Abstract:
A flowpath apparatus for a gas turbine engine includes: a plurality of ducts arranged in an array, each duct including a peripheral wall structure having a closed perimeter that defines a flow channel from an upstream end to a downstream end thereof; and a support structure positioning a the plurality of ducts in an array configuration.

Description:
[0001]    The U.S. Government may have certain rights in this invention pursuant to contract no. FA8650-09-D-2922 awarded by the Department of the Air Force. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates generally to gas turbine engines and in particular to flowpath structures within a gas turbine engine. 
         [0003]    A typical gas turbine engine includes a turbomachinery core having a high pressure compressor, a combustor, and a high pressure turbine in serial flow relationship. The core is operable in a known manner to generate a primary gas flow. In practical applications the core is typically combined with other elements such as power turbines, fans, augmentors, etc. to create a useful engine for a specific application, such as turning a propeller, powering an aircraft in flight, or driving a mechanical load. 
         [0004]    Gas turbine engines include a flowpath defined in part by ducts, liners, tubes, and similar structures that directs a working fluid through the various components of the engine. Some portions of the flowpath are subject to hot, high-velocity gases. Prior art flowpath components, particularly those in the hot section of the engine, often use metal alloy structures protected with a thermal barrier coating (“TBC”). 
         [0005]    Metallic structures can be replaced with materials having lower density, such as ceramic matrix composites (CMCs). Such materials offer significant weight savings compared to metal alloys. 
         [0006]    One problem with CMC materials is that they cannot be fabricated or mechanically fastened in the same way as components made from metal alloys, and therefore cannot be substituted directly for metallic components. 
         [0007]    Another problem with CMC materials is that they have relatively low tensile ductility or low strain to failure when compared to metallic materials. Also CMCs have a coefficient of thermal expansion (CTE) significantly different from metal alloys. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    At least one of the above-noted problems is addressed by a flowpath assembly including two or more ducts each having a perimeter wall structure that defines a flow channel, the ducts being assembled into an array using a support structure. 
         [0009]    According to one aspect of the technology described herein, a flowpath apparatus for a gas turbine engine includes: a plurality of ducts arranged in an array, each duct including a peripheral wall structure having a closed perimeter that defines a flow channel extending from an upstream end to a downstream end thereof; and a support structure positioning the plurality of ducts in an array configuration. 
         [0010]    According to another aspect of the technology described herein, a flowpath apparatus for a gas turbine engine includes: an annular central member; a plurality of ducts arranged in a ring around the annular central member, each duct comprising a peripheral wall structure having a closed perimeter that defines a flow channel extending from an upstream end to a downstream end thereof; at least one ring surrounding the plurality of ducts; and a radial array of radial members extending between the central member and the at least one ring. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
           [0012]      FIG. 1  is a side elevation view of an exemplary duct; 
           [0013]      FIG. 2  is an aft elevation view of the duct of  FIG. 1 ; 
           [0014]      FIG. 3  is a top plan view of the duct of  FIG. 1 ; 
           [0015]      FIG. 4  is a side half-sectional view of an exemplary flowpath assembly using the duct shown in  FIGS. 1 and 2 ; 
           [0016]      FIG. 5  is a view taken along lines  5 - 5  of  FIG. 4 ; 
           [0017]      FIG. 6  is a view taken along lines  6 - 6  of  FIG. 5 ; 
           [0018]      FIG. 7  is a half-sectional view of an exemplary flowpath assembly; 
           [0019]      FIG. 8  is a view taken along lines  8 - 8  of  FIG. 7 ; 
           [0020]      FIG. 9  is a half-sectional view of an exemplary flowpath assembly; 
           [0021]      FIG. 10  is a view taken along lines  10 - 10  of  FIG. 9 ; and 
           [0022]      FIG. 11  is a view taken along lines  11 - 11  of  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,  FIG. 1  depicts an exemplary duct  10  which may be used to construct various types of flowpath assemblies as described in more detail below. The duct  10  includes a perimeter wall structure  12  that extends from an upstream end  14  to a downstream end  16 . The perimeter wall structure  12  extends around a closed perimeter thereby surrounding and defining a flow channel  19  that extends from the upstream end  14  to the downstream end  16 . 
