JP2014202102A - Centrifugal compressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a centrifugal compressor capable of easily suppressing degradation of compression efficiency and further providing correction for suppressing the degradation of compression efficiency after designing a diffuser.SOLUTION: The centrifugal compressor includes: a diffuser 7 formed on an outer periphery side of an impeller 2 while being defined by a pair of opposed wall faces; and a scroll flow path 5c provided outside of the diffuser 7 in a radial direction. The diffuser 7 has a plurality of vanes 8. The plurality of vanes 8 are arranged around a position P eccentric to a rotation center O of the impeller 2 equally in a peripheral direction of the diffuser 7. The eccentric position P is set so that blade angles of the plurality of vanes 8 to the rotation center O of the impeller 2 are non-uniform in the peripheral direction of the diffuser 7 to produce less-variable static pressure in the diffuser 7.

Description

  The present invention relates to a centrifugal compressor.

  The centrifugal compressor sucks air from the axial direction by an impeller that rotates at a high speed, gives high-speed velocity energy thereto, and discharges it radially outward. A diffuser is provided on the outer peripheral side of the impeller, and the discharge air is gradually decelerated in the diffuser to increase the pressure. Further, a spiral scroll passage is provided on the outer side in the radial direction of the diffuser, and deceleration and pressure increase are performed in the scroll passage so that high-pressure (supercharging pressure) air is supplied to the engine. Yes.

  By the way, the diffuser is usually partitioned by a pair of opposing wall surfaces formed by the compressor housing and the seal plate. Therefore, the diffuser is a ring-shaped flow having a constant width and a constant flow area surrounding the impeller from the outside in the radial direction. It is a road. That is, the impeller and the diffuser are designed on the assumption that the back pressure of the diffuser is constant in the circumferential direction. Here, considering the case of a vaneless diffuser, the air flow in the diffuser rotates in the circumferential direction while being directed radially outward under the influence of centrifugal force and rotational force, and then flows into the scroll flow path. It is like that.

  However, although the impeller and the diffuser are uniformly formed and arranged with respect to the central axis, the scroll flow path is spiral and not uniform with respect to the central axis, so the back pressure (static pressure) of the diffuser generated by the flow described above. Are not constant along the circumferential direction and have variations. Therefore, it is considered that the compression efficiency is lower than the design value because the flow in the diffuser is not uniform in the circumferential direction. In the case of the diffuser with vanes, the vanes are evenly arranged in the diffuser around the rotation shaft of the impeller.

  Conventionally, for example, the flow passage area of the diffuser is changed in the circumferential direction in order to improve the reduction in compression efficiency due to such flow variations (see, for example, Patent Document 1 and Patent Document 2).

JP-A-10-176699 Special table 2010-529358

  However, in order to change the flow passage area of the diffuser, it is necessary to change the design of the compressor housing and the seal plate that form the diffuser. End up. In addition, once the diffuser is designed, if the variation in flow is determined by simulation (calculation), etc., and the reduction in compression efficiency has not been resolved, the diffuser must be redesigned, which is also costly. Will increase.

  The present invention has been made in view of the above circumstances, and the object of the present invention is to easily suppress a decrease in compression efficiency, and to make a correction for suppressing a decrease in compression efficiency after designing a diffuser. It is to provide a centrifugal compressor.

  A centrifugal compressor according to the present invention includes a diffuser formed by being partitioned by a pair of opposing wall surfaces on an outer peripheral side of an impeller, and a scroll passage provided on a radially outer side of the diffuser, and the diffuser includes a plurality of vanes. The plurality of vanes are evenly arranged in a circumferential direction of the diffuser with a position eccentric with respect to a rotation center of the impeller as the center, and the eccentric positions include the impellers of the plurality of vanes. The blade angle with respect to the rotation center of the diffuser is set to be nonuniform in the circumferential direction of the diffuser, so that variation in static pressure in the diffuser is reduced.

  Further, in the centrifugal compressor, the vane angle of the vane arranged in the vicinity of the tongue portion on the downstream side in the rotation direction of the impeller with respect to the tongue portion of the scroll flow path with respect to the rotation center of the impeller, The eccentric position is preferably set so as to be smaller than the blade angle with respect to the eccentric position.

  Further, in the centrifugal compressor, the impeller is disposed on the downstream side in the rotation direction of the impeller with respect to the tongue portion of the scroll flow path and in the vicinity of the position on the opposite side in the circumferential direction. It is preferable that the eccentric position is set such that the vane angle of the vane with respect to the rotation center of the impeller is larger than the vane angle with respect to the eccentric position.

