Double wall combustor arrangement

Abstract

A double wall structure for a combustor of a gas turbine engine comprising an inner wall, an outer wall and a rail assembly, the inner wall formed by discrete tiles, wherein each tile is secured to the outer wall by the rail assembly.

Description

[0001] This invention relates to improvements to a combustor of a gas turbine engine and in particular to a heat resistant tile of a combustor wall.

[0002] In a double walled combustor of a gas turbine engine it is known to provide an inner wall which comprises tiles with pedestals extending toward the outer wall thereby improving heat removal by the cooling fluid flow between the walls. The tiles are secured to the outer wall by brazed studs, which are so arranged to allow the tiles to expand and contract with the thermal cycle of the engine. However, the studs have a tendency to “lock up” preventing the tile from undergoing thermal movements. This problem is particularly significant at the downstream edge of the tile, which distorts away from the outer wall. Where this occurs the cooling flow does not properly flow through the pedestals thus reducing the cooling efficiency. This results in the trailing edge undergoing some oxidation at elevated temperatures and there is then a tendency for spalling of the trailing edge to occur.

[0003] U.S. Pat. No. 4,555,901 discloses a frictionally slideable mounted combustor liner assembly employing a tongue and groove type arrangement and a retaining ring. The circumferentially segmented liner panels are assembled in axially rearward sequence. The liner and combustor structural wall are independent of the structural and thermal stresses of each other. However, a disadvantage of the assembly is that failure of an upstream tile would intrinsically lead to the downstream tile failing. A further disadvantage is that removal of an upstream tile may only be facilitated by removal of downstream tiles first.

[0004] It is the object of the present invention to provide an improved mounting assembly to allow tiles to expand and contract with the thermal cycles of the combustor and a stiffer tile.

[0005] According to the present invention a double wall structure for a combustor of a gas turbine engine comprises an inner wall, an outer wall and a rail assembly, the inner wall formed by discrete tiles, wherein each tile is secured to the outer wall by the rail assembly.

[0006] It is an advantage of the present invention to provide combustor tiles which, in use, are able to freely expand and contract during the thermal cycle of the gas turbine engine combustor. It is also an advantage of the present invention that the tiles are secured independently from one another, to the outer combustor wall, thus failure of one tile does not lead to failure of another. It is also an advantage of the present invention to provide a stiffer tile and in particular a stiffer tile downstream edge.

[0007] A further advantage of the present invention is that individual or circumferential rows of tiles may be assembled or disassembled independently without first placing or removing a downstream tile or row of tiles.

[0008] Preferably, the gas turbine engine comprises a main engine axis and the combustor is annular and generally coaxial with the main engine axis and the rail assembly is substantially annular and coaxial with respect to the main engine axis.

[0009] Preferably, the rail assembly comprises co-operating and generally L-shaped cross-section hook features, the inner wall and outer wall define a gap therebetween and the hook features extend generally into the gap, one hook feature attached to the tile and one attached to the outer wall so that, in use, the hook features co-operate to secure the tile to the outer wall.

[0010] Alternatively, the inner wall and outer wall define a gap therebetween and the rail assembly comprises a generally T-shaped hook feature and generally L-shaped hook features, the T-shaped hook feature attached to the tile and co-operating with the L-shaped hook features attached to the outer wall, the hook features extend into the gap and co-operate to secure the tile to the outer wall.

[0011] Preferably, wherein a generally L-shaped cross-section hook feature defines a loading gap, the loading gap provided to allow the tiles to be assembled to the outer wall of the combustor.

[0012] Preferably, the rail assembly comprises a locking key, the locking key so configured to, in operation, substantially fill the loading gap and thereby secure the tiles to the outer wall.

[0013] Preferably, the rail assembly comprises a locking plate.

[0014] Preferably, the tile comprises an edge and the rail assembly is located in close proximity to the edge of the tile to provide stiffening thereof.

[0015] Preferably the tile comprises an edge and the edge of the tile is profiled and the profiled edge of the tile comprises an end wall.

[0016] Alternatively, the profiled edge of the tile comprises a cooling passage.