         [0024]    A longitudinal axis “A” is shown in  FIG. 1  representing an axial or longitudinal direction. A radial axis “R” is perpendicular to the longitudinal axis A and represents a radial direction. As seen in  FIG. 2 , a tangential axis “T” is perpendicular to both the longitudinal axis A in the radial axis R, and represents a circumferential or tangential direction. As used herein, directional terms such as axial, radial, and tangential used for purposes of convenient reference in description and do not require that the described structures have any particular absolute orientation. 
         [0025]    The perimeter wall structure  12  may take any convenient form as required for a particular application. In the specific example illustrated, the perimeter wall structure  12  includes a pair of spaced-apart lateral walls  18 . Inboard ends of the lateral walls  18  are connected by an inboard wall  20 , which is a body of revolution generated about longitudinal axis A. Outboard ends of the lateral walls  18  are connected by an outboard wall  22 , which is also a body of revolution, generated about longitudinal axis A. In this configuration, the flow channel  19  has a roughly trapezoidal flow area. 
         [0026]    The perimeter wall structure  12  may be built up from a group of components. The components could be bonded, mechanically fastened or otherwise joined. Alternatively, the perimeter wall structure  12  may be an integral, unitary or monolithic structure. 
         [0027]    As noted above, other forms are possible to suit particular applications. For example, the separate inboard wall  20  could be eliminated and the pair of lateral walls  18  could merge together at their mutual inboard ends, forming a roughly triangular flow area. Other possibilities include polygonal and curvilinear shapes. 
         [0028]    The flow channel  19  may have a constant flow area from the upstream end  14  to the downstream end  16 . Alternatively, the ratio of flow area at the downstream end  16  to the upstream end  14  may be other than unity. In other words, the area may increase or decrease in the direction of flow through the flow channel  19 , with the result that the duct  10  then functions as a nozzle or diffuser. 
         [0029]    The flow channel  19  may be axially aligned, or it may be oriented to affect the tangential velocity of a fluid flowing through it. For example it may be used to increase or decrease the tangential velocity or “swirl” of the fluid. A non-axial orientation is illustrated by dashed lines in  FIG. 3 . 
         [0030]    The duct  10  may be constructed in whole or in part from a low density, high-temperature capable material. Examples of such materials include composite materials such as ceramic matrix composites (“CMC”). Generally, commercially available CMC materials include a ceramic type fiber carried in a ceramic type matrix. Examples of known types of CMC materials are referred using broad classifications of SiC/SiC, C/SiC, C/C, and Ox/Ox (oxide-oxide). 
         [0031]    In general, such materials have a low density, high-temperature capabilities, and high strength-to-weight ratios, but also have lower ductility than metal alloys and are generally more difficult to fabricate and to mechanically fasten than metal alloys. These materials will be referred to generally herein as “ceramic-based composites”. 
         [0032]    As a general principle, two or more of the ducts  10  described above may be assembled to define a flowpath structure by using a support structure, for example one or more struts, braces, brackets, or rings, to support and position the ducts  10  in an array of two or more ducts. Nonlimiting examples of arrays include lines, rectangles, polygons, arcs, or ring configurations. Nonlimiting examples of structures utilizing such arc or ring configurations include inlet and exhaust systems, flowpaths, and turbine frames. In creating the flowpath structure, the ducts  10  may have different wedge shapes, orientation angles, etc. to accommodate the support structure (for example, struts of varying sizes). Furthermore, some or all of the ducts  10  could be of different contours assembled into a serpentine or other shaped non-round exhaust system or other flowpath. 
         [0033]      FIGS. 4-6  illustrate an exemplary flowpath assembly  24 . This specific example would be located just aft of a final turbine stage or a turbine rear frame (not shown) in a mixed-flow turbofan engine and upstream of an augmentor or afterburner (not shown) in such an engine. The basic components of the flowpath assembly  24  include a hub  26 , an inner diffuser liner  28 , a centerbody  30 , an array of ducts  10 , an array of forward closeouts  32 , an array of aft closeouts  34 , a forward ring  36 , and an aft ring  38 . Each of these components will be described in more detail below. 
         [0034]    The hub  26  is a central structural member and is generally annular with a forward end  40  and an aft end  42 . It may be constructed, for example, from a metal alloy. An array of forward tabs  44  extend axially forward from the forward end  40 . An array of aft tabs  46  extends axially aft from the aft end  42 . Each of the forward tabs  44  and aft tabs  46  is a relatively thin elongated member which is able to resiliently flex such that its distal end can move inward or outward in the radial direction. 
