JP2002161897A - Centrifugal fluid machinery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a low noise with an inexpensive structure while maintaining a high efficiency in a centrifugal fluid machinery. SOLUTION: A resonance frequency in a flow passage space including gap spaces 7, 8 between a centrifugal impeller 2 and casings 12, 13 is analyzed. When a blade passing sound frequency N×Zi generated in the case where the centrifugal impeller 2 is rotated at a rotation frequency N or n degree higher harmonic component n×N×Zi is coincident with the resonance frequency f obtained by an analysis, it is judged whether or not a noise is amplified. Thereby, an operation at a singular or plural rotation frequency at which the noise obtained by this judgment amplifies or a rotation frequency near the rotation frequency is avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a centrifugal fluid machine, and more particularly to a centrifugal fluid machine having a bladed diffuser used as a centrifugal compressor or an electric blower of a vacuum cleaner.

[0002]

2. Description of the Related Art A centrifugal fluid machine often uses a diffuser with blades of a centrifugal impeller in order to improve its efficiency. However, the outlet flow velocity of the centrifugal impeller of the centrifugal fluid machine is not uniform in the circumferential direction, that is, in the blade pitch direction. As a result, a periodically fluctuating flow flows into the diffuser, and the frequency of the fluctuating flow becomes equal to the blade passing frequency of the centrifugal impeller, that is, (number of blades) × (rotation frequency). For this reason, there is a problem in that a diffuser with blades generates more noise at the blade passing frequency than a diffuser without blades.

Therefore, as a conventional centrifugal compressor, as shown in JP-A-6-307392 (prior art 1), the blade passing frequency component of the centrifugal compressor noise is reduced, and In order to provide a centrifugal compressor in which the friction loss of the centrifugal compressor is also reduced, in a centrifugal compressor including a centrifugal impeller and a diffuser with blades, the diffuser has a pair of diffuser plates and a leading edge radius of a circular blade row shape therebetween is equal. It is composed of guide vanes of different lengths, and one or more short guide vanes are installed between adjacent long guide vanes,
The total number of guide blades is 1.5 to 1.
In some cases, the throat is formed only in a part of the inter-blade flow path of the guide blade.

As a conventional electric blower used in a vacuum cleaner or the like, a centrifugal impeller driven by a motor as disclosed in Japanese Patent Application Laid-Open No. 62-70695 (prior art 2) is known. An air guide having a passage for guiding the airflow sent from the impeller to the motor from the outer periphery of the impeller, a casing enclosing the impeller and the air guide, and a support rubber covered on the outer periphery of the casing for attachment to the device. In some cases, a hole is formed near the outer periphery of the impeller of the casing, and a concave portion is formed in the support rubber so as to face the hole to reduce high-frequency noise, which is particularly problematic in electric blowers.

Further, as an electric blower used in a conventional vacuum cleaner, as disclosed in Japanese Patent Application Laid-Open No. 8-164,096 (prior art 3), in an electric blower having a diffuser, each blade of the diffuser is used. A plurality of holes located between the diffuser plate are provided, and a cavity communicating with the hole is provided on the back side of the diffuser plate,
In some cases, noise is reduced by providing a sound absorbing material in the cavity.

[0006]

However, the prior art 1 has a problem that the shape of the guide vanes of the diffuser is complicated and the number of guide vanes is increased, so that the manufacturing cost is increased.

Further, in the prior art 2, since the hole of the impeller and the concave portion of the support rubber are formed only on the outer peripheral portion, the noise is not reduced over the entire radial space of the gap between the impeller and the casing. There was a problem that noise could not be reduced sufficiently.

Further, in the prior art 3, there is a problem that the efficiency of the electric blower is reduced due to an increase in flow resistance due to the presence of the opening and the cavity communicating with the opening at the blade portion of the diffuser.

In the prior arts 1 to 3, the resonance frequency in the flow path space including the space between the impeller and the casing is analyzed, and the resonance frequency is matched with the blade passing sound frequency to check the noise. No attempt is made to reduce this.

