JP2013096378A - Centrifugal air blower - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a centrifugal air blower in which noise reduction effects are improved.SOLUTION: A centrifugal air blower 51 includes an impeller 23 which is rotated around a rotation axis A and includes an air intake port 19a. The impeller 23 includes a plurality of blades 21 which are disposed around the rotation axis A. At a rear edge 62 of the blade 21, a recess 71 is provided which is recessed toward the side of a front edge 61, in an area opposite to the air intake port 19a. In the direction of the rotation axis A, a ratio (h1/H) of a length h1 of the recess 71 with respect to a length H of the rear edge 62 is settled within the range of 0.25-0.5.

Description

  The present invention relates to a centrifugal blower for an air conditioner.

  Conventionally, a centrifugal blower is used as a blower of an air conditioner. The centrifugal blower includes an impeller having a plurality of blades. When this impeller is rotated by a fan motor, air is sucked into the air conditioner. The sucked air is guided to the air inlet of the impeller (the air inlet of the shroud) by the bell mouth. The air that has flowed into the impeller from the air suction port is blown out from the impeller through a gap between the blades.

  In such an air conditioner, various structures such as a heat exchanger are disposed in addition to the centrifugal blower. Therefore, the airflow blown out from the impeller interferes with the structure around the impeller, thereby generating discrete frequency noise (BPF (Blade Passing Frequency) noise).

  For example, FIG. 29 of Patent Document 1 discloses a technique for reducing the blowing sound by forming a plurality of concave portions arranged in a sawtooth shape along the trailing edge of each blade.

Japanese Patent No. 4396775

  By the way, in recent years, since the air conditioner has been made compact, the distance between the blade and the surrounding structure tends to be small. Along with this, BPF noise is likely to occur, and therefore further reduction of noise caused by the centrifugal blower is required.

  Then, this invention is made | formed in view of this point, The place made into the objective is to provide the centrifugal blower excellent in the noise reduction effect.

  The centrifugal blower of the present invention includes an impeller (23) that rotates about the rotation shaft (A) and has an air suction port (19a). The impeller (23) includes a plurality of blades (21) arranged around the rotation axis (A). The rear edge (62) of the blade (21) is provided with a recess (71) that is recessed toward the front edge (61) in a region opposite to the air suction port (19a). In the direction of the rotation axis (A), the ratio (h1 / H) of the length (h1) of the recess (71) to the length (H) of the rear edge (62) is 0.25 to 0.5. It is in the range.

  In this configuration, the rear edge (62) of the blade (21) is provided with a recess (71) larger than the recess disclosed in Patent Document 1. Specifically, in this configuration, the recess (71) with respect to the length (H) of the trailing edge (62) is provided in a region opposite to the air suction port (19a) in the trailing edge (62) of the blade (21). By providing the recess (71) having a length (h1) ratio (h1 / H) in the range of 0.25 to 0.5, noise can be effectively reduced. The reason is as follows.

  That is, the speed of the airflow blown out from the gap between the blades (21) is higher on the opposite side than on the air suction port (19a) side. Therefore, in this configuration, by providing a concave portion (71) larger than the conventional one in a region where the airflow velocity is high, the airflow velocity in the region can be effectively reduced. Thereby, the outstanding noise reduction effect can be acquired.

  In the centrifugal blower, a mode in which the number of the concave portions (71) provided in the trailing edge (62) is one can be exemplified.

  In this configuration, the air volume is suppressed from being excessively reduced by providing a single recess (71) instead of providing a plurality of recesses (71) at the trailing edge (62) of the blade (21). Thus, an increase in the number of rotations of the motor that rotates the impeller is suppressed.

  In the centrifugal blower, when the impeller (23) is rotated around the rotating shaft (A), the blade (21) passes through a virtual plane (P) including the rotating shaft (A). Thus, the shape of the recess (71) drawn on the virtual plane (P) is a shape that is line-symmetric with respect to the straight line (S) that intersects the rotation axis (A) in the virtual plane (P). preferable.

  In this configuration, since the shape of the recess (71) is symmetrical with respect to the straight line (S) intersecting the rotation axis (A) in the plane (P), the trailing edge (62) of the blade (21) BPF noise can be reduced while suppressing the generation of vortices near the recess (71).

  In the centrifugal blower, when the shape of the recess (71) drawn on the virtual plane (P) is an arc shape, the maximum wind speed of the airflow sent from the impeller blade (21) to the outside (airflow on the hub side) In order to reduce the maximum wind speed), the wind speed distribution of air can be changed gently, so that the noise reduction effect (particularly the BPF noise reduction effect) can be enhanced.

