Abstract:
A gas turbine combuster ia provided with a dome heat shield having a fuel nozzle opening, the opening receiving a floating collar assembly for permitting relative movement between nozzle and heat shield. The floating collar is provided with a louver to provide film cooling to the face of the combustor heat shield and, thus, improve cooling thereof.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to gas turbine engine combustors and, more particularly, to a combustor floating collar and heat shield assembly. 
       BACKGROUND OF THE ART 
       [0002]    Gas turbine combustors are the subject of continual improvement, to provide better cooling, better mixing, better fuel efficiency, better performance, etc. at a lower cost. For example, heat shields are known to provide better protection to the combuster, but heat shields also require cooling. Cooling of the downstream or combustion side of the heat shield is challenging and there is a continuing need for improvement in order to ensure constant and effective cooling to this heat shield area. 
       SUMMARY 
       [0003]    It is therefore an aim of the present invention to provide improved cooling. 
         [0004]    Therefore, there is provided a floating collar and heat shield assembly for allowing relative movement between a combustor and a fuel nozzle while providing sealing therebetween, comprising an axially extending floating collar body adapted to be mounted in a fuel nozzle opening defined in the combustor, the axially extending floating collar body defining a passage adapted to be aligned with the fuel nozzle opening for receiving the fuel nozzle, the floating collar body having an upstream end adapted to extend into the combuster, the upstream end being provided with a radially disposed annular louver, a heat shield fitted about said floating collar body downstream of said annular louver, said louver and said heat shield defining a controlled gap therebetween, and a sealing ring mounted to said floating collar body downstream of said heat shield and in sealing engagement therewith, said sealing ring defining at least one hole for feeding cooling air to said controlled gap. 
         [0005]    In accordance with another general aspect, there is provided a floating collar and heat assembly for gas turbine engine combustor, comprising a heat shield adapted to be mounted in the combuster, the heat shield defining a central aperture, a collar floating received in said central aperture for receiving a fuel nozzle, the central aperture accommodating radial excursion of said collar relative to the heat shield, the collar having a front end portion projecting forwardly of a front side of the heat shield and a rear end portion projecting rearwardly of a rear side of the heat shield, a cooling louver provided at said front end portion of said collar for directing a fluid cooling film along said front side of said heat shield, and a sealing ring provided at said rear end portion of the collar for sealing engagement with said rear side of said heat shield. 
         [0006]    In accordance with a further general aspect, there is provided a gas turbine engine combustor comprising a shell enclosing a combustion chamber, a fuel nozzle opening defined in the combustor shell, a floating collar mounted in said fuel nozzle opening and having a downstream end portion projecting into said combustion chamber, the floating collar defining an axial aperture, a fuel nozzle slidably engaged in said axial aperture, a heat shield fitted about said floating collar between the shell and a laterally extending louver integral to said downstream end portion of the floating collar, the louver and the heat shield defining a controlled gap connected in flow communication with a source of coolant, the louver directing a film of coolant along a hot front surface of the heat shield. 
         [0007]    In accordance with a further general aspect, there is provided a method of providing a floating collar and heat shield assembly, comprising: providing a collar body having first and second axially opposed ends, said first end having a radially outwardly extending flange; providing a heat shield having a central aperture having an inner diameter greater than an outer diameter of said collar body but smaller than said flange, loosely fitting said heat shield over said collar body from said second end opposite said flange, and trapping the heat shield between the flange and a sealing ring by mechanically attaching the sealing ring to the collar body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Reference is now made to the accompanying figures, in which 
           [0009]      FIG. 1  is a schematic cross-sectional view of a gas turbine engine having an annular combustor; 
           [0010]      FIG. 2  is an enlarged cross-sectional view of a dome portion of the combuster, showing a splash louver on a floating collar to provide film cooling to the hot front face of a dome heat shield; and 
           [0011]      FIG. 3  is enlarged view of details  3  shown in  FIG. 2 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0012]      FIG. 1  illustrates a gas turbine engine  10  generally comprising in serial flow communication a fan  12  (not provided with all types of engine) through which ambient air is propelled, a multistage compressor  14  for pressurizing the air, a combustor  16  in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine  18  for extracting energy from the combustion gases. 
