JPH11257290A - Diffuser of centrifugal compressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate no peeling at the pressure surface side of a guide vane even at a hub side with a small flow-out angle and to prevent the increase of the total pressure loss of a diffuser, so as to improve the efficiency. SOLUTION: In a diffuser 20, a passage space held between the side walls 10H and 10S of a casing 10 is partitioned by plural guide vanes 21 provided in the peripheral direction, at the outer peripheral side of an impeller 30, the downstream from a throat forms an expansion passage at a specific expanding angle between the guide vane 21 and an adjacent guide vane, and the guide vane 21 is incliningly formed at a specific angle, in the direction to make an angle θ made by its pressure surface and the inner surface 20H of a hub side side wall 10H, narrower than 90 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a diffuser in a centrifugal compressor, which converts kinetic energy of fluid into pressure energy by an enlarged passage formed by guide vanes.

[0002]

2. Description of the Related Art In a centrifugal compressor, a diffuser is formed by an enlarged passage around an outer peripheral side of an impeller, and the kinetic energy of fluid given by rotation of the impeller is converted into pressure energy by the diffuser. .

[0003] As such a diffuser, there is one having a guide blade in an enlarged passage.

A diffuser with blades is shown in FIG. 4 in a partial schematic sectional view of a diffuser portion of a centrifugal compressor, and FIG. 5 is a sectional view taken along line CC of FIG. A passage space (the inner surface 20H of the hub side wall 10H and the shroud side) sandwiched between the front and rear side walls 10H, 10S (the hub side wall 10H corresponding to the hub side of the impeller, the shroud side wall 10S corresponding to the shroud side of the impeller). The space between the inner surfaces 20S of the side walls 10S is partitioned by a plurality of guide vanes 21 (21 ')... Arranged in the circumferential direction, and a predetermined spread angle is formed between the guide vane 21 and the adjacent guide vane 21'. It is configured to form an enlarged passage.

The guide blade 21 is a two-dimensional blade having a constant cross-sectional shape in the height direction (the thickness direction of the passage) and its shape is set based on the outflow angle of the fluid from the impeller 30. The outflow angle from the wheel 30 depends on the shape of the impeller 30 in the thickness direction of the passage (the direction parallel to the rotation axis of the impeller 30).
Differently, as shown in FIG. 7, the flow rate is large on the shroud side of the impeller 30 and small on the hub side, and the flow rate also has a distribution depending on the position in the thickness direction. It is set so that high efficiency is obtained.

Incidentally, the thickness of the passage is usually set to a constant value, but there is a case where the outer shape of the compressor is rarely formed so as to reduce the outer shape of the entire compressor.

[0007]

However, the difference in the outflow angle due to the shape of the impeller 30 is as large as 20 to 30 °, and when the shape of the guide blade 21 is set averagely as in the above-mentioned conventional case, particularly, There has been a problem that fluid separation occurs on the pressure surface 21A of the guide blade 21 corresponding to the hub side of the impeller having a small outflow angle. That is, as shown in FIG. 6 and FIG. 7 which is a passage exit view corresponding to the view taken in the direction of arrow E, a low-speed region where peeling occurs near the hub-side inner surface 20H at the rear end of the guide blade 21 is shown. There is.

[0008] When such peeling occurs, the total pressure loss of the diffuser increases and the performance decreases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and does not cause separation on the pressure surface side of the guide blade even on the hub side having a small outflow angle, thereby increasing the total pressure loss of the diffuser. It is an object of the present invention to provide a diffuser for a centrifugal compressor, which can improve efficiency by preventing the occurrence of a diffuser.

[0010]

According to the present invention, there is provided a diffuser for a centrifugal compressor according to the present invention for converting kinetic energy of fluid into pressure energy by an enlarged passage formed by guide vanes in the centrifugal compressor. The guide blade is characterized in that an angle formed between a pressure surface thereof and a side wall surface corresponding to the hub side of the impeller is inclined at a predetermined angle in a direction in which the angle is smaller than 90 °.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a partial schematic cross-sectional view of a diffuser part of a compressor to which a configuration example of a diffuser of a centrifugal compressor according to the present invention is applied, and FIG. 2 is a cross-sectional view along AA.

The illustrated compressor 1 has a casing 10 in which a diffuser 20 is formed between an impeller chamber 11 and a spiral chamber 12 on the outer periphery thereof, and an impeller 30 disposed in the impeller chamber 11 is provided. Are rotationally driven by rotation driving means (not shown) to apply kinetic energy in the radial direction to the fluid sucked from the intake port 13 and convert the fluid into pressure energy by the diffuser 20 and discharge the pressure energy to the spiral chamber 12.

