The present application is based on PCT filing PCT/JP2020/018281, filed Apr. 30, 2020, the entire contents of which is incorporated herein by reference.
The present disclosure relates to an air-sending device including a propeller fan, and a bell mouth surrounding an outboard area of the propeller fan.
Some proposed air-sending devices in the related art include a propeller fan, and a bell mouth surrounding an outboard area of the propeller fan. Such air-sending devices are used for applications such as ventilators and air-conditioners. Rotation of the propeller fan causes a leakage flow to occur near the outboard edge of each blade of the propeller fan, whereby air flows from the pressure surface toward the suction surface. The leakage flow gives rise to a blade tip vortex near the suction surface. Accordingly, some proposed air-sending devices in the related art including a propeller fan and a bell mouth are designed such that, to mitigate noise resulting from such a blade tip vortex, the outboard part of each blade of the propeller fan is bent toward the suction side to form a bent part, with the bent part gradually increasing in width in the radial direction from the leading edge to the trailing edge (see Patent Literature 1). The radial direction refers to a direction perpendicular to the rotational axis of the propeller fan. The above-mentioned bent part of each blade of the propeller fan described in Patent Literature 1 will be hereinafter referred to as reflexed part.
Exemplary bell mouths include semi-open bell mouths and ducted bell mouths. In the case of a semi-open bell mouth, the bell mouth faces a region of the outboard edge of each blade of the propeller fan, the region extending from the middle of the outboard edge to the trailing edge of the blade. By contrast, in the case of a ducted bell mouth, the bell mouth faces most of the outboard edge of each blade of the propeller fan. For example, in the case of a ducted bell mouth, when the ducted bell mouth and each blade are observed in a direction perpendicular to the rotational axis of the propeller fan, greater than or equal to 90% of the outboard edge of the blade faces the bell mouth. The air-sending device described in Patent Literature 1 is an air-sending device with a semi-open bell mouth.
A bell mouth includes a contraction part that gradually decreases in diameter in the direction of flow of an airflow generated by rotation of the propeller fan, and a cylindrical part through which an airflow guided by the contraction part flows. In the case of an air-sending device with a ducted bell mouth, the cylindrical part of the bell mouth, and the outboard edge of each blade face each other over a wide region in comparison to an air-sending device with a semi-open bell mouth. Due to the above-mentioned difference in bell mouth shape, an air-sending device with a ducted bell mouth, and an air-sending device with a semi-open bell mouth greatly differ in how air flows in the vicinity of the outboard edge of each blade of the propeller fan. This means that using the propeller fan used for the air-sending device described in Patent Literature 1, which is an air-sending device with a semi-open bell mouth, in combination with a ducted bell mouth fails to sufficiently mitigate noise caused by blade tip vortex.
Specifically, in a region where the cylindrical part of the bell mouth and the outboard edge of the blade face each other, the cylindrical part and the outboard edge are at a short distance from each other. Consequently, in the region where the cylindrical part of the bell mouth and the outboard edge of the blade face each other, a blade tip vortex is generated as air flows from the pressure surface of the blade toward the suction surface. The generated blade tip vortex interferes with the cylindrical part of the bell mouth. As a result, in the region where the cylindrical part of the bell mouth and the outboard edge of the blade face each other, the flow of air in the vicinity of the outboard edge of the blade becomes turbulent. This leads to increased pressure fluctuations and consequently increased noise. The larger the region where the cylindrical part of the bell mouth and the outboard edge of the blade face each other, the greater the noise mentioned above. Consequently, the noise is greater for an air-sending device with a ducted bell mouth than for an air-sending device with a semi-open bell mouth. In this regard, for the air-sending device described in Patent Literature 1, a blade shape capable of noise mitigation has been contemplated based on the assumption of using a combination of a semi-open bell mouth and a propeller fan. This means that using a ducted bell mouth in combination with the propeller fan of the air-sending device described in Patent Literature 1 fails to sufficiently mitigate noise caused by blade tip vortex. That is, related-art air-sending devices with a ducted bell mouth are still inadequate in mitigating noise caused by blade tip vortex.
The present disclosure is directed to addressing the problem mentioned above. Accordingly, it is an object of the present disclosure to provide an air-sending device including a ducted bell mouth and capable of reducing noise caused by blade tip vortex in comparison to the related art.
