JP2008064044A - Centrifugal fan impeller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a centrifugal fan impeller capable of achieving a reduction of noise by preventing the periodicity of the noise even with a large number of wings and achieving a rotation balance for restraining rotational oscillation at a low level. <P>SOLUTION: The centrifugal fan impeller 1 comprises a main board 2 directly linked with a driving source, a side board disposed by facing the main board 2, and a plurality of wings 4 arranged circumferentially between the main board 2 and the side board, wherein the mounting angles θ<SB>1</SB>to θ<SB>7</SB>of the wings 4 are set uneven. Here, the mounting angles of the wings 4 provided adjacently are different with each other. The outlet pitches of the wings 4 are set even. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an impeller for a centrifugal fan, in which a plurality of blades are arranged in a circumferential direction between a main plate and a side plate disposed opposite thereto.

  The centrifugal fan is used to blow air to a heat exchanger such as a condenser or an evaporator in an air conditioning facility, for example, and performs a necessary blowing action by rotating the impeller (impeller) in the casing. Is.

  By the way, such centrifugal fans inevitably generate noise due to rotation. These noises include turbulent noise and rotational noise, and are formed by arranging a plurality of blades at equal pitches in the circumferential direction. In the pitch fan, rotational noise having an integral multiple of the fundamental frequency f based on the number Z of blades is generated. Here, the fundamental frequency f of the rotational noise is expressed by the following equation.

f = N × Z (Hz) (1)
Where N is the rotational speed of the centrifugal fan (rpm)
Z: Number of wings (sheets)
As a known technique for reducing the rotational noise, an unequal pitch fan is known in which the pitches on the inlet side and the outlet side of the blades are both unequal pitches. According to this unequal pitch fan, rotational noise based on the number of blades is known. Since the periodicity of the sound is broken and the sound components are dispersed, the noise can be reduced.

  However, since the exit pitch of the blades of the impeller (circumferential pitch on the outer diameter side) is unequal, there is a problem that it is difficult to balance the rotation of the impeller, and vibration is likely to occur due to poor balance. . In addition, in an impeller having a large number of blades, the ratio of the unequal pitch of the wings is reduced, so that the noise reduction effect due to the unequal pitch is also reduced.

  On the other hand, Patent Document 1 proposes that the pitches of the blades are equal on the inlet side and unequal on the outlet side.

  By the way, since the flow velocity differs between the side plate side and the main plate side of the impeller blade of the centrifugal fan (that is, in the blade width direction) due to the difference in flow direction turning, the flow velocity is slow on the side plate side, which causes vortexes. Noise is generated.

Therefore, Patent Document 2 proposes to continuously increase the exit angle of the blade from the main plate side along the side plate side.
JP 55-012227 A JP-A-8-247091

  However, even in the configuration proposed in Patent Document 1, there is a problem that the rotational balance of the impeller is difficult to achieve because the exit pitch of the blades of the impeller is unequal, and rotational vibration is likely to occur.

  Further, in the configuration proposed in Patent Document 2, since the blowing conditions between the blades are the same over the entire circumference, there is a problem that it is not possible to reduce rotational noise whose component is an integral multiple of the fundamental frequency. It was.

  The present invention has been made in view of the above problems, and an object thereof is to provide an impeller for a centrifugal fan that can reduce noise periodicity and reduce noise even when the number of blades is large. There is.

  Another object of the present invention is to provide an impeller for a centrifugal fan that is easy to balance rotation and can suppress rotational vibration to a small level.

  In order to achieve the above-mentioned object, the invention described in claim 1 includes a main plate directly connected to a drive source, a side plate disposed opposite to the main plate, and a plurality of plates arranged in the circumferential direction between the main plate and the side plate. A centrifugal fan impeller having a single blade is characterized in that the mounting angle of each blade is non-uniform.

  The invention according to claim 2 is characterized in that, in the invention according to claim 1, the mounting angles of the adjacent blades are made different from each other.

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein when the number of blades is an even number, the mounting angle of odd-numbered blades is set to the basic mounting angle θ, and the mounting of even-numbered blades is performed. The angle is alternately set to θ + Δθ and θ−Δθ.

  The invention according to claim 4 is the invention according to claim 1 or 2, wherein when the number of the blades is odd, the attachment angle of the blades except the last odd number is set to the basic attachment angle θ, and the even number The blade mounting angles are alternately set to θ + Δθ, θ−Δθ, and the last odd numbered blade mounting angle is set to θ−Δθ or θ + Δθ with respect to the previous even numbered blade mounting angle θ + Δθ or θ−Δθ. It is characterized by being set to.

