JP7608825B2 - Multi-blade fan and indoor unit - Google Patents

Description

The present invention relates to a multi-blade fan and an indoor unit.

Multi-blade fans are known that have multiple blades that extend along the axial direction of a rotating shaft and are arranged around the rotating shaft. Examples of this type of multi-blade fan include centrifugal fans and cross-flow fans (cross-flow fans) that are installed in air conditioners (Patent Document 1).

Patent No. 2014-190543

In the multi-blade fan described above, blade pitch noise (periodic noise), which is the wind noise of the airflow between the blades, is generated when the blades rotate, and becomes noise during rotation. This blade pitch noise is generally called Nz noise, and its frequency is expressed by the product (N x z) of the rotation speed N of the multi-blade fan and the number of blades z. The frequency of the blade pitch noise increases as the number of blades increases.

The disclosed technology has been developed in consideration of the above, and aims to provide a multi-blade fan and indoor unit that can suppress noise caused by blade pitch sound that occurs when the blades rotate.

One aspect of the multi-blade fan disclosed in the present application is a cross-flow fan having a plurality of blades extending along the axial direction of a rotating shaft and arranged at a predetermined pitch around the rotating shaft, the plurality of blades including at least two blades on at least one of the positive pressure side and negative pressure side, which are the blade surfaces of the blades, and on at least one of the inner and outer circumferential sides of the blade, on which a recess that is recessed in the thickness direction of the blade is formed along the axial direction of the rotating shaft, and adjacent blades in the arrangement direction of the plurality of blades have different cross-sectional shapes perpendicular to the rotating shaft at the position on the rotating shaft where the recess is formed in one of the blades, and the recess is formed so that the blade chord lengths are different, and at least two adjacent blades have different lengths of the recess in the axial direction of the rotating shaft.

According to one aspect of the multi-blade fan disclosed in this application, it is possible to suppress noise caused by blade pitch sounds that occur when the blades rotate.

FIG. 1 is a cross-sectional view showing an indoor unit of the embodiment. FIG. 2 is a perspective view showing the multi-blade fan of the embodiment. FIG. 3 is a cross-sectional view showing a multi-blade fan according to an embodiment of the present invention. FIG. 4 is a schematic diagram for explaining an example of a blade of the multi-blade fan of the embodiment. FIG. 5 is a schematic diagram for explaining an example of a blade of the multi-blade fan of the embodiment. FIG. 6 is a schematic diagram for explaining an example of a blade of the multi-blade fan of the embodiment. FIG. 7 is a cross-sectional view showing a plurality of blades in the multi-blade fan of the embodiment. FIG. 8 is a cross-sectional view showing a first modified example of a plurality of blades in the multi-blade fan of the embodiment. FIG. 9 is a cross-sectional view showing a second modified example of the blades in the multi-blade fan of the embodiment. FIG. 10 is a plan view showing a third modified example of the plurality of blades in the multi-blade fan of the embodiment. FIG. 11 is a perspective view showing a fourth modified example of the plurality of blades in the multi-blade fan of the embodiment. FIG. 12 is a plan view showing a fifth modified example of the plurality of blades in the multi-blade fan of the embodiment. FIG. 13 is a plan view showing a sixth modified example of the plurality of blades in the multi-blade fan of the embodiment. FIG. 14 is a schematic diagram showing another example of the blades in the multi-blade fan of the embodiment. FIG. 15 is a cross-sectional view showing a seventh modification of the blades in the multi-blade fan of the embodiment. FIG. 16 is a diagram for explaining the noise level in the multi-blade fan of the embodiment.

Below, examples of the multi-blade fan and indoor unit disclosed in the present application are described in detail with reference to the drawings. Note that the multi-blade fan and indoor unit disclosed in the present application are not limited to the following examples.

(Configuration of indoor unit)
Fig. 1 is a cross-sectional view showing an indoor unit of the embodiment. Fig. 2 is a perspective view showing a multi-blade fan of the embodiment. As shown in Fig. 1, the indoor unit 1 of the embodiment is an indoor unit constituting a refrigeration cycle device, for example, an air conditioner (not shown), and includes a heat exchanger 5, a multi-blade fan 6 into which air that has passed through the heat exchanger 5 flows, a fan casing 7 that forms a flow path for the airflow sent from the multi-blade fan 6, and a main body casing 8 that houses the heat exchanger 5, the multi-blade fan 6, and the fan casing 7 inside. The main body casing 8 has an air intake port 8a and an air outlet 8b.