An air-sending device according to an embodiment of the present disclosure includes a propeller fan configured to rotate about a rotational axis, and a bell mouth surrounding an outboard area of the propeller fan. The propeller fan includes a boss, and a plurality of blades projecting from the boss in a direction outboard of the boss. Each of the plurality of blades includes a reflexed part in its outboard portion, the reflexed part being bent upstream of an airflow, the airflow being generated in a direction of the rotational axis in response to rotation of the propeller fan. The bell mouth includes a contraction part and a cylindrical part, the contraction part gradually decreasing in diameter in a direction of the airflow, the cylindrical part being a part of the bell mouth through which the airflow flows after being guided by the contraction part. When the bell mouth and each of the plurality of blades are observed in a direction perpendicular to the rotational axis, greater than or equal to 90% of an outboard edge of the blade faces the bell mouth. In each of the plurality of blades, the following features are defined: a circle of a given radius centered on the rotational axis is defined as an imaginary circle; a cross-section of the blade taken along a plane passing through the imaginary circle and parallel to the rotational axis is defined as a first cross-section; a given point on a chord line in the first cross-section is defined as an imaginary point; a value obtained by dividing a distance in the first cross-section from the imaginary point to a leading edge of the blade, by a distance in the first cross-section from the imaginary point to a trailing edge of the blade is defined as a position ratio; a line formed by connecting, while varying a radius of the imaginary circle, points that are identical to each other in the position ratio is defined as an imaginary line; a cross-section of the blade taken along a plane passing through the imaginary line and parallel to the rotational axis is defined as a second cross-section; a view of the second cross-section as projected onto a plane passing through the rotational axis is defined as a projection view; in the projection view, an intersection point between a pressure surface of the blade and the boss is defined as an inboard point; in the projection view, an inflection point of the reflexed part on the pressure surface is defined as a reflex point; in the projection view, a straight line passing through the inboard point and perpendicular to the rotational axis is defined as a first straight line; in the projection view, a straight line passing through the inboard point and a given point on the pressure surface is defined as a second straight line; in the projection view, a tangent passing through an outboard end of the blade is defined as a third straight line; of angles formed by the first straight line and the second straight line, an acute angle diverging outboard of the propeller fan is defined as a blade inclination angle; a direction in which the blade inclination angle diverges upstream of the airflow relative to the first straight line is defined as a positive direction of the blade inclination angle; a direction in which the blade inclination angle diverges downstream of the airflow relative to the first straight line is defined as a negative direction of the blade inclination angle; the blade inclination angle formed when the second straight line passes through the reflex point is defined as a first blade inclination angle; and, of angles formed by the second straight line and the third straight line, an angle diverging outboard of the propeller fan and upstream of the airflow is defined as a reflex angle. With these features defined as described above, within an area where the position ratio is greater than or equal to at least 1, the first blade inclination angle has a negative value, and in at least a portion of an area where the cylindrical part of the bell mouth and the outboard edge of the blade face each other in the direction perpendicular to the rotational axis, the reflex angle is greater than or equal to 90 degrees.
The air-sending device according to an embodiment of the present disclosure includes a so-called ducted bell mouth. In the air-sending device according to an embodiment of the present disclosure, within its area where the position ratio is greater than or equal to at least 1, the first blade inclination angle has a negative value. This helps to reduce the length of each blade of the propeller fan in the direction of the rotational axis. As a result, in the direction of the rotational axis, the region where the cylindrical part of the bell mouth and the outboard edge of each blade face each other can be reduced. Further, in the air-sending device according to an embodiment of the present disclosure, in at least a portion of the area where the cylindrical part of the bell mouth and the outboard edge of each blade face each other in a direction perpendicular to the rotational axis, the reflex angle is greater than or equal to 90 degrees. This helps to ensure that in at least a portion of the area where the cylindrical part of the bell mouth and the outboard edge of each blade face each other in the direction perpendicular to the rotational axis, when a blade tip vortex generated by flow of air from the pressure surface of the blade toward the suction surface interferes with the cylindrical part of the bell mouth, turbulence that occurs in the flow of air in the vicinity of the outboard edge can be mitigated. This makes it possible to mitigate pressure fluctuations in the vicinity of the outboard edge. Therefore, the air-sending device according to an embodiment of the present disclosure is capable of, when implemented as an air-sending device including a ducted bell mouth, reducing noise caused by blade tip vortex in comparison to the related art.