  The invention according to claim 5 is the invention according to claim 3 or 4, characterized in that the Δθ is set in a range of (0.015 to 0.03) θ.

  The invention described in claim 6 is characterized in that, in the invention described in any one of claims 1 to 5, the exit pitch of the blades is made uniform.

  According to the first aspect of the present invention, since the mounting angles of the blades are made non-uniform, the blowing direction of air from the blades becomes non-uniform, the periodicity of the rotational noise of the impeller collapses, and the noise Noise can be reduced by interference (energy dispersion).

  According to the second to fourth aspects of the present invention, since the mounting angles of the adjacent blades are made different from each other, even if the number of blades is large, the mounting angle (blowing direction) varies greatly between the adjacent blades. Therefore, the noise periodicity can be destroyed to reduce noise.

  By the way, when the mounting angle of the odd-numbered blades is set to the basic mounting angle θ and the mounting angles of the even-numbered blades are alternately set to θ + Δθ and θ−Δθ as in the invention of claim 3 or 4, As a result of obtaining an appropriate value range of the change rate α (= Δθ / θ) with respect to the basic mounting angle θ of even-numbered blades from the viewpoint of the rotational noise reduction rate and the unbalance, α = 1.5% to 3 % (Optimum value of 2%) should be set.

  Therefore, according to the fifth aspect of the present invention, it is possible to simultaneously reduce noise and suppress rotational vibration.

  According to the invention described in claim 6, since the exit pitches of the blades are made uniform, the rotation balance (dynamic balance) can be easily obtained, and the rotation vibration can be suppressed small.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a perspective view of an impeller for a centrifugal fan according to the present invention, FIG. 2 is a cross-sectional view along the LL plane of FIG. 1 showing blade mounting angles (when the number of blades is 7 (odd number)), FIG. 3 is a cross-sectional view along the LL plane of FIG. 1 showing the mounting angle of the blades (when the number of blades is 8 (even number)), FIG. 4 is a velocity vector diagram in the blade arrangement shown in FIG. 2, and FIG. 3 is a velocity vector diagram in the blade arrangement shown in FIG. 3, FIG. 6 is a diagram in the direction of arrow A in FIG. 1 showing a comparison of velocity vectors at the same passing point of the blade, and FIG. FIG. 7B is a diagram showing the relationship between the mounting angle change rate and the ratio unbalance, and FIG. 8 is a graph showing the noise frequency characteristics of the centrifugal fan impeller according to the present invention. FIG. 9 is a diagram showing the noise frequency characteristics of the impeller, and FIG. 9 is a diagram illustrating the distribution of the blade mounting angle with respect to the number of blades of the centrifugal fan impeller according to the present invention. Relationship diagram, FIG. 10 is a sequence relationship diagram of the velocity vector for the wing number of the centrifugal fan impeller according to the present invention.

  As shown in FIG. 1, an impeller 1 for a centrifugal fan according to the present invention includes a flat disk main plate 2 and a short nozzle disk-shaped side plate (shroud) 3 disposed opposite to the main plate 2 at a predetermined distance. And a plurality of (7 in the example shown in FIG. 1) blades 4 arranged in the circumferential direction between the main plate 2 and the side plates 3. A frustoconical boss 5 is erected at the center of the shaft of the main plate 2, and an output shaft (motor shaft) of a motor (not shown) as a drive source is inserted and fixed to the boss 5. Therefore, the impeller 1 is directly connected to a motor (not shown) that is a drive source via the boss 5.

  Here, in the impeller 1 according to the present invention, the arrangement of the blades 4 when the number of blades 4 is 7 (odd number) and when the number is 8 (even number) is shown in FIG. 2 and FIG. The present invention is characterized in that the mounting angles of the blades 4 are non-uniform, and the outlet pitch of each blade 4 (the circumferential pitch between adjacent blades 4) is uniform. The blade 4 mounting angle is defined as an angle formed by a straight line drawn from the rotation center of the impeller 1 to the trailing edge of each blade 4 and a chord of the blade 4, and an air blowing angle from each blade 4. Matches.