As shown in FIG. 2, the multi-blade fan 6 includes an impeller 11 with multiple blades 12 arranged around a rotating shaft 13. A plurality of impellers 11 are arranged in the axial direction X of the rotating shaft 13, and are connected with partition plates 14 sandwiched between each impeller 11. End plates 15 supported by the rotating shaft 13 are provided on both ends of the rotating shaft 13 in the axial direction X, and both ends of the multi-blade fan 6 are supported by the rotating shaft 13.

The impellers 11 are connected to each other with a shift in the circumferential direction around the rotating shaft 13, i.e., in the arrangement direction of the multiple blades 12. This creates a phase difference in the blade pitch sound between the impellers 11 aligned in the axial direction X of the rotating shaft 13, thereby suppressing noise generated when the multi-blade fan 6 rotates.

(Configuration of multi-blade fan)
3 is a cross-sectional view of the multi-blade fan 6 of the embodiment. The multi-blade fan 6 of the embodiment is used as a so-called cross-flow fan in which air flows through the multi-blade fan 6 in a direction intersecting with the axial direction X of the rotating shaft 13.

The multi-blade fan 6, as shown in FIG. 2, extends along the axial direction X of the rotating shaft 13, and as shown in FIG. 3, includes a plurality of blades 12 arranged at a predetermined pitch P around the rotating shaft 13. The blade surface 17 of the blade 12 is curved so as to be convex in the opposite direction to the rotation direction R of the multi-blade fan 6, and has a positive pressure surface 17a and a negative pressure surface 17b. The blade 12 has an inner peripheral side portion 18a located on the side of the rotation center O of the multi-blade fan 6, and an outer peripheral side portion 18b located on the opposite side of the rotation center O.

4, 5 and 6 are schematic diagrams for explaining an example of the blades 12 of the multi-blade fan 6 of the embodiment. As shown in FIG. 4, the multiple blades 12 include blades 12 in which recesses 20 (20A-20D) are formed at four locations: the positive pressure surface 17a of the inner circumferential side portion 18a, the negative pressure surface 17b of the inner circumferential side portion 18a, the positive pressure surface 17a of the outer circumferential side portion 18b, and the negative pressure surface 17b of the outer circumferential side portion 18b, which are recessed in the thickness direction of the blade 12 from the outer diameter of the blade visible on the far side of the page (the positive pressure surface 17a and the negative pressure surface 17b in FIG. 4). Note that the blade may have a recess 20 formed at at least one of the four locations. In other words, the blades 12 include blades 12 with recesses 20 formed on at least one of the blade surfaces, the positive pressure surface 17a and the negative pressure surface 17b, and at least one end of the inner peripheral side portion 18a and the outer peripheral side portion 18b of the blade 12, and the blades 12 have 15 different formation patterns in cross-sectional shapes due to combinations in which the recesses 20 are formed at any of the four locations.

The blade 12 is formed so that the thickest part of the blade 12 is located closer to the inner circumferential side 18a than the center of the blade chord. The recess 20 is formed, for example, on either the inner circumferential side 18a or the outer circumferential side 18b of the thickest part (dashed line in FIG. 4).

As shown in FIG. 5, when a recess 20A is formed on the negative pressure surface 17b of the inner circumferential side portion 18a and a recess 20C is formed on the negative pressure surface 17b of the outer circumferential side portion 18b, the recesses 20A and 20C may be formed as one continuous recess 20. When a recess 20 (20A, 20C) is formed from the tip of the inner circumferential side portion 18a to the tip of the outer circumferential side portion 18b in this way, the recess 20 (20A, 20C) is formed in a part of the blade 12 in the axial direction X of the rotating shaft 18, and the presence of the recess 20 (20A, 20C) can be visually confirmed from the appearance of the negative pressure surface 17b of the blade 12. Similarly, as shown in FIG. 6, when a recess 20B is formed on the positive pressure surface 17a of the inner circumferential side portion 18a and a recess 20D is formed on the positive pressure surface 17a of the outer circumferential side portion 18b, the recesses 20B and 20D may be formed as one continuous recess 20. In this way, when a recess 20 (20B, 20D) is formed that continues from the tip of the inner peripheral side portion 18a to the tip of the outer peripheral side portion 18b, the recess 20 (20B, 20D) is formed in a part of the blade 12 in the axial direction X of the rotating shaft 18, and the presence of the recess 20 (20B, 20D) can be seen from the outside of the pressure surface 17a of the blade 12.

