US3749520A - Centrifugal compressor blading - Google Patents

Abstract

A centrifugal compressor, which may otherwise be conventional, has the tip portion of the impeller blades made of a porous material to allow some of the air to flow from the forward face of the blade through the blades to the rear face to promote more uniform velocity at the impeller exit and thus reduce mixing losses and improve the slip factor of the compressor.

Description

United States Patent 11 1 Bandukwalla 1 July 31, 1973 [54] CENTRIFUGAL COMPRESSOR BLADING 3,411,794 11/1968 Allen 416/95 X [75] Inventor: Phiroze Bandukwalla, lndianapolis, OR PATE TS 0R APPLICATIONS 112,269 10/1964 Czechoslovakia 416/231 858,284 12 1952 G 416 185 [73] Assgnw g 9 2 860,898 12/1952 416/231 etmn 875,984 5/1953 Germany 416/231 22 Filed: Oct. 4 1971 1,046,247 12/1958 Gennany v 416/186 942,648 11/1963 Great Britain 416/231 [21] Appl. No.: 186,302

' Primary Examiner-Everette A. Powell, Jr. 521 U.S. c1 416/183, 416/181, 416/188, Ftzlamck 416/231 51 1111.01. Fold 5/04 [57] ABSTRACT [58] Field of Search ..4l6/l81183, A centrifugal compressor. which y Otherwise be 185 1 13g 231 227 22 conventional, has the tip portion of the impeller blades made of a porous material to allow some of the air to 5 R f n Cited flow from the forward face of the blade through the UNITED STATES PATENTS blades to the rear face to promote more uniform velocl 071 660 8 1913 B 4 ity at the impeller exit and thus reduce mixing losses l622930 341927 ZEZE'Q 'Q' and improve the slip factor of the compressor. 2,161,182 6/1939 Massey 416/231 UX 2 Claims, 4 Drawing Figures CENTRIFUGAL COMPRESSOR BLADING The invention described and claimed herein was made in the course of work under a contract with the Department of Defense.

My invention relates to centrifugal compressors, and particularly to an improvement of the rotor blades of such compressors to improve flow conditions and therefore the efficiency and stability of operation of such compressors.

Centrifugal compressors for air and other gases are very well known and widely employed and have great advantages, particularly in lower pressure ranges, because of the simplicity of their structure as compared to axial-flow compressors.

Such a compressor is described in Atkinson U.S. Pat. No 2,819,012 for Centrifugal Compressor, Jan. 7, 1958. Air enters the compressor through an annular entrance generally parallel to the axis of rotation and is accelerated circumferentially of the rotor while moving radially outward under the influence of centrifugal force, the discharge of air from the impeller being primarily tangential, with a substantial radial component and ordinarily little axial component of velocity.

The high velocity discharge from the rotor or impeller is diffused in structure providing a diverging flow path and the dynamic head is thus in large measure converted to pressure head, so that the discharge is at a substantial rise in pressure above atmospheric or other inlet pressure. Such compressors are found in gas turbine engines, turbochargers, air conditioning machines, and various other environments.

Since the movement of the air is accomplished by the paddle-like action of the face of a generally radial blade pushing the air generally tangentially, the flow in the space between adjacent blades in not uniform, the flow tending to concentrate on the forward or advancing face of the blade, where the air is at higher pressure and the velocity is greater than adjacent the rear or retreating blade face. Thus, with the multibladed rotor, the discharge at any fixed point is to some extent pulsating, with greater radial velocity of discharge adjacent the forward face of each passing blade.

It has occurred to me that flow through the diffuser and, in general, the efficiency and resistance to surge of the compressor may be improved by suitable expedients to smooth out the radial velocity of flow from the impeller without undue energy losses. This has led me to the concept that, by making the tip portion of the blades of a porous material so that air may flow from the forward to the rear face of the blade through passages distributed over the area of the blade tip, the inequality of flow may be largely counteracted and the mixing losses in the space into which the air is discharged and the efficiency of the diffuser can be sub stantially improved.

Having become aware of the existence of metallic materials having small closely distributed pores which have been developed for use as transpiration-cooled turbine blades, seals, and other hot parts of turbine engines, I have concluded that a material of this general character will provide the requisite structural properties and the controllable porosity to implement my in vention.

