Patent Publication Number: US-2017356653-A1

Title: Combustion chamber

Description:
The present disclosure relates to a combustion chamber and in particular to a gas turbine engine combustion chamber. 
     One known type of combustion chamber comprises one or more walls each of which comprises a double, or dual, wall structure. A dual wall structure comprises an annular outer wall and an annular inner wall spaced radially from the annular outer wall by rails to define a chamber. The annular outer wall has a plurality of impingement apertures to supply coolant into the chamber and the annular inner wall has a plurality of effusion apertures to supply coolant from the chamber over an inner surface of the annular inner wall to provide a film of coolant on the inner surface of the annular inner wall. 
     The annular inner wall comprises a plurality of rows of circumferentially arranged tiles. These rows of tiles produce a discontinuity, or a number of discontinuities, in the inner surface of the annular inner wall that has a detrimental effect on the film of coolant on the inner surface of the annular inner wall. The downstream ends of the tiles have lips which extend axially towards but are spaced from the upstream ends of the adjacent row of tiles and the annular outer wall has one or more rows of apertures to direct coolant onto the lips and then to assist in re-forming a film of coolant over the inner surface of the upstream ends of the adjacent row of tiles. 
     The row or rows of apertures in the annular outer wall which direct coolant onto the lips of the tiles reduce the strength of the annular outer wall and it is possible for cracks to initiate and propagate circumferentially around the annular outer wall. The problem is exacerbated by the rails at the downstream ends of the tiles which are positioned close to the row of rows of apertures in the annular outer wall because the rails conduct heat from the tiles to the annular outer wall. At the points where the fasteners, studs, used to secure the tiles to the annular outer wall are close to the rails the clamping loads due to the fasteners produces perfect conduction of heat from the tiles through the rails to the annular outer wall and hence increasing the stress in the annular outer wall adjacent the row or rows of apertures in the annular outer wall which direct coolant onto the lips of the tiles. The annular outer wall may have a bend and the bend may be subject to significant thermal and vibrational stresses. If the bend is positioned close to the row or rows of apertures in the annular outer wall then this may further increase the stress in the annular outer wall adjacent the row or rows of apertures in the annular outer wall which direct coolant onto the lips of the tiles. 
     Hence, this may lead to a reduction in the working life of the annular outer wall of the combustion chamber. 
     Accordingly the present disclosure seeks to provide a combustion chamber which reduces, or overcomes, the above mentioned problem. 
     According to a first aspect of the present disclosure there is provided a combustion chamber arrangement comprising an annular outer wall and an annular inner wall spaced from the annular outer wall, the annular inner wall comprising at least one row of tiles, each row of tiles comprising a plurality of circumferentially arranged tiles, the downstream end of each tile in the at least one row of tiles having a rail extending from the downstream end of the tile towards and sealing with an inner surface of the annular outer wall and a lip extending in a downstream direction from the downstream end of the tile, the annular outer wall having at least one row of apertures to direct coolant onto the outer surfaces of the lips at the downstream ends of the tiles in the at least one row of tiles, each tile in the at least one row of tiles having at least one fastener positioned upstream of the rail, the at least one fastener of each tile in the at least one row of tiles extending from the tile and through a corresponding mounting aperture in the annular outer wall to secure the tile to the annular outer wall, the rail of at least one tile defining at least one slot with the inner surface of the annular outer wall, the at least one slot of the at least one tile being arranged in a region downstream of the at least one fastener and none of the apertures in the at least one row of apertures in the annular outer wall being arranged in the region downstream of the at least one fastener of the at least one tile. 
     The rail of the at least one tile may define a plurality of slots with the inner surface of the annular outer wall and the plurality of slots of the at least one tile being arranged in the region downstream of the at least one fastener. 
     The rail of each tile may define at least one slot with the inner surface of the annular outer wall, the at least one slot of each tile being arranged in a region downstream of the at least one fastener and none of the apertures in the at least one row of apertures being arranged in the region downstream of the at least one fastener of each tile. 
     The rail of each tile may define a plurality of slots with the inner surface of the annular outer wall and the plurality of slots of each tile being arranged in the region downstream of the at least one fastener. 
     Each tile in the at least one row of tiles may have a plurality of fasteners positioned upstream of the rail, each fastener extending from the tile and through a corresponding mounting aperture in the annular outer wall to secure the tile to the annular outer wall. 
     The rail of each tile in the at least one row of tiles may define a plurality of slots with the inner surface of the annular outer wall, at least one slot of each tile being arranged in a region downstream of each fastener and none of the apertures in the at least one row of apertures in the annular outer wall being arranged in the region downstream of each fastener of each tile. 
