Abstract:
The manifold includes supports which slidably engage a heat shield to floatingly suspend it around the manifold. The manifold is part of a heat shield assembly inside a gas turbine engine. The assembly comprises a plurality of radially-extending supports extending from a casing of the engine to the manifold. A heat shield encloses the manifold. The heat shield has openings through which the supports pass to slidably engage the heat shield. The supports floatingly suspend the heat shield relative to the manifold.

Description:
TECHNICAL FIELD 
   The field of the invention relates generally to heat shields for use in gas turbine engines. 
   BACKGROUND OF THE ART 
   In gas turbine engines, internal manifolds used for distributing fuel to fuel nozzles must be insulated since the intense heat may cause fuel passage coking. However, conventional heat shields are attached to manifolds by welding which introduces zones of high mechanical stresses and conduction points, through which heat may be relatively easily transmitted from the heat shield to the manifold by conduction. The high mechanical stresses are the result of the welding process itself, as well as sharp thermal gradients between the hot heat shield and the relatively cooler manifold. Also, the thermal expansion and contraction of the heat shield create further stresses at the welded fixing locations. 
   Accordingly, there is a need to provide an improved heat-shielded manifold. 
   SUMMARY OF THE INVENTION 
   In one aspect, the present invention provides a heat shield assembly for a fuel manifold inside a gas turbine engine, the assembly comprising a plurality of radially-extending supports extending form the engine to the manifold, a heat shield for enclosing the manifold, the heat shield having openings through which the supports pass to slidably engage the heat shield and thereby floatingly suspend the heat shield relative to the manifold. 
   In a second aspect, the present invention provides heat-shielded manifold comprising: an annular manifold body; at least three supports radially extending from the manifold body and being symmetrically disposed therearound; a heat shield body spaced-apart from and enclosing the manifold body, the heat shield body having an opening therethrough corresponding to each support; and a set of bosses mounted to the heat shield in said openings, each boss slidably engaging the supports relative to the heat shield and thereby the heat shield relative to the manifold. 
   In a third aspect, the present invention provides fuel manifold for a gas turbine engine, the manifold comprising: an annular manifold body configured for assembly inside a gas turbine engine; an annular heat shield surrounding the manifold body and spaced radially outward therefrom; manifold support means for supporting the manifold body relative to the engine; and heat shield support means for slidingly supporting the heat shield relative to the manifold. 
   Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below. 

   
     DESCRIPTION OF THE DRAWINGS 
     Reference is now made to the accompanying figures depicting aspects of the present invention, in which: 
       FIG. 1  is a schematic cross-sectional view of a generic gas turbine engine to illustrate an example of a general environment in which the invention can be used; 
       FIG. 2  is a schematic side view of a fuel manifold provided with a heat shield in accordance with a possible embodiment of the present invention; and 
       FIG. 3  is a schematic cross-sectional view taken along line III-III in  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  schematically illustrates an example of a gas turbine engine  10  of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan  12  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 section  18  for extracting energy from the combustion gases. Fuel is provided to combustor  16  through fuels nozzles (not shown) fed by an internal fuel manifold. This figure illustrates an example of the environment in which the present invention can be used. 
     FIG. 2  is a schematic side view of an example of an annular fuel nozzle manifold  20  provided within a heat shield  22  in accordance with the present invention. This manifold  20  is located adjacent the combustor  16  of the engine  10 . The manifold  20  comprises a body  20   a  which is preferably surrounded on all sides by the heat shield  22 , as shown in  FIG. 3 , to help shield it from heat inside the engine  10 . 
   The manifold  20  comprises a plurality, and preferably at least three, radially-extending supports  24 . These supports  24  are preferably symmetrically disposed on a radially outer wall of the manifold  20 . The supports  24  are welded or otherwise attached to the manifold  20 . The supports  24  preferably in the form of pins having a circular cross-section, although other shapes are possible as well. The manifold  20  comprises a plurality of fuel nozzles (not shown) connected to one of the radially extending walls. The fuel nozzles project out of the heat shield  22  through corresponding holes (not shown). Fuel is supplied into the manifold  20  through at least one of the supports  24  and is distributed inside the manifold  20  through its internal cavity  20   b.    
     FIG. 3  shows that the heat shield  22  is preferably made of a main U-shaped part  22   a  which is closed, on one of its side, by an side wall  22   b  crimped to the U-shaped part  22   a . Other configurations are also possible, as will be understood by the skilled reader. 
   The heat shield  22  includes a plurality of holes (not indicated) corresponding to the supports  24 , and preferably also comprises bosses  26 , one for each hole and support  24 . Each hole and boss  26  is slidably engaged over a corresponding support  24 . These supports  24  project out of these holes, which are provided in a radially outer wall of the heat shield  22 . Each boss  26  is preferably rigidly connected to the periphery of one corresponding hole. The bosses  26  act as guides to guide the heat shield as it thermally expands relative to the supports. Such expansion for an annular body is usually radial in direction (if the heat shield is otherwise unconstrained) and thus the supports  24  are preferably radially oriented. The supports are thus preferably adapted to facilitate at least one degree of freedom for thermal expansion. In this embodiment, the adaptation includes radial orientation and sliding fit, but in other embodiments the adaptation may be any suitable for that embodiment. 
   As can be appreciated, using supports  24  and the corresponding holes in heat shield  22 , and with preferably corresponding bosses  26  preferably installed within the holes, allows the heat shield  22  being floatingly suspended relative to the manifold  20  and therefore be maintained in position but out of contact with the manifold body  20   a . When heated, the heat shield  22  may expand (in this case, radially) without imposing any stress on the manifold  20 , and yet guided to maintain its general relative position vis-a-vis the manifold  20 . 
   Each support  24  is preferably made of a material having a low thermal conductivity. This will reduce the amount of heat transmitted to the manifold body  20   a , either from the tip of the supports  24  or from the heat shield  22 , or the engine case. 
   The present invention also provides a method of heat shielding an annular fuel nozzle manifold  20 . This method comprises providing at least three radially-extending supports  24  on a radially outer wall of the manifold  20 . The manifold  20  is then enclosed in a heat shield  22  and the two of them are maintained in a spaced-apart relationship. The radially-extending supports  24  of the manifold  20  then project out of the heat shield  22  through the corresponding holes located on a radially outer wall of the heat shield  22 . Each hole is provided with a boss  26  located on its periphery and engaged over one corresponding support  24 . 
   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 shape, configuration and construction of the manifold  20  and/or heat shield  22  can be any suitable for a given application. Any suitable number of supports  24  can be provided. The supports need not be “pins” per se, but rather may be any suitable support arrangement having the functions herein disclosed. The invention may be applied to any suitable engine. Bosses need not support the heat shield relative to the supports, and any suitable alternative may be used, such as floating collars, sliding guides, etc. Fuel may also be provided through another inlet that is not one of the supports  24 . 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.