JP2009019563A - Diffuser structure of centrifugal compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diffuser structure of a centrifugal compressor capable of increasing a natural frequency of a blade member, capable of preventing resonance of the blade member by avoiding coincidence of an excitation frequency of compressed air by passing through an impeller and the natural frequency of the blade member, capable of restraining vibration and noise in operation, and capable of avoiding adverse influence to the blade member. <P>SOLUTION: The blade member 7 of a diffuser member 8 is constituted by a housing side cantilever blade 7a protruding from a housing 1 side, and a seal plate side cantilever blade 7b protruding from a seal plate 5 side so as to confront the housing side cantilever blade 7a. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a diffuser structure for a centrifugal compressor.

  In general, centrifugal compressors are widely used in industrial gas compressors, turbochargers, jet engines, and the like.

  FIG. 7 is a schematic sectional view showing an example of a conventional centrifugal compressor. In the centrifugal compressor, an impeller 2 in which a plurality of impeller blades 2b are arranged on an impeller disk 2a in a housing 1 is provided as a rotor shaft. 3, and a diffuser portion 4 that is provided on the back surface of the impeller disk 2 a of the impeller 2 and that is formed larger than the outer diameter of the impeller 2 and decelerates compressed air between the housing 1 and the housing 1. A diffuser member in which a seal plate 5 to be formed is provided, and a plurality of blade members 7 for decelerating and rectifying compressed air are disposed on an annular member 6 on an outer peripheral portion of the seal plate 5 forming the diffuser portion 4 8 is attached by a countersunk screw or the like (not shown).

  In the centrifugal compressor shown in FIG. 7, the impeller 2 is rotationally driven by the rotor shaft 3 at a high speed, the air is compressed, and the compressed air is decelerated and rectified by the blade member 7 of the diffuser member 8 and discharged. It has become so.

An example of a general technical level of a diffuser structure of a centrifugal compressor is disclosed in Patent Document 1.
Japanese Patent Laid-Open No. 5-71498

  However, in the conventional centrifugal compressor as described above, since the wing member 7 of the diffuser member 8 has a structure like a cantilever projecting from the seal plate 5 side, the natural frequency is low. In the centrifugal compressor having a large flow rate, the overhang length of the blade member 7 is also increased, the excitation frequency of the compressed air caused by passing through the impeller 2 matches the natural frequency of the blade member 7, and the blade member 7 resonates. In addition to causing vibration and noise during operation, the strength of the wing member 7 itself may be affected.

  In view of such circumstances, the present invention can increase the natural frequency of the wing member, and avoid the coincidence between the excitation frequency of the compressed air caused by the impeller passage and the natural frequency of the wing member. Therefore, it is an object of the present invention to provide a diffuser structure for a centrifugal compressor that can prevent the occurrence of vibration and noise during operation and can also avoid adverse effects on the blade member itself.

The present invention includes a seal plate that is located on the back surface of the impeller and is formed larger than the outer diameter of the impeller and that forms a diffuser portion that decelerates the compressed air between the housing and the compressed air. In a diffuser structure of a centrifugal compressor in which a plurality of wing members for decelerating and rectifying are disposed,
The wing member is composed of a housing-side cantilever wing projecting from the housing side, and a seal plate-side cantilever wing projecting from the seal plate side so as to be opposed to the housing-side cantilever wing. The present invention relates to a diffuser structure of a centrifugal compressor.

  According to the above means, the following operation can be obtained.

  As described above, when the wing member is composed of the housing-side cantilever wing projecting from the housing side and the seal plate-side cantilever wing projecting from the seal plate side so as to be opposed to the housing-side cantilever wing, Both the cantilever blade on the housing side and the cantilever blade on the seal plate as a member have a structure like a cantilever, but the overhang length of the cantilever blade on the housing side and the overhang length of the cantilever blade on the seal plate side Therefore, the excitation frequency of the compressed air due to the impeller passage does not match the natural frequency of the cantilever blade on the housing side and the cantilever blade on the seal plate side, and the cantilever blade on the housing side and the cantilever side on the seal plate side The blades do not resonate and vibration and noise during operation are less likely to occur, and the strength of the blade member itself composed of the housing side cantilever blade and the seal plate side cantilever blade is increased. Worry on the sound is eliminated.

  In the diffuser structure of the centrifugal compressor, an overlap portion can be formed on the tip portion of the housing side cantilever blade and the tip portion of the seal plate side cantilever blade.

