Patent Publication Number: US-6984101-B2

Title: Turbine vane plate assembly

Description:
STATEMENT REGARDING FEDERALLY SPONSORED DEVELOPMENT 
     Development for this invention was supported in part by Contract No. DE-FC21-95MC32267, awarded by the U.S. Department of Energy. Accordingly, the United States Government may have certain rights in this invention. 
    
    
     FIELD OF THE INVENTION 
     The invention relates in general to turbine engines and, more particularly, to a turbine vane plate assembly configured to direct the flow of a coolant through the vane and a method of assembling the same. 
     BACKGROUND OF THE INVENTION 
     Turbine engines include a plurality of stationary vane assemblies, which are exposed to extreme thermal loads. Accordingly, provisions must be made to cool the vane assemblies. Typically, vane assemblies are cooled by routing a coolant, such as steam or compressed air, through a plurality of interior passageways formed in the vane. At least a portion of the interior cooling passages can be formed by a cooperative arrangement between a vane shroud and a shroud end cap. While such end caps have been successfully used to close and direct coolant flow in a turbine vane, the design suffers from a number of disadvantages. 
     For example, due to the complexity of the interfacing surfaces of the shroud and the need for internal coolant paths, shroud end caps are typically cast, such as by investment casting, and/or require extensive machining. Thus, replication in a production environment is not possible. Moreover, due to the construction of the end cap, quality inspection cannot be conducted on various brazed or welded joints between the end cap and the surrounding shroud. Further, design considerations occasionally require an increase in the height of the shrouds, which results in commensurate increases in the thickness of the end cap. Consequently, structural interferences with other components are sometimes experienced during engine installation. 
     Thus, one object according to aspects of the present invention is to provide a turbine vane plate assembly that can be fabricated, assembled, and inspected using conventional manufacturing methods. Another object according to aspects of the present invention is to allow replication in a production environment using conventional methods. Yet another object according to aspects of the present invention is to reduce or eliminate the use of thick solid cast and machined plates for turbine vane end caps, and preferably to use standard gauge plates. A further object according to aspects of the present invention is to permit quality inspection at each layer of assembly and fabrication. Still another object according to aspects of the invention is to provide a turbine vane assembly with a plurality of plenums and passages for directing the flow of coolant throughout the vane. An additional object according to aspects of the present invention is to provide a turbine vane assembly having engine attachment structures. These and other objects according to aspects of the present invention are addressed below. 
     SUMMARY OF THE INVENTION 
     Aspects of the present invention relate to a turbine vane assembly that includes a turbine vane having first and second shrouds with an elongated airfoil extending between. Each end of the airfoil transitions into a shroud at a respective junction. Each of the shrouds has a plurality of cooling passages, and the airfoil also has a plurality of cooling passages extending between the first and second shrouds. The assembly further includes a substantially flat inner plate and an outer plate coupled to each of the first and second shrouds so as to form inner and outer plenums. 
     Each inner plenum is defined between at least the junction and the substantially flat inner plate; each outer plenum is defined between at least the substantially flat inner plate and the outer plate. Each inner plenum is in fluid communication with a respective outer plenum through at least one of the cooling passages in the respective shroud. The inner and outer plenums and coolant passages can direct coolant flow throughout the vane including coolant flow within the plenums generally transverse to the elongated direction of the airfoil. 
     The substantially flat inner plates and at least one of the outer plates can be gauge plate. At least one of the outer plates can include an outward-facing surface with one or more integral attachments. Each of the substantially flat inner plates can be coupled to a respective shroud by brazing or welding. Each of the outer plates can be coupled to a respective shroud by structural welding. Each of the first and second shrouds can have inner and outer ledge portions, which can be substantially parallel to each other. Each of the substantially flat inner plates can be coupled to a respective shroud proximate to the inner ledge portion; each of the outer plates can be coupled to a respective shroud proximate to the outer ledge portion. 