  In the centrifugal blower, the ratio (C / L) of the depth (C) of the recess (71) to the chord length (L) of the blade (21) is preferably 0.10 to 0.30. .

  In this configuration, since the ratio (C / L) in the recess (71) is in the above range, the effect of reducing the speed of the airflow in the region (hub side region) opposite to the air suction port (19a) is obtained. It is obtained more reliably.

  In the centrifugal blower, a preferable range of a region (a region opposite to the air suction port (19a)) where the recess (71) is provided in order to reduce the velocity in a region where the air velocity is large is as follows. Become. That is, in the direction of the rotation axis (A), the end (714) on the opposite side of the air inlet (19a) in the blade (21) from the end (712) in the front edge direction of the recess (71). ) Is preferably in the range of 0.18 to 0.28 times the length (H) of the trailing edge (62).

  In the centrifugal blower, in the rear edge (62), the region closer to the air suction port (19a) than the recess (71) is longer than the recess (71) in the direction of the rotation axis (A). Further, it is preferable that a plurality of second recesses (72) arranged in a sawtooth shape along the rear edge (62) are provided with a small depth in the front edge direction.

  In this configuration, in addition to the noise reduction effect by reducing the airflow speed in the region by providing a large recess (71) in the region where the airflow velocity is high, the rear edge (62) is more than the recess (71). Further, by providing the plurality of second recesses (72) as described above in the region on the air inlet (19a) side, the following effects can be obtained. That is, the air flowing along the inner surface (21A) of the blade (21) and the air flowing along the outer surface (21B) are subdivided in the plurality of second recesses (72), respectively, so that the trailing edge (62) Vortex shedding is reduced. By reducing the eddy current in this way, the blowing sound is reduced.

  ADVANTAGE OF THE INVENTION According to this invention, the centrifugal blower excellent in the noise reduction effect can be provided.

It is sectional drawing which shows the indoor unit provided with the centrifugal blower which concerns on one Embodiment of this invention. It is a bottom view which shows the positional relationship of the impeller in the said indoor unit, a heat exchanger, and a blower outlet. It is a perspective view which shows the impeller of the said centrifugal blower. (A) is a perspective view which shows the blade | wing of the said impeller, (B) is the IVB-IVB sectional view taken on the line of (A). It is a figure for demonstrating the shape of the blade | wing drawn on the virtual plane containing the said rotating shaft. It is the perspective view which expanded a part of trailing edge of the said blade | wing. (A) is the schematic which shows the air flow and wind speed distribution in the centrifugal fan which concerns on this embodiment, (B) is the schematic which shows the air flow and wind speed distribution in the conventional centrifugal fan. It is the schematic which shows a blade | wing of the said impeller and a part of said heat exchanger. It is the graph which compared the noise level of the centrifugal blower which concerns on this embodiment, and the conventional centrifugal blower. It is a figure which shows the modification of the said impeller.

  Hereinafter, a centrifugal blower 51 and an indoor unit 31 including the centrifugal blower 51 according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the indoor unit 31 is a ceiling-embedded cassette indoor unit. The indoor unit 31 includes a substantially rectangular parallelepiped housing 33 embedded in an opening provided in the ceiling 35, and a decorative panel 47 attached to the lower portion of the housing 33. The decorative panel 47 is slightly larger in plan view than the housing 33 and is exposed to the room in a state of covering the opening of the ceiling. The decorative panel 47 has a rectangular suction grill 39 provided in the center thereof, and four elongated rectangular outlets 37 provided along each side of the suction grill 39.

  The indoor unit 31 includes a centrifugal blower (turbo fan) 51, a fan motor 11, a heat exchanger 43, a drain pan 45, an air filter 41, and the like in a housing 33. Centrifugal blower 51 includes an impeller 23 and a bell mouth 25. The fan motor 11 is fixed to the approximate center of the top plate of the housing 33. The shaft 13 of the fan motor 11 extends in the vertical direction.

  As shown in FIGS. 1 and 2, the heat exchanger 43 has a flat shape with a small thickness. The heat exchanger 43 is disposed so as to surround the periphery of the impeller 23 in a state where it rises upward from a dish-shaped drain pan 45 extending along the lower end portion thereof. The drain pan 45 stores water droplets generated in the heat exchanger 43. The stored water is discharged through a drainage path (not shown).

