US3383033A - Sealing means for axial flow compressor discharge - Google Patents

Description

y 4, 1968 c. c. MOORE 3,383,033

SEALING MEANS FOR AXIAL FLOW COMPRESSOR DISCHARGE Filed April 2'7, 1966 3 Sheets-Sheet l a a E 'El E.

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INVENTOR. (l/fl ffl/l/ I, A/flflff C. C. MOORE May 14, 1968 SEALING MEANS FOR AXIAL FLOW COMPRESSOR DISCHARGE 3 Sheets-Sheet 2 Filed April 27, 1966 y 4, 1968 c. c. MOORE 3,333,033

SEALING MEANS FOR AXIAL FLOW COMPRESSOR DISCHARGE Filed April 27, 1966 3 Sheets-Sheet 5 United States Patent 3,383,033 SEALING MEANS FOR AXIAL FLOW COMPRESSOR DISCHARGE Clinton C. Moore, Cincinnati, Ohio, assignor to General Electric Company, a corporation of New York Filed Apr. 27, 1966, Ser. No. 545,611 12 Claims. (Cl. 230-132) ABSTRACT OF THE DISCLOSURE The invention concerns an axial flow compressor having a rotor, an outer casing forming an annular flow path for pressurized gases, an inner frame forming with the outer casing a continuation of the flow path, and fluid biased axially movable seal means between the frame and the rotor.

The present invention relates to improvements in axial flow compressors and more particularly to improvements in providing improved sealing means between the usual rotor thereof and adjacent stationary frame members at the discharge of the compressor.

A compressor rotor defines the inner surface of an annular flow path which is defined by a relatively stationary frame member in directing the presurized air to a point of ultimate use. The amount of air lost at the juncture of the rotor and frame member is an important factor to the efficiency of axial flow compressors.

The importance of high compressor efiiciencies is perhaps best exemplified by their use in gas turbine engines. In such engines an axial flow compressor provides pressurized air to maintain combustion and provide a hot gas stream of a high energy level which may be discharged through a nozzle to provide a propulsive force or may drive a turbine which provides a rotative power output. Particularly in the propulsion of aircraft it is essential that the overall engine operate at a high efficiency level in order that the full advantages of the gas turbine engine may be realized. Loss of air from the compressor thus detracts not only from the efiiciency of the compressor itself but also the overall eficiency of operation of the engine.

The object of the invention is, therefore, to provide an improved, reliable, highly effective, and economical seal between the rotor of an axial flow compressor and the adjacent frame member which define a flow path for the pressurized air discharged from the compressor.

In the recited environment of an axial flow compressor these ends are attained through the use of sealing means characterized by the provision of an axially movable ring member adjacent the rear end of the compressor rotor. Primary sealing means are formed on the ring and rotor and comprise a radial sealing surface and an annular tooth projecting theretowards which coact to prevent leakage of pressurized air. Air bearing means spaced radially inwardly from the primary sealing means are also formed by cooperative portions of the ring member and rotor. The air bearing means are effective when the ring member and rotor are in close proximity to maintain an accurate, closely spaced rleation of the primary sealing means, whereby the sealing means are highly effective. The ring member, the compressor rotor, and the adjacent frame form an annular chamber opening into the flow path for pressurized air discharged from the compressor. The radial area of the ring member which is exposed to this chamber is sufficiently great to provide a yieldable force which displaces the ring member into close proximity with the compressor rotor when the pressure of the air discharged from the compressor reaches ice ing means to thus maintain a highly effective seal at the juncture of the inner frame and rotor.

In normal operation there is no contact between the stationary and rotating elements and thus essentially no wear. Further means are provided for urging the ring member to an axially retracted position when the discharge pressure of the compressor falls below a given level. The air bearing and air pressure force which displaces the ring provide for effective sealing action in spite of variations in the axial position of the compressor rotor.

It is also preferable to vent the area between the primary sealing means and the air bearing to a substantially lower pressure, usually atmospheric, in order to obtain greater effectiveness of the air bearing.

Further, it is preferred that secondary. sealing means he formed on the ring member and rotor and comprise a cylindrical surface; and a tooth projecting radially theretowards. Thus at relatively low compressor discharge pressures, or Where the primary sealing means is for some reason inoperative, delivery of pressurized air Will be maintained albeit at a reduced level.