     The assembly can further include at least one coolant supply tube for supplying coolant to a trailing edge portion of the airfoil. The supply tube bypassingly extends through one pair of inner and outer plenums. The assembly can further include a first coolant supply duct extending between one of the outer plates and a respective substantially flat inner plate. The first duct can allow externally-supplied coolant to enter the inner plenum of one of the shrouds and to enter at least one of the cooling passageways in the airfoil. In addition, there can be a second coolant supply duct extending between the other substantially flat inner plate and the airfoil. The second duct can allow coolant entering at least one of the cooling passageways in the airfoil from the first duct to pass into the outer plenum of the other shroud. 
     The assembly can further include an exit duct extending between the airfoil and one of the substantially flat inner plates. One of the outer plates can include an opening that is fluidly aligned with at least a portion of the exit duct such that coolant can exit the assembly. 
     The inner plenum of the outer shroud can be in fluid communication with the inner plenum of the inner shroud through at least one of the cooling passages extending through the airfoil. 
     In other aspects, the present invention relates to a method of assembling a turbine vane including the following steps. 
     (a) Providing a turbine vane including an outer shroud, an inner shroud and an airfoil extending between the inner and outer shrouds. Each shroud has first and second ledge portions. The airfoil includes an inner and an outer landing surface at each of its ends, each landing surface having a plurality of openings. The shrouds and airfoil include a plurality of internal cooling passages. 
     (b) Securing a first end of a duct to the inner airfoil landing. The duct is fluidly aligned with one of the plurality of openings in the inner airfoil landing. 
     (c) Securing a first end of a channel to the outer airfoil landing. The channel is fluidly aligned with one of the plurality of opening in the outer airfoil landing. 
     (d) Securing a first end of a tube to the outer airfoil landing. The tube is fluidly aligned with one of the plurality of opening in the outer airfoil landing. 
     (e) Securing first and second substantially flat inner plates to the inner and outer shrouds. 
     (f) Securing a first substantially flat inner plate to the inner shroud substantially adjacent to the first ledge portion of the inner shroud. The first plate has an opening and is positioned such that the opening is fluidly aligned with a second end of the duct. 
     (g) Securing a second substantially flat plate to the outer shroud substantially adjacent to the first ledge portion of the outer shroud. The second plate has first, second and third openings and is positioned such that the first opening is secured in fluid alignment to a second end of the channel and such that the second end of the tube extends through the third opening. 
     (h) Securing a third plate to the inner shroud substantially adjacent to the second ledge portion of the inner shroud. 
     (i) And, securing a fourth substantially flat plate to the outer shroud substantially adjacent to the second ledge portion of the outer shroud. The fourth plate includes a plurality of openings such that a second end of the channel is secured in fluid alignment to one of the plurality of openings, and a second end of the tube is secured in fluid alignment to another of the plurality of openings. 
     The vane assembly provides a series of plenums and passages to direct flow of a coolant throughout the vane assembly. 
     Each of the securing steps can be performed by either welding or brazing. The third plate and the fourth substantially flat plate can be secured to a respective shroud by structural welding. The first ledge portion can be substantially parallel to the second ledge portion. The first, second and fourth substantially flat plates can be gauge plates; the third plate can be substantially flat on an inwardly-facing side and can provide at least one attachment on an outwardly-facing side. The method can further include substantially sealingly closing at least one core print opening in the airfoil landing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of a turbine vane according to aspects of the present invention. 
         FIG. 2  is an exploded isometric view of an outer shroud of a turbine vane according to aspects of the present invention. 
         FIG. 3  is an exploded isometric view of an inner shroud of a turbine vane according to aspects of the present invention. 
         FIG. 4  is a cross-sectional view of a turbine vane according to aspects of the present invention, taken along line  4 — 4  of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Aspects of the present invention address the drawbacks associated with prior vane assembly configurations. Aspects of the present invention relate to a turbine vane plate assembly that forms a series of plenums that, in addition to a plurality of cooling passages, direct coolant flow throughout the vane. Other aspects of the present invention are directed to a method of assembling such a turbine vane. 
