JP2003269379A - Mixed flow compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mixed flow compressor which keeps stable operation by restraining a corner stall, and prevents surging even when curvature of an impeller passage is large. <P>SOLUTION: This mixed flow compressor has a bypass hole 10 for communicating the positive pressure surface side and the negative pressure surface side of an impeller blade. The bypass hole 10 is arranged in the size enough to restrict a leakage flow rate leaking to the negative pressure surface side from the positive pressure surface side to a prescribed range in a root part of a hub 12 or the impeller blade 3 in the vicinity where the curvature gets most tightened in the impeller passage 11. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mixed flow compressor capable of suppressing corner stall.

[0002]

2. Description of the Related Art A mixed flow compressor (Mixed Flow C)
The ompressor is a compressor that centrifugally compresses the gas sucked in from the axial direction along a flow path (impeller passage) inclined with respect to the axis, and is located between the centrifugal type and the axial flow type. For this reason, it has a characteristic intermediate between the two, has a characteristic feature that it can process a larger flow rate than the centrifugal type, and has a larger pressure ratio and head than the axial type.

Further, an impeller of a mixed flow compressor (Mixed
The flow impeller (Impeller) has a curvature on the side plate side smaller than that of the centrifugal type, so that the load distribution in the impeller is relatively gentle, the secondary flow loss is small, and the efficiency is high.

[0004]

FIG. 4 is a diagram showing the flow of the air flow in the mixed flow compressor. (A) is a schematic sectional view of the mixed flow compressor, (B) is an enlarged view of part A, (C) is a BB sectional view.

In FIG. 4A, 1 is an impeller rotating about the Z-Z axis, 2 is a hub of the impeller, 3 is an impeller blade spirally provided on the hub, and 4 is a casing surrounding the impeller 1. is there. An inclined impeller passage (passage) is provided between the hub 2 and the casing 4, and the impeller blades 3 rotate in this impeller passage. When the impeller blades 3 rotate, the rotation imparts a centrifugal force to the gas flowing between the blades from the inner end of the impeller, driving / compressing the gas outward along the impeller passage and compressing it from the outer end. The discharged gas is discharged. In this example, both the inflowing gas and the outflowing gas are shown by the axial flow, but one or both of them may be a diagonal flow.

In the above-described mixed flow compressor, the load condition on the suction surface side of the impeller blade becomes extremely severe due to the curvature of the impeller passage (passage) and the shape of the impeller near the outlet of the impeller, and the flow cannot bear the load, and the hub side is not supported. It is easy to have a corner stall. That is, as schematically shown in FIGS. 4B and 4C, the boundary layer on the negative pressure side of the impeller blade 3 becomes extremely thick near the portion A where the curvature near the impeller outlet is large, and the boundary layer is partially separated. Easy to stall.
This stall is called a corner stall. As a result, the inflow angle on the hub side that flows into the diffuser 5 on the downstream side of the impeller becomes larger than the design point, deteriorating the performance of the diffuser 5 and eventually causing surging as a whole to make it impossible to maintain stable operation. There is.

The present invention was created to solve such problems. That is, the present invention is to provide a mixed flow compressor capable of suppressing corner stall, preventing surging and maintaining stable operation even when the curvature of the impeller passage is large.

[0008]

According to the present invention, there is provided an impeller (1) which rotates about a rotation axis Z and a casing (4) which surrounds the impeller, the impeller being inclined between the casing and the casing. A hub (2) forming an impeller passage and an impeller blade (3) spirally provided on the hub, and centrifugally compresses gas sucked from the inner end of the impeller along the impeller passage. Hole (10) for connecting the pressure side and the suction side of the impeller blade in the machine
A mixed-flow compressor is provided.

According to a preferred embodiment of the present invention, the bypass hole (10) is located at the root of the hub or the impeller blade in the vicinity of the impeller passage where the curvature is the tightest, from the pressure side to the suction side. It is provided with a size that limits the leakage flow rate to a predetermined range.

Further, in the impeller passage side surface shape represented by R = f (z), it is preferable to provide the bypass hole (10) on the downstream side of the portion where the reduction rate of dR / dz is the largest. Where z is the axial position and R is the radial position.

According to the above-described structure of the present invention, near the point where the curvature is the highest, that is, near the portion where the reduction rate of dR / dz is the largest, a large positive pressure is generated on the ventral side of the impeller blade, and the dorsal side is generated. Is under negative pressure. Therefore, the bypass hole (1 that connects the pressure side and the suction side of the impeller blade)
By providing 0), gas can be leaked from the pressure side to the suction side.

Due to this leak flow, the impeller load at the portion where stall is likely to occur on the negative pressure side can be reduced and the development of the boundary layer can be suppressed.

Further, due to the blowing effect of this leakage flow to the negative pressure side (back side), the mixing of the flow in the boundary layer is promoted, the separation is delayed, the stall of the impeller is prevented, and the flow flowing into the diffuser is made as uniform as possible. Can be

If the amount of leakage is too large, the compression efficiency will decrease. Therefore, the flow rate should be set as small as possible depending on the size and number of bypass holes within the range where the stall prevention effect can be obtained.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below with reference to the drawings. In addition, in each figure, the same parts are denoted by the same reference numerals.