[0010] An object of the present invention is to provide a centrifugal fluid machine that is inexpensive and that can achieve high noise while maintaining high efficiency.

[0011]

A representative example of the present invention for achieving the above object is a centrifugal impeller provided with a plurality of impeller blades having a number of blades Zi in a circumferential direction, and a centrifugal impeller of the centrifugal impeller. In a centrifugal fluid machine including a diffuser arranged downstream and having a plurality of guide blades having the number of blades Zd in the circumferential direction, and a casing installed before and after the centrifugal impeller, the centrifugal impeller and the casing The resonance frequency in the flow path space including the gap space is analyzed, and the blade passing sound frequency N × Zi generated when the centrifugal impeller rotates at the rotation frequency N or its nth harmonic component n × N
By determining whether or not the noise is amplified when × Zi matches the resonance frequency obtained by the analysis, one or more rotation frequencies at which the noise obtained by this determination is amplified and the rotation around the rotation frequency are determined. The configuration is such that operation at a frequency is avoided.

Preferably, the blade passing sound frequency N × Zi generated when the centrifugal impeller rotates at a rotation frequency N
And whether or not noise increases when the resonance frequency obtained by the analysis coincides is determined by determining whether the order m of the circumferential mode of the centrifugal impeller of the resonance mode corresponding to the resonance frequency is M1 = Mod (Zi, Zd) or M2 = Zd-mod (Zi, Zd),
This is to determine the resonance frequency at which the noise increases.

Preferably, the n-th harmonic component n × N × Zi of the blade passing sound frequency generated when the centrifugal impeller rotates at the rotation frequency N matches the resonance frequency obtained by the analysis. It is determined whether or not the noise to be performed increases when the order m of the circumferential mode of the centrifugal impeller of the resonance mode corresponding to the resonance frequency is M1 =
mod (nZi, Zd) or M2 = Zd-mod (n
Zi, Zd) is determined to be a resonance frequency at which noise increases.

Another typical example of the present invention for achieving the above object is a centrifugal impeller provided with a plurality of impeller blades in a circumferential direction, and a centrifugal impeller arranged downstream of the centrifugal impeller and having a guide blade. In a centrifugal fluid machine including a plurality of diffusers provided in a circumferential direction and a casing installed before and after the centrifugal impeller, sound is absorbed in the casing side facing a clearance space between the centrifugal impeller and the casing. The means is provided over a wide area extending in the circumferential direction with a long dimension in the radial direction.

Another typical example of the present invention for achieving the above object is a centrifugal impeller provided with a plurality of impeller blades in a circumferential direction, and a guide blade disposed downstream of the centrifugal impeller and having a guide blade. In a centrifugal fluid machine including a plurality of diffusers provided in a circumferential direction and a casing installed before and after the centrifugal impeller, noise propagation extending in a circumferential direction into a clearance space between the centrifugal impeller and the casing is provided. That is, a shielding means is provided.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. In the second and subsequent embodiments, the description overlapping with the first embodiment will be omitted. The same reference numerals in the drawings of the respective embodiments indicate the same or corresponding components.

First, a centrifugal fluid machine according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a sectional view of a main part of a centrifugal fluid machine according to a first embodiment of the present invention, FIG. 2 is a sectional view taken along line AA of FIG. 1, FIG. FIG. 4 is a diagram illustrating a comparison between the analysis result of the resonance frequency of the centrifugal fluid machine and the measured noise value, and FIG. 5 is a mode diagram at the resonance frequency of the gap space of the centrifugal fluid machine.

The centrifugal impeller 2 is provided with a rotating shaft 1 of a driving device 14.
And is rotated by the rotation of the rotating shaft 1 by the driving device 14. Further, the centrifugal impeller 2 is provided with a plurality of impeller blades 10 provided in a circumferential direction, and is configured to suck air from a front central portion and to blow out from an outer peripheral side surface between the impeller blades 10. I have. The driving device 14 is, for example, a motor whose rotation speed is controlled by the control device 20.

