EP0138480A2

EP0138480A2 - Centrifugal compressor

Info

Publication number: EP0138480A2
Application number: EP19840306634
Authority: EP
Inventors: Daniel A. Gutknecht; Richard Holtkamp; Dendall R. Swenson
Original assignee: Garrett Corp
Current assignee: Garrett Corp
Priority date: 1983-10-03
Filing date: 1984-09-28
Publication date: 1985-04-24
Also published as: JPS6081498A

Abstract

© A turbocharger centrifugal compressor has a volute (12) which overlaps itself and a divider neck or tongue (40) which divides flow from the impeller (26) into upstream and downstream parts of the volute where it overlaps itself, and in order to reduce noise the neck extends to a region adjacent the outlet of the impeller, whether by being connected to the outlet end of a diffuser blade (34A) where there is a vaned diffuser between the impeller and volute, or by connection across the diffuser (42 in Figure 7) if the diffuser is a vaneless diffuser.

Description

This invention relates to a compressor and in particular to a compressor housing, for example, for use in conjunction with turbomachinery having a rotor adapted to operate at exceedingly high blade tip speeds.
In general, turbomachinery as a fluid handling device is susceptible to noise generation as a result of high fluid velocities through and about fixed and moving blades, vanes, and channels. Localised pressure fields resulting from the interaction between the fluid and the fluid handling structures result in the generation of regular cyclical pressure waves which cause noise. Elimination and/or suppression of turbomachinery noise can be accomplished by redesigning the noise generating mechanism itself or by attenuating the effectiveness of the noise transmission mechanism.
The compressor is preferably a centrifugal compressor. In a radial outflow centrifugal compressor with or without a vaned diffuser, the geometry of the housing leads to the formation of an asymmetrical pressure field around the compressor wheel. As the compressor wheel blades pass through regions of higher and lower pressure, pressure impulses travel along the blade and cause noise. Furthermore, reduction of the circumferential pressure gradient will result in a reduction in the amplitude of the pressure pulse generated by the rotating wheel.
Turbomachinery may include a radial outflow centrifugal compressor with a vaned diffuser located radially outward from the compressor impeller. The compressor impeller imparts energy to the air by increasing the velocity or kinetic energy of the air. Between each-pair of adjacent vanes of a diffuser plate is formed a channel of carefully controlled geometry wherein the air is diffused or slowed down in order to convert the dynamic pressure to static head pressure. The diffuser, through-the design of the vanes, serves to guide the flow from the impeller through channels between the vanes of increasing flow cross sectional area to provide optimal pressure recovery. Diffusion results in an increase in pressure and fluid density in the region around the diffuser plate.
The compressor housing design serves several purposes; it guides the air into the compressor impeller through its inlet, it shrouds the impeller and prevents leakage around the blades, it forms a sidewall for the diffuser and it collects the flow from the diffuser and channels it through its volute and discharges through the compressor outlet. The geometry of the construction of the housing results in the formation of an asymmetrical field around the compressor impeller which assists in the undesirable generation of noise as discussed above.
As stated above, one of the compressor housing's functions is to collect flow from the diffuser and deliver it to the inlet manifold of the engine. The design features pertinent to this function have been determined to be a major cause of noise. Such compressor housings may have a divider located at the point where the volute overlaps itself and which diverts the flow from the diffuser either to the compressor outlet or around the volute inside the compressor housing and thereafter through the compressor housing outlet. As a stationary projection in the flow channel, the divider causes almost total stagnation of the fluid striking it and that creates a localized region of high static pressure. This non-uniform pressure distribution occurring in the compressor housing generates a circumferentially asymmetrical pressure field causing noise.
In contrast to the above-described prior art compressor housing design, the present invention contemplates a compressor housing with revised geometry which minimizes the magnitude of the asymmetrical circumferential pressure gradient. More particularly, the present invention encompasses a design in which a divider neck or tongue extends to within close proximity of a region adjacent the compressor outlet where the fluid energy is substantially kinetic energy. For example, it may extend to one of the diffuser vanes thereby substantially eliminating the projection in the flow path and the region of high pressure stagnant air which is present in the existing designs.
If the compressor includes a circumferential diffuser, the divider can extend to the diffuser inlet adjacent the compressor wheel outlet.
The invention may be carried into practice in various ways, and some embodiments will be described by way of example, in relation to the prior art, with reference to the accompanying drawings in which:-