  The impeller 1 according to the present invention is characterized in that the mounting angles of the adjacent blades 4 are different from each other. Specifically, there is a slight difference in how the mounting angles are arranged depending on whether the number of blades 4 is an even number or an odd number, and when the number of blades 4 is an even number, 4 is set to the basic mounting angle θ, and the mounting angles of the even-numbered blades 4 are alternately set to θ + Δθ and θ−Δθ. On the other hand, when the number of blades 4 is an odd number, the mounting angle of the blades 4 except the last odd number is set to the basic mounting angle θ, and the mounting angles of the even numbered blades 4 are alternately set to θ + Δθ, θ−. At the same time, the mounting angle of the last odd numbered blade 4 is set to θ−Δθ or θ + Δθ with respect to the mounting angle θ + Δθ or θ−Δθ of the previous even numbered blade 4. This will be described more specifically with reference to FIGS. 2, 3 and 9 in the case where the number of blades 4 is 7 (odd number) and 8 (even number).

1) When the number of blades is 7 (odd number):
As shown in FIG. 2, when numbers “1” to “7” are sequentially assigned to the seven blades 4 along the clockwise direction in FIG. 2, as shown in FIG. The mounting angles θ ₁ , θ ₃ , and θ ₅ of the _first , _third , and fifth blades 4 that are odd-numbered except for the th are set to the basic mounting angle θ.

The mounting angle θ ₂ of the even-numbered second blade 4 is set to θ + Δθ larger by Δθ than the basic mounting angle θ, and the mounting angle θ 4 of the fourth blade ₄ is larger than the basic mounting angle θ. The mounting angle θ ₆ of the _sixth blade 4 is set to θ + Δθ which is larger by Δθ than the basic mounting angle θ. As described above, the mounting angles θ ₂ , θ ₄ , and θ ₆ of the even-numbered blades 4 are set to values θ + Δθ, θ−Δθ, θ + Δθ, respectively, in which addition and subtraction of Δθ are alternately repeated with respect to the basic mounting angle θ. Has been. In the example shown in FIG. 9, Δθ = 0.02θ is set.

Then, the mounting angle θ ₇ of the last odd-numbered seventh blade 4 is −Δθ having an opposite sign to + Δθ of the mounting angle θ ₆ (= θ + Δθ) of the even-numbered sixth blade 4 before that. Is added to θ (actually, Δθ is subtracted from θ) to θ−Δθ.

In summary, the mounting angles θ _{1 to} θ ₇ of the blades 1 are set as follows.

θ ₁ = θ ₃ = θ ₅ = θ
θ ₂ = θ ₆ = θ + Δθ
θ ₄ = θ ₇ = θ−Δθ
2) When the number of blades is 8 (even):
As shown in FIG. 3, when the numbers of “1” to “8” are sequentially assigned to the eight blades 4 along the clockwise direction of FIG. 3, as shown in FIG. The mounting angles θ ₁ , θ ₃ , θ ₅ , θ ₇ of the _fifth , _seventh blades 4 are set to the basic mounting angle θ.

In addition, the mounting angles θ ₂ , θ ₄ , θ ₆ , and θ ₈ of the even-numbered ₂ , ₄ , ₆ , and _8th blades 4 were alternately repeated by adding and subtracting Δθ from the basic mounting angle θ The values θ + Δθ, θ−Δθ, θ + Δθ, and θ−Δθ are set. In the example shown in FIG. 9, Δθ = 0.02θ is set.

In summary, the mounting angles θ _{1 to} θ ₈ of the blades 1 are set as follows.

θ ₁ = θ ₃ = θ ₅ = θ ₇ = θ
θ ₂ = θ ₆ = θ + Δθ
θ ₄ = θ ₈ = θ−Δθ
In the above, the method of setting the mounting angle of each blade 4 has been specifically described in the case where the number of blades 4 is 7 and 8. However, the mounting of each blade 4 is also performed in the case of other numbers. The angle is set according to the above law. Although FIG. 9 shows the case where the number of blades 4 is 3 to 11, the mounting angle of each blade 4 is similarly set when the number of blades 4 is 12 or more.

Thus, when the number of blades 4 is 7 or 8 as described above, the mounting angles θ _{1 to} θ ₇ and θ _{1 to} θ _{8 of} each blade 4 are shown in FIGS. 9 and FIG. 9, as a result of setting the three values θ, θ + Δθ, and θ−Δθ, the velocity belt of the air blown out from each blade 4 of the impeller 1 is shown in FIGS. 4, 5, and 10. As shown in FIG. 3, the directions are different from each other in W1, W2, and W3. This will be described more specifically with reference to FIGS. 4, 5, and 10 when the number of blades 4 is 7 (odd number) and 8 (even number).

