JPH01399A - high speed centrifugal compressor diffuser - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a diffuser for a centrifugal compressor, and particularly to a diffuser suitable for a high-speed centrifugal compressor that obtains a high pressure ratio in a single stage.

[Conventional technology]

A high-speed centrifugal compressor generally has a structure as shown in FIGS. 10 and 11, and generates an airflow in the direction shown by an arrow 2 by rotating an impeller 1. In a high-speed centrifugal compressor made to obtain a high pressure ratio in a single stage, the speed of the airflow 2 flowing out from the impeller 1 exceeds the speed of sound, so the airflow 2 comes to rest on the outer periphery of the impeller on the downstream side of the impeller 1. A diffuser 3 with vanes is provided and is designed to convert the velocity energy of the fluid discharged from the impeller 1 into pressure energy.

As shown in FIG. 11, a plurality of stationary blades 4 constituting the diffuser 3 are provided radially around the outer circumference of the impeller 1, and a diffuser flow path 5 is formed between the blades of these stationary blades 4. ing. Arrows 6 indicate these diffuser channels 5
It shows the direction of flow within.

In such a compressor, under conditions of relatively high rotation speed and small flow rate, a separated flow region occurs on the negative pressure surface of the stationary blade 4.
There is a problem in that a surge phenomenon occurs in which a sufficient pressure increase cannot be obtained. As a diffuser for a high-speed centrifugal compressor that solves this problem and is less likely to cause surging even under high-speed and low-flow conditions, a diffuser as previously proposed by the applicant of the present application and disclosed in Japanese Patent Application Laid-open No. 159998/1983 has been proposed. A known proposal is to provide a rotatable aileron at the inlet to control the fluid flowing through the diffuser. Furthermore, as disclosed in Japanese Patent Application Laid-Open No. 119411/1983, a vaned diffuser is constructed with a double circular blade row, and the length of the blades of the inner circular blade row is set to 0 of the blade spacing.
．． There is also a known proposal to make it 9 times or less.

[Problem that the invention seeks to solve]

However, with the former, the diffuser flow path formed between the stationary blades is suddenly expanded immediately downstream of the ailerons, which causes pressure loss and reduces the choke flow rate, resulting in a reduction in diffuser performance. . In addition, although the latter does not have the problem of choke flow reduction, if the flow at the inlet of the blades that make up the inner circular blade row exceeds the speed of sound, loss occurs due to the strong shear flow that occurs downstream of the blades of the inner circular blade row. There was a problem that performance deteriorated.

An object of the present invention is to solve the above problems and provide a diffuser for a high-speed centrifugal compressor that has a wide operating range and high performance.

[Means for solving problems]

In order to achieve the above object, the present invention provides a centrifugal system of a type in which a plurality of stationary blades are arranged around the outer periphery of an impeller and the kinetic energy of fluid discharged from one impeller is converted into pressure energy by the action of the stationary blades. In the diffuser of the compressor, an aileron blade having a shorter chord length than the stationary blade is provided on a side closer to the inner circumference between the plurality of stationary blades, and only one wing surface of the aileron is opposed to the stationary blade. In addition, the auxiliary blade is arranged at a position that intersects a circle centered on the rotation axis of the impeller and passing through the inner circumferential end of the stationary blade.

Further, the present invention provides a plurality of stationary blades arranged around the outer periphery of the impeller,
In a diffuser for a centrifugal compressor that converts the kinetic energy of fluid discharged from an impeller into pressure energy by the action of stationary blades, a chord is placed between the plurality of stationary blades on a side closer to the inner circumference than the stationary blades. A short auxiliary blade is provided, only one wing surface of the auxiliary blade is opposed to the stationary blade, and the auxiliary blade is centered around the rotation axis of the impeller and passes through the inner peripheral end of the stationary blade. An intermediate blade having a chord length shorter than that of the stationary blade is provided at a position intersecting a circle between the plurality of stationary blades and closer to the outer periphery between the plurality of stationary blades, and the intermediate blade has a chord length shorter than that of the stationary blade. It passes through the midpoint of the perpendicular line drawn to the inner extension of the adjacent stationary wing.

