Axial blower

Abstract

To provide a technique for reducing a swirl component in a swirl flow.SOLUTION: The casing 100 has a first opening 112, a second opening 122, and a hollow space 130. The electric motor 200 is disposed in the hollow space 130. The axial fan 210 is attached to the rotating shaft 300 of the electric motor 200 and is rotatable. The first hub cone portion 220 is disposed closer to the first opening 112 than the axial fan 210 in the hollow space 130, and rectifies the flow of air including the swirling flow from the axial fan 210. The first decreased diameter portion 150 is arranged between the first hub cone portion 220 and the first opening 112 in the hollow space 130, and decreases the diameter of the hollow space 130 toward the first opening 112.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an axial flow fan that generates an airflow by rotating a plurality of blades. [Background technology]

[0002] Axial flow fans (jet fans) are used for ventilation or smoke extraction inside tunnels. The axial flow fan comprises a cylindrical casing with openings at both ends, an electric motor inside the casing, an axial flow fan that is rotatable in both forward and reverse directions and attached to the rotating shaft of the electric motor, and a hub cone that straightens the air flow, including the swirling flow, from the axial flow fan. The axial flow fan has multiple blades attached radially. The rotation of the multiple blades generates an airflow (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-42734 Summary of the Invention [Problem to be solved by the invention]

[0004] When the axial fan in an axial flow fan rotates, a swirling flow is generated that moves in a spiral shape inside the casing. In the swirling flow, if the swirling component that rotates around the rotation axis becomes large, the forward axial component becomes small, and the ventilation capacity of the axial flow fan decreases. On the other hand, it is required to increase the ventilation capacity of an axial flow fan by increasing the thrust. In order to increase the ventilation capacity, it is necessary to reduce the swirling component.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a technique for reducing the swirling component in a swirling flow. [Means for solving the problem]

[0006] To solve the above problems, an axial flow fan according to one embodiment of the present disclosure includes a cylindrical casing having a first opening at a first end, a second opening at a second end opposite the first end, and a hollow space connecting the first opening and the second opening, an electric motor arranged in the hollow space, an axial flow fan rotatably attached to a rotary shaft of the electric motor, and a hub cone portion arranged in the hollow space closer to the first opening than the axial flow fan and rectifying the flow of air including the swirling flow from the axial flow fan. The casing includes a tapered portion arranged in the hollow space between the hub cone portion and the first opening and tapering the diameter of the hollow space toward the first opening. [Effects of the Invention]

[0007] According to the present disclosure, the swirling component in the swirling flow can be reduced. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional perspective view showing the structure of an axial flow fan according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing the structure of the axial flow fan of FIG. [Figure 3] FIG. 3 is an enlarged view of the vicinity of the first reduced diameter portion in FIG. [Figure 4] FIG. 4 is a cross-sectional perspective view showing the structure of an axial flow fan according to a second embodiment. [Figure 5] FIG. 5 is a cross-sectional view showing the structure of the axial flow fan of FIG. [Figure 6] FIG. 6 is an enlarged view of the vicinity of the first reduced diameter portion and the first expanded diameter portion in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] Example 1 An axial flow fan according to an embodiment will be described below with reference to the drawings. The dimensional proportions in the drawings have been exaggerated for the sake of explanation and may differ from the actual proportions. The x-axis and y-axis are axes that are perpendicular to each other on a horizontal plane, and the z-axis is an axis that is perpendicular to the horizontal plane. The positive direction of the x-axis is sometimes called the "front side," the negative direction of the x-axis is sometimes called the "rear side," the positive direction of the y-axis is sometimes called the "right side," the negative direction of the y-axis is sometimes called the "left side," the positive direction of the z-axis is sometimes called the "upper side," and the negative direction of the z-axis is sometimes called the "lower side."

