JPH0226079B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to an axial flow fan used in ventilation fans, air conditioners, etc., and particularly relates to an axial flow fan that makes it possible to minimize aerodynamic noise. be.

[Conventional technology]

Axial flow fans are widely used in air conditioners and ventilation fans, and it is socially important to reduce the noise generated by the fans as much as possible. However, there is no established method for reducing noise from axial fans that minimizes the noise generated by axial fans without degrading the fan's aerodynamic performance. Noise reduction methods were used.

Among them, as a method for reducing the noise of an axial flow fan, there is an example published in Japanese Patent Application Laid-Open No. 1983-92510, which attempts to reduce noise through the relationship between the axial flow impeller and the casing. Figure 19 is Japanese Patent Application Publication No. 1973-
FIG. 9 is a side view showing the relationship between the axial flow impeller and the casing in Publication No. 92510. In the figure, 1 is a battledore-shaped impeller, 2 is the boss of the impeller, 3 is the rotation axis of the impeller, 7 is the air flow flowing into the impeller 1, 1
0 is a casing where the radius of curvature of the suction port is 0 or an extremely small value, B _R is a casing of 10
, D _B is the inner diameter of the casing 10 , and D _T is the outer diameter of the impeller 1 . Furthermore, Z
is the distance from the leading edge of blade 1 to casing 10,
C is the length of the blade 1 in the axial direction.

Next, the operation will be explained.

In the conventional example, when the radius of curvature B _R of the suction port of the casing 10 is extremely small, the front edge of the impeller 1 is moved from the front surface of the casing 10 to the suction side to reduce noise. Since the radius of curvature B _R of the suction port is extremely small, the air flow 7 separates at the inlet and a very turbulent flow occurs downstream.
When the impeller 1 is rotated in a turbulent flow, noise increases due to interference with the turbulence. Therefore, it was thought that if the impeller 1 was moved to the suction side, the area of the impeller 1 rotating in the turbulent flow would be reduced, and the noise could be reduced.

FIGS. 20a and 20b show the relationship between the flow rate coefficient, power level (PWL: dB), and total pressure coefficient according to the conventional example.
In the figure, the △ mark indicates Z/C=-0.46, and the □ mark indicates Z/C=-0.46.
C=-0.18, + mark is Z/C=0.4, × mark is Z/C=
The value at 0.67 is shown, and the circle mark indicates the value when the impeller is not moved to the suction side and the bell mouth is placed on the suction side. The noise level certainly decreases as Z/C increases. Further, the relationship between the power level and the flow rate coefficient tends to increase monotonically from the open operating point to the closed operating point, similar to a general axial flow fan. On the other hand, looking at the relationship between the flow rate coefficient and the total pressure coefficient (Fig. 20b), in the case of a fan in which the impeller 1 is moved to the suction side of the casing 10, it is not moved and has a bell mouth (marked with a circle). The total pressure rise is smaller compared to Therefore, in order to compare aerodynamic performance and noise performance at the same time,
Evaluate based on the specific noise level, which is the noise level per unit air volume and unit pressure. When evaluated in terms of specific noise level, a fan in which the impeller 1 is moved to the suction side of the linear casing has a higher specific noise level than a fan having a bell mouth and completely inserted into the casing.

[Problem to be solved by the invention]

Since the conventional axial flow fan was configured as described above, it was not possible to reduce the specific noise level simply by moving the impeller to the suction side. Furthermore, there were other problems such as the inability to determine the optimal casing shape to best reduce the specific noise level in accordance with the shape of the low-noise impeller.

This invention and another invention of this invention have been made to solve the above-mentioned problems, and provide an axial flow fan that can significantly reduce the specific noise level in the operating range from the open operating point to the surging operating point. The purpose is to obtain.

[Means for Solving the Problems] The axial flow fan according to the present invention has a blade leading edge and a blade trailing edge in a cross section when the impeller is cut along a cylindrical surface with a radius R centered on the rotation axis. The chord line center point P _R , which is the midpoint, and the chord line center point P _b in the cross section when cut through the cylindrical surface of the blade boss radius R _b
, and the distance from the plane S _c perpendicular to the axis of rotation is l _s
Then, in a coordinate system with the suction side of the airflow in the positive direction, the chord line center point P _R is always located in the positive direction with respect to the above S _c plane, and δ _z = tan ^-1 l _s /R- Let the value of δ _z that can be expressed by R _b be δ _z = 12.5° to 32.5°, and in the projection plane when the impeller is projected onto a plane orthogonal to the rotation axis, the cylindrical surface of the blade boss radius R _b In a coordinate system, the center point of the chord line in the cross section when cut at is P _b ', the axis of rotation is the origin O, and the straight line connecting point O and P _b ' is the X axis. When the center point of the chord line when cut on the cylindrical surface is P _R ′, and the angle between the straight line P _R ′-O and the X axis is δ〓, the radial distribution of δ〓 is δ〓＝δ〓 _t ×R−R _b /R _t −R _b (R _t : Blade outer radius, R _b : Blade boss radius,
δ〓 _t : Angle between the straight line _{P t} ′-O and _the Connect to the straight part l _{and d} ,
In a suction bell mouth that has an inner diameter D _B with respect to the outer diameter D _T of the blade, when the distance between the trailing edge on the outer periphery of the blade and the end of the duct is l _x , B _R = 0.07D _T ~
0.2D _T , _ld = 0.04D _T ~ 0.1D _T , D _B = 1.01D _T ~ 1.04D _T ,
It is characterized in that l _x =0 to 0.04D _T.

