ANNULAR SEAL ASSEMBLY

Abstract: A seal assembly (28) is provided for sealing between a static sidewall (12), a rotating disk (22) disposed therein, and a concentric rim (32) disposed between the sidewall (12) and disk (22). The rim (32 ) is supportably secured to a semi-cylindrical arc valve (18) which extends axially from the rim (32 ).

Description: The present invention relates to a seal for an annular gap formed between multiple rotatable members. The use of annular seals to form a gas tight barrier between two concentric members is well known. Likewise, the use of such seals to provide a gas tight barrier about rotatable concentric members is also known. For more complex arrangements having multiple concentric rotatable members having axially extended appendages and subject to harsh local environments, certain adaptations may be required to provide an annular seal which is both effective and practicable for achieving the desired sealing effect without impeding the movement of the rotatable members. One such application, for example, is the exhaust nozzle of a gas turbine engine having a plurality of thrust vectoring flaps and surfaces for interacting with the high temperature engine exhaust gases. One particular configuration requiring an annular seal is a two dimensional thrust vectoring nozzle having a pair of spaced apart vertical sidewalls defining the lateral boundaries of the exhaust nozzle flow path and upper and lower movable flap assemblies for defining variable upper and lower gas path boundaries whereby nozzle outlet throat area and thrust direction may be changed by manipulation of such upper and lower flap assemblies. In particular, one 2-D nozzle arrangement includes a convergent flap extending transversely between first and second spaced apart sidewalls and secured at each span end thereof to a rotatable disk disposed within the corresponding sidewall. This particular nozzle arrangement also includes a part-cylindrical arc valve, rotatable about a common axis with the convergent flap and comprised of a part-cylindrical hood member extending between first and second annular rims disposed concentrically about the sidewall disks of the convergent flap. Rotation of the arc valve at the proper time admits a flow of exhaust gas into an alternate gas exhaust flow passage for thrust reversing and/or vectoring as desired. The annular region defined by the circumference of each corresponding convergent flap disk, annular rim, and surrounding sidewall must be sealed against the high temperature, elevated pressure exhaust gases flowing within the nozzle to avoid undesirable leakage of the exhaust gases into the surrounding flap structure which includes supporting bearings, linkages, and other relatively temperature sensitive structure. As exhaust gas temperatures in an afterburning mode may reach 4,000F (2,200C) or higher and have a pressure of 30-50psig (200-350kPa), the annular seal for this region must not only accommodate the independent movement of the convergent disk and the surrounding annular rim and part-cyclindrical arc valve, but also must achieve an effective and temperature resistant gas tight seal against the high temperature, high pressure exhaust gases contained within the exhaust nozzle. The state of the art referred to is disclosed in US-A-4 714 197, which has been filed before the priority date of this patent application but has been published after the priority date of this patent application. It is therefore the object of the present invention to provide a means for sealing an annular gap defined between two concentric, coaxially rotatable members and a surrounding static structure wherein one of the rotatable members includes an arc valve or the like extending therefrom. According to the present invention, to achieve this, there is provided a seal assembly for an annular region defined by a circular disk disposed in a static wall and having a concentric annular rim disposed therebetween, the disk and rim being independently rotatable about a common axis oriented substantially perpendicular to the static wall, the rim further including a part-cyclindrical arc valve extending parallel to the rotation axis and secured to a sector of the rim, characterized in that it comprises in combination a first annular seal for sealing between the static wall and the rim, a second annular seal disposed radially outward of the disk and sealingly engaged therewith, an annular web radially extending between the first annular seal and the second annular seal, the web including a part-cylindrical opening extending circumferentially around the portion of the annular region coincident with the arc valve, said first annular seal being sealingly secured to said annular web and said second annular seal having a portion sealingly secured to the arc valve over the arc valve sector of the rim, and the remaining portion of the second annular seal being sealingly secured to said annular web. The seal assembly in one embodiment of the present invention further provides protection of the individual