[0010] Fig. 1 is a cross-sectional perspective view showing the structure of axial flow fan 1000. Fig. 2 is a cross-sectional view showing the structure of axial flow fan 1000. Axial flow fan 1000 is a ventilation device installed in a tunnel for automobiles to expel harmful substances such as soot, carbon monoxide, and nitrogen oxides emitted from automobiles out of the tunnel and send fresh air into the tunnel. Axial flow fan 1000 includes a casing 100, an electric motor 200, an axial flow fan 210, a first hub cone portion 220, and a second hub cone portion 230.

[0011] The casing 100 is a tubular structure extending from a first end 110 to a second end 120, and may be cylindrical or rectangular. In this embodiment, the casing 100 is cylindrical. A first opening 112 is disposed on the first end 110 side of the casing 100, and a second opening 122 is disposed on the second end 120 side. The first opening 112 and the second opening 122 are connected to a hollow space 130 disposed inside the casing 100. The casing 100 is installed, for example, by hanging it near the ceiling of a tunnel using mounting brackets. The casing 100 may also have a sound-absorbing section formed inside using sound-absorbing material, a perforated plate, or the like. The central axis of the casing 100, i.e., the central axis of the hollow space 130, is parallel to a rotation shaft 300 of the electric motor 200, which will be described later.

[0012] The electric motor 200 is installed in the hollow space 130 by a motor stay (not shown). For example, the electric motor 200 is installed in the hollow space 130 so that the distance from the first opening 112 and the distance from the second opening 122 are equal, and the electric motor 200 is installed near the center in the inner diameter direction of the hollow space 130. The electric motor 200 has a rotating shaft 300, which is connected to the axial fan 210. The electric motor 200 rotates the axial fan 210 around the rotating shaft 300. Furthermore, the electric motor 200 is also capable of reversing the rotation direction of the rotating shaft 300.

[0013] The axial fan 210 is connected to the rotating shaft 300 of the electric motor 200. The axial fan 210 generates an airflow within the hollow space 130 by rotating. When viewed from the rear side from the first opening 112 side, the axial fan 210 can rotate clockwise or counterclockwise, i.e., in both forward and reverse directions. The axial fan 210 includes a base 212 and multiple blades 214. The base 212 is cylindrical, and multiple blades 214 are attached at equal intervals around the periphery. The base 212 is adjacent to the electric motor 200 and connected to the rotating shaft 300. For example, six blades 214 are attached to the base 212, and the cross section of the blades 214 is an axisymmetric airfoil shape. Note that the number of blades 214 may be any number, such as three or five. The cross section of the blades 214 may also be an asymmetric airfoil shape.

[0014] In this embodiment, a case will be mainly described in which the electric motor 200 rotates the axial fan 210 in a clockwise rotation direction 310 when viewed from the first opening 112 side toward the rear. In this case, in the axial flow fan 1000, air flows from the second opening 122 toward the first opening 112, that is, toward the front. This air includes a swirling flow 330 that moves forward while rotating around the rotation axis 300, that is, moves in a spiral. Of the swirling flow 330, the component that moves straight along the rotation axis 300 is the axial flow 320, and the component that rotates around the rotation axis 300 is the swirling component.

[0015] On the other hand, when viewed from the rear side from the first opening 112 side, if the motor 200 rotates the axial fan 210 counterclockwise, the air in the axial flow fan 1000 flows from the first opening 112 to the second opening 122, that is, toward the rear side. By switching the rotation direction of the axial flow fan 210, the air blowing direction can be switched in response to changes in the volume of automobile traffic passing through the tunnel, the direction of natural wind, or a fire occurring inside the tunnel, for example.

[0016] First hub cone portion 220 is disposed in front of electric motor 200 in hollow space 130. This can also be said to be disposed closer to first opening 112 than axial fan 210. First hub cone portion 220 is supported by a stay portion (not shown). First hub cone portion 220 has a generally conical shape that protrudes forward. The forward-most apex of generally conical first hub cone portion 220 is first tip portion 222. First hub cone portion 220 has an internal sound-absorbing portion formed of sound-absorbing material, a perforated plate, or the like. First hub cone portion 220 may have a hemispherical shape instead of a generally conical shape. First hub cone portion 220 rectifies the flow of air, including swirling flow 330, from axial fan 210.