The casing 12 and the casing 13 are arranged so as to surround the centrifugal impeller 2 before and after the centrifugal impeller 2, and have clearance spaces 7, 8 between the casing 12 and the centrifugal impeller 2. A scroll 6 is provided on the outermost periphery of the casing 12.
Are formed. Then, the suction pipe 9 is connected to the centrifugal impeller 2.
Are arranged so as to form a suction passage in communication with a suction port at a central portion of the front surface of the casing 12, and are attached to the front surface of the casing 12.

The diffuser 11 is provided over the entire outer periphery on the downstream side of the centrifugal impeller 2 and is composed of diffuser plates 3 and 4 and the guide blades 5 located therebetween. The diffuser plate 3 is mounted inside the casing 12, and the diffuser plate 4 is shared with the outer peripheral portion of the casing 13. As shown in FIG. 4, a plurality of guide vanes 5 are provided in a circular cascade.

Here, the reason why noise is generated in the centrifugal fluid machine will be described.

When the driving device 14 is driven by the control of the control device 20, the rotating shaft 1 is rotated, and the centrifugal impeller 2 is rotated accordingly. Thereby, as shown by an arrow in FIG. 1, the air flow is accelerated by the centrifugal force received from the suction pipe 9 and received from the rotating impeller blades 10 and discharged from the centrifugal impeller 2 in the direction of the diffuser 11. Is done. The discharged flow is the centrifugal impeller 2 shown in FIG.
As shown by the velocity vector v of the flow emitted from the impeller blade 10 installed at the position, the speed is reduced at the position of the impeller blade 10.

For this reason, at the tip of the guide blade 5 provided in the diffuser 11, the blade passing sound frequency (N × N × N) which is the product of the rotation frequency N of the centrifugal impeller 2 and the number Zi of impeller blades.
It receives a fluctuating pressure at the frequency of Zi) and its harmonic components (n × N × Zi). Due to the fluctuating pressure, the blade passing sound component 202 of the noise shown in FIG. 4 is generated, and the noise overall value 201 of the noise is greatly increased. This increase in noise is caused by acoustic resonance occurring in the flow channel due to the fluctuating pressure generated at the tip of the guide blade 5.

The flow path of this flow passes through the diffuser 11 from the suction pipe 9 through the centrifugal impeller 2, passes through the scroll 6, and the casings 12 and 13 located in front and rear of the centrifugal impeller 2 in the axial direction. Clearance space 7 with impeller 2,
8. Generally, acoustic resonance occurs in a portion having a shape close to a closed space that surrounds the surroundings. Therefore, resonance easily occurs in the gap spaces 7 and 8 in the flow path of the centrifugal fluid machine illustrated in FIG.

Therefore, in the present invention, as shown in FIG.
First, the resonance frequency in the flow path including the clearance spaces 7 and 8 between the centrifugal impeller 2 and the casings 12 and 13 is analyzed (step 101), and the fluctuating pressure frequency generated at the tip of the guide blade 5, that is, It is determined whether or not noise is amplified when the blade passing sound frequency (N × Zi) or its harmonic component (n × N × Zi) matches the resonance frequency, and the noise amplification range is determined (step 102). Is controlled or the rotation speed is limited so as to avoid operation at the rotation speed of the noise amplification range 203 determined as shown in FIG.
With the configuration 3), the noise of the centrifugal fluid machine is reduced. These points will be specifically described below.

First, the resonance frequency analysis method 101 will be specifically described.

The clearance spaces 7 and 8 are respectively provided in the casing 1
2, a diffuser plate 3 and a centrifugal impeller 2, and a double cylindrical space surrounded by the rotating shaft 1, the diffuser plate 4 and the casing 13. Therefore, the analysis of the resonance frequency is an analysis problem of the resonance frequency in the space inside the double cylinder,
For example, Theoretic Acoustics (PM.
Morse, K.M. U. Ingard: Theoret
Ial Acoustics: Magraw-Hil
1 (1968)), as described on page 356, using the following method.