sealing elements as well as nearby mechanical components such as bearings or the like from a high temperature environment occurring adjacent to the wall structure such as in an exhaust nozzle of a gas turbine engine. To accomplish this, the seal assembly provides one or more internal annular volumes for conducting a flow of cooling gas such as air circumferentially around the seal assembly. The air exits the seal assembly in the disclosed embodiment via controlled internal leakage paths (not shown) provided in the sealing elements and opening into the exhaust nozzle stream for enhancing the cooling of the assembly and adjacent structures. Undesirable gas leakage is further reduced and the aforementioned cooling enhanced by supplying the annular volumes with cooling air at an elevated pressure as compared to the gas adjacent the wall. For a seal assembly according to the present invention having a radially outward opening sealing element, such elevated pressure cooling air acts to energize the outward opening sealing element into a more positive sealing contact with the surrounding sidewall. A similar positive energizing effect is achieved at the sealing element disposed about the disk wherein the present invention provides an L-shaped seal which is urged against the disk by the high pressure cooling air admitted within the corresponding adjacent annular volume. The seal assembly thus provides a gas tight seal for a mechanical arrangement of two concentric, rotating members, one of which includes a part-cyclindrical arc valve projecting axially therefrom and a surrounding static structure. The seal is further adapted to integrate the functions of active seal cooling and energization of the individual seal elements by means of a flow of pressurized cooling gas supplied to the seal assembly. Both these and other features and advantages of the seal assembly will be apparent to those skilled in the art upon review of the following specification and the appended claims and drawing figures, wherein: Figure 1 shows a cut away isometric view of an exhaust nozzle having concentric, rotatable flap members disposed therein. Figure 2 shows a cross sectional view of the members and seal according to one embodiment of the present invention taken in the plane of the axis of rotation. Figure 3 shows a detailed cross sectional view of the seal according to one embodiment of the present invention. Referring now to the drawing Figures, and in particular to Figure 1 thereof, the general operating environment of an exemplary embodiment of the seal assembly according to the present invention will be described. Figure 1 shows a cut away isometric view of a portion of an exhaust nozzle 10 for a gas turbine engine. The exhaust nozzle 10 is a two dimensional nozzle, having a pair of vertical, spaced apart sidewalls, one of which 12 is shown in Figure 1, defining the lateral nozzle gas flow boundaries. The lower gas flow boundary is defined by a generally horizontal static structure 14 and one or more movable surfaces for directing the flow of exhaust gas 20 as desired for thrust vectoring, reversing, etc. A similar upper gas flow boundary may be provided and is not shown in Figure 1. In the exhaust nozzle 10 of Figure 1, the flow directing surfaces consist of a convergent flap 16 extending between a first sidewall disk 22 and a second sidewall disk (not shown) in the opposite sidewall (also not shown). The disks 22 and hence flap 16 are rotatable about a transverse axis 24 and may be positioned as desired to divert, block, or otherwise interact with the exhaust gas 20. The second gas directing surface comprises a part-cylindrical member, termed an arc valve 18, coaxially disposed about the sidewall disk 22 and extending axially between the first sidewall 12 and the second sidewall (not shown). The function of the arc valve 18 is to regulate the flow of exhaust gas 20 into an alternate exhaust flow passage 26 whence the flow may be directed forwardly for inducing a reversing thrust or laterally for inducing an augmented pitching moment in the nozzle and associated aircraft. The arc valve 18 and convergent flap 16 are independently positioned by a mechanical actuator system (not shown) responsive to the desired thrust and exhaust gas flow path. The exhaust gas 20 typically passes through the nozzle 10 at a relatively elevated temperature and pressure with respect to the surrounding environment. These temperatures, up to 4,000F (2,200C) or higher, and pressures 30-50psig (200-350kPa), require that the annulus formed between the first disk 22 and the surrounding sidewall be sealed against leakage of the exhaust gas 20 therethrough. The seal assembly 28 achieves a gas tight barrier in the annular region so defined and maintains said barrier as the flow directing surfaces rotate independently responsive to the nozzle control. Figure 2 is a sectional view taken through the common rotation axis 24 adjacent the sidewall 12. The disk 22 is shown disposed within the static sidewall 12 and rotatable about the common axis 