     Embodiments of the invention will be explained in the context of a turbine vane assembly, but the detailed description is intended only as exemplary. Embodiments of the invention are shown in  FIGS. 1–4 , but the present invention is not limited to the illustrated structure or application. 
     As shown in  FIG. 1 , aspects of the present invention relate to a turbine vane assembly  10 . The assembly  10  comprises a variety of components including a vane  12 . The vane generally has inner and outer shrouds  14 ,  16  with an elongated airfoil  18  extending between the two shrouds  14 ,  16 . The inner and outer shrouds  14 ,  16  may also be referred to herein as first and second shrouds, respectively. The vane  12  can be formed by a variety of methods, but typically the vane  12  is a casting. The vane  12  can be cast as a single piece; alternatively, each shroud  14 ,  16  and the airfoil  18  can be cast separately and joined together in a subsequent operation. Secondary processes can be employed to form additional features such as cooling passages, or they can be employed to further refine or define features that were only roughly cast in any of these subcomponents including, for example, one or more ledge portions in a shroud. 
     Regardless of how the vane  12  is formed, one end of the airfoil  18   a  transitions into the outer shroud  16  to form a junction  20 , and the other end of the airfoil  18   b  transitions into the inner shroud  14  which also forms a junction  22 . The junctions  20 ,  22  can have any configuration and, in one aspect, the junction can be generally planar. Further, the junction  22  at the inner end of the vane assembly  10  does not need to be identical or even similar to the junction  20  at the outer end of the vane assembly  10 . 
     The vane casting  12  can be provided with a series of cooling passages, any of which can be formed as part of the initial casting or can be formed by secondary processes such as machining. During these secondary processes, it may be necessary to remove a portion of material from the exterior of the vane casting  12  in order to cut the desired passages. For example, the cooling passages  100 ,  102 ,  104 ,  106  ( FIG. 4 ) can be formed at least in part by drilling through the sides of the shroud  16 , the airfoil  18  or the junction  20 . In such case, a plug  26  can be used to seal the cooling passages  100 ,  102 ,  104 ,  106  from the outer environment so as to form an internal cooling passage. The plug  26  can be secured to the vane casting  12  in any number of ways including, for example, by welding or brazing. 
     The airfoil  18  can have a plurality of cooling passageways extending between the first and second shrouds  14 ,  16 . For example, one series of cooling passageways  108  can extend through the thickness of an outer wall of the airfoil  18 . Such cooling passages  108  may be provided about the entire periphery of the airfoil  18  or may be provided in certain portions of the airfoil  18  such as substantially along the leading edge portion  54 . The passages  108  can have any conformation including, for example, being generally round and comprising one or more substantially straight portions. However, the passages  108  can have any cross-section and orientation so long as the passages  108  can allow the flow a coolant. 
     The airfoil  18  can further be provided with cooling passages  30 ,  32 ,  34 ,  35  that can span the generally hollow interior of the airfoil  18 . These passages  30 ,  32 ,  34 ,  35  can have any configuration. For example,  FIGS. 2 and 3  show the outer and inner airfoil landing surfaces  36 ,  38 , respectively; the airfoil landing surfaces  36 ,  38  can comprise the extreme longitudinal ends of the airfoil  18 . Each of the landing surfaces  36 ,  38  and/or the junctions  20 ,  22  can include a plurality of openings. For example, the outer airfoil  36  landing can include three openings  40 ,  42 ,  44 . The inner airfoil landing  38  can include four openings  46 ,  48 ,  50 ,  52 , possibly, but not necessarily, corresponding to openings  40 ,  42 ,  44  at the outer airfoil landing  36 . For example, the openings  46 ,  48  at the inner airfoil landing  38  generally correspond to the single opening  40  in the outer airfoil landing  36 . Each of the openings provide just a few examples of possible cross-sectional geometry for the cooling passages  30 ,  32 ,  34  extending through the airfoil  18 . 