         [0013]    The combuster  16  is housed in a plenum  17  supplied with compressed air from the compressor  14 . As shown in  FIG. 2 , the combuster  16  comprises a combustor shell  20 , typically formed by sheet metal inner and outer liners, defining a combustion chamber  21 . A plurality of circumferentially spaced-apart fuel nozzles  22  ( FIG. 1 ) are typically mounted in respective fuel nozzle openings  24  defined in a dome or bulkhead portion of the combuster shell  20 . As shown in  FIG. 2 , a floating collar  26  is mounted in each opening  24  to allow relative movement between the fuel nozzle  22  and the combustor shell  20  while minimizing leakage therebetween. Each floating collar  26  has an axially extending tubular body portion  26   a  defining a central passage  26   b  adapted to axially slidably receive one fuel nozzle  22 . A dome heat shield  28 , typically made out of a cast material, is loosely fitted about each floating collar  26  and fixedly accured to the combustor shell  20  by suitable fastening means, such as bolting or brazing. The heat shield  28  has a central aperture  28   c  which is oversized relative to the body portion  26 a of the collar  26  in order to accommodate radial movement of the collar  26  and the fuel nozzle  22  relative to the combuster shell  20  and the heat shiel  28 . 
         [0014]    The rear or upstream surface  28   a  of the heat shield  28  is generally cooled by means of impingement augmented by the use of pin fins (not shown) provided at the back thereof. A combination of impingement and effusion cooling can also be used. Impingement holes (not shown) are typically defined through the dome portion of the combustor shell  20  to cause cooling air from the plenum  17  to impinge upon the upstream surface  28   a  of the heat shield  28 . 
         [0015]    Film cooling is used to cool down the front or downstream surface  28   b  of the heat shield  28 . As shown in  FIGS. 2 and 3 , the floating collar  26  is provided at a front or downstream end thereof with a integral flange acting as splash louver  26   c  to provide film cooling to the downstream surface  28   b  of the heat shield  28 . The integration of the louver  26   c  to the floating collar body  26   a  greatly simplifies the cooling of the downstream surface  28 b of the heat shield  28 . The floating collar body  26   a  and the louver  26   c  are of unitary construction and can be made out of a same combination of suitable materials to provide the best durability in wear and oxidation resistance. For instance, high temperature casting materials could be used. The louver  26   c  extends radially outwardly from the downstream end of the body portion  26   a  about passage  26   c.  The louver  26   c  is generally parallel to the front face or downstream surface  28   b  of the heat shield  28  and is spaced axially therefrom so sa to form a controlled gap or plenum  30 . 
         [0016]    A sealing ring  32  is fixedly mounted on the collar body  26   a  for sealing engagement with a corresponding sealing interface on the upstream surface  28   a  of the heat shield  28 . The sealing ring  32  can be mechanically attached or joined to the collar body  26   a  by any suitable means, such as welding or brazing. The sealing ring  32  is preferably abutted against a localization shoulder  26   d  ( FIG. 3 ) defined in the outer surface of the collar body  26   a.  A plurality of circumferentially distributed holes  32   a  are defined in the scaling ring  32  for feeding cooling air from the plenum  17  to the controlled gap  30  as depicted by arrows  34  in  FIGS. 2 and 3 . The holes  32   a  communicate with the controlled gap  30  via the annular gap between the heat shield  28  and the collar  26 . The annular gap results from the oversizing of the heat shield central passage  28   c  for accommodating the relative movement between the fuel nozzle  22  and the combustor shell  20  and, thus, the relative movement between the floating collar  26  and the heat shield  28 . It is understood that other cooling holes could be defined through the heat shield  28  for allowing the cooling air to flow into the controlled gap  30 . The louver  26   c  directs the cooling air flowing into the controlled gap  30  along the downstream surface  28   b  of the heat shield  28 . The air deflected by the louver  26   c  forms a cooling film over the downstream surface  28   b.  This provides a simple and economical way to increase the heat shield cooling effectiveness. 
         [0017]    The floating collar  26  and the sealing ring  32  are assembled to the heat shield  28  from both sides, trapping the heat shield  28  when the floating collar  26  is mechanically attached to the sealing ring  32 . The floating collar  26  is then swaged to provide a radially outwardly flaring end  26   c  opposite the louver  26   c  to facilitate the subsequent installation of the fuel nozzle  22  in the floating collar  26 , as well as to provide retention of the floating collar  26  on the combustor shell  20  in the event of a brazing or welding failure between the sealing ring  32  and the collar  26 . 
         [0018]    The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. For example, the invention may be provided in any suitable heat shield configuration and in any suitable combustor configuration, and is not limited to application in turbofan engines. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.