Abstract:
A combustor swirler for a gas turbine engine and method of manufacturing by metal injection molding an inner component and an outer cylindrical component. Indentations are molded in one of the inner and outer components and sealed by the engagement of the components together to form a series of fluid flow passages. The inner and outer components are molded with interlocking features for ensuring proper alignment of the components during assembly.

Description:
TECHNICAL FIELD 
   The invention relates generally to a combustor for gas turbine engines and, more particularly, to a combustor swirler and method of manufacturing same. 
   BACKGROUND OF THE ART 
   Gas turbine engine combustor air swirlers are exposed to a hot, corrosive environment. It is therefore necessary that they be fabricated of special high temperature alloys. Conventionally employed swirler manufacturing techniques include casting and/or milling combined with subsequent machining steps such as drilling and deburring. Due to the aerodynamic function of the component, care is required to ensure a suitable air flow is produced through the device. However, the special materials employed are not easily cast nor machined. A major disadvantage of casting lies in the difficulty of attaining the close tolerances required for the type of metallic seals involved. 
   Still further, most swirlers include critical guide air metering holes that are typically drilled one by one; thus, entailing a lengthy time consuming process that is expensive. Also, substantial effort is involved in deburring the holes which further increases costs. Not only does manual finishing considerably raise costs and require great precision to complete, but the result is variable due to its manual nature. It can be concluded that conventional machining, drilling and finishing operations for manufacturing combustor swirlers are time and cost ineffective. Consequently, the swirlers are undesirably expensive to manufacture by conventional means. Therefore, opportunities for cost-reduction exist. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of this invention to provide an improved aerodynamic combustor swirler for a gas turbine engine which addresses the above-mentioned issues. 
   In one aspect, the present invention provides a combustor air swirler comprising: a metal injection moulded outer component, a metal injection moulded inner component concentrically assembled to the outer component such that an annular gap is defined therebetween, the annular gap having an opening defined between a first end of the inner component and the outer component, a series of indentations provided in a first one of said inner and outer components, the indentations being sealed by a sealing surface provided on a second one of said inner and said outer components to form a series of fluid flow passages in flow communication with the annular gap. 
   In another aspect, the present invention provides method of manufacturing a combustor swirler for a gas turbine engine comprising: metal injection moulding an inner component, the inner component defining an inner cavity adapted to receive a fuel nozzle, metal injection moulding an outer component adapted to be fitted over the inner component; one of said inner and said outer components being moulded with a series of slots in a surface thereof, sealing the slots to form corresponding fluid flow passages by assembling the inner component coaxially with the outer component. 
   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 view of a gas turbine engine, in partial cross-section; 
       FIG. 2  is a perspective view of a combustor swirler, in accordance with a first embodiment of the present invention, engaged with a fuel nozzle and mounted into an opening in a dome of a combustion chamber of the gas turbine engine of  FIG. 1 ; 
       FIG. 3  is an exploded view of the combustor swirler of  FIG. 2 , showing a first perspective of inner and outer cylindrical components thereof; 
       FIG. 4  is an exploded view of the combustor swirler of  FIG. 2 , showing a second perspective of the inner and outer cylindrical components thereof; 
       FIG. 5  is a cross-sectional view of the combustor swirler of  FIG. 2 ; and 
       FIG. 6  is an exploded view of a three-piece combustor swirler showing an inner and outer cylindrical component and an annulus. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates a gas turbine engine  10  according to one embodiment of the present invention, the gas turbine engine 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  18  for extracting energy from the combustion gases. 
     FIG. 2  illustrates the combustor  16  having a combustion chamber  20  and an annular combustor dome  22  defining an opening  24  therein. An embodiment of a combustor swirler  26  is illustrated mounted in the opening  24  of the combustor dome  22  and engaged with a fuel nozzle  28 . In use, the combustor swirler, which is an aerodynamic component, receives and mixes pressurized air from the compressor  14  with fuel that it receives from the fuel nozzle  28 . Notably, imparting an aerodynamic swirl to the fuel and to the air yields a relatively high degree of air-fuel blending. The fuel and air mixture is discharged from the swirler  26  to pass through the dome  22  into the combustor  16  wherein it is conventionally ignited for generating the hot combustion gases. Thus, the expanding gases caused by the fuel ignition drives the turbine  18  in a manner well known in the art. 
   Notably, the combustor  16  may take any conventional form, and typically includes a plurality of swirlers and respective fuel nozzles. In such an arrangement, the swirlers and fuel nozzles are generally equally spaced about the combustion chamber  20  and must supply exactly the same quantity of fuel and impart the correct aerodynamic effect in order to permit a substantially uniform temperature distribution to promote efficient burning of the fuel in the combustion chamber. 
   Now referring concurrently to  FIGS. 2 to 5 , the combustor swirler  26  is illustrated comprising an outer and an inner cylindrical component  30  and  32  respectively. The outer component  30  has first and second peripheral edges  34  and  36  respectively and exterior and interior surfaces  38  and  40  respectively. The outer component  30  defines an axial bore  42  circumscribed by the aerodynamic interior surface  40 . 