In the multi-blade fan 6 of this embodiment, for example, a recess 20 is formed in each of the multiple blades 12, but this structure is not limited to this, and it is sufficient that at least one of the multiple blades 12 has a recess 20. In the multi-blade fan 6 of this embodiment, adjacent blades in the arrangement direction of the multiple blades 12 have different cross-sectional shapes perpendicular to the rotating shaft 13 at the position on the rotating shaft 13 where the recess 20 is formed in one of the blades. This makes it possible to make the frequency of the blade pitch sound different between adjacent blades 12 with different cross-sectional shapes.

In addition, with the multi-blade fan 6, it is possible to easily make the cross-sectional shapes of the adjacent blades 12 different by changing the formation pattern of the recesses 20 between the adjacent blades 12. Therefore, the frequency of the blade pitch noise can be easily changed between the adjacent blades 12.

Although not shown, the multi-blade fan 6 may have a structure in which, for example, a blade 12 having a recess 20 and a blade 12 without a recess 20 are arranged side by side. In this structure, the effect of suppressing noise of the multi-blade fan 6 is obtained by dispersing the frequency of the blade pitch sound between the blade 12 having the recess 20 and the blade 12 without the recess 20.

As described above, the cross-sectional shapes of adjacent blades 12 are different when the cross-sectional shapes of adjacent blades 12 perpendicular to the axial direction X of the rotation shaft 13 are compared at a position passing through the recess 20 of one of the blades 12 in the axial direction X of the rotation shaft 13. Such different cross-sectional shapes of the blades 12 include structures in which the formation patterns of the recess 20 are different, structures in which the cross-sectional shapes of the recess 20 are different, and structures in which the positions of the recess 20 in the direction along the blade chord are different.

Figure 7 is a cross-sectional view showing multiple blades 12 in a multi-blade fan 6 of an embodiment. As shown in Figures 3 and 7, for example, in the cross section of the blade 12 perpendicular to the axial direction X of the rotation shaft 13, all of the multiple blades 12 of the multi-blade fan 6 have the recesses 20 (20A to 20D) of adjacent blades 12 in the arrangement direction of the multiple blades 12 at different positions. Note that in the multi-blade fan 6, the recesses 20 of at least two blades 12 are provided at different positions in the arrangement direction of the multiple blades 12, and it is sufficient that these two blades 12 are arranged adjacent to each other, and the frequency of the blade pitch sound can be dispersed between adjacent blades 12 with the recesses 20 provided at different positions.

Each recess 20 (20A-20D) has a bottom surface 21a with an arc-shaped cross section. The recess 20 is formed across the axial direction X of the rotating shaft 13 in the blade 12, but may be formed in a part of the blade 12 in the axial direction X. Also, in one blade 12, the cross-sectional shape of the recess 20 is formed to be the same shape in the axial direction X of the rotating shaft 13, but the cross-sectional shape of the recess 20 in one blade 12 may be formed to change along the axial direction X of the rotating shaft 13.

(Variation 1)
8 is a cross-sectional view showing a first modified example of the plurality of blades 12 in the multi-blade fan 6 of the embodiment. As shown in FIG. 8, in all of the plurality of blades 12 in the first modified example, the number of recesses 20 (20A to 20D) of adjacent blades 12 in the arrangement direction among the plurality of blades 12 is different from each other in the cross section of the blade 12 perpendicular to the axial direction X of the rotation shaft 13. This makes it possible to disperse the blade pitch noise between the adjacent blades 12. The number of recesses 20 of each blade 12 increases and decreases regularly along the rotation direction R of the multi-blade fan 6, but is not limited to this structure and may change irregularly.

(Variation 2)
9 is a cross-sectional view showing a second modification of the plurality of blades 12 in the multi-blade fan 6 of the embodiment. As shown in FIG. 9, in all of the plurality of blades 12 in the second modification, the cross-sectional shapes of the recesses 20 of the blades 12 adjacent to each other in the arrangement direction are different from each other in the cross section of the blade 12 perpendicular to the axial direction X of the rotating shaft 13. For example, the recesses 20 extend from the tip surface of the inner peripheral side portion 18a toward the outer peripheral side portion 18b, and have an end surface 21b of the recesses 20 intersecting with the negative pressure surface 17b. This allows the frequency of the blade pitch noise to be dispersed between the adjacent blades 12. As for the cross-sectional shape of the recesses 20, it is sufficient that the depth of the recesses 20 in the thickness direction of the blade 12, the length of the recesses 20 in the direction along the blade chord, the angle between the blade surface 17 and the end surface 21b in the cross section perpendicular to the axial direction X of the rotating shaft 13, etc. are different. Furthermore, the multi-blade fan 6 may be a combination of, for example, variant 1 and variant 2, which can further distribute the frequency of the blade pitch noise between adjacent blades 12.