The propeller fan 1 is configured to rotate about a rotational axis 2 in a direction represented by an arcuate arrow in
Each of the blades 10 includes a leading edge 11, a trailing edge 12, an inboard edge 13, an outboard edge 14, a pressure surface 15, and a suction surface 16. The leading edge 11 is the edge at the leading part of the blade 10 in the direction of rotation of the blade 10. The trailing edge 12 is the edge at the trailing part of the blade 10 in the direction of rotation of the blade 10. The inboard edge 13 is the edge at the inboard part of the blade 10 and where the blade 10 is connected with the boss 3. The outboard edge 14 is the radially outboard end of the blade 10. The pressure surface 15 is a surface of the blade 10 that pushes out air. In
When the propeller fan 1 rotates by means of a motor (not illustrated), an airflow F is generated in the direction of the rotational axis 2 as represented by an open arrow in
Each of the blades 10 of the propeller fan 1 according to Embodiment 1 includes, in its outboard portion, a reflexed part 20 that is bent upstream. That is, in
Although the propeller fan 1 is depicted in
The bell mouth 50 according to Embodiment 1, and the bell mouth 250 according to Comparative Example 1 each surround an outboard area of the propeller fan 1. The bell mouth 50 according to Embodiment 1, and the bell mouth 250 according to Comparative Example 1 each include a contraction part 51 that gradually decreases in diameter in the direction of the airflow F, and a cylindrical part 52 through which the airflow F flows after being guided by the contraction part 51. That is, the cylindrical part 52 is disposed downstream from the contraction part 51. The cylindrical part 52 is equal in diameter to the smallest-diameter portion of the contraction part 51. The cylindrical part 52 does not change in diameter. This means that for the bell mouth 50 according to Embodiment 1 and the bell mouth 250 according to Comparative Example 1, the cylindrical part 52 represents a portion of the bell mouth located at a short distance to the outboard edge 14 of the blade 10. The bell mouth 50 according to Embodiment 1, and the bell mouth 250 according to Comparative Example 1 each also include an expansion part 53 located downstream from the cylindrical part 52 and having a diameter that gradually increases in the direction of the airflow F. The airflow F exits through the expansion part 53.
Exemplary related-art bell mouths include semi-open bell mouths, and ducted bell mouths. In the case of a semi-open bell mouth, the bell mouth faces a region of the outboard edge of each blade of the propeller fan, the region extending from the middle of the outboard edge to the trailing edge of the blade. By contrast, in the case of a ducted bell mouth, the bell mouth faces most of the outboard edge of each blade of the propeller fan. For example, when the ducted bell mouth and each blade are observed in a direction perpendicular to the rotational axis of the propeller fan, greater than or equal to 90% of the outboard edge of the blade faces the bell mouth.
That is, the bell mouth 250 according to Comparative Example 1 illustrated in
Detailed reference is now made to the configuration of each blade 10 of the propeller fan 1. In describing the configuration of the blade 10 in detail, an imaginary circle R, a first cross-section 30, an imaginary point 31, a position ratio P, an imaginary line SL, and a second cross-section 40 are defined as illustrated in
As illustrated in
Reference is now made to
As illustrated in
Specifically, in the projection views of
Of the angles formed by the first straight line L1 and the second straight line L2, an acute angle diverging outboard of the propeller fan 1 is defined as the blade inclination angle α. The blade inclination angle α formed when the second straight line L2 passes through the reflex point 21 is defined as the first blade inclination angle α1.
As illustrated in
The above-mentioned configuration of the propeller fan 1 helps to reduce the length of the blade 10 of the propeller fan 1 in the direction of the rotational axis 2. As a result, in the direction of the rotational axis 2, the region where the cylindrical part 52 of the bell mouth 50 and the outboard edge 14 of the blade 10 face each other can be reduced. In this regard, in the case of an air-sending device with a ducted bell mouth, in a region where the cylindrical part of the bell mouth and the outboard edge of the blade face each other, the cylindrical part and the outboard edge are at a short distance from each other. This means that for a related-art air-sending device with a ducted bell mouth, in a region where the cylindrical part of the bell mouth and the outboard edge of the blade face each other, a blade tip vortex generated due to flow of air from the pressure surface of the blade toward the suction surface interferes with the cylindrical part of the bell mouth. As a result, in the region where the cylindrical part of the bell mouth and the outboard edge of the blade face each other, the flow of air in the vicinity of the outboard edge of the blade becomes turbulent. This leads to increased pressure fluctuations and consequently increased noise. By contrast, the air-sending device 100 according to Embodiment 1 makes it possible to reduce the region where the cylindrical part 52 of the bell mouth 50 and the outboard edge 14 of the blade 10 face each other, that is, reduce the region where noise increases. This helps to reduce noise caused by blade tip vortex.
