JPH022000B2 - - Google Patents

Description

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

[Prior Art] Axial flow impellers are widely used in air conditioners, ventilation fans, etc., and it is socially important to reduce the noise generated from the impellers as much as possible. However, a design method for low-noise impellers that reduces the noise generated from the impeller as much as possible and does not reduce the aerodynamic performance of the impeller has not been established, and it is only an ad-hoc trial that corresponds to each individual product. Misguided design methods have been adopted.

Among these conventional techniques, many techniques are used to reduce noise, such as making the front surface of the impeller protrude in the direction of rotation, as seen in Japanese Patent Publication No. 50-39241. was.
FIG. 10 is a plan view showing the main parts of a conventional axial flow impeller disclosed in, for example, Japanese Patent Publication No. 50-39241.
In the figure, 1 is the blade of the impeller, 1a is the tip of the blade, 1b is the leading edge of the blade, 1c is the trailing edge of the blade, and 1d is the blade of the impeller.
2 is the outer circumferential part of the blade, 2 is the boss part to which the blade 1 is attached,
Rt is the outer diameter radius of the impeller, and Re is the radius at the blade tip 1a. Moreover, FIG. 11 is a sectional view of the blade showing the relative relationship of the flow with respect to the blade 1.
0 is a sectional view taken along the line XI-XI of FIG. In the figure, 5 is a warp line, 5a is a blade negative pressure surface, 5b is a blade pressure surface,
6 is a line parallel to the rotation axis, 7 is the gas inflow vector with respect to the blade surface, 8 is the separation area on the pressure surface side, α is the suppression angle, γ is the unequilibrium inflow angle, ε is the inflow angle, ξ is the blade twist angle, θ It is the angle of curvature. The blade 1 has a circumference composed of a blade leading edge 1b, a blade outer peripheral part 1d, and a blade trailing edge 1c.

Next, the operation will be explained.

In the case of conventional impellers, there are no clear criteria for determining the position of the outer circumferential portion 1d of the blade and the leading edge portion 1b of the blade, and methods such as simply defining the shape based on the specificity of the front surface shape are used. It was getting worse.
In Fig. 10, the blade tip 1a has a radius ratio of
By being located at a location where Re/Rt = approximately 0.88 and not near the outer periphery of the impeller (that is, Re/Rt≈1.0), the area of the outer periphery of the impeller, where the amount of work is greatest, is substantially reduced. As a result, the air volume and static pressure characteristics decrease, and the actual noise level increases. The blade tip 1a in an axial impeller is very important from an aerodynamic point of view, and the fact that its shape has a large radius in the direction of rotation creates a large resistance to the flow and causes the front of the blade to This induces leading edge separation at the edge 1b, increasing noise generated from the blade surface. In addition, in conventional impellers, the shape is determined by considering the flow to the blades as a mere two-dimensional flow, so although it is possible to improve the noise characteristics at the open point, it is not possible to improve the noise characteristics at the open point, but when static pressure is generated, which is the actual usage of the impeller. Since the flow in has a strong three-dimensionality, the noise cannot be reduced. That is, in order to reduce the noise generated from the blades, the three-dimensional characteristics of the flow must be considered and the blade element distribution of the blades must be clarified.

In addition, as a conventional method for reducing the noise of axial flow impellers, the flow pattern of the impeller has been changed to a free vortex (the amount of work of the blades from the boss to the outer circumference of the impeller is constant. (The distribution in the radial direction is almost constant from the inlet to the outlet.) Therefore, we created a forced vortex type flow pattern that does more work at the outer circumference of the impeller, where the circumferential speed is high, and the impeller can be improved without reducing the air volume or static pressure. There was also a method to reduce the noise by lowering the rotation speed of the engine. However, the fluid flowing into the blade is
Unless an external force is applied, its own flow pattern is a free vortex with a constant total pressure. Therefore, even if the flow state between the blades of the impeller is a forced vortex, the flow before entering the blade is a free vortex (the axial inflow velocity of the flow is constant at each radial position of the blade).
Therefore, in an impeller designed with forced vortices (the blade stagger angle ξ is almost constant from the boss to the blade tip), the inflow angle ε becomes large near the boss 2, as shown in Figure 11. . Since the unbalanced inflow angle with respect to the blade 1 is γ, the relationship ε>γ holds, and the flow 7 flowing into the blade 1 causes leading edge separation at the pressure surface 5b of the blade, and the separation area 8 increases, Broadband noise generated from the blade 1 increases. This tendency is particularly noticeable near the open point where the air volume is high.
That is, as the air volume increases, the inflow angle ε becomes larger and the separation area 8 increases. Therefore, if the blade stagger angle ξ is made smaller in an attempt to reduce the noise at the open point, static pressure is applied to the blade 1 and the air volume is reduced, but the suppression angle α to the airflow becomes larger at the blade tip 1a. becomes too much, and the flow separates from the negative pressure surface 5a of the blade,
Blade 1 stalled and the noise tended to increase rapidly.

[Problems to be solved by the invention] Conventional axial flow impellers are constructed as described above, so the three-dimensional shape of the blades is not treated at all, and the noise generated when static pressure is generated is not so great. Does not decrease. For this reason, there was a problem in that it was not possible to dramatically improve the noise characteristics and construct an axial flow impeller with ultra-low noise.

This invention and other inventions of this invention have been made to solve the above-mentioned problems by clarifying the essential parameters that determine the three-dimensional shape of the impeller, and determining the opening point as well as the static pressure generation. The purpose of the present invention is to obtain an axial flow impeller that can significantly reduce noise from the impeller during operation.