         [0035]    A plurality of ducts  10  as described above and shown in  FIGS. 1-3  are arrayed in an annulus or ring around the hub  26 . The ducts  10  are positioned such that one of the lateral walls  18  of a first duct  10  lies closely adjacent to one of the lateral walls  18  of the adjacent duct  10 , thus defining a gap  48  between the two adjacent ducts  10 . In the illustrated example, the ducts  10  serve as mixers. In order to accomplish this function, the perimeter wall structure  12  is perforated with a plurality of holes  50 . In operation, a core flow stream “C” passes through the flow channel  19 , while the space exterior to the ducts  10  is exposed to a fan flow stream “F” which has a higher static pressure than the core flow stream C. In operation, the fan flow stream F passes through the holes  50  and mixes with the core flow stream C. 
         [0036]    The forward ring  36  surrounds the upstream ends  14  of the ducts  10  and maintains their lateral spacing. Any suitable means of attachment may be used. In the illustrated example, mechanical fasteners  52  extend through the forward ring  36  and through corresponding holes  54  in the duct  10 . Various means may be used to prevent concentrated loads from being applied to the ducts  10  by the mechanical fasteners  52 . 
         [0037]    The forward closeouts  32  are arrayed in an annulus or ring around the hub  26 . Each forward closeout  32  is positioned in tangential alignment with the gap  48  between two adjacent ducts  10 . As seen in  FIG. 6 , the forward closeout  32  has a generally C-shaped section which accepts the lateral walls  18  of adjacent ducts  10  and seals the gap  48 . The outboard ends of the forward closeouts  32  are coupled to the forward ring  36 , for example using the illustrated fasteners  55 . The inboard ends of the forward closeouts  32  are coupled to the hub  26 . In the illustrated example, the forward closeouts  32  include pins  56  that extend radially inward through holes  58  in the hub  26 . 
         [0038]    The aft ring  38  surrounds the downstream ends  16  of the ducts  10  and maintains their lateral spacing. Any suitable means of attachment may be used. In the illustrated example, mechanical fasteners  60  extend through the aft ring  38  and through corresponding holes  62  in the duct  10 . Various means may be used to prevent concentrated loads from being applied to the ducts  10  by the mechanical fasteners  60 . 
         [0039]    The aft closeouts  34  are arrayed in an annulus or ring around the hub  26 . Each aft closeout  34  is positioned in tangential alignment with the gap  48  between two adjacent ducts  10 . The aft closeout  34  has a generally C-shaped section similar to that of the forward closeout  32 , which accepts lateral walls  18  of adjacent ducts  10  and seals the gap  48 . The outboard ends of the aft closeouts  34  are coupled to the aft ring  38 , for example using the illustrated fasteners  64 . The inboard ends of the aft closeouts  34  are coupled to the hub  26 . In the illustrated example, the aft closeouts  34  include pins  66  that extend radially inward through holes  68  in the hub  26 . 
         [0040]    In the illustrated example, the aft closeouts  34  also function as a portion of an augmentor or afterburner. One or more of the aft closeouts  34  incorporate a radial flameholder  70  and one or more of the aft closeouts  34  incorporate a radial spraybar  72  which is operable to receive fuel and discharge it through a series of holes or nozzles. The fuel would then be ignited and burned to produce additional thrust in a downstream combustion section of an augmentor or afterburner (not shown). 
         [0041]    The inner diffuser liner  28  is a generally annular structure and may be made from a ceramic-based composite. An aft end  74  of the inner diffuser liner  28  sits over the ring of forward tabs  44  and may be attached thereto by the illustrated fasteners  76 . This arrangement permits some radial compliance between the hub  26  and the inner diffuser liner  28 . 
         [0042]    The centerbody  30  is a generally conical structure and may be made from a ceramic-based composite. A forward end  78  of the centerbody  30  sits over the ring of aft tabs  46  and may be attached thereto by the illustrated fasteners  80 . This arrangement permits some radial compliance between the hub  26  and the centerbody  30 . 
         [0043]    In operation, the hub  26 , the forward closeouts  32 , aft closeouts  34 , the forward ring  36 , and the aft ring  38  define a support structure which position the ducts  10  so that they define a flowpath. The ducts  10  are thus able to perform the function of containing and guiding a flow of hot high velocity gases. It is believed that the complete flowpath assembly  24  would weigh less than an equivalent structure constructed solely of metal alloys. 