As illustrated in
An air-sending device 200b according to Comparative Example 2, and an air-sending device 200c according to Comparative Example 3 each include a propeller fan 201. In
The air-sending device 200b according to Comparative Example 2 is an air-sending device including a combination of the propeller fan 201, and the bell mouth 250 described above with reference to the air-sending device 200a according to Comparative Example 1. That is, the air-sending device 200b according to Comparative Example 2 is an air-sending device with a semi-open bell mouth. The air-sending device 200c according to Comparative Example 3 is an air-sending device including a combination of the propeller fan 201, and the bell mouth 50 according to Embodiment 1. That is, the air-sending device 200c according to Comparative Example 3 is an air-sending device with a ducted bell mouth.
As illustrated in
However, as illustrated in
As with the air-sending device 200c according to Comparative Example 3 illustrated in
The region of strong flow varies with the shape of the blade 10. Accordingly, the area with the reflex angle β greater than or equal to 90 degrees is preferably positioned in the region of strong leakage flow. Further, it is preferable to increase the reflex angle β with increasing strength of the leakage flow. In the air-sending device 100 according to Embodiment 1, most of the outboard edge 14 of the blade 10 faces the cylindrical part 52 and the expansion part 53 of the bell mouth 50 in a direction perpendicular to the rotational axis 2. Accordingly, in Embodiment 1, the leakage flow at the outboard edge 14 of the blade 10 is strong in a region that is closer to the trailing edge 12 than is the near mid-chord region. Therefore, according to Embodiment 1, it is preferred that the reflex angle β be greater than or equal to 90 degrees in a region that is closer to the trailing edge 12 than is the near mid-chord region.
The reflexed part 20 illustrated in
The reflexed part 20 illustrated in
Lastly, the results of examination made to examine the noise mitigation effect of the air-sending device 100 according to Embodiment 1 are presented below.
As illustrated in
As illustrated in
As described above, the air-sending device 100 according to Embodiment 1 includes the propeller fan 1 configured to rotate about the rotational axis 2, and the bell mouth 50 surrounding an outboard area of the propeller fan 1. The propeller fan 1 includes the boss 3, and the blades 10 projecting from the boss 3 in a direction outboard of the boss 3. Each of the blades 10 includes the reflexed part 20 in its outboard portion, the reflexed part being bent upstream of the airflow F that is generated in the direction of the rotational axis 2 in response to rotation of the propeller fan 1. The bell mouth 50 includes the contraction part 51 that gradually decreases in diameter in the direction of the airflow F, and the cylindrical part 52 through which the airflow F flows after being guided by the contraction part 51. When the bell mouth 50 and each of the blades 10 are observed in a direction perpendicular to the rotational axis 2, greater than or equal to 90% of the outboard edge 14 of the blade 10 faces the bell mouth 50. In each of the blades 10, a circle of a given radius centered on the rotational axis 2 of the propeller fan 1 is defined as the imaginary circle R. A cross-section of the blade 10 taken along a plane passing through the imaginary circle R and parallel to the rotational axis 2 is defined as the first cross-section 30. A given point on a chord line in the first cross-section 30 is defined as the imaginary point 31. A value obtained by dividing the distance in the first cross-section 30 from the imaginary point 31 to the leading edge 11 of the blade 10, by the distance in the first cross-section 30 from the imaginary point 31 to the trailing edge 12 of the blade 10 is defined as the position ratio P. A line formed by connecting, while varying the radius of the imaginary circle R, points that are identical to each other in the position ratio P is defined as the imaginary line SL. A cross-section of the blade 10 taken along a plane passing through the imaginary line SL and parallel to the rotational axis 2 is defined as the second cross-section 40. A view of the second cross-section 40 as projected onto a plane passing through the rotational axis 2 is defined as a projection view. In the projection view, the intersection point between the pressure surface 15 of the blade 10 and the boss 3 is defined as the inboard point 17. In the projection view, an inflection point of the reflexed part 20 on the pressure surface 15 is defined