[0017] Embodiments of the invention will now be described by way of example only, with reference to the accompanying diagrammatic drawings, in which:

[0018] FIG. 1 is a sectional side view of a gas turbine engine.

[0019] FIG. 2 shows a prior art sectional side view of part of a combustor of the engine shown in FIG. 1;

[0020] FIG. 3 shows a prior art sectional side view of a part of a radially outer wall structure of a combustor showing a wall element;

[0021] FIG. 4 is a sectional side view of part of a radially inner wall structure of a combustor showing a wall element of the present invention;

[0022] FIG. 5 is a sectional side view of a radially inner wall of a combustor showing a wall element of an embodiment of the present invention.

[0023] FIG. 6 is an isometric cut away view of tiles mounted on a radially outer wall of a combustor showing assembly details of the present invention.

[0024] FIG. 6A is a sectioned view of a locking plate.

[0025] FIG. 6B is an isometric view of a locking key.

[0026] FIG. 7 is a sectional side view of tiles mounted on a radially outer wall of a combustor showing a wall element of an embodiment of the present invention.

[0027] FIG. 8 is a sectional side view of tiles mounted on a radially outer wall of a combustor showing a wall element of an embodiment of the present invention.

[0028] With reference to FIG. 1, a ducted fan gas turbine engine generally indicated at 10 has a principal axis X-X. The engine 10 comprises, in axial flow series, an air intake 11, a propulsive fan 12, an intermediate pressure compressor 13, a high pressure compressor 14, combustion equipment 15, a high pressure turbine 16, an intermediate pressure turbine 17, a low pressure turbine 18 and an exhaust nozzle 19.

[0029] The gas turbine engine 10 works in the conventional manner so that air entering the intake 11 is accelerated by the fan to produce two air flows: a first air flow into the intermediate pressure compressor 13 and a second air flow which provides propulsive thrust. The intermediate pressure compressor 13 compresses the air flow directed into it before delivering that air to the high pressure compressor 14 where further compression takes place.

[0030] The compressed air exhausted from the high pressure compressor 14 is directed into the combustion equipment 15 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive, the high, intermediate and low pressure turbine 16, 17 and 18 before being exhausted through the nozzle 19 to provide additional propulsive thrust. The high, intermediate and low pressure turbines 16, 17 and 18 respectively drive the high and intermediate pressure compressors 14 and 13 and the fan 12 by suitable interconnecting shafts.

[0031] Referring to FIG. 2, the prior art combustor 15 is constituted by an annular combustion chamber 20 having radially inner and outer wall structures 21 and 22 respectively. The combustor 15 is secured to a wall 23 by a plurality of pins 24 (only one of which is shown). Fuel is directed into the chamber 20 through a number of fuel nozzles 25 located at an upstream end 26 of the chamber 20. The fuel nozzles 25 are circumferentially spaced around the engine 10 and serve to spray fuel into air derived from the high pressure compressor 14. The resultant fuel/air mixture is then combusted within the chamber 20.

[0032] The combustion process which takes place within the chamber 20 naturally generates a large amount of heat. It is necessary, therefore, to arrange that the inner and outer wall structures 21 and 22 are capable of withstanding the heat.

[0033] The radially inner and outer wall structures 21 and 22 each comprise an outer wall 27 and an inner wall 28. The inner wall 28 is made up of a plurality of discrete wall elements in the form of tiles 29A and 29B.

[0034] Each of the tiles 29A, 29B has circumferentially extending edges 30 and 31, and the tiles are positioned adjacent each other, such that the edges 30 and 31 of adjacent tiles 29A, 29B overlap each other. Alternatively, the edges 30, 31 of adjacent tiles can abut each other. Each tile 29A, 29B comprises a base portion 32 which is spaced from the outer wall 27 to define therebetween a space 44 (see FIG. 3) for the flow of cooling fluid in the form of cooling air as will be explained below. Heat removal features in the form of pedestals 45 (see FIG. 3) are provided on the base portion 32 and extend into the space 44 towards the outer wall 27.

[0035] Conventionally, and as shown in the prior art arrangement of FIG. 2, securing means are in the form of studs 35 comprising threaded plugs 34 and nuts 36. Each tile 28 has a plurality of threaded plugs 34 extending from the base portions 32 of the tiles 29A, 29B through apertures in the outer wall 27. Nuts 36 are screwed onto the plugs 34 to secure the tiles 29A, 29B to the outer wall 27.