     Aside from the landing surfaces  36 ,  38 , the airfoil  18  and, for that matter, the vane  12  itself can be viewed as having two basic sections—a leading edge portion  54  and a trailing edge portion  56 . The leading edge  54  generally being the forward portion in relation to the oncoming flow of the working gas from a combustor. The trailing edge portion  56  generally being the rearward portion generally facing away from the oncoming combustion gases. 
     As mentioned above, each end  18   a ,  18   b  of the airfoil  18  can transition into a shroud  14 ,  16 . The shrouds  14 ,  16  can have any of a variety of shapes. As shown in  FIG. 1 , for example, the shrouds  14 ,  16  can be generally rectangular in conformation, but the shrouds  14 ,  16  are not limited to such a conformation. For example, the outer shroud  16  can have a radial aspect to it; that is, the outer shroud  16  can be formed on a radius as shown in  FIGS. 1 and 2 . The inner and outer shrouds  14 ,  16  can have a generally open interior defining an inner periphery. 
     Other features may be added to the shroud  14 ,  16  like cooling holes as discussed previously. In addition, the shrouds  14 ,  16  can be provided with one or more ledge portions. As shown in  FIGS. 2–4 , both the inner and outer shroud  14 ,  16  have at least two ledge portions such as outer and inner ledge portions  58 ,  60 , which are generally disposed at different elevations with respect to each other. Other than with respect to the shrouds  14 ,  16 , the relative terms “outer” and “inner” are used herein to describe the spatial relationship of a component to the airfoil  18  section of the vane assembly  10 . For example, the inner ledge portion  60  is generally disposed closer to the airfoil  18  than the outer ledge portion  58 . Aside from being at different elevations, the inner and outer ledge portions  58 ,  60  can be substantially parallel to each other. The term “substantially parallel” includes true parallel and deviations therefrom. 
     The ledge portions  58 ,  60  can have any of a number of configurations. For example, the ledges  58 ,  60  can be substantially planar or they can be slightly curved about a radius. Preferably, the ledges  58 ,  60  can continuously extend about the interior periphery of the shroud  14 ,  16 , but the ledges  58 ,  60  need not be continuous. For example, ledges  58 ,  60  can be provided on two opposing sides of the generally rectangular interior periphery of the shroud. Alternatively, the ledges  58 ,  60  may comprise a plurality of relatively short surfaces to form broken ledges  58 ,  60  about the interior periphery of the shroud  14 ,  16 . In some embodiments, a vane assembly  10  may only have a single ledge portion or none at all. In conformation, the ledges  58 ,  60  can be substantially identical to or completely different from each other. 
     The ledges  58 ,  60  can be cast in the shrouds  14 ,  16  and/or they can be refined or added in after casting, such as by machining. The ledges  58 ,  60  can be a variety of widths and need not be at a constant width around the inner periphery of the shroud  14 ,  16 . The width of the ledges  58 ,  60  can be the minimum dimension to provide a sufficient braze or weld joint with an abutting plate (for example, plates  68 ,  70 ,  86  and  90  discussed below). In one embodiment, the width of the ledge can be from about 2 millimeters to about 5 millimeters, and more preferably from about 2 millimeters to about 4 millimeters, and, even more preferably about 3 millimeters. 
     The ledge portions  58 ,  60  can serve as an aid during installation by providing a surface for supporting various components of the assembly  10  such as the plates (such as plates  68 ,  70 ,  86  and  90  discussed below) while those components are secured, such as by welding or brazing, to the shroud  14 ,  16 . Moreover, the ledge portions  58 ,  60  can further assist in separating the cooling passages in the shroud by providing an area of overlap with the plates ( 68 ,  70 ,  86  and  90 ). 
     Additional ledges can be provided for other purposes as well. For example, the outer shroud  16  can include a ledge  62  for providing an exit point for coolant traveling as shown in  FIG. 4 . Not only may the outer shroud  16  and inner shroud  14  be different structurally, but also functionally. For example, the outer shroud  16  can be structured to be coupled to a cooling system by way of a coolant inlet port and an exhaust port. The inner shroud  14  can include various structures for attaching to other engine components. In the particular vane assembly  10  shown in  FIGS. 1–4 , the configuration of each of the inner and outer shrouds  14 ,  16  is different. Therefore, examples of individual components that can make up each shroud  14 ,  16  will be discussed in turn. 