   Referring particularly to  FIGS. 3 and 4 , the outer cylindrical component  30  comprises a plurality of aerodynamic indentations  44  circumferentially defined along the first peripheral edge  34  extending from the exterior surface  38  to the interior surface  40 . The indentations  44  can be provided as rounded slots, and more specifically U-shaped slots. 
   The outer component  30  comprises a mounting flange  46  disposed proximal to the second peripheral edge  36  extending from the exterior surface  38 . The mounting flange  46  includes a plurality of holes  48  enabling fluid flow communication for purging the combustor dome region and preventing re-circulation or entrainment of hot gases back to the dome  22 . The holes  48  are circumferentially distributed proximal to the exterior surface  38  of the outer cylindrical component  30 . The holes  48  are angled towards the axial bore  42 . 
   Furthermore, the mounting flange  46  includes an anti-rotation catch  50 , for engagement with a corresponding feature in the dome  22  to prevent rotation of the combustor swirler  26  as will be described in detail furtheron. In the present exemplary embodiment, the anti-rotation catch  50  is provided as a tang extending radially from the mounting flange  46 . It should be understood that other alternatives obvious to a person skilled in the art exist. 
   The inner component  32  has an aerodynamic exterior surface  52  and interior surface  54  respectively and defines an axial bore  56  circumscribed by the interior surface  54 . The axial bore  56  is adapted to sealingly receive the fuel nozzle  28 . The inner component  32  has a first and a second end  58  and  60  respectively and a flange  62  extending from the exterior surface  52  at a first end  58  thereof. 
   Now referring to  FIG. 5 , when the outer and inner components  30 ,  32  are concentrically assembled, an annular gap  64  is defined therebetween. An annular gap opening  66  is defined between the second end  60  of the inner component  32  and the second peripheral edge  36  of the outer cylindrical component  30 . The flange  62  of the inner cylindrical component  32  abutting the first peripheral edge  34  of the outer component  30  thereby enclosing the indentations  44  to form aerodynamic fluid flow passages  68  for communicating and swirling a flow of fluid into the annular gap  64 . The fluid exiting the annular gap opening  66  mixing with fuel ejected by the fuel nozzle  28  in the combustor  16 . 
   The indentations  44  forming the fluid flow passages  68  are angled and radially offset. By varying the angle and radial offset the swirl strength is also varied such that a given fuel placement within the combustion chamber  20  will result. Thus, by appropriately selecting the slot offset and corresponding aerodynamic swirl strength, the desired radial spray pattern can be achieved. The size of the indentations  44  is chosen such as to achieve a desired stiochiometry in the primary zone of the combustion chamber  20   n  in co-operation with various other fuel nozzle aerodynamic parameters. 
   Furthermore, to assist in concentrically aligning the outer and inner components  30  and  32  during assembly, alignment means are employed as best shown in  FIGS. 3 and 4 . The alignment means are provided as detents  70  on flange  62  of the inner component  32  for engagement with the outer component  30  by snap fitting into corresponding grooves  72  provided on the second peripheral edge  36  thereof. Notably, the grooves  72  do not interfere with the indentations  44  on the second peripheral edge  36 . The number and shapes of detents can vary. It should be understood that any suitable alignment means may be used. 
   Now referring to  FIG. 2 , the assembled combustor swirler  26  mounted to the combustor  16  and engaged with the fuel nozzle  28  is illustrated. In order that the fuel nozzle  28  sealingly engage the combustor swirler  26  while allowing for thermal expansion and contraction of the diameter of the combustor  16 , the combustor swirler  26  must be received in the opening  24  defined in the dome  22  such that it is allowed to ‘float’ on the combustor. Once the fuel nozzle  28  is in place, air pressure acting on the combustor swirler  26  will push the latter against the combustor  16  thereby sealing any leakage past the combustor swirler  26 . The mounting flange  46  of the combustor swirler  26  is adapted to be received within the combustion chamber  20  between a pair of rails  74  such that it circumscribes the opening  24 . Partial movement of the combustor swirler  26  relative to the combustor  16  is feasible. 
   More specifically as depicted in  FIG. 2 , the combustor swirler  26  is trapped within the combustor dome  22  by an outer sheet metal skin  76  and an inner float wall  78  that is bolted to the combustor  16 , the skin  76  and the float wall  78  acting as the rails  74 . A cut-out  80  in the float wall  78  is provided to receive the anti-rotation catch  50  for restricting swirler rotation. Such a feature is advantageous in reducing the wear of the part by preventing vibration induced spinning. 
   Now referring to  FIG. 6 , it can be seen, that the mounting flange  46  can be provided as a separate entity in the form of an annulus identified by reference numeral  82 . The annulus  82  has an inside perimeter  84  defining a plurality of indentations  86  in a similar fashion to the indentations  44  defined along the first peripheral edge  34 . 
