Abstract:
A ceramic matrix composite wall structure ( 20 A) constructed of interlocking layers ( 22 A,  24 A) of woven material with integral cooling channels ( 28 A,  32 A). The CMC layer closest to the hot gas path ( 41 ) contains internal cooling tubes ( 26 A,  30 A) protruding into a ceramic insulating layer ( 40 A). This construction provides a cooled CMC lamellate wall structure with an interlocking truss core.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to ceramic matrix composites (CMC), and more particularly to a cooled CMC wall structure suitable for fabrication with oxide-oxide CMC materials. 
       BACKGROUND OF THE INVENTION 
       [0002]    Engine components exposed to the hot combustion gas flow of combustion turbine engines may be formed of a ceramic refractory material. A ceramic matrix composite (CMC) lamellate wall structure with a high temperature ceramic insulation coating, commonly referred to as friable grade insulation (FGI), is described in commonly assigned U.S. Pat. No. 6,197,424. Current materials of this type provide strength and temperature stability to temperatures approaching 1700° C. Cooling of such structures is generally limited to back side air impingement cooling. 
         [0003]    Future combustion turbine designs are expected to require ever increasing firing temperatures that may exceed the operating limits of such designs. An actively cooled CMC wall structure is described in commonly assigned U.S. Pat. No. 6,746,755 where cooling tubes are disposed between the layers of CMC material. Further improvements to permit operation at even higher temperatures are desired. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    The invention is explained in the following description in view of the drawings that show: 
           [0005]      FIG. 1  is a perspective sectional view of a CMC wall structure in an exemplary embodiment A of the invention; 
           [0006]      FIG. 2  is a sectional view of first and second CMC sheets with integral cylindrical tubes used to assemble the wall structure of  FIG. 1 ; 
           [0007]      FIG. 3  is a sectional view of the wall structure of  FIG. 1  showing fluid inlet, transfer, and outlet channels; 
           [0008]      FIG. 4  is a sectional view of first and second CMC sheets with semi-cylindrical tubes in an exemplary embodiment B of the invention; 
           [0009]      FIG. 5  is a sectional view of a CMC wall structure assembled from the sheets of  FIG. 4 ; 
           [0010]      FIG. 6  is an enlarged sectional view of two CMC cooling tubes and an integrally formed span between them; 
           [0011]      FIG. 7  is a view as in  FIG. 6  illustrating a geometry with generally uniform wall thickness of the tubes and the span; 
           [0012]      FIG. 8  is sectional view of a CMC wall structure in an exemplary embodiment C that combines a first CMC sheet from embodiment A with a second CMC sheet from embodiment B. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    The present inventors have found that existing 2D laminate CMC structures are sometimes limited by their relatively low interlaminar strength. An increase in the thickness of the CMC structure will often compensate for relatively low interlaminar strength, however, an increased thickness increases cost, size and weight and reduces the effectiveness of backside cooling. Three dimensional CMC architectures may be used; however, the present inventors have also found that 3D architecture preforms that are significantly greater in thickness than a single fabric ply cannot be infiltrated readily with current matrix infiltration methods. The CMC wall structure geometry of the present invention provides improved performance in interlaminar strength while also providing a means for effective matrix infiltration. 
         [0014]      FIG. 1  is a sectional view of a first of three embodiments of the present invention that are described herein. Reference numerals used to describe features illustrated in the drawings may include the suffix “A” for features unique to the first described embodiment, or they may include the suffix “B” for features unique to the second described embodiment. The third described embodiment includes features selected from the first (A) and the second (B) embodiments. 
         [0015]    CMC wall  20 A of  FIG. 1  is assembled from first and second CMC sheets  22 A,  24 A formed of thin 3D weaves with integral cylindrical tubes  26 A,  30 A providing fluid cooling channels  28 A,  32 A. In each sheet, the tubes  26 A or  30 A are connected in a parallel sequence by spans  29 A that are generally aligned between the centerlines of each pair of adjacent tubes  26 A or  30 A. This forms a corrugated first and second surface  36 A,  38 A on each sheet  22 A,  24 A. The sheets  22 A,  24 A are stacked in a nested configuration as in  FIG. 1  to construct an interlocking CMC sandwich with a corrugated front surface  36 A that provides an improved bonding surface (when compared to prior art non-corrugated planar or curved surfaces) for an insulating layer  40 A. The nested CMC corrugations  36 A,  38 A also provide improved bonding between the CMC sheets  22 A,  22 B. The resulting insulated CMC structure  20 A has a front surface  42 A exposed to hot combustion gasses  41 , and a corrugated back surface  44 A, and it exhibits improved interlaminar shear and tensile strength when compared to prior art designs. The front row of cooling tubes  26 A (i.e. closest to the heated surface  42 A) protrudes into the insulating layer  40 A and provides improved cooling effectiveness for the entire volume of CMC material throughout the wall structure. 