The outer peripheral end of the intermediate blade reaches a circle passing through the outer peripheral end of the stationary blade, and the length of the intermediate blade located on the inner peripheral side from the midpoint of the perpendicular line is 20% or less of the total length of the intermediate blade, and The shape of the entire intermediate blade is characterized in that when the intermediate blade is virtually rotated around the rotation axis of the impeller, it is included inside the stationary blade.

[Effect]

According to the above structure, only one surface of the aileron faces the stationary vane constituting the diffuser, so the aileron does not intrude into a region where the flow is strongly restricted by the adjacent stationary vane. Therefore, a sudden increase in the cross-sectional area of the flow path and a decrease in the choke flow rate immediately downstream of the aileron do not occur. Also, since only one surface of the aileron faces the stationary wing,
The distance between the leading edge of the region sandwiched between the stationary blades and the trailing edge of the aileron is short, so the section where strong shear flow occurs is short and losses occur less.

Furthermore, it is desirable to make the inner peripheral side aileron as thin as possible, but a certain thickness is required for strength reasons.

For this reason, it is necessary to set the number of stationary blades to a level that can ensure a sufficient cross-sectional area of the flow path, but if this is done, the spacing between the stationary blades will be too large in the flow path near the outer periphery of the stationary blade, resulting in a decrease in performance. However, on the side near the outer periphery between the stationary blades, the intermediate blade extends so as to pass through the midpoint of the perpendicular drawn from the outer peripheral edge of the stationary blade to the blade surface of the adjacent stationary blade. Near the outer peripheral edge of the blade, the spacing between the stationary blades is substantially at an appropriate value, thereby preventing performance deterioration.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a diffuser for a high-speed centrifugal compressor according to the present invention will be described below with reference to the drawings.

An embodiment of the present invention is shown in FIGS. 1 to 6.

In the figures, parts that are the same or equivalent to those of the conventional example shown in FIGS. 10 and 11 are denoted by the same reference numerals, and explanations thereof will be omitted. The feature of this embodiment lies in the auxiliary blades 7 and the intermediate blades 12 provided within the diffuser 3.

As shown in FIG. 2, the auxiliary blades 7 are arranged so as to intersect with a circle 9 centered on the center of the rotating shaft 8 of the impeller 1 and passing through the inner peripheral end (leading edge) of the stationary blade 4. There is.

Further, when a perpendicular drawn from the leading edge of the stationary blade 4b on the center side of the radius of curvature to the other stationary blade 4a among the adjacent stationary blades 4a and 4b is 10, the aileron 7 does not intersect with this perpendicular 10. It is arranged like this. The intermediate wing 12 is a stationary wing 4
The trailing edge of the intermediate blade 12 passes through the midpoint of the perpendicular line 13 drawn from the trailing edge (outer edge) of a to the adjacent stationary blade 4b, and the trailing edge of the intermediate blade 12
It is arranged so as to reach a circle 14 passing through the trailing edge of.

Further, the length of the intermediate blade 12 extending from the midpoint of the perpendicular line 13 to the inner circumferential side is within 20% of the overall length of the intermediate blade 12, and the intermediate blade 12
The overall shape is included inside the stationary blade 4 when the intermediate blade 12 is virtually rotated about the center of the rotation axis 8 . Further, the stationary blades 4, the auxiliary blades 7, and the intermediate blades 12 each have their face ends defined by the opposing walls 11 of the diffuser 3, and the space formed by these defines the diffuser passage 5.