     A plurality of slots of each tile may be arranged in a region downstream of each fastener. 
     The annular inner wall may comprise an upstream row of tiles and a downstream row of tiles, the downstream end of each tile in the upstream row of tiles having a lip extending in a downstream direction towards but spaced from the upstream ends of the tiles in the downstream row of tiles, the annular outer wall having at least one row of apertures to direct coolant onto the outer surfaces of the lips at the downstream ends of the tiles in the upstream row of tiles, each tile in the upstream row of tiles having at least one fastener positioned upstream of the rail, the at least one fastener of each tile in the upstream row of tiles extending from the tile and through a corresponding mounting aperture in the annular outer wall to secure the tile to the annular outer wall, the rail of at least one tile defining at least one slot with the inner surface of the annular outer wall, the at least one slot of the at least one tile being arranged in a region downstream of the at least one fastener and none of the apertures in the at least one row of apertures in the annular outer wall being arranged in the region downstream of the at least one fastener of the at least one tile. 
     Each tile in the upstream row of tiles may have a plurality of fasteners positioned upstream of the rail, each fastener extending from the tile and through a corresponding mounting aperture in the annular outer wall to secure the tile to the annular outer wall. 
     The annular outer wall may have a bend, the rail at the downstream end of each tile in the upstream row of tiles being arranged upstream of the bend in the annular outer wall. 
     The at least one row of apertures in the annular outer wall may be arranged upstream of the bend in the annular outer wall and downstream of the rail at the downstream end of each tile in the upstream row of tiles. 
     The at least one row of apertures in the annular outer wall may be arranged downstream of the bend in the annular outer wall and downstream of the rail at the downstream end of each tile in the upstream row of tiles. 
     The upstream end of each tile in the downstream row of tiles may have a rail extending from the upstream end of the tile towards and sealing with an inner surface of the annular outer wall. 
     The rail at the upstream end of each tile in the downstream row of tiles may extend in an upstream direction. 
     The rail at the upstream end of each tile in the downstream row of tiles may be arranged downstream of the bend in the annular outer wall. 
     The annular outer wall may have a bend, the rail at the downstream end of each tile in the at least one row of tiles being arranged upstream of the bend in the annular outer wall. 
     The at least one row of apertures in the annular outer wall may be arranged upstream of the bend in the annular outer wall and downstream of the rail at the downstream end of each tile in the at least one row of tiles. 
     The at least one slot in the rail of the at least one tile may be arranged perpendicular to the surface of the rail or at angle to the surface of the rail. 
     A plurality of slots may be arranged in a region downstream of the at least one fastener, the region downstream of the at least one fastener having a circumferential dimension of up to four times the diameter of the at least one fastener. 
     At least one slot may be arranged in a region downstream of the at least one fastener, the region downstream of the at least one fastener having a circumferential dimension of up to four times the diameter of the at least one fastener. 
     The annular outer wall may not have any apertures arranged in a region downstream of the at least one fastener, the region downstream of the at least one fastener having a circumferential dimension of up to four times the diameter of the at least one fastener. The annular outer wall may be imperforate in the region downstream of the at least one fastener, the region downstream of the at least one fastener having a circumferential dimension of up to four times the diameter of the at least one fastener. 
     The annular outer wall may not have any apertures arranged in a region downstream of the at least one fastener, the region downstream of the at least one fastener having a circumferential dimension of up to twice the diameter of the at least one fastener. The annular outer wall may be imperforate in the region downstream of the at least one fastener, the region downstream of the at least one fastener having a circumferential dimension of up to twice the diameter of the at least one fastener. 
     The combustion chamber may be an annular combustion chamber, the annular combustion chamber comprising a radially inner annular wall structure, a radially outer annular wall structure and an upstream end wall structure, the radially outer annular wall structure comprising the annular inner wall and the annular outer wall and the annular inner wall is spaced radially inwardly from the annular outer wall. 
     The combustion chamber may be an annular combustion chamber, the annular combustion chamber comprising a radially inner annular wall structure, a radially outer annular wall structure and an upstream end wall structure, the radially inner annular wall structure comprising the annular inner wall and the annular outer wall and the annular inner wall is spaced radially outwardly from the annular outer wall. 
     The combustion chamber may be a tubular combustion chamber and the annular inner wall is spaced radially inwardly from the annular outer wall. 
     The combustion chamber may be a gas turbine engine combustion chamber. 
     The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects of the invention may be applied mutatis mutandis to any other aspect of the invention. 
    
    
     
       Embodiments of the invention will now be described by way of example only, with reference to the Figures, in which: 
         FIG. 1  is a sectional side view of a turbofan gas turbine engine having a combustion chamber arrangement according to the present disclosure. 