(Variation 3)
Fig. 10 is a plan view showing a third modification of the plurality of blades 12 in the multi-blade fan 6 of the embodiment. As shown in Fig. 10, in the third modification, the cross-sectional shapes of the recesses 20 in the direction along the blade chord are the same between adjacent blades 12 in the arrangement direction of the plurality of blades 12, and the lengths H of the recesses 20 in the axial direction X of the rotation shaft 13 are different. In the third modification, since the lengths H of the recesses 20 are different between adjacent blades 12, for example, in the D-D cross section in Fig. 10, the cross-sectional shapes of the blades 12 between adjacent blades 12 are different, and therefore the frequency of the blade pitch noise can be dispersed between adjacent blades 12.

Although not shown, in the third modification, the lengths H of the recesses 20 may be different between adjacent blades 12 in combination with the structures of the recesses 20 in the above-described embodiment and modifications 1 and 2, further enhancing the effect of the embodiment.

(Variation 4)
Fig. 11 is a perspective view showing a fourth modified example of the plurality of blades 12 in the multi-blade fan 6 of the embodiment. The fourth modified example is an example in which the above-described embodiment and the third modified example are combined, and as shown in Fig. 11, in each of the plurality of blades 12, a recess 20 is formed at any one of four locations, i.e., the positive pressure surface 17a of the inner circumferential side portion 18a, the negative pressure surface 17b of the inner circumferential side portion 18a, the positive pressure surface 17a of the outer circumferential side portion 18b, and the negative pressure surface 17b of the outer circumferential side portion 18b, and the positions of the recesses 20 are different between adjacent blades 12.

In addition, in variant 4, in each of the multiple blades 12, the length H of the recess 20 relative to the axial direction X of the rotating shaft 13, and the width of the recess 20 extending along the blade surface 17 in a cross section perpendicular to the axial direction X of the rotating shaft 13, are different between adjacent blades 12, and the position of the recess 20 is different from one another. In this way, the position, length H, and width of the recess 20 are different in all blades 12, which increases the change in frequency of the blade pitch sound between adjacent blades 12 and effectively distributes the frequency of the blade pitch sound, thereby further suppressing noise caused by the blade pitch sound.

(Variation 5)
FIG. 12 is a plan view showing a fifth modified example of the plurality of blades 12 in the multi-blade fan 6 of the embodiment. As shown in FIG. 12, a plurality of recesses 20 having the same cross-sectional shape perpendicular to the axial direction X of the rotating shaft 13 are formed in each of the blades 12 adjacent to each other in the arrangement direction of the plurality of blades 12, lined up in the axial direction X of the rotating shaft 13. The number of recesses 20 arranged at intervals in the axial direction X of the rotating shaft 13 is different between the blades 12 adjacent to each other in the arrangement direction of the plurality of blades 12. The number of recesses 20 of each blade 12 changes so as to repeatedly increase and decrease in a predetermined cycle along the rotation direction R of the multi-blade fan 6, but is not limited to this structure and may change irregularly. In the fifth modified example, the number of recesses 20 is different between the adjacent blades 12, so that, for example, in the E-E cross section in FIG. 12, the cross-sectional shapes of the adjacent blades 12 are different, and thus the blade pitch noise can be dispersed between the adjacent blades 12.

(Variation 6)
FIG. 13 is a plan view showing a sixth modified example of the plurality of blades 12 in the multi-blade fan 6 of the embodiment. As shown in FIG. 13, the cross-sectional shape of the recesses 20 perpendicular to the axial direction X of the rotating shaft 13 and the number of recesses 20 arranged in the axial direction X of the rotating shaft 13 are the same for the blades 12 adjacent to each other in the arrangement direction of the plurality of blades 12, but the positions of the recesses 20 in the axial direction X of the rotating shaft 13 are different. The positions of the recesses 20 of each blade 12 are gradually shifted toward one side in the axial direction X of the rotating shaft 13 along the rotation direction R of the multi-blade fan 6, but this structure is not limited thereto, and the positions of the recesses 20 may change irregularly. In the sixth modified example, the positions of the recesses 20 in the axial direction X of the rotating shaft 13 are different for the adjacent blades 12, so that the blade pitch noise can be dispersed between the adjacent blades 12, for example, by the cross-sectional shapes of the blades 12 of the adjacent blades 12 being different in the G-G cross section in FIG. 13.

