JP2002098094A - Diffuser of centrifugal compressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To construct a diffuser of a centrifugal compressor for reducing incident mismatches to control reduction of static pressure recovery rate. SOLUTION: In a diffuser surrounding an impeller 2 of a centrifugal compressor and provided with plural passages 3 of roughly circle section shape to reduce speed of fluid from the impellor 2 with a fixed interval in a circumference direction, each passage is provided in a manner that a center line 4 thereof contacts a base circle 5 coaxial with the impeller 2 and a diameter of the base circle is set to a designated value to make a leading edge 6 formed on a crossing part of passages next to each other arranged in an appropriate direction according to a flowing out direction of fluid from the impeller 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention surrounds an impeller of a centrifugal compressor, and a plurality of passages for decelerating fluid from the impeller are provided at a constant interval in a circumferential direction with a substantially circular cross section. It is about a diffuser.

[0002]

2. Description of the Related Art A diffuser is provided in a manner surrounding an impeller in order to reduce the flow from an impeller of a centrifugal compressor to restore dynamic pressure to static pressure. In order to increase the efficiency, a configuration in which a plurality of passages communicating the inner peripheral side and the outer peripheral side are provided in the circumferential direction is widely used.

[0003] The above-mentioned passage is generally defined by sandwiching a plurality of blade members spaced at a fixed interval in the circumferential direction between a pair of wall members. In addition, Japanese Patent Publication No. 8-6711 As disclosed in the gazette, there is known a so-called pipe diffuser in which a hole having a substantially circular cross section is formed as a passage. In this type of pipe diffuser, as shown in FIGS. 8 and 9, a leading edge (front edge) 26 having an arc shape is formed at a portion where adjacent passages 23 intersect at an acute angle.

[0004]

However, in the conventional diffuser, the passage 23 is provided such that the center line 24 of the passage 23 contacts the outer peripheral circle 28 of the impeller 22 at the contact point B '. 24 is always O
Although it is arranged in a direction perpendicular to B ′, the outflow angle of the fluid flowing out of the impeller 22 differs depending on the form of the impeller 22, so that the incident angle of the fluid and the arrangement angle of the leading edge may be large in some cases. It may be shifted, which causes a remarkable incident mismatch (shift of the incident angle) near the leading edge and causes blockage (blocking) at the throat portion of the passage 23. Is a factor that reduces

[0005] The present invention has been devised to solve such problems of the prior art, and its main objects are as follows.
An object of the present invention is to provide a diffuser for a centrifugal compressor configured to reduce an incident mismatch and suppress a decrease in a static pressure recovery rate.

[0006]

According to the present invention, there is provided an impeller for a centrifugal compressor.
And a passage 3 for decelerating the fluid from the impeller
However, in a diffuser having a plurality of diffusers opened at regular intervals in the circumferential direction with a substantially circular cross section, each passage is provided such that its center line 4 is in contact with a reference circle 5 concentric with the impeller, and the reference circle is The required diameter is set so that the leading edge (leading edge) 6 formed at the intersection of the adjacent passages is arranged in an appropriate direction according to the outflow direction of the fluid from the impeller.

According to this, the leading edge on the side of the passage wall can be arranged in a direction along the actual flow of the fluid. Therefore, the incidence mismatch near the leading edge can be reduced, and the blockage at the throat portion is suppressed, so that the static pressure recovery rate can be increased.

In particular, the present invention is preferably applied to a configuration in which the number of the passages is 10 or more. Number of passages is 1
If it is less than 0, the difference between the outer diameter of the impeller and the diameter of the reference circle becomes extremely large, and the desired effect cannot be obtained. More preferably, the number of passages should be 18 to 22. A particularly preferable embodiment is a configuration having 20 passages.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 and FIG. 2 show a diffuser of a centrifugal compressor constructed according to the present invention. The diffuser 1 is provided so as to surround the impeller 2 of the centrifugal compressor, and the passage 3 for decelerating the fluid from the impeller 2 so as to communicate the inner peripheral side and the outer peripheral side has a substantially circular cross section. A plurality of passages 3 are provided at regular intervals in the circumferential direction, and all the passages 3 are provided such that their center lines 4 are in contact with a reference circle 5 concentric with the impeller 2.
Is set to have a required diameter such that a leading edge (leading edge) 6 formed at the intersection of the adjacent passages 3 is arranged in an appropriate direction according to the outflow direction of the fluid from the impeller 2. I have.

The passage 3 has an outer peripheral portion whose diameter is enlarged at a required divergence angle, and its center line 4 is a straight line, and can be obtained by drilling a hole by a cutting means such as a drill. The leading edge 6 formed at the intersection of the adjacent passages 3 becomes straight in a front view (see FIG. 1) due to the intersection of the passages 3 of the same diameter, and has an arc shape in a side view (see FIG. 1). (See FIG. 2).

As shown in detail in FIG. 3, the leading edge 6 includes, in a front view, an intersection A between both center lines of the adjacent passages 3 and an end point C located at the deepest position of the bowing leading edge 6. The leading edge setting angle β, that is, the angle formed by the straight line AC connecting the end point C and the intersection point A of the leading edge 6 and the straight line OC connecting the center point O and the end point C is the reference circle 5. The diameter changes depending on whether the diameter is smaller or larger than the outer diameter of the impeller 2, and can be set to an arbitrary value by increasing or decreasing the diameter of the reference circle 5.