1) When the number of blades is 7 (odd number):
When the number of the blades 4 is 7, as shown in FIGS. 4 and 10, the air blowing direction at the odd-numbered first, third, and fifth blades 4 is the vector W1 direction (mounting angle θ The air blowing direction at the even and second and sixth blades 4 is the vector W2 direction (corresponding to the mounting angle θ + Δθ), the even-numbered fourth and odd-numbered seventh blade 4. The air blowing direction is the vector W3 direction (corresponding to the mounting angle θ−Δθ).

  In summary, the air blowing directions at the blades 4 are as follows.

1st, 3rd and 5th wings = vector W1
2nd and 6th wings = vector W2
4th and 7th wing = vector W3
1) When the number of blades is 8 (even number):
When the number of the blades 4 is 8, as shown in FIGS. 5 and 10, the air blowing direction at the odd-numbered first, third, fifth and seventh blades 4 is the vector W1 direction (attachment). (Corresponding to the angle θ), the air blowing direction of the even-numbered second and sixth blades 4 is the vector W2 direction (corresponding to the mounting angle θ + Δθ), and the even-numbered fourth and eighth blades 4 The blowing direction is the vector W3 direction (corresponding to the mounting angle θ−Δθ).

  In summary, the air blowing directions at the blades 4 are as follows.

1st, 3rd, 5th and 7th wings = vector W1
2nd and 6th wings = vector W2
4th and 8th wings = vector W3
FIG. 10 shows the case where the number of blades 4 is 3 to 11, but the air blowing direction in each blade 4 is the same as above even when the number of blades 4 is 12 or more. Determined according to.

  Thus, as a result of the above, the velocity belt of the air blown out from each blade 4 of the impeller 1 is directed to three different directions of W1, W2, and W3 with respect to the same passing point as shown in FIG.

  By the way, when the mounting angle of the odd-numbered blades 4 is set to the basic mounting angle θ and the mounting angles of the even-numbered blades 4 are alternately set to θ + Δθ and θ−Δθ as described above, As a result of obtaining the range of the appropriate value of the change rate α (= Δθ / θ) with respect to the basic mounting angle θ from the viewpoint of unbalance with the rotational noise reduction rate, as shown in FIGS. 7 (a) and 7 (b). Results were obtained. As is apparent from these drawings, a range of α = 1.5% to 3% (optimum value 2%) is obtained as an appropriate value of the change rate α.

  In the present embodiment, α = 2% is set (see FIG. 9). For example, when the basic mounting angle θ is set to θ = 20 °, Δθ = 0.02θ = 0.02 × 20 ° = 0. Since it is .4 °, the mounting angle of the even-numbered blades 4 is alternately repeated at 20.4 ° and 19.6 °.

  Note that JIS B 0905 “Rotating body—Rigid rotor balance” is known as a balance standard, and according to this, the recommended balance grade for fans is G6.3. The “ratio imbalance” is defined as a value obtained by dividing the static imbalance in the rigid rotor by the mass of the rotor, and is equal to the deviation of the center of mass of the rotor from the axial center line.

  Thus, the centrifugal fan impeller 1 according to the present invention is driven to rotate at a predetermined speed in the direction of arrow R in FIG. 1 within a casing (not shown) when a motor (not shown) is started. Then, air is introduced into the impeller 1 from the opening 3 a of the side plate 3 of the impeller 1 in the axial direction (from the upper side to the lower side in FIG. 1), and this air is between the plurality of blades 4 in the impeller 1. As shown in FIG. 4, when static pressure and dynamic pressure are applied from the blades 4 when passing through the blades, they flow outward in the radial direction under centrifugal force. For example, when the number of blades 4 is seven, as shown in FIG. On the other hand, when the number of blades 4 is 8, as shown in FIG. 5, the blades 4 are blown from the rear edges of the blades 4 in the direction of the speed vectors W1, W2, and W3, respectively. Made.

  In the above, in the centrifugal fan impeller 1 according to the present invention, since the mounting angles of the blades 4 are non-uniform, the blowing direction of air from the blades 4 is non-uniform, and the impeller 1 rotates. The periodicity of the noise is lost, and the noise is reduced by noise interference (energy dispersion).