The sound pressure p in the space inside the double cylinder is constant in the sound pressure distribution in the direction of the rotation axis because the gap spaces 7 and 8 are thin in the direction of the rotation axis. If i is decomposed in a coordinate system in the circumferential direction φ and i is an imaginary unit, it is expressed by the following equation (1).

[0029]

(Equation 1) Here, when the equation (1) is substituted into the wave equation (2), two equations of the equations (3) and (4) are obtained from the independence of the variables.

[0030]

(Equation 2)

(Equation 3)

(Equation 4) Here, k is a wave number, and has a relationship of k = ω / c = 2πf / c with respect to the frequency f or the angular velocity ω of the sound.

Of the two equations (3) and (4), the general solution of Φ is cos (mφ), sin (mφ)
(M is the order of the resonance mode in the circumferential direction and is an integer of 0 or more)
It is. Further, the general solution of R is the Bessel function Jm (k
× w) (bessel function of the first kind or Bessel function in a narrow sense) and Nm (k × w) (Bessel function of the second kind or Neumann function).

On the outer (radius w1) and inner (radius w2) cylinder surfaces of the double cylinder, the particle velocity in the radial direction is set to 0.
Then, when equation (4) is modified, the following equation (5) is obtained.

[0033]

(Equation 5) Therefore, the circumferential resonance mode m = 2 and the radii w1 and w2 outside and inside the gap space 7 or 8 are substituted into the expression (5) to satisfy F (k) = 0 in the expression (5). By obtaining the value of k, the resonance frequency of the gap space 7 or 8 can be obtained. For example, when the circumferential resonance mode is m = 2,
The value of k satisfying the expression (5) is changed from the smaller value to k0, k1,
Assuming that k2, each k has a resonance mode shown in FIG. 5 having nodes of 0, 1, and 2 in the radial direction.
At this time, the corresponding resonance frequency f is f = (c / 2π) k
Is obtained by

As a method of analyzing the resonance frequency, a more accurate analysis can be performed by performing an eigenvalue analysis of the flow path including the gaps 7 and 8 by a finite element method or the like.

Next, the method 102 for determining the noise amplification range will be specifically described.

In order to cause resonance in the clearance spaces 7 and 8 in FIG. 1, an exciting force having a mode order m must exist in the circumferential direction at the resonance frequency f which is a solution of the equation (5). The circumferential mode is such that the centrifugal impeller 2 of the centrifugal fluid machine has the number of blades Zi, and the diffuser 11 has the number of blades Z.
When d is obtained, it can be obtained as follows.

As shown in FIG. 2, if the rotational frequency of the centrifugal impeller 2 is set to N in a state where the fluctuation pressure of the blade 10a on the centrifugal impeller 2 interferes with the guide blade 5a, the blade 10a The time T until the interference with the guide blade 5b is given by the following equation (6).

T = 1 / (N × Zd) (6) Further, the blade passing sound frequency at which interference between the centrifugal impeller 2 and the guide blade 5 of the diffuser 11 occurs is determined by the rotation frequency N of the centrifugal impeller 2 and the centrifugal impeller. This is the product N × Zi of the number of blades Zi of 2. At this blade passing sound frequency, during the time T until the blade 10a interferes with the guide blade 5a after interfering with the guide blade 5a, the phase of the sound at the blade passing sound frequency is expressed by the following equation (7). Advance by θ. That is, the phase of the fluctuating pressure at the tip of the guide blade 5b has a waveform delayed by θ in the following equation (7) with reference to the phase of the fluctuating pressure at the tip of the guide blade 5a.

