JP3720217B2 - Centrifugal compressor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a centrifugal compressor provided with an impeller and a diffuser that have improved fluid performance and reliability when handling a small volume of gas at a relatively high pressure.
[0002]
[Prior art]
Diffusers for centrifugal compressors can be broadly classified into vaneless diffusers and vaned diffusers, and each has functional advantages and disadvantages.
[0003]
First, since the direction of the flow discharged from the rotating impeller changes with the flow rate, a vaneless diffuser is often used for a centrifugal compressor in which the operating state and the flow rate change over a wide range.
[0004]
However, when applied to a so-called low specific speed compressor with a small handling flow rate, the impeller is designed to reduce its outflow angle, that is, the diffuser inlet flow angle, and the flow path height is low. When a vaneless diffuser is used as a diffuser, there is a problem that friction loss increases and efficiency decreases.
[0005]
In the case of a vaneless diffuser, in a low specific speed compressor, in many cases, a rotating stall occurs in the vaneless diffuser, and in a compressor that handles a high-pressure fluid, the operating range is limited by fluid excitation due to the rotating stall. There was a problem.
[0006]
On the other hand, in the diffuser with vanes, the vane outlet outer peripheral radius R1 and the diffuser vane leading edge are provided in order to provide a vaneless diffuser section in which the flow flowing out of the impeller decelerates to some extent and the wake of the vane outlet becomes uniform. Many configurations have a constant distance δ between the diameters R3.
[0007]
As an example, U.S. Pat. No. 3,771,925 and U.S. Pat. No. 3,824,029 show a centrifugal compressor having a configuration in which a vane-less diffuser section is equally formed if this distance δ is sufficiently taken.
[0008]
First, in the centrifugal compressor disclosed in US Pat. No. 3,771,925, the impeller is an open type having no side plate, the outer diameter of the core plate is larger than the outer diameter of the blade outlet, and the outer periphery of the blade outlet and the diffuser The aim is to reduce the shock wave by widening the space between the leading edges of the vanes and reducing the speed during this period.
[0009]
Next, in the centrifugal compressor disclosed in U.S. Pat. No. 3,824,029, the outer diameter of the impeller core plate and side plate is made considerably larger than the outer diameter of the blade outlet, and is decelerated at this rotating flow path portion. Immediately after that, a scroll for introducing the fluid is arranged.
[0010]
[Problems to be solved by the invention]
However, if the distance δ is excessively large, the configuration becomes close to the vaneless diffuser, so that the diffuser inlet flow angle becomes small in use at a low specific speed stage in which turning stall becomes a problem. In particular, the fluid near the wall surface tends to flow backward to the impeller outlet as the pressure gradient in the radial direction suddenly increases at the impeller outlet. This reverse flow is also considered to trigger a turning stall, and such a diffuser, that is, a configuration in which the distance δ is set too large, does not sufficiently suppress the turning stall.
[0011]
Therefore, in order to prevent the backflow near the wall surface, the ratio between the diffuser vane leading edge radius R3 and the impeller outer peripheral radius R2, that is, the diffuser vane leading edge radius ratio R3 / R2 is reduced, so that A method of constraining the mainstream with a diffuser vane and eliminating the portion where backflow occurs can be considered.
[0012]
However, this method is effective in preventing the rotation stall, but in the conventional impeller having the general configuration, the outer radius R1 of the vane outlet is equal to the outer radius R2 of the impeller, and therefore the leading edge radius of the diffuser vane. When the ratio R3 / R2 is reduced, the distance δ between the blade outlet outer peripheral radius R1 and the diffuser vane leading edge radius R3 is also reduced, and a high-speed air flow immediately after exiting the impeller collides with the diffuser vane, resulting in noise. It may become large or cause vibration.
[0013]
In other words, if the diffuser vane leading edge radius ratio R3 / R2 can be reduced to prevent turning stall without reducing the distance δ, a centrifugal compressor with lower noise and higher reliability can be provided. be able to.
[0014]
Here, the above prior art in an example of a centrifugal compressor in which a vane-less diffuser section is equally formed when the distance δ is sufficiently taken into consideration will be examined.
[0015]
First, U.S. Pat.No. 3,771,925 does not take into account turning stall at all, and the diameter of the disk is increased only for the core plate for shock wave countermeasures, but the distance from the leading edge of the diffuser vane is therefore long, And since it is an open type impeller without a side plate, there is a high possibility that a reverse flow on the side plate side will cause a turning stall, and this known example is not effective in preventing turning stall.
[0016]
Next, in US Patent No. 3,824,029, the outer diameter of both the core plate and the side plate is increased, aiming at effective deceleration at the rotating flow path, but compared to the diffuser with vane. The deceleration is small and the efficiency is not high. In addition, in order to configure all the functions of the diffuser with a rotating flow path, it is necessary to make the outer diameters of both the core plate and the side plate considerably larger than the outer diameter of the blade outlet. Due to the above constraints, there is a problem that it is not practical.