Therefore, I propose to form the tips of centrifugal impeller blades of laminated material having an array of fine closely distributed pores over the surface to provide for flow of air from the forward to the rear face of the blade for the reasons set out above.

I am aware of blowing slots in airfoils and of the slotted centrifugal rotor blades proposed by US. Pat. No. 2,819,838 of Warner, Jan. 14, l958.

The principal objects of my invention are to improve the performance and utility of centrifugal compressors, to provide smoother flow in the discharge from a centrifugal compressor rotor, and to provide an impeller structure with porous blade tips which is readily fabricated and which will withstand the forces encountered in operation.

The manner in which these and other objects of my invention are accomplished and the nature of the invention will be apparent to those skilled in the art from the succeeding detailed description of preferred embodiments of the invention and the accompanying drawings thereof.

FIG. 1 is a partial sectional view of a centrifugal compressor, taken principally on a plane containing the axis of rotation.

FIG. 2 is a greatly enlarged view of a portion of FIG. 1.

FIG. 3 is a view similar to FIG. 2 of a modified structure.

FIG. 4 is a partial sectional view taken on the plane indicated by the first line 44 in FIG. 2.

Referring first to FIG. 1, the centrifugal compressor, illustrated more or less schematically, comprises a housing 2 having a front wall'3 and a rear wall 4. A rotor or impeller 6 disposed between the walls is suitably fixed to a shaft 7. The shaft is rotatably supported in a bushing 8 mounted in a bearing support 10 suitably supported from the front wall and in a bushing 11 mounted in the rear wall 4. The front wall 3 and bearing support 10 define an annular air entrance or eye 12. The front and rear walls define between them a diffuser or diffusing space 14, which may have any suitable configuration, only the inner part of which is illustrated.

The rotor 6 comprises a hub or disk 15 fixed on shaft 7. The hub defines the inner and rear boundary of the gas flow path through the compressor rotor. The front wall 3 defines the outer and forward boundary of this flow path.

The air is moved by a ring of generally radially extending blades 16, the initial portions of which, as shown in the lower portion of FIG. 1, are curved forwardly to act as the inducer portion of the impeller and the rear or radially outer portions of which lie approximately or exactly in surfaces parallel to the axis of the shaft 7. The blades terminate at a tip 18 which may be at the same radius as the periphery of the disk 15.

The structure so far described is known, and may be the same as that described at greater length in the aforementioned Atkinson patent.

My invention is embodied in the portion of each blade adjacent the tip 18, which we may call the tip portion 19, and which may preferably involve approximately the outermost 10 percent of the radius of the impeller. Referring to FIGS. 2 and 4 for details of structure, FIG. 4 illustrates a blade having a slightly forward leaning tip, but the tip may be strictly radial or backward leaning so far as the present invention is concerned. However, I beleive it to be more beneficial with a forward-raked blade.

The tip portion 19 of the blade is a laminated porous body comprising three sheets; a from sheet 20, a middie sheet 22, and a rear sheet 23. All of these sheets bear a two-dimensional array of closely spaced perforations 24 with the perforations in each registering with those in adjacent sheets so that numerous small pores are provided through the tip portion. One such pore is indicated by the arrow 26 in FIG. 4. It will be understood that the structure is greatly enlarged for clarity of delineation in FIGS. 2 and 4. The sheets 20, 22, and 23 may be of the order of 0.010 inch thick and the perforations of about the same diameter. The several sheets may be brazed, diffusion bonded, or otherwise fixed together into a unitary structure. The perforations may be made in any suitable manner, including photoetching or whatever technique is suitable to the materials involved. Preferably, the perforations are aligned somewhat out of register so that the trend of the pores 26 is radially outwardly from the forward to the rear face of the tip portion so that the air flowing through these pores from the high pressure face of the blade to the lower pressure face has a radially outward component of How Because of the substantial centrifugal force, a positive attachment of the tip portion to the body of the blade 16 is required. One mode of retention which is favorably regarded is shown in FIGS. 2 and 4. In this case, the middle sheet 22 has an inner border at 27 radially outward of the inner borders of the other sheets. Holes 28 are etched, punched, or otherwise provided in the two outer sheets. The impeller is bicast to the tip portion so that the metal of the impeller blade 16 extends into the gap between the front and rear sheets and forms bosses 30 extending into theholes 28 locking the tip portion onto the body of the blade.