[Means for Solving the Problems] (1) The axial flow impeller according to the present invention has a chord line center point P in a cross section when the impeller is cut on a cylindrical surface with a radius R centered on the rotation axis. When Ls is the distance between _R and a plane Sc that passes through the chord line center point Pb and perpendicularly intersects the axis of rotation in the cross section when the boss part of the blade is cut by a cylindrical surface with radius Rb, the suction side of the airflow is In the coordinate system where the chord line center point P _R is always located in the positive direction with respect to the Sc plane, the value of δz that can be expressed as δz = tan ^-1 Ls / R - Rb is δz = 12.5° ~ 32.5° And, on the projection plane when the impeller is projected onto a plane perpendicular to the rotation axis, the center point of the chord line in the cross section when the boss part of the blade is cut by a cylindrical surface with radius Rb is Pb′, In a coordinate system where the axis of rotation is the origin O and the straight line connecting points O and Pb' is the X axis, the center point of the chord line when the blade is cut by a cylindrical surface with radius R is P _R ', and the straight line P _R If the angle between '-O and the X axis is δ, then the radial distribution _of δ is as follows: δ = δ ,
δ〓 _t : Angle between the straight line Pt'- _O and the In the developed view obtained by the expansion, if the shape of the warp line in the cross section of the blade is a circular arc shape, and the central angle for forming the circular arc is θ, then the radial distribution of θ is expressed as θ=(θt−θb )×(R-Rb)/(Rt-Rb)+θb (θt: Warp angle at the blade tip, θb: Warp angle at the blade boss), θt=20°~30°, θb=27°~
37°, and θt<θb.

(2) An axial flow impeller according to another aspect of the present invention has a chord line center point in a cross section when the impeller is cut along a cylindrical surface with a radius R centered on the rotation axis.
_Ls
Then, in a coordinate system with the suction side of the airflow in the positive direction, the above chord line center point P _R is always located in the positive direction with respect to the above Sc plane, and δ _z = tan ^-1 Ls / R - Rb. Let the value of δ _z that can be expressed be δ _z = 12.5° to 32.5°, and in the projection plane when the impeller is projected onto a plane perpendicular to the rotation axis, the boss part of the blade is a cylindrical surface with radius Rb. The center point of the chord line in the section when cut is Pb', the rotation axis is the origin O, and the straight line connecting the O point and Pb' point is X.
In the coordinate system with the axis as the axis, the center point of the chord line when the blade is cut by a cylindrical surface with radius _R is a straight line.
If the angle between P _R ′-O and the X axis is δ, then the radial distribution _of δ is δ=δ boss radius,
δ〓 _t : Angle between the straight line Pt'- _O and the In the developed view obtained by unfolding, when the angle ξ 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, the radial distribution of ξ is expressed as ξ=( ξt−ξb)×(R−Rb)/(Rt−Rb)+ξb (ξt: Bite angle at the blade tip, ξb: Bite angle at the blade boss), ξt=62° to 72°, ξb= 53° to 63°, ξt>ξb.

(3) Still another invention of the present invention provides the above-mentioned invention (1), furthermore, in the developed view, the chord line of the blade and the straight line parallel to the rotation axis and passing through the leading edge of the blade. When the angle formed by The following conditions are added: ξt = 62° to 72°, ξb = 53° to 63°, and ξt > ξb.

(4) Still another invention of the present invention is based on the invention of (3) above, and further provides that in the developed view, the chord length of the blade is L, and the pitch between the blades at the same radius point is T. Then, the condition that the ratio of T and L at each radius point is T/L=1 to 1.1 is added.

[Operation] The axial flow impeller of this invention and another invention of this invention clarify the three-dimensional distribution of blade element centers, which is the key point for determining the blade shape. More specifically, the blade element center of the blade is tilted toward the gas suction side, and at the same time moves forward in the rotation direction, and the distribution of each is optimized, so it is extremely difficult to use, especially when static pressure is generated. Generated noise can be reduced.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing an embodiment of the axial flow impeller according to the present invention. For example, there is a three-blade type.
However, the same applies to other blades. In the figure, 1 is a blade with a three-dimensional shape, 2
3 is the boss part for attaching the blade 1, 3 is the blade 1
, and 4 is the rotation direction. A feature of this blade 1 is that the blade surface is spatially twisted and tilted forward greatly toward the gas suction side, forming a three-dimensional curved surface shape.

In this impeller, the three-dimensional curved shape of the blade 1 can be specifically defined by clarifying the various factors constituting the blade 1. Therefore, the factors constituting the axial flow impeller according to the present invention will be specifically described.

In this invention, as an important factor for determining the three-dimensional curved shape of the blade 1, the chord line center point P _R , which is the center of the blade element of the blade 1, is considered. For axial flow impellers, basically, if the angle of attack, deflection angle, and chord length of the blades at the center of the blade element are determined, then according to the two-dimensional blade cascade theory, the air volume and static pressure of the impeller are uniquely determined.
The spatial distribution of wing element centers is irrelevant. However, when considering the mechanism of noise generation, the spatial distribution of blade elements becomes extremely important. Noise generated from an axial flow impeller is caused by a boundary layer on the blade surface and various vortices emitted from the blade surface. When the spatial distribution of the blade element center changes, the flow on the blade surface changes,
Since the conditions of the boundary layer and shedding vortices change, the generated noise will also be affected. That is, although the spatial distribution of the center of the blade element does not affect the air volume and static pressure characteristics of the impeller two-dimensionally, it has a great influence on the noise characteristics. Therefore, in order to define the position of the chord line center point P _R , first consider the position in the rotational direction.