(Variation 7)
Fig. 14 is a schematic diagram showing another example of the blade 12 in the multi-blade fan 6 of the embodiment. Fig. 15 is a cross-sectional view showing a seventh modified example of the plurality of blades 12 in the multi-blade fan 6 of the embodiment. As shown in Fig. 14, the blade 12 has recesses 20 (20F, 20G) formed on the inner circumferential side portion 18a and the outer circumferential side portion 18b. The recesses 20 (20F, 20G) are formed in parts of the blade 12 in the axial direction X of the rotating shaft 13.

The bottom surface 21a of the recess 20F of the inner circumferential side portion 18a is curved in the same direction as the direction in which the negative pressure surface 17b of the blade surface 17 on which the recess 20F is formed is curved. In the cross section of the blade 12 perpendicular to the axial direction X of the rotating shaft 13, the bottom surface 21a of the recess 20F is formed as a single curved surface that smoothly continues from the tip of the inner circumferential side portion 18a, which is one end of the blade chord length L, to the negative pressure surface 17b on which the recess 20F is formed. In addition, the recess 20F is formed by cutting out the tip of the inner circumferential side portion 18a so as to be continuous with the positive pressure surface 17a and the negative pressure surface 17b, and the blade chord length L is shortened by forming the recess 20F.

Similarly, the bottom surface 21a of the recess 20G of the outer peripheral side portion 18b is curved in the same direction as the curved direction of the positive pressure surface 17a on which the recess 20G is formed. In a cross section of the blade 12 perpendicular to the axial direction X of the rotating shaft 13, the bottom surface 21a of the recess 20G is formed as a single curved surface that smoothly continues from the tip of the outer peripheral side portion 18b, which is one end of the blade chord length L, to the positive pressure surface 17a on which the recess 20G is formed. In addition, the recess 20G is formed by cutting out the tip of the outer peripheral side portion 18b so as to be continuous with the positive pressure surface 17a and the negative pressure surface 17b, and the blade chord length L is shortened by forming the recess 20G.

As described above, the bottom surface 21a is formed as a single curved surface, and the recesses 20 (20F, 20G) are formed in a part of the blade 12 in the axial direction X of the rotating shaft 18, so that the presence of the recesses 20 (20F, 20G) can be seen from the outside of the negative pressure surface 17b of the blade 12.

The bottom surface 21a of the recess 20F is smoothly connected to the negative pressure surface 17b at a position closer to the inner circumferential side 18a than the center of the chord. The bottom surface 21a of the recess 20G is smoothly connected to the positive pressure surface 17a at a position closer to the outer circumferential side 18a than the center of the chord. The position where the bottom surface 21a of the recess 20 (20F, 20G) and the blade surface 17 are connected is not limited to variant example 7. For example, when the tip surface of the inner circumferential side 18a of the blade 12 is formed to include an arc-shaped curved surface, the bottom surface 21a of the recess 20F is formed to intersect with the arc-shaped curved surface, and the bottom surface 21a is smoothly connected to the blade surface 17.

In this way, the bottom surface 21a of the recess 20F is formed to smoothly connect to the negative pressure surface 17b, and the bottom surface 21a of the recess 20G is formed to smoothly connect to the positive pressure surface 17a. This reduces eddies in the airflow flowing along the bottom surfaces 21a of the recesses 20F and 20G and reduces turbulence downstream of the blades 12, thereby reducing pressure loss in the airflow along the blade surfaces 17 and reducing the power consumption of the motor (not shown) that drives the multi-blade fan 6. In other words, by reducing the pressure loss in the airflow along the blade surfaces 17 of the blades 12, the air volume of the multi-blade fan 6 can be increased.

As shown in FIG. 15, two adjacent blades 12 in the arrangement direction of the blades 12 have different blade chord lengths L due to the difference in cross-sectional shape, which is the size of the recesses 20 (20F, 20G) formed as described above. This makes it possible to change the frequency of the blade pitch noise between the adjacent blades 12 and disperse the frequency of the blade pitch noise between the adjacent blades 12.

The blades 12 may be made smaller to about 20% of the chord length L of the blades 12 before the recesses 20G, 20F are formed, as shown by the inner peripheral side portion 18a and the outer peripheral side portion 18b in FIG. 14 by the dashed lines. If the blades 12 are smaller than 20% of the chord length L, it is not preferable because it is not possible to ensure an appropriate flow path between adjacent blades 12, turbulence is generated between the adjacent blades 12, and pressure loss occurs in the airflow between the blades 12.