Next, the operation of this embodiment will be explained. When the airflow 2 flowing out from the impeller 1 passes through the diffuser 3, kinetic energy is converted into pressure energy and compressed. In a high-speed centrifugal compressor, the flow velocity of the airflow 2 flowing into the diffuser 3 exceeds the sonic velocity, so shock waves are generated and the flow velocity is reduced to subsonic velocity. Figure 3 shows that the Matsuha number of airflow 2 is close to 1 (for example, 1
．． 1 or less), the strong wave that occurs near the leading edge of each blade 4, 7, which greatly affects the flow, is shown. Although the angle θ between the airflow 2 and the stationary blade 4 changes depending on the flow rate of the gas compressed by the compressor, the situation shown in FIG. 3 does not change because a strong shock wave is generated at the leading edge of the blade. The shock wave 15 generated near the leading edge of the stationary wing 4 is generated only near the stationary wing 4, and is not caused by other ailerons 7 or the stationary wing 4.
There will be no collision. The reason will be explained in detail below. When the Matsuha number of the airflow 2 is close to 1, the shock wave 15a generated at the leading edge of the stationary blade 4a extends almost perpendicularly to the stationary blade 4a, so that it does not collide with the aileron 7 or the adjacent stationary blade 4b. A subsonic flow 17 flows in a portion sandwiched between the auxiliary blade 7 and the suction surface 16 of the stationary blade 4a, and a portion sandwiched downstream between the dashed line 18 and the suction surface 16. Since a shock wave is generated when a supersonic flow is decelerated to a subsonic flow, the shock wave 1 generated at the leading edge of the stationary blade 4b facing the stationary blade 4a.
5b only reaches the dashed line 18 and does not reach the suction surface 16 of the stationary blade 4a. By providing the ailerons 7 as described above, it is possible to prevent shock waves from reaching the suction surface 16, making it difficult to cause a surging phenomenon and expanding the operating range. The reason for this will be further explained below.

In general, the airflow flowing through a vaned diffuser is.

As the flow rate of the compressor decreases, the pressure in the direction of flow increases, and when it exceeds a certain limit, backflow occurs and normal compression is no longer possible, causing the so-called surging phenomenon, which prevents the compressor from operating normally. Unable to drive. The limit at which the diffuser causes backflow varies depending on the shape of the stationary blade, etc.
Backflow tends to occur when the airflow separates from the surface of the stationary vane or from the walls sandwiching both sides of the stationary vane.9 Separation from the suction surface of the stationary vane is usually the main cause. If the shock wave reaches the suction surface at this time, the boundary layer along the suction surface will rapidly thicken, cause partial separation, or in some cases large-scale separation may occur due to the strong pressure increase before and after the shock wave. There is. Therefore, if the shock wave is prevented from reaching the negative pressure surface, separation of the airflow layer on the negative pressure surface can be almost prevented, and the limit for causing backflow can be shifted to the small flow rate side.

In other words, it is possible to suppress the surging phenomenon caused by the diffuser.

The limit on the high flow rate side of the airflow is determined by the minimum cross-sectional area of the flow path in the diffuser. Therefore, in FIG. 3, it is determined by the length of the perpendicular line 1o drawn from the leading edge of the stationary blade 4b to the suction surface 16 of the stationary blade 4a. At this time, the aileron 7 does not intersect this perpendicular line 1o, and the perpendicular line 10 is not shortened, so that it does not affect the limit on the large flow rate side. As described above, the aileron 7 allows the limit on the small flow rate side to be moved to the smaller flow rate side without reducing the limit on the large flow rate side.

The above-mentioned effect of expanding the flow range by the aileron 7 is that the aileron 7
If the following conditions are met, the effect will be strong (and the performance of the diffuser will not deteriorate).

The first condition is that the trailing edge of the aileron 7 is located upstream of the perpendicular 10. If the aileron 7 intersects the perpendicular line 10, not only will the maximum flow rate be reduced as described above, but also a pressure loss will occur due to the rapid expansion of the cross-sectional area of the flow path. In other words, the flow path downstream of the perpendicular 10 is sandwiched between the stationary blades 4a and 4b on both sides, and when the trailing edge of the aileron 7 is downstream of the perpendicular 10, the width of the flow path expands rapidly by the thickness h of the trailing edge. It is from.