24. Actuating force for rotating the disk 22 is delivered via the disk shaft 30 or by such other means well known in the art. Concentrically disposed about the disk 22 is an annular rim 32 which includes the part-cylindrical arc valve 18 secured to a sector thereof and extending axially with respect to the rotational axis 24. An annular supporting bearing 34 is disposed between the outer circumference of the disk 22 and the inner radius of the rim 32. The rim 32 is likewise rotated by mechanical means operable on the rim hub 36 or the like. As will be appreciated by those skilled in the art, the nozzle interior volume 38 through which the exhaust gas 20 passes must be separated from the bearings 34 and other nozzle structure by a gas tight barrier to prevent undesirable leakage of the hot exhaust gases into the otherwise unprotected bearings 34 and other structure. This is accomplished by the seal assembly 28 which includes a first sealing element 40 disposed between an axially extending annular portion 12' of the sidewall 12 and the annular rim 32 and having seal legs 40'. According to the disclosed embodiment of the seal assembly 28, the first sealing element 40 comprises a seal element opening radially outward with respect to the axis 24 and being compressed between the static structure 12, 12' and the rim 32. A second sealing element 44 includes an L-shaped sealing element having an annular, axially extending sealing leg 44' sealingly contacting the circumference of the disk 22, and a radially outwardly extending leg 44''. The undeflected radius of the sealing leg 44' is sized to achieve a spring bias against the outer circumference of the disk 22 when the second sealing element 44 is disposed therearound. The seal assembly 28 is completed by an annular web member 46 secured between the first sealing element 40 and the second L-shaped sealing element 44 over that portion of the rim circumference which is not secured to the arc valve 18. The first and second sealing elements 40, 44 linked by the impermeable web member 46 establish an unbroken, gas tight barrier between the static sidewall 12, 12' and the disk 22. The seal assembly 28 is retained against relative circumferential motion with respect to the rim 32 by a plurality of radial locating pins 42 inserted through the central portion of the first sealing element 40 and the web member 46 into the rim 32. The assembly 28 bridges over the rotatable rim 32 which, over this particular portion of its circumference, does not form a part of the gas tight barrier adjacent the nozzle interior 38. For that portion of the seal assembly 28 which is coincident with the sector of the rim 32 secured to the arc valve 18, the gas tight barrier is achieved by sealing between the rim 32 and static sidewall 12' with the first seal 40, and between the arc valve 18 and the disk 22 with the L-shaped seal 44. In this portion of the seal assembly 28, the axially extending arc valve 18 forms the gas tight bridge between the first sealing element 40 and the second sealing element 44. The L-shaped seal over the arc valve sector is secured to the arc valve by axially extending pins 48 passing through the radially extending second leg 44'' into the arc valve 18. The arc valve 18 is received within a corresponding opening in the web 46 as it extends into the nozzle interior 38. Figure 3 is a detailed cross section of the seal assembly 28 which more clearly shows an internal flow passage 50 providing fluid communication between a first annular volume 52 formed by the first sealing element 40 and the static structure 12' and a second annular volume 54 defined by the web 46, second L-shaped sealing element 44, the annular rim 32 and the bearing 34. During operation of the seal assembly 28 adjacent a high temperature environment such as a gas turbine engine exhaust stream, cooling air is admitted into the first annular volume 52 via one or more cooling flow passages 56 disposed in the static sidewall structure 12'. Cooling air flows into the first annular volume 52 moving circumferentially about the seal assembly 28 and entering the internal flow openings 50 which conduct the cooling air into the second annular volume 54 for cooling the web 46 and adjacent bearings 34. The cooling air may exit the second annular volume 54 by flow openings placed in the L-shaped sealing element leg 44', by leakage across the bearings 34, or by other means, such as transpiration openings in the seal or nozzle elements. The present arrangement, by defining one or more annular volumes for conducting a flow of cooling air therethrough, is well adapted to both resist the effects of the adjacent high temperature gases on the seal assembly structure as well as to protect adjacent, temperature sensitive structure such as the annular bearings 34 from overheating. Such cooling flow is likewise available to that portion of the seal assembly 28 coincident with the sector of the rim 32 secured to the arc valve 18 whereby cooling gas may flow circumferentially through the contiguous second annular volume 