(Function of the recess)
As described above, adjacent blades 12 of the multi-blade fan 6 have any of the recesses 20 in the embodiment and modified examples 1 to 7, so that the cross-sectional shapes of the blades 12 differ, and the frequency of the blade pitch noise of each blade 12 changes. This makes it possible to distribute the frequency of the blade pitch noise between adjacent blades 12, and suppresses noise due to the blade pitch noise generated when the blades 12 rotate.

Figure 16 is a diagram for explaining the noise level of the multi-blade fan 6 of the embodiment. In Figure 16, the vertical axis indicates the noise level [dB], and the horizontal axis indicates the noise frequency [Hz]. In Figure 16, the multi-blade fan 6 of the embodiment is shown by a dashed line, and the multi-blade fan of the comparative example is shown by a solid line.

In the multi-blade fan of the comparative example, the blades 12 do not have recesses 20, the cross-sectional shapes of the blades 12 are the same in the arrangement direction of the multiple blades 12, and the blades 12 are arranged at equal pitch. As shown in FIG. 16, in the multi-blade fan 6 of the embodiment, the cross-sectional shapes of the blades 12 having recesses 20 are different between adjacent blades 12 in the arrangement direction of the blades 12, so that the frequency of the blade pitch sound is changed between adjacent blades 12 and the frequency of the blade pitch sound is dispersed between adjacent blades 12, thereby reducing the noise level near the primary frequency indicated by arrow F1 and near the secondary frequency indicated by arrow F2.

(Inner/Outer diameter ratio of blade)
3, the multiple blades 12 of the multi-blade fan 6 described above have an inner/outer diameter ratio (A/B) of 0.720 or more and 0.800 or less, where A is the diameter (inner diameter) of an inscribed circle C1 of the blade 12 relative to the rotation center O of the rotation shaft 13 and B is the diameter (outer diameter) of a circumscribed circle C2 of the blade 12. With such an inner/outer diameter ratio (A/B) of the blade 12, the frequency of the blade pitch sound can be controlled by the recess 20 in the embodiment, thereby reducing noise compared to a multi-blade fan without the recess 20.

In addition, if the inner/outer diameter ratio (A/B) of the blades 12 is enlarged to increase the air volume of the multi-blade fan 6, and the inner/outer diameter ratio (A/B) of the blades 12 exceeds 0.800, the wind speed passing between the blades 12 so as to penetrate the multi-blade fan 6 increases, which may cause the noise to worsen. Even in such a case, the frequency of the blade pitch sound can be controlled by the recess 20, thereby increasing the air volume while avoiding the noise from worsening.

(effect)
As described above, the multiple blades 12 of the multi-blade fan 6 include at least two blades 12 in which the recesses 20 recessed in the thickness direction of the blades 12 are formed along the axial direction X of the rotation shaft 13 on at least one of the positive pressure surface 17a and the negative pressure surface 17b of the blades 12 and at least one of the inner peripheral side portion 18a and the outer peripheral side portion 18b of the blades 12. The blades 12 adjacent to each other in the arrangement direction of the multiple blades 12 have different cross-sectional shapes perpendicular to the axial direction X of the rotation shaft 13 at the position on the rotation shaft 13 where the recesses 20 are formed in any one of the blades 12. The at least two blades 12 described above have different lengths of the recesses 20 relative to the axial direction X of the rotation shaft 13. As a result, by changing the frequency of the blade pitch noise of the adjacent blades 12 in the multiple blades 12, it is possible to disperse the frequency of the blade pitch noise between the adjacent blades 12, and it is possible to suppress noise due to the blade pitch noise generated when the blades 12 rotate. In addition, by changing the position at which the recess 20 is formed on the blade surface 17 of the blade 12, the cross-sectional shape of the blade 12 can be easily made different, so that the frequency of the blade pitch sound between adjacent blades 12 can be easily changed.

In addition, by making the length H of the recess 20 different between adjacent blades 12, the frequency of the blade pitch noise changes between adjacent blades 12, so that the frequency of the blade pitch noise between adjacent blades 12 can be dispersed, thereby suppressing noise caused by the blade pitch noise.

