EP2503157A1

EP2503157A1 - Multi-blade fan for centrifugal blower

Info

Publication number: EP2503157A1
Application number: EP10831457A
Authority: EP
Inventors: Masatoshi Kawasaki
Original assignee: Sanden Corp
Current assignee: Sanden Corp
Priority date: 2009-11-19
Filing date: 2010-11-04
Publication date: 2012-09-26
Also published as: CN102667173A; JP2011127586A; WO2011062062A1

Abstract

Disclosed is a multi-blade fan for a centrifugal blower, the multi-blade fan having a plurality of annularly-disposed blades and being characterized in that at least the number of blades (Z), the inner/outer diameter ratio, which is defined as the ratio (D1/D2) between the diameter (D1) of the circle inscribing the blades and the diameter (D2) of the circle circumscribing the blades, the angle of inclination (a degrees) of each blade, which is defined as the angle between a line connecting the position of said blade on the inscribed circle and the position thereof on the circumscribed circle and a line extending radially from the center of the inscribed circle and passing through said position on the inscribed circle, and the tongue clearance ratio, which is defined as the ratio (S/D2) between the tongue clearance (S) and the diameter (D2); of the circumscribed circle are all within optimal ranges (30=Z=55; 0.72=D1/D2=0.86; 15==a=48; and 0.09=S/D2=0.15). Thus, it is possible to design a multi-blade fan for a centrifugal blower that produces little noise by determining the optimal ranges for parameters that were found to be effective and combining those optimal ranges for use.

Description

Technical Field of the Invention

The present invention relates to a multi-blade fan, which has a plurality of annularly-disposed blades, for centrifugal blowers, and specifically relates to a technology to enable to design the multi-blade fan optimally as achieving high fan efficiency and low noise generation.

Background Art of the Invention

A centrifugal blower having a large number of blades disposed annularly is suitably used as a blower in an automotive air conditioning system. Such a centrifugal blower is desired to achieve low noise generation, as well as high fan efficiency.
It is known that a noise caused by a multi-blade fan of a centrifugal blower can be effectively suppressed when a suppression of a noise caused by the air flow passing between blades is suppressed. Therefore the optimization of a structure provided with blades is required, however, design optimization technologies of multi-blade fans have not been established so far. For example, patent document I suggests that the inner/outer diameter ratio and the number of blades should be set within a certain range so as to achieve a low noise generation for a multi-blade fan of centrifugal blowers. Actually, even if those design parameters are set properly, noises could not always be eliminated surely and sufficiently.

Prior art documents

Patent documents

Patent document 1: JP2009-62953-A
Non-patent documents

Non-patent document 1: "Turbofan and compressor" written by Takefumi Namai and Masahiro Inoue, CORONA PUBLISHING CO., LTD, 1988, p292 - 297

Summary of the Invention

Problems to be solved by the Invention

Accordingly, in order to ensure low noise generation while maintaining the high fan efficiency, an object of the present invention is to find out what kind of design factors (parameters) would work particularly for eliminating noise generation and then optimum ranges of the factors which are found would be combined to enable the design of a reasonably optimum multi-blade fan of centrifugal blowers.