         FIG. 2  is an enlarged cross-sectional view of a combustion chamber arrangement according to the present disclosure. 
         FIG. 3  is a further enlarged cross-sectional view of a portion of a combustion chamber arrangement according to the present disclosure. 
         FIG. 4  is an enlarged perspective view of the portion of the combustion chamber arrangement shown in  FIG. 3 . 
         FIG. 5  is a further enlarged perspective view of a portion of the downstream end of a tile used in a combustion chamber arrangement according to the present disclosure. 
         FIG. 6  is a plan view in the direction of arrow A in  FIG. 3  showing a portion of the downstream end of a tile and the surrounding outer wall used in a combustion chamber arrangement according to the present disclosure. 
     
    
    
     With reference to  FIG. 1 , a turbofan gas turbine engine is generally indicated at  10 , having a principal and rotational axis 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 . A nacelle  21  generally surrounds the engine  10  and defines the intake  11 , a bypass duct  22  and a bypass exhaust nozzle  23 . 
     The gas turbine engine  10  works in the conventional manner so that air entering the intake  11  is compressed by the fan  12  to produce two air flows: a first air flow A into the intermediate pressure compressor  13  and a second air flow B which passes through a bypass duct  22  to provide 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. 
     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 turbines  16 ,  17 ,  18  before being exhausted through the nozzle  19  to provide additional propulsive thrust. The high  16 , intermediate  17  and low  18  pressure turbines drive respectively the high pressure compressor  14 , intermediate pressure compressor  13  and fan  12 , each by suitable interconnecting shaft  24 ,  25  and  26  respectively. 
     Combustion equipment  15  according to the present disclosure, as shown more clearly in  FIGS. 2 to 6 , comprises an annular combustion chamber arrangement and comprises a radially inner annular wall structure  40 , a radially outer annular wall structure  42  and an upstream end wall structure  44 . The radially inner annular wall structure  40  comprises a first annular wall  46  and a second annular wall  48 . The radially outer annular wall structure  42  comprises a third annular wall  50  and a fourth annular wall  52 . The second annular wall  48  is spaced radially from and is arranged radially around the first annular wall  46  and the first annular wall  46  supports the second annular wall  48 . The fourth annular wall  52  is spaced radially from and is arranged radially within the third annular wall  50  and the third annular wall  50  supports the fourth annular wall  52 . The upstream end of the first annular wall  46  is secured to the upstream end wall structure  44  and the upstream end of the third annular wall  50  is secured to the upstream end wall structure  44 . The upstream end wall structure  44  has a plurality of circumferentially spaced apertures  54  and each aperture  54  has a respective one of a plurality of fuel injectors  56  located therein. The fuel injectors  56  are arranged to supply fuel into the annular combustion chamber  15  during operation of the gas turbine engine  10 . 
     The first annular wall  46  has a plurality of mounting apertures  58  extending there-though and the second annular wall  48  has a plurality of fasteners  60  extending radially there-from. Each fastener  60  on the second annular wall  48  extends radially through a corresponding mounting aperture  58  in the first annular wall  46 . A cooperating fastener  62  locates on each of the fasteners  60  extending through the mounting apertures  58  in the first annular wall  46 . A washer  64  is positioned between each fastener  60  on the second annular wall  48  and the cooperating fastener  62 . Each washer  64  has a first surface  66  abutting an outer surface of the first annular wall  46  and a second surface  68  abutting a surface of the cooperating fastener  62 . The second annular wall  48  comprises a plurality of segments, or tiles,  48 A,  48 B and  48 C and the segments, or tiles,  48 A,  48 B and  48 C are arranged circumferentially and axially around the first annular wall  46 . The axially extending edges of adjacent segments, or tiles,  48 A,  48 B and/or  48 C may abut each other or may overlap each other and the circumferentially extending ends of adjacent segments, or tiles,  48 A,  48 B and  48 C are spaced from each other. 
     Similarly, the third annular wall  50  has a plurality of mounting apertures  70  extending there-though and the fourth annular wall  52  has a plurality of fasteners  72  extending radially there-from. Each fastener  72  on the fourth annular wall  52  extends radially through a corresponding mounting aperture  70  in the third annular wall  50 . A cooperating fastener  74  locates on each of the fasteners  72  extending through the mounting apertures  70  in the third annular wall  50 . A washer  76  is positioned between each fastener  72  on the fourth annular wall  52  and the cooperating fastener  74 . Each washer  76  has a first surface  78  abutting an outer surface of the third annular wall  50  and a second surface  80  abutting a surface of the cooperating fastener  74 . The fourth annular wall  52  comprises a plurality of segments, or tiles,  52 A,  52 B and  52 C and the segments, or tiles,  52 A,  52 B and  52 C are arranged circumferentially and axially adjacent to each other to define the fourth annular wall  52 . The axially extending edges of adjacent segments, or tiles,  52 A,  52 B and/or  52 C may abut each other or may overlap each other and the circumferentially extending ends of adjacent segments, or tiles,  52 A,  52 B and  52 C are spaced from each other. 