54 and outward through openings in the L-shaped seal 44 as discussed hereinabove. Cooling air supplied to the portion of the first annular volume 52 disposed adjacent this sector of the rim 32 may also pass out of the first volume 52 and into a radially outward portion 54' of the second annular volume, however it should be noted that the seal, valve, bearing, and other structures adjacent the arc valve 18 are already protected against the high temperature gases contained in the nozzle interior 38 by the presence of the internally cooled arc valve 18 adjacent thereto. The cooling openings 56, 50 and other flow directing structure are therefore distributed about the circumference of the seal assembly 28 to achieve the desired amount of local cooling and to thereby avoid having an unnecessarily large flow of cooling air. One further feature of the seal assembly 28 is the ability of the seal to be energized by the presence of an elevated pressure cooling gas within the annular volumes 52, 54. As will be appreciated by viewing the drawing Figures, especially Figures 2 and 3, both the first seal element 40 and the L-shaped second seal element 44 have their respective seal legs 40', 44' urged more firmly against their respective sealing surfaces by the presence of an elevated pressure gas within the adjacent corresponding annular volumes 52, 54. The presence of the elevated pressure cooling air not only serves to achieve this positive energization of the seal elements 40, 44, but also provides the necessary pressure head to insure that the cooling air will flow into the nozzle interior 38 if desired. It may be required, depending upon the particular construction of the annular bearing 34, to provide an annular sealing washer 57 or the like for preventing unwanted and excessive flow of cooling air through the bearing 34. Such sealing washer 57 is placed intermediate the annular bearing 34 and the second annular volume 54 and extends radially outward to span any gap which may exist between the inner and outer bearing races. It is thus apparent that the seal assembly 28 is well adapted to achieve the objects and advantages as set forth hereinafter.

Claims: Seal assembly (28) for an annular region defined by a circular disk (22) disposed in a static wall (12') and having a concentric annular rim (32) disposed therebetween, the disk (22) and rim (32) being independently rotatable about a common axis (24) oriented substantially perpendicular to the static wall (12'), the rim (32) further including a part-cyclindrical arc valve (18) extending parallel to the rotation axis (24) and secured to a sector of the rim (32), the seal assembly comprising in combination a first annular seal (40) for sealing between the static wall (12') and the rim (32), a second annular seal (44) disposed radially outward of the disk (22) and sealingly engaged therewith, and an annular web (46) radially extending between the first annular seal (40) and the second annular seal (44), the web (46) including a part-cyclindrical opening extending circumferentially around the portion of the annular region coincident with the arc valve (18), said first annular seal (40) being sealingly secured to said annular web (46) and said second annular seal (44) having a portion sealingly secured to the arc valve (18) over the arc valve sector of the rim (32), and the remaining portion of the second annular seal (44) being sealingly secured to said annular web (46). Seal assembly as recited in claim 1, characterized in that the first annular seal (40) comprises a radially outward facing sealing member being compressed between the rim (32) and the static wall (12'); that the second annular seal (44) is L-shaped, the L comprising an annular, axially extending sealing leg (44') contacting the circumference of the disk (22), and a radially outwardly extending second leg (44'') sealingly secured to the arc valve (18) and to the annular web (46); and that the web (46) radially spans the annular region. Seal assembly as recited in claim 1 or 2, characterized by further comprising means (56) for admitting a flow of cooling air into a first annular volume (52) defined by the static wall (12') and the first annular seal (40). Seal assembly as recited in claim 3, characterized by further comprising an annular bearing (34), disposed between the circular disk (22) and the annular rim (32) and axially spaced apart from the annular web (46); and means (50) for conducting at least a portion of the flow of cooling air from the first annular volume (52) into a second annular volume (54) defined by the circular disk (22), the annular rim (32), the annular web (46) and the annular bearing (34). Seal assembly as recited in claim 4, characterized by further comprising means, disposed in the axially extending leg (44') of the second annular seal (44) for conducting at least a portion of the flow of cooling air therethrough.

Inventors: STARKE, ROY RICHARD
Applicants: UNITED TECHNOLOGIES CORPORATION
Application year: 1988
Main classification: F16J15
IPC codes: F16J15, F02C7