  The air filter 41 has a size that covers the inlet of the bell mouth 25, and is provided along the suction grill 39 between the bell mouth 25 and the suction grill 39. The air filter 41 captures dust in the air when the air sucked into the housing 33 from the suction grill 39 passes through the air filter 41.

  As shown in FIGS. 1 to 3, the impeller 23 includes a hub (main plate) 15, a shroud (side plate) 19, and a plurality of blades 21. The hub 15 is fixed to the lower end portion of the shaft 13 of the fan motor 11. The hub 15 has a circular shape centered on the rotation axis A in plan view. The impeller 23 rotates about the rotation axis A.

  The shroud 19 is arranged to face the front side F of the shaft 13 in the direction of the rotation axis A with respect to the hub 15. The shroud 19 has an air suction port 19a that opens in a circle around the rotation axis A. The outer diameter of the shroud 19 becomes larger toward the back side R.

  As shown in FIG. 1, the bell mouth 25 is disposed to face the shroud 19 on the front side F in the rotation axis A direction. The bell mouth 25 has a through hole 25a penetrating in the front-rear direction. A part of the rear side R of the bell mouth 25 is inserted into the shroud 19 from the air suction port 19a in a state where a predetermined gap is provided between the peripheral portion 19e of the air suction port 19a. Thereby, the bell mouth 25 can guide the air sucked toward the back side R through the through hole 25a to the air suction port 19a of the shroud 19.

  As shown in FIG. 3, the plurality of blades 21 are arranged around the rotation axis A between the hub 15 and the shroud 19. The number of the plurality of blades 21 is not particularly limited, but in the present embodiment, the number of the blades 21 is an odd number (for example, 7) from the viewpoint of reducing noise caused by a periodic pressure change. These blades 21 are arranged at equal intervals or unequal intervals in the circumferential direction. When the impeller 23 rotates, it is preferable that the plurality of blades 21 are arranged at unequal intervals rather than at equal intervals from the viewpoint of reducing noise caused by periodic pressure changes.

  As shown in FIG. 3, each blade 21 is a backward blade that is inclined in the direction opposite to the rotational direction (backward) with respect to the radial direction of the hub 15. Each blade 21 in the present embodiment has a three-dimensional shape extending in the direction of the rotation axis A while being twisted between the hub 15 and the shroud 19. In addition, each blade | wing 21 may not have the above twist.

  As shown in FIGS. 3 and 4A, 4B, each blade 21 includes a blade inner surface 21A facing radially inward in the impeller 23, a blade outer surface 21B facing radially outward, and the impeller 23. It has a front edge 61 that is a front edge during rotation and a rear edge 62 that is a rear edge. Further, the edge 21 </ b> F on the front side F of each blade 21 is joined to the inner surface of the shroud 19. An edge 21 </ b> R on the rear side R of each blade 21 is joined to the inner surface of the hub 15.

  FIG. 5 is a diagram for explaining the shape of the blade 21 drawn on the virtual plane P including the rotation axis A by the following method. First, one arbitrary plane (virtual plane) P including the rotation axis A is determined, and one target blade 21 is determined. Next, it is assumed that the target blade 21 passes through the virtual plane P by rotating the impeller 23 about the rotation axis A. At this time, each part of the blade 21 passes through any part on the virtual plane P. The shape of the blade 21 shown in FIG. 5 is a shape drawn on the virtual plane P by all the portions where the blade 21 has passed on the virtual plane P in this way. The shape of the blade | wing 21 shown in FIG. 5 has shown the shape of the front edge 61 of the blade | wing 21, the rear edge 62, the edge 21F, and the edge 21R.

  As shown in FIGS. 3, 4 (A), (B) and FIG. 5, the rear edge 62 of each blade 21 is provided with one recess (first recess) 71 and a plurality of second recesses 72. It has been. The 1st recessed part 71 is provided in the area | region (area | region on the opposite side to the air inlet 19a) in the hub 15 side in the rear edge 62. FIG. The 1st recessed part 71 is dented toward the front edge 61 side, and has a shape where a part of rear edge 62 of the blade | wing 21 was notched.

  As shown in FIGS. 4A, 5 and 6, the first recess 71 is smoothly curved in an arc shape. The recess 71 has an end 711 on the hub 15 side, a bottom 712 located closest to the front edge 61 (a bottom 712 in the direction of the front edge 61), and an end 713 on the shroud 19 side.

