Abstract:
A gas turbine engine with: a compressor section; a turbine section; a combustor, disposed between the compressor and turbine sections, having at least one combustor mounting assembly connecting the combustor to the engine. Each combustor mounting assembly has: a longitudinal axis; and an articulating joint having a first and second portion constrained from relative translation transverse to the longitudinal axis, and where said first and second portion have a multiple rotational degrees of freedom relative to each other about axes transverse to the longitudinal axis.

Description:
TECHNICAL FIELD  
       [0001]     The invention relates to a gas turbine engine combustor mounting assembly which facilitates relative sliding translation and rotation between the combustor and engine casing.  
       BACKGROUND OF THE ART  
       [0002]     During gas turbine engine operation cycles, the thermally induced strain, i.e.: expansion and contraction of the combustor duct walls relative to the surrounding engine casing, is conventionally accommodated by fixing the upstream end of the combustor, either with the fuel nozzle support tubes or other combustor supports, and permitting the downstream end to expand and contract relatively freely in an axially sliding joint. The axial component of the thermally induced strain is generally accommodated by an sliding axial joint at the downstream outlet end of the combustor, whereas the radial component of thermally induced strain may be accommodated by means effectively securing the combustor such that the combustor is restrained axially at the upstream end while radial movement is accommodated by various combustor mounting devices.  
         [0003]     Due to the harsh temperature environment and the need for simple, robust, maintenance free, and low cost mechanical devices to mount the combustor, conventional combustor mounting assemblies include simple devices such as a cylindrical locating pin slidably engaged in a combustor boss within a cylindrical recess for example which prevents lateral translation transverse to the pin while permitting relative sliding movement between the cylindrical pin and the cylindrical recess within the combustor boss.  
         [0004]     It is an object of the present invention to provide a simple robust low cost combustor mount assembly that can accommodate the harsh temperature levels of the combustor and accommodate thermally induced expansion and contraction.  
         [0005]     Further objects of the invention will be apparent from review of the disclosure, drawings and description of the invention below.  
       DISCLOSURE OF THE INVENTION  
       [0006]     The invention provides a gas turbine engine with: a compressor section; a turbine section; a combustor, disposed between the compressor and turbine sections, having at least one combustor mounting assembly connecting the combustor to the engine. Each combustor mounting assembly has: a longitudinal axis; and an articulating joint having a first and second portion constrained from relative translation transverse to the longitudinal axis, and where said first and second portion have a multiple rotational degrees of freedom relative to each other about axes transverse to the longitudinal axis.  
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0007]     In order that the invention may be readily understood, embodiments of the invention are illustrated by way of example in the accompanying drawings.  
         [0008]      FIG. 1  is an axial cross-sectional view through a typical turbofan gas turbine engine showing the arrangement of engine components and specifically the combustor housed within the compressed air plenum and supplied with liquid fuel via fuel nozzles.  
         [0009]      FIG. 2  is an axial sectional view through the area surrounding the combustor showing a fuel nozzle and a conventional combustor mount assembly secured to the relatively thin duct walls of the combustor.  
         [0010]      FIG. 3  is a detailed axial sectional view of through a conventional combustor boss with combustor locating pin inserted therein.  
         [0011]      FIG. 4  is a like axial sectional view through a combustor mount assembly in accordance with the present invention showing a preferred example with a spherical articulating joint that is also slidably disposed within the combustor boss.  
         [0012]      FIG. 5  is a detailed sectional view of the articulating joint showing spherical sliding surfaces and cylindrical sliding surfaces between the assembled components.  
         [0013]      FIG. 6  is a further detailed view illustrating the ability of the articulating joint to accommodate misalignment during installation or operation of the engine. 
     
    
       [0014]     Further details of the invention and its advantages will be apparent from the detailed description included below.  
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0015]      FIG. 1  shows an axial cross-section through a typical turbofan gas turbine engine. It will be understood however that the invention is applicable to any type of engine with a combustor and turbine section such as a turboshaft, a turboprop, auxiliary power unit, gas turbine engine or industrial gas turbine engine. Air intake into the engine passes over fan blades  1  in a fan case  2  and is then split into an outer annular flow through the bypass duct  3  and an inner flow through the low-pressure axial compressor  4  and high-pressure centrifugal compressor  5 . Compressed air exits the compressor  5  through a diffuser  6  and is contained within a plenum  7  that surrounds the combustor  8 . Fuel is supplied to the combustor  8  through fuel nozzles  9  which is mixed with air from the plenum  7  when sprayed through nozzles into the combustor  8  as a fuel air mixture that is ignited. A portion of the compressed air within the plenum  7  is admitted into the combustor  8  through orifices in the side walls to create a cooling air curtain along the combustor walls or is used for cooling to eventually mix with the hot gases from the combustor and pass over the nozzle guide vanes  10  and turbines  11  before exiting the tail of the engine as exhaust. It will be understood that the foregoing description is intended to be exemplary of only one of many possible configurations of engine suitable for incorporation of the present invention.  
         [0016]      FIG. 2  shows a detailed view of the area of the engine surrounding the combustor  8  in a conventional gas turbine engine whereas  FIG. 3  shows a detailed view of the prior art connection between the combustor boss  13  and the locating pin  14 . As best seen in  FIG. 2 , the pin  14  is rigidly connected at an outer end to the plenum casing  12  with bolt  15  for example whereas the inward end of the pin  14  restrains axial motion of the boss  13  and combustor  8  while permitting sliding in a generally radial direction between the boss  13  and the inner end of the pin  14 . As shown in  FIG. 2 , the downstream end of the combustor  8  includes an axial sliding joint  16  between the combustor  8  and the nozzle guide vane  10 . The combustor nozzles  17  are mounted to the end wall of the combustor  8  using a floating collar connection of a type well known to those skilled in the art that accommodates relative movement caused by varying thermal conditions.  
