surfaces  51   a  and  51   c , a front surface  51   b , a back surface  51   d , a top surface  51   e , and a bottom surface  51   f . The side surface  51   a  and the back surface  51   d  are provided with openings through which air is suctioned from outside. Further, in the front surface  51   b , a front panel  52  is provided with an air outlet  53  serving as an opening through which air is blown out. Furthermore, the air outlet  53  is covered with a fan grille  54 , whereby safety measures are taken by preventing contact between an object outside the outdoor unit body  51  and the axial flow fan  100 . The arrow AR of  FIG. 28  indicates the flow of air. 
     The outdoor unit body  51  houses the axial flow fan  100  and a fan motor  61 . The axial flow fan  100  is connected via a rotation shaft  62  to the fan motor  61 , which is a drive source provided on the back surface  51   d , and is driven by the fan motor  61  to rotate. The fan motor  61  applies a drive force to the axial flow fan  100 . 
     The outdoor unit body  51  has its interior divided by a divider  51   g  serving as a wall into a blast room  56  in which the axial flow fan  100  is placed and a machine room  57  in which the compressor  64  or other machines are placed. In the blast room  56 , the side surface  51   a  and the back surface  51   d  are provided with a heat exchanger  68  extending in a substantially L shape in a plan view. The heat exchanger  68  functions as the condenser  72  during heating operation and functions as the evaporator  73  during cooling operation. 
     A bellmouth  63  is disposed further radially outward than the axial flow fan  100  disposed in the blast room  56 . The bellmouth  63  is located further outward than an outer peripheral end of each of the blades  20 , and forms an annular shape along the direction of rotation of the axial flow fan  100 . Further, the divider  51   g  is located at one side of the bellmouth  63 , and a part of the heat exchanger  68  is located at the other side of the bellmouth  63 . 
     The bellmouth  63  has its front edge connected to the front panel  52  of the outdoor unit  50  so as to surround the outer periphery of the air outlet  53 . The bellmouth  63  may be integrated with the front panel  52  or may be prepared as a separate entity configured to be connected to the front panel  52 . A flow passage between a suction side and a blowout side of the bellmouth  63  is formed by the bellmouth  63  as an air trunk near the air outlet  53 . That is, the air trunk near the air outlet  53  is separated by the bellmouth  63  from another space in the blast room  56 . 
     The heat exchanger  68 , which is provided at a suction side of the axial flow fan  100 , includes a plurality of fins arranged so that plate surfaces are parallel and a heat-transfer pipe passing through the fins in the direction in which the fins are arranged. Refrigerant circulating through the refrigerant circuit flows through the heat-transfer pipe. The heat exchanger  68  of the present embodiment is configured such that the heat-transfer pipe extends in a L shape from the side surface  51   a  to the back surface  51   d  of the outdoor unit body  51  and a plurality of the heat-transfer pipes meander through the fins. Further, the heat exchanger  68  constitutes the refrigerant circuit  71  of the air-conditioning apparatus by being connected to the compressor  64  via a pipe  65  or other pipes and further connected to an indoor-side heat exchanger, an expansion valve, or other components (not illustrated). Further, the machine room  57  accommodates a substrate box  66  containing a control substrate  67  configured to control the pieces of equipment mounted in the outdoor unit. 
     (Working Effects of Refrigeration Cycle Apparatus  70 ) 
     Embodiment 8 brings about advantages that are similar to those of a corresponding one of Embodiments 1 to 7. For example, the axial flow fans  100  to  100 F inhibit the growth of a blade tip vortex at the trailing edge  22 . Therefore, mounting any one or more of these axial flow fans  100  to  100 F in the air-sending device allows the air-sending device to send an increased volume of air with low noise and high efficiency. Further, mounting the axial flow fan  100  or other axial flow fans in an air conditioner or a hot water supply outdoor unit that is the refrigeration cycle apparatus  70  constituted by the compressor  64  and the heat exchanger or other components makes it possible to attain a large volume of pass-by air with low noise and high efficiency and increase the amount of heat that is exchanged in the heat exchanger  68 . Therefore, the refrigeration cycle apparatus  70  allows the pieces of equipment to achieve reduced noise and improved energy conservation. Further, mounting the axial flow fan  100  or other axial flow fans in the refrigeration cycle apparatus  70  allows the refrigeration cycle apparatus  70  to change to a heat exchanger  68  that is smaller than that used in a conventional axial flow fan and contribute to a reduction in amount of refrigerant. 
     The configurations shown in the foregoing embodiments show examples of contents of the present disclosure and may be combined with another publicly-known technology, and parts of the configurations may be omitted or changed, provided such omissions and changes do not depart from the scope of the present disclosure. 
     REFERENCE SIGNS LIST 
       10 : hub,  20 : blade,  20 A: blade,  20 B: blade,  20 C: blade,  20 D: blade,  20 E: blade,  20 F: blade,  20 L: blade,  21 : leading edge,  22 : trailing edge,  22   b : basal portion,  23 : outer peripheral edge,  24 : inner peripheral edge,  25 : pressure surface,  25   a : pressure surface,  25   e : pressure surface,  26 : suction surface,  26   a : suction surface,  26   e : suction surface,  30 : indentation,  31 : intersection portion,  32 : trailing edge end portion,  33 : apex,  34 : minimum thickness portion,  36 : maximum thickness portion,  37 : center,  38 : inner peripheral area,  39 : outer peripheral area,  40 : blade tip indentation,  41 : notch,  42 : mountain portion,  44 : apex,  44   a : position,  45 : valley portion,  45   a : position,  50 : outdoor unit,  51 : outdoor unit body,  51   a : side surface,  51   b : front surface,  51   c : side surface,  51   d : back surface,  51   e : top surface.  51   f : bottom surface,  51   g : divider,  52 : front panel,  53 : air outlet,  54 : fan grille,  56 : blast room,  57 : machine room,  61 : fan motor,  62 : rotation axis,  63 : bellmouth,  64 : compressor,  65 : pipe,  66 : substrate box,  67 : control substrate,  68 : heat exchanger,  70 : refrigeration cycle apparatus,  71 : refrigerant circuit,  72 : condenser,  72   a : condenser fan,  73 : evaporator,  73   a : evaporator fan,  74 : expansion valve,  100 : axial flow fan,  100 A: axial flow fan,  100 B: axial flow fan,  100 C: axial flow fan,  100 D: axial flow fan,  100 E: axial flow fan,  100 F: axial flow fan,  100 L: axial flow fan