Patent Publication Number: US-8113004-B2

Title: Wall element for use in combustion apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is entitled to the benefit of British Patent Application No. GB 0720662.6, filed on Oct. 23, 2007. 
     FIELD OF THE INVENTION 
     This invention relates to combustion apparatus for a gas turbine engine. More particularly, the invention relates to a wall element for use in a wall structure of such a combustion apparatus. 
     BACKGROUND OF THE INVENTION 
     A typical gas turbine engine combustor includes a generally annular chamber having a plurality of fuel injectors at an upstream head end. Combustion air is provided through the head and in addition through primary and intermediate mixing ports provided in the combustor walls downstream of the fuel injectors. 
     In order to improve the thrust and fuel consumption of gas turbine engines, i.e., the thermal efficiency, it is necessary to use high compressor pressure and combustion temperatures. This results in the combustion chamber experiencing high temperatures and there is a need to provide effective cooling of the combustion chamber walls. Various cooling methods have been proposed including the provision of a double walled combustion chamber whereby cooling air is directed into a gap between spaced outer and inner walls, thus cooling the inner wall. This air is then exhausted into the combustion chamber through apertures in the inner wall. The exhausted air forms a cooling film, which flows along the hot, internal side of the inner wall, thus preventing the inner wall from overheating. 
     The inner wall may comprise a number of heat resistant tiles. The tiles are generally rectangular in shape and are bowed to conform to the overall shape of the annular combustor wall. The tiles are conventionally longer in the circumferential direction of the combustor than in the axial direction. 
     It is known to provide pedestals, which extend from an outer surface of the tile towards the inner surface of the outer wall. The pedestals increase the surface area of the tile and facilitate heat removal from the tile “hot” side by primarily convection as cooling air passes between the pedestals and secondly by conduction from the pedestal to the outer “cold” wall of the combustor where the pedestal and wall contact. 
     The tiles and outer “cold” wall of the combustor are typically of cast construction. Cast components generally cannot be produced to very high tolerances and this inevitably results in gaps between some of the pedestals and the outer wall. Indeed, the pedestals, are typically arranged to provide a gap between the pedestal and the outer wall to prevent damage to the wall or tile caused by differences in thermal expansion between these two components. 
     Such a gap is undesirable since it reduces the effect of heat removal by conduction and additionally the effect of heat removal by convection since the air can pass over the pedestal tip rather than across the pedestal surface. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to seek to address this and other problems. 
     According to a first aspect of the invention, there is provided a wall element for use as part of an inner wall of a gas turbine engine combustor wall structure including inner and outer walls defining a space therebetween, the wall element being provided with deformable cooling pedestals extending into the space and which on contact with the outer wall deform against the outer wall of the wall structure. 
     Preferably, the wall element further comprises fastening elements for securing the wall element to the outer wall. 
     Preferably, the pedestals are at an angle other than 90° to the inner wall. 
     Preferably, the wall element includes a body portion for providing the inner wall of the combustor wall structure and elongate edge portions projecting from the body portion towards the outer wall of the combustor wall structure in use and wherein the pedestal means are provided on the body portion which project in the same direction as and extend beyond the edge portions. 
     The pedestals may have the form of a helical or omega spring. 
     Preferably, the wall element is generally rectangular and includes axial and circumferential edges, the axial edges being generally oriented in an axial direction of the gas turbine engine combustor in use and the circumferential edges being generally oriented in a circumferential direction of the gas turbine engine combustor in use. 
     Seal means may be provided on or near the axial edges of the wall element. Seal means may be provided also on or near the circumferential edges of the wall element. 
     The wall element may be for use in a backplate region of a combustor. The wall element may have generally sector shaped, including spaced radial edges and spaced circumferential edges. 
     According to a second aspect of the invention there is provided a wall structure for a gas turbine engine combustor, the wall structure including inner and outer walls defining a space therebetween, wherein the inner wall includes at least one wall element according to any preceding claim. 
     Preferably, the wall structure includes a plurality of wall elements, and edges of the wall elements at least partially overlap. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a ducted fan gas turbine engine having an annular combustor; 
         FIG. 2  is a diagrammatic cross-section of an annular combustor; 
         FIG. 3  is a diagrammatic cross-section of a further annular combustor; 
         FIG. 4  is a diagrammatic cross-section of a wall element in accordance with the invention, while  FIG. 4A  is a diagrammatic cross-section of the wall element with pedestals deformed; 
         FIG. 5  depicts alternative cooling pedestal arrangements. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to  FIG. 1 , a ducted fan gas turbine engine generally indicated at  10  comprises, in axial flow series, an air intake  12 , a propulsive fan  14 , an intermediate pressure compressor  16 , a high pressure compressor  18 , combustion equipment  20 , a high pressure turbine  22 , an intermediate pressure turbine  24 , a low pressure turbine  26  and an exhaust nozzle  28 . 
     The gas turbine works in the conventional manner so that air entering the intake  12  is accelerated by the fan  14  to produce two air flows, a first air flow into the intermediate pressure compressor  16  and a second airflow which provides propulsive thrust. The intermediate pressure compressor  16  compresses the air flow directing it into the high pressure compressor  18  where further compression takes place. 
     The compressed air exhausted from the high pressure compressor  18  is directed into the combustion equipment  20  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  22 ,  24  and  26  respectively before being exhausted through the nozzle  28  to provide additional propulsive thrust. The high, intermediate and low pressure turbines  22 ,  24  and  26  respectively drive the high and intermediate pressure compressors  16  and  18  and the fan  14  by suitably interconnecting shafts (not shown). 