Means for solving the Problems

To achieve the above-described object, a multi-blade fan for a centrifugal blower according to the present invention is a multi-blade fan for a centrifugal blower having a plurality of annularly-disposed blades, characterized in that at least, number of blades Z, an inner/outer diameter ratio defined as a ratio D1/D2 of a diameter D1 of an inscribed circle of the blades to a diameter D2 of a circumscribed circle of the blades, an angle of inclination α (deg) of each blade defined as an angle between a line which connects a position of the blade on the inscribed circle to a position thereof on the circumscribed circle, and a line extending radially from a center of the inscribed circle and passing through the position on the inscribed circle, and a tongue clearance ratio defined as a ratio S/D2 between the tongue clearance S and the diameter D2 of the circumscribed circle are all within following ranges. $30 \leq Z \leq 55$
$0.72 \leq D 1 / D 2 \leq 0.86$
$15 \leq α \leq 48$
$0.09 \leq S / D 2 \leq 0.15$
Here, the number of blades is preferably within 33 ≤ Z ≤ 50, and is more preferably within 35 ≤ Z ≤ 45. The inner/outer diameter ratio D1/D2 is preferably within 0.76 ≤ D1/D2 ≤ 0.85, and is more preferably within 0.8 ≤ D1/D2 ≤ 0.84. The angle of inclination α (deg) of the blade is preferably within 20 ≤ α ≤ 42, and is more preferably within 25 ≤ α ≤ 35.
Thus the number of blades Z, the inner/outer diameter ratio D1/D2, the angle of inclination α of the blade, and the tongue clearance ratio S/D2 are set within the above-described ranges, so that the flow rate of the airflow between the blades can be controlled within the optimum range and the shear flow fluctuation of the airflow can be suppressed, and therefore the noise generation can be reduced actually. As a result, desirable low noise generation can be achieved as maintaining high fan efficiency, and therefore the optimum design of the multi-blade fan is enabled.
In order to aim more suitable design of the multi-blade fan for a centrifugal blower of the present invention, it is preferable that an exit angle β2 (deg) of the blade, which is defined as an angle between a tangent line of the circumscribed circle and a tangent line of the blade at a position of each blade on the circumscribed circle, is within 148 ≤ β2 ≤ 175. It is more preferably within 152 ≤ β2 ≤ 170, and is further preferably within 155 ≤ β2 ≤ 165. When the exit angle β2 of the blade is optimized, the flow rate of the airflow between the blades can be surely controlled within the optimum range and the shear flow fluctuation of the airflow can be suppressed, and therefore the noise generation can be reduced more surely.
In order to aim at further suitable design, it is preferable that an entrance angle β1 (deg) of the blade, which is defined as an angle between a tangent line of the inscribed circle and a tangent line of the blade at a position of each blade on the inscribed circle, is within a range of 50 ≤β1 ≤ 90. It is more preferably within 55 ≤ β1 ≤ 85, and is further preferably within 60 ≤ β1 ≤ 80. When the entrance angle β1 of the blade is optimized, a condition of the airflow flowed between blades can be more surely controlled optimally, so as to achieve desirable low noise generation surely.
Further, in order to aim at a mass production feasibility as balancing blade strength, weight saving, resin molding precision, cost and low noise generation by the inter-blade flow rate suppression, it is preferable that a thickness of each blade is within a range of 0.6 - I mm, though the multi-blade fan for a centrifugal blower according to the present invention is not limited thereto.
The structure of the multi-blade fan for a centrifugal blower according to the present invention is basically applicable to every multi-blade fan, and is suitable to be applied to a blower of an automotive air conditioning system, which is required to have a small size, a low noise and a high efficiency.

Effect according to the Invention

The multi-blade fan for a centrifugal blower according to the present invention makes it possible that a multi-blade fan is designed optimally, that the high fan efficiency is maintained and that desirable low noise generation is achieved, because the number of blades Z, an inner/outer diameter ratio D1/D2, an angle of inclination α (deg) of the blade and a tongue clearance ratio S/D2 are all set within predetermined ranges, and preferably, an exit angle β2 and an entrance angle β1 of the blade as well as a thickness of each blade may be set within predetermined ranges.

Brief explanation of the drawings

[Fig. 1] Fig. 1is a schematic front view showing a multi-blade fan for a centrifugal blower according to an embodiment of the present invention.
[Fig. 2] Fig. 2 is a partially enlarged sectional view of a multi-blade fan of Fig. 1, for explaining each parameter in the present invention.
[Fig. 3] Fig. 3 is a diagram of a relationship among the Number of Blades, Specific Noise and Fan Efficiency.
[Fig. 4] Fig. 4 is an explanation drawing which exemplifies each condition of airflow with each Number of Blades.
[Fig. 5] Fig. 5 is a diagram of a relationship among Inner/Outer Diameter Ratio, Specific Noise and Fan Efficiency.
[Fig. 6] Fig. 6 is an explanation drawing which exemplifies each condition of airflow with each Inner/Outer Diameter Ratio.
[Fig. 7] Fig. 7 is a diagram of a relationship among Angle of Inclination, specific noise and fan efficiency.
[Fig. 8] Fig. 8 is an explanation drawing which exemplifies each condition of airflow with each Angle of Inclination.
[Fig. 9] Fig. 9 is a diagram of a relationship between Tongue Clearance Ratio and NZ-Noise.
[Fig. 10] Fig. 10 is an explanation drawing which exemplifies a casing of which Tongue Clearance Ratio has been increased.
[Fig. 11] Fig. 11 is a diagram of a relationship among Exit Angle of the blade, Specific Noise and Fan Efficiency.
[Fig. 12] Fig. 12 is an explanation drawing which exemplifies each condition of airflow with each Exit Angle.
[Fig. 13] Fig. 13 is a diagram of a relationship among Entrance Angle of the blade, Specific Noise and Fan Efficiency.
[Fig. 14] Fig. 14 is an explanation drawing which exemplifies each condition of airflow with each Entrance Angle.