It is also preferable that the ring member be configured such that the summation of torque forces about the center of gravity of the longitudinal half section thereof, resulting from pressurization of the annular chamber which is defined thereby, be substantially zero. Thus any tendency to twist the ring member is minimized, if not eliminated, and the effectiveness of the primary sealing means is maintained at a high level over a wide range of compressor discharge pressures.

The above and other related objects and features of the invention will be apparent from a reading of the following description of the disclosure found in the accompanying drawings and the novelty thereof pointed out in the appended claims.

In the drawings:

FIGURE 1 is a diagrammatic view of a gas turbine engine having an axial flow compressor and sealing means therefor which embody the present invention;

FIGURE 2 is an enlarged longitudinal section of the discharge portion of the axial flow compressor seen in FIGURE 1, under a condition of relatively high discharge pressure;

FIGURE 3 is a section similar to FIGURE 2 illustrating a condition of relatively low compressor discharge pressure;

FIGURE 4 is a section taken on line IVIV in FIGURE 3; and

FIGURE 5 is a longitudinal section through the discharge portion of an axial flow compressor illustrating sealing means embodying an alternate embodiment of the invention.

FIGURE 1 schematically shows a gas turbine engine 10 in which the present invention finds particular utility. The engine 10 comprises a compressor 12, a combustor 14, a turbine 16, and a discharge nozzle 18. The compressor 12 includes a rotor 20 having a plurality of blades 22 arranged in stages along its length and cooperating with stator blades 24 extending inwardly from an outer casing 28, thereby forming an axial flow compressor for delivering pressurized air to support combustion in the combustor 14. The hot gas stream thus generated drives the turbine 16 to derive power for rotating the compressor rotor 20, being connected thereto by a hollow shaft 30. After passing through the turbine 16, the hot gas stream may be discharged through the nozzle 18 to provide a propulsive force in the operation of aircraft.

It will be apparent that the compressor casing 28, in combination with the rotor 20, defines an annular flow path leading to the combustor 14. This annular flow path, beyond the compressor 12, is defined by an extension of the casing 28 and a frame member 32 which is generally aligned with the rear end of the rotor 20. One of the serious problems in attaining high efficiency in the operation of gas turbine engines is to minimize loss of pressurized air discharged from the compressor at this juncture between the rapidly rotating compressor rotor and the stationary frame member 32.

The rear end of the compressor rotor 20 (FIGURES 24) comprises a disc 34 to which is secured an annular sealing plate 36 means of bolts 38. The stationary frame 32 is compositely formed by a frame member 40 which has a lip 42 substantially aligned with the outer circumference of the rear end of the rotor 20 and is closely spaced therefrom to provide a smooth flow path for pressurized air discharged from the compressor. Bolts 44 join this compositely formed frame structure.

A ring member or seal body 46 is guided for movement toward and away from the rotor 20 by cooperating flanges 48 and 50. A circumferential labyrinth sealing tooth 52 projects from the ring member 46 towards the sealing plate 36. The ring member 46 is also provided with a radial flange 54 which terminates in a labyrinth sealing tooth 56. A flange 58 projects from the sealing plate 36 and overlies the tooth 56 in all positions of the ring member 46.

The rotor 20, the ring member 46, and the frame member 40 define an annular chamber 60 which opens into the flow path of air discharged from the compressor 12, and therefore, the chamber 60 is pressurized to substantially the same value as the compressor discharge pressure. A split ring 62 provides a seal for the chamber 60 between the axially movable ring member 46 and the frame member 40, being maintained in sealing engagement therewith by pressurization of chamber 60. It will be noted that the contact area of ring 62 engaging the frame 40 and ring member 46 is relatively small in order to minimize frictional drag on the latter as it is displaced toward and away from the rotor 20, as later described.

In normal compressor operation a highly effective compressor discharge seal is provided by the labyrinth tooth 52 which is closely spaced from the plate 36, in the order of .001 inch. A force derived from the compressor discharge air yieldingly urges the ring member 46 towards the sealing plate 36 and the close spacing of the labyrinth sealing tooth 52 is maintained by an air bearing 63 between the ring member 46 and plate 36. The ring member 46 thus can float and accommodate, Within limits, variations in the axial position of the compressor rotor 20,

Expansible chamber means are shown in FIGURES 2-4 for obtaining the force urging the ring member toward the plate 36. These expansible chamber means comprise a plurality of pistons 64 which are slidable axially in the ring member 46 with their outer ends bearing against the frame member 40. Passageways 66 lead from the annular chamber 60 to chambers 68 in which the pistons 44 are slidable. The pistons are provided with radial holes 70 so that pressurized air leaking therethrough will minimize friction to facilitate displacement of the ring member 46.