         [0017]      FIG. 3  shows details of the inner end of the prior art pin  14  which is inserted into the combustor boss  13 . The prior art boss  13  has an internal cylindrical surface which is engaged by a spherical portion  18  formed on the inward end of the pin. A disadvantage of this conventional arrangement however is that fretting occurs between the spherical portion  18  and the cylindrical interior surface of the combustor boss  13  due to the limited contact surface between these components. Effectively, the contact surface amounts to a relatively thin band around the periphery of the spherical portion  18  which is subjected to relative movement, vibration stress and is exposed to the heat of gases contained within the combustor  8 .  
         [0018]      FIGS. 4, 5  and  6  show details of an embodiment of the invention which provides distinct advantages over the prior art. The combustion boss  13  need not pass entirely through the wall of the combustor  8  and therefore does not necessarily expose the associated components to combustion gases. Further, it will be apparent to those skilled in the art that during an engine overhaul or retrofit the conventional combustor mounting assembly (which is shown in  FIGS. 2 and 3 ) can be easily replaced and upgraded by the invention shown in  FIG. 4  replacing the combustor boss  13  and optionally the pin  14  if necessary. It is contemplated however that the pin  14  may simply be re-machined to accept the articulating joint  19 , the details of which will be described below.  
         [0019]     Referring to  FIG. 4 , the combustor mounting assembly of the present invention connects the combustor  8  to the engine structure, in the embodiment illustrated, consisting of the plenum casing  12 . Each combustor mounting assembly has a longitudinal axis  20 , which is typically aligned radially relative to the engine, and includes an articulated joint  19 . The articulating joint  19  has a first portion  21  and second portion  22  which mate and engage on convex and concave surfaces, and are thereby constrained from relative translation in a direction transverse to the longitudinal axis  20  by engagement within the combustor boss  13  (it being understood that a direction which is “transverse” to the longitudinal axis  20  is one which has a component which is normal to axis  20 ). However, as best illustrated in  FIGS. 4 and 5 , the first and second portions  21  and  22  of the articulating joint  19  have a plurality of rotational degrees of freedom relative to each other about multiple axes transverse to the longitudinal axis  20  of course, in the application shown, the degree of rotational movement required around the rotational axes transverse to the longitudinal access is very limited but is sufficient to provide for the expected thermal expansion and contraction as indicated. As also shown in  FIG. 6  with arrow aligned with the longitudinal axis  20 , the articulating joint  19  has a translational degree of freedom parallel to the longitudinal axis  20 .  
         [0020]     In the example shown, the simple robust structure of the articulating joint  19  includes at least one longitudinal slide surface. For example, as shown in  FIG. 5 , the external cylindrical slide surface of the articulating joint  19  is slidably housed within the internal cylindrical surface  24  of the boss  13 . Therefore, the articulating joint  19  is free to slide parallel to the longitudinal axis  20  relative to the boss  13  while it is constrained transverse to the longitudinal axis  20  by mechanical interference between the cylindrical slide surfaces  23  and  24 .  
         [0021]     Alternatively, or in addition to the above described mechanism, the pin  20  can be designed with clearance relative to the first portion  21  such that the exterior surface of the pin  14  constitutes a cylindrical external slide surface and the internal surface of the first portion  21  can comprise a cylindrical internal slide surface. To this end, the combustor boss  13  includes a hollow chamber  25  to permit clearance of the end of the pin  14  and accommodate radial movement of the boss  13  and combustor  8  relative to the stationary pin  14 .  
         [0022]     In the embodiment shown, the combustor mounting assembly includes an outwardly projecting boss  13  and the articulating joint  19  is housed entirely within the internal surface of the boss  13 . It will be apparent to those skilled in the art however, that this is not the only arrangement possible within the teaching of the invention. For example, the pin  14  may comprise a hollow tube and the first and second portions  21  and  22  may be fitted within a tubular pin  14 . In such an alternative, the boss  13  would comprise an interior stud that is restrained within the interior surface of the first portion  21 . Many other examples within the teaching of the invention will be recognized by those skilled in the art, such as replacing the spherical articulating joint  19  with a ball in socket joint, a universal joint, a gimble device, or a linkage structure.  
         [0023]     In the embodiment shown in  FIGS. 4, 5  and  6 , the first and second portion  21 ,  22  of the articulating joint  19  have opposing spherical joint surfaces  26  and  27 . The first and second portions  21  and  22  are shown as mutually nested sleeves however other arrangements are certainly possible such as a ball and socket joint. However due to limited range of movement that is required for this application, the size of the spherical surfaces  26  and  27  can also be limited.  
         [0024]     Comparison between  FIG. 5  and  FIG. 6  will illustrate a further advantage of the invention in that the articulating joint  19  not only serves to accommodate relative rotational movement between the combustor  8  and the pin  14 , as well as relative radial movement, but further the articulating joint is mounted to accommodate any misalignment in the installation.  FIG. 6  shows a misalignment between the second portion  22  and the interior surface of the combustor boss  13 . Further  FIG. 6  shows downward protrusion of the bottom of the pin  14  into the hollow chamber  25 .  
         [0025]     In conclusion therefore, the invention provides a relative simple, inexpensive and robust means to join the combustor  8  to the engine while accommodating thermal expansion and contraction that adapts to relative radial movement and rotational movement simultaneously. The invention may be applied to newly manufactured engines and to retrofit applications with relative ease.  
         [0026]     Although the above description relates to a specific preferred embodiment as presently contemplated by the inventor, it will be understood that the invention in its broad aspect includes mechanical and functional equivalents of the elements described herein.