     In the embodiment shown in  FIGS. 1–4 , the inner shroud  14  includes a variety of components that cooperate to provide cooling plenums and passages for cooling the inner portion of the vane  10 . Examples of such components include a plug  64 , a duct  66 , a substantially flat inner plate  68 , and an outer plate  70 . Each of the components will be discussed below. 
     The duct  66  serves to route coolant into select regions of the vane assembly  10 . As shown in  FIG. 4 , the duct  66  allows coolant to be supplied to an outer plenum  200  while bypassing an inner plenum  202  of the inner shroud  14 . The duct  66  can have any of a variety of configurations such as circular, rectangular, polygonal, trapezoidal to name a few. Similarly, the opening  66   a  in the duct can be any of any shape as well. Preferably, the opening  66   a  generally conforms to the opening  50  in the airfoil landing  38  over which the duct  66  is placed so as to be fluidly aligned. The duct  66  can be made of any material so long as the material can withstand the turbine operating environment and can be welded or brazed to the material comprising the airfoil landing  38 . As an example, one weldably compatible material can include Inconel  625 . 
     The inner shroud  14  can further include a substantially flat inner plate  68 . Preferably, the substantially flat inner plate  68  is of a standardized size such as a gauge plate. The plate  68  is contoured so as to be received in the inner shroud  14 . In one embodiment, the substantially flat inner plate  68  is disposed substantially proximate or substantially adjacent to the inner ledge portion  60  of the inner shroud  14 . Further, the substantially flat inner plate  68  can include one or more openings for receiving and/or fluidly communicating with other structures such as the duct  66 . The substantially flat inner plate  68  can be made of numerous materials including Inconel  625 , and preferably it can be made of a material that is weldably or brazably compatible with the inner shroud  14  as well as the duct  66 . 
     The outer plate  70  can be used to close the inner shroud  14  and can further be used to provide attachments for securing the vane to other components of the turbine engine. The outer plate  70  can have any shape so long as it can be received in the inner shroud  14 . The outer plate  70  can be made of a multitude of materials, but preferably it can be made of a material that can be coupled, such as by structural welding, to the inner shroud. 
     In one embodiment, the outer plate  70  can be a substantially flat plate without an associated attachment structure. In another embodiment, an attachment  76  is provided and is secured to the plate  70  in any of a number of manners including, for example, welding. In this case, it is preferred if the outer plate  70  is gauge plate and is substantially flat. In still another embodiment, the outer plate  70  can be a cast part with any desired features such as the attachment structure  76  formed during the casting process. In embodiments where attachment structures  76  are provided, it is preferred if the attachment structures  76  are only associated with the outwardly-facing side  70   a  of the outer plate  70 , which is the side that faces away from the airfoil section  18  of the vane assembly  10 . Thus, the inwardly-facing side  70   b  of the outer plate  70 , which faces toward the airfoil section  18  as well as the substantially flat inner plate  68 , can be substantially flat. 
     Another component that can be used is a plug  64 . The plug  64  can be used for a variety of purposes including to sealingly close core print openings. For example, the inner airfoil landing  38  can have a plurality of openings. One opening, for example, can be a core print opening  52 . The size, location and geometry of the core print opening  52  can vary based on the particular core print used. In the embodiment shown, it is preferred if the core print opening  52  is sealingly closed so as to substantially prevent leakage, but whether the plug  64  is needed can be determined by the process used to create the airfoil  18 . 
     The plug  64  may be made of any material and, ideally, one that is weldably or brazably compatible with the airfoil landing surface  38 . The plug  64  can be placed over the opening  52  so as to substantially cover the opening  52 . Alternatively, the plug  64  can be placed inside the opening  52 , or the plug  64  can be configured so that a portion of the plug  64  extends into the opening  52  and a portion of the plug  64  covers the opening  52 . Accordingly, the plug  64  can have any shape or configuration. 