  As shown in FIG. 6, the first recess 71 has a concave surface that connects the blade inner surface 21 </ b> A and the blade outer surface 21 </ b> B of the blade 21. The width of the concave surface gradually increases from the end portion 711 on the hub 15 side to the bottom portion 712 or the vicinity thereof, and gradually decreases from the bottom portion 712 or the vicinity thereof to the end portion 713 on the shroud 19 side. That is, the concave surface includes a concave surface portion 71A located on the hub 15 side (back surface side R), a concave surface portion 71C located on the shroud 19 side (front surface side F), and a concave surface portion 71B located therebetween. The width of the concave surface portion 71B is larger than the width of the concave surface portion 71A and the width of the concave surface portion 71C.

  Here, the fact that the first recess 71 is provided in a region on the hub 15 side (region on the side opposite to the air suction port 19a) means the following. That is, the first recess 71 is provided in the region on the hub 15 side in the shape of the blade 21 shown in FIG. 5 in which the bottom 712 of the first recess 71 is the length of the rear edge 62 in the direction of the rotation axis A. It means that it is located on the hub 15 side relative to the position of 1/2 of H. Note that, from the viewpoint of reducing the airflow speed on the hub 15 side more intensively, the entire first recess 71 is located on the hub 15 side than the position of 1/2 of the length H of the rear edge 62. Is more preferable.

  As shown in FIG. 5, in the direction of the rotation axis A, the ratio (h1 / H) of the length h1 of the first recess 71 to the length H of the trailing edge 62 is in the range of 0.25 to 0.5. It is preferable to be in the range of 0.35 to 0.46.

  As shown in FIGS. 4B and 5, the ratio (C / L) between the chord length L of the blade 21 and the depth C of the first recess 71 in the direction toward the front edge 61 is 0. .10 to 0.30 is preferable, 0.15 to 0.25 is more preferable, and 0.15 to 0.20 is still more preferable. When the ratio (C / L) is in the range of 0.10 to 0.30, it is possible to effectively reduce the Nz sound while suppressing the reduction of the air volume.

  The depth C of the first recess 71 refers to the distance between the bottom 712 and a straight line (imaginary straight line) connecting the end 711 on the hub 15 side and the end 713 on the shroud 19 side in FIG. The chord length L refers to the distance between the leading edge 61 and the imaginary straight line in a cross section when the first blade 211 is cut along a plane orthogonal to the rotation axis A and passing through the bottom portion 712.

  Further, as shown in FIG. 5, the distance h2 between the bottom 712 and the end 714 of the blade 21 on the hub 15 side in the rotation axis A direction is 0.18 to the length H of the trailing edge 62 in the rotation axis A direction. It is preferably in the range of 0.28 times.

  The shape of the first recess 71 shown in FIG. 5 is preferably a shape that is axisymmetric with respect to a straight line S orthogonal to the rotation axis A in the virtual plane P. In the present embodiment, the shape of the first recess 71 drawn on the virtual plane P is an arc shape or a shape close to an arc shape. The shape of the first recess 71 drawn on the virtual plane P may be, for example, an elliptical arc shape or a bow shape.

  As shown in FIGS. 4A, 5, and 6, the plurality of second recesses 72 are provided in a region closer to the shroud 19 (air intake port 19 a side) than the first recess 71 at the rear edge 62. Yes. Each second recess 72 is recessed toward the front edge 61 side. Each of the second recesses 72 has a length in the direction of the rotation axis A and a depth in the direction of the front edge 61 smaller than the first recesses 71 and is arranged in a sawtooth shape along the rear edge 62.

  Next, the flow of air in the centrifugal blower 51 will be described. FIG. 7A is a schematic diagram showing the air flow and the wind speed distribution in the centrifugal blower 51 according to the present embodiment. When the motor 11 of the centrifugal blower 51 operates and the impeller 23 rotates, the air is guided along the bell mouth 25 to the air suction port 19a of the shroud 19 as shown in FIG. The airflow guided to the air suction port 19a flows in the impeller 23 toward the back side R along the direction of the rotation axis A. The air flow gradually changes in the radial direction while flowing to the back side R, and is blown out of the impeller 23 from between the blades 21.

