JP2006194238A - Centrifugal compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a centrifugal compressor preventing or inhibiting separation of a boundary layer of gas with respect to a suction surface of an inducer portion even when a flow rate of the gas is low. <P>SOLUTION: The centrifugal compressor has an impeller 21 journaled to a housing 13 and compresses the gas sucked into the housing 13 through rotation of the impeller 21 at least by centrifugal force. The impeller 21 has the inducer portion formed with a pressure surface m and the suction surface n and a communication hole 24 is provided for connecting the pressure surface m and the suction surface n. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a centrifugal compressor provided with an impeller (impeller).

A centrifugal compressor is known as one of compressors for compressing gas.
For example, as shown in FIG. 4, the conventional centrifugal compressor includes a rotating shaft 12 and a housing 13 to which an impeller 11 (impeller) is attached.
The housing 13 includes a housing body 14 that supports the rotating shaft 12 and a shroud housing 15.
The housing body 14 accommodates drive means (not shown) connected to the rotating shaft 12.
The shroud housing 15 forms a suction port 16 communicating with the impeller 11 and a volute 17 (vortex chamber).
The housing body 14 and the shroud housing 15 form a diffuser 18 on the outer periphery of the impeller 11.
The diffuser 18 communicates with a volute 17 that leads to a discharge port (not shown).
The impeller 11 includes rotary blades 19 attached in a radial manner.
An inducer portion 19a is formed on the upstream side of the rotor blade 19, and the remaining portion is formed as a blade portion 19b.
Although the boundary between the inducer portion 19a and the blade portion 19b is not clear, the inducer portion 19a is a portion that occupies a certain region on the suction port 16 side in the rotor blade 19, and the remaining portion corresponds to the blade portion 19b.

This centrifugal compressor sucks gas into the housing 13 by the rotation of the impeller 11.
The sucked gas is sent to the diffuser 18 through the impeller 11 and compressed at least by centrifugal force.
The gas compressed by the impeller 11 becomes a swirl flow including radial and circumferential velocity components and is pumped from the diffuser 18 to the volute 17.

FIG. 5 is a diagram showing a cross-sectional shape of the rotary blade 19.
The upstream blade tip P of the rotor blade 19 (the left end of the inducer portion 19a in FIGS. 5A and 5B) and the downstream blade tip Q (the right end of the blade portion 19b in FIGS. 5A and 5B). A straight line connecting the two is a chord line S.
5 (a) and 5 (b), the upper chord of the rotary blade 19 is set longer than the lower chord.
The gas from the upstream blade tip P toward the downstream blade tip Q flows separately along the upper and lower surfaces of the inducer portion 19a.
Since the gas flows separated at the upstream wing tip P simultaneously merge at the downstream wing tip Q due to the continuous conditions, the gas flowing on the upper surface has a higher speed than the gas flowing on the lower surface, and the upper surface side is faster than the lower surface side. Low pressure.
That is, in FIGS. 5A and 5B, the lower surface of the rotary blade 19 is the pressure surface m, and the upper surface is the suction surface n.

Usually, the angle between the direction of the gas flow with reference to the upstream blade tip P of the inducer 19a (arrow T in FIG. 5) and the chord line S of the inducer 19a is the incidence (this angle is the “incident angle”). Also called).
Incidence is determined by the combination of the peripheral speed of the upstream blade tip P and the gas inflow speed in the inducer portion 19a in combination with the rotation of the impeller 11.
Therefore, the incidence varies depending on the gas flow rate under the condition that the rotation speed of the impeller 11 is constant.

For example, when the rotational speed of the impeller 11 is constant, the incidence decreases as the gas flow rate increases as shown in FIG.
When the incidence is small, the pressure difference between the pressure surface m and the suction surface n is relatively small, and the gas boundary layer BL (not shown in FIG. 5A) is relative to the pressure surface m and the suction surface n. It is not in a state of peeling.
When the gas flow rate decreases, the incidence increases as shown in FIG.
When the incidence is large, the pressure difference between the pressure surface m and the suction surface n is large, and the gas boundary layer BL on the suction surface n may peel from the suction surface n.
The separation of the boundary layer BL from the suction surface n is more likely to occur as the incidence increases.
In the centrifugal compressor, the high flow rate operation shown in FIG. 5A is not concerned about the separation of the boundary layer BL from the suction surface n, but the low flow rate operation has a high risk of the separation of the boundary layer BL from the suction surface n.
The separation of the boundary layer BL on the negative pressure surface n causes backflow.
In this way, separation of the boundary layer BL is a factor that degrades the performance of the compressor, such as causing inducer stall or surging (self-excited vibration).