FIG. 1 is a sectional view of the mixed flow compressor of the present invention. As shown in this figure, the mixed flow compressor of the present invention includes a hub 2 and an impeller blade 3 that rotate about a rotation axis Z, and a casing 4 that surrounds the impeller blade 3.

The hub 2 forms an inclined impeller passage 11 with the casing 4. The surface shape of the hub 2 on the impeller passage side can be represented by R = f (z), where z is the axial position and R is the radial position. f (z)
Is a function of z, in this example both inflow and outflow gases are axial flows, in the z-axis direction (dR / dz = 0) at the inner and outer ends of the impeller, and between them dR / Dz
Has a shape that once increases, has a maximum value (maximum slope), and then decreases. As a result, the side cross section has a substantially S-shaped surface shape as shown in the figure.

The impeller blades 3 are provided integrally with the hub 2 in a spiral shape. The impeller blades 3 are formed by, for example, casting or shaving.

In this figure, 6 is a vane provided on the upstream side (suction side) and guides the inflowing gas in an axial flow. Also, unlike this example, one or both of the inflowing / outflowing gas may be a mixed flow.

With the mixed flow compressor having the above-described structure, the gas sucked from the inner end of the impeller by the rotation of the impeller 1 can be centrifugally compressed along the impeller passage.

FIG. 2 is a partial sectional view of FIG. 1, in which (A) is a sectional view taken along line AA of FIG. 1 and (B) is a sectional view taken along line BB.

As shown in FIGS. 1 and 2, the mixed flow compressor of the present invention has a bypass hole 10 which connects the pressure side and the suction side of the impeller blade 3 to each other. In this example, the bypass hole 10 is provided in the lower hub 2 of the impeller blade 3 in the impeller passage 11 where the curvature is the strongest. Unlike this example, it may be provided at the root of the impeller blade itself. The installation position of the bypass hole 10 is R = f
In the surface shape of the impeller passage side represented by (z), it is preferable that it is on the downstream side of the portion where the reduction rate of dR / dz is the largest.

Further, the bypass hole 10 is provided with a size that limits the flow rate of leakage from the pressure surface side to the suction surface side within a predetermined range. That is, when the leak amount passing through the bypass hole 10 is small, as will be described later, it has an effect of preventing the stall of the impeller. ,
Set the flow rate as small as possible according to the size and number of bypass holes. The size and number of bypass holes can be optimally set by simulation or test.

FIG. 3 is a diagram showing the flow of air flow in the mixed flow compressor of the present invention. In this figure, (A) is a schematic sectional view of a mixed flow compressor, (B) is an enlarged view of part A, and (C) is B-.
It is a B sectional view.

According to the above-described structure of the present invention, in the vicinity of the maximum curvature, that is, in the vicinity of the portion having the largest reduction rate of dR / dz, a large positive pressure is generated on the ventral side of the impeller blade 3, and Negative pressure is generated on the side. Therefore, the bypass hole 1 that connects the pressure side and the suction side of the impeller blade 3
By providing 0, the gas can be leaked from the positive pressure surface side to the negative pressure surface side, as indicated by the broken line arrow in FIGS.

This leak flow can reduce the impeller load in the negative pressure side where stall is likely to occur and suppress the development of the boundary layer.

Further, due to the blowing effect of this leak flow to the negative pressure side (back side), mixing of the flow in the boundary layer is promoted to delay separation, stall of the impeller is prevented, and the flow flowing into the diffuser is made as uniform as possible. Can be

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

[0029]

As described above, the mixed flow compressor of the present invention is excellent in that corner stall can be suppressed, surging can be prevented, and stable operation can be maintained even when the curvature of the impeller passage is large. Have the effect.

[Brief description of drawings]

FIG. 1 is a sectional view of a mixed flow compressor of the present invention.

FIG. 2 is a partial cross-sectional view of FIG.

FIG. 3 is a diagram showing the flow of airflow in the mixed flow compressor of the present invention.

FIG. 4 is a diagram showing a flow of an air flow in a conventional mixed flow compressor.

[Explanation of symbols]

1 impeller, 2 impeller hub, 3 impeller blades,
4 casings, 5 diffusers, 6 vanes, 10
Bypass hole, 11 impeller passage

Claims (3)

[Claims] 1. An impeller (1) rotating about a rotation axis Z, and a casing (4) surrounding the impeller,
The impeller includes a hub (2) forming an inclined impeller passage between the impeller and a casing, and an impeller blade (3) spirally provided on the hub. The impeller sucks gas sucked from an inner end of the impeller. A mixed flow compressor that centrifugally compresses along a passage, characterized by having a bypass hole (10) communicating between the pressure side and the suction side of the impeller blade. 2. The bypass hole (10) has a flow rate of leaking from a pressure surface side to a suction surface side within a predetermined range at a root portion of a hub or an impeller blade near a portion where the curvature is most tight in an impeller passage. The mixed flow compressor according to claim 1, wherein the mixed flow compressor is provided in a size that limits the size. 3. The bypass hole (10) is provided on the downstream side of a portion having the largest reduction rate of dR / dz in the impeller passage side surface shape represented by R = f (z). Item 1. The mixed flow compressor according to Item 1.