Figure 2 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;
2 is a boss part, 3 is a rotating shaft, and when the blade 1' is cut on a cylindrical surface with a radius R from the rotating shaft 3, the circular arc 1b _R ′-P _R ′-1c _R ′ in the projected plane is the cross-sectional shape of the blade. Become. 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 ′ in the projection plane, when the impeller is cut on a cylindrical surface with the blade boss radius Rb, the center point of the chord line of the boss part in the projection plane is set as Pb′,
A straight line connecting the rotation axis 3 with the position O on the projection plane
Coordinates with Pb'-O as the X axis and O as the origin are formed on the projection plane. Pt' is the chord line center point at the outer circumference 1d, and P〓' is the line formed by the tangent of the chord line center point locus Pb'-P _R' -Pt' at the chord line center point P _R ' and the radius R. Show angle. Further, symbols with a dash (') indicate each portion on the projection plane. In the above coordinate system, let the angle between the straight line P _R ′-O and the X-axis be δ〓,
If the distance is R, the position of P _R ' can be expressed using polar coordinates (R, δ〓). In this invention, a straight line
If the _{angle between} Pt'-O and the
δ〓 _t : Angle between the straight line Pt'-O and the X axis), δ〓 _t
= 40° to 50°. In this way, the position of the chord line center point P _R has been defined on the plane orthogonal to the rotating shaft 3, so next the axial position is defined. Figure 3 shows the center point of the boss chord line in Figure 2.
Regarding the radial trajectory Pb'-P _R' -Pt' from Pb' to the outer chord line center point Pt', the chord line center point P _R at an arbitrary radius R is plotted on the plane OX plane with a radius R. It shows the radial distribution of the rotationally projected chord line center point P _R and the cross section of the blade 1 at the same position. In the figure, 9 is the centrifugal force when the impeller rotates, 9a, 9b
indicate the suction surface normal component of the centrifugal force 9, the tangential component of the centrifugal force 9, and the gas inflow direction of arrow A, respectively. Therefore,
Center point of the chord line of the blade 1 on the outer periphery of the boss portion 2
Consider a plane Sc passing through Pb and perpendicular to the rotation axis 3. When the chord line center point at an arbitrary radius R is P _R , the distance between the Sc plane and the P _R point is Ls, and the angle between the boss chord line center point Pb and the Sc plane is δz, then δz= tan ^-1 Ls/R-Rb. Therefore, by determining Ls or δz and giving the radius R, the axial position of the chord line center point P _R can be defined.

To configure the impeller, the chord line center point P _R
It is sufficient to set the relative origin at the relative origin, form a blade cross section with a warp there, and make the entire blade surface a smooth curved surface.

Figure 4 shows the result obtained by cutting the blade 1 with a cylindrical surface of radius R and developing the cross section into a two-dimensional plane when the blade surface is formed using the chord line center point P _R as the relative origin. A developed view is shown. Let the warp line 5 of the blade 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 PR. In this embodiment, the radial distribution of θ is set as θ=(θt−θb)×(R−Rb)/(Rt−Rb)+θb, where θt is the warp angle at the vane tip, that is, at the vane tip. The central angle of the warp line, θb is given by the warp angle at the blade boss, that is, the central angle of the warp line at the blade boss, θt = 20° ~ 30°, θb = 27° ~ 37°, θt < θb
It is said that

Also, the attachment position of the blade is the chord line 1b-
1c and a straight line 6 that is parallel to the rotating shaft 3 and passes through the blade leading edge 1b is defined as the stagger angle ξ, which is determined by giving ξ a distribution in the radial direction.
That is, the radial distribution of ξ is set as ξ = (ξt - ξb) x (R - Rb) / (Rt - Rb) + ξb, where ξt is the brushing angle at the blade tip,
ξb is given by the wedge angle at the blade boss, and ξt=
62° to 72°, ξb = 53° to 63°, and ξt > ξb.

Furthermore, L in this figure is the blade chord length, and using the circumferential distance T between the blades shown in Figure 5, T/
The size of the blade in the radial direction is limited by the parameter L. Figure 5 is a plan view of the impeller, and L
is the chord length of the blade 1, and T is the pitch between the blades 1 and 1 at the same radius point, and the ratio of T and L at each radius point is T/L=1 to 1.1.

In this way, by setting the five parameters to unique values, an impeller with ultra-low noise can be obtained. Specifically, the values as an example of the essential parameters that determine the basic blade shape are shown below, and the noise characteristics due to differences in the leading edge shape will be described.