Further, in an axial flow fan according to another aspect of the present invention, the midpoint between the leading edge of the blade and the trailing edge of the blade in a cross section when the impeller is cut along a cylindrical surface with a radius R centered on the rotation axis. The distance between a certain chord line center point P _R and a plane S _c that passes through the chord line center point P b in the cross section taken by the cylindrical surface of the blade boss radius R _b and is orthogonal to _the axis of rotation is l. When _s is the center point of the chord line in the coordinate system with the suction side of the airflow in the positive direction.
P _R is always located in the positive direction with respect to the S _c plane, and δ _z =
When the value of δ _z that can be expressed as tan ^-1 l _s / R - R _b is set to δ _z = 12.5° to 32.5°, and the impeller is projected on a plane orthogonal to the rotation axis, the impeller is Let P _b ' be the center point of the chord line in the cross section when cut at the cylindrical surface with radius R _b of the boss part, and let the axis of rotation be the origin O,
A coordinate system with the straight line connecting point O and point P _b ′ as the X axis,
When the impeller is cut by a cylindrical surface with radius R, the center point of the chord line is P _R ′, and the angle between the straight line P _R ′-O and the X axis is δ〓, then the radial distribution of δ〓 is δ〓＝δ〓 _t ×R−R _b /R _t −R _b (R _t : Blade outer circumferential radius, R _b : Blade boss radius,
δ〓 _t : Angle between the straight line P _t ′ _-O and the In the developed view obtained by developing the blade on a plane, if the shape of the warp line in the cross section of the blade is an arc shape, and the central angle for forming the arc is the warp angle θ, then the radial distribution of θ is as follows: θ= (θ _t −θ _b )×R−R _b /R _t −R _b +θ _b (θ _t : Warp angle at the blade outer circumference, θ _b : Warp angle at the blade boss), θ _t = 20° ~ 30°, θ _b =
27° to 37°, θ _t < θ _b , and in the developed view, when the angle between the chord line of the blade and a straight line parallel to the axis of rotation and passing through the leading edge of the blade is the stagger angle ξ, the radius of ξ The directional distribution is given by ξ = (ξ _t − _{ξ b} ) × R − R _b / R _t − _{R b} + ξ _b (ξ _t : stagger angle at the blade outer periphery, ξ _b : stagger angle at the blade boss part), and ξ _t =62゜〜
72°, ξ _b = 53° to 63°, ξ _t > ξ _b , and has a plane perpendicular to the rotation axis, from which it is narrowed down by a curved surface with radius B _R and connected to the straight part l _d , In a suction bell mouth having an inner diameter D _B with respect to the outer diameter D _T of the blade,
When the distance between the rear edge of the impeller and the end of the duct is l _x , B _R = 0.07D _T ~ 0.2D _T , l _d =
0.04D _T ~0.1D _T , D _B =1.01D _T ~1.04D _T , l _x =0~
It is characterized by having a diameter of 0.04D _T.

[Effect]

The impeller in this invention has a shape in which the center point of the chord line is inclined forward toward the gas suction side and moved forward in the rotation direction, and furthermore, the inlet curvature radius of the suction bell mouth with respect to the impeller is By optimizing the length, inner diameter, and length of the straight duct to cover the blade tip of the impeller, the specific noise level can be significantly reduced in the operating range from the open operating point to the surging operating point.

Moreover, the impeller in another invention of this invention is
The center point of the chord line is tilted forward toward the gas suction side, and at the same time is moved forward in the direction of rotation, and the shape is further optimized with the warp angle and stagger angle. In contrast, we have optimized the inlet radius of curvature of the suction bell mouth, the length and inner diameter of the straight duct, and the length that covers the blade tip of the impeller, thereby reducing the specific noise level in the operating range from the opening operating point to the surging operating point. can be significantly reduced.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing an impeller and a suction casing of an axial fan according to an embodiment of the present invention.
For example, the blade has a three-blade shape, and the operation description will mainly be given for the case of one blade, but the same applies to other blades. In the figure, 1 is an impeller with a three-dimensional shape, 2 is an impeller 1
3 is the rotation axis of the impeller 1, 4 is the rotation direction of the impeller 1, 10 is the bell mouth main body, and 10a is the bell mouth 1 perpendicular to the rotation axis 3.
0 is the suction plane, 10b is the R portion having the radius of curvature of the inlet of the bell mouth 10, and 10c is the straight duct portion of the bell mouth 10. That is, the bell mouth 10 has a shape constricted from the suction plane 10a by the R portion 10b to form a straight duct portion 10c.

FIG. 2 is a sectional view showing the relative positional relationship between the impeller 1 and the bell mouth 10. In the figure, 7 is the air flow, B _R is the radius of curvature of the inlet R portion 10b of the bell mouth 10, D _B is the inner diameter of the bell mouth 10, D _T is the outer diameter of the impeller 1, and l _d is the straight line of the bell mouth 10. The length of the duct 10c, _lx , is the distance from the terminal end of the straight duct 10c to the rear edge of the outer periphery of the impeller 1.

Figure 3 is a projection view of the blade 1 projected onto a plane perpendicular to the rotation axis 3, where 1' is the blade on the projection plane;
1a' is the tip of the blade, 1b' is the leading edge of the blade, 1c' is the trailing edge of the blade, 1d' is the outer periphery of the blade, 2 is the boss, and 3 is the rotating shaft. Arc 1b _R ′ in the projection plane when blade 1′ is cut by the plane
−P _R ′−1C _R ′ is the blade cross-sectional shape. here,
P _R ′ is the midpoint of the arc 1b _R ′−1C _R ′, and is the center point of the chord line in the projection plane. In order to clarify the position of P _R ′ on the projection plane, when the impeller is cut on a cylindrical surface with boss radius R _b , the center point of the chord line of the boss section on the projection plane is defined as P _b ′, and the rotation axis 3 _O
Create a coordinate system with the origin at the projection plane. P _t ′ is the chord line center point at the outer circumference 1d′ of the blade at the outer circumferential radius R _t , and P〓′ is the chord line center point locus P _b ′−P _R ′− at the chord line center point P _R ′. The angle between the tangent to P _t ' and the radius R is shown. Further, symbols with a dash (') indicate each portion on the projection plane. In the above coordinate system, if the angle between the straight line P _R ′-O and the X-axis is δ and the distance is R, then the position of P _R ′ is (R,
It can be expressed in a polar coordinate system called δ〓). _In this example _, if the angle _between the straight line P _t ′ _-O and _{the t} : Blade outer radius, R _b : Blade boss radius,
δ〓 _t : Angle between the straight line P _t ′-O and the X axis), δ〓 _t
= 40° to 50°. In this way, since the position of the chord line center point P _R has been defined on the plane perpendicular to the rotating shaft 3, the axial position will be defined next.