     The fasteners  60  and  72  on the second and fourth annular walls  48  and  52  are threaded studs which are cast integrally with the segments, or tiles,  48 A,  48 B,  48 C,  52 A  52 B and  52 C or may be secured to the segments, or tiles,  48 A,  48 B,  48 C,  52 A,  52 B and  52 C by welding, brazing etc. Alternatively, the fasteners, e.g. threaded studs are formed by additive layer manufacturing integrally with the segments, or tiles  48 A,  48 B,  48 C,  52 A  52 B and  52 C. The cooperating fasteners  62  and  74  are nuts. 
     The first and third annular walls  46  and  50  form outer walls of the annular combustion chamber  15  and the second and fourth annular walls  48  and  52  form inner walls of the annular combustion chamber  15 . The second annular wall  48  comprises at least one row of circumferentially arranged tiles and in this example there are three rows  48 A,  48 B and  48 C of circumferentially arranged tiles and the tiles  48 A form an axially upstream row of circumferentially arranged tiles, the tiles  48 B form an axially intermediate row of circumferentially arranged tiles and the tiles  48 C form an axially downstream row of circumferentially arranged tiles. Similarly, the fourth annular wall  52  comprises at least one row of circumferentially arranged tiles and in this example there are three rows  52 A,  52 B and  52 C of circumferentially arranged tiles and the tiles  52 A form an axially upstream row of circumferentially arranged tiles, the tiles  52 B form an axially intermediate row of circumferentially arranged tiles and the tiles  52 C form an axially downstream row of circumferentially arranged tiles. The tiles  52 A are an upstream row of tiles with respect to the tiles  52 B and similarly the tiles  52 B are a downstream row of tiles with respect to the tiles  52 A. The tiles  52 B are an upstream row of tiles with respect to the tiles  52 C and similarly the tiles  52 C are a downstream row of tiles with respect to the tiles  52 B. The second annular wall  48  and/or the fourth annular wall  52  may comprise any suitable number of rows of tiles. 
     The combustion chamber in this arrangement also comprises a plurality of dilution ports  71  in the radially inner annular wall structure  40  and a plurality of dilution ports  73  in the radially outer annular wall structure  42 . The dilution ports  73  in the radially outer annular wall structure  42  comprise a plurality of aligned apertures  79  and  81  in the annular outer wall  50  and the tiles  52 B of the annular inner wall  52 . The dilution ports  71  in the radially inner annular wall structure  40  comprise a plurality of aligned apertures  75  and  77  in the annular outer wall  46  and the tiles  48 B of the annular inner wall  48 . The dilution ports  71  and  73  supply dilution air H into the combustion chamber to control emissions. 
     The annular outer wall  50  has a plurality of impingement cooling apertures  67  extending there-through to direct coolant onto the outer surface of the tiles  52 A,  52 B and  52 C and the tiles  52 A,  52 B and  52 C have effusion cooling apertures  69  extending there-through to provide a film of coolant onto the inner surfaces of the tiles  52 A,  52 B and  52 C respectively. The impingement cooling apertures  67  are generally arranged perpendicularly to the surfaces of the annular outer wall  50  and the outer surfaces of the tiles  52 A,  52 B and  52 C respectively. However, the impingement cooling apertures  67  may be arranged at other suitable angles to the surfaces of the annular outer wall  50  and the outer surfaces of the tiles  52 A,  52 B and  52 C respectively. The effusion cooling apertures  69  are generally arranged at an angle, for example 30°, to the inner surfaces of the tiles  52 A,  52 B and  52 C but other suitable angles may be used. Some effusion cooling apertures  69  may be arranged perpendicularly to the inner surfaces of the tiles  52 A,  52 B and  52 C and some of the effusion cooling apertures  69  may be arranged at an angle, for example 30°, to the inner surfaces of the tiles  52 A,  52 B and  52 C. 
