JPS5896197A - Air intake of centrifugal compressor - Google Patents

Abstract

PURPOSE:To prevent surging in a compressor by furnishing two or more low guide vanes at the inside surface of the passage's outer walls just before the inlet to the impeller of a centrifugal compressor, by giving the stream at this inlet to impeller a mild swirling at its outer zones, and by preventing defoliation owing to distortion of the flow. CONSTITUTION:Two or more guide vanes 9, sufficiently low compared with the diameter of the passage, are installed on a circumference at the inner surface of a bell-mouth 3 forming a ring-shaped passage's exterior walls just before the inlet to impeller 1 projecting a little aslant with respect to the axis of a rotary shaft 2. Thereby the air stream taken in at the suction hole 5 is given by the guide vanes 9 a mild swirling only at the zone nearer the inside surface of bell-mouth 3 as exterior walls of ring-shaped passage A to lower the relative Mach number to the impeller inducer 8. Therefore defoliation owing to distortion of the flow is prevented to hinder the compressor from being put in the surging state. Thus the operating range of a centrifugal compressor can be widened.

Description

[Detailed description of the invention] The present invention relates to the structure of an air intake port for a centrifugal compressor.

In a centrifugal compressor with a turbine construction of 7 mm, when the impeller is rotating at high speed, the relative velocity between the impeller and the air flow approaches the speed of sound at the end of the inline inducer. At this time, if distortion occurs in the velocity distribution of the flow, the distortion will locally increase the Matsuha number, and if the Matsuha number exceeds 1, a shock wave will be generated and the flow will separate at the outermost diameter part of the inline inducer. . As a result, the compacting machine enters a surge state and becomes inoperable.

FIG. 1 shows the structure of an air intake port in such a conventional centrifugal compressor, which is also described, for example, in Japanese Patent Publication No. 53-22964, in which an impeller 1 is fixed to a rotating shaft 2:' Fixed bell mouth 3 and intake box 4
Air flowing in from the intake port 5 is introduced into the inlet 4 through the air passage A formed by the intake port 5 and the intake port 5.

Note that 61d is a diffuser vane, 7 is a shroud forming the outer wall of the impeller inlet passage, and 8 is an impeller inducer.

However, in such a conventional air intake port for centrifugal pressure md, the intake port 5 is provided at an upper position aligned approximately 90 degrees with respect to the axial direction of the rotation shaft 2 of the impeller 1. The air flow entering from the intake port 5 ends up entering the impeller 1 through various paths.

As a result, the velocity distribution at the impeller inlet is distorted, and the pressure surge as described above begins at an early stage, which limits the operating range and lowers the pressure ratio, resulting in a significant deterioration of performance.

This invention has been made in view of the above points, and is made by applying a method to the diameter of the annular or cylindrical passage on the same circumference of the inner surface of the outer wall of the annular or cylindrical passage just before the inlet of the air intake of the centrifugal compressor. A plurality of guide vanes with a sufficiently low height compared to the above are installed at a slight angle with respect to the rotational axis of the inlet cover to give a weak pre-swirl to the flow near the outer wall of the passage, thereby reducing compressor surge. The aim is to prevent

The present invention will be described in detail below with reference to FIG.
The same parts as in FIG. 1 are given the same reference numerals, and explanations of those parts will be omitted.

In FIG. 2, on the same circumference of the inner surface of the bell mouth forming the outer wall of the annular passage just before the entrance of the impeller 1, there are a plurality of guides Jli! whose height is sufficiently low compared to the passage diameter. 9,
It protrudes and is slightly inclined with respect to the axial direction of the rotating shaft 2.

The rest of the structure is the same as the conventional example shown in FIG.

According to this air intake, the flow of air flowing in from the intake port 5 is slightly swirled by the guide vanes 9 only in a portion close to the inner surface of the bell mouth 3, which is the outer wall of the annular passage A, and the impeller inducer 8 The relative Matsuha number becomes lower.

Therefore, separation caused by flow distortion is prevented, the compressor is prevented from entering a surge, and the operating range of the centrifugal compressor can be expanded.

In addition, in the above embodiment, the present invention was applied to a case where the passage to the impeller inlet was annular, but it can also be applied to a case where the passage is cylindrical without any problem. Needless to say.

As described above, according to the present invention, a plurality of low-height guide vanes are provided on the inner surface of the outer wall of the passage immediately in front of the impeller inlet of a centrifugal compressor, so that the flow from the inlet covering the inner wall is changed into a weak swirling flow at the outer part. Therefore, the relative Matsuha number with the in-lined inducer is reduced.

This eliminates separation caused by flow distortion, makes it difficult for the centrifugal compressor to experience surges, and has the excellent effect of expanding the operating range.

Further, since the pre-swirling given to the flow described above is in the very outer part of the passage and the amount of swirling is extremely small with respect to the entire flow, almost no change in pressure ratio occurs.

Furthermore, the height of the guide vanes is sufficiently low compared to the diameter of the passage.
Moreover, since a plurality of guide vanes are provided, the amount of vortices generated from these guide vanes is very small, and there is no risk of exerting external force on the impeller, so that the performance of the centrifugal compressor is not impaired.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an air intake port of a conventional centrifugal compressor, and FIG. 2 is a sectional view showing an embodiment of the present invention. 1... Impeller 2... Rotating shaft 3... Pel 4th 4... Intake is 5... Intake port 6... Diffuser vane 7... Shroud 8. γ impeller inducer 1 figure

Claims (1)

[Claims] 1. On the same circumference of the inner surface of the outer wall of the annular or cylindrical passage just before the impeller inlet of the centrifugal compressor, a plurality of guide vanes whose height is sufficiently low compared to the diameter of the passage are installed relative to the axis of rotation of the impeller. An air intake port for a centrifugal compressor, characterized in that the air intake port of a centrifugal compressor is provided so as to project at a slight slant to give a pre-swirl to the flow.