[0036] Referring to FIG. 3, during engine operation, some of the air exhausted from the high pressure compressor 14 is permitted to flow over the exterior surfaces of the chamber 20. The air provides chamber 20 with cooling and some of the air is directed into the interior of the chamber 20 to assist in the combustion process. First and second rows of mixing ports 38, 39 are provided in the tiles 29B and are axially spaced from each other. The ports 38 correspond to apertures 40 in the outer wall 27, and the ports 39 correspond to apertures 41 in the outer wall 27.

[0037] Referring particularly to the tiles 29B, arrow A in FIG. 3 indicates air exiting via the open upstream edge 30 of the tile 29B and mixing with downstream air flowing from the upstream adjacent tile 29A, as indicated by arrow B The arrow C indicates the resultant flow of air. Angled effusion holes 46 are provided centrally of the tile 293 between the ports 38 and 39. Arrow D indicates a flow of air exiting from the space 44 through the holes 46. Also, a flow of downstream air exits from the open downstream edge 31 of the tile 29B after mixing with upstream air flowing from the adjacent tile 29A, as indicated by arrow E. Air flows indicated by arrows C and E provide a film of cooling air over the interior surface of the tiles 29A and 29B thereby preventing overheating caused by the combustion of gases in the chamber 20.

[0038] During a normal operation cycle of the engine 10 the combustor 20 will be subject to varying amounts of combustion heat. This causes the tiles 29A and 29B to thermally expand relative to the outer wall 27. These thermal expansions are usually accommodated by the studs 35 which allow the tiles 29A and 29B to slide. During the working life of this combustor wall arrangement, although relatively rare, the studs 35 have a tendency to lock-up and prevent the tiles from thermally expanding. This problem is particularly significant at the downstream edge 31 of the tiles 29A and 29B, which then distorts away from the outer wall 27. Where this occurs, the cooling flow, through the space 44, does not properly flow through and around the pedestals which in turn reduce the cooling efficiency and effectiveness of the tiles. This results in the trailing edge 31 undergoing oxidation at elevated temperatures and there is then a tendency for spalling of the trailing edge 31 to occur. This may ultimately lead to a complete failure of the combustor wall 20 and may lead to the combustor flame breaking though the wall 20.

[0039] FIG. 4 is a sectional side view of part of a wall structure of a combustor showing a wall element of the present invention and is a preferred embodiment. The studs 35 of the prior art have been replaced with rail assemblies 48, 54 to secure the tiles 29A, 29B to the outer wall 27. The rail assemblies 48, 54 comprise co-operating hook features 50, 52 and 56, 58 respectively. Hooks 50 and 56 are attached to tile 29A, and hooks 52 and 58 are attached to outer wall 27. Each hook feature 50, 52 and 56, 58 is cast integrally with the tiles 29A, 29B and outer wall 27 or alternatively the hooks feature 50, 52 and 56, 58 may be attached by brazing or welding.

[0040] Each hook 50, 52, 56, 58 is of substantially L-shaped cross-section and comprises a flange 60, substantially oriented in the direction Y-Y, and a web 62 extending substantially perpendicular to the Y-Y axis from the tile 29A, 29B or outer wall 27, the flange 60 being disposed to the distal end of the web 62 from the tiles 29A, 29B or outer wall 27 accordingly. The web 62 defines a plurality of holes 66 through which cooling air passes.

[0041] As shown in FIG. 4, the rail assemblies 48, 54 are oriented so as to operate in co-operative association with one another, hook 50 opposing relative upstream displacement and hook 56 opposing relative downstream displacement of the tile 29A, 29B. Alternatively, the orientation of the hooks 48, 54 may be reversed.

[0042] It is an advantage to use rail assemblies 48, 54, as shown in FIG. 4, as thermal expansions in the Y-Y axis direction may be easily accommodated by a gap 64 between the distal end of the flange 60 and the web 62 of the cooperating hook. Thermal expansions and contractions in the plane of the tile 29A, 29B and perpendicular to the axis YY may also be accommodated by the rail arrangement 48, 54 as sliding may take place freely in that direction.