Embodiments for carrying out the Invention

Hereinafter, details of the present invention will be explained concretely as referring to figures.
Fig. 1 shows a multi-blade fan of a centrifugal blower according to an embodiment of the present invention, where (A) is a schematic front view showing blades and (B) is a schematic front view showing a casing which houses blades. Multi-blade fan 1 comprises a plurality of (many) blades 2 disposed annularly, and is housed in casing 11. In Fig. 1(A), symbol D1 shows a diameter of inscribed circle 3 many blades 2, and symbol D2 shows a diameter of circumscribed circle 4 of many blades 2. In Fig. 1(B), symbol S shows a clearance between circumscribed circle 4 of tongue 12 and casing 11.
As shown in Fig. 2, the Inner/Outer Diameter Ratio is defined as D1/D2, which is a ratio of diameter D1 (mm) of inscribed circle 3 to diameter D2 (mm) of circumscribed circle 4 of blades 2. Angle of Inclination α (deg) of the blade is defined as an angle between line 5, which is drawn from one end of each blade 2 at inscribed circle 3 side to the other end at circumscribed circle 4 side, and line 6, which is drawn radially from the other end at inscribed circle 3 side as extending to the center of the inscribed circle. Exit Angle β2 (deg) of blade 2 is defined as an angle between tangent line 7 of circumscribed circle 4 and tangent line 8 of blade 2, at circumscribed circle 4 side of each blade 2. Entrance Angle β1 (deg) of blade 2 is defined as an angle between tangent line 9 of inscribed circle 3 and tangent line 10 of blade 2, at inscribed circle 3 side of each blade 2. As described above, it is preferable that the thickness of blade 2 is set within 0.6-1mm though the thickness of each blade 2 is not limited thereto.
Analysis results of the relationship between Specific Noise [dB(A)] and Fan Efficiency [%] as to Number of Blades Z of blade 2 are shown in Fig. 3 and Table 1. Specific Noise [dB(A)] is calculated with the following formula. $Specific Noise = L_{A} - 10 \log (QP) (^{2}) + 20$

Here,

L_A:: Noise level [dB(A)]
Q:: Quantity of airflow (m³/h)
P:: Total pressure of Fan (Pa).

As shown in Fig. 3, Number of Blades Z of blades 2 is set within an appropriate range of 30-55 concerning Specific Noise. It is more preferable to set it within 33 ≤ Z ≤ 50, and is further preferable to set it within 35 ≤ Z ≤ 45. In a case where Number of Blades Z of blade 2 is less than the above-described appropriate range, the airflow between blades cannot reattach, so that the shear flow is greatly fluctuated as increasing noises as shown in Fig. 4(A). In a case where Number of Blades Z of blade 2 is more than the above-described appropriate range, the narrow gap makes the outflow higher so as to generate high noise even though the airflow between blades can reattach as shown in Fig. 4(C). When Number of Blades Z of blade 2 is set within the above-described appropriate range, the airflow between blades can reattach, so that appropriate suppression of flow rate between blades makes it possible to achieve the low noise generation as shown in Fig. 4(B). In addition, the fan efficiency level becomes desirable. Those phenomena are shown in Table 1.

[Table 1]

Number of Blades	Less	Optimum	More
Phenomena	Reattaching isn't achieved. The shear flow is greatly fluctuated as increasing noises and decreasing the fan efficiency.	Reattaching is achieved. Suppression of the flow rate between blades makes it possible to achieve the low noise generation and the high efficiency.	Though reattaching is performed, the narrow gap makes the flow rate of the outflow higher so as to generate high noise.

In the present invention, Inner/Outer Diameter Ratio, which is defined by D1/D2, is set within the appropriate range of 0.72-0.86 as shown in Fig. 5. It is more preferable to set it within the range of 0.76 ≤ D1/D2 ≤ 0.85, and is further preferable to set it within the range of 0.8 ≤ D1/D2 ≤ 0.84. Further, the Inner/Outer Diameter Ratio D1/D2 is set within the above-described appropriate range of 0.72-0.86 as considering the fan efficiency. In a case where Inner/Outer Diameter Ratio D1/D2 is greater than the above-described appropriate range, the airflow between blades cannot reattach, so that the shear flow is greatly fluctuated as increasing noises and decreasing the fan efficiency as shown in Fig. 6(A). In a case where Inner/Outer Diameter Ratio D1/D2 is smaller than the above-described appropriate range, D1 becomes smaller to increase the flow rate of the inflow so as to increase the noise level though the airflow between blades can reattach as shown in Fig. 6(C). In addition, because the blade length becomes longer so as to increase the friction loss, so that the fan efficiency is decreased. When Inner/Outer Diameter Ratio D1/D2 is set within the above-described appropriate range, the airflow between blades can reattach, so that appropriate suppression of flow rate between blades makes it possible to achieve the low noise generation as shown in Fig. 6(B). In addition, the fan efficiency becomes within a desirable range. Those phenomena are shown in Table 2.