     The downstream end of each tile  52 A in the upstream row of tiles  52 A has a rail  53  which extends from the outer surface of the tile  52 A at the downstream end of the tile  52 A towards and seals with an inner surface of the annular outer wall  50  and a lip  63  extends in a downstream direction towards but is spaced from the upstream ends of the tiles  52 B in the downstream row of tiles  52 B. The lip  63  extends from the junction between the rail  53  at the downstream end of the tile  52 A and the main body of the tile  52 A. The inner surface of the lip  63  forms a continuation of the inner surface of the main body of the tile  52 A. The annular outer wall  50  has at least one row of apertures  57  to direct coolant F onto the outer surfaces of the lips  63  at the downstream ends of the tiles  52 A in the upstream row of tiles  52 A. The at least one row of apertures  57  is arranged to supply the coolant F to a chamber, e.g. an annular chamber,  65  defined between the inner surface of the annular outer wall  50 , the rails  53  at the downstream ends of the tiles  52 A and the lips  63  at the downstream ends of the tiles  52 A in the upstream row of tiles  52 A. The upstream end of each tile  52 A in the upstream row of tiles  52 A has a rail  51  which extends from the upstream end of the tile  52 A towards and seals with the inner surface of the annular outer wall  50 . Each tile  52 A in the upstream row of tiles  52 A also has two rails  55 , each rail  55  extends axially along a respective one of the circumferentially spaced edges and each rail  55  also extend towards and seal against the inner surface of the annular outer wall  50 . Thus, each tile  52 A has rails  51 ,  53  and  55  which extend around the periphery of the tile  52 A to form a closed chamber between each tile  52 A and the annular outer wall  50 . 
     The downstream end of each tile  52 B in the intermediate row of tiles  52 B has a rail  53  which extends from the outer surface of the tile  52 B at the downstream end of the tile  52 B towards and seals with the inner surface of the annular outer wall  50  and a lip  63  extends in a downstream direction towards but is spaced from the upstream ends of the tiles  52 C in the downstream row of tiles  52 C. The lip  63  extends from the junction between the rail  53  at the downstream end of the tile  52 B and the main body of the tile  52 B. The inner surface of the lip  63  forms a continuation of the inner surface of the main body of the tile  52 B. The annular outer wall  50  has at least one row of apertures  57  to direct coolant onto the outer surfaces of the lips  63  at the downstream ends of the tiles  52 B in the intermediate row of tiles  52 B. The at least one row of apertures  57  is arranged to supply the coolant to a chamber, e.g. an annular chamber,  65  defined between the inner surface of the annular outer wall  50 , the rails  53  at the downstream ends of the tiles  52 B and the lips  63  at the downstream ends of the tiles  52 B in the intermediate row of tiles  52 B. The upstream end of each tile  52 B in the intermediate row of tiles  52 B has a rail  51  which extends from the upstream end of the tile  52 B towards and seals with the inner surface of the annular outer wall  50 . The rail  51  at the upstream end of each tile  52 B in the intermediate row of tiles  52 B in this particular example also extends in an upstream direction. Each tile  52 B in the intermediate row of tiles  52 B also has two rails  55 , each rail  55  extends axially along a respective one of the circumferentially spaced edges and each rail  55  also extend towards and seal against the inner surface of the annular outer wall  50 . Thus, each tile  52 B has rails  51 ,  53  and  55  which extend around the periphery of the tile  52 B to form a closed chamber between each tile  52 B and the annular outer wall  50 . 
     The downstream end of each tile  52 C in the downstream row of tiles  52 C has a rail (not shown) which extends from the outer surface of the tile  52 C at the downstream end of the tile  52 C towards and seals with the inner surface of the annular outer wall  50 . The upstream end of each tile  52 C in the downstream row of tiles  52 C has a rail  51  which extends from the upstream end of the tile  52 C towards and seals with the inner surface of the annular outer wall  50 . The rail  51  at the upstream end of each tile  52 C in the downstream row of tiles  52 C in this particular example also extends in an upstream direction. Each tile  52 C in the downstream row of tiles  52 C also has two rails  55 , each rail  55  extends axially along a respective one of the circumferentially spaced edges and each rail  55  also extend towards and seal against the inner surface of the annular outer wall  50 . Thus, each tile  52 C has rails  51 ,  53  and  55  which extend around the periphery of the tile  52 C to form a closed chamber between each tile  52 C and the annular outer wall  50 . The tiles  52 C in the downstream row of tiles  52 C may have dilution apertures or may not have dilution apertures. Similarly, the tiles  52 A in the upstream row of tiles  52 A may have dilution apertures or may not have dilution apertures. Additionally, the tiles  52 B in the intermediate row of tiles  52 B may not have dilution apertures. 