On the other hand, in the distance p between the trailing edge of the auxiliary wing 7 and the perpendicular 10, the airflow 17 is decelerated to subsonic speed by being sandwiched between the auxiliary wing 7 and the stationary wing 4b. # Since the shock wave 15b contacts and mixes with the supersonic flow 19 on the upstream side, a large pressure loss occurs. Therefore, the distance f'lp needs to be sufficiently small, for example, 50 of the distance m between the leading edge of the stationary g4b and the perpendicular 1o.
% or less.

The second condition is the distance r between the aileron 7 and the stationary wing 4a.
and the distance q on the entrance side, the ratio r/q is close to 1.

For example, it is set to 1 to 1.1. This is because if r/q is out of this value range, the flow will separate from the blade surface of the auxiliary blade 7 and the loss to the downstream side of the auxiliary blade X7 will increase.

The third condition is the ratio of the length n of the overlapping portion of the aileron 7 and the stationary wing 4a facing χ to the distance q between the leading edge of the stationary wing 4a and the surface of the aileron 7. n/q is greater than 1 to ensure that the airflow 17 is subsonic.

According to this embodiment, since the aileron 7 does not enter the region where the flow is strongly restricted between the opposing stationary g4a and 4b, the flow passage cross-sectional area immediately downstream of the aileron 7 suddenly expands and the choke flow rate increases. No decrease occurs. Also, since only one surface of the aileron 7 faces the stationary blade 4a, the stationary blade 3i4a,
4b and the trailing edge of the aileron 7 are short, the section where strong shear flow occurs is short, and the generation of pressure loss is small. Since it is located between the leading edge and the leading edge of stationary g4b, ? The rf shock wave does not reach the surface of the stationary blade 4a, and the airflow 17 becomes difficult to separate from the surface of the stationary blade 14a, and the diffuser 3
is operating normally and can expand the flying range.

Figure 4 shows that the Matsuha number of airflow 2 flowing into the diffuser is
For example, in a preferred embodiment when exceeding 1.1, the aileron 7
The leading edge of the stationary blade 4a is located upstream of the leading edge of the stationary blade 4a. As the Matsuha number of the airflow 2 increases, the shock wave 15.20 becomes curved. Therefore, in order to prevent the shock wave 15a from colliding with the surface of the aileron 7, a shock wave 20 is generated at the leading edge of the aileron 7 to make the flow in the passage 21 between the aileron 7 and the stationary wing 4a a subsonic flow. It is something.

Although it is desirable for the aileron 7 to be as thin as possible from an aerodynamic standpoint, it must be thick enough to ensure strength and structure. In other words, the length is commensurate with the thickness (for example, 5 to 10 times the thickness)
However, in this case, it is necessary to select the number of stationary blades so as to satisfy the above-mentioned relationship between the stationary blades 4 and the ailerons 7, and the number must be reduced by at least 20% compared to the case where the ailerons 7 are not provided. No. If the number of stationary blades 4 is reduced in this way, the interval between the stationary blades 4 will be too large near the outer periphery, and the flow will be
Performance deteriorates because the flow no longer follows the blade surface.

5 and 6 are diagrams showing the action of the intermediate blade 12. FIG. 5 shows a case where the intermediate blade 12 is not provided, and the flow does not follow the blade surface on the negative pressure surface 21 near the trailing edge of the stationary blade 4a, resulting in a large-scale separation area 22. The occurrence of large separation areas reduces diffuser deceleration by reducing the substantial cross-sectional area of the flow and reduces diffuser performance due to the generation of kinetic energy dispersion within the separation area. This large-scale separation can be prevented by reducing the load (deceleration) on the suction surface 21 near the trailing edge. The situation will be explained below using the 6th IA. Using the -dimensional flow theory, the amount of deceleration near the trailing edge of the suction surface 21 of the stationary blade 4a is determined by the circumferential distance between the trailing edge 23 of the stationary blade 4a and the trailing edge 24 of the stationary blade 4b, and the exit of the stationary blade. Using the product of the sine of the angle β and the length f of the perpendicular drawn from the trailing edge 23 of the stationary blade 4a to the adjacent stationary blade 4b, hsimβ/f
-1. The larger this value is, the larger the deceleration load is. The value of hsimβ/f-1 is determined by the shape and number of stationary blades, and increases as the number of blades increases. 1st
An example is shown in the table. From the same idea, if intermediate X12 is provided, the deceleration amount gsimβ/e-
It is represented by 1. Table 1 also shows the deceleration load when intermediate blades are provided. As shown in Table 1, even when the number of stationary blades is 17, the deceleration of 23% is reduced to 19% by the intermediate blade 12.
The amount of deceleration can be reduced by 20%, and large-scale peeling near the trailing edge of the negative pressure surface can be suppressed.