In addition, in the multi-blade fan 6, the recesses 20 of two adjacent blades 12 in the arrangement direction of the multiple blades 12 differ from each other in the position (formation pattern of the recesses 20) of the positive pressure surface 17a, the negative pressure surface 17b, the inner peripheral side portion 18a, and the outer peripheral side portion 18b. In this way, by changing the formation pattern of the recesses 20 between adjacent blades 12, it is possible to easily make the cross-sectional shape of each blade 12 different. Therefore, the frequency of the blade pitch sound between adjacent blades 12 can be easily changed, and the frequency of the blade pitch sound between adjacent blades 12 can be dispersed.

In addition, in the multi-blade fan 6, two adjacent blades 12 in the arrangement direction of the multiple blades 12 have different numbers of recesses 20 in the cross section of the blade 12 perpendicular to the axial direction X of the rotation shaft 13. In this way, by changing the number of recesses 20 between adjacent blades 12, it is possible to easily make the cross-sectional shapes of each blade 12 different. Therefore, it is possible to easily change the frequency of the blade pitch noise between adjacent blades 12 and disperse the frequency of the blade pitch noise between adjacent blades 12.

In addition, in the multi-blade fan 6, two adjacent blades 12 in the arrangement direction of the multiple blades 12 have different cross-sectional shapes of the recesses 20 in the cross section of the blade 12 perpendicular to the axial direction X of the rotation shaft 13. In this way, by changing the cross-sectional shape of the recesses 20 between adjacent blades 12, it is possible to easily make the cross-sectional shapes of each blade 12 different. Therefore, it is possible to easily change the frequency of the blade pitch noise between adjacent blades 12 and disperse the frequency of the blade pitch noise between adjacent blades 12.

In addition, in the multi-blade fan 6, two adjacent blades 12 in the arrangement direction of the multiple blades 12 have different numbers of recesses 20 aligned in the axial direction X of the rotating shaft 13. In this way, it is possible to easily make the cross-sectional shapes of each blade 12 different by changing the number of recesses 20 aligned in the axial direction X of the rotating shaft 13 between adjacent blades 12. Therefore, it is possible to easily change the frequency of the blade pitch noise between adjacent blades 12 and disperse the frequency of the blade pitch noise between adjacent blades 12.

In addition, in the multi-blade fan 6, the recess 20 of the blade 12 is formed in a part of the blade 12 in the axial direction X of the rotating shaft 13. The bottom surface 21a of the recess 20 (20F, 20G) is curved in the same direction as the blade surface 17 on which the recess 20 (20F, 20G) is formed, and this bottom surface 21a is formed as a single curved surface that continues from one end of the blade chord length L to the blade surface 17 on which the recess 20 (20F, 20G) is formed in the cross section of the blade 12 perpendicular to the axial direction X of the rotating shaft 13. This reduces the vortex generated in the airflow flowing over the blade surface 17 along the bottom surface 21a of the recess 20F, 20G, and suppresses the turbulence generated downstream of the blade 12, thereby suppressing the pressure loss generated in the airflow along the blade surface 17 and reducing the power consumption of the motor (not shown) that drives the multi-blade fan 6. This reduces the pressure loss of the airflow along the blade surface 17 of the blade 12, thereby increasing the air volume of the multi-blade fan 6.

In the multi-blade fan 6, the recesses 20 of the blades 12 are formed by cutting out the tip of either the inner circumferential side portion 18a or the outer circumferential side portion 18b, continuing from the positive pressure surface 17a and the negative pressure surface 17b. This makes it possible to easily differentiate the cross-sectional shapes of the blades 12 by changing the blade chord length L between adjacent blades 12. Therefore, the frequency of the blade pitch noise between adjacent blades 12 can be easily changed.

In the multi-blade fan 6, the blades 12 have an inner/outer diameter ratio (A/B) of 0.720 or more and 0.800 or less, where A is the diameter of the inscribed circle C1 of the blade 12 relative to the center of rotation O of the rotating shaft 13, and B is the diameter of the circumscribed circle C2 of the blade 12. With this type of inner/outer diameter ratio (A/B) of the blade 12, the frequency of the blade pitch sound can be controlled by the recess 20, thereby reducing noise compared to a multi-blade fan without the recess 20.

In the multi-blade fan 6, the blades 12 have an inner/outer diameter ratio (A/B) of more than 0.800, where A is the diameter of the inscribed circle C1 of the blade 12 relative to the center of rotation O of the rotating shaft 13 and B is the diameter of the circumscribed circle C2. If the inner/outer diameter ratio (A/B) of the blade 12 exceeds 0.800, the wind speed passing between the blades 12 so as to penetrate the multi-blade fan 6 increases, which may cause noise to worsen. However, by controlling the frequency of the blade pitch sound using the recess 20, it is possible to increase the air volume while avoiding noise deterioration.