Patent Document 1 discloses a centrifugal compressor in which a fluid introduction hole is formed upstream of an induce sub lead hole.
However, this technology introduces gas from the outside of the centrifugal compressor and mitigates the choke phenomenon that occurs immediately downstream of the inducer-throat section, while maintaining the improved efficiency of the impeller of the inducer sublead, This is a technique for improving the efficiency of the entire centrifugal compressor.
JP-A-8-291800

In the conventional centrifugal compressor, there is a problem that the boundary layer of the suction surface in the inducer part peels from the suction surface during low flow operation.
Incidentally, as a method of preventing such separation of the boundary layer, for example, a method of reducing the incidence by reducing the rotational speed of the centrifugal compressor in accordance with the flow rate of the gas can be considered.
However, the basic specifications of the centrifugal compressor are almost fixed depending on the required performance.
Therefore, the low speed rotation of the impeller that deviates from the operating conditions based on the basic specifications cannot realize the performance required as a centrifugal compressor, and is not realistic.
The centrifugal compressor described in Patent Document 1 still cannot solve the above problem.
The present invention has been made in view of the above problems, and an object of the present invention is to prevent or suppress the separation of the gas boundary layer from the negative pressure surface of the inducer even when the gas flow rate is low. There is in providing a centrifugal compressor that can do.

In order to achieve the above object, the present invention is a centrifugal compressor that includes an impeller that is pivotally supported by a housing, and that compresses the gas sucked into the housing by rotation of the impeller by at least centrifugal force, and the impeller has a pressure surface. And an inducer part formed with a suction surface, and a through hole for communicating the pressure surface and the suction surface is provided.
According to the present invention, when the gas flow is operated at a low flow rate, a part of the gas on the pressure surface side of the inducer portion flows through the through hole to the suction surface.
Some gas flowing from the pressure surface to the suction surface prevents separation of the boundary layer on the suction surface.
In the present invention, the through hole may be provided near the upstream blade tip of the inducer portion.
Further, in the present invention, a plurality of the through holes may be provided. For example, the plurality of through holes may be arranged in a substantially radial direction of the impeller.

  According to the present invention, even when the gas flow rate is low, peeling of the gas boundary layer from the negative pressure surface of the inducer can be prevented or suppressed.

Hereinafter, an embodiment of a centrifugal compressor according to the present invention will be described with reference to FIGS.
In addition, about the element which is common or similar to a prior art, the same code | symbol is used and a part of description of a prior art is used.
The centrifugal compressor of this embodiment includes a rotating shaft 12 and a housing 13 to which an impeller 21 (impeller) is attached.
FIG. 1 is a side view showing a schematic outline of a centrifugal compressor. FIG. 2 is a front view showing the suction port 16 of the impeller 21. FIG. 3 is a diagram illustrating a cross-sectional shape of the rotor blade 23 and explaining a gas state in the high flow rate operation and the low flow rate operation.

The centrifugal compressor according to this embodiment is the same as that of the conventional impeller shown in FIG. 4 except that the structure is different.
The impeller 21 shown in FIGS. 1 and 2 includes a disk 22 having a shaft hole 22a for the rotating shaft 12, and two types of rotary blades 23 and 25 formed radially on the disk 22.
The impeller 21 is disposed between the housing body 14 and the shroud housing 15 and is rotatable with respect to the housing 13.
The impeller 21 has a function of sucking gas from the suction port 16 by rotation, compressing the gas by at least centrifugal force, and sending it to the diffuser 18.

A known disk 22 can be used for the impeller 21.
In this embodiment, the disk 22 is formed with two types of rotary blades, a long blade 23 and a short blade 25, as shown in FIG.
As shown in FIG. 2, there are six long blades 23 and short blades 25, and both 23 and 25 are thin plates.
The long wings 23 and the short wings 25 are alternately arranged on the disk 22 and have a relationship of maintaining the same angle.
For this reason, the short blade 25 is located next to the long blade 23, and the long blade 23 is located next to the short blade 25.
The long blade 23 includes an inducer portion 23 a and a blade portion 23 b, and the short blade 25 includes only a portion substantially corresponding to the blade portion 23 b of the long blade 23.
The long blade 23 reaches the outer peripheral edge 22b of the disk 22 while retreating in the direction opposite to the rotation direction of the disk 22 from the edge of the shaft hole 22a.
The short blades reach the outer peripheral edge 22b of the disk 22 while retreating with a starting point (not shown) at a point away from the shaft hole 22a in the disk 22.