     It is to be noted that the annular outer wall  50  has a bend  82  and the rail  53  at the downstream end of each tile  52 A is upstream of the bend  82  in the annular outer wall  50  and the rail  51  at the upstream end of each tile  52 B is downstream of the bend  82  in the annular outer wall  50 . It is also to be noted that the apertures  57  in the outer annular wall  50 , which are arranged to direct coolant onto the lip  63  at the downstream end of each tile  52 A, are positioned upstream of the bend  82  in the annular outer wall  50  and downstream of the rail  53  at the downstream end of each tile  52 A. Likewise, the annular outer wall  46  may have a bend and the rail at the downstream end of each tile  48 A is upstream of the bend in the annular outer wall  46  and the rail at the upstream end of each tile  48 B is downstream of the bend in the annular outer wall  46 . It is also to be noted that the apertures in the outer annular wall  46 , which are arranged to direct coolant onto the lip at the downstream end of each tile  48 A, are positioned upstream of the bend in the annular outer wall  46  and downstream of the rail at the downstream end of each tile  48 A. However, it may be equally possible to provide the apertures  57  in the outer annular wall  50 , which are arranged to direct coolant onto the lip  63  at the downstream end of each tile  52 A, downstream of the bend  82  in the annular outer wall  50  and downstream of the rail  53  at the downstream end of each tile  52 A. Similarly, it may be equally possible to provide the apertures in the outer annular wall  46 , which are arranged to direct coolant onto the lip at the downstream end of each tile  48 A, downstream of the bend in the annular outer wall  46  and downstream of the rail at the downstream end of each tile  48 A. The apertures in the row of apertures  57  in the outer annular wall  50  may be arranged perpendicularly to the outer surfaces of the lips  63  of the tiles  52 A or may be arranged at other suitable angles. The apertures in the row of apertures  57  in the outer annular wall  46  may be arranged perpendicularly to the outer surfaces of the lips of the tiles  48 A or may be arranged at other suitable angles. 
     The fasteners  60  are generally provided at the corners of the tiles  48 A,  48 B,  48 C and the fasteners  72  are generally provided at the corners of the tiles  52 A,  52 B and  52 C. The row, or rows, of apertures  57  in the annular outer wall  50  which direct coolant onto the lips  63  of the tiles  52 A reduce the strength of the annular outer wall  50 . The rails  53  at the downstream ends of the tiles  52 A are positioned close to the row, or rows, of apertures  57  in the annular outer wall  50 . The points where the fasteners  72  used to secure the tiles  52 A to the annular outer wall  50  are close to the rails  53  at the downstream ends of the tiles  52 A. The bend  82  in the annular outer wall  50  is positioned close to the row or rows of apertures  57  in the annular outer wall  50 . 
     The rail  53  at the downstream end of each tile  52 A is provided with at least one groove  86  at its end remote from the tile  52 A and the at least one groove  86  defines at least one slot with the inner surface of the annular outer wall  50 . The at least one groove  86  and hence the at least one slot is arranged in a region  84  downstream of a fastener  72  at the downstream end of the tile  52 A. In this arrangement the rail  53  at the downstream end of each tile  52 A is provided with a plurality of grooves  86  at its end remote from the tile  52 A and each groove  86  defines a slot with the inner surface of the annular outer wall  50 . Each tile  52 A has a plurality of grooves  86 , and hence a plurality of slots, are arranged in the region  84  downstream of the fastener  72 . As mentioned above each tile  52 A has a plurality of fasteners  72  positioned upstream of the rail  53  and the rail  53  of each tile  53 A has a plurality of grooves  86  which define a plurality of slots with the inner surface of the annular outer wall  50 . At least one groove  86 , and hence at least one slot, of each tile  52 A is arranged in a region  84  downstream of each fastener  72 . In this arrangement the rail  53  at the downstream end of each tile  52 A is provided with a plurality of grooves  86  at its end remote from the tile  52 A and each groove  86  defines a slot with the inner surface of the annular outer wall  50  and a plurality of grooves  86 , and hence a plurality of slots, of each tile  52 A are arranged in a region  84  downstream of each fastener  72 . There may for example be five grooves  86  in each region  84  and each region  84  may have a circumferential dimension of up to four times the diameter of a fastener  72 . There may be one groove  84  and hence one slot, or a plurality of grooves  84  and hence a plurality of slots, arranged in each region  84  and each region  84  downstream of a corresponding fastener  72  may have a circumferential dimension of up to four times the diameter of the corresponding fastener  72 . The grooves  86  in this arrangement are arranged perpendicularly to the surfaces of the rail  53 , but the grooves  86  may be arranged at any suitable angle to the surfaces of the rail  53 . The number of grooves  86 , the depth of the grooves  86 , the pitch of the grooves  86 , and the orientation, e.g. angle, of the grooves  86  may be optimised for a particular geometry. The pitch of the apertures in the row of apertures  57  may be optimised for a particular geometry. 