The diffuser 20 is sandwiched on the outer peripheral side of the impeller 30 by the side wall of the casing 10 (hub side wall 10H corresponding to the hub side of the impeller 30, shroud side wall 10S corresponding to the shroud side of the impeller 30). Passage space (the inner surface 20H of the hub side wall 10H and the shroud side wall 1).
The space between the inner surfaces 20S of the outer and outer guides 21S is partitioned by a plurality of guide vanes 21 (21 ')... An enlarged passage is formed at a predetermined spread angle.

Here, the guide blade 21 has its pressure surface 21
A and the angle formed by the inner surface 20H of the hub side wall 10H: θ
Are inclined at a predetermined angle in a direction that is narrower than 90 °. The cross-sectional shape of the guide blade 21 in the impeller rotation axis direction is constant and formed so as to have a constant entrance angle and a constant exit angle. Therefore, the cross-sectional shape of the enlarged passage in the direction intersecting with the guide blade 21 is shown in FIG. 2 shows a parallelogram as shown in FIG. 3 which is a passage exit view corresponding to the view on arrow B of FIG.

As described above, the pressure surface 21A of the guide blade 21
And the inner surface 20H of the hub side wall 10H has an angle of 90 °.
案 内 Because it is formed at a narrower angle, the guide blade 21
Can be prevented from developing at the rear end.

That is, in the enlarged passage formed by the adjacent guide vanes 21, the pressure surface side 21A of the guide vanes 21
However, due to the outflow distribution in the thickness direction of the passage caused by the shape of the impeller 30, the outflow distribution in the inner surface 20H of the shroud-side side wall 10H having a large outflow angle is located within the boundary layer of the guide blade 21 from the negative pressure surface 21B side. A secondary flow that flows to the pressure surface 21A side is generated, and after the secondary flow collides with the pressure surface 21A, the hub side wall 10H (the inner surface 20H) along the pressure surface 21A.
Therefore, the separation is suppressed at the tip of the guide blade 21 where the secondary flow is large,
A peeling region is formed near the inner surface 20H of the hub side wall 10H at the rear end of the guide blade 21.

Since the angle formed between the pressure surface 21A of the guide blade 21 forming the separation area and the inner surface 20H of the hub side wall 10H is made narrow, the flow velocity is improved, and the flow rate is improved as shown in FIG.
As shown in the figure, the low flow velocity region is reduced and the separation can be suppressed.

Inner surface 2 of hub side wall 10H of pressure surface 21A
Is set to such an extent that the low-speed region disappears without increasing the flow velocity in the main flow region, and 75 ° to 45 °.
゜ is preferred. FIG. 4 shows an example in which the angle is approximately 45 °.

As described above, the guide blade 21 is formed to be inclined at a predetermined angle in a direction in which the angle θ formed by the pressure surface 21A and the inner surface 20H of the hub side wall 10H is smaller than 90 °. The pressure surface 21 of the guide blade 21
The fluid separation area in the vicinity of the rear end of A is reduced, and as a result, an increase in the total pressure loss of the diffuser can be prevented and the efficiency can be improved.

[0020]

As described above, according to the diffuser of the centrifugal compressor according to the present invention, the angle between the pressure surface of the guide blade and the side wall surface corresponding to the hub side of the impeller is 90 °. Since it is inclined at a predetermined angle in the direction of becoming narrower, fluid separation near the rear end of the pressure surface of the guide blade can be suppressed, and the total pressure loss of the diffuser is prevented from increasing, improving efficiency. That can be done.

[Brief description of the drawings]

FIG. 1 is a partial schematic cross-sectional view of a diffuser part of a compressor to which a configuration example of a diffuser of a centrifugal compressor according to the present invention is applied.

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

FIG. 3 is a view showing a low speed region at a passage exit corresponding to a view taken in the direction of arrow B in FIG. 2;

FIG. 4 is a partial schematic sectional view of a diffuser portion of a compressor as a conventional example.

FIG. 5 is a sectional view taken along the line CC of FIG. 5;

FIG. 6 is a diagram showing a low speed region at a passage exit corresponding to a view taken in the direction of arrow D in FIG. 5;

FIG. 7 is a diagram showing an outflow angle distribution in a thickness direction of a passage.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Compressor (centrifugal compressor) 20 Diffuser 20H Inner surface of side wall on hub side (side wall surface corresponding to hub side of impeller) 21 Guide blade 21A Pressure surface θ Pressure surface of guide blade and side wall surface corresponding to hub side of impeller Angle between

Claims (1)

[Claims] 1. A diffuser for converting kinetic energy of fluid into pressure energy by an enlarged passage of a guide blade in a centrifugal compressor, wherein the guide blade has a pressure surface and a side corresponding to a hub side of an impeller. A diffuser for a centrifugal compressor, wherein the diffuser is inclined at a predetermined angle in a direction in which an angle formed by a wall surface is smaller than 90 °.