δz＝22.5゜(constant in radial direction) δ〓＝45゜×R−Rb／Rt−Rb θ＝−7.5゜×R−Rb／Rt−Rb＋32゜ ξ＝9゜×R−Rb／Rt−Rb＋57゜T/L = 1.05 (constant in the radial direction) (Rt: blade tip radius, Rb: blade boss radius). In this basic blade, the radial distribution of δ〓 is linear with respect to the radius R, so the angle P〓′ in Fig. 2 increases rapidly from the boss portion 2 toward the blade outer circumference 1d. The degree of advance increases from the blade outer peripheral portion 1d. In addition to it,
By arranging the chord line center point P _R so that δz = 22.5°, the actual warp line shape of the blade 1 with respect to the flow at the blade leading edge 1b is the virtual shape shown by the broken line in Fig. 11. The apparent warp angle θ as shown by the warp line 5c
becomes smaller. Since the blade 1 is rotating, a centrifugal force acts on the fluid on the surface of the blade 1, and the flow flowing in from the blade leading edge 1b does not flow from the direction perpendicular to the radial direction, but from the second direction.
As shown by arrow 7 in the figure, it points slightly toward the outer periphery. When the flow flows in this way, since the forward inclination angle δz is 22.5°, the axial movement distance of the flow on the blade surface becomes almost zero. Therefore, the flow flowing into the blade 1 flows in an unbalanced manner, and the apparent warp angle θ becomes small. That is, ε≒γ in FIG. 11, and the peeling region 8 on the pressure surface disappears.
Noise generation becomes extremely small.

The most desirable combination of the forward inclination angle _δz and the forward angle δ〓 is the basic form described above, but when designing the impeller, this value must be changed due to axial dimension restrictions, etc. In some cases. Therefore, as a result of experimentally manufacturing several types of blades with each parameter set to the optimum value and changing the other value, the results shown in FIGS. 6 and 7 were obtained. Figures 6a and b are graphs of the noise level (Hong) and minimum specific noise level Ks ( _Hong ) against the forward inclination angle δz, respectively, and Figure 7 is the graph of the minimum specific noise level Ks (Hong) against the forward angle δ〓 of the blade tip. ). Here, the specific noise level Ks (hon) is defined as in the following equation.

Ks=SPL−10Log Q Ps ^2.5 SPL: Noise characteristics (Sound Pressure Level) Q: Flow rate Ps: Static pressure Also, the broken line in the figure shows the value in the conventional device.

As can be seen from Figure 6b, the value of the anteversion angle δ _z is
If the angle is between 12.5° and 32.5°, the value of the minimum specific noise level Ks is sufficiently small, and the noise is extremely low. Also, if we look only at the noise level at the open point, the larger the forward inclination angle δ _z is, the lower the noise level is, but the degree of reduction is saturated at forward inclination angles δ _z = 32.5° or more.
From the viewpoint of strength, it is desirable that the maximum value of the forward inclination angle δ _z is approximately 32.5°. According to FIG. 7, if the condition of advancing angle δ>40° is satisfied, the minimum specific noise level Ks is greatly reduced. Practically speaking, the larger the advancing angle δ〓, the lower the specific noise level, but from the point of view of bending strength, the maximum is about 50°. Therefore, if the advancing angle δ=40° to 50°, the specific noise level can be made sufficiently low.

Furthermore, since the forward inclination angle δz toward the suction side and the advance angle δ〓 in the rotational direction are given to the chord line center point _PR , the portion of the blade surface that is inclined toward the suction side increases. Therefore, the centrifugal force caused by the flow between the blades that passes while drawing an arcuate trajectory on the blade surface greatly acts on the suction surface of the blade 1. In FIG. 3, the suction surface normal component force 9a of the centrifugal force 9 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 suction surface 5a increases in proportion to the boundary layer thickness, the component force 9
When the boundary layer becomes thinner due to a, the generated noise decreases by that amount. In addition, a compressive force such as the suction surface side normal component force 9a is acting on the boundary layer, so
This has the effect of suppressing the entire separation of the boundary layer due to the increase in the angle of attack of the blades 1 in a low air volume region, making it difficult for the blades 1 to stall, and making it possible to form an impeller having a wider operating range. Here, the ability to widen the operating range will be explained in detail. FIG. 12 is a characteristic curve showing the influence of the forward inclination angle _δz of the chord center line in the suction direction on the air blowing and noise performance. In the figure, the horizontal axis shows the flow coefficient, the vertical axis shows the total pressure coefficient, and the noise (hon), and is a characteristic curve when the forward inclination angle δ _z is changed from -22.5° to 45°.
As the anteversion angle increases, the total pressure coefficient increases and reaches its maximum when δ _z =22.5°. On the other hand, as the forward inclination angle increases, the surging point (near flow coefficient = 0.25: the point where the total pressure coefficient curve becomes a downward-sloping curve to the left with respect to the flow coefficient) moves toward the open point, and the effective operating area (open point tend to narrow the surging point).

Looking at the noise performance curve, the noise level decreases as the forward inclination angle δ _z increases closer to the open point than the surging point. A wing with δ _z −22.5° at the open point and
Comparing the 45° wing, the 45° wing is about 9 phons lower.
However, as the air volume decreases and the total pressure increases, the noise level of the 45° blade increases rapidly at a flow coefficient of 0.3. Moreover, this point of sharp increase in noise is located on the open side rather than the surging point, which narrows the effective operating range. On the other hand, when the forward inclination angle is made smaller, the noise level at the open point increases, but the point where the noise suddenly increases tends to move toward the closed side. In other words, forward tilting of the chord center line toward the suction side reduces noise, but it also has the effect of narrowing the effective operating range. Therefore, if the latter drawback can be eliminated, the chord center line can be tilted forward in the suction direction, thereby significantly reducing noise.

Therefore, before considering the phenomenon in which noise increases rapidly in the medium air volume range, let's consider the cause of noise reduction by tilting the chord center line forward toward the suction side. In addition to the above-mentioned reasons, the following may be considered as the reason why noise is reduced when the chord center line is given an advance angle in the suction direction as shown in the present invention.