Table 1 Effects of intermediate blades The intermediate blades 12 prevent large-scale separation near the trailing edges of the stationary blades 4a due to the effects described above, so the intermediate blades 12 ensure the flow near the trailing edges of the stationary blades. Stationary wings 4a for restraint
The trailing edge 25 intersects a perpendicular drawn from the trailing edge 23 to the adjacent stationary wing 4b, and the trailing edge 25 reaches the circle 14. If the blade length of the intermediate blade is too large, the area in contact with the flow will increase, so the length L of the intermediate blade on the inner peripheral side of the perpendicular line is 20% of the total length of the intermediate blade.
within. Since the flow upstream from the perpendicular line has relatively little bias, the intermediate X12 passes through the midpoint of the perpendicular line to divide the flow equally, thereby making the flow uniform at the diffuser outlet. Prevent additional losses from occurring. In addition, the overall shape of the intermediate blade 12 is such that when the intermediate blade 12 is virtually rotated around the center of the rotating shaft 8, it is included inside the stationary blade 4, so that the flow can pass through smoothly, reducing loss. Occurrence is low.

FIG. 7 shows an example in which the chord length of the stationary blade 4 is so short that a perpendicular line cannot be drawn from the trailing edge of the stationary blade 14a to the adjacent stationary blade 4b. In this case, the average thickness line at the leading edge of the stationary blade 14b is extended. A perpendicular line 27 drawn to line 26 is used. The extension line 26 may be a straight line, but the same effect can be obtained by using a logarithmic line passing through the leading edge of the stationary wing 4b and forming an artificial angle η.

FIG. 8 shows another embodiment of the present invention. This example is an auxiliary
lt7 is rotatably supported by a support shaft 28 parallel to the rotation axis 8 of the impeller 1 by an angle δ. Then, during high-flow operation, the length of the perpendicular line a27 extending from the leading edge of the stationary blade 4b to the aileron blade 7 is lengthened, and during low-flow operation, the length of the perpendicular line 27 is shortened to further expand the flow range by the throttling effect. That is. In this embodiment, the aileron 7
The support shaft 28 may be rotated manually, or the support shaft 28 may be automatically operated in conjunction with a control device of a device equipped with the centrifugal compressor according to this embodiment. It's okay. According to this embodiment, the flow rate range can be expanded by the repetition, and the practical effect can be further enhanced.

FIG. 9 shows another embodiment of the invention. In this embodiment, the intermediate blade 12 is rotatably supported by a support shaft 30 parallel to the rotation axis 8 of the impeller 1 by an angle γ. The sum of the length of the perpendicular line 28 drawn from the leading edge of the intermediate blade 12 to the adjacent stationary blade 4a and the length of the perpendicular line 29 drawn from the trailing edge of the intermediate blade 12 to the adjacent stationary blade 4b is calculated as follows: This is sometimes shortened to expand the flow rate range by the throttling effect as in the embodiment shown in FIG. 8, and is even more effective when combined with rotary movable control of the aileron 7.