[0017] In the hollow space 130, a first reduced diameter section 150 is disposed between the first tip portion 222 of the first hub cone portion 220 and the first opening 112. The portion of the hollow space 130 other than the first reduced diameter section 150 and the second reduced diameter section 160 (described later) is referred to as the air passage section 140. The first reduced diameter section 150 is a portion of the hollow space 130 whose inner diameter is smaller than that of the air passage section 140. As a cross section of the hollow space 130 along the yz plane, assuming that the cross-sectional area of ​​the air passage section 140 is "100%, " the cross-sectional area of ​​the first reduced diameter section 150 is 70% or more and less than 100%. The cross-sectional area of ​​the first reduced diameter section 150 is particularly preferably 70% or more and less than 90%. Furthermore, the opening areas of the first opening 112 and the second opening 122 are also less than 100%. That is, in this configuration, the cross-sectional area of ​​air passage section 140 and the opening area of ​​first opening 112 (second opening 122) are different, and the opening areas of first opening 112 and second opening 122 are smaller than the cross-sectional area of ​​air passage section 140.

[0018] Here, in order to explain the structure of the first diameter-reducing portion 150 in more detail, FIG. 3 is also used. FIG. 3 is an enlarged view of the vicinity of the first diameter-reducing portion 150. The first diameter-reducing portion 150 and the air passage portion 140 are separated by a boundary 156. The first diameter-reducing portion 150 includes a diameter-reducing inclined surface 152 and a diameter-reducing surface 154. The diameter-reducing inclined surface 152 is provided on the front side of the boundary 156, and the diameter-reducing surface 154 is provided on the front side of the diameter-reducing inclined surface 152. The diameter-reducing inclined surface 152 has a tapered shape that inclines inward in diameter toward the front with respect to the inner wall 142 of the air passage portion 140. Due to the tapered shape of the first diameter-reducing portion 150, the pressure loss due to diameter reduction is reduced. The taper angle "θ3" of the first diameter-reducing portion 150 is 60 degrees or less, preferably 30 degrees or less. The diameter-reducing surface 154 maintains the inner diameter reduced by the diameter-reducing surface 154. That is, the first diameter-reducing portion 150 reduces the hollow space 130 as it goes from the air passage portion 140 toward the first opening 112, that is, as it goes toward the front side.

[0019] The vector of the swirling flow 330 in the air passage portion 140 is indicated as "V1". The vector "V1" of the swirling flow 330 is a composition of the axial flow component "A1" and the swirling component "B1". When the swirling flow 330 passes through the first diameter-reducing portion 150, since the wind speed of the swirling flow 330 increases, the axial flow component "A1" increases and becomes the axial flow component "A2". A1 < A2. Accordingly, the swirling component "B1" decreases and becomes the swirling component "B2". B1 > B2. The composition of the axial flow component "A2" and the swirling component "B2" is indicated as the vector "V2". As a result, the swirling flow 330 that was advancing in the front direction with an angle of "θ1" in the air passage portion 140 decreases to an angle of "θ2" in the first diameter-reducing portion 150. θ1 > θ2. That is, when the air passes through the first diameter-reducing portion 150, the swirling component decreases and the linear component increases. Return to FIGS. 1 and 2.

[0020] The second hub cone portion 230 is disposed rearward of the axial fan 210 in the hollow space 130. This can also be said to mean that the second hub cone portion 230 is disposed closer to the second opening 122 than the axial fan 210. The second hub cone portion 230 is also supported by a stay portion (not shown). The second hub cone portion 230 has a generally conical shape that protrudes rearward. The rearmost vertex of the generally conical second hub cone portion 230 is the second tip portion 232. The second hub cone portion 230 may have a hemispherical shape instead of a generally conical shape. When air flows rearward in the axial flow blower 1000, the second hub cone portion 230 straightens the air flow, including the swirling flow from the axial fan 210, i.e., the air flow moving rearward.