Figure 13 shows the rotating impeller 1 of this invention.
It is a side view seen from the side. In the figure, B,
C is a point where the chord center line 21 intersects the blade tip and the center of the blade span. The pressure on the suction surface of the blade 1 is B and C at the blade tip and the center of the blade span, respectively.
It decreases the most at the point. Due to the forward inclination of the chord line center line 21 toward the suction side, point B is located on the suction side from point C. Therefore, the static pressure on the suction surface is lower on the suction side at the tip of the blade where point B is located than at the center of the blade span where point C is located. Therefore, the streamlines 22 on the suction surface are inclined in the radial direction as they pass through the blade, inducing a radial velocity component V _r on the suction surface. In the relative flow field, the radial velocity component generates Coriolika F _c .
Figure 14 shows the radial velocity on the suction surface of blade 1.
Vr23, Coriolika F _c 24=2V _r 〓, Coriolika
The relationship of normal component force F _c ⊥25 to the negative pressure surface of F _c is shown.

In the figure, arrow D indicates the rotation direction of the blade 1. Here, ω is the angular velocity of the impeller. A pressure gradient P _A 26 toward the suction surface is generated on the suction surface in order to counter Coriolika F _c ⊥. Due to this P _A 26, the transition of the boundary layer on the suction surface from laminar to turbulent flow is delayed, and the laminar flow state continues until the trailing edge of the blade. 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 line center line forward toward the suction side, Coriolika is generated in the normal direction of the suction surface, which delays the development of a turbulent boundary layer, and causes turbulence, which is trailing edge noise. This reduces flow noise.

Next, we will explain that a new problem arises when the chord center line is tilted forward toward the suction side. By inclining the chord line center line 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 tip also increases. As shown in FIG. 15, as the amount of the blade tip vortex 27 increases, the point 28 where the vortex separates from the blade tip gradually moves from the trailing edge to the leading edge. 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.
As the separation point 28 of the blade tip vortex moves toward the leading edge, the blade tip vortex moves away from the suction surface of the trailing edge of the blade, interferes with the bell mouth, is stretched in the direction of rotation, and finally interferes with the adjacent blade. do. Since the blade tip vortex 27 is extremely turbulent, large pressure fluctuations occur on the pressure surface of the adjacent blade with which the vortex collides, resulting in a sudden increase in low frequency noise. This is considered to be the cause of the rapid increase in noise that narrows the effective operating range of the impeller shown in FIG. Therefore, if the chord line center is tilted toward the suction side, the noise near the open point will be reduced, but the separation point of the blade tip vortex will tend to move toward the leading edge, so when the flow rate decreases, the noise will be closer to the open point. The disadvantage is that the noise tends to increase rapidly due to interference between the blade tip vortices and adjacent blades. Therefore, if this drawback can be resolved, the chord line of the impeller can be given a forward inclination angle in the suction direction, thereby significantly reducing noise.

In order to prevent interference between the blade tip vortices and adjacent blades as much as possible when the flow rate decreases, the amount of vortices flowing away from the blade tips should be reduced. Therefore, in this invention, the chord line center line 21 is moved forward in the rotation direction.
As shown in Fig. 16a, when the chord line center line 21 is advanced in the rotational direction, only part a of the flow from the leading edge of the blade becomes a vortex from the blade tip and is lost. Most of the flow that enters from the edge flows out from the trailing edge. On the other hand, in a blade whose chord line centerline 21 does not move forward in the rotational direction as shown in FIG. It flows out from the edge. From the figure, since a'>a, in an impeller without an advancing angle, the amount of blade tip vortices 27 increases, and interference with adjacent blades occurs closer to the open point. Therefore, the chord line centerline 2
When the advance angle in the rotational direction is given to 1, the amount of blade tip vortices flowing out from the blade tip is reduced, and the operating point where noise rapidly increases can be moved closer to the shutoff side.

FIG. 17 shows the relationship between the advance angle δ of the chord center line 21 at the blade tip and the flow rate coefficient and pressure coefficient 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. Moreover, the movement effect is δ〓
It tends to be saturated within the range of 15° to 45°, and when the angle exceeds 45°.

Next, the distribution of the warp angle θ and the stagger angle ξ, which are one of the functional elements of the blade, will be described. Warp angle θ
is an important quantity that determines the amount of work performed by the vane elements in the case of an impeller with an arcuate blade shape. Generally, the larger the warp angle θ, the more work the blade does during the same rotation, but as the warp angle θ increases, noise tends to increase. FIG. 8 shows the results of measuring the noise of several types of blades with different distributions of the warp angle θ using all other parameters of the basic type. Figure 8 shows θb=
Minimum specific noise level Ks for θt when set at 32°
This is a graph showing (Hon). In other words, in the distribution formula θ = (θt - θb) x (R - Rb) / (Rt - Rb) + θb, when performing an experiment with θb = 32°, the specific noise level is sufficient at θt = 20° to 30°. It can be seen that the blades become smaller and have extremely low noise. Although not shown, this tendency did not change even when the value of θb was changed from 27° to 37°.