         [0044]      FIGS. 7 and 8  illustrate an example of a another type of flowpath assembly  124  that may be constructed using ducts as described above. The basic components of the flowpath assembly  124  include a sump housing  126 , an array of ducts  100 , an array of forward closeouts  132 , an array of aft closeouts  134 , a forward ring  136 , and an aft ring  138 . Each of these components will be described in more detail below. 
         [0045]    The sump housing  126  is a central structural member and is generally annular with a forward end  140  and an aft end  142 . It may be constructed, for example, from a metal alloy. The sump housing  126  surrounds a shaft  182 . The annular volume located between the sump housing  126  and the shaft  182  is referred to as a “sump”  184 . Within the sump  184 , the shaft  182  is mounted in a rolling-element bearing  186 . The bearing  186  is bounded by seal assemblies  188 . An annular bearing support arm  190  extends radially inward from the body and receives an outer race  192  of the bearing  186 . An inner race  194  of the bearing  186  is mounted to the shaft  182 . 
         [0046]    A pair of annular seal support arms  196  extend inward from the bearing sump housing  126 . Each seal support arm  196  carries a stationary portion of a seal assembly  188 . A rotating portion of each seal assembly  188  is mounted to the shaft  182 . In the illustrated example, the seal assemblies  188  are noncontact seals such as labyrinth seals. 
         [0047]    A plurality of ducts  100  are arrayed in an annulus or ring around the sump housing  126 . The ducts  100  are generally similar in construction to the ducts  10  described above and include upstream and downstream ends  114 ,  116 , respectively, a pair of spaced-apart lateral walls  118 , an inboard wall  120 , and an outboard wall  122 . Elements of the ducts  100  not specifically described may be assumed to be identical to the ducts  10  described above. The ducts  100  are positioned such that one of the lateral walls  118  of a first duct  100  lies closely adjacent to one of the lateral walls  118  of the adjacent duct  100 , thus defining a gap  148  between the two adjacent ducts  100 . 
         [0048]    The forward ring  136  surrounds the upstream ends  114  of the ducts  100  and maintains their lateral spacing. In the illustrated example, mechanical fasteners  152  extend through the forward ring  136  and through corresponding holes  154  in the duct  100 . 
         [0049]    The forward closeouts  132  are arrayed in an annulus or ring around the sump housing  126 . Each forward closeout  132  is positioned in tangential alignment with the gap  148  between two adjacent ducts  10 . The forward closeout  132  may include a generally C-shaped section which accepts the lateral walls  118  of adjacent ducts  100  and seals the gap  148 . The outboard ends of the forward closeouts  132  are coupled to the forward ring  136 , for example using the illustrated fasteners  155 . The inboard ends of the forward closeouts  132  are coupled to the sump housing  126 , for example using the illustrated mechanical fasteners  156 . 
         [0050]    The aft ring  138  surrounds the downstream ends  116  of the ducts  100  and maintains their lateral spacing. In the illustrated example, mechanical fasteners  160  extend through the aft ring  138  and through corresponding holes  162  in the duct  100 . 
         [0051]    The aft closeouts  134  are arrayed in an annulus or ring around the sump housing  126 . Each aft closeout  134  is positioned in tangential alignment with the gap  148  between two adjacent ducts  100 . The aft closeout  134  may include a generally C-shaped section similar to that of the forward closeout  132 , which accepts lateral walls  118  of adjacent ducts  100  and seals the gap  148 . The outboard ends of the aft closeouts  134  are coupled to the aft ring  138 , for example using the illustrated fasteners  164 . The inboard ends of the aft closeouts  134  are coupled to the sump housing  126 , for example using the illustrated mechanical fasteners  166 . The forward and aft closeouts  132  and  134  serve as a structural connection between the sump housing  126  and the ring  136  and  138 , so that the ducts  100  do not carry external structural loads. 
         [0052]      FIGS. 9-11  illustrate an example of another type of flowpath assembly  224  that may be constructed using ducts as described above. The basic components of the flowpath assembly  224  include a sump housing  226 , an array of ducts  200 , an array of struts  231 , an array of forward closeouts  232 , an array of aft closeouts  234 , a forward ring  236 , and an aft ring  238 . Each of these components will be described in more detail below. 