  In particular, since the mounting angles of adjacent blades 4 are different from each other, even if the number of blades 4 is large, the mounting angle (blowing direction) can be greatly changed between the adjacent blades 4. Noise periodicity can be destroyed and noise reduction can be achieved. In this case, since the exit pitches of the blades 4 are equalized, it is easy to achieve a rotational balance (dynamic balance), and the rotational vibration of the impeller 1 can be suppressed to a small level.

  Here, the noise frequency characteristic when the impeller 1 having seven blades 4 is rotationally driven at 500 rpm is compared with the noise frequency characteristic when the conventional impeller is rotationally driven under the same conditions as shown in FIG. Show. In FIG. 8, the horizontal axis represents the center frequency (Hz), the vertical axis represents the noise level (dB), the solid line represents the noise frequency characteristic of the impeller according to the present invention, and the broken line represents the noise frequency characteristic of the conventional impeller. Each is shown.

The basic frequency f of the impeller is from the above equation (1).
f = 500 × 7/60 = 58.3 Hz
Thus, as shown in FIG. 8, it was confirmed that the primary component of noise at the fundamental frequency f is 48 dB in the conventional impeller, but is reduced to 36 dB in the impeller according to the present invention.

  Further, as shown in FIG. 8, the secondary component of the noise at the fundamental frequency f × 2 = 116.6 Hz is 41 dB in the conventional impeller, but is reduced to 33 dB in the impeller according to the present invention. Was confirmed.

  INDUSTRIAL APPLICABILITY The present invention is suitable for an air conditioner equipped with a heat exchanger or a filter on the outlet side of a centrifugal fan, a device that requires rectification such as an air cleaner, and the like.

It is a perspective view of the impeller for centrifugal fans concerning the present invention. FIG. 2 is a cross-sectional view (when the number of blades is 7 (odd number)) along the LL plane of FIG. FIG. 2 is a cross-sectional view (when the number of blades is 8 (even number)) along the LL plane of FIG. FIG. 3 is a velocity vector diagram in the blade arrangement shown in FIG. 2. FIG. 4 is a velocity vector diagram in the blade arrangement shown in FIG. 3. It is a figure of the arrow A direction of FIG. 1 which compares and shows the velocity vector in the same passing point of a wing | blade. (A) is a figure which shows the relationship between an attachment angle change rate and a rotation noise reduction rate, (b) is a figure which shows the relationship between an attachment angle change rate and a ratio imbalance. It is a figure which compares the noise frequency characteristic of the impeller for centrifugal fans which concerns on this invention with the noise frequency characteristic of the conventional impeller. It is an arrangement | sequence relational diagram of the attachment angle of the blade | wing with respect to the number of blades of the impeller for centrifugal fans which concerns on this invention. It is an arrangement | sequence relational diagram of the speed vector with respect to the number of blades of the impeller for centrifugal fans which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Centrifugal fan impeller 2 Main plate 3 Side plate 3a Side plate suction port 4 Blade 5 Boss θ _{1 to} θ ₈ Blade mounting angle W1 to W3 Speed vector

Claims (6)

In a centrifugal fan impeller comprising a main plate directly connected to a drive source, a side plate opposed to the main plate, and a plurality of blades arranged in the circumferential direction between the main plate and the side plate,
An impeller for a centrifugal fan, wherein the mounting angles of the blades are non-uniform.   The impeller for a centrifugal fan according to claim 1, wherein the mounting angles of the adjacent blades are different from each other.   When the number of blades is an even number, the mounting angle of odd-numbered blades is set to a basic mounting angle θ, and the mounting angles of even-numbered blades are alternately set to θ + Δθ and θ−Δθ. Item 3. An impeller for a centrifugal fan according to item 1 or 2.   When the number of blades is an odd number, the blade mounting angle except for the last odd number is set to the basic mounting angle θ, and the mounting angles of the even numbered blades are alternately set to θ + Δθ and θ−Δθ. 3. The centrifugal fan according to claim 1, wherein the mounting angle of the odd numbered blades is set to θ−Δθ or θ + Δθ with respect to the mounting angle θ + Δθ or θ−Δθ of the previous even numbered blades. Impeller.   5. The impeller for a centrifugal fan according to claim 3, wherein the Δθ is set in a range of (0.015 to 0.03) θ.   The centrifugal fan impeller according to any one of claims 1 to 5, wherein an outlet pitch of the blades is made uniform.

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