The air bearing 63 is preferably externally pressurized by the provision of passageways 72 which direct pressurized air from the chambers 68 between the opposed surfaces of the ring member 46 and sealing plate 36 which comprise the air bearing. It is also preferable that the area between the air bearing and the labyrinth sealing tooth 52 be vented to a lower pressure, usually atmospheric, for most effective air bearing operation. To this end a counter bored clearance hole 74 opens into the area between the air bearing and the sealing tooth 52 so that air from this area may be vented through the ring member 46 and then through holes 76 in the frame 40 to the opposite side thereof which is at atmospheric pressure or substantially so.

The y'ieldable force provided by the pistons 64, in combination with the described air bearing, maintains the desired spacing of the labyrinth sealing tooth 52 and a highly effective sealing action regardless of any variations in the axial position of the compressor rotor 20.

The present seal has the further benefit of being highly effective over a wide range of compressor discharge pressures. This results from the fact that there is no substan tial twisting moment on the ring member. More specifically there is no twisting moment on the illustrated, longitudinal half section of the ring member. Thus, it will be evident that the effective force vector F of the air bearing 63 and the effective force vector F of the expansible chambers on the ring member are equal and opposite, with no resultant twisting or torque force on the ring member. Further, the radially inward force exerted on the outer surface of the ring member 46 which defines the chamber 60 is distributed from the tooth 52 to the point of engagement of the sealing ring 62 therewith. The effective radial force vector F passes through the center of gravity cg of the ring member 46 so that there is no resultant twisting force therefrom. The air pressure forces on opposite sides of the flange 54 are equal and opposite and consequently there is no resultant effective force vector in an axial direction.

The described air pressure forces are the only forces of significance which could tend to deform the ring member 46 by twisting and result in a change in the orientation of the end face of the tooth 52 relative to the sealing plate 36. Thus, the end face of the tooth 52 may be accurately machined to provide an effective sealing action over the full range of compressor discharge pressures.

At low rates of rotation of the compressor rotor 20 sufficient air pressure may not be available for effective operation of the air bearing. To prevent contact between the ring member 46 and the rotor 20, means are provided for yieldingly urging the ring member in spaced relation therefrom. These means comprise a plurality of springs 78 which are coiled about bolts 80. The outer set of bolts 80 extend through the counter bored clearance holes 74, pass through the frame 40, and have nuts 82 threaded thereon to adjust the force exerted by the springs 78 on the ring member 46. The inner set of bolts 80 similarly pass through the ring member 46 and frame 40 and are likewise provided with adjusting nuts 82. When the compressor discharge pressure falls below a given level the springs 78 displace the ring member 46 to the retracted position shown in FIGURE 3.

When operation of the engine 10' is initiated, the ring member 46 is maintained in spaced relation from the rotor 20 by the springs 78. As compressor discharge pressure builds up there is a pressure increase in the annular chamber 60 due to the sealing action of the tooth 56. This develops a pressure differential on opposite sides of the flange 54 with a resultant force tending to displace the ring member to its operative position contiguous with the sealing plate 36. Simultaneously there is a pressure increase in the chambers 68 which also tends to develop a force displacing the ring member to its operative position wherein the tooth 52 becomes the primary sealing means, as above described.

If for some reason the air bearing should fail to maintain the ring member 46 in spaced relation from the plate 36, it is desired that damage be maintained at a minimum and preferably that no damage occur to any of the rotating parts. Thus, the portion of the ring member 46 which forms a part of the air bearing 63 is surfaced with a layer 84 of sacrificial material, such as a low melting point metal alloy. In the event of air bearing failure the sacrificial layer 84 will be melted by friction without injury to the plate 36. The tooth 52 being a relatively thin section will also burn or melt away without injury to the plate 36. It will be noted that the coils of springs 78 are arranged so that their solid heights will serve as a positive limit to displacement of the ring member 46 towards the rotor 20 so that engagement of the substrate to which the layer 84 is bonded with the plate 36 is prevented.

In the event of such a malfunction, excessive leakage of compressor discharge air is prevented by the labyrinth tooth 56 which thus functions as a secondary sealing means. Operation of the engine 10 is maintained as a sufficient volume of air continues to be delivered to the combustor 14 for generating a hot gas stream, albeit at a reduced energy level.