According to the centrifugal compressor of the present invention, the plurality of vanes are arranged uniformly in the circumferential direction of the diffuser around the position eccentric with respect to the rotation center of the impeller, and the eccentric positions of the plurality of vanes are The blade angle with respect to the rotation center of the impeller is not uniform in the circumferential direction of the diffuser. It is possible to suppress a decrease in compression efficiency due to the above.
In addition, the vane angle of each vane can be changed simply by decentering the center of the vane, making it easy to design and manufacture the vane, and after designing the diffuser The vane blade angle can be easily redesigned and modified to match the diffuser characteristics.

(A) is a longitudinal cross-sectional view which shows schematic structure of the centrifugal compressor which concerns on one Embodiment of this invention, (b) is a principal part enlarged view of (a). It is AA arrow sectional drawing of Fig.1 (a). It is a figure which shows the static pressure distribution of a diffuser inlet_port | entrance part. It is a figure for demonstrating the change of the blade angle of each vane by eccentricity.

Hereinafter, the centrifugal compressor of the present invention will be described in detail with reference to the drawings. In the following drawings, the scale of each member is appropriately changed to make each member a recognizable size.
Fig.1 (a) is a longitudinal cross-sectional view which shows schematic structure of the centrifugal compressor of this embodiment, FIG.1 (b) is a principal part enlarged view of (a). In addition, this centrifugal compressor is used suitably for industrial and marine centrifugal compressors, for example.

As shown in FIG. 1A, the centrifugal compressor 1 of this embodiment includes an impeller 2, a shaft 3, a seal plate 4, a compressor housing 5, and a diffuser 7.
The impeller 2 includes a plurality of blades 2b that are fixed to the base 2a. The impeller 2 is rotationally driven to give velocity energy to the air X (fluid) sucked from the axial direction and send it out in the radial direction. The shaft 3 is fixed to the center of the impeller 2 when viewed from the air X suction direction of the impeller 2, and transmits the rotational power generated by a drive source (not shown) (motor, turbine, etc.) to the impeller 2. It has become.

  The seal plate 4 is disposed opposite to the back surface of the impeller 2 and has a through hole (not shown) for inserting the shaft 3 in the center. The compressor housing 5 is fastened to the seal plate 4 with bolts 6 and is a casing that covers the impeller 2 from the air X suction side. As shown in FIG. 1A, the compressor housing 5 has a suction port 5a for sucking air X, a discharge port 5b for discharging air X, and air X sent from the impeller 2 to the discharge port 5b. A scroll channel 5c for guiding and an extending portion 5d are provided.

  The scroll flow path 5c is formed in a spiral shape on the outside of the impeller 2 so as to surround the impeller 2 when viewed from the air X intake direction, and the impeller 2 is centered when viewed from the same direction. The air X is guided in the circumferential direction and flows into the extending portion 5d. That is, the air X in the scroll flow path 5 c flows in a spiral shape in the circumferential direction around the rotation axis of the impeller 2.

  The diffuser 7 surrounds the impeller 2 from the outside in the radial direction, and is partitioned by a pair of opposed wall surfaces formed by the compressor housing 5 and the seal plate 4, that is, a compressor housing 5 side 7a and a seal plate 4 side wall 7b. It is provided between the impeller 2 and the scroll flow path 5c. These wall surfaces 7a and 7a are parallel to each other, have a predetermined length along the radial direction, and form a ring-shaped flow path continuously in the circumferential direction. With such a configuration, the diffuser 7 is a flow path that communicates with the impeller 2 on the inner side and that communicates with the scroll flow path 5c on the outer side in the radial direction.

  The diffuser 7 is provided with a plurality of vanes 8 as shown in FIG. 2, which is a cross-sectional view taken along line AA in FIG. In FIG. 2, 11 vanes 8 are schematically illustrated, but in actuality, the number may be more or less. These vanes 8 are integrally formed on the wall surface 7b of the seal plate 4 or the wall surface 7a of the compressor housing 5, for example, and the height thereof is the width of the diffuser 7 as shown in FIG. That is, it is formed so as to substantially coincide with the distance between the opposing wall surfaces 7a, 7a.

  These vanes 8 are arranged at appropriate intervals along the circumferential direction of the diffuser 7 as shown in FIG. These vanes 8 are uniformly formed and arranged from the center point P with one point as the center. That is, all the vanes 8 are formed at the same distance from the center point P and in the same shape and angle as viewed from the center point P.