  FIG. 7B is a schematic diagram showing air flow and wind speed distribution in a conventional centrifugal blower. Similarly, in the conventional centrifugal blower shown in FIG. 7 (B), the air flow guided to the air suction port 19a gradually changes its direction outward in the radial direction while flowing to the rear side R, and the impeller is interposed between the blades 121. Be blown out of. In the conventional centrifugal blower, the speed of the airflow blown out from the gap between the blades 121 is higher than the airflow flowing on the shroud 19 side as shown by the arrow in the speed distribution V2 in FIG. There is a tendency that the airflow that flows through is larger.

  On the other hand, in the present embodiment, since the first recess 71 is provided in the region on the hub 15 side of the trailing edge 62 of the blade 21, as shown in the velocity distribution V1 in FIG. Compared with the velocity distribution V2 in FIG. 7B, the velocity of the airflow flowing through the hub 15 can be locally reduced. Thereby, in this embodiment, a maximum wind speed can be reduced compared with the conventional centrifugal blower.

  Incidentally, in the air conditioner, various structures such as the heat exchanger 43 are disposed in addition to the centrifugal blower. Therefore, as shown in FIG. 8, since the impeller rotates in the rotation direction RD and the airflow blown out from the impeller interferes with a structure such as the heat exchanger 43 located in the vicinity of the blade 21 (121), for example. BPF noise is generated. The BPF noise is caused by an air flow having a high velocity that particularly flows on the hub 15 side.

  FIG. 9 is a graph comparing the noise levels of the centrifugal blower 51 (this embodiment) shown in FIG. 7A and the conventional centrifugal blower (comparative example) shown in FIG. 7B. As shown in FIG. 9, in the centrifugal blower 51 according to the present embodiment, it can be seen that the level of BPF noise is reduced compared to the centrifugal blower of the comparative example. Moreover, when the centrifugal blower 51 which concerns on this embodiment was used, the effect that the input (power consumption) of a fan motor reduces about 5% compared with the centrifugal blower of the comparative example was acquired.

  As described above, in the present embodiment, the ratio (h1 / H) of the length h1 of the recess 71 to the length H of the rear edge 62 is 0.25 in the region on the hub 15 side of the rear edge 62 of the blade 21. By providing the first recess 71 in the range of ˜0.5, noise can be effectively reduced.

  In the present embodiment, the air flow is suppressed from being excessively reduced by not providing the plurality of first recesses 71 at the trailing edge 62 of the blade 21 but by providing the single first recess 71. The increase in the number of rotations of the motor that rotates the impeller is suppressed.

  In the present embodiment, since the shape of the first recess 71 drawn on the virtual plane P is an arc shape, the wind speed distribution of the air sent from the impeller blades 21 to the outside can be changed gently. Thereby, the noise reduction effect can be enhanced.

  In the present embodiment, the ratio (C / L) of the depth C in the front edge direction of the first recess 71 to the chord length L of the blade 21 is 0.15 to 0.20. The effect of reducing the velocity of the airflow in the region opposite to 19a can be obtained more reliably.

  In the present embodiment, in addition to the noise reduction effect by reducing the speed of the airflow in the region by providing the large first recess 71 in the region where the speed of the airflow is high, the first recess 71 is further provided at the trailing edge 62. By providing a plurality of second recesses 72 in the region closer to the air suction port 19a, the following effects can be obtained. That is, the air flowing along the inner surface 21A of the blade 21 and the air flowing along the outer surface 21B are subdivided in the plurality of second recesses 72, respectively. Disturbance is suppressed. Thereby, the blowing sound generated in the vicinity of the trailing edge 62 of the blade 21 can be reduced.

<Other embodiments>
As mentioned above, although embodiment of this invention was described, this invention is not limited to these embodiment, A various change, improvement, etc. are possible in the range which does not deviate from the meaning.

  For example, in the above-described embodiment, the centrifugal blower 51 is applied to a ceiling-embedded indoor unit, but the present invention is not limited to this. The centrifugal blower of the present invention can also be applied to other types of indoor units such as a ceiling-mounted type, an air handling unit, a rooftop type such as a rooftop type, and a floor-standing type.

  In the said embodiment, the case where the some 2nd recessed part 72 arranged in a sawtooth shape along the rear edge 62 was provided in the area | region of the air inlet 19a side from the 1st recessed part 71 in the rear edge 62 was illustrated. However, as shown in FIG. 10, the second recess 72 may be omitted and only the first recess 71 may be provided on the rear edge 62.

  In the above embodiment, the case where the entire first recess 71 is located closer to the hub 15 than the half of the length H of the rear edge 62 is exemplified. However, a part of the first recess 71 is rearward. You may be located in the shroud 19 side rather than the position of 1/2 of the length H of the edge 62. FIG.