[Table 2]

Inner/Outer Diameter Ratio	Greater	Optimum	Smaller
Phenomena	Reattaching isn't achieved. The shear flow is greatly fluctuated as increasing noises and decreasing the fan efficiency.	Reattaching is achieved. Suppression of the flow rate between blades makes it possible to achieve the low noise generation and the high efficiency.	- Though reattaching is performed, smaller D1 makes the flow rate of the inflow higher so as to generate high noise.
			- Longer blades make the friction loss greater so as to decrease the fan efficiency.

As shown in Fig. 7, Angle of Inclination α (deg) of the blade is set within the appropriate range of 15-48 deg, where the α is defined as an angle between a line, which is drawn from one end of each blade at the inscribed circle side to the other end at the circumscribed circle side, and another line, which is drawn radially from the other end at the inscribed circle side. It is more preferable to set it within the range of 20 ≤ α ≤ 42, and is further preferable to set it within the range of 25 ≤ α ≤ 35. In a case where Angle of Inclination α is greater than the above-described appropriate range, the narrow gap between the blades makes the flow rate of the outflow higher so as to generate high noise even though the airflow between blades can reattach as shown in Fig. 8(A). In a case where Angle of Inclination α is smaller than the above-described appropriate range, the airflow between blades cannot reattach, so that the shear flow is greatly fluctuated so as to generate high noise as shown in Fig. 8(C). When Angle of Inclination α is set within the above-described appropriate range, the airflow between blades can reattach, so that appropriate suppression of flow rate between blades makes it possible to achieve the low noise generation as shown in Fig. 8(B). In addition, the fan efficiency becomes desirable. Those phenomena are shown in Table 3.

[Table 3]

Angle of Inclination	Greater	Optimum	Smaller
Phenomena	Though reattaching is performed, the narrow gap makes the flow rate of the outflow higher so as to generate high noise.	Reattaching is achieved. Suppression of the flow rate between blades makes it possible to achieve the low noise generation and the high efficiency.	Reattaching isn't achieved.
			The shear flow is greatly fluctuated as increasing noises and decreasing the fan efficiency.

As shown in Fig. 9, Tongue Clearance Ratio defined as a ratio S/D2, where S is a clearance between circumscribed circle 4 of tongue 12 and casing 11 and where D2 is a diameter of circumscribed circle 4, is set within the appropriate range of 0.09-0.15. In a case where Tongue Clearance Ratio is smaller than the above-described appropriate range, dissonant NZ-Noise, which is generated when the outflow from the blade interferes at the tongue, significantly increases. In a case where Tongue Clearance is greater than the above-described appropriate range, the size of the casing outline becomes excessive like casing 11a shown in Fig. 10. When Tongue Clearance is set within the above-described appropriate range, a casing with an appropriate size can suppress the NZ-Noise generation, so as to achieve a low noise condition.
Thus in the present invention, parameters, such as Number of Blades Z, Inner/Outer Diameter Ratio D1/D2, Angle of Inclination α (deg) of the blade and Tongue Clearance Ratio S/D2, are set within the above-described appropriate range, so that the low noise is surely achieved with a casing having an appropriate size, as maintaining the high fan efficiency.
Further, in the present invention, it is preferable to set other parameters, specifically blade Exit Angle β2 (deg) and blade Entrance Angle β1 (deg), as well as Number of Blades Z, Inner/Outer Diameter Ratio D1/D2, Angle of Inclination α (deg) of the blade and Tongue Clearance Ratio S/D2, within appropriate ranges, so as to surely achieve low noise thereby.
As shown in Fig. 11, Exit Angle β2 (deg) of the blade is preferably set within the range of 148 ≤ β2 ≤ 175, and is more preferably set within the range of 152 ≤ β2 ≤ 170, and is further preferably set within the range of 155 ≤ β 2 ≤ 165. In a case where Exit Angle β2 is greater than the above-described appropriate range, the narrow gap of the blades makes the outflow higher so as to generate high noise even though the airflow between blades can reattach as shown in Fig. 12(A). In a case where Exit Angle β2 is smaller than the above-described appropriate range, the airflow between blades cannot reattach, so that the shear flow is greatly fluctuated as shown in Fig. 12(C). When Exit Angle β2 is set within the above-described appropriate range, the airflow between blades can reattach, so that appropriate suppression of flow rate between blades makes it possible to achieve the low noise generation as shown in Fig. 12(B). In addition, the fan efficiency becomes desirable. Those phenomena are shown in Table 4.