as the reflex point 21. In the projection view, a straight line passing through the inboard point 17 and perpendicular to the rotational axis 2 is defined as the first straight line L1. In the projection view, a straight line passing through the inboard point 17 and a given point on the pressure surface 15 is defined as the second straight line L2. In the projection view, a tangent passing through the outboard end 18 of the blade 10 is defined as the third straight line L3. Of the angles formed by the first straight line L1 and the second straight line L2, an acute angle diverging outboard of the propeller fan 1 is defined as the blade inclination angle α. The direction in which the blade inclination angle α diverges upstream of the airflow F relative to the first straight line L1 is defined as the positive direction of the blade inclination angle α. The direction in which the blade inclination angle α diverges downstream of the airflow F relative to the first straight line L1 is defined as the negative direction of the blade inclination angle α. The blade inclination angle α formed when the second straight line L2 passes through the reflex point 21 is defined as the first blade inclination angle α1. Of the angles formed by the second straight line L2 and the third straight line L3, an angle diverging outboard of the propeller fan 1 and upstream of the airflow F is defined as the reflex angle β. With the first blade inclination angle α1 and the reflex angle β being defined as described above, in the air-sending device 100 according to Embodiment 1, within an area where the position ratio P is greater than or equal to at least 1, the first blade inclination angle α1 has a negative value. Further, in the air-sending device 100 according to Embodiment 1, in at least a portion of the area where the cylindrical part 52 of the bell mouth 50 and the outboard edge 14 of the blade 10 face each other in the direction perpendicular to the rotational axis 2, the reflex angle β is greater than or equal to 90 degrees.
In the air-sending device 100 according to Embodiment 1, within the area where the position ratio P is greater than or equal to at least 1, the first blade inclination angle α1 has a negative value. This makes it possible for the air-sending device 100 according to Embodiment 1 to reduce the length of each blade 10 of the propeller fan 1 in the direction of the rotational axis 2, and reduce noise caused by blade tip vortex as described above. Further, in the air-sending device 100 according to Embodiment 1, in at least a portion of the area where the cylindrical part 52 of the bell mouth 50 and the outboard edge 14 of the blade 10 face each other in a direction perpendicular to the rotational axis 2, the reflex angle β is greater than or equal to 90 degrees. This helps to further reduce noise caused by blade tip vortex. Therefore, the air-sending device 100 according to Embodiment 1 is capable of, when implemented as an air-sending device including a ducted bell mouth, reducing noise caused by blade tip vortex in comparison to the related art.
Shaping each blade 10 of the propeller fan 1 as described below makes it possible to further reduce noise caused by blade tip vortex. In the following description of Embodiment 2, matters not particularly mentioned are assumed to be similar to those described above with reference to Embodiment 1, and functions and features identical to those of Embodiment 1 are designated by the same reference signs as those used for Embodiment 1.
Each of the blades 10 of the propeller fan 1 according to Embodiment 2 includes the intermediate inflection part 19 between the inboard edge 13 and the reflexed part 20. In a projection view obtained by projecting the second cross-section 40 onto a plane passing through the rotational axis 2, when the blade 10 is viewed from the inboard point 17 in a direction outboard of the propeller fan 1, the blade 10 is bent in the intermediate inflection part 19 toward the suction surface 16. Due to the above-mentioned configuration of each blade 10, air flowing radially outward along the pressure surface 15 is deflected in the intermediate inflection part 19 so as to be directed upstream of the airflow F, before being guided to the reflexed part 20. Consequently, due to the above-mentioned configuration of each blade 10, the air flowing radially outward along the pressure surface 15 can be smoothly guided to reach the outboard end 18. Therefore, the above-mentioned configuration of each blade 10 helps to further mitigate fluctuations of the pressure on the wall surface of the bell mouth 50, and consequently reduce noise caused by blade tip vortex.