  In this case, the overlap portion can be formed in a wedge shape with tapered surfaces facing each other.

  In addition, the overlap portion may have a stepped shape facing each other so that the notch portions are fitted to each other.

  According to the diffuser structure of the centrifugal compressor of the present invention, it is possible to increase the natural frequency of the blade member, avoiding coincidence between the excitation frequency of the compressed air caused by the impeller passage and the natural frequency of the blade member. The resonance of the member can be prevented, and the excellent effects of suppressing the generation of vibration and noise during operation and avoiding the adverse effect on the blade member itself can be obtained.

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

  1 and 2 show an example of an embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 7 denote the same components, and the basic configuration is the conventional configuration shown in FIG. As shown in FIGS. 1 and 2, the feature of the illustrated example is that the wing member 7 of the diffuser member 8 is protruded from the housing 1 side, the housing side cantilever wing 7a, The seal plate side cantilever blades 7b project from the seal plate 5 side so as to face the housing side cantilever blades 7a.

  In the case of the illustrated example, the seal plate side cantilever blade 7b is embedded in the outer peripheral portion of the seal plate 5 forming the diffuser portion 4 in the same manner as the blade member 7 (see FIG. 7) of the conventional diffuser member 8. The housing-side cantilever blade 7a is disposed on the annular member 6 'that is attached so as to be embedded in the position of the housing 1 facing the annular member 6, The tip of the housing side cantilever 7a and the tip of the seal plate cantilever 7b are abutted as shown in FIG. Note that the gap c formed at this time is desirably as small as possible.

  Next, the operation of the illustrated example will be described.

  As described above, the wing member 7 has the housing-side cantilever wing 7a projecting from the housing 1 side, and the seal-plate-side cantilever wing 7b projecting from the seal plate 5 side so as to be opposed to the housing-side cantilever wing 7a. The housing side cantilever wing 7a and the seal plate side cantilever wing 7b as the wing member 7 are both structured like cantilever beams. Since the overhang length of the seal plate side cantilever blade 7b is shortened, the excitation frequency of the compressed air caused by the impeller passage matches the natural frequency of the housing side cantilever blade 7a and the seal plate side cantilever blade 7b. The housing-side cantilever blade 7a and the seal plate-side cantilever blade 7b do not resonate, making it difficult for vibration and noise during operation to occur. Affect concern the intensity of the wing member 7 itself consisting of a and the sealing plate side piece Jitsubasa 7b is eliminated.

但し、Ｅ：縦弾性係数［Ｎ／ｍ²］
Ｉ：断面二次モーメント［ｍ⁴］
Ａ：断面積［ｍ²］
ρ：密度［ｋｇ／ｍ³］
λ_r：振動モードによって定まる無次元係数
という式で表され、故に

となり、ｌを小さくすれば、固有振動数ｆ_rを大きくすることができる。 Here, the wing member 7 (housing cantilever 7a on the housing side, cantilever 7b on the seal plate side) has a straight uniform cross section having a height b, an overhang length l and a thickness t as shown in FIG. When considered as a cantilever beam, its natural frequency _fr is

E: Longitudinal elastic modulus [N / m ² ]
I: Sectional moment of inertia [m ⁴ ]
A: Cross-sectional area [m ² ]
ρ: Density [kg / m ³ ]
λ _r : Expressed by the equation of dimensionless coefficient determined by the vibration mode.

Next, by reducing the l, it is possible to increase the natural frequency f _r.

  On the other hand, a gap c is formed at the center of the flow path in the diffuser portion 4 having a width W. If the gap c is about 1% or less of the width W, the compressed air leaks from the gap c. The pressure loss due to does not significantly reduce the performance of the centrifugal compressor. In the case of a centrifugal compressor having a width W of about 20 [mm], the gap c can be set to about 0.1 [mm]. Further, as shown in FIG. 4, with reference to an arbitrary reference line extending in the radial direction from the central axis of the centrifugal compressor, compressed air from the intersection of the reference line and a circle passing through the base end of the blade member 7 is used. Is the inflow angle θ of the compressed air with respect to the wing member 7, the loss coefficient for the inflow angle θ of the compressed air is the wing member 7 of the present invention in which a gap c is formed in the center of the flow path (FIG. 4). The numerical simulation also shows that there is almost no change between the conventional wing member 7 (see the broken line in the diagram shown in FIG. 4) and the conventional wing member 7 (see the solid line in the diagram shown in FIG. 4).