[0021] In hollow space 130, second reduced diameter section 160 is disposed between second tip portion 232 of second hub cone portion 230 and second opening 122. Second reduced diameter section 160 has a configuration similar to that of first reduced diameter section 150, and reduces the diameter of hollow space 130 from air passage section 140 toward second opening 122, that is, toward the rear. If air does not flow toward the rear in axial flow fan 1000, second reduced diameter section 160 may not be provided.

[0022] Here, the size within the hollow space 130 will be described. As shown in the figure, the distance between the first tip portion 222 of the first hub cone portion 220 and the first reduced diameter portion 150 is defined as "D1," and the distance between the second tip portion 232 of the second hub cone portion 230 and the second reduced diameter portion 160 is defined as "D2." The distance "D1" is set to be equal to or greater than the radius of the first reduced diameter portion 150. Furthermore, the distances "D1" and "D2" are set to be the same. In this case, the length of the second hub cone portion 230 in the front-rear direction is set to be shorter than the length of the first hub cone portion 220 in the front-rear direction. This is because the electric motor 200 is to be positioned at the center of the hollow space 130 in the front-rear direction. When the center of the combination of the electric motor 200 and the axial flow fan 210 is to be positioned at the center of the hollow space 130 in the front-rear direction, the length of the second hub cone portion 230 in the front-rear direction is set to be equal to the length of the first hub cone portion 220 in the front-rear direction. Furthermore, the length along the front-rear direction (length along the direction of the rotation axis) is smaller in the order of air passage section 140, first reduced diameter section 150 (second reduced diameter section 160).

[0023] According to the present embodiment, since the casing 100 includes the first reduced diameter section 150, it is possible to change at least a portion of the swirling flow 330 that has passed through the first reduced diameter section 150 into the axial flow 320. Furthermore, since at least a portion of the swirling flow 330 that has passed through the first reduced diameter section 150 is changed into the axial flow 320, it is possible to suppress the swirling component of the swirling flow 330. Furthermore, since the first tip portion 222 and the first reduced diameter section 150 are separated by a distance equal to or greater than the radius of the first reduced diameter section 150, it is possible to rectify the swirling flow 330 that enters the first reduced diameter section 150. Furthermore, since the swirling flow 330 that enters the first reduced diameter section 150 is rectified, it is possible to significantly suppress the swirling component of the swirling flow 330 by the first reduced diameter section 150. Furthermore, the length along the direction of rotation axis 300 decreases in the order of air path section 140 and first reduced diameter section 150, so it is possible to increase the length of air path section 140. Furthermore, since second reduced diameter section 160 is provided on the opposite side of first reduced diameter section 150, the swirling component of the swirling flow can be suppressed even when the airflow direction is switched.

[0024] An outline of one aspect of the present disclosure is as follows. (Item 1) a cylindrical casing (100) having a first opening (112) on a first end (110) side, a second opening (122) on a second end (120) side opposite the first end (110) side, and a hollow space (130) connecting the first opening (112) and the second opening (122); an electric motor (200) disposed in the hollow space (130); an axial flow fan (210) attached to a rotating shaft (300) of the electric motor (200) and capable of rotating; a hub cone portion (220) disposed closer to the first opening (112) than the axial flow fan (210) in the hollow space (130) and rectifying the flow of air including a swirling flow from the axial flow fan (210), The casing (100) a tapered portion (150) disposed between the hub cone portion (220) and the first opening (112) in the hollow space (130), the tapered portion (150) narrowing the diameter of the hollow space (130) toward the first opening (112); Axial blower (1000).

[0025] (Item 2) 2. The axial flow fan according to claim 1, wherein a tip end portion (222) of the hub cone portion (220) on the first end (110) side and the reduced diameter portion (150) are spaced apart by a distance equal to or greater than the radius of the reduced diameter portion (150).