Figure 4 shows the center point of the boss chord line in Figure 3.
Regarding the radial trajectory P _b ′−P _R ′−P _t ′ from P _b ′ to the outer chord center point P _t ′, the chord center point P _R at an arbitrary radius R is expressed as the plane OX plane. 2 shows the radial distribution of the chord line center point P _R rotated and projected with a radius R, and the cross section of the impeller 1 at the same position. In the figure, 5a is the suction surface of the impeller 1, 5b is the pressure surface of the impeller 1, 9 is the centrifugal force generated when the impeller 1 rotates, and 9a and 9b are the normal direction of the suction surface of the centrifugal force 9. Force, tangential component force, 27 indicates a blade tip vortex generated on the outer circumference 1d of the blade, and arrow A indicates the direction of gas inflow. Therefore, passing through the center point P _b of the chord line in the cross section when cut on the cylindrical surface of the boss radius R _b ,
Consider a plane S _c that is orthogonal to the rotation axis 3. When the center point of the chord line at an arbitrary radius R is P _R , the distance between the S _c plane and the point P _R is l _s , and the center point of the chord line of the boss part P _b and S _c
Let the angle formed by the plane be δ _z . In a coordinate system with the suction side of airflow A in the positive direction, the chord line center point P _R
is always positioned in the positive direction with respect to the S _c plane, and δ _z =12.5° to 32.5°, which can be expressed as δ _z =tan ⁻¹ l _s /R−R _b . By determining l _s or δ _z in this way and giving the radius R, the axial position of the chord line center point P _R can be defined.

When an impeller is configured with the above values of δ〓 and _δz , its chord line center point will be inclined forward toward the gas suction side within the range of _δz , and will move forward in the rotational direction within the range of δ〓. It becomes a shape.

Furthermore, in this embodiment, the blade cross section is warped, and the entire blade surface is configured to be a smooth curved surface.

Figure 5 shows that when the blade surface is formed with the chord line center point P _R as the relative origin, the impeller 1 has a radius R.
A developed view obtained by cutting the cross section along a cylindrical surface and developing the cross section on a two-dimensional plane is shown. Sled wire 5 of impeller 1
Let be a circular arc, the warp angle which is the central angle for forming the circular arc be θ, and the radius forming the circular arc be RR. In this embodiment, the radial distribution of θ is set as θ=(θ _t −θ _b )×(R−R _b )/(R _t −R _b )+θ _b . θ _t is the warp angle at the blade outer periphery, that is, the central angle of the warp line at the blade outer periphery, θ _b is the warp angle at the blade boss, that is, the central angle of the warp line at the blade boss, and θ _t = 20゜~30゜, θ _b =27゜~37゜, θ
_t <
It is assumed that θ _b .

The mounting position of the blade is based on its chord line 1b-1c,
The angle formed by the straight line 6 parallel to the rotating shaft 3 and passing through the front edge 1b is defined as the stagger angle ξ, and is determined by giving ξ a distribution in the radial direction. L is the chord length. Therefore, the radial distribution of ξ is set as ξ=(ξ _t −ξ _b )×(R−R _b )/(R _t −R _b )+ξ _b . At this time, ξ _t is the stagger angle at the blade outer circumference, ξ _b is the stagger angle at the blade boss, and
ξ _t = 62° to 72°, ξ _b = 53° to 63°, and ξ _t > ξ _b .

Next, the relationship between the noise reduction mechanism of the impeller according to this embodiment and the bell mouth that enhances the effect will be explained.

FIG. 6 is a characteristic curve showing the influence of the forward inclination angle _δz of the chord center line in the suction direction on air blowing and noise. Here, the chord line center line is a curved line that connects the chord line center points _PR . In the figure, the horizontal axis is the flow coefficient (φ), the vertical axis is the total pressure coefficient (φ), and the noise (hon).
This is a characteristic curve when the forward inclination angle δ _z is changed from −22.5° to 45°. As the anteversion angle δ _z increases, the total pressure coefficient φ increases and reaches its maximum when δ _z =22.5°. On the other hand, the surging operating point (near φ = 0.25°: the point where the curve of the total pressure coefficient φ becomes a downward-sloping curve to the left with respect to the flow coefficient φ) becomes more open operating point (φ = 0.35°) as the forward inclination angle δ _z increases. (near) side, which tends to narrow the effective operating area (from the opening operating point to the surging operating point).

Looking at the noise performance, the noise level decreases as the forward inclination angle δ _z increases on the side of the opening operation point from the surging operation point. A blade with δ _z of −22.5° at the open operating point (marked ▽ in the figure) and a blade with δ z of 45° (marked ◇ in the figure)
Compared to , the 45° blade is approximately 9 dB(A) lower. However, as the flow rate decreases and the total pressure increases, the noise level of the 45° blade increases rapidly at the point where the flow coefficient φ is 0.3. Furthermore, since this sudden noise increase point is located much closer to the open operating point than the surging operating point (φ=0.24), the effective operating range is narrowed. On the other hand,
When the forward inclination angle δ _z is decreased, although the noise level at the opening operating point increases, the point of sudden noise increase tends to move toward the closing point. That is, forward inclination of the chord center line toward the suction side reduces noise, but it also has the effect of narrowing the effective operating area.

The reason why noise is reduced by tilting the chord center line forward toward the suction side is considered to be as follows.
As shown in FIG. 4, the centrifugal force due to the flow on the blade surface passing along the blade surface 5a while drawing an arcuate trajectory acts largely on the negative pressure surface of the impeller 1. A component force 9a of the centrifugal force 9 in the direction normal to the suction surface acts as a large compressive force on the boundary layer developed on the suction surface 5a, making the boundary layer extremely thin. Since the aerodynamic noise generated from the negative pressure surface 5a increases in proportion to the thickness of the boundary layer, if the boundary layer becomes thinner due to the component force 9a, the generated noise can be reduced by that amount.