The multi-blade fan disclosed in this application is used as a cross-flow fan in the examples, but is not limited to a cross-flow fan. The multi-blade fan may also be used as a centrifugal fan, such as a sirocco fan, and the same effects as in this example can be obtained.

REFERENCE SIGNS LIST 1 Indoor unit 5 Heat exchanger 6 Multi-blade fan 12 Blade 13 Rotating shaft 17 Blade surface 17a Positive pressure surface 17b Negative pressure surface 18a Inner peripheral side portion 18b Outer peripheral side portion 20 (20A to 20G) Recess 21a Bottom surface 21b End surface A, B Diameter (A/B) Inner/outer diameter ratio C1 Inscribed circle C2 Circumscribed circle H Length L Blade chord length X Axial direction

Claims (11)

A cross-flow fan including a plurality of blades extending along an axial direction of a rotation shaft and arranged at a predetermined pitch around the rotation shaft,
the plurality of blades include at least two blades, each of which has a recess formed along the axial direction of the rotation shaft on at least one of a pressure side and a suction side that are blade surfaces of the blade and on at least one of an inner peripheral side portion and an outer peripheral side portion of the blade, the recess being recessed in a thickness direction of the blade,
The recesses are formed so that adjacent blades in an arrangement direction of the plurality of blades have different cross-sectional shapes perpendicular to the rotation axis and different blade chord lengths at a position on the rotation axis where the recess is formed in one of the blades,
A multi-blade fan, wherein the at least two adjacent blades have different lengths of the recesses in the axial direction of the rotation shaft. The two wings have the recesses,
The positions of the pressure surface, the suction surface, the inner circumferential side portion, and the outer circumferential side portion of each of the two concave portions of the blades are different from each other.
The multi-blade fan according to claim 1 . The two blades have different numbers of recesses in cross sections of the blades perpendicular to the axial direction of the rotation shaft.
The multi-blade fan according to claim 1 or 2. The two blades have different cross-sectional shapes of the recesses in cross sections of the blades perpendicular to the axial direction of the rotation shaft.
The multi-blade fan according to any one of claims 1 to 3. The two blades have different numbers of the recesses arranged in the axial direction of the rotation shaft.
The multi-blade fan according to any one of claims 1 to 4. The recess is formed in a part of the blade in the axial direction of the rotation shaft,
A bottom surface of the recess is curved in the same direction as the blade surface on which the recess is formed, and the bottom surface is formed as a single curved surface that is continuous from one end of a chord length to the blade surface on which the recess is formed in a cross section of the blade perpendicular to the axial direction of the rotation shaft.
The multi-blade fan according to any one of claims 1 to 5. the recess is formed by cutting out a tip of either the inner circumferential side portion or the outer circumferential side portion so as to be continuous with the positive pressure surface and the negative pressure surface.
The multi-blade fan according to any one of claims 1 to 6. A cross-flow fan including a plurality of blades extending along an axial direction of a rotation shaft and arranged at a predetermined pitch around the rotation shaft,
the plurality of blades include at least two blades, each of which has a recess that is recessed in a thickness direction of the blade, the recess continuing from a tip of an inner circumferential side portion to a tip of an outer circumferential side portion of the blade on at least one of a pressure side and a suction side that are blade surfaces of the blade, and which is formed along a portion of the blade in the axial direction of the rotation shaft,
adjacent blades in an arrangement direction of the plurality of blades have different cross-sectional shapes perpendicular to the rotation axis at a position on the rotation axis where the recess is formed in one of the blades,
A multi-blade fan, wherein the at least two blades have different lengths of the recesses in the axial direction of the rotation shaft. a ratio of inner and outer diameters (A/B) of the blades is 0.720 or more and 0.800 or less, where A is a diameter of an inscribed circle of the blades relative to the center of the rotation shaft and B is a diameter of a circumscribed circle of the blades.
The multi-blade fan according to any one of claims 1 to 8. the plurality of blades have an inner/outer diameter ratio (A/B) of more than 0.800, where A is a diameter of an inscribed circle of the blade relative to the center of the rotation shaft and B is a diameter of a circumscribed circle of the blade relative to the center of the rotation shaft;
The multi-blade fan according to any one of claims 1 to 8. A heat exchanger;
A multi-blade fan according to any one of claims 1 to 10, into which air that has passed through the heat exchanger flows;
An indoor unit equipped with

Images