Incidentally, from the [Expression 2] where, if the is also to increase the thickness t of the wing member 7 it is possible to increase the natural frequency f _r, increasing the thickness t of the wing member 7, compression This is not preferable because air resistance increases, leading to a reduction in efficiency and a disadvantage in performance. If the wing member 7 is fixed at both ends instead of being cantilevered, the natural frequency _fr can be increased without increasing the thickness t, but the wing member 7 is fixed at both ends. Is not preferable because it is difficult to manufacture and leads to an increase in cost.

  Thus, the natural frequency of the blade member 7 can be increased, and the resonance of the blade member 7 can be prevented by avoiding the coincidence between the excitation frequency of the compressed air caused by the impeller 2 and the natural frequency of the blade member 7. In addition, the occurrence of vibration and noise during operation can be suppressed and the influence on the strength of the blade member 7 itself can be avoided.

  FIG. 5 is a cross-sectional view showing a modification of the facing portion of the housing-side cantilever blade 7a and the seal plate-side cantilever blade 7b according to an embodiment of the present invention. The parts denoted by the same reference numerals represent the same items, and the basic configuration is the same as that shown in FIGS. 1 and 2, but the features of the illustrated example are as shown in FIG. The overlapping portion 9 is formed at the tip of the housing-side cantilever blade 7a and the tip of the seal plate-side cantilever blade 7b, and the tapered surface 10 is opposed to each other. This is in the shape of a wedge.

  As shown in FIG. 5, when an overlap portion 9 is formed on the tip of the housing side cantilever 7a and the tip of the seal plate side cantilever 7b, the housing side cantilever 7a and the seal are formed. It becomes possible to further reduce the pressure loss due to the leakage of the compressed air from the gap at the opposing portion of the plate-side cantilever blade 7b, which helps to prevent the performance of the centrifugal compressor from being lowered.

  Further, the overlap portion 9 is formed in a stepped shape so that the notch portions 11 are fitted to each other as shown in FIG. 6 instead of a wedge shape in which the tapered surfaces 10 face each other as described above. You can also.

  In addition, the diffuser structure of the centrifugal compressor of the present invention is not limited to the illustrated example described above, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

It is a schematic sectional drawing which shows an example of the form which implements this invention. It is sectional drawing which shows the opposing part of the housing side cantilever blade and seal plate side cantilever blade in an example which implements this invention, Comprising: It is the II-II cross-section equivalent figure of FIG. It is a perspective view at the time of considering the wing | blade member in an example of embodiment which implements this invention as a cantilever with a straight uniform cross section. It is the diagram which compared the loss coefficient with respect to the inflow angle of the compressed air in an example which implements this invention with the loss coefficient in a prior art example. It is sectional drawing which shows the modification of the opposing part of the housing side cantilever blade and seal plate side cantilever blade in an example which implements this invention, Comprising: It is the II-II cross-section equivalent view of FIG. It is sectional drawing which shows the other modification of the opposing part of the housing side cantilever blade and seal plate side cantilever blade in an example which implements this invention, Comprising: It is the II-II cross-section equivalent view of FIG. It is a schematic sectional drawing which shows an example of the diffuser structure of the conventional centrifugal compressor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Housing 2 Impeller 2a Impeller disk 2b Impeller blade 3 Rotor shaft 4 Diffuser part 5 Seal plate 6 Ring member 6 'Ring member 7 Wing member 7a Housing side cantilever 7b Seal plate side cantilever 8 Diffuser member 9 Overlap Part 10 Tapered surface 11 Notch

Claims (4)

A seal plate is provided on the back surface of the impeller and is formed larger than the outer diameter of the impeller and forms a diffuser portion that decelerates the compressed air with the housing. The diffuser portion decelerates and straightens the compressed air. In a diffuser structure of a centrifugal compressor in which a plurality of wing members are arranged,
The wing member is composed of a housing-side cantilever wing projecting from the housing side, and a seal plate-side cantilever wing projecting from the seal plate side so as to be opposed to the housing-side cantilever wing. Diffuser structure of centrifugal compressor.   The diffuser structure of the centrifugal compressor according to claim 1, wherein an overlapping portion is formed on each of a front end portion of the housing side cantilever blade and a front end portion of the seal plate side cantilever blade.   The diffuser structure of the centrifugal compressor according to claim 2, wherein the overlap portion has a wedge shape with tapered surfaces facing each other.   The diffuser structure of the centrifugal compressor according to claim 2, wherein the overlap portion has a stepped shape facing each other so that the notch portions are fitted to each other.

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