Regarding the radial distribution of the blade's wedge angle ξ, δ〓 and δz are optimized as described above, and the flow pattern at the blade leading edge 1b is made to be close to a free vortex type, so regarding the inlet angle ε, The blade twist angle ξ also has a strong influence. Therefore, we set the radial distribution of ξ as ξ = (ξt - ξb) x (R - Rb) / (Rt - Rb) + ξb, and measured the specific noise level for several blades with all other parameters as the basic shape. The results shown in Figure 9 were obtained. FIG. 9 is a graph showing the minimum specific noise level Ks (hon) with respect to the wedge angle ξt at the blade tip. As can be seen from the figure, ξt=62°~72° and ξb=ξt−9°,
That is, it is clear that if ξb=53° to 63°, an impeller with very low noise can be obtained. Further, in this embodiment, the nodal/string ratio T/L is set to 1.05. That is, it is clear from FIG. 8 that the longer the chord length L is for the same amount of work, the smaller the warp angle θ can be, and the lower the noise. However, when forming the blade 1 from a single plate using a press or the like, T/L = 1.0 is the limit, and even when plastic molding is used, this value is the limit due to the mold relationship in the case of inexpensive blades. It's coming. On the other hand, increasing T/L causes an increase in noise, as described above. Therefore, as the maximum value of T/L, the noise deterioration is only about 2 phons, T/L=
1.1 is the limit value. Regarding the distribution of T/L in the radial direction, since the leading edge portion 1b of the blade has a special shape as described above, it is best to keep it almost constant in the radial direction. Increasing the noise level will result in an increase in noise.

Looking at the axial flow impeller of this example from the viewpoint of strength, it basically has a structure in which the center points of the chord lines are arranged on a truncated conical surface, and the distribution of the warp angle θ is 24.5° at the outer circumference of the blade. Because the angle is set at 32 degrees at the boss, the overall shape of the blade is curved in the radial direction, resulting in significantly increased bending strength compared to conventional planar blades. Therefore, the conventional product has a
In contrast to blades that would otherwise require the use of thicker plates, the blades can now be constructed from plates of approximately 2 mm, significantly reducing material costs. Furthermore, since the thickness of the blades can be reduced, the weight of the impeller can be reduced, which allows it to be driven by a motor, resulting in energy savings. Furthermore, since the structure is such that the boundary layer on the negative pressure surface of the blade can be strongly compressed, secondary flow generated on the blade surface can also be suppressed, which has the advantage of improving efficiency. Although this embodiment has been described with three blades, if the essential parameters are configured as described above,
Similar effects can be expected regardless of the number of blades.

[Effects of the Invention] (1) As described above, according to the present invention, the chord line center point _P Coordinates with the suction side of the airflow in the positive direction, where Ls is the distance from the plane Sc passing through the chord line center point Pb and perpendicular to the rotation axis in the cross section when the boss part of is cut by a cylindrical surface with radius Rb In the system, the chord line center point P _R is always located in the positive direction with respect to the Sc plane, and the value of δz that can be expressed as δz = tan ^-1 Ls/R - Rb is set to δz = 12.5° to 32.5°, and When the impeller is projected onto a plane perpendicular to the rotation axis, the radius of the boss part of the blade is
The center point of the chord line in the cross section when cut by the cylindrical surface of Rb is Pb', the rotation axis is the origin O, and the O point and
In a coordinate system with the straight line connecting points Pb' as the X axis, the chord line center point when the blade is cut by a cylindrical surface with radius R is P _R ', and the angle between the straight line P _R '-O and the X axis is δ〓
In _the case of
δ〓 _t : Angle between the straight line Pt'- _O and the In the developed view obtained from the developed view, 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 θ, then the radial distribution of θ is as follows: θ = (θt - θb) × Given by (R-Rb)/(Rt-Rb)+θb (θt: warp angle at the blade tip, θb: warp angle at the blade boss), θt=20°~30°, θb=27°~
37°, θt < θb, and the forward inclination angle δz toward the suction side, the advance angle δ〓 in the rotational direction, and the warp angle θ, which are essential parameters that define the spatial distribution of the blade chord line center point _P R, are optimized. Since the axial flow impeller is configured in this manner, it is possible to obtain an axial flow impeller that can operate over a wide effective operating range, have large air volume, high static pressure, and significantly reduce noise.

(2) An axial flow impeller according to another aspect of the present invention has a chord line center point in a cross section when the impeller is cut along a cylindrical surface with a radius R centered on the rotation axis.
_Ls
Then, in a coordinate system with the suction side of the airflow in the positive direction, the above chord line center point P _R is always located in the positive direction with respect to the above Sc plane, and it is expressed as δz = tan ^-1 Ls / R - Rb. The value of _δz that can be obtained is δz = 12.5° to 32.5°, and the boss portion of the blade is cut by a cylindrical surface with radius Rb on the projection plane when the impeller is projected onto a plane perpendicular to the rotational axis. In a coordinate system where the center point of the chord line in the cross section is Pb', the rotation axis is the origin O, and the straight line connecting the O point and the Pb' point is the X axis, the blade is cut on a cylindrical surface with a radius R. When P _R ′ is the center point of the chord line, draw a straight line.
If the angle between P _R ′−O and the X axis is δ, then δ
_The radial distribution of
δ〓 _t : Angle between the straight line Pt'- _O and the In the developed view obtained by unfolding, the angle formed by 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 ξ
When , the radial distribution of ξ is: ξ = (ξt - ξb) x (R - Rb) / (Rt - Rb) + ξb (ξt: wedge angle at the blade tip, ξb: wedge angle at the blade boss) ), ξt = 62° to 72°, ξb = 53° to 63°, ξt > ξb, and the forward inclination angle toward the suction side is an essential parameter that defines the spatial distribution of the blade chord center point P _R. The axial flow impeller is constructed by optimizing δz, the advance angle in the rotational direction δ〓, and the stagger angle ξ, so the axial flow impeller can span a wide effective operating range, produce large air volume, high static pressure, and significantly reduce noise. There is an effect that can be obtained.