Furthermore, the following noise reduction mechanism also exists. FIG. 7 is a side view of the rotating impeller 1 seen from the side. In the figure, B and C are points where the chord center line 21 intersects with the blade outer circumference 1d and the blade span center. The chord line center line 21 is a curved line that connects the chord line center points _PR . The pressure on the suction surface of the blade 1 decreases the most at points B and C in the blade outer circumference 1d and the blade span center, respectively. Due to the forward inclination of the chord center line 21 toward the suction side, point B is located on the suction side from point C. Therefore, the static pressure on the negative pressure surface is lower on the suction side at the blade outer circumferential portion 1d where point B is located than at the center portion of the blade span where point C is located. Therefore, the streamlines 22 on the suction surface are inclined in the radial direction when passing through the blades,
A radial velocity component V _r is induced on the suction surface.
In the relative flow field, the radial velocity component generates a Coriolis force F _c . Figure 8 shows the radial velocity V _r 23 and the Coriolis force on the suction surface of the impeller 1.
F _c 24 = 2V _r ω, which shows the relationship between normal component force F _c ⊥25 to the negative pressure surface of Coriolis F _c . In the figure, arrow D indicates the rotation direction of the impeller 1. Here, ω is the angular velocity of the impeller 1. Coriolika F _c on the suction surface
pressure gradient towards the suction surface to counteract ⊥
PA26 occurs. Due to this PA26, the boundary layer on the negative pressure surface delays the transition from laminar flow to turbulent flow, and the laminar flow state continues up to the blade trailing edge 1c. As a result, the broadband noise (turbulence noise) generated when the turbulent boundary layer passes the trailing edge is extremely reduced and almost no longer occurs. To summarize the above, by tilting the chord center line 21 forward toward the suction side, Coriolika is generated in the normal direction of the suction surface, and Coriolika suppresses the development of a turbulent boundary layer, resulting in trailing edge noise. Turbulent noise is reduced.

Next, it will be explained that a new problem arises when the chord center line 21 is tilted forward toward the suction side. By tilting the chord line center line 21 forward toward the suction side, the flow in the radial direction on the suction surface increases, and as a result, the amount of blade tip vortices 27 generated when the flow is lost from the blade outer circumference 1d also increases. To increase. As shown in FIG. 9, as the amount of the blade tip vortex 27 increases, the point 28 where the vortex separates from the blade outer circumference 1d gradually moves from the trailing edge 1c to the leading edge 1b. As the flow rate decreases and the static pressure increases, the radial flow increases more and more to balance the pressure, and the separation point 28 moves further toward the leading edge 1b. Separation point 2 of wing tip vortex
8 moves toward the leading edge 1b, the tip vortex 2
7 moves away from the suction surface of the blade trailing edge 1c, interferes with the bell mouth 10, is stretched in the rotational direction, and finally interferes with the adjacent blade. Since the blade tip vortex 27 is highly turbulent, large pressure fluctuations occur on the pressure surface of the adjacent blade with which the blade tip vortex collides, resulting in a sudden increase in low frequency noise. Therefore, if the chord line centerline 21 is tilted forward toward the suction side, the noise near the opening operating point will be reduced, but the separation point of the blade tip vortex 27 will tend to move to the leading edge 1b, resulting in a decrease in flow rate. This has the disadvantage that interference between the blade tip vortex 27 and the adjacent blades begins closer to the open operating point, and noise tends to increase rapidly. Therefore, if this drawback can be eliminated, the chord line center line 21 of the impeller 1 can be given a forward inclination angle δ _z in the suction direction, thereby significantly reducing noise.

In order to prevent the blade tip vortex 27 from interfering with the adjacent blades as much as possible when the flow rate decreases, the amount of vortices flowing away from the outer periphery of the blade should be reduced. Therefore,
In this embodiment, the chord line center line 21 is advanced in the rotational direction within a range of δ〓. As shown in FIG. 10a, when the chord line center line 21 is advanced in the rotational direction, only part a of the flow that enters from the front edge 1b of the impeller flows out from the outer circumference 1d of the blade as a vortex. As a result, most of the flow flowing in from the leading edge 1b flows out from the trailing edge 1c. On the contrary, the 10th
As shown in Figure b, in the impeller 1 where the chord line center line 21 does not move forward in the rotational direction, the flow from a', which is the majority of the flow that entered the blade from the leading edge 1b, flows to the blade outer circumference 1d. flows out from. From the figure, since a′≫a, in the impeller 1 without the advance angle δ〓, the blade tip vortex 2
7 increases, and interference with adjacent blades occurs closer to the open operating point. Therefore, when the advancing angle δ in the rotational direction is given to the chord line center line 21, the amount of the blade tip vortex 27 flowing out from the blade outer circumferential portion 1d is reduced, and the operating point where the noise rapidly increases is moved closer to the shut-off side. Can be moved.

FIG. 11 shows the relationship between the advance angle δ of the chord line center line 21 at the blade outer peripheral portion 1d, and the flow coefficient φ and pressure coefficient ψ at the operating point where the noise rapidly increases as the air volume decreases. From the figure, it can be seen that as the advance angle δ becomes larger, the point of sharp increase in noise moves to the low air volume and high static pressure side, and the effective operating area expands. Furthermore, the movement effect is large from 15° to 45°, and tends to saturate when δ exceeds 45°.

The effect of tilting the chord center line 21 of the impeller 1 forward in the suction direction within the range of δ〓 and moving it forward in the direction of the range of δ〓 has been described above. Next, the shape of the bell mouth 10 for maximizing these effects will be explained.