In the projection view obtained by projecting the second cross-section 40 onto a plane passing through the rotational axis 2, the amount by which the blade inclination angle α changes due to a movement by a unit length from the inboard point 17 in a direction outboard of the propeller fan 1 along the pressure surface 15 is defined as a rate of change in the blade inclination angle α. With the rate of change in the blade inclination angle α being defined as described above, the rate of change between the inboard point 17 and the intermediate inflection part 19 is less than the rate of change between the intermediate inflection part 19 and the reflex point 21 of the reflexed part 20. Further, the rate of change between the intermediate inflection part 19 and the reflex point 21 of the reflexed part 20 is less than the rate of change between the reflex point 21 of the reflexed part 20 and the outboard end 18. Due to the above-mentioned configuration of each blade 10, air flowing radially outward along the pressure surface 15 can be gradually deflected so as to be directed upstream of the airflow F. Consequently, the above-mentioned configuration of each blade 10 helps to further ensure that air flowing radially outward along the pressure surface 15 can be smoothly guided to reach the outboard end 18. Therefore, the above-mentioned configuration of each blade 10 helps to further mitigate fluctuations of the pressure on the wall surface of the bell mouth 50, and consequently further reduce noise caused by blade tip vortex.
In the foregoing description of Embodiment 1 and Embodiment 2, no particular mention has been made to chordwise variation of the reflex height Lb of the reflexed part 20. The reflex height Lb of the reflexed part 20 may be varied chordwise as described below with reference to Embodiment 3. In the following description of Embodiment 3, matters not particularly mentioned are assumed to be similar to those described above with reference to Embodiment 1 or Embodiment 2, and functions and features identical to those of Embodiment 1 or Embodiment 2 are designated by the same reference signs as those used for Embodiment 1 or Embodiment 2.
As illustrated in
With regard to a blade tip vortex generated near the outboard edge 14 of each blade 10 of the propeller fan 1, the location where the blade tip vortex occurs and the path taken by the blade tip vortex vary greatly between when the propeller fan 1 operates at a relatively high airflow rate and when the propeller fan 1 operates at a relatively low airflow rate. When the propeller fan 1 operates at a relatively high airflow rate, the blade tip vortex occurring near the outboard edge 14 of each blade 10 is strong in a region of the blade 10 that is closer to the leading edge 11 than is the near mid-chord region. Accordingly, if the propeller fan 1 operates often at a relatively high airflow rate, it is preferable that, as with Embodiment 3, the location at which the reflex height Lb has a maximum value be positioned in a region that is closer to the leading edge 11 than is the near mid-chord region. In other words, if the propeller fan 1 operates often at a relatively high airflow rate, each blade 10 preferably has a location of the maximum reflex height Lb that is positioned within an area where the position ratio P is less than 1. The above-mentioned configuration of the blade 10 helps to ensure that when the propeller fan 1 operates at a relatively high airflow rate, in a region where a strong blade tip vortex occurs at this time due to a leakage flow, a component of the leakage flow that is directed toward the cylindrical part 52 of the bell mouth 50 can be further reduced. This helps to further mitigate fluctuations of the pressure on the wall surface of the bell mouth 50. Therefore, the above-mentioned configuration of the blade 10 leads to an improved noise mitigation effect when the propeller fan 1 operates at a relatively high airflow rate.
For reference, the results of examination made to examine the noise mitigation effect of the air-sending device 100 according to Embodiment 3 are presented below.
As illustrated in
The reflex height Lb of the reflexed part 20 may be varied chordwise as described below with reference to Embodiment 4. In the following description of Embodiment 4, matters not particularly mentioned are assumed to be similar to those described above with reference to any one of Embodiments 1 to 3, and functions and features identical to those of any one of Embodiments 1 to 3 are designated by the same reference signs as those used for the one of Embodiments 1 to 3.