[0026] (Item 3) a portion of the hollow space (130) other than the reduced diameter portion (150) is an air passage portion (140); 3. The axial flow fan according to claim 1, wherein lengths of the air passage portion and the reduced diameter portion along the direction of the rotation shaft decrease in the order of the air passage portion and the reduced diameter portion.

[0027] (Item 6) the hub-cone portion (220) is a first hub-cone portion (220), the reduced diameter portion (150) is a first reduced diameter portion (150), The axial flow fan (210) is rotatable in both forward and reverse directions. The axial flow fan (1000) the second hub cone portion (230) is arranged closer to the second opening (122) than the axial flow fan (210) in the hollow space (130), and rectifies the flow of air including the swirling flow from the axial flow fan (210), The casing (100) The hollow space (130) further includes a second reduced diameter portion (160) that is disposed between the second hub cone portion (230) and the second opening (122) and reduces the diameter of the hollow space (130) toward the second opening (122). 10. The axial flow fan (1000) of claim 1.

[0028] Example 2 Next, a second embodiment will be described. Like the first embodiment, the second embodiment relates to an axial flow fan 1000. The axial flow fan 1000 according to the first embodiment includes a first reduced diameter section 150 and a second reduced diameter section 160. With this configuration, the cross-sectional area of ​​the air passage section 140 and the opening area of ​​the first opening 112 (second opening 122) are equal. Generally, the specifications of the axial flow fan 1000 are such that the cross-sectional area of ​​the air passage section 140 and the opening area of ​​the first opening 112 (second opening 122) are equal. The axial flow fan 1000 according to the second embodiment includes a first expanded diameter section 170 and a second expanded diameter section 180 in addition to the configuration of the first embodiment in order to equalize the cross-sectional area of ​​the air passage section 140 and the opening area of ​​the first opening 112 (second opening 122). Here, the differences from the first embodiment will be mainly described.

[0029] FIG. 4 is a cross-sectional perspective view showing the structure of the axial flow fan 1000. FIG. 5 is a cross-sectional view showing the structure of the axial flow fan 1000. These are shown in the same manner as FIGS. 1 and 2. In the hollow space 130, a first expanded diameter section 170 is disposed between the first reduced diameter section 150 and the first opening 112. In this case, the air passage section 140 described above corresponds to the portion of the hollow space 130 other than the first reduced diameter section 150, the second reduced diameter section 160, the first expanded diameter section 170, and the second expanded diameter section 180 described below. The first expanded diameter section 170 is a portion of the hollow space 130 whose inner diameter is larger than that of the first reduced diameter section 150. For example, the inner diameter of the first expanded diameter section 170 is set to be the same as the inner diameter of the air passage section 140. Here, as a cross section along the yz plane of the hollow space 130, the cross-sectional area of ​​the air passage section 140 is set to "100%", and when the cross-sectional areas of the first narrowing section 150 and the second narrowing section 160 are set to 70% or more but less than 100%, the cross-sectional area of ​​the first expanding section 170 is set to "100%".

[0030] Here, Figure 6 will also be used to explain the structure of first expanding diameter section 170 in more detail. Figure 6 is an enlarged view of the vicinity of first reducing diameter section 150 and first expanding diameter section 170. First reducing diameter section 150 and air passage section 140 are separated by boundary 156, and first reducing diameter section 150 and first expanding diameter section 170 are separated by boundary 176. First reducing diameter section 150 is the same as before. First expanding diameter section 170 includes an expanding inclined surface 172 and an expanding diameter surface 174.