As mentioned above, the impeller 1 in this embodiment is
The generation of a strong radial flow 23 on the suction surface 5a of the blade suppresses the transition of the boundary layer to turbulence. In order to exhibit this effect, the chord line centerline 21 of the impeller 1 is tilted forward toward the suction side. In order to further enhance this effect, the second
The shape of the bell mouth 10 in the figure is important.
When the impeller 1 is rotated in the bell mouth 10 where there is no straight duct 10c covering the impeller 1, there is no boundary around the impeller 1, so the centrifugal force due to the swirling flow generated between the blades is opposed. Strong static pressure gradients that would otherwise occur do not occur. Therefore, the influence of centrifugal force due to the swirling flow strongly acts on the flow between the blades, and the flow between the blades has a radial velocity. As a result, the effect of tilting the chord center line 21 forward toward the suction side, that is, the effect of generating a radial flow on the suction surface 5a of the impeller 1, can be increased, and turbulence noise can be significantly reduced. be able to. Impeller 1
A similar phenomenon occurs even when the gap between the outer peripheral portion 1d and the straight duct 10c is wide.

On the other hand, if there is a bell mouth 10 outside the impeller 1 that has a straight duct 10c with a length l _d that covers the entire impeller 1, a boundary wall against static pressure exists around the impeller 1. Therefore, in order to counteract the centrifugal force due to the swirling flow, a pressure gradient is generated in the counterradial direction within the straight duct 10c. This pressure gradient makes it difficult for the flow between the blades to move in the radial direction, and even if the chord line centerline 21 is tilted forward toward the suction side, it becomes difficult to generate a strong radial flow. As a result, the transition of the boundary layer to turbulence progresses and turbulence noise increases.

Therefore, the effect of reducing turbulence noise by tilting the chord center line 21 forward toward the suction side is
It is increased by shortening the length l _d of the straight duct 10c covering the duct, and decreased by lengthening it.
Furthermore, when the gap between the impeller 1 and the straight duct 10c is wide, the forward tilting effect of the chord center line is further enhanced.

The effect of advancing the chord line centerline 21 in the rotational direction is to reduce the amount of flow that flows out from the blade outer circumferential portion 1d as a blade tip vortex 27 among the flow that flows in from the leading edge portion 1b, and to The aim is to move the operating point, where noise increases rapidly due to interference, closer to the cut-off point. On the other hand, on the outside of the outer peripheral portion 1d of the impeller 1, a leakage flow exists from the pressure surface 5b to the negative pressure surface 5a due to the pressure difference between the upper and lower surfaces of the blade, and this flow strengthens the blade tip vortex 27. The amount of leakage flow varies depending on the size of the gap between the outer peripheral portion 1d of the impeller 1 and the bell mouth 10. In particular, the gap between the outer circumference 1d and the straight duct 10c at the trailing edge 1c, where the pressure difference between the upper and lower surfaces of the impeller 1 is large, has a strong influence on this phenomenon. A straight duct 1 that covers the outer circumference 1d at the rear edge 1c of the impeller 1
When the length l _d of 0c is short or when the gap between the outer circumferential portion 1d and the straight duct 10c is wide, the amount of leakage flow increases and the strength of the blade tip vortex 27 increases. Furthermore, since the leakage flow has the effect of blowing the blade tip vortex 27 toward the adjacent blade, interference between the blade tip vortex 27 and the adjacent blade starts from the open operating point side. That is, if the length l _d of the straight duct 10c is shortened or the gap between the impeller 1 and the straight duct 10c is widened, the effect of advancing the chord center line 21 in the rotational direction (noise increases rapidly) moving the operating point closer to the cutoff point).

The effects of the forward inclination of the chord line center line 21 in the suction direction and the forward movement in the rotation direction, and the bell mouth 10
The relationship can be summarized as follows. By shortening the straight duct 10c of the bell mouth 10 or widening the gap between the outer periphery 1d of the impeller and the straight duct 10c, the effect of tilting the chord center line 21 forward in the suction direction is enhanced and turbulent noise is reduced. Decrease level.
However, the effect of advancing the chord center line 21 in the rotational direction is reduced, and the operating point at which the noise rapidly increases moves toward the open point, narrowing the effective operating area.

On the other hand, if the straight duct 10c of the bell mouth 10 is lengthened or the gap between the outer circumference 1d of the blade and the straight duct 10c is narrowed, the effect of advancing the chord center line 21 in the rotational direction will be enhanced, and the noise will suddenly increase. Although the increasing operating point moves toward the cut-off point and the effective operating region becomes wider, the effect of tilting the chord center line 21 forward in the suction direction decreases.

Therefore, in order to effectively exhibit the effect of tilting the chord center line forward in the suction direction or moving it forward in the rotation direction, the straight duct 10 of the bell mouth 10 must be
There is an optimum value for the length l _d of c and the distance between the outer circumferential portion 1d of the impeller and the straight duct 10c. FIG. 12 shows this relationship.

In the figure, the horizontal axis is l _d /D _T (length of straight duct/outer diameter of impeller), and the vertical axis is noise (hon).
The curve K _s is a specific noise level indicating the noise level per unit air volume and unit static pressure of the axial fan. K _s is defined as K _s = SPL−10LOG (Q×P _s ^2.5 ), where SPL is the noise level, Q is the flow rate, and P _s is the static pressure. From the figure, as the length _ld of the straight duct increases, the noise level SPL increases monotonically. On the other hand, as the straight duct length l _d increases, the operating point where the noise rapidly increases moves closer to the cut-off point, so the term Q x P _s ^2.5 increases, and the aerodynamic work of the fan changes into the amount of noise. The converted −10LOG (Q×P _s ^2.5 ) decreases almost monotonically. Therefore, the specific sound level K _s is the noise level SPL and the noise equivalent amount of aerodynamic work -
Since it is defined by the sum of 10 LOG (Q×P _s ^2.5 ), as shown in FIG. 12, with respect to the straight duct length l _d , it becomes a downwardly convex curve and an optimal range exists.