FIGURE 1 is a side elevational view of a turbocharger compressor;
FIGURE 2 is an end sectional view of the turbocharger compressor housing of a type known in the art having a dividing neck;
FIGURE 3 is a fragmented front view on the line 3-3 of FIGURE 2 or FIGURE 5;
FIGURE 4 is a fragmented front view on the line 4-4 of FIGURE 2;
FIGURE 5 is a view similar to FIGURE 2 but of a turbocharger compressor housing having a vaned diffuser embodying the present invention;
FIGURE 6 is a fragmented front view taken on the line 6-6 of FIGURE 5; and
FIGURE 7 is a view similar to FIGURE 5 but a turbocharger compressor housing having a vaneless diffuser and embodying the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A compressor housing which may be used in a turbocharger of an internal combustion engine is composed of a volute section 12 and an integral shroud and diffuser plate section 14 having a shroud 16 and a diffuser plate 20. The volute section 12 defines a volute 13 having an increasing cross-sectional area. The end having the greatest cross-sectional area defines a compressor outlet 38 having its axis geneally tangential to the volute 13. The shroud portion 16 is generally cylindrical on the outside with a venturi shaped cental opening therein. The convergent portion of the venturi defines a compressor inlet 18. The divergent portion expands radially outwards into the diffuser plate section 20. A backplate 22 ( not shown in FIGURES 2,5, or 7) separates the compressor housing 10 from the centre housing ( not shown) of the turbocharger. The backplate and the diffuser plate 20 defines between them an annular diffuser passage.
A compressor impeller 26 which is mounted on a drive shaft 28 for rotation by a prime mover (not shown), has a hub 30 of generally disc-shaped configuration with a plurality of circumferentially spaced blades 32 projecting from the hub 30 generally radially. The blades 32 provide passages through which fluid flows by centrifugal force in response to the rotation of the impeller 26 to discharge radially about the compressor impeller; additional air flows axially through the compressor inlet 18 into the passages at the centre of the wheel to replace the air discharged. The blades 32 are suitably curved to enhance the flow of the air into the passages.
In the compressor housing design, shroud 16 is provided adjacent the outer edges of the blades 32 to confine the fluid in the passages formed thereby. As is usual in the type of compressor shown, the diffuser element or plate 20 is provided around the periphery of the impeller 26. The plate 20 consists of a circular plate and with a plurality of vanes 34 extending axially from one side of the plate. Vanes 34 are spaced radially from the centre and extend to the circumference of the plate 20 and are generally tangential to the periphery of the compressor impeller 26. Adjacent vanes, together with the diffuser plate 20 and a backplate 22 break up the annular diffuser passage 24 into a plurality of diffuser vane passages 36. The diffuser vane passages 36 receive the fluid discharged at high velocity from the impeller and convert the velocity - (kinetic energy) - into the pressure - (static energy). The housing volute 13 surrounding the periphery of the diffuser vane passages receives the fluid under pressure.
Also known in the art are "vaneless" diffusers which as the name implies does not have any of the vanes 34 on the diffuser plate 20. Therefore, the diffuser passage 24 is annular in shape and is bounded axially by the diffuser plate 20 and backplate 22.
According to turbocharger compressor housings of the present type, the volute section 12 defines a scroll-shaped air discharge chamber or volute 13 which extends at least 360° around the compressor inlet 18 and is in spaced relation thereto. Hence, at least a portion of the volute section 12 overlaps itself and therefore a portion of the larger end of the volute is in flow communication with the smaller end of the volute via an overlapping passage 44 ( shown in FIGURES 2 and 4). The volute section 12 has a wall 15 which extends from the compressor outlet around to a dividing neck 40 which extends into the overlapping passage 44. Airflow from the smaller end of the volute can be discharged directly into the larger end of the volute through the overlapping passage 44 without travelling around the volute 13 and out the compressor outlet 38. The overlapping passage 44 therefore creates a second flowpath for air leaving the diffuser passage 24 near the dividing neck 40.
As known in the art, ambient air enters axially through the compressor inlet 18, is compressed by the rotating compressor impeller 26 and flows radially through the diffuser passage 24 and into the compressor housing volute 13 before exiting through the compressor outlet 38 for communication to the inlet manifold of the engine.
As the fluid flows from the impeller through the diffuser vane passages 36, to the compressor housing volute 13 and into the outlet 38,.any resistance to the flow can cause buildup of static fluid pressure. In the compressor housing designs of the prior art, FIGURES 1-4 the greatest resistance to flow has been found to exist in the area where air exits the diffuser passage 24 near the dividing neck 40; i.e. where flow can either enter the volute nearest to the compressor housing outlet 38 ( the larger end of the volute) or flow into the volute 13 at its smaller end. This resistance creates a zone A of stagnant high pressure which, along with the rotating impeller causes noise as discussed above.
In order to eliminate this source of noise, the invention as shown in FIGURES 5 to 7 has eliminated the zone A of stagnant air by extending the dividing neck 40 in order to close overlapping passage 44. FIGURE 5 shows a fragmented side view of the compressor housing 10 including the outlet 38. An extension 42 of the dividing neck 40 extends into the throat of the volute 13 such that its leading edge lies on the periphery of, or is connected to, the diffuser plate 20. This extension 42 of the dividing neck 40 guides flow within the volute 13 such that flow through diffuser vane passage 36A must flow into the volute 13 at its smallest cross-section and counterclockwise as viewed in FIGURE 5. Flow from the adjacent diffuser vane passage 36B must exit straight to the compressor outlet 38. Air flowing from either passage 36A or 36B does so without encountering the resistance to its flow experienced with the compressor housing design of FIGURE 2. The air flow through diffuser vane passages 36A or 36B does not strike the neck 40, but is guided to flow on either side of it, and this eliminates the high pressure region of stagnant air ( shown as zone A in FIGURE 2), and thus eliminates a cause of turbocharger noise.
As shown in FIGURES 5 and 6, the dividing neck extension 42 extends into the volute 13 and together with one of the diffuser vanes 34A co-operates to eliminate any direct passage of air flow from diffuser vane passage 36A into the larger end of volute 13 immediately upstream of the compressor outlet 38. The dividing neck extension 42 has been cross hatched in FIGURE 6 in order to show its shape clearly.
Comparison may be made with FIGURE 4 which shows the air passage connecting the volute at its smallest end and the volute immediately upstream of the compressor outlet in a prior proposal. However, even though it has been cross-hatched, the extension 42 is integral with the wall of the volute section 12. It is evident that the extension 42 has extended the wall 15 of the volute section 12 from the compressor outlet 38 to the periphery of the diffuser 20, and, with the diffuser vane 34A effectively to the periphery of the impeller 26.
It should be noted that although the inention has been described with respect to a vaned diffuser section, the concept of eliminating the stagnant, high pressure zone ( designated as zone A in FIGURE 2) can be accomplished in a vaneless compressor. This is done by extending the dividing neck 40 radially inward to a point at the periphery of the compressor impeller 26 as shown at 42 in FIGURE 7. This design is most feasible in the case where the diffuser plate 20 and the dividing neck 40 and its extension 42 are cast as an integral part of the housing.
Various modifications to the depicted and described apparatus will be apparent to those skilled in the art. Accordingly, the foregoing detailed description of the preferred embodiment of the invention should be considered exemplary in nature, and not as limiting to the scope and spirit of the invention as set forth in the appended claims.