The long blade 23 has an inducer portion 23a on the shaft hole 22a side (upstream side), and the remaining portion (downstream side from the inducer portion 23a) is formed as a blade portion 23b.
In FIG. 2, the boundary between the two wings 23a and 23b in the long wing 23 is indicated by a dotted line for the sake of convenience, but the boundary between the two wings 23a and 23b is not clear.
The blade width of the inducer portion 23a is set wider than that of the blade portion 23b, and the upstream blade tip P of the inducer portion 23a substantially coincides with the radial direction of the disk 22.
The blade width of the blade portion 23 b is narrower than the blade width of the inducer portion 23 a and further narrows to reach the outer peripheral edge 22 b of the disk 22.
The inducer portion 23a has a function of guiding the blade portion 23b by changing the direction of the gas sucked by the impeller 21.
The blade surface on the suction port 16 side in the inducer portion 23a is the suction surface n, and the blade surface facing the disk 22 side is the pressure surface m.
In this embodiment, the impeller 21 is provided with the long blade 23 having the inducer portion 23a and the blade portion 23b and the short blade 25. However, the impeller having only the long blade 23 may be used.
Alternatively, an impeller having an inducer portion 23a provided independently of the blade portion 23b may be used, and at least an impeller having an inducer portion 23a may be used.
Furthermore, the number of rotor blades 23 and 25 is not limited to six, and an appropriate number of rotor blades 23 and 25 may be set.

The inducer portion 23a has a circular hole 24 that communicates the positive pressure surface m and the negative pressure surface n.
That is, the circular hole 24 is a through hole penetrating both blade surfaces of the inducer portion 23a.
In this embodiment, each of the inducer portions 23a is formed with three circular holes 24, and these circular holes 24 are arranged in a substantially radial direction near the upstream end blade tip P of each inducer portion 23a. It is arranged.
That is, these circular holes 24 are arranged in a direction substantially perpendicular to the gas flow direction in the inducer portion 23.
The circular hole 24 is a through hole through which gas can pass from the pressure surface m to the suction surface n.
The circular hole 24 is provided to prevent the gas boundary layer BL from peeling off from the negative pressure surface n when the centrifugal compressor is operated at a low flow rate.
That is, the circular hole 24 is a through hole for reducing the load on the suction surface n by allowing gas to pass from the pressure surface m to the suction surface n.

Although the through hole of this embodiment is a circular hole 24, the through hole is not limited to the circular hole 24, and may be an elliptical hole, a long hole, a polygonal hole, an indeterminate hole, a slit, or the like. There is no particular limitation.
The number of through holes is not limited, and an appropriate number of at least one through hole may be provided.
When a plurality of through holes are provided, through holes having different shapes may be combined, and the arrangement of the plurality of through holes is not limited to a substantially right-angle direction in the flow direction (substantially radial direction of the inducer portion 23a). What is necessary is just to arrange | position to a position.
The position of the through hole should basically be at a position where peeling at the negative pressure surface n can be eliminated during low flow operation, and there are various requirements such as the capacity required for the centrifugal compressor and the cross-sectional shape of the inducer 23a. What is necessary is just to set suitably in consideration of conditions.
For example, it is preferably provided on the upstream blade tip P side of the long blade 23 (upstream half of the inducer portion 23a).
That is, it is sufficient that a through hole exists on the upstream side of the peeling start point on the negative pressure surface n.
However, this does not prevent the provision of the through hole downstream of the starting point of peeling.
In this way, by providing an appropriate number of through holes in an appropriate shape and position, the gas on the pressure surface m side is guided to the suction surface n side.
The shape, position, number, and the like of the holes may be set to optimum conditions for preventing peeling depending on the peeling state in the inducer portion 23a.

FIG. 3A shows a state of high flow operation of the centrifugal compressor.
When the centrifugal compressor operates at a high flow rate, the gas incidence to the inducer 23a is smaller than that during the low flow rate operation.
In the high flow rate operation in which the incident is set to be sufficiently small, the gas boundary layer BL (not shown in FIG. 3A) on the negative pressure surface n of the inducer portion 23a is difficult to separate from the negative pressure surface n.
In other words, the smaller the incidence, the lower the possibility that an unstable air flow will occur around the inducer 23a.
During high flow rate operation, the pressure surface n side has a lower pressure than the pressure surface m side, so that part of the gas passes through the circular hole 24 and flows from the pressure surface m to the suction surface n.
At this time, a part of the gas passing through the circular hole 24 does not significantly affect the centrifugal compressor during the high flow operation.