   When the annulus  82  is assembled to the outer cylindrical component  30 , the inside perimeter  84  is in abutting relation with the exterior surface  38  of the outer cylindrical component  30 . Thus, the indentations  86  are enclosed thereby forming a fluid flow path for a purge flow as previously described. Again, aligning means such as detents (not shown) can be used between the inside perimeter  84  and the exterior surface  38  for alignment purposes. 
   The combustor swirler  26  exemplified herein was carefully designed to allow for a manufacturing method that would yield a low cost component and yet provide aerodynamic surfaces of sufficient quality to meet the demands of very high efficiency gas turbine engines. All features of the combustor swirler  26 , except for the purge holes in  FIGS. 1 to 5 , are deliberately designed to exploit metal injection moulding (MIM) manufacturing methods. For example, the utilization of indentations to form aerodynamic air flow passages for swirling and metering the air entering the annular gap rather then conventionally drilled holes illustrates the incorporation of a feature propitiously suited for MIM into the design. 
   Moreover, MIM processes allow for maintaining tight tolerances with difficult materials, such as high temperature alloys and/or ceramic metal composites. To employ MIM techniques, a special tool (not shown) is designed, into which feedstock, which consists of an atomized metal and a binding agent, is injected through a gate in the tool and then elements of the tool retracted such that the injected component is easily removed. Conventional, angled air feed holes are purposely avoided. Such holes require pins in the tool around which the feedstock is injected. These pins are very small in diameter based on the amount of air required through the combustor swirler. Consequently the pins are susceptible to bending since injection moulding is performed at high pressures. Furthermore, the pins would need to be individually retracted since the holes are angled. As a result using angled holes in an injection-moulded swirler is not considered cost effective and robust from a process perspective. Alternatively, the use of enclosed indentations to swirl and meter the air entering the annular gap allow for a design that can be readily produced by MIM. 
   Particularly, one way in which the indentations can be produced is by injecting feedstock into a tool followed by simple axial and/or radial withdrawal thereof, allowing for easy part removal. 
   Therefore, a method of manufacturing the combustor swirler  26  comprises the steps of metal injection moulding the inner component  32  having flange  62  at first end  58  and the outer component  30  having the plurality of circumferentially distributed indentations  44  defined along the first peripheral edge  34 . The method of manufacturing further comprises assembling the inner component  32  coaxially with the outer component  30  such that the flange  62  abuts the first peripheral edge of the outer component enclosing the indentations  44  to form radial fluid flow passages. Each of the two components is injected separately: into separate tools and may be oversized. 
   The method can further comprise the step of producing a seamless interface between the abutting surfaces of the inner and outer component  32  and  30 . The seamless interface can be produced by co-sintering the inner and outer component  32  and  30  to yield a single inseparable combustor swirler  26 . 
   Still further, the inner and outer component  32  and  30  can be partially deboud. Debinding is achieved by placing the inner and outer component  32  and  30  in an aqueous solution. The solution is selected in corresponding relation to the binding agent employed during MIM. Remaining binder is removed by co-sintering parts to get one inseparable piece. Parts can be individually sintered but would then require brazing or welding to attach them subsequently. At this stage the components shrink to their final intended size. Subsequently the inner and outer component  32  and  30  are assembled and co-sintered to form a single densified inseparable final piece as above-mentioned. Once successful sintering is complete, no metallurgical boundary exists at the mating interface of the inner and outer component  32  and  30 . 
   Advantageously, the detents  70  provide additional surface area for co-sintering and enhance the strength of the attachment between the inner and outer component  32  and  30  during sintering. However, the detents  70  are designed such that they can be readily moulded and thus involve no additional cost. 
   Moreover, the sintered combustor swirler  26  can further be hot isostatically pressed (HIP) to achieve full densification, and thus, superior material properties. Any remaining vestige at gating surfaces can also be removed by various low cost finishing methods. 
   In the case of  FIG. 6  in which three components are involved, the same method of manufacturing applies. Each component is individually injected and then the three components are simultaneously co-sintered. However, co-sintered attachment is along two surfaces as opposed to just one. With the indentations  86  defined along the inside perimeter  84  of the annulus  82 , the annulus can be easily moulded and does not need to be later drilled. 
   The result of this design and corresponding manufacturing method is a low cost component with superior quality. Advantageously, the manufacturing process is readily repeatable, thus the part exhibits very reproducible airflow results. In the exemplified method of manufacturing, no brazing or welding is required to produce a seamless interface between the inner and outer component  32  and  30  and no finishing or deburring is required to finalize the enclosed indentations on the injection moulded part. What&#39;s more, any number of indentations can be chosen with no extra recurring cost involved in moulding as the combustor swirler design exemplified herein is propitiously suited for MIM manufacturing methods. 
   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 department from the scope of the invention disclosed. 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.