     The combustion equipment  20  includes an annular combustor  30  having radially inner and outer wall structures  32  and  34  respectively. Fuel is directed into the combustor  30  through a number of fuel nozzles (not shown) located at the upstream end of the combustor  30 . The fuel nozzles are circumferentially spaced around the engine  10  and serve to spray fuel into air derived from the high pressure compressor  18 . The resultant fuel is then combusted in the combustor  30 . 
     The combustion process which takes place within the combustor  30  naturally generates a large amount of heat. Temperatures within the combustor may be between 1,850K and 2,600K. It is necessary therefore to arrange that the inner and outer wall structures  32  and  34  are capable of withstanding these temperatures while functioning in a normal manner. The radially inner wall structure can be seen more clearly in  FIG. 2 . 
     Referring to  FIG. 2 , the wall structure includes an inner wall  36  and an outer wall  38 . The inner wall comprises a plurality of discrete tiles  40 , which are all of substantially the same rectangular configuration and positioned adjacent each other. The majority of the tiles  40  are arranged to be equidistant from the outer wall  38 , and the tiles are arranged such that a downstream edge of each tile  40  overlaps an upstream edge of an adjacent tile  40 . Each tile  40  is provided with integral studs  41  which facilitate its attachment to the outer wall  38 . 
     The air temperature outside the combustor  30  is about 800K to 900K. Feed holes (not shown in  FIG. 2 ) are provided in the outer wall  38  such that high pressure, relatively cool air flows into a space  50  between the tiles  40  and the outer wall  38 . Effusion holes are provided within the tiles  40  such that the cooling air flows through the tiles  40  and forms a cool air film over the hot, internal surface of the tiles  40 . This air film prevents the tiles  40  from overheating. 
     The cooling film flows over the tiles  40  in the general direction of fluid flow through the combustor  30 , i.e. to the right as shown in  FIG. 2 and 3 . 
       FIG. 3  illustrates an alternative arrangement of tiles  40  in a combustor wall structure  32 ,  34 . The arrangement is generally similar to that of  FIG. 2 , and the same reference numerals are used for equivalent parts. However, instead of the tiles  40  being in overlapping relationship, they lie generally in the same plane. 
     The tiles  40  may be provided with sealing rails, which extend around part or all of the periphery of the tile. The rails extend from the tile plate portion towards the outer wall such that a discrete space  50  is defined between each tile  40  and the outer wall  38 . 
     Referring to  FIG. 4 , each tile  40  includes a main body portion  42 , which is shaped to conform to the general shape of the combustor wall structure  32 ,  34 . At an axially directed edge of each tile, a sealing rail  44  extends from the main body portion  42  of the tile towards the outer wall  38  (which is shown with exaggerated irregularity). The sealing rails are intended to minimize the leakage of air from the space  50  around the edges of the tiles  40 , and into the combustor  30 . However, due to manufacturing tolerances, there is a small gap between the sealing rail  44  of each tile  40  and the outer wall  38 . Adjacent sealing rails  44  of adjacent tiles  40  are located a small distance apart, resulting in an axial gap. 
     Each tile has an array of pedestals  52 , which extend from the main body portion of the tile towards the outer wall  38  and which project from the main body portion of the tile a greater distance than the side rails. 
     The pedestals  52  are made of a material and have dimensions and arrangements, which allow them to deform or compress upon contact with the outer skin. 
     In the preferred embodiment, the pedestals are angled with respect to the surface of the outer wall. Where rails are provided, each pedestal protrudes slightly beyond the rail positions so that as the tile is secured to the cold wall via appropriate means each pedestal deflects, as shown in  FIG. 4A . The amount of deflection will depend partly on the local position of the outer wall at the point of contact with the pedestal. The deflection may be via a pivot point close to the pedestal join with the wall element, or via a bending of the pedestal to the exemplary form shown by dashed lines in  FIG. 4  and shown by solid lines in  FIG. 4A . The deflection may be permanent in that the pedestal does not regain its initial form once the tile has been removed from the combustor following use. 
     Since each pedestal is designed to deflect contact with the outer wall is ensured allowing conduction from the tile to the outer wall through the pedestal. The elliptical shape of the contact point further increases the contact surface area. The length of the pedestal is also increased without having to further increase the volume beneath the tile or the distance between the tile and the outer wall. Thus, the combustor may, where it is desirable, be retro fitted without having to make significant changes to the combustor design. Additionally, cooling air is forced to pass between the pedestals rather than escaping under them. 
     One method of forming the tile can be through a process known as additive manufacture. In this process, the tile structure is formed by direct addition of media to the substrate. In the preferred method, a laser is used to melt the inner surface of the tile and a powder head scans over the surface to deposit a volume of powder into the melt pool. The laser traverses from the deposition location which allows the molten powder to cool forming a solidified, raised profile. By repeated deposition at the same location, higher deposits can be formed. If depositions overlap, it is possible to form the angled pedestals as shown. The powder used should have the same composition as that of the desired pedestal. 
     One of the benefits of forming the pedestal through a direct additive manufacture method is that other, more complex, forms of pedestal may be created. For example, the pedestals could have an omega or helical spring form, as shown in  FIG. 5 , that will further increase the length of each pedestal beyond that of a straight pedestal arranged perpendicular to the outer wall. Other flexible pedestal forms may be used as will be apparent to one of skill in the art.