[0043] It is a further advantage of the rail arrangement 48, 54 that the web 62 and flange 60 arrangement contributes to an increase in the stiffness of the tile 29A, 29B. To this effect the rail arrangement 54 is positioned near to the edge 30 of the tile 29A, 29B, thereby further reducing the Likelihood of the edge 30 distorting out of its original plane as a consequence of thermal expansion.

[0044] Furthermore, FIG. 4 illustrates profiling of the tile edge 30 in order to further increase the stiffness locally of the tile 29A, 29B edge 30. The profiling may take many forms, of which two are shown in FIGS. 7 and 8 and are discussed in more detail below.

[0045] Referring now to FIG. 5, which shows a second rail arrangement 69. The second rail arrangement 69 is configured in a general and inverted T-shape with the flange 68 extending either side of the web 70. The flange 68 and web 70 are in operative association with hooks 72 and 74. Each tile 29A, 29B comprises at least one second rail arrangement 69. The number of second rail assemblies 69 is dictated by the size of each tiles 29A, 29B, the thermal and structural stresses imposed on the tiles 29A, 29B and stiffness requirements thereof.

[0046] The T-shaped second rail arrangement 69 provides stiffening to the tiles 29A, 29B in the same way as the substantially L-shaped cross-section hooks described hereinbefore and with reference to FIG. 4. Similarly, a gap 76 is designed to accommodate thermal expansions thereby preventing deformation of the edges 30, 31 of the tiles 29A, 29B.

[0047] Although FIG. 5 shows the generally T-shaped second rail assembly 69 disposed to the tile 29A, it may equally effectively be disposed to the outer wall 27 and the cooperating L-shaped cross-section hook features 72, 74 may be disposed to the tile 29A.

[0048] Anti-frettage coating, as known in the art, may be provided to any contacting surfaces of the rail assemblies 48, 54 and second rail assembly 69. The anti-frettage coatings also may be used to modify, and beneficially so, the co-efficient of friction between contacting surfaces.

[0049] FIG. 6 is an isometric cut away view of tiles 29A, 29B mounted on the combustor wall 27 and shows details of the assembly of the tiles 29A, 29B. The tiles 29A are assembled to the combustor wall 27 through a loading gap 78 in the substantially circumferential rails 48, 54 mounted on the outer wall 27. The tiles 29A are circumferentially disposed around the combustor outer wall 27 and are abutted to one another.

[0050] There is a tendency for the tiles 29A to displace circumferentially during normal engine 10 operation and a locking plate 80 is used to prevent this circumferential movement.

[0051] FIG. 6A shows the locking plate 80 in more detail. The locking plate 80 is attached to the combustor outer wall 27 by conventional means and in this case is attached by a threaded extension 88 which co-operates with a washer 84 and nut 86. The plate 82 blocks the circumferential path of the co-operating hook feature 52 of the tile 29A. Further locking plates 80 may be located around the rail assemblies 48, 54 at suitable locations.

[0052] FIG. 6B shows a locking key 90 which is used to retain the tiles 29A where there is a discontinuity in the hook feature 50 of the combustor outer wall 27. The locking key 90 is secured to the outer wall 27 by conventional securing means including the means as described above for the locking plate 80. It is preferable to arrange the tiles 29A such that approximately half their circumferential length extends into the loading gap 78. The loading gap 78 may then be partially or entirely filled by the locking key 90. The locking key 90 may comprise more than one securing means.

[0053] A further advantage of the present invention is that where two rail assemblies 48, 54 are utilised to secure a Circumferential row of tiles 29A only one of the rail assemblies 48 is required to have a loading gap 78. Thus the co-operating hook feature 56 of the rail assembly 54 (FIG. 4) may be completely annular and therefore carry hoop stresses, present in the combustor outer wall 27 of both or one of the radially inner wall 21 and radially outer wall 22, derived from the high pressure air egressing from the high pressure compressor 14 and combustion heat.

[0054] This enables the outer wall 27 to be constructed of thinner material or permitted to carry a greater load.