[0017]
As described above, particularly in a centrifugal compressor with a low specific speed, in addition to performance such as efficiency, prevention of turning stall generated in the diffuser and high reliability with low noise and low vibration are required. There was a problem that the technology did not satisfy all of these simultaneously.
[0018]
Therefore, in view of the above-mentioned problems, the object of the present invention is to operate in a relatively low specific speed and high pressure range, prevent the turning stall generated in the diffuser, and have high efficiency, low noise and low vibration reliability. It is to provide a highly efficient centrifugal compressor.
[0019]
[Means for Solving the Problems]
In order to achieve the above object, the centrifugal compressor according to the present invention adopts the following configuration.
[0020]
(1) A centrifugal impeller composed of two discs of a core plate and a side plate and a plurality of blades narrowed between them, and a diffuser with a vane in which a plurality of stationary vanes are provided downstream on the outer peripheral side of the centrifugal impeller In the centrifugal compressor provided, the outer diameters of the discs of the core plate and the side plates are made larger than the outer diameter of the blade outlet of the centrifugal impeller, and the inner diameter of the leading edge of the stationary vane is the inner diameter of the centrifugal impeller. A configuration in which the ratio R3 / R1 between the outer peripheral diameter R1 of the centrifugal impeller and the inner peripheral diameter R3 of the stationary vane is set to 1.1 or less by being installed close to the outer periphery of the core plate and the side plate. And
[0021]
Thus the present invention by configuring takes a predetermined radial distance between the vane leading edge of the blade outlet diffuser of the impeller, adjacent possible to weaken the interference of the impeller and the diffuser vanes, the impeller outlet Noise and vibration when the flow flows into the diffuser can be kept low.
[0022]
Furthermore, by configuring a rotating flow path (rotating diffuser) consisting of the impeller core plate and side plates immediately after the blade outlet, centrifugal force acts on the fluid near the rotating wall surface, and this part is likely to occur on the stationary wall. It acts to suppress backflow and separation on the wall surface, that is, to suppress the occurrence of turning stall.
[0023]
Since the flow that has passed through the rotating flow path portion flows into the diffuser vane immediately after that, the flow is turned and decelerated by the vane here. That is, it is possible to effectively decelerate and compress the flow while suppressing the backflow in the vicinity of the wall surface that triggers the turning stall.
[0024]
Further, by setting the ratio R3 / R1 before Symbol centrifugal impeller vane exit outside diameter R1 and the stationary vane of the leading edge inner circumferential diameter R3 to 1.1 or less, the strength constraints due to the centrifugal stress of the core plate, the side plate It becomes possible to suppress the turning stall without causing a problem.
[0025]
(2) The present invention also includes a centrifugal impeller composed of two discs, a core plate and a side plate, and a plurality of blades narrowed therebetween, and a plurality of stationary vanes on the outer peripheral side downstream of the centrifugal impeller. In the centrifugal compressor provided with the diffuser with vane to be installed, the outer diameters of the discs of the core plate and the side plate are made larger than the outer diameter of the blade outlet of the centrifugal impeller, and the inner diameter of the front edge of the stationary vane is The centrifugal impeller is installed close to the outer circumference of the core plate and the side plate, and the outer diameter of one of the two discs, the core plate and the side plate of the centrifugal impeller , is set from the other. also small, the stationary vane leading edge thereof in the circumference and configuration which is installed in an inclined leading edge to proximate to both the disc outer periphery of the core plate and the side plate.
By configuring in this way, the basic action (1) is obtained, and the generated impact is dispersed because the timing until the impeller outlet flow reaches the diffuser vane leading edge varies depending on the vane height direction. Thus, it is possible to reduce the overall noise and vibration.
[0026]
By configuring in this way, the impact that occurs because the timing until the impeller outlet flow reaches the leading edge of the diffuser vane varies depending on the vane height direction, so that the generated impact is dispersed and the overall noise and vibration can be reduced. It becomes possible.
[0027]
( 3 ) Also in ( 2 ) above, preferably, the ratio R3m / R1 of the blade outlet outer peripheral diameter R1 of the centrifugal impeller and the average front edge inner peripheral diameter R3m of the stationary vane is 1.1 or less. It is possible to suppress the rotation stall without causing a problem of strength restriction due to the centrifugal stress of the core plate / side plate.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0029]
First, FIG. 1 is a sectional view in the axial direction when the centrifugal compressor to which the present invention is applied is in the form of a multistage compressor. In this figure, five centrifugal compressors having different outlet heights in stages are connected to a single rotating shaft 4 and are provided with a return channel 10 in a fluid flow path between the centrifugal compressors of each stage. Further, the rotary shaft 4 of each stage compressor is hermetically sealed by labyrinth seals 12 and 13 and covered with a casing 8.