Therefore, specific effects regarding the embodiment will be explained. Below, the values for each part of a bellmouth shaped to lower the minimum specific noise level are shown.

B _R = 0.117D _T l _d = 0.0667D _T D _B = 1.017D _T l _x = 0 Here, B _R is the radius of curvature of the inlet R portion of the bell mouth 10, D _T is the outer diameter of the impeller 1, and l _d is the length of the straight duct 10c of the bell mouth 10, D _B is the inner diameter of the bell mouth 10, and l _x is the distance between the end of the straight duct 10c of the bell mouth 10 and the rear edge 1c on the outer periphery of the impeller 1. be.

When incorporating a fan into equipment, the shape of the bell mouth may have to be changed due to dimensional constraints, so the inlet curvature radius B _R of the bell mouth 10,
Characteristic tests were conducted by varying the straight duct length _ld . However, all other shapes were the same as those of the embodiment shown above.

FIG. 13 shows the results of determining the minimum specific noise level _Ks for B _R by varying the radius of curvature of the entrance of the bellmouth 10. From the figure, it can be seen that an axial flow fan with sufficiently low noise can be obtained if B _R =0.07D _T to 0.2D _T.

Figure 14 shows the straight duct 10c of the bell mouth 10.
This is the result of determining the relationship between the length l _d and the minimum specific noise level K _s . The optimal range of l _d is between 0.04D _T and 0.1D _T ,
It can be seen that within this range, a fan with sufficiently low noise can be obtained.

Regarding the inner diameter D _B of the bell mouth 10, it is advantageous to have it closer to the outer diameter D _T of the impeller 1 because the operating point where noise increases rapidly can be moved closer to the cutoff point.
In the case of a low-cost axial flow fan, D _B =1.01D _T is the limit from a manufacturing point of view. Furthermore, as D _B increases, the operating point at which the noise increases rapidly moves toward the open point, resulting in an increase in the specific noise level. In this case, the increase in specific noise level is about 3 phons.
D _B = 1.04D _T is the limit for increasing the diameter.

The end of the straight duct 10c and the outer periphery 1d of the impeller 1
The distance l _x from the trailing edge end 1c should basically be 0, but since the trailing edge position of the boss part 2 is located on the discharge side from the outer circumferential part, the impeller 1 is Even if the impeller 1 is moved to the suction side by l _x = 0.04D _T to avoid contact with internal parts, etc., there will be no significant change in performance, and it will become a low-noise axial flow fan. Become.

Next, when the bell mouth 10 is optimized for the impeller 1, the forward inclination angle δ _z of the chord center line 21 in the suction direction, which is a parameter that determines the shape of the impeller 1,
The optimum ranges of the advance angle δ〓 in the rotational direction, the blade warp angle θ, and the stagger angle ζ were determined. Note that when examining the influence of each parameter, the values of other parameters were set to basic values, and the basic parameter values of the impeller were set as follows.

δ _z = 22.5° (constant in the radial direction) δ = 45° x R-R _b /R _t -R _b θ = -7.5° x R-R _b / R _t -R _b +32° ξ = 9° x R-R _b /R _t -R _b +57° (R _t : radius of blade outer periphery, R _b : radius of blade boss part) Figure 15 shows the forward inclination angle δ _z of the chord center line 21 in the suction direction and the minimum value. The relationship with the specific noise level K _s (hon) is shown. From the figure, if the value of the forward inclination angle δ _z is between 12.5° and 32.5°, the minimum specific noise level is sufficiently small, and a significant reduction in noise can be achieved.

FIG. 16 shows the relationship between the advance angle δ〓 _t at the outer peripheral portion 1d of the blade in the rotational direction of the chord center line 21 and the minimum specific noise level K _s (hon). According to the figure, if the condition of advance angle δ〓 _t >40° is satisfied, the minimum specific noise level is significantly reduced. As the advancing angle δ〓 _t increases, the specific noise level tends to decrease, but from the point of view of bending strength, the maximum limit is about 50°. Therefore,
By setting the advancing angle δ〓 _t in the range of 40° to 50°, the specific noise level can be significantly lowered.

Fig. 17 shows the warpage angle θ _t of the impeller 1 at the outer circumference 1d of the impeller 1 and the specific noise level K _s (hon).
shows the relationship between Generally, the larger the warp angle θ, the more work the blade can do, but if it is too large, noise tends to increase. According to the figure, when the warpage angle θ _b at the boss portion was set to 32°, the specific noise level decreased significantly in the range of θ _t from 20° to 30°. Although not shown,
This tendency did not change even when θ _b was changed from 27° to 37°.

FIG. 18 shows the relationship between the stagger angle ξ _t and the specific noise level K _s (hon) at the outer peripheral portion 1 d of the impeller 1.
From the figure, the specific noise level can be significantly reduced by changing ξ _t from 62° to 72°. In this embodiment, ξ _b =ξ _t −9°, but the same effect can be obtained if ξ _b =53° to 63°.

In addition, in this embodiment, the number of blades of the impeller 1 is 3.
Although the description has been made regarding the number of blades, if the essential parameters are configured as described above, the same effect can be expected regardless of the number of blades.

Also, the chord line center point P _b for each parameter
The radius R _b of the boss when defined does not have to be strictly the radius of the boss, but if it is a value close to the radius of the boss, an impeller with the same shape as the above example can be obtained and the effect will also be obtained. Something similar to the above example is obtained.

In addition, in this example, the parameters δ〓, _δz , which determine the shape of the blade, the warp angle θ, the discrepancy angle ξ,
and the parameter B _R that determines the shape of the bell mouth,
The structure was configured with all of l _d , D _B , and l _x set to optimal values, but
As the parameters that determine the shape of the blade, δ〓 and _δz alone can have a sufficient effect.