     As discussed later, the assemblage of the above described components can provide a series of plenums  200 ,  202  and passages for directing coolant into and out of the inner shroud  14 . Turning now to the outer shroud  16 , any number of components can be used to complete the vane assembly  10 . For example, the outer shroud  16  can comprise a channel  82 , a tube  84 , a substantially flat inner plate  86 , a duct and an outer plate. Each of these components will be discussed below. 
     The above discussion of the substantially flat inner plate, outer plate and duct in connection with the inner shroud  14  is of equal application to the outer shroud with exceptions noted below. The substantially flat inner plate includes three openings for fluidly communicating with the channel, the duct and the tube. Preferably, the outer plate associated with the outer shroud preferably does not have attachment structure associated with it. More preferably, the outer plate can be a substantially flat plate such as a gauge plate. Also, the outer plate of the outer shroud can have one or more openings, for example, three openings as shown in  FIG. 2 . The duct  88  can be identical or similar to the duct  66  that can be used in the inner shroud  14 . Preferably, to reduce the number of unique parts, the ducts  66 ,  88  are identical. 
     The vane assembly  10  can further include a channel  82 . The channel  82  can have any of a variety of conformations such as circular, rectangular, polygonal, trapezoidal, to name a few. Similarly, the opening  82   a  in the channel can be any shape as well. Preferably, the opening in the channel  82  generally conforms to the opening  44  in the airfoil landing  36  over or into which the channel  82  can be placed so as to be fluidly aligned. The channel  82  can be made of any material so long as the material can withstand the turbine operating environment and can be brazed or welded to the airfoil landing  36 . An example of a weldably or brazably compatible material is Inconel  625 . 
     The assembly can further comprise a tube  84 . The tube  84  can have any number of holes and the holes can have any geometry. In one embodiment, shown in  FIG. 2 , the tube  84  has two generally circular holes  92  extending through the tube  84 . The quantity and shape of the holes  92  can be dictated by engineering considerations including the geometry of the turbine component which interfaces with the tube  86  to supply coolant. The tube  86  can be made of any of a variety of materials, and it can be a material that is weldably and brazably compatible with the material comprising the airfoil landing  36 . 
     The tube  86  can have many different conformations, and, in one possible conformation shown in  FIG. 2 , the tube generally has an upper half  94  and a lower half  96 . The lower half  96  can be longer than the upper half  94 ; the upper and lower halves  94 ,  96  can be disposed such that the sides of the upper half  94  are in substantial continuity with the lower half  96 . However, the halves  94 ,  96  can be disposed such that a portion of the lower half  96  extends past the overlap region between the upper and lower halves  94 ,  96  so as to form a shelf portion  98 . Further, it is preferred if the lower half  96  of the tube  84  generally conforms to the opening  44  in the airfoil landing  36  over or into which the tube  84  can be placed so that the airfoil opening  44  and the holes  92  in the tube  84  are fluidly aligned. 
     Having described the individual components according to aspects of the present invention, one illustrative manner in which these components can be assembled will now be described. The following description is merely an example of a sequence in which the individual steps can occur. The described steps can be performed in almost any order and not every step described must occur. 
     Any core print openings or other undesired openings in the airfoil landing surface can be sealingly closed, by which applicant means that the opening is closed in any manner so as to prevent or substantially prevent a fluid from passing through. As shown in  FIG. 3 , the inner airfoil landing  38  can include a single core print opening  52 . A plug  64  can be placed in and/or over the opening, and then the plug  64  can be secured to the airfoil landing  38  by, for example, brazing or welding. Any manner of securement is possible so long as it can sealingly close the core print opening  52 . 