(3) Still another invention of the present invention provides the above-mentioned invention (1), furthermore, in the developed view, the chord line of the blade and the straight line parallel to the rotation axis and passing through the leading edge of the blade. When the angle formed by By adding the conditions ξt = 62° to 72°, ξb = 53° to 63°, and ξt > ξb, in addition to invention (1), the warp angle θ and the wedge angle ξ can be optimized. Since the axial flow impeller is constructed using the above-mentioned method, it is possible to obtain an axial flow impeller that can operate over a wide effective range, have a large air volume, high static pressure, and significantly reduce noise.

(4) Still another invention of the present invention is based on the invention of (3) above, and further provides that, in the developed view, the chord line of the blades is L, and the pitch between the blades at the same radius point is T. At this time, we added the condition that the ratio of T and L at each radius point is T/L = 1 to 1.1, and in addition to invention (3), we configured an axial flow impeller by optimizing the blade pitch, resulting in a large air volume, This further enhances the effect of an axial flow impeller that can achieve high static pressure and significantly reduce noise.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an embodiment of an axial flow impeller according to the present invention, and FIG. Figure 3 shows the trajectory Pb'-P R '-Pt' in the radial direction from the chord line center point Pb' of the boss section to the outer chord line center point _Pt ' in Fig. 2 at an arbitrary radius R. FIG. 4 is a cross-sectional view showing the radial distribution of the chord line center point P _R which is rotationally projected onto the plane OX surface with a radius _R , and the cross section at the same position of the blade. According to one embodiment, when a blade surface is formed with the chord line center point P _R as the relative origin, the blade is cut by a cylindrical surface with a radius R, and the cross section is developed into a two-dimensional plane. A developed view, FIG. 5 is a plan view showing an impeller according to an embodiment, and FIG.
Figures a and b are graphs of the noise level (hon) and minimum specific noise level Ks (hon) as a function of the forward inclination angle δ _z , respectively, and Figure 7 shows the minimum specific noise level Ks (hon) as a function of the advance angle δ〓 at the blade tip. Graph, Figure 8 is a graph showing the minimum specific noise level Ks (hon) versus θt when θb = 32°, Figure 9 is a graph showing the minimum specific noise level Ks (hon) versus the wedge angle ξt at the blade tip.
10 is a plan view showing the main parts of a conventional axial flow impeller, and FIG. 11 is a cross-sectional view of the blade showing the relative relationship of the flow to the blade.
12 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, and FIG. 13 is an example Side view of the blade according to the 14th
15 are explanatory diagrams each explaining the flow on the blade surface, FIGS. 16 a and b are explanatory diagrams explaining the flow with and without an advance angle, and FIG. 17 is an explanatory diagram explaining the flow with and without an advance angle. FIG. 3 is a characteristic diagram showing the relationship between the flow rate coefficient and the pressure coefficient at 1...Blade, 1'...Blade in plan projection view,
1a...Blade tip, 1a'...Blade tip in plan view, 1b...Blade leading edge, 1b'...Blade leading edge in plan view, 1c...Blade trailing edge, 1c' ...Blade trailing edge in plan projection view, 1
d...Blade outer circumference, 1d'...Blade outer circumference in plan projection, 2...Boss portion, 3...Rotation axis. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1. A chord line center point P _R in a cross section when the impeller is cut on a cylindrical surface with a radius R centered on the rotation axis;
When the distance from the chord line center point Pb of the cross section of the blade boss section cut by a cylindrical surface with radius Rb to the plane Sc perpendicular to the axis of rotation is Ls, the suction side of the airflow is the positive direction. In the coordinate system, the above chord line center point P _R is always located in the positive direction with respect to the above Sc plane, and the value of δ _z that can be expressed as δ _z = tan ^-1 Ls/R-Rb is δ _z = 12.5° ~32.5°, and on the projection plane when the impeller is projected onto a plane perpendicular to the rotation axis, the chord line center point of the cross section when the boss part of the blade is cut by a cylindrical surface with radius Rb is Pb', in a coordinate system with the rotation axis as the origin O and the straight line connecting the O point and the Pb' point as the X axis, the chord line center point when the blade is cut by a cylindrical surface with radius R is If the angle between the straight line P _R ′-O and the above X axis is δ as P _R ′, then the radial distribution of δ is δ = δ _t ×R-Rb/Rt-Rb (Rt: blade Chip radius, Rb: Blade boss radius,
δ〓 _t : Angle between the straight line Pt'- _O and the In the developed view obtained by the expansion, if the shape of the warp line in the cross section of the blade is a circular arc shape, and the central angle for forming the circular arc is θ, then the radial distribution of θ is expressed as θ=(θt−θb )×(R-Rb)/(Rt-Rb)+θb (θt: Warp angle at the blade tip, θb: Warp angle at the blade boss), θt=20°~30°, θb=27°~ 37°,
An axial flow impeller characterized in that θt<θb. 2 The chord line center point P _R in the cross section when the impeller is cut on a cylindrical surface with radius R centered on the rotation axis,