〔Effect of the invention〕

As described above, according to the present invention, a diffuser equipped with a plurality of stationary blades that converts velocity energy of an air flow flowing out from an impeller of a high-speed centrifugal compressor into pressure energy,
Only one wing surface faces the stationary wing, an aileron is provided at a position that intersects a circle passing through the leading edge of the stationary wing, and the midpoint of a perpendicular drawn from the trailing edge of the stationary wing to the adjacent stationary wing is By providing an intermediate vane that reaches a circle that passes through the trailing edge of the stationary vane, the operating flow range of the diffuser can be expanded without reducing performance, and the operating flow range of the high-speed centrifugal compressor can be significantly expanded.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing one embodiment of a diffuser for a high-speed centrifugal compressor according to the present invention, FIG. 2 is a view taken along arrow A-A in FIG. 1, and FIGS. 7 to 9 are enlarged views of main parts showing other embodiments of the present invention, FIG. 10 is a vertical sectional view showing a conventional high-speed centrifugal compressor, and FIG. 11 is a diagram showing the operation of the example. 10 is a view taken along the line B-B in FIG. 10. FIG. 1... Impeller, 3... Diffuser, 4... Stationary blade, 7... Aileron, 8... Rotating shaft, 9...
・Circle, 12...middle wing, 16...perpendicular line.

Claims (7)

[Claims] (1) A diffuser for a centrifugal compressor in which a plurality of stationary blades are arranged around the outer periphery of the impeller, and the kinetic energy of fluid discharged from the impeller is converted into pressure energy by the action of the stationary blades. An aileron whose chord length is shorter than that of the stationary blade is provided on the side closer to the inner circumference between the stationary blades, and only one wing surface of the aileron faces the stationary blade. 1. A diffuser for a high-speed centrifugal compressor, characterized in that the diffuser is disposed at a position that is centered at the center of the rotational axis of the impeller and intersects a circle that passes through the inner peripheral end of the stationary blade. (2) The aileron is disposed at a position intersecting a perpendicular line perpendicular to the stationary wing at an inner peripheral end of the stationary wing facing the aileron. A diffuser for a high-speed centrifugal compressor as described in Section 1. (3) The diffuser for a high-speed centrifugal compressor according to claim 1 or 2, wherein the ailerons are rotatably supported by a support shaft parallel to the rotation axis of the impeller. (4) The diffuser for a high-speed centrifugal compressor according to claim 1, wherein the distances from the inner circumferential end and outer circumferential end of the aileron vane to the stationary vane facing the aileron vane are different. (5) A diffuser for a centrifugal compressor in which a plurality of stationary blades are arranged around the outer periphery of the impeller, and the kinetic energy of the fluid discharged from the impeller is converted into pressure energy by the action of the stationary blades. An aileron whose chord length is shorter than that of the stationary blade is provided on the side closer to the inner circumference between the stationary blades, and only one wing surface of the aileron faces the stationary blade. disposed at a position that intersects a circle centered on the rotational axis of the impeller and passing through the inner circumferential end of the stationary blade;
and an intermediate blade having a shorter chord length than the stationary blade is provided on a side closer to the outer periphery between the plurality of stationary blades, and the intermediate blade extends from the outer peripheral end of the stationary blade to the inner peripheral side of the adjacent stationary blade. passing through the midpoint of a perpendicular drawn to the line, the outer circumferential edge of the intermediate wing reaches a circle passing through the outer circumferential edge of the stationary wing, and the length of the intermediate wing that is inside the midpoint of the perpendicular line is The length of the intermediate blade is 20% or less of the total length of the intermediate blade, and the shape of the entire intermediate blade is such that when the intermediate blade is virtually rotated around the rotation axis of the impeller, it is included inside the stationary blade. High speed centrifugal compressor diffuser. (6) The diffuser for a high-speed centrifugal compressor according to claim 5, wherein the intermediate blade is rotatably supported by a support shaft parallel to the rotation axis of the impeller. (7) The diffuser for a high-speed centrifugal compressor according to claim 5, wherein the distances from the inner peripheral end and outer peripheral end of the intermediate blade to the stationary blade facing the intermediate blade are different.