Θ = 2πT / (1 / (N × Zi)) = 2πZi / Zd (7) Accordingly, the outer periphery of the clearance spaces 7 and 8 corresponds to the respective positions of the Zd guide blades 5 of the diffuser 11. Thus, there is a sound source whose phase is delayed by θ in the rotation direction of the centrifugal impeller 2. Here, the value of θ exceeds 2π when, for example, Zi> Zd from the above-mentioned equation (7). Since the actual phase of θ does not change even if 2π and its integral multiple are added or subtracted, a value converted to θ1 of 2π or less in the following equation (8) in order to obtain a low-order value at which resonance is most likely to occur. Is used.

Θ1 = (2π / Zd) mod (Zi, Zd) (8) As described above, the exciting force delayed by θ1 in phase at the blade passing sound frequency corresponding to the position of the diffuser causes the centrifugal impeller 2 Resonance occurs when the sound wave propagating in the rotational direction matches the resonance frequency in space. The mode M1 of the circumferential excitation force at this time is obtained by the following equation (9).

M1 = Zd × θ1 / 2π = mod (Zi, Zd) (9) Further, since the phase delay θ2 of the sound wave rotating in the reverse rotation direction of the centrifugal impeller 2 becomes θ2 = 2π−θ1, The circumferential exciting mode M2 in the reverse rotation direction is expressed by the following equation (1).
0).

M2 = Zd−mod (Zi, Zd) (10) Accordingly, in the noise amplification range determination method 102 of FIG. 3, the order of the resonance mode in the circumferential direction of the gap spaces 7 and 8 at the resonance frequency f is expressed by the following equation ( 9) or M1 or M2 in equation (10), it is determined that the noise is amplified, and in this case, the resonance frequency f and the frequency in the vicinity thereof are determined as the noise amplification range. Can be requested. The noise amplification range is determined to be 5% before and after the resonance frequency.

As a method 102 for determining the noise amplification range, a response analysis of the flow path including the gaps 7 and 8 by the finite element method, the boundary element method, or the like is combined with the above to quantitatively determine the amplification factor. By obtaining it, it is possible to perform more accurate analysis.

Next, a comparison between the determination result of the noise amplification range and the actually measured value of the noise will be described with reference to FIG.

FIG. 4 shows that the number of blades of the centrifugal impeller 2 is 11
The calculation results in the case of a centrifugal fluid machine with a combination of 12 blades and 12 diffuser guide blades are shown.
Modes M1 = 1 and M obtained from equations (9) and (10)
The result obtained by calculating the resonance frequency of the gap space 7 or 8 corresponding to 2 = 11 from the equation (6) and converting it into the number of rotations is shown by a white triangle or a black triangle in FIG. 4, respectively. Where M
Since the frequency corresponding to 2 = 11 is not in the illustrated range,
Only the mode corresponding to M1 = 1 is shown. The resonance frequency indicated by the open triangle or the closed triangle is the actually measured value 202 of the noise passing sound component and the actually measured value 2 of the overall noise.
It is clear from FIG. 4 that the peak coincides with the peak of No. 01. Further, the noise amplification range 203 determined to be 5% before and after the resonance frequency by the noise amplification range determination method 102 is substantially the same as the range in which the peak of the measured value of the noise passing sound component 202 of the noise and the measured value of the overall noise value are generated. It is clear from FIG. Therefore, it can be understood that by performing the above-described noise amplification range determination, the rotational speed at which the resonance phenomenon actually occurs can be predicted.

The noise amplification range judging method 10 shown in FIG.
In the case of using the nth harmonic component of the blade passing frequency as another method related to the blade number 2, the number N of blades of the centrifugal impeller 2
Should be regarded as n times, and the equations (9) and (10) may be replaced by the following equations (11) and (12), respectively.

M1 = mod (nZi, Zd) (11) M2 = Zd−mod (nZi, Zd) (12) Next, the method 103 for operating at a rotation speed that avoids a frequency at which noise is amplified will be specifically described. .