FIGURE illustrates an alternate embodiment of the invention wherein a different form of ring member 46' is provided with a primary sealing tooth 52 which is arranged to cooperate with the sealing plate 36 which is mounted on the compressor 20, as before described. The ring member 46 likewise has a secondary sealing tooth 56, projecting from a radial flange 54 which cooperaates with the sealing plate flange 58.

The annular chamber 60 is again defined by the rotor 20, a modified frame member 40, and the ring member 46'. This chamber is further provided with a sealing ring 62 which seals the chamber 60 at the juncture of the frame 40 and ring member 46' while permitting the ring member 46' to be displaced toward and away from the compressor rotor 20. The sealing ring 62 is again relieved so that frictional forces are minimized to facilitate such displacement of the ring member 46'. A garter spring 83 and a plurality of compression springs 85 are provided to insure effective sealing by the split ring 62' when the pressure in chamber 60 is relatively low.

Passageways 86 extend from the chamber 60 to passageways 88 which direct pressurized air between the opposed surfaces of the ring member 46' and sealing plate 36 to provide an air hearing, as before, which accurately spaces the sealing tooth 52 from the sealing plate 36 and thus maintains a highly efficient sealing action. Angularly spaced passageways 90 vent the area between the air bearing 63 and the sealing tooth 52 to atmosphere for optimum sealing operation.

The primary difference in the present embodiment is that the expansible chamber means have been eliminated in utilizing the compressor discharge pressure to yieldably maintain the ring member in a position where the air hearing accurately positions it. T 0 this end the ring member 46 is configured so that there is a pressure differential on opposite sides of the radial flange 54' due to the location of the primary sealing tooth 52. Thus there is provided a resultant effective force F which displaces and yieldably maintains the ring member 46 in its operative position wherein the sealing tooth 52 is closely spaced from the plate 36.

In this alternate embodiment provision is also made to prevent any substantial twisting of the ring member which would tend to reduce the effectiveness of the sealing action particularly over a wide range of compressor discharge pressures. This end is similarly achieved by a balance of the effective air pressure forces on the longitudinal half section of the ring member 46' as illustrated in FIGURE 5. The axial force vector F produces a counterclockwise turning moment about the center of gravity C.G., on this longitudinal half section. The effective force vector F of the air bearing likewise produces a counterclockwise torque about the center of gravity. These counterclockwise torque force are balanced by equal torque force provided by the effective force vector F resulting from the radially inward air pressure force on the outer surface of the ring member. The net result is that there is no twisting moment from these air pressure forces about the center of gravity of the longitudinal half section. To repeat, this balance of torque forces enables effective sealing action to be maintained.

As in the previous embodiment, means are provided for retracking the ring member 46 from the compressor rotor 20 when compressor discharge pressure falls below a given value. Thus studs 92 project through the frame member 40' and have springs 94 coiled there-abouts and confined by nuts 96 so that there will be no contact between the ring member 46 and the rotor 20 at low pressure levels.

Other modifications will occur to those skilled in the art and the scope of the present invention is therefore to be derived solely from the following claims.

Having thus described the invention, what is claimed as novel and desired to be secured by Letters Patent of the United States is:

1. In an axial flow compressor having a rotor and an outer casing forming an annular flow path for pressurized gas to be discharged therefrom, an inner stationary frame aligned with and adjacent the dischage end of said rotor and forming, in combination with said casing, a continuation of said flow path,

sealing means for preventing, or at least minimizing,

the loss of highly pressurized air at the juncture of said inner frame and said rotor, said sealing means comprising, an axially movable ring member, primary sealing means respectively formed on said ring and rotor and comprising a radial sealing surface and an annular tooth projecting towards said surface,

air bearing means spaced radially inwardly from said primary sealing means and formed by cooperative portion on said rotor and said ring member, said air bearing means being effective when said ring and rotor are in close proximity to maintain an accurate, closely spaced relation of said primary sealing means,

means urging said ring member to an axially retracted position to said rotor when the discharge pressure of the compressor falls below a given level,

said rotor, said ring member, and said inner frame forming an annular chamber opening into the flow path for pressurized air discharged from said compressor,

the radial area of said ring member exposed to said chamber being suificiently great that a force is provided for displacing said ring member into said close proximity with said rotor upon the pressure of air discharged from said compressor reaching a given value whereby the air bearing means may accurately control the spacing between said tooth and said radial sealing surface and thus maintain a highly effective seal at the juncture of the inner frame and rotor.

2. Sealing means as in claim 1 wherein,

the air bearing means is externally pressurized by way of passageways extending thereto through said ring, from said chamber.