[0030]
Hereinafter, only one of the centrifugal compressors among them will be described.
[0031]
FIG. 2 shows a cross-sectional shape of the centrifugal compressor of the present embodiment. An impeller 1 is attached to a rotating shaft 4, and the impeller 1 includes a core plate 1b, a side plate 1c, and a plurality of blades 1a. On the outer periphery of the impeller 1, a diffuser 2 with a vane including a plurality of vanes 2a is installed in the vicinity of the outer edges of the core plate 1b and the side plate 1c of the impeller 1.
[0032]
Details of the vicinity of the exit of the impeller in FIG. 2 are shown in FIG. FIG. 4 shows a view in the direction AA in FIG. The main flow 3 flows out of the impeller 1 and is guided to the diffuser 2, and is composed of the core plate 1 b and the side plate 1 c of the impeller 1 after flowing out between the blades 1 a of the impeller and before flowing into the diffuser 2. It flows in the rotating flow path 7.
[0033]
In this rotating flow path 7, centrifugal force due to the viscous effect of the core plate 1b and the side plate 1c of the impeller 1 acts on the fluid 3a flowing near the wall surface, thereby suppressing separation near the wall surface. In the present invention, since the vane 2a of the diffuser is disposed immediately after the exit of the rotating flow path 7, the flow exiting the impeller 1 is guided to the diffuser vane 2a without being backflowed and restrained, thereby causing a turning stall. Is suppressed.
[0034]
In the present embodiment, since a predetermined distance δ1 can be taken between the outer periphery of the blade 1a of the impeller 1 and the front edge of the diffuser vane 2a, the interference action between the impeller 1 and the diffuser vane 2a is weakened. Noise and vibration generated when the vehicle outlet flow flows into the diffuser 2 can be reduced.
[0035]
In the embodiment of FIG. 3, it is desirable that the radial clearance distance δ2 be as small as physically possible. According to the literature (Senoo Y., Ishida M .: Behavior of Severly Asymmetric Flow In a Vaneless Diffuser ,: ASME J. of Engineering for Power, Vol. 99 (1977-3), It is said that it is uniform in the circumferential direction at a position 1.1 times the outer diameter of the outlet, so if the flow becomes uniform, the interference action of the diffuser vane 2a becomes weak, so the vane leading edge radius ratio R3 / R1 Therefore, the outer diameter R1 of the blade 1a of the impeller 1 and the radius R3 of the leading edge of the vane 2a are required in order to exhibit the effect of reducing the flow rate by the diffuser vane and increase the efficiency. The ratio R3 / R1 is preferably 1.1 or less.
[0036]
When R1 and R3 are selected in this way, the range of the impeller outer peripheral radius R2 is R2 / R1 of 1.1 or less, and within this range, the strength constraint due to the centrifugal stress of the core plate / side plate is not a problem. .
[0037]
In the second embodiment shown in FIG. 5, the radii R2h and R2s of the core plate 1e and the side plate 1d of the impeller 1 are set differently. However, the distance δ2 between the outer periphery of each disk and the front edge of the diffuser is made as small as in the case of FIG. 2, and the front edge of the vane 2d of the diffuser is inclined with respect to the rotational axis direction accordingly. ing. As a result, the radius R3h on the core plate side and the radius R3s on the side plate side of the front edge of the vane 2d are also different.
[0038]
In the case of a centrifugal compressor having a low specific speed and a low flow rate, on which the present invention is presumed to be applied, the flow velocity / flow rate distribution immediately after the impeller outlet is uniform in the outlet height direction except for a small part of the wall surface. 2 or 3, if the vane has a leading edge that is perpendicular to the wall surface (parallel to the outlet height direction and rotation axis direction), the vane flows out of the impeller. The resulting flow collides simultaneously with the height direction of the leading edge of the vane, and as a result, the largest impact is intensively generated.
[0039]
On the other hand, in this embodiment shown in FIG. 5, in addition to the effects of the embodiment of FIG. 2 or 3, the front edge of the vane 2d of the diffuser is inclined with respect to the rotation axis direction, thereby impeller 1 The distance until the flow that has flowed out reaches the leading edge of the diffuser vane 2d differs in the vane height direction. As a result, the impact that occurs because the flow collides with the vane 2d leading edge changes in the direction of the vane height (in time series), and as a result, the blade passing frequency noise (number of impeller blades × rotation) Generation of frequency component noise) can be suppressed, and the overall noise or vibration can be reduced.