[0055] It should be noted that the term rail assembly 48, 54 comprises the co-operating L-shaped hook features 50, 52, and 56, 58 and may also comprise the loading gap 78, the locking key 90 and the locking plate 80.

[0056] Referring to FIG. 7 which is a sectional side view of tile 29A mounted on a radially outer wall 27 of a combustor 15 showing a wall element of an embodiment of the present invention. The tile edge 30 comprises a profiled configuration having a cooling passage 92 therethrough.

[0057] The cooling passage 92 increases the cooling and stiffness of the edge 30 of the tiles 29A thereby rendering the edge 30 less susceptible to thermal distortions.

[0058] FIG. 8 is a sectional side view of tiles 29A mounted on a radially outer wall 27 of a combustor 15 showing a wall element of an embodiment of the present invention.

[0059] This embodiment comprises a thickened end wall 94 which provides increased stiffness to the edge 30 of the tile 29A.

[0060] The various embodiments of the geometric configuration of the profiled tile edge 30 may easily be made to increase the stiffness thereof, but are intended to be within the scope of the present invention.

[0061] A further advantage of the present invention and one that is partially shown in FIG. 3 is that the tiles 29A, 29B are independently secured to the outer wall 27. This has the advantage that failure of one tile 29A, 29B does not lead to failure of another adjacent tile.

[0062] The rail assembly 48, 54, 69 also permits individual circumferential rows of tiles 29A, 29B to be fitted and disassembled to the combustor outer wall 27 without disturbing upstream or downstream circumferential rows of tiles 29A, 29B. The configuration of the rail assembly 48, 54, 69 and the circumferential rows of tiles 29A, 29B means that failure of one tile 29A, 29B does not lead to failure or disturbance of an upstream or downstream tile 29A, 29B.

[0063] Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1. A double wall structure for a combustor of a gas turbine engine comprising an inner wall, an outer wall and a rail assembly, the inner wall formed by discrete tiles, wherein each tile is secured to the outer wall by the rail assembly.

2. A double wall structure for a combustor of a gas turbine engine as claimed in claim 1 wherein the gas turbine engine comprises a main engine axis and the combustor is annular and generally coaxial with the main engine axis and the rail assembly is substantially annular and coaxial with respect to the main engine axis.

3. A double wall structure for a combustor of a gas turbine engine as claimed in claim 1 wherein the rail assembly comprises co-operating and generally L-shaped cross-section hook features, the inner wall and outer wall define a gap therebetween and the hook features extend generally into the gap, one hook feature attached to the tile and one attached to the outer wall so that, in use, the hook features co-operate to secure the tile to the outer wall.

4. A double wall structure for a combustor of a gas turbine engine as claimed in claim 1 wherein the inner wall and outer wall define a gap therebetween and the rail assembly comprises a generally T-shaped hook feature and generally L-shaped hook features, the T-shaped hook feature attached to the tile and co-operating with the L-shaped hook features attached to the outer wall, the hook features extend into the gap and co-operate to secure the tile to the outer wall.

5. A double wall structure for a combustor of a gas turbine engine as claimed in claim 3 wherein the generally L-shaped cross-section hook feature defines a loading gap, the loading gap provided to allow the tiles to be assembled to the outer wall of the combustor.

6. A double wall structure for a combustor of a gas turbine engine as claimed in claim 5 wherein the rail assembly comprises a locking key, the locking key so configured to, in operation, substantially fill the loading gap and thereby secure the tiles to the outer wall.

7. A double wall structure for a combustor of a gas turbine engine as claimed in claim 1 wherein the rail assembly comprises a locking plate.

8. A double wall structure for a combustor of a gas turbine engine as claimed in claim 1 wherein the tile comprises an edge and the rail assembly is located in close proximity to the edge of the tile to provide stiffening thereof.

9. A double wall structure for a combustor of a gas turbine engine as claimed in claim 1 wherein the tile comprises an edge and the edge of the tile is profiled.

10. A double wall structure for a combustor of a gas turbine engine as claimed in claim 9 wherein the profiled edge of the tile comprises an end wall.

11. A double wall structure for a combustor of a gas turbine engine as claimed in claim 9 wherein the profiled edge of the tile comprises a cooling passage.