In the present embodiment, the drive unit 14 is controlled by the control unit 20 to control the rotation speed, so that the drive unit 14 is not operated at a constant speed in the noise amplification range. That is, when the rotation speed command value is within the noise amplification range, the rotation speed is changed to a rotation command value outside the noise amplification range, and the constant speed operation is performed outside the noise amplification range. Therefore, the constant speed operation in the drive device 14 is controlled by the variable speed that skips the noise amplification range. Thereby, the noise of the centrifugal fluid machine can be significantly reduced. In the case where the driving device is of a constant speed type in which the rotation speed is not controlled, the resonance frequency is analyzed in advance to determine the noise amplification range, and the centrifugal fluid in which the rotation speed is controlled to avoid the noise amplification range is limited. By configuring the machine, significant noise reduction can be achieved.

Next, a second embodiment of the present invention will be described with reference to FIGS.
This will be described with reference to FIG. FIG. 6 is a sectional view of a main part of a centrifugal fluid machine according to a second embodiment of the present invention, and FIG. 7 is a sectional view taken along line BB of FIG.

In this embodiment, in order to suppress the resonance phenomenon occurring in the gap spaces 7 and 8 in FIG.
The sound absorbing members 70 and 80 constituting the sound absorbing means are provided over a wide range extending in the circumferential direction with a long dimension in the radial direction on the surface opposed to the centrifugal impeller 2. In this way, with a simple configuration in which the sound absorbing members 70 and 80 are provided facing the clearance spaces 7 and 8, an increase in noise due to resonance can be suppressed, so that noise of the centrifugal fluid machine can be reduced. Specifically, since the sound absorbing members 70 and 80 are provided substantially over the front surfaces of the clearance spaces 7 and 8, an increase in noise due to resonance can be significantly suppressed. Further, by combining this embodiment with the above-described first embodiment, it is possible to further reduce noise.

Next, a third embodiment of the present invention will be described with reference to FIGS.
This will be described with reference to FIG. FIG. 8 is a sectional view of a main part of a centrifugal fluid machine according to a third embodiment of the present invention, and FIG. 9 is a sectional view taken along the line CC of FIG.

In this embodiment, in order to suppress the resonance phenomenon occurring in the clearance spaces 7 and 8 in FIG. 6, the protrusions 71, 72, 81,
By providing the 82 and 83 so as to extend in the circumferential direction and blocking the propagation of the sound wave in the radial direction of the centrifugal impeller 2, it is possible to suppress the occurrence of the resonance mode in the radial direction. Specifically, as is apparent from FIG.
Since 1, 72, 81, 82 and 83 are provided, the propagation of sound waves in the radial direction of the centrifugal impeller 2 can be remarkably cut off. In particular, since the increase in noise due to the outermost resonance can be reduced, the noise of the centrifugal fluid machine can be significantly reduced. Since the resistance to the rotation of the centrifugal impeller 2 due to the protrusions provided in the circumferential direction is small, the efficiency of the centrifugal fluid machine is hardly reduced. Further, if a sound absorbing material is provided in the circumferential direction at a portion sandwiched between the protrusions, noise transmitted in the circumferential direction can be reduced, and further noise reduction can be achieved. Further, by combining these with the first embodiment, it is possible to further reduce noise.

[0053]

As described above, according to the present invention,
It is possible to obtain a centrifugal fluid machine capable of realizing significantly low noise while maintaining high efficiency with an inexpensive structure.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a centrifugal fluid machine according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is an explanatory diagram showing a procedure for configuring the centrifugal fluid machine.

FIG. 4 is a diagram illustrating a comparison between an analysis result of a resonance frequency of the centrifugal fluid machine and a measured noise value.

FIG. 5 is a mode diagram at a resonance frequency of a gap space of the centrifugal fluid machine.

FIG. 6 is a sectional view of a main part of a centrifugal fluid machine according to a second embodiment of the present invention.