  In the said embodiment, although the case where the number of the 1st recessed parts 71 provided in the rear edge 62 of each blade | wing 21 was one was illustrated, it is not limited to this. A plurality of (for example, two) first recesses 71 may be provided on the rear edge 62 of each blade 21 in the region on the hub 15 side.

  In the said embodiment, although the case where the 1st recessed part 71 was provided in each blade | wing 21 was illustrated, it is not limited to this. The form which provides the 1st recessed part 71 only in the one part blade | wing 21 of the some blade | wing 21 may be sufficient. Specifically, the blade 21 provided with the first recess 71 and the blade 21 not provided with the first recess 71 may be alternately arranged. Moreover, the form which the blade | wing 21 in which the 1st recessed part 71 is not provided between the blade | wing 21 in which the 1st recessed part 71 is provided intervenes can be illustrated.

  In the above-described embodiment, the shape of the first recess 71 drawn on the virtual plane P is exemplified as a shape that is line-symmetric with respect to a straight line orthogonal to the rotation axis A in the virtual plane P. Not. For example, the shape of the first recess 71 drawn in the virtual plane P may be a shape that is line symmetric with respect to a straight line that intersects the rotation axis A in the virtual plane P. Specifically, as a straight line intersecting with the rotation axis A, in FIG. 5, for example, a straight line inclined about several degrees to several tens of degrees with respect to a straight line orthogonal to the rotation axis A (horizontal line in FIG. 5). . The shape of the first recess 71 may not be line symmetric with respect to a straight line orthogonal to the rotation axis A in the virtual plane P.

  In the said embodiment, although the shape of the recessed part 71 drawn on the virtual plane P illustrated the case where it was circular arc shape, it is not limited to this. As described above, the shape of the recess 71 drawn on the virtual plane P may be an elliptical arc shape, a bow shape, or the like, or may have a straight or flat portion.

19 Shroud 19a Air inlet 21 Blade 23 Impeller 25 Bell mouth 31 Indoor unit 51 Centrifugal blower 61 Front edge 62 Rear edge 71 Concave portion (first concave portion)
712 End 714 in the front edge direction of the first recess 714 End 72 of the blade opposite to the air suction port 72 Second recess A Rotating shaft C Depth of the first recess in the leading edge direction H of the trailing edge in the rotating shaft direction Length h1 Length of the recess in the direction of the rotation axis h2 Distance L from the end of the recess in the front edge direction to the end of the blade on the hub side L Chord length

Claims (7)

Comprising an impeller (23) rotating about the rotation axis (A) and having an air inlet (19a);
The impeller (23) includes a plurality of blades (21) arranged around the rotation axis (A),
The rear edge (62) of the blade (21) is provided with a recess (71) that is recessed toward the front edge (61) in a region opposite to the air suction port (19a).
In the direction of the rotation axis (A), the ratio (h1 / H) of the length (h1) of the recess (71) to the length (H) of the rear edge (62) is 0.25 to 0.5. Centrifugal blower in the range of   The centrifugal blower according to claim 1, wherein the number of the recesses (71) provided in the rear edge (62) is one.   When the impeller (23) is rotated about the rotation axis (A), the virtual plane (P) is passed through the virtual plane (P) including the rotation axis (A), thereby the virtual plane ( The shape of the recess (71) drawn in P) is a shape that is line-symmetric with respect to a straight line (S) that intersects the rotation axis (A) in the virtual plane (P). The centrifugal blower described.   The centrifugal blower according to claim 3, wherein a shape of the concave portion (71) drawn on the virtual plane (P) is an arc shape.   The ratio (C / L) of the depth (C) of the recess (71) to the chord length (L) of the blade (21) is 0.10 to 0.30. The centrifugal blower of Claim 1.   In the direction of the rotation axis (A), from the end (712) in the front edge direction of the recess (71) to the end (714) of the blade (21) opposite to the air inlet (19a) The distance (h2) of the centrifugal blower according to any one of claims 1 to 5, wherein the distance (h2) is in a range of 0.18 to 0.28 times the length (H) of the trailing edge (62).   The region of the rear edge (62) closer to the air suction port (19a) than the recess (71) has a length in the direction of the rotation axis (A) relative to the recess (71) and the direction of the front edge. The centrifugal blower according to any one of claims 1 to 6, wherein a plurality of second recesses (72) having a small depth and arranged in a sawtooth shape along the rear edge (62) are provided.

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