[Table 4]

Exit Angle	Greater	Optimum	Smaller
Phenomena	Though reattaching is performed, the narrow gap makes the flow rate of the outflow higher so as to generate high noise.	Reattaching is achieved. Suppression of the flow rate between blades makes it possible to achieve the low noise generation.	Reattaching wasn't achieved. The shear flow is greatly fluctuated as increasing noises and decreasing the fan efficiency.

As shown in Fig. 13, Entrance Angle β1 (deg) of the blade is preferably set within the range of 50 ≤ β1 ≤ 90, and is more preferably set within the range of 55 ≤ β1 ≤ 85, and is further preferably set within the range of 60 ≤ β1 ≤ 80. In a case where Entrance Angle β1 is greater than the above-described appropriate range, the great difference between the inflow angle and the entrance angle increases an anterior burble, so as to generate higher noise as shown in Fig. 14(A). In a case where Entrance Angle β1 is smaller than the above-described appropriate range, too much turning from the inflow into the blades to the outflow from them causes higher noise as shown in Fig. 14(C) as well. When Entrance Angle β1 is set within the above-described appropriate range, the smooth turning from the inflow into the blades to the outflow from them makes it possible to achieve the low noise generation as shown in Fig. 14(B). In addition, the fan efficiency becomes desirable. Those phenomena are shown in Table 5.

[Table 5]

Entrance Angle	Greater	Optimum	Smaller
Phenomena	Great difference between the inflow angle and the entrance angle increases an anterior barble.	Smooth turning to the inflow into blades and the outflow from them makes it possible to achieve the low noise generation and the high efficiency.	Too much turning to the inflow into blades and the outflow from them causes higher noise.

Thus, when even Exit Angle β2 and Entrance Angle β1 of the blade are optimized, the airflow condition between the blades can be more surely controlled optimally, so as to achieve desirable lower noise more surely.

Industrial Applications of the Invention

The structure of the multi-blade fan for a centrifugal blower according to the present invention is suitable for a blower used in an air conditioning system for vehicles, which strongly demands low noise generation.

Explanation of symbols

1: multi-blade fan
2: blade
3: inscribed circle of blade
4: circumscribed circle of blade
5, 6: line for determining angle of inclination
7: tangent line of circumscribed circle
8: tangent line of blade
9: tangent line of inscribed circle
10: tangent line of blade
11, 11a: casing
12: tongue
S: tongue clearance
α: angle of inclination
β1: entrance angle
β2: exit angle

Claims

A multi-blade fan for a centrifugal blower having a plurality of annularly-disposed blades, characterized in that:
at least, number of blades Z, an inner/outer diameter ratio defined as a ratio D1/D2 of a diameter D1 of an inscribed circle of the blades to a diameter D2 of a circumscribed circle of the blades, an angle of inclination α (deg) of each blade defined as an angle between a line which connects a position of the blade on the inscribed circle to a position thereof on the circumscribed circle, and a line extending radially from a center of the inscribed circle and passing through the position on the inscribed circle, and a tongue clearance ratio defined as a ratio S/D2 between the tongue clearance S and the diameter D2 of the circumscribed circle are all within following ranges.

30 ≤ Z ≤ 55

0.72 ≤ D1/D2 ≤ 0.86

15 ≤ α ≤ 48

0.09 ≤ S/D2 ≤ 0.15
The multi-blade fan for a centrifugal blower according to claim 1, wherein an exit angle β2 (deg) of the blade, which is defined as an angle between a tangent line of the circumscribed circle and a tangent line of the blade at a position of each blade on the circumscribed circle, is within 148 ≤ β2 ≤ 175.
The multi-blade fan for a centrifugal blower according to claim 1, wherein an entrance angle β1 (deg) of the blade, which is defined as an angle between a tangent line of the inscribed circle and a tangent line of the blade at a position of each blade on the inscribed circle, is within a range of 50 ≤β1 ≤ 90.
The multi-blade fan for a centrifugal blower according to claim 1, wherein a thickness of each blade is within a range of 0.6 - 1 mm.
The multi-blade fan for a centrifugal blower according to claim 1, wherein the centrifugal blower is a blower of an air conditioning system for vehicles.