When the distance from the chord line center point Pb of the cross section of the blade boss section cut by a cylindrical surface with radius Rb to the plane Sc perpendicular to the axis of rotation is Ls, the suction side of the airflow is the positive direction. In the coordinate system, the above chord line center point P _R is always located in the positive direction with respect to the above Sc plane, and the value of δ _z that can be expressed as δ _z = tan ^-1 Ls/R-Rb is δ _z = 12.5° ~32.5°, and on the projection plane when the impeller is projected onto a plane perpendicular to the rotation axis, the chord line center point of the cross section when the boss part of the blade is cut by a cylindrical surface with radius Rb is Pb', in a coordinate system with the rotation axis as the origin O and the straight line connecting the 0 and Pb' points as the X axis, the chord line center point when the blade is cut by a cylindrical surface with radius R is If the angle between the straight line P _R ′-O and the above X axis is δ as P _R ′, then the radial distribution of δ is δ = δ _t ×R-Rb/Rt-Rb (Rt: blade Chip radius, Rb: Blade boss radius,
δ〓 _t : Angle between the straight line Pt'- _O and the In the developed view obtained by unfolding, when the angle formed by 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 ξ, the radial distribution of ξ is expressed as ξ= Given by (ξt - ξb) x (R - Rb) / (Rt - Rb) + ξb (ξt: bite angle at the blade tip, ξb: bite angle at the blade boss), ξt = 62° to 72°,
An axial flow impeller characterized in that ξb=53° to 63° and ξtξb. 3 The chord line center point P _R in the cross section when the impeller is cut on a cylindrical surface with radius R centered on the rotation axis,
When the distance from the chord line center point Pb of the cross section of the blade boss section cut by a cylindrical surface with radius Rb to the plane Sc perpendicular to the axis of rotation is Ls, the suction side of the airflow is the positive direction. In the coordinate system, the above chord line center point P _R is always located in the positive direction with respect to the above Sc plane, and the value of δ _z that can be expressed as δ _z = tan ^-1 Ls/R-Rb is δ _z = 12.5° ~32.5°, and on the projection plane when the impeller is projected onto a plane perpendicular to the rotation axis, the chord line center point of the cross section when the boss part of the blade is cut by a cylindrical surface with radius Rb is Pb', in a coordinate system with the rotation axis as the origin O and the straight line connecting the O point and the Pb' point as the X axis, the chord line center point when the blade is cut by a cylindrical surface with radius R is If the angle between the straight line P _R ′-O and the above X axis is δ as P _R ′, then the radial distribution of δ is δ = δ _t ×R-Rb/Rt-Rb (Rt: blade Chip radius, Rb: Blade boss radius,
δ〓 _t : Angle between the straight line Pt'- _O and the In the developed view obtained by the expansion, if the shape of the warp line in the cross section of the blade is a circular arc shape, and the central angle for forming the circular arc is θ, then the radial distribution of θ is expressed as θ=(θt−θb )×(R-Rb)/(Rt-Rb)+θb (θt: Warp angle at the blade tip, θb: Warp angle at the blade boss), θt=20°~30°, θb=27°~ 37°,
When θt<θb and in the above development diagram, 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 ξ, then the radial distribution of ξ is ξ = (ξt - ξb) × (R - Rb) / (Rt - Rb) + ξb (ξt: Bite angle at the blade tip, ξb: Bite angle at the blade boss), ξt = 62° to 72°,
An axial flow impeller characterized in that ξb=53° to 63° and ξtξb. 4 The chord line center point P _R in the cross section when the impeller is cut on a cylindrical surface with radius R centered on the rotation axis,
When the distance from the chord line center point Pb of the cross section of the blade boss section cut by a cylindrical surface with radius Rb to the plane Sc perpendicular to the axis of rotation is Ls, the suction side of the airflow is the positive direction. In the coordinate system, the above chord line center point P _R is always located in the positive direction with respect to the above Sc plane, and the value of δ _z that can be expressed as δ _z = tan ^-1 Ls/R-Rb is δ _z = 12.5° ~32.5°, and on the projection plane when the impeller is projected onto a plane perpendicular to the rotation axis, the chord line center point of the cross section when the boss part of the blade is cut by a cylindrical surface with radius Rb is Pb', in a coordinate system with the rotation axis as the origin O and the straight line connecting the O point and the Pb' point as the X axis, the chord line center point when the blade is cut by a cylindrical surface with radius R is If the angle between the straight line P _R ′-O and the above X axis is δ as P _R ′, then the radial distribution of δ is δ = δ _t ×R-Rb/Rt-Rb (Rt: blade Chip radius, Rb: Blade boss radius,
δ〓 _t : Angle between the straight line Pt'- _O and the In the developed view obtained by the expansion, if the shape of the warp line in the cross section of the blade is a circular arc shape, and the central angle for forming the circular arc is θ, then the radial distribution of θ is expressed as θ=(θt−θb )×(R-Rb)/(Rt-Rb)+θb (θt: Warp angle at the blade tip, θb: Warp angle at the blade boss), θt=20°~30°, θb=27°~ 37°,
When θt<θb and in the above development diagram, 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 ξ, then the radial distribution of ξ is ξ = (ξt - ξb) × (R - Rb) / (Rt - Rb) + ξb (ξt: Bite angle at the blade tip, ξb: Bite angle at the blade boss), ξt = 62° to 72°,
ξb = 53° to 63°, ξtξb, and in the above development diagram, when the chord length of the blade is L and the pitch between the blades at the same radius point is T, the ratio of T and L at each radius point is An axial flow impeller characterized in that T/L is 1 to 1.1.