When the propeller fan 1 operates at a relatively low airflow rate, the blade tip vortex occurring near the outboard edge 14 of each blade 10 is strong in a region of the blade 10 that is located closer to the trailing edge 12 than is the near mid-chord region. Accordingly, if the propeller fan 1 operates often at a relatively low airflow rate, it is preferable that, as with Embodiment 4, the location at which the reflex height Lb has a maximum value be positioned in a region that is closer to the trailing edge 12 than is the near mid-chord region. However, positioning the location of the maximum reflex height Lb at the trailing edge 12 can cause a deterioration of the air-sending performance of the air-sending device 100 if the propeller fan 1 used is one that characteristically undergoes an increase in pressure at the outboard region of the trailing edge 12. For this reason, if the propeller fan 1 operates often at a relatively low airflow rate, the location of the maximum reflex height Lb is preferably positioned at a location that is closer to the trailing edge 12 than is the near mid-chord region, and that is not at the trailing edge 12. That is, the reflexed part 20 of the blade 10 according to Embodiment 4 is shaped such that in a region of the reflexed part 20 located closer to the trailing edge 12 than is the near mid-chord region, the reflexed part 20 is, for example, convex upstream of the airflow F. In other words, if the propeller fan 1 operates often at a relatively low airflow rate, each blade 10 preferably has a location at which the maximum reflex height Lb has a maximum value, the location being within an area where the position ratio P is greater than 1 and being not at the trailing edge 12.
The above-mentioned configuration of the blade 10 helps to ensure that when the propeller fan 1 operates at a relatively low airflow rate, in a region where a strong blade tip vortex occurs at this time due to a leakage flow, a component of the leakage flow that is directed toward the cylindrical part 52 of the bell mouth 50 can be further reduced. This helps to further mitigate fluctuations of the pressure on the wall surface of the bell mouth 50. Therefore, the above-mentioned configuration of the blade 10 leads to an improved noise mitigation effect when the propeller fan 1 operates at a relatively low airflow rate.
For reference, the results of examination made to examine the noise mitigation effect of the air-sending device 100 according to Embodiment 3 are presented below.
In
The reflex height Lb of the reflexed part 20 may be varied chordwise as described below with reference to Embodiment 5. In the following description of Embodiment 5, matters not particularly mentioned are assumed to be similar to those described above with reference to any one of Embodiments 1 to 4, and functions and features identical to those of any one of Embodiments 1 to 4 are designated by the same reference signs as those used for the one of Embodiments 1 to 4.
As described above with reference to Embodiment 3 and Embodiment 4, varying the location of the maximum reflex height Lb makes it possible to effectively mitigate noise in accordance with the airflow rate of the propeller fan 1. Accordingly, if, for example, the propeller fan 1 operates often at a plurality of operating points corresponding to different airflow rates, then as illustrated in
The above-mentioned configuration of each blade 10 leads to an improved noise mitigation effect when the propeller fan 1 operates at a plurality of operating points corresponding to different airflow rates.
1: propeller fan, 2: rotational axis, 3: boss, 10: blade, 11: leading edge, 12: trailing edge, 13: inboard edge, 14: outboard edge, 15: pressure surface, 16: suction surface, 17: inboard point, 18: outboard end, 19: intermediate inflection part, 19a: reflex point, 20: reflexed part, 21: reflex point, 30: first cross-section, 31: imaginary point, 40 (41, 42, 43): second cross-section, 50: bell mouth, 51: contraction part, 52: cylindrical part, 53: expansion part, 100: air-sending device, 200a, 200b, 200c: air-sending device (comparative example), 201: propeller fan (comparative example), 220: reflexed part (comparative example), 250: bell mouth (comparative example), F: airflow, L1: first straight line, L2: second straight line, L3: third straight line, L18: curve, L21: curve, La: reflex width, Lb: reflex height, Lb1: minimal value, Lb2: maximal value, Lc: blade width, P: position ratio, R: imaginary circle, SL (SL1, SL2, SL3): imaginary line, W: blade tip vortex, α: blade inclination angle, α1: first blade inclination angle, β: reflex angle.
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/JP2020/018281 | 4/30/2020 | WO |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2021/220469 | 11/4/2021 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
20140246180 | Nakashima et al. | Sep 2014 | A1 |
20180335055 | Goto | Nov 2018 | A1 |
Number | Date | Country |
---|---|---|
3629702 | Mar 2005 | JP |
2010-236371 | Oct 2010 | JP |
2012-233420 | Nov 2012 | JP |
2018-193876 | Dec 2018 | JP |
Entry |
---|
International Search Report and Written Opinion dated Jul. 7, 2020, received for PCT Application PCT/JP2020/018281, filed on Apr. 30, 2020, 9 pages including English Translation. |
Extended European Search Report dated May 30, 2023, in corresponding European Patent Application No. 20933470.5, 7pp. |
Number | Date | Country | |
---|---|---|---|
20230122146 A1 | Apr 2023 | US |