  However, in the present invention, the center point P is the center of the diffuser 7, that is, the rotational axis of the impeller 2, and is arranged eccentrically with respect to the rotational center O of the impeller 2 that is the center of the scroll flow path 5c. . That is, the center point P is “a position that is eccentric with respect to the rotation center O of the impeller 2” in the present invention.

  Here, the impeller 2 and the diffuser 7 are arranged uniformly with respect to the rotation center O of the impeller 2, whereas the scroll flow path 5 c is spiral and is arranged equally with respect to the rotation center O. Not. Therefore, in the diffuser 7, for example, the back pressure increases or decreases in the vicinity of the tongue 9 of the scroll flow path 5c, that is, in the vicinity of the tongue 9 serving as a boundary between the extension 5d and the scroll flow path 5c. That is, as described above, the back pressure of the diffuser 7 is not constant along the circumferential direction, but varies.

  FIG. 3 is a circumferential position in the rotation direction of the impeller 2 (clockwise direction in this example) indicated by an arrow in FIG. 2 with the position of the tongue 9 viewed from the rotation center O shown in FIG. 2 being 0 °. It is a figure which shows an example of the result of having calculated | required the static pressure (back pressure) in the inlet part (impeller 2 side) of the diffuser 7, ie, a figure which shows an example of the static pressure distribution of a diffuser inlet part. However, FIG. 3 shows the results obtained without the vane 8.

  As shown in FIG. 3, the static pressure in the diffuser 7 varies in the circumferential direction due to the non-uniformity of the scroll passage 5c that is spiral. Therefore, in the present embodiment, the center point P (a position decentered with respect to the rotation center O of the impeller 2) is set so as to reduce the variation in the circumferential direction of the static pressure in the diffuser 7. Yes.

  That is, conventionally, the vanes 8 are also uniformly formed and arranged with respect to the rotation center O of the impeller 2. In other words, the positions of the vanes 8 are designed so as to be uniformly formed and arranged with respect to the rotation center O designed in advance. Based on this design, the seal plate 4 or the compressor housing 5 is formed by a shaving method or a casting method. Therefore, each vane 8 is formed on the wall surface 7a or the wall surface 7b.

  On the other hand, in the present embodiment, the static pressure (back pressure) distribution of the diffuser 7 without vanes as shown in FIG. 3, that is, the variation in the circumferential direction of the static pressure in the diffuser 7 is shown. The center point P is set (designed) so as to decrease, and the vanes 8 are formed and arranged based on this setting.

When the center point P of the vane 8 is decentered with respect to the rotation center O of the impeller 2 as described above, the vane angle of each vane 8 with respect to the rotation center O of the impeller 2 is set in the circumferential direction of the diffuser 7 as shown in FIG. Becomes uneven.
FIG. 4 is a diagram for explaining a change in the blade angle of each vane 8 due to the eccentricity. A circle B indicated by a two-dot chain line in FIG. 4 is a circle centered on the center point P which is an eccentric position. Each vane 8 has an inner end located on the circle B, and the rotation direction of the impeller 2. (Arrow direction) Extends outward. The vanes 8 are formed and arranged equally around the center point P, that is, at the same interval, the same length, and the same blade angle.

A circle C indicated by a solid line in FIG. 4 is a circle centered on the rotation center O of the impeller 2 and is a circle along the circumferential direction of the diffuser 7.
Since the vanes 8 are evenly arranged around the center point P as described above, the inclination angle with respect to a straight line extending from the center point P in the radial direction, that is, the blade angle with respect to the eccentric position (center point P). Of course, θ1 is the same. On the other hand, the inclination angle with respect to a straight line extending in the radial direction from the rotation center O of the impeller 2, that is, the blade angle θ2 with respect to the rotation center O of the impeller 2 varies depending on the position where the vane 8 is formed. 7 is uneven in the circumferential direction.

  Here, the fluid (air) that actually flows in the diffuser 7 is affected by the blade angle θ <b> 2 with respect to the rotation center O of the impeller 2. Specifically, if the blade angle θ2 becomes relatively small (if the vane 8 rises), the pressure at this point increases, and if the blade angle θ2 becomes relatively large (if the vane 8 lies down), The pressure at this point decreases.