[0031] The diameter-expanding inclined surface 172 is provided on the front side of the boundary 176, and the diameter-expanding surface 174 is provided on the front side of the diameter-expanding inclined surface 172. The diameter-expanding inclined surface 172 has a tapered shape that inclines outward in the inner diameter direction as it goes toward the front side with respect to the diameter-reducing surface 154. Due to the tapered shapes of the first diameter-reducing portion 150 and the first diameter-expanding portion 170, the pressure loss due to diameter reduction and diameter expansion is reduced. The taper angle "θ4" of the first diameter-reducing portion 150 is 60 degrees or less, preferably 30 degrees or less. Also, the taper angle "θ5" of the first diameter-expanding portion 170 is 60 degrees or less. The diameter-expanding surface 174 maintains the inner diameter enlarged by the diameter-expanding inclined surface 172. The diameter-expanding surface 174 is made to have, for example, the same inner diameter as the inner wall 142. That is, the first diameter-expanding portion 170 expands the hollow space 130 reduced in diameter in the first diameter-reducing portion 150 as it goes toward the first opening 112, that is, as it goes toward the front side.

[0032] The vector is "V1" and the vector "V2" is shown as in FIG. 3. When the swirling flow 330 passes through the first diameter-expanding portion 170, the wind speed decreases due to the diameter expansion, so the axial flow component "A2" decreases and becomes the axial flow component "A3". A2 > A3. Accordingly, the swirling component "B2" increases and becomes the swirling component "B3". B2 < B3. The synthesis of the axial flow component "A3" and the swirling component "B3" is shown as the vector "V3". As a result, the swirling flow 330 that had an angle of "θ2" and was advancing in the front side direction in the first diameter-reducing portion 150 increases to an angle of "θ3" in the first diameter-expanding portion 170. θ2 ≦ θ3 < θ1.

[0033] When air passes through the first diameter-expanding portion 170, the swirling component increases and the axial flow component decreases compared to when it passed through the first diameter-reducing portion 150, but due to inertia, the increase in the swirling component and the decrease in the axial flow component are small. Therefore, in the air that has passed through the first diameter-expanding portion 170, the swirling component decreases and the linear component increases compared to the air passing through the air passage portion 140. Return to FIGS. 4 and 5.

[0034] In the hollow space 130, a second expanded diameter section 180 is disposed between the second reduced diameter section 160 and the second opening 122. The second expanded diameter section 180 expands the diameter of the hollow space 130, which has been reduced in diameter at the second reduced diameter section 160, toward the second opening 122, i.e., toward the rear. The second expanded diameter section 180 has a configuration similar to that of the first expanded diameter section 170. If air does not flow toward the rear in the axial flow fan 1000, the second expanded diameter section 180 does not need to be provided. Furthermore, the length along the front-rear direction (length along the direction of the rotation axis) is smaller in the order of the air passage section 140, the first expanded diameter section 170 (second expanded diameter section 180), and the first reduced diameter section 150 (second reduced diameter section 160).

[0035] According to this embodiment, as one moves forward, the first reduced diameter section 150 is followed by the first expanded diameter section 170, so that air can be blown out without changing the diameter (specifications) of the first opening 112. Furthermore, as one moves forward, the second reduced diameter section 160 is followed by the second expanded diameter section 180, so that air can be blown out without changing the diameter (specifications) of the second opening 122. Furthermore, the length along the direction of the rotation axis 300 decreases in the order of air path section 140, first expanded diameter section 170, and first reduced diameter section 150, so that the length of air path section 140 can be increased.

[0036] An outline of one aspect of the present disclosure is as follows. (Item 4) The hollow space (130) further includes an expanding diameter portion (170) that is disposed between the reducing diameter portion (150) and the first opening (112) and expands the diameter of the hollow space (130) toward the first opening (112). 3. An axial flow fan (1000) according to claim 1 or 2.

[0037] (Item 5) a portion of the hollow space (130) other than the reduced diameter portion (150) and the expanded diameter portion (170) is an air passage portion (140); 5. The axial flow fan (1000) according to claim 4, wherein lengths of the air passage portion (140), the reduced diameter portion (150), and the expanded diameter portion (170) along the direction of the rotation shaft (300) decrease in the order of the air passage portion (140), the expanded diameter portion (170), and the reduced diameter portion (150).