         [0016]      FIG. 2  illustrates two CMC sheets  22 A,  24 A before stacking. The tubes  26 A,  30 A may be woven around circular rods  34 A and connected by spans  29 A aligned with the rod centerlines. The rods  34 A may be of a fugitive material. This forms a substantially symmetric sheet structure  22 A that can be nested and interlocked with one or more other sheets  24 A as shown in  FIG. 1 , providing increased bond surfaces and tortuous interlaminar stress paths in the wall  20 A. The walls of the tubes  26 A,  30 A and the spans  29 A between them are fully accessible prior to stacking of the sheets  22 A,  24 A, so they can be infiltrated using conventional matrix transfer methods. While prior art full 3D weave options have been proven for non-oxide CMCs and polymer composites, they have not been feasible for processing oxide-matrix CMCs. The present invention may advantageously be applied to oxide-matrix CMCs. In one embodiment the thickness of the spans  29 A is between 1 and 2 times the thickness of the walls of the tubes  26 A,  30 A. The CMC layers may be bonded with an adhesive (not shown) or an integral sinter bond formed by co-processing of the layers. The insulating layer  40 A may be cast directly onto the corrugated surface  36 A and may be co-processed with the CMC material in one embodiment. 
         [0017]      FIG. 3  illustrates a CMC wall structure as in  FIG. 1  with coolant fluid inlets  46 ,  47 , transfer channels  48 , and fluid outlets  50 ,  52 ,  54 . These fluid paths  46 ,  47   48 ,  50 ,  52 ,  54  are shown schematically in the same plane for clarity only. For example, the fluid inlets  46  may be offset from the transfer channels  48  along an axial length of each back row tube  30 A, and the transfer channels  48  may be offset from the fluid outlets  50 ,  52 ,  54 , along an axial length of each front row tube  26 A, so that a cooling fluid  56  flows within a cooling channel  28 A,  32 A for given distance before exiting it. The fluid inlets  46 ,  47  conduct a cooling fluid  56  such as air from the back side  44 A of the wall structure  20 A into the cooling channels  32 A,  28 A. The fluid  56  may flow along a cooling channel then transfer to another channel via a transfer channel  48 . The heated cooling fluid may then exit the front surface  42 A of the insulating layer  40 A. Alternate fluid outlet configurations  50 ,  52 , and  54  are shown as examples. A plurality of fluid outlets such as  52  along each front row cooling channel  28 A may be angled relative to normal to the surface  42 A and/or may be fan shaped at the exit for maximum film cooling effectiveness. Cooling fluid may first enter a front row channel  28 A through inlet  47  so that the coolest cooling fluid is applied to the highest temperature location of the wall. After passing along a distance of channel  28 A, the somewhat heated fluid may then pass through a transfer channel  48  to a back row channel  32 A where the cooling demand is somewhat reduced due to the increased distance from the heated surface  42 A. After being further heated in channel  32 A, the now-spent cooling fluid may pass into the hot combustion fluid gas path  41  through outlet  54 . The various inlets, outlets and transfer channels may be formed by processes well known in the art, such as by using fugitive materials during lay-up of the wall fibers, or by mechanical removal of material from the wall such as by drilling. 
         [0018]      FIGS. 4 and 5  illustrate an embodiment B in which first and second CMC sheets  22 B,  24 B each have semi-cylindrical tubes  26 B,  30 B providing fluid cooling channels  28 B,  32 B. In each sheet, these tubes  26 B,  30 B are connected in a parallel sequence by spans  29 B that are generally aligned along a common side of the tubes  26 B,  30 B. This forms a smooth first surface  36 B and a corrugated second surface  38 B on each sheet  22 B,  24 B. The sheets  22 B,  24 B are stacked in a nested configuration with meshing corrugated surfaces as shown in  FIG. 5  to construct an interlocking CMC sandwich with non-corrugated surfaces. An insulating layer  40 B may be applied to a front surface  36 B of this sandwich, resulting in a CMC wall  20 B with smooth, non-corrugated (either planar or smoothly curved) front and back surfaces  42 B,  44 B. Embodiment B provides improved 3D weave CMC matrix infiltration and interlaminar bonding when compared to prior art designs. As in embodiment A, each of the sheets  22 B,  24 B can be impregnated individually with a ceramic matrix more effectively than if the complete CMC sandwich structure were made from an integrally woven preform. The interlocking corrugations  38 B provide superior shear strength and interlaminar tensile strength. The resulting assembly forms an interlocked truss-core wall structure.  FIG. 6  illustrates that the spans  29 B of each sheet  22 B,  24 B may be formed integrally with the respective tubes  26 B,  30 B, including continuous ceramic fibers or tows  58  crossing the spans.  FIG. 7  illustrates a geometry in which the spans  29 B have generally the same thickness as the walls of the tubes  26 B. 
         [0019]      FIG. 8  shows an embodiment C that combines a front sheet  22 A of embodiment A with a back sheet  24 B of embodiment B to form a hybrid wall structure  20 C. This embodiment provides improved interlaminar strength, improved surface layer bonding strength, and a smooth back surface  44 B, which can allow a thinner wall structure  20 C than wall  20 A of  FIG. 1 . 
         [0020]    While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. For example, the fluid inlet  46 , transfer  48 , and outlet channels  50 ,  52 ,  54  shown in  FIG. 3  may optionally be used with any of the embodiments A, B, C. Further, while only two sheets of CMC material are illustrated, additional layers may be used. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.