     The rails  55  along the axially extending edges of the tiles  52 A may be provided with at least one groove  88  at its end remote from the tile  52 A and the at least one groove  88  defines at least one slot with the inner surface of the annular outer wall  50 . There may be a plurality of grooves  88  in each of the rails of each tile  52 A. The grooves  88  may be arranged perpendicular to the surfaces of the rails  55  or at any other suitable angle to the surfaces of the rails  55 . 
     None of the apertures  57  in the at least one row of apertures in the annular outer wall  50  are arranged in a region  90  downstream of the at least one fastener  72  of the at least one tile  52 A and in particular none of the apertures  57  in the at least one row of apertures in the annular outer wall  50  are arranged in a region  90  downstream of each fastener  72  of the at least one tile  52 A. Each region  90  may have a circumferential dimension of up to four times the diameter of a fastener  72 , but in this example each region  90  has a circumferential dimension less than the circumferential dimension of the corresponding region  84 . Each region  90  may have a circumferential dimension of up to twice the diameter of the fastener  72 . Thus, in the, or each, region  90  downstream of a fastener  72  the annular outer wall  50  is imperforate. The region  90  may have the same circumferential dimension as the corresponding region  84 . 
     However, in some circumstances the region  84  may have a circumferential dimension greater than four times the diameter of a fastener  72  and/or the region  90  may have a circumferential dimension greater than twice the diameter of the fastener  72  to suit the need of a particular design. 
     The inner surface of the tiles  48 A,  48 B,  48 C,  52 A,  52 B and  52 C are provided with a thermal barrier coating  92  to further protect the tiles from the heat in the combustion chamber  15 . 
     In operation the coolant F is directed with high velocity from the apertures  57  in the annular outer wall  50  to impinge upon the lips  63  at the downstream ends of the tiles  52 A. The coolant flows from the lips  63  of the tiles  52 A such that the coolant G flows predominantly axially over and across the rails  51  at the upstream ends of the tiles  52 B and across and over the upstream ends of the tiles  52 B. This axial flow of coolant G reduces, or prevents, the ingress of hot gases into the chamber  65  defined between the rails  53  and lips  63  of the tiles  52 A and the annular outer wall  50 . The axial flow of coolant G also enables an effective film of coolant to be formed, or re-formed, on the inner surfaces of the tiles  52 B in the regions of the tiles  52 B immediately upstream of the dilution apertures  81  of the tiles  52 B. This reduces the temperature of the upstream ends of the tiles  52 B and the downstream ends of the tiles  52 A and the temperature of the annular outer wall  50  between the rails  53  of the tiles  52 A and the rails  51  of the tiles  52 B. 
     As mentioned previously, coolant is directed to flow through the impingement cooling apertures  67  onto the outer surface of the tiles  52 A,  52 B and  52 C and coolant is directed through the effusion cooling apertures  69  to provide a film of coolant on the inner surfaces of the tiles  52 A,  52 B and  52 C respectively. Some of the coolant supplied by the impingement cooling apertures  67  flows around the fasteners  72  at the downstream ends of the tiles  52 A, through the grooves  86  into the chamber  65  to mix with and join the flow of coolant F from the apertures  57 . 
     The grooves  86  in the rail  53  in the region  84  downstream of each fastener  72  reduce the conduction of heat from the tile  52 A into the annular outer wall  50  by reducing the area of contact between the rail  53  and the annular outer wall  50  in the region  84  downstream of the fastener  72 . The grooves  86  allow a flow of coolant I over the inner surface of the annular wall  50  in the region  84  downstream of each fastener  72 . The grooves  86  also enhance the flow of coolant around the fasteners  72  to cool the fasteners  72  and hence reduce the temperature of the tiles  52 A in the region of the fasteners  72  and in particular the base of the fasteners  72 . This reduces the potential for cracks to initiate and propagate in the annular outer wall  50  by reducing the temperature of the annular outer wall  50  and removing the stress concentration features. The cooling of the fasteners  72  reduces creep of the fasteners  72  and maintains the clamping load of the fastener  72  and tile  52 A onto the annular outer wall  50 . 
     The at least one row of apertures  57  in the annular outer wall  50  is arranged such that there are no apertures in each region  90  downstream of a fastener  72  of each tile  52 A, each region  90  downstream of a fastener  72  of the annular outer wall  50  is imperforate. These regions  90  are arranged to arrest crack propagation should any crack be initiated and propagated in the annular outer wall  50 . 
     The provision of the grooves  86  in the regions  84  of the rails  53  provides a flow of coolant over the inner surface of the annular outer wall  50  and the outer surfaces of the lips  63  of the tiles  52 A which compensates for the regions  90  of the annular wall  50  where there are no apertures  57  to direct coolant through the annular outer wall  50  and onto the outer surfaces of the lips  63  of the tiles  52 A. 