     Next, the duct  66  can be placed over one of the plurality of openings  50  in the inner airfoil landing  38  so that the duct  66  can be in fluid alignment with the opening  50  in the inner airfoil landing  38 . Fluid alignment means that the two or more components in issue are situated to as to allow fluid communication between the components. The duct  66  can be positioned in several ways so as to be fluidly aligned with the opening  50 . For example, the duct  66  can be positioned at least partially into the opening  50  or the duct  66  can rest on the airfoil landing  38  such that the opening  50  of the duct  66  conformingly surrounds the opening  50  in the airfoil landing  38 . Regardless of how the duct  66  and opening  50  are fluidly aligned, one end of the duct  66  can be secured to the airfoil landing  38  by any of a variety of methods including, for example, brazing or welding. The duct  66  can be made of any material, preferably one that is weldably or brazably compatible with the particular material comprising the airfoil landing  38 . 
     A substantially flat inner plate  68  can be placed into the inner shroud  14  such that it can be disposed substantially adjacent or substantially proximate to the inner ledge portion  60  of the inner shroud  14 . The inner plate  68  can have an opening  68   a , and the inner plate  68  can be positioned so that opening  68   a  can be fluidly aligned with the duct  66 . Preferably, the other end of the duct  66  extends into the opening  68   a  and through the thickness of the plate  68  so that the end of the duct  66  can be disposed substantially flush with the plate  68 . The end of the duct  66  can be secured to the plate  68  by, for example, brazing or welding. Similarly, the periphery of the plate  68  can be secured to the inner shroud  14 , which can include at least a portion of the substantially proximate ledge  60 , by any of a variety of methods including brazing or welding. 
     Finally, the outer plate  70  can be inserted into the inner shroud  14  so as to be substantially adjacent or substantially proximate to the outer ledge portion  58  of the inner shroud  14 . The outer plate  70  can be secured to the outer shroud  14  which can include at least a portion of the substantially proximate ledge  58 , in various manners, but preferably by structurally welding about the perimeter of the outer plate  70 . 
     As a result of the above assembly, a pair of plenums  200 ,  202  are formed in the inner shroud  14 . An inner plenum  202  can be generally defined by the space between at least the junction  22  and the substantially flat inner plate  68 . An outer plenum  200  can be generally defined by the space between at least the substantially flat inner plate  68  and the outer plate  70 . The inner plenum  202  of the inner shroud  14  can be in fluid communication with the outer plenum  200  of the inner shroud  14  through one or more cooling passages  100 ,  102  in the respective shroud. The inner and outer plenums  200 ,  202  and coolant passages  100 ,  102  of the inner shroud  14  can direct coolant flow throughout the vane  10  including coolant flow within the plenums  200 ,  202  generally transverse to the elongated direction of the airfoil  18 . 
     Turning to the outer shroud side, the channel  82  can be placed over one of the plurality of openings  40  in the airfoil landing  36  such that the opening  82   a  in the channel  82  is in fluid alignment with the opening  40  in the airfoil landing  36 . The channel  82  can be positioned in several ways so as to be fluidly aligned with the opening  40 . For example, the channel  82  can be positioned at least partially into the opening  40 , or the channel  82  can rest on the airfoil landing  36  such that the opening  82   a  of the channel  82  conformingly surrounds the opening  40  in the airfoil landing  36 . Regardless of how the channel  82  and opening  40  are fluidly aligned, one end of the channel  82  can be secured to the airfoil landing  36  by any of a variety of methods including, for example, brazing or welding. 
     Similarly, the tube  84  can be placed proximate to one  44  of the plurality of openings in the airfoil landing  36  such that the holes  92  in the tube  84  are fluidly aligned with the opening  44  in the airfoil landing  36 . For example, the tube  84  can be positioned at least partially into the opening  44  or the tube  84  can rest on the airfoil landing  36  such that the lower half  96  of the tube  84  covers the opening  44  in the airfoil landing  36 . Regardless of how the tube  84  and opening  44  are fluidly aligned, the lower half of the tube  84  can be secured to the airfoil landing  36  by any of a variety of methods including, for example, brazing or welding. 