3. Sealing means as in claim 2 wherein,

means are provided for venting the area between said air bearing and said primary sealing means to a substantially lower pressure.

4. Sealing means as in claim 1 wherein,

secondary sealing means are respectively formed on said ring member and rotor and comprise a cylindrical surface and a tooth projecting radially towards said surface, the axial extent of said cylindrical surface being suflicient to form a seal with said radially projecting tooth throughout the range of axial movement of the ring member.

5. Sealing means as in claim 1 wherein,

expansible chamber means are provided between said ring and said frame and passageway means connect said expansible chamber means with said annular chamber whereby said expansible chamber means is pressurized by air discharged from the compressor to provide the force which is effective to displace said ring to its position wherein the air bearing means accurately positions the primary sealing means.

6. Sealing means as in claim 2 wherein,

the ring member has a plurality of axially disposed pistons slidable therein and angularly spaced from one another around the ring member, the outer ends of said pistons engaging said frame member and the inner ends of said pistons defining expansible chambers,

passageway means connect said expansible chambers with said annular chamber, whereby pressurization of said annular chamber and the expansible chambers will provide the force for displacing said ring member into close proximity with said rotor to render the air bearing effective in maintaining the desired spacing of the primary sealing means, and further wherein,

passageway means extend from said expansible chambers to said air bearing to provide external pressurization thereof from said annular chamber.

7. Sealing means as in claim 6 wherein the inner ends of said pistons are hollow and said pistons have radial passageways extending therethrough to provide an air film which minimizes friction between the pistons and the ring member.

8. Sealing means as in claim 6 wherein,

said ring member has a flange extending radially outwardly therefrom into said annular chamber and terminates in a labyrinth tooth,

said rotor has a flange projecting into overlying relation with said radial flange to provide in cooperation with the tooth thereon a secondary sealing means,

the opposite sides of said radial flange having essentially the same area so that there is no resultant effective force in an axial direction resulting from pressurization of said annular chamber,

considered in longitudinal half section, the effective force vector of the air bearing on said ring member is essentially aligned with the axes of said pistons,

the ring member is configured so that the radially inwardly effective force vector on its outer surface defining aid annular chamber passes essentially through the center of gravity of the half section,

whereby the eflectiveness of the primary sealing means is maintained at a high level over a wide range of compressor discharge pressures.

9. Sealing means as in claim 8 wherein,

the means for urging said ring member to an axially retracted position comprise a plurality of compression springs which are compressed as the ring member is displaced towards said rotor,

the annular tooth of the primary sealing means is formed on said ring member,

the portion of the air bearing means formed on said ring member is surfaced with a layer of sacrifical material bonded thereto and,

the solid height of the compression springs serves as a limit to displacement of the ring member towards said rotor and prevents contact between the rotor and the substrate to which said sacrificial layer is said bonded in the event of a failure of said air bearing means.

10. Sealing means as in claim 1 wherein,

one of the cooperative portions of said ring member and rotor forming said air bearing means is surfaced with a layer of sacrificial material bonded thereto and means are provided for limiting displacement of the ring member towards said rotor and preventing contact therebetween with the substrate to which the sacrificial layer is bonded.

11. Sealing means as in claim 3 wherein,

the ring member is configurated such that there is no substantial turning moment about the center of gravity of its longitudinal half section resulting from air pressure force-s thereon.

12. Sealing means as in claim 3 wherein,

the ring member has a flange extending radially outwardly therefrom into said annular chamber and terminates in a labyrinth tooth,

said rotor has a flange projecting into overlying relation with said radial flange to provide in cooperation with the tooth thereon a secondary sealing means,

the tooth of the primary sealing means i formed on said ring member and projects from said flange and defines the base of said radial flange, the side of said flange towards said rotor having a lesser area than the opposite side whereby pressurization of said annular chamber results in an effective force which displaces said ring member toward said rotor to render the air bearing means effective to position the pimary sealing means,

the effective force vector on said radial flange and the eflective force vector of the air bearing means on said ring member producing a torque on the longitudinal half section of the ring member in one direction relative to its center of gravity,

ring member being configured such that the radial force vector thereon resulting from pressurization of said annular chamber produces a torque thereon relative to its center of gravity which balances the torque resulting from said other effective force vectors, whereby there is no resultant twisting moment on the longitudinal half section relative to its center of gravity.

References Cited UNITED STATES PATENTS EVERETI'E A. POWELL, 1a., Primary Examiner.

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