     The tiles  52 B and  52 C of the radially outer annular wall structure  42  may be arranged in a similar manner to the tiles  52 A. Thus, the rails at the downstream ends of the tiles  52 B may be provided with grooves  86  downstream of at least one fastener  72  and the row of apertures  57  arranged to direct coolant onto the lips  63  may be provided with a region without apertures and/or the rails at the downstream ends of the tiles  52 C may be provided with grooves  86  downstream of at least one fastener  72  and the row of apertures  57  arranged to direct coolant onto the lips  63  may be provided with a region without apertures. 
     The tiles  48 A,  48 B and  48 C of the radially inner annular wall structure  40  may be arranged in a similar manner to the tiles  52 A. Thus, the rails at the downstream ends of the tiles  48 A may be provided with grooves downstream of at least one fastener  60  and the row of apertures arranged to direct coolant onto the lips may be provided with a region without apertures and/or the rails at the downstream ends of the tiles  48 B may be provided with grooves downstream of at least one fastener  60  and the row of apertures arranged to direct coolant onto the lips may be provided with a region without apertures and/or the rails at the downstream ends of the tiles  48 C may be provided with grooves downstream of at least one fastener  60  and the row of apertures arranged to direct coolant onto the lips may be provided with a region without apertures. 
     Each of the tiles  48 A,  48 B and  48 C and each of the tiles  52 A,  52 B and  52 C is parallelogram in shape in a plan view and in particular each of the tiles  48 A,  48 B and  48 C and each of the tiles  52 A,  52 B and  52 C is rectangular in a plan view. Each of the tiles  48 A,  48 B and  48 C and each of the tiles  52 A,  52 B and  52 C has longitudinally, axially, spaced ends and laterally, circumferentially, spaced edges. Each of the tiles  48 A,  48 B and  48 C and each of the tiles  52 A,  52 B and  52 C is arcuate and in particular is curved between its laterally spaced edges. Each of the tiles  48 A,  48 B and  48 C has a rail extending around the periphery of a first surface, a radially inner surface, and the first surface is concave between its laterally spaced edges. Each of the tiles  52 A,  52 B and  52 C has a rail extending around the periphery of a first surface, a radially outer surface, and the first surface is convex between its laterally spaced edges. 
     An advantage of the present disclosure is that the row or rows of apertures in the annular outer wall which direct coolant onto the lips of the tiles are provided with circumferential regions where there are no apertures to increase the strength of the annular outer wall and to arrest the propagation of any cracks circumferentially around the annular outer wall. The rails at the downstream ends of the tiles which are positioned close to the row of rows of apertures in the annular outer wall are provided with grooves at their ends remote from the tiles to reduce the conduction of heat from the tiles to the annular outer wall and hence reduce the stress in the annular outer wall adjacent the row or rows of apertures in the annular outer wall which direct coolant onto the lips of the tiles. The mechanical integrity of the annular outer wall and the fasteners of the tiles are improved by reducing the possibility of crack initiation and increasing the possibility of preventing the propagation of cracks around the annular outer wall whilst preserving cooling effectiveness. The arrangement reduces the loss of clamping load of the tiles. 
     Although the present disclosure has referred to the use of studs and nuts to secure the tiles to the particular supporting annular wall it may be possible to use bolts which are inserted through apertures in the tiles and respective apertures in the supporting annular wall and threaded into associated nuts or it may be possible to use threaded bosses on the tiles and bolts which are inserted through apertures in the supporting annular wall and into threaded into the respective bosses. 
     The combustion chamber may be an annular combustion chamber and the annular inner wall is spaced radially inwardly from the annular outer wall. 
     The combustion chamber may be an annular combustion chamber and the annular inner wall is spaced radially outwardly from the annular outer wall. 
     Although the present disclosure has referred to an annular combustion chamber is equally applicable to a tubular combustion chamber in which the annular inner wall is spaced radially inwardly from the annular outer wall. 
     The combustion chamber is a gas turbine engine combustion chamber. 
     Although the present disclosure has been described with reference to a turbofan gas turbine engine it is equally applicable to a turbojet gas turbine engine, a turbo-shaft gas turbine engine and a turbo-propeller gas turbine engine. 
     Although the present disclosure has been described with reference to an aero gas turbine engine it is equally applicable to a marine gas turbine engine, an automotive gas turbine engine and an industrial gas turbine engine. 
     The tiles may be made by casting or by additive layer manufacturing, e.g. direct laser deposition (DLD) or powder bed laser deposition. The tiles may comprise a nickel based superalloy, a cobalt based superalloy or an iron based superalloy. 
     It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.