〔Effect of the invention〕

As described above, according to the present invention, the chord line is the midpoint between the leading edge of the blade and the trailing edge of the blade in the cross section when the impeller is cut along the cylindrical surface of radius R centered on the rotation axis. Center point P _R and the center point of the chord line in the cross section when cut through the cylindrical surface of the blade boss radius R _b
The distance between P _b and the plane S _c perpendicular to the axis of rotation is
When l _s , in a coordinate system with the suction side of the airflow in the positive direction, the chord line center point P _R is always located in the positive direction with respect to the S _c plane, and δ _z = tan ^-1 l _s /R The value of δ _z that can be expressed as −R _b is δ _z = 12.5° to 32.5°, and in the projection plane when the impeller is projected onto a plane perpendicular to the axis of rotation, the boss of the blade is a cylinder with radius R _b . In a coordinate system where the center point of the chord line in the cross section when cut by the plane is P _b ′, the rotation axis is the origin 0, and the straight line connecting the 0 point and P _b ′ is the X axis, the impeller has a radius R When the center point of the chord line when cut on the cylindrical surface is P _R ′, and the angle between the straight line P _R ′-0 and the X axis is δ〓, the radial distribution of δ〓 is δ〓=δ _t ×R−R _b /R _t −R _b (R _t : Blade outer radius, R _b : Blade boss radius,
δ〓 _t : Angle between the straight line P _t ′-0 and the X axis), δ〓 _t
= 40° to 50°, and has a plane perpendicular to the axis of rotation, which is narrowed by a curved surface with radius B _R to form a straight part l _d
In a suction bell mouth with an inner diameter D _B and an outer diameter D _T of the blade, when the distance between the trailing edge and the end of the duct on the outer circumference of the blade is l _x , B _R
= 0.07D _T ~ 0.2D _T , l _d = 0.04D _T ~ 0.1D _T , D _B =
Since we set 1.01D _T to 1.04D _T and l _x = 0 to 0.04D _T , we can give the shape of the impeller and the shape of the bell mouth, and the specific noise level in the operating region from the opening operating point to the surging operating point. This has the effect of obtaining an axial flow fan that can significantly reduce the flow rate.