HO. 3 illustrates a modified structure in which a tip portion 32 has dovetail slots 34 cut in the radially inner margin of the front and rear sheets, these dovetail slots being filled with dovetails 3S integral with the blade 16 when the impeller is cast.

Obviously, other modes of retention may be employed suited to the particular installation. For example, with rotor structures of some materials, the tip may be spot-welded to the rotor or a pinned connection may be used.

FIG. 2 illustrates another feature of structure which may be employed. In this case, a slot 36 is provided between the disk and the tip portion 19 which also provides for flow of air from the leading to the trailing face of the blade. This slot in the example discussed might be approximately 0.010 inch in width. The provision of a slot at the junction of the blade tip and disk is, however, the subject matter of my patent application Ser. No. 186,303 filed Oct. 4, l97l.

It may be noted that it is preferred to have the porosity of the tip portion increased towards the tip, either by having larger pores toward the tip or by closer spacing of the pores.

in the operation of the compressor, the air under higher pressure at the forward face of the blade is forced by the pressure differential across the blade through the blades so that some of this air emerges at the trailing face of the blade and adds to the flow at this point. By reducing flow at the forward face and increasing flow at the rearward face, the disparity between radial flow rates across the gap between adjacent blades is very substantially reduced and flow patterns are improved.

The detailed description of preferred embodiments of the invention for the purpose of explaining the principles thereof is not to be considered as limiting or restricting the invention, since many modifications may be made by the exercise of skill in the art.

I claim:

1. A centrifugal compressor rotor mounted for rotation about an axis and including fluid-impelling blades adapted to impel fluid flowing radially outward from the axis circumferentially with respect to the axis, the blades extending generally parallel to the axis and generally radially from the axis and terminating in blade tips generally parallel to the axis at the extremity of the blades remote from the axis, the portion of each blade adjacent the tip being a laminated structure of plural layers of sheet metal having an array of numerous distributed pores extending through the structure from the forward face to the rearward face to allow diffusion of air through the blade tip in response to the pressure differential across the blade, the pores being defined by communicating perforations in the layers, and the per forations being so overlapped that each pore extends radially outwardly from the forward to the rearward face.

2. A centrifugal compressor rotor mounted for rotation about an axis and including fluid-impelling blades adapted to impel fluid flowing radially outward from the axis circumferentially with respect to the axis, the blades extending generally parallel to the axis and generally radially from the axis and terminating in blade tips generally parallel to the axis at the extremity of the blades remote from the axis, the portion of each blade adjacent the tip being a laminated structure of plural layers of sheet metal having an array of numerous distributed pores extending through the structure from the forward face to the rearward face to allow diffusion of air through the blade tip in response to the pressure differential across the blade, the pores being defined by communicating perforations in the layers, and the porosity of the tip portion increasing in the direction toward the blade tip.

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Claims (2)

1. A centrifugal compressor rotor mounted for rotation about an axis and including fluid-impelling blades adapted to impel fluid flowing radially outward from the axis circumferentially with respect to the axis, the blades extending generally parallel to the axis and generally radially from the axis and terminating in blade tips generally parallel to the axis at the extremity of the blades remote from the axis, the portion of each blade adjacent the tip being a laminated structure of plural layers of sheet metal having an array of numerous distributed pores extending through the structure from the forward face to the rearward face to allow diffusion of air through the blade tip in response to the pressure differential across the blade, the pores being defined by communicating perforations in the layers, and the perforations being so overlapped that each pore extends radially outwardly from the forward to the rearward face.

2. A centrifugal compressor rotor mounted for rotation about an axis and including fluid-impelling blades adapted to impel fluid flowing radially outward from the axis circumferentially with respect to the axis, the blades extending generally parallel to the axis and generally radially from the axis and terminating in blade tips generally parallel to the axis at the extremity of the blades remote from the axis, the portion of each blade adjacent the tip being a laminated structure of plural layers of sheet metal having an array of numerous distributed pores extending through the structure from the forward face to the rearward face to allow diffusion of air through the blade tip in response to the pressure differential across the blade, the pores being defined by communicating perforations in the layers, and the porosity of the tip portion increasing in the direction toward the blade tip.

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