FIG. 7 is a sectional view taken along the line BB of FIG. 6;

FIG. 8 is a sectional view of a main part of a centrifugal fluid machine according to a third embodiment of the present invention.

FIG. 9 is a sectional view taken along the line CC in FIG. 8;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Rotating shaft, 2 ... Centrifugal impeller, 3, 4 ... Diffuser plate, 5 ... Guide blade, 6 ... Scroll, 7, 8 ... Clearance space, 9 ... Suction pipe, 10 ... Impeller blade, 11 ... Diffuser, 12 , 13 ... casing, 14 ... drive device, 20 ...
Control device, 70, 80 ... sound absorbing means, 71, 72, 81,
82, 83... Protrusions.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hiromi Kobayashi 603 Kandamachi, Tsuchiura-shi, Ibaraki F-term in Industrial Machinery Systems Division, Hitachi, Ltd. 3H021 AA01 BA06 BA16 CA08 DA06 EA04 EA13 3H034 AA02 AA13 BB02 BB03 BB06 BB20 CC03 DD05 DD21 DD28 EE06

Claims (5)

[Claims] 1. A centrifugal impeller provided with a plurality of impeller blades of a number Zi in the circumferential direction, and a diffuser arranged downstream of the centrifugal impeller and provided with a plurality of guide blades of the number of blades Zd in the circumferential direction. And a casing disposed before and after the centrifugal impeller, wherein the resonance frequency in a flow path space including a gap space between the centrifugal impeller and the casing is analyzed, and the centrifugal fluid is analyzed. When the impeller rotates at the rotation frequency N, the noise is amplified when the blade passing sound frequency N × Zi or its nth harmonic component n × N × Zi matches the resonance frequency obtained by the analysis. By determining whether or not to perform, it is configured to avoid driving at one or more rotation frequencies at which the noise obtained by this determination is amplified and at rotation frequencies in the vicinity thereof. Centrifugal fluid machine to be. 2. The method according to claim 1, further comprising the step of determining whether or not noise increases when the blade passing sound frequency N × Zi generated when the centrifugal impeller rotates at a rotation frequency N matches the resonance frequency obtained by the analysis. It is determined that the order m of the circumferential mode of the centrifugal impeller in the resonance mode corresponding to the resonance frequency is M1 = mod (Zi, Zd) or M2 = Zd−
The centrifugal fluid machine according to claim 1, wherein when it matches mod (Zi, Zd), it is determined that the resonance frequency is such that the noise increases. 3. An n-th harmonic component nx of a blade passing sound frequency generated when the centrifugal impeller rotates at a rotation frequency N.
The determination as to whether or not noise increases when N × Zi matches the resonance frequency obtained by the analysis is based on the order m of the circumferential mode of the centrifugal impeller in the resonance mode corresponding to the resonance frequency. Is M1 = mod (nZi, Z
2. The centrifugal fluid machine according to claim 1, wherein when d) or M2 = Zd-mod (nZi, Zd), the resonance frequency at which the noise increases is determined. 4. A centrifugal impeller provided with a plurality of circumferentially arranged impeller blades, a diffuser arranged downstream of the centrifugal impeller and provided with a plurality of circumferentially arranged guide blades, and front and rear of the centrifugal impeller. In the centrifugal fluid machine having a casing installed in the centrifugal impeller and the casing, facing the clearance space between the centrifugal impeller and the casing, the sound absorbing means is provided on the casing side in a radially long dimension extending in a circumferential direction over a wide range. A centrifugal fluid machine characterized by being provided. 5. A centrifugal impeller provided with a plurality of impeller blades in a circumferential direction, a diffuser arranged downstream of the centrifugal impeller and provided with a plurality of guide blades in a circumferential direction, and front and rear of the centrifugal impeller. A centrifugal fluid machine, comprising: a casing installed in the centrifugal impeller; and a noise propagation shielding means extending in a circumferential direction in a space between the centrifugal impeller and the casing.