  Therefore, in the present embodiment, the center point P is decentered in the direction of 90 ° in the circumferential direction of the diffuser 7 with respect to the rotation center O of the impeller 2 as shown in FIGS. As a result, the vane 8a disposed on the downstream side in the rotation direction of the impeller 2 from the tongue 9 of the scroll flow path 5c and in the vicinity of the tongue 9 has vane angles θ2 and θ1 of the vane 8a schematically shown in FIG. As can be seen from the relationship, the blade angle θ2 of the vane 8a is smaller than the blade angle θ1. Therefore, the pressure is increased at the location where the vane 8a is disposed as compared with the conventional case where the vane 8 is evenly disposed with respect to the rotation center O of the impeller 2. That is, it is possible to increase the pressure at a location (between 30 ° and 60 °) where the static pressure of the diffuser 7 is lowest as shown in FIG. Therefore, variation in static pressure in the diffuser 7 can be reduced.

  In addition, the scroll passage 5c is disposed on the downstream side in the rotational direction of the impeller 2 from the position on the opposite side (180 °) in the circumferential direction with respect to the tongue 9 (0 °), and in the vicinity of the position on the opposite side in the circumferential direction. As can be seen from the relationship between the vane angle θ2 and θ1 of the vane 8b schematically shown in FIG. 4, the vane angle θ2 of the vane 8a is larger than the vane angle θ1. Accordingly, the pressure is reduced at the place where the vane 8b is disposed. That is, the pressure can be reduced at a location (between 210 ° and 270 °) where the static pressure of the diffuser 7 is relatively high, as shown in FIG. Therefore, variation in static pressure in the diffuser 7 can be reduced.

  Thus, in the centrifugal compressor 1 of the present embodiment, the plurality of vanes 8 are evenly distributed in the circumferential direction of the diffuser 7 around the position (center point P) that is eccentric with respect to the rotation center O of the impeller 2. The vane angle θ2 of the plurality of vanes 8 with respect to the rotation center O of the impeller 2 becomes non-uniform in the circumferential direction of the diffuser 7, so Since the pressure variation is set to be small, the flow variation in the diffuser 7 can be reduced, and the reduction of the compression efficiency due to the variation can be suppressed.

Further, since the vane angle θ2 of each vane 8 with respect to the rotation center O of the impeller 2 can be changed by simply decentering the center of the vane 8, the vane 8 can be easily designed and manufactured. Can do.
Furthermore, after the design of the diffuser 7, the characteristics (for example, static pressure distribution) of the designed diffuser 7 are obtained by calculation or the like, and the blade angle θ 2 of the vane 8 is easily redesigned and corrected according to the obtained result. Can do.

The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention.
For example, in the embodiment described above, the center point P is decentered in the direction of 90 ° in the circumferential direction of the diffuser 7 with respect to the rotation center O of the impeller 2 corresponding to the static pressure distribution shown in FIG. When the static pressure distribution also changes due to the design, the eccentric position of the center point P is set based on the changed static pressure distribution so as to reduce the variation of the static pressure.

DESCRIPTION OF SYMBOLS 1 ... Centrifugal compressor, 2 ... Impeller, 4 ... Seal plate, 5 ... Compressor housing, 7 ... Diffuser, 7a, 7b ... Wall surface, 8, 8a, 8b ... Vane, 9 ... Tongue part, O ... Rotation center of impeller, P ... Center point (eccentric position)

Claims (3)

A diffuser formed by being partitioned by a pair of opposing wall surfaces on the outer peripheral side of the impeller, and a scroll flow path provided on the radially outer side of the diffuser,
A plurality of vanes in the diffuser;
The plurality of vanes are evenly arranged in a circumferential direction of the diffuser with a position eccentric with respect to a rotation center of the impeller as a center.
The eccentric position is set such that variation in static pressure in the diffuser is reduced by making the blade angles of the plurality of vanes with respect to the rotation center of the impeller uneven in the circumferential direction of the diffuser. A centrifugal compressor characterized by having   The vane angle of the vane, which is arranged downstream of the tongue of the scroll passage in the rotation direction of the impeller and in the vicinity of the tongue, is smaller than the vane angle with respect to the eccentric position of the vane. The centrifugal compressor according to claim 1, wherein the eccentric position is set so that The vane, which is disposed on the downstream side in the rotation direction of the impeller with respect to the tongue portion of the scroll flow path and in the vicinity of the position on the opposite side in the circumferential direction, with respect to the rotation center of the impeller The centrifugal compressor according to claim 1 or 2, wherein the eccentric position is set such that the blade angle is larger than the blade angle with respect to the eccentric position.

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