[0038] (Item 7) a first expanding diameter portion (170) that is disposed in the hollow space (130) between the first reducing diameter portion (150) and the first opening (112) and expands the diameter of the hollow space (130) toward the first opening (112); a second expanding diameter portion (180) that is disposed in the hollow space (130) between the second reducing diameter portion (160) and the second opening (122) and expands the diameter of the hollow space (130) toward the second opening (122), 7. An axial flow fan (1000) according to claim 6.

[0039] The present disclosure has been described above based on examples. These examples are merely illustrative, and it will be understood by those skilled in the art that various modifications are possible in the combination of each component or each treatment process, and that such modifications are also within the scope of the present disclosure. [Explanation of symbols]

[0040] 100 casing, 110 first end, 112 first opening, 120 second end, 122 second opening, 130 hollow space, 140 air duct section, 142, 144 inner wall, 150 first reduced diameter section, 152 reduced diameter inclined surface, 160 second reduced diameter section, 170 first expanded diameter section, 172 expanded diameter inclined surface, 180 second expanded diameter section, 200 electric motor, 210 axial flow fan, 212 base section, 214 blade, 220 first hub cone section, 222 first tip section, 230 second hub cone section, 232 second tip section, 300 rotating shaft, 310 rotation direction, 320 axial flow, 330 swirl flow, 1000 axial flow fan.

Claims

1. a cylindrical casing having a first opening on a first end side, a second opening on a second end side opposite to the first end side, and a hollow space connecting the first opening and the second opening; an electric motor disposed in the hollow space; a rotatable axial flow fan attached to a rotary shaft of the electric motor; a hub cone portion that is disposed closer to the first opening than the axial flow fan in the hollow space and that rectifies the flow of air including the swirling flow from the axial flow fan, The casing comprises: a tapered portion disposed in the hollow space between the hub cone portion and the first opening, the tapered portion narrowing the diameter of the hollow space toward the first opening; Axial blower.

2. The axial flow fan according to claim 1 , wherein the tip of the hub cone portion on the first end side and the reduced diameter portion are spaced apart by at least a length of the radius of the reduced diameter portion.

3. a portion of the hollow space other than the reduced diameter portion is an air passage portion, 3. The axial flow fan according to claim 1, wherein lengths of the air passage portion and the reduced diameter portion along the rotation axis direction decrease in the order of the air passage portion and the reduced diameter portion.

4. the hollow space further includes an expanding diameter portion that is disposed between the reducing diameter portion and the first opening and expands the diameter of the hollow space toward the first opening; 3. The axial flow fan according to claim 1 or 2.

5. a portion of the hollow space other than the reduced diameter portion and the expanded diameter portion is an air passage portion, 5. The axial flow fan according to claim 4, wherein lengths of the air passage portion, the reduced diameter portion, and the expanded diameter portion along the rotation axis direction decrease in the order of the air passage portion, the expanded diameter portion, and the reduced diameter portion.

6. the hub cone portion is a first hub cone portion, the reduced diameter portion is a first reduced diameter portion, The axial flow fan is rotatable in both forward and reverse directions, The axial flow fan is a second hub cone portion that is disposed closer to the second opening than the axial flow fan in the hollow space and that rectifies the flow of air including the swirling flow from the axial flow fan, The casing comprises: a second tapered portion disposed in the hollow space between the second hub cone portion and the second opening, the second tapered portion tapering the hollow space toward the second opening; 2. The axial flow fan according to claim 1.

7. a first expanding diameter portion disposed between the first reducing diameter portion and the first opening in the hollow space and expanding the diameter of the hollow space toward the first opening; a second expanding diameter portion disposed in the hollow space between the second reducing diameter portion and the second opening, and expanding the diameter of the hollow space toward the second opening, 7. The axial flow fan according to claim 6.

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