[0040]
In the present embodiment shown in FIG. 5, the core plate 1e of the impeller is formed with an outer diameter larger than that of the side plate 1d, and the inner periphery on the side plate side of the front edge of the vane 2d is accordingly adjusted from the inner periphery on the core plate side. However, the present invention is not limited to this, and can be configured by reversing all the magnitude relations, and the effect of suppressing noise / vibration is also exhibited. is there.
[0041]
In the present embodiment of FIG. 5 as well, for the same reason as described above, the average of the outer peripheral diameter R1 of the impeller blade 1a and the leading edge of the vane 2d is exhibited in order to exert the effect of reducing the flow by the diffuser vane and increase the efficiency. The ratio with the radius R3m, R3m / R1, is preferably 1.1 or less. Here, R3m is R3m = (R3s + R3h) / 2.
[0042]
Further, the values of the above-mentioned radius ratios R3 / R1 and R3m / R1 will be described in more detail. In order to make the flow from the impeller uniform and weaken the interference action to the diffuser vane, a contradiction arises in that it is desired to set the value as high as possible.
[0043]
In actual design, the radius ratio is set by considering the balance between these two factors. At present, a value of 1.05 is the most desirable value in actual cases, and the material of the impeller It is known that a value of about 1.07 is most desirable when a high-strength material is selected.
[0044]
【The invention's effect】
According to the present invention, in a low specific speed centrifugal compressor using a vaned diffuser as a diffuser, with high efficiency and by taking a predetermined distance between the outer periphery of the impeller blade and the vane of the diffuser, Since the interference between the impeller and the diffuser is suppressed, low noise and vibration are realized, and there is an effect of preventing the rotating stall at the diffuser portion, it is possible to provide a compressor having a wide operation range and high reliability.
[Brief description of the drawings]
FIG. 1 is an axial sectional view of a multistage compressor to which the present invention is applied.
FIG. 2 is a partial cross-sectional view of a centrifugal compressor representing an embodiment of the present invention.
3 is a detailed partial cross-sectional view of an impeller outlet and a diffused portion of FIG. 2. FIG.
4 is a view in the AA direction of FIG. 3;
FIG. 5 is a partial cross-section of a centrifugal compressor representing a second embodiment of the present invention.
[Explanation of symbols]
1 impeller 1a impeller blade 1b, 1e impeller core plate 1c, 1d impeller side plate 2 diffuser 2a, 2d diffuser vane 3 main flow direction 3a flow direction of fluid flowing near wall surface 4 rotating shaft 5 vaneless Diffuser 6 Rotating direction 7 Rotating flow path (rotating diffuser) section 8 Casing 9 Bearing 10 Return channel 11 Discharge scroll 12, 13 Labyrinth seal R1 Blade outlet outer radius R2 Impeller outer radius R3 Diffuser vane leading edge radius δ1 Blade outlet and diffuser vane Clearance distance between the leading edge δ2 Clearance distance between the outer periphery of the impeller and the leading edge of the diffuser vane

Claims (3)

A centrifugal impeller comprising two discs of a core plate and a side plate and a plurality of blades narrowed therebetween, and a vaned diffuser for installing a plurality of stationary vanes on the outer peripheral side downstream of the centrifugal impeller In the compressor,
The outer diameter of the core plate and the side plate is larger than the outer diameter of the blade outlet of the centrifugal impeller, and the inner diameter of the front edge of the stationary vane is the circle of the core plate and the side plate of the centrifugal impeller. Install it close to the outer periphery of the plate ,
A centrifugal compressor characterized in that a ratio R3 / R1 between a blade outlet outer peripheral diameter R1 of the centrifugal impeller and a front edge inner peripheral diameter R3 of the stationary vane is 1.1 or less . A centrifugal impeller comprising two discs of a core plate and a side plate and a plurality of blades narrowed therebetween, and a vaned diffuser for installing a plurality of stationary vanes on the outer peripheral side downstream of the centrifugal impeller In the compressor,
The outer diameter of the core plate and the side plate is larger than the outer diameter of the blade outlet of the centrifugal impeller, and the inner diameter of the front edge of the stationary vane is the circle of the core plate and the side plate of the centrifugal impeller. Install it close to the outer periphery of the plate,
The outer diameter of one of the two discs of the core plate and the side plate of the centrifugal impeller is made smaller than the other, and the inner diameter of the front edge of the stationary vane is equal to that of the core plate and the side plate. A centrifugal compressor characterized in that the front edge is inclined so as to be close to the outer circumferences of both disks.   The centrifugal compressor according to claim 2, wherein a ratio R3m / R1 of a blade outlet outer peripheral diameter R1 of the centrifugal impeller and an average front edge inner peripheral diameter R3m of the stationary vane is 1.1 or less. Compressor.

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