     Next, the substantially flat inner plate  86  can be placed in the outer shroud  16  such that it is disposed substantially adjacent or proximate to the inner ledge portion  60 . In addition, the plate  86  can be provided with openings. For example, as shown in  FIG. 2 , the plate can include three openings  86   a ,  86   b ,  86   c . The openings can be for a variety of purposes; for example, one opening  86   b  can be provided for coolant supply and the other two openings  86   a ,  86   c  can be provided to accommodate the tube  84  and the channel  82 . The plate  86  can positioned in the outer shroud  16  such that the channel  82  extends into the opening  86   a  and sits substantially flush with the top side of the plate  86 . Further, the plate  86  can be positioned such that the upper half  94  of the tube  84  extends through and beyond the respective opening  86   c  in the substantially flat inner plate  86  and such that the shelf portion  98  of the lower half  96  is disposed substantially adjacent to the underside of the inner plate  86 . The tube  84  and the channel  82  can be secured to the inner plate  86  by, for example, brazing or welding. Plate  86  can be secured about its periphery to the outer shroud  16 , possibly including at least a portion of inner landing  60 , by various methods such as brazing or welding. 
     The duct  88  can placed in substantial fluid alignment with the opening  86   b  in the substantially flat inner plate  86 . Once aligned, one end of the duct  88  can be secured to the substantially flat inner plate  86  by any of a variety of methods including, for example, welding or brazing. 
     Lastly, the outer plate  90  can be placed into the outer shroud  16  so that the outer plate  90  can be substantially proximate or substantially adjacent to the outer ledge portion  58 . The outer plate  90  has openings  90   a ,  90   b ,  90   c , so that when the plate  90  is in position, the opening  90   b  can be in substantial fluid alignment with the other end of the duct  88 . In such case, the duct  88  can extend into the opening  90   b  so as to be substantially flush with the outwardly-facing side  91  of the outer plate  90 . In addition, when the outer plate  90  is in position, the upper half  94  of the tube  84  can extend into the opening  90   c  so as to be substantially flush with the outwardly-facing side  91  of the outer plate  90 . The other end of the duct  88  and the upper half  94  of the tube  84  can then be secured such as by brazing or welding to the outer plate  90 . The outer plate  90  can be secured, preferably by structural welding, to the outer shroud  16  which can include at least a portion of the outer ledge portion  58 . 
     As a result of the above assembly, a pair of plenums  204 ,  206  are formed in the outer shroud  16 . An inner plenum  206  can be generally defined by the space between at least the junction  20  and the substantially flat inner plate  86 . An outer plenum  204  can be generally defined by the space between at least the substantially flat inner plate  86  and the outer plate  90 . The inner plenum  202  of the inner shroud  14  can be in fluid communication with the inner plenum  206  of the outer shroud  16  through at least one of the cooling passages  108  in the airfoil  18 . The inner and outer plenums  204 ,  206  and coolant passages  104 ,  106  of the outer shroud  16  can direct coolant flow throughout the vane  10  including coolant flow within the plenums  204 ,  206  generally transverse to the elongated direction of the airfoil  18 . 
     As is evident from the above assembly example, aspects of the present invention allow the vane to be assembled in such a way so as to allow for inspection of the welds or braze joints as the assembly is constructed. Also, the relative simplicity of the components and assembly lends itself to replication in a production environment. 
     Having described an assortment of components and a manner in which the components can be arranged to form a turbine vane assembly in accordance with aspects of the present invention, an example of the operation of such a vane  10  will be described below. Of course, aspects of the present invention can be employed with respect to myriad vane designs as one skilled in the art would appreciate. 
     One example of a vane having an internal cooling structure that is facilitated by aspects of the present invention is shown in  FIG. 4 . A coolant, for example steam, can be supplied to the vane assembly  10  through the duct  88 . A portion of the entering coolant will be directed into the inner plenum  206  of the outer shroud  16 . The coolant can flow laterally, that is, transverse to the elongated direction of the airfoil  18 , through the inner plenum  206 , flowing around the tube  84  and the channel  82 , both of which extend through the inner plenum  204 . As coolant flows toward the side walls of the plenum  206 , the coolant can, in some areas, flow through the various cooling passages in the airfoil  18 , the shroud  16  and/or the junction  20 . For example, coolant can enter the passages  104 ,  106