Claims

1. A centrifugal compressor in which an impeller (26) delivers fluid under pressure to a surrounding volute (12) which overlaps itself, and a neck (40) divides flow from the impeller into upstream and downstream parts of the volute where it overlaps itself; characterised in that the neck extends (at 42) to a region adjacent the impeller outlet where the fluid energy is substantially kinetic energy.

2. A compressor as claimed in Claim 1 in which the impeller discharges into a circumferential diffuser (20) for converting kinetic fluid energy into static fluid energy, and the neck (42) extends to the inlet to the diffuser adjacent the impeller outlet.

3. A compressor as claimed in Claim 2 in which the diffuser includes a number of circumferentially spaced vanes (34) and the neck extends to the outer end of one vane (34A).

4. A compressor as claimed in Claim 3 in which the diffuser vanes extend with a substantially tangential component in the direction of flow around the volute .

5. A compressor as claimed in Claim 2 in which the diffuser is a vaneless diffuser and the neck extends across the diffuser to a point adjacent the impeller outlet.

6. A compressor as claimed in any of the preceding claims in which the volute extends for substantially 360° around the outlet from the impeller and/or the diffuser.

7. A compressor as claimed in any of the preceding claims in which the volute increases in cross section from an inlet end to an outlet, overlapping end.

8. A compressor as claimed in any of Claims 3,4,6 and 7, in which the neck extension (42) constitutes means for preventing air flow from any one of the passages between adjacent diffuser vanes from simultaneously entering the upstream and downstream parts of the volute.

9. A compressor as claimed in any of the preceding claims in which the neck extension (42) effectively closes the overlapping part of the volute.

10. A compressor as claimed in any of the preceding claims in which the volute has a wall extending from the periphery of the impeller and/or the diffuser to the outlet from the volute for directing the air flow to travel in the volute in one direction.