Here, both center lines 4 of the adjacent passages 3 are
Assuming that the total number of passages 3 is N, they intersect at an intersection A at an angle of 2π / N. In addition, a straight line drawn by the leading edge 6 in a front view, that is, the impeller 2 at the intersection A
Is π / N at the intersection A between the tangent line of the outer peripheral circle 8 of FIG.
Intersect at an angle of

In FIG. 3, the diameter of the reference circle 5 is set smaller than the outer diameter of the impeller 2, and the outer circle 8 of the impeller 2 passes through the intersection A between the two center lines of the adjacent passages 3, and this intersection A
Overlap the ends 6a and 6b of the leading edge 6 on the shroud side and the hub side in a front view (see FIGS. 2 and 4). Then, a straight line drawn by the leading edge 6 in a front view becomes a tangent to the outer circumferential circle 8 of the impeller 2, and three-dimensionally,
A plane including the bow-shaped leading edge 6 and the intersection point A comes into contact with the cylindrical surface including the outer circumferential circle 8 of the impeller 2.

In this case, if the radius of the impeller 2 is R _IMP and the angle between the diameter OA and the diameter OB is α, the passage 3
The radius R _tan a reference circle 5 in which the center line 4 are in contact, and is indicated by R _tan = R _IMP × cosα, the angle α, α = π / N since the radius R _tan a reference circle 5, R _tan = R _IMP × cos (π / N)

Here, the leading edge 6 is viewed from the front.
Is assumed to be in contact with the outer peripheral circle of the impeller 2, but considering the gap δ between the impeller 2 and the leading edge 6 due to structural necessity, the radius R of the reference circle
_tan is represented by R _tan = R _IMP × cos (π / N) + δ.

The number of passages 3 is preferably 10 or more, and is 13 in this case (see FIG. 1). Ratio of diameter of the reference circle 5 with respect to the outer peripheral ¥ 8 of the impeller 2, i.e. the ratio to the outer diameter R _IMP of the impeller 2 of the difference between the diameter R _tan outer diameter R _IMP and reference circle 5 of the impeller 2 (R _IMP -R
_As shown in FIG. 5, the ratio of _tan ) / R _IMP decreases as the number of passages increases, but it is desirable that the ratio be kept to about 5%. It is good to If the number of passages is less than 10, impeller 2
The diameter of the reference circle 5 becomes extremely small with respect to the outer diameter of, and the desired effect cannot be obtained.

The leading edge setting angle β shown in FIG.
As shown in FIG. 6, when the number of passages is the same, the ratio R _tan / R _IMP of the diameter of the reference circle 5 to the outer diameter of the impeller 2 increases as the ratio increases. Further, the leading edge set angle β decreases as the number of passages increases. Here, if the leading edge setting angle β is determined according to the outflow direction of the fluid from the impeller 2 determined by the shape of the blades of the impeller 2, an optimum number of passages can be obtained from FIG.

FIG. 7 shows an example in which the reference circle 5 is set to be larger in diameter than the outer diameter of the impeller 2. Here, the intersection A between the two center lines 4 of the adjacent passages 3 is located outside the outer circumferential circle 8 of the impeller 2, and the leading edge setting angle β is smaller than the leading edge setting angle β in the example shown in FIG. Is also getting bigger.

[0020]

As described above, according to the present invention, by setting the reference circle to be larger or smaller than the outer diameter of the impeller, the leading edge is arranged at the outflow angle of the fluid from the impeller determined according to the shape of the impeller. By adjusting the angle, the incidence mismatch near the leading edge can be reduced, and the blockage at the throat portion of the passage is suppressed. Therefore, a great effect is obtained in increasing the static pressure recovery rate.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a diffuser of a centrifugal compressor according to the present invention.

FIG. 2 is a sectional view of the diffuser shown in FIG. 1 cut along a center line.

FIG. 3 is an enlarged sectional view of a main part of the diffuser shown in FIG. 1;

FIG. 4 is a perspective view of a main part of the diffuser shown in FIG. 1;

FIG. 5 is a graph showing the relationship between the number of passages and the ratio of the diameter reduction of the reference circle.

FIG. 6 is a graph showing a relationship between a ratio of a diameter of a reference circle to an outer diameter of an impeller and a leading edge setting angle.

FIG. 7 is an enlarged sectional view of a main part showing another embodiment of the diffuser according to the present invention.

FIG. 8 is an enlarged sectional view of a main part showing a conventional diffuser.

FIG. 9 is a perspective view of a main part of the diffuser shown in FIG. 8;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diffuser 2 Impeller 3 Passageway 4 Centerline of passage 5 Reference circle 6 Leading edge 8 Outer circle of impeller

Claims (2)

[Claims] 1. A diffuser which surrounds an impeller of a centrifugal compressor and has a plurality of diffusers formed at regular intervals in a circumferential direction with a substantially circular cross section, the passage being configured to decelerate fluid from the impeller, Each passage is disposed such that its center line is in contact with a reference circle concentric with the impeller, and the reference circle has a leading edge formed at the intersection of the adjacent passages.
A diffuser having a required diameter set so as to be disposed in an appropriate direction according to a flow direction of a fluid from the impeller. 2. The diffuser according to claim 1, wherein the number of the passages is 10 or more.