FIG. 3B shows a state of low flow rate operation of the centrifugal compressor.
When the centrifugal compressor operates at a low flow rate, the incidence on the inducer 23a is set larger than that at the high flow rate operation.
In the low flow rate operation where the incidence increases, the gas boundary layer on the negative pressure surface n of the inducer portion 23a is easily separated from the negative pressure surface.
At this time, the circular hole 24 allows part of the gas on the pressure surface m side to pass through and flows the gas to the suction surface n.
The negative pressure surface n side is supplied with gas from the positive pressure surface m side, so that the gas boundary layer BL (not shown in FIG. 3B) is difficult to peel off.
That is, a part of the gas that passes through the circular hole 24 during the low flow rate operation (indicated by a broken line arrow in FIG. 3B) prevents or suppresses separation between the negative pressure surface n and the boundary layer BL.

Since the centrifugal compressor according to this embodiment has the above-described configuration and operates as described above, the following effects can be obtained.
(1) The impeller 21 includes an inducer portion 23a having a pressure surface m and a suction surface n, and has a through hole (circular hole 24) that communicates the pressure surface m and the suction surface n. However, a part of the gas passes through the through hole from the pressure surface m side to the suction surface n side, and prevents or suppresses the separation of the suction surface n and the boundary layer BL as compared with the conventional centrifugal compressor. Can do. For this reason, inducer stall and surging can be prevented or suppressed. That is, stable operation of the centrifugal compressor can be achieved.
(2) Since a plurality of through holes (circular holes 24) are provided, there is less risk of impairing the function required for the inducer portion 23a. That is, by providing a plurality of through holes (circular holes 24), the degree of freedom for preventing or suppressing the peeling of the negative pressure surface n and the boundary layer BL is increased as compared with the case of providing a single through hole.
(3) Since the plurality of through holes (circular holes 24) are arranged in the substantially radial direction of the impeller 21, the separation of the boundary layer can be prevented or suppressed in the direction perpendicular to the flow (the width direction of the blade surface). It is also possible to prevent separation of the boundary layer BL in the inducer portion 23a.
(4) The through hole (circular hole 24) provided in the inducer portion 23a does not significantly affect the function of the inducer portion 23a in the high flow rate operation. For this reason, the performance of a centrifugal compressor is maintained similarly to the conventional centrifugal compressor.
(5) By simply providing the through hole (circular hole 24) in the inducer portion 23a, the negative pressure surface n and the boundary layer BL can be prevented from being peeled off or suppressed. For this reason, by providing a through hole (circular hole 24) in the inducer portion 23a of the conventional centrifugal compressor, the centrifugal compressor can be modified to prevent or suppress peeling of the negative pressure surface n and the boundary layer BL. .

The centrifugal compressor according to the above-described embodiment shows an embodiment of the present invention, and the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the gist of the invention. Is possible.
Moreover, a well-known component and a means can be suitably employ | adopted for the component except an inducer part.

It is a side view which fractures | ruptures and shows the outline | summary of the centrifugal compressor which concerns on embodiment of this invention. It is a front view which shows the impeller in the centrifugal compressor which concerns on embodiment of this invention. It is explanatory drawing explaining the flow of the gas in an inducer part. It is a side view which fractures | ruptures and shows the outline | summary of the conventional centrifugal compressor. It is explanatory drawing explaining the flow of the gas in the inducer part which concerns on a prior art.

Explanation of symbols

11, 21 Impeller 12 Rotating shaft 13 Housing 14 Housing body 15 Shroud housing 16 Suction port 17 Volute 18 Diffuser 19 Rotating blade 22 Disc 22a Shaft hole 22b Outer peripheral edge 23 Long blade 23a Inducer portion 23b Blade portion 24 Circular hole (through hole) )
25 short wing

Claims (4)

A centrifugal compressor comprising an impeller pivotally supported on a housing and compressing at least centrifugal gas sucked into the housing by the rotation of the impeller, wherein the impeller includes an inducer portion having a positive pressure surface and a negative pressure surface. A compressor provided with a through hole communicating the positive pressure surface and the negative pressure surface. The centrifugal compressor according to claim 1, wherein the through hole is provided near the upstream blade tip of the inducer. The centrifugal compressor according to claim 1 or 2, wherein a plurality of the through holes are provided. The centrifugal compressor according to claim 3, wherein the plurality of through holes are arranged in a substantially radial direction of the impeller.

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