Further, in an axial flow fan according to another aspect of the present invention, the midpoint between the leading edge of the blade and the trailing edge of the blade in a cross section when the impeller is cut along a cylindrical surface with a radius R centered on the rotation axis. The distance between a certain chord line center point P _R and a plane S _c that passes through the chord line center point P b in the cross section taken by the cylindrical surface of the blade boss radius R _b and is orthogonal to _the axis of rotation is l. When _s is the center point of the chord line in the coordinate system with the suction side of the airflow in the positive direction.
P _R is always located in the positive direction with respect to the S _c plane, and δ _z =
When the value of δ _z that can be expressed as tan ^-1 ls/R-R _b is δ _z = 12.5° to 32.5°, and the impeller is projected on a plane perpendicular to the rotation axis, the boss of the blade is Let P _b ' be the center point of the chord line in the cross section when cut by a cylindrical surface with radius R _b , and let the axis of rotation be the origin 0,
A coordinate system with the straight line connecting the 0 point and the P _b ′ point as the X axis,
When the blade is cut by a cylindrical surface with radius R, the center point of the chord line is P _R ′, and the angle between the straight line P _R ′-0 and the X axis is δ〓
_{In the case of _ _}
δ〓 _t : Angle between the straight line P _t ′-0 and the X axis), δ〓 _t
= 40° to 50°, and in a developed view obtained by cutting the impeller at a cylindrical surface with radius R and developing the cross section on a two-dimensional plane, the shape of the warp line in the blade cross section is an arc shape. , when the central angle for forming the circular arc is the warp angle θ, the radial distribution of θ is expressed as θ=(θ _t −θ _b )×R−R _b /R _t −R _b +θ _b (θ _t : Warp angle at the blade outer circumference, θ _b : Warp angle at the blade boss), θ _t = 20° to 30°, θ _b =
27° to 37°, θ _t < θ _b , and in the developed view, when the angle between the chord line of the blade and a straight line parallel to the rotation axis and passing through the leading edge of the blade is the stagger angle ξ, then The radial distribution is given by ξ = (ξ _t − _{ξ b} ) × R − R _b / R _t − _{R b} + ξ _b (ξ _t : stagger angle at the blade outer circumference, ξ _b : stagger angle at the blade boss). , ξ _t = 62°~
72°, ξ _b = 53° ~ 63°, ξ _t > ξ _b , and has a plane perpendicular to the rotation axis, which is narrowed by a curved surface with radius B _R and connected to the straight part l _d , and the blade In a suction bell mouth with an inner diameter D _B relative to an outer diameter D _T ,
When the distance between the rear edge of the impeller and the end of the duct is l _x , B _R = 0.07D _T ~ 0.2D _T , l _d =
0.04D _T ~0.1D _T , D _B =1.01D _T ~1.04D _T , l _x =0~
Since it is set to 0.04D _T , in addition to the above invention, it is possible to give the shape of each part of the bell mouth in an impeller that takes into account the warp angle and the stagger angle, and the specific noise in the operating range from the opening operating point to the surging operating point is reduced. This has the effect of obtaining an axial flow fan that can significantly reduce the level.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an axial flow fan according to an embodiment of the present invention, FIG. 2 is a sectional view taken along a plane including the rotating shaft, and FIG. 3 is an embodiment of the invention. As an example, the projected view of the blade on a plane perpendicular to the rotation axis, FIG. 4, is the distance from the boss chord center line P _b ′ to the outer circumference chord center line P _t ′ in FIG. 3. The trajectory in the radial direction until P _b ′−P _R ′−
Regarding P _t ′, the radial distribution of the chord line center point P _R at an arbitrary radius R and the rotational projection of the chord line center point P _R at the radius R onto the plane 0X, and the cross section showing the cross section at the same position of the blade. 5 and 5 relate to an embodiment of the present invention, when an impeller is formed with the chord line center point P _R as the relative origin, the blade is cut at a cylindrical surface with a radius R, and its cross section is Figure 6 is a developed diagram obtained by expanding on a dimensional plane, and Figure 6 is a characteristic diagram showing the total pressure coefficient and noise (hon) with respect to the flow coefficient at various forward inclination angles δ _z of the chord center line in the suction direction. FIG. 7 is a side view of an impeller according to one embodiment, FIGS. 8 and 9 are explanatory diagrams illustrating the flow on each blade surface,
Figures 10a and b are explanatory diagrams explaining the flow with and without advance angles, Figure 11 is a characteristic diagram showing the relationship between flow coefficient and pressure coefficient at various advance angles δ, and Figure 12. is a graph showing the relationship between the noise (hon) and the length l _d of a straight duct, Fig. 13 is a characteristic diagram showing the minimum specific noise level (hon) versus the radius of curvature B _R of the entrance of the bell mouth, and Fig. 14 is a straight line. Minimum specific noise level (hon) for duct length l _d
FIG. 15 is a characteristic diagram showing the minimum specific noise level K _s (hon) with respect to the forward inclination angle δ _z , and FIG. 16 is a characteristic diagram showing the minimum specific noise level K s (hon) with respect to the forward angle δ〓 _t at the outer circumference of the impeller _. Characteristic diagram showing (Hon), No. 17
The figure is a characteristic diagram showing the minimum specific noise level K _s (hon) for each warp angle θ _t at the outer periphery of the impeller.
Figure 18 shows the discrepancy angle ξ _t at the outer periphery of the impeller.
Figure 19 is a _cross -sectional view showing a conventional axial flow fan;
FIGS. 20a and 20b are characteristic diagrams showing the relationship between the flow rate coefficient and the total pressure coefficient, and the relationship between the flow rate coefficient and PWL (power level) (dB), regarding a conventional axial flow fan.
In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. A chord line center point P R that is the midpoint between the leading edge of the blade and the trailing edge of the blade in a cross section when the impeller is cut on a cylindrical surface of radius _R centered on the rotation axis. When the distance between the chord line center point P _b of the cross section taken through the cylindrical surface of the vane boss radius R _b and the plane S _c perpendicular to the axis of rotation is l _s , the suction of airflow is In a coordinate system with the side in the positive direction, the chord line center point P _R is always located in the positive direction with respect to the S _c plane, and δ _z can be expressed as δ _z = tan ^-1 l _s / R - R _b When the value of δ _z = 12.5° to 32.5° and the impeller is projected onto a plane perpendicular to the rotation axis, the blade is cut at a cylindrical surface with radius R _b of the boss part of the blade. In a coordinate system where the center point of the chord line in the cross section is P _b ′, the rotation axis is the origin 0, and the straight line connecting the 0 point and P _b ′ is the X axis, the impeller is defined as a cylindrical surface with a radius R. If the center point of the chord line when cut at is P _R ′, and the angle between the straight line P _R ′-0 and the X axis is δ〓, then δ〓
_{The radial distribution of _ _ _ _} The _angle formed by the
From there, in the suction bell mouth which is constricted by a curved surface of radius B _R and connected to the straight part l _d and has an inner diameter D _B with respect to the outer diameter D _T of the impeller, the rear edge at the outer periphery of the impeller and the duct are connected. An axial flow fan characterized by having the size of each parameter set to the following values, where the distance to the end is _lx . B _R = 0.07D _T ~ 0.2D _T l _d = 0.04D _T ~ 0.1D _T D _B = 1.01D _T ~ 1.04D _T l _x = 0 ~ 0.04D _T 2 Cylindrical surface with radius R centered on the rotation axis A cross section when cutting the impeller at the chord line center point P _R , which is the midpoint between the leading edge of the blade and the trailing edge of the blade, and the cylindrical surface of the blade boss radius R _b . When the distance between the chord line center point P _b and the plane S _c perpendicular to the rotation axis is defined as l _s , the chord line center point P _R is defined in the coordinate system with the suction side of the airflow in the positive direction. It is always located in the positive direction with respect to the above S _c plane, the value of δ _z that can be expressed as δ _z = tan ^-1 l _s / R - R _b is set to δ _z = 12.5 to 32.5 degrees, and the rotation axis is In the projected plane when the impeller is projected onto a perpendicular plane, the center point of the chord line in the cross section taken by the cylindrical surface of the boss portion radius R _b of the blade is P _b ′, and the rotation axis is the origin 0. In a coordinate system with the straight line connecting the above point 0 and point P _b as the X axis, the chord line center point when the above impeller is cut on a cylindrical surface with radius R is the straight line P _R ′.
If the angle between P _R ′-0 and the above X-axis is δ〓,
The radial distribution of δ is δ = δ = _t × R - R _b / R _t - R _b (R _t : radius of blade outer circumference, R _b : radius of blade boss part,
δ〓 _t : Angle between the straight line _{P t} ′-0 and the In the developed view obtained by expanding on a dimensional plane, if the shape of the warp line in the cross section of the blade is an arc shape, and the central angle for forming the arc is the warp angle θ, then the radial distribution of θ is θ= It is given by (θ _t −θ _b )×(R−R _b )/(R _t −R _b )+θ _b (θ _t : Warp angle at the blade outer circumference, θ _b : Warp angle at the blade boss), and θ _t =20°~30°, θ _b =
27° to 37°, θ _t < θ _b , and in the above development view, when the angle between the chord line of the blade and a straight line parallel to the rotation axis and passing through the leading edge of the blade is the stagger angle ξ, _{The radial distribution of ξ is expressed as} (discrepancy angle), ξ _t = 62°~
72°, ξ _b = 53° to 63°, ξ _t > ξ _b , and has a plane perpendicular to the rotation axis, and is narrowed from there by a curved surface with a radius B _R and connected to the straight part l _d , Above blade outer diameter
For D _T , in a suction bell mouth with an inner diameter D _B , when the distance between the trailing edge of the impeller and the duct end is l _x , the size of each parameter was set to the following values. This is an axial flow fan that is characterized by: B _R =0.07D _T ~0.2D _T l _d =0.04D _T ~0.1D _T D _B =1.01D _T ~1.04D _T l _x =0~0.04D _T