         [0053]    The sump housing  226  is a generally annular central structural member. It may be constructed, for example, from a metal alloy. The sump housing  226  surrounds a shaft  282  and defines a sump  284 . Within the sump  284 , the shaft  282  is mounted in a rolling-element bearing  286 . The bearing  286  is bounded by a pair of seal assemblies  288 . The construction of the sump housing  226 , the bearing  286 , and the seal assemblies  288  is similar to those described above. 
         [0054]    A plurality of ducts  200  are arrayed in an annulus or ring around the sump housing  226 . The ducts  200  are generally similar in construction to the ducts  10  described above and include upstream and downstream ends  214 ,  216 , respectively, a pair of spaced-apart lateral walls  218 , an inboard wall  220 , and an outboard wall  222 . Elements of the ducts  200  not specifically described may be assumed to be identical to the ducts  10  described above. The ducts  200  are positioned such that one of the lateral walls  218  of a first duct  200  lies closely adjacent to one of the lateral walls  218  of the adjacent duct  200 , thus defining a gap  248  between the two adjacent ducts  200 . 
         [0055]    The struts  231  are arrayed in an annulus or ring around the sump  226  and extend between the sump housing  226  and an outer ring  233 . The outer ring  233  may be continuous or segmented. The struts  231  are coupled to the sump  226 , and are also coupled to the outer ring  233 . In the illustrated example the struts  231  are shown as being integrally formed with the sump housing  226  and the outer ring  233 . The mechanical configuration of the struts  231  is not critical to the present invention and other arrangements are possible. For example the struts  231  may be separate components which are connected to the sump housing  226  and/or the outer ring  233  using mechanical fasteners. The struts  231  serve as a structural connection between the sump  226  and the outer ring  233 , so that the ducts  200  do not carry external structural loads. 
         [0056]    The forward ring  236  surrounds the upstream ends  214  of the ducts  200  and maintains their lateral spacing. In the illustrated example, mechanical fasteners  252  extend through the forward ring  236  and through corresponding holes  254  in the duct  200 . 
         [0057]    The forward closeouts  232  are arrayed in an annulus or ring around the sump housing  226 . Each forward closeout  232  is positioned in tangential alignment with the gap  248  between two adjacent ducts  10 . The forward closeout  232  may include a generally C-shaped section which accepts the lateral walls  218  of adjacent ducts  200  and seals the gap  248 . The outboard ends of the forward closeouts  232  are coupled to the forward ring  236 , for example using the illustrated fasteners  255 . The inboard ends of the forward closeouts  232  are coupled to the sump housing  226 , for example using the illustrated mechanical fasteners  256 . 
         [0058]    The aft ring  238  surrounds the downstream ends  216  of the ducts  200  and maintains their lateral spacing. In the illustrated example, mechanical fasteners  260  extend through the aft ring  238  and through corresponding holes  262  in the duct  200 . 
         [0059]    The aft closeouts  234  are arrayed in an annulus or ring around the sump housing  226 . Each aft closeout  234  is positioned in tangential alignment with the gap  248  between two adjacent ducts  200 . The aft closeout  234  may include a generally C-shaped section similar to that of the forward closeout  232 , which accepts lateral walls  218  of adjacent ducts  200  and seals the gap  248 . The outboard ends of the aft closeouts  234  are coupled to the aft ring  238 , for example using the illustrated fasteners  264 . The inboard ends of the aft closeouts  234  are coupled to the sump housing  226 , for example using the illustrated mechanical fasteners  266 . 
         [0060]    The flowpath assembly  224  is similar in configuration to a conventional turbine frame. In this arrangement the ducts  200  are effectively used as liners for the frame assembly. 
         [0061]    The flowpath assemblies described herein have numerous advantages over prior art flowpath structures. A frame assembly constructed using arrayed composite docs is overall less complex and less costly than a composite diffusing frame that might be constructed using discreet composite vanes in an attempt to directly mimic metallic component construction. This approach could be used as a means to line any frame such as a turbine center frame or a turbine rear frame. This approach can be adapted for inlets as well as exhaust systems. 
         [0062]    The foregoing has described a flowpath structure for a gas turbine engine. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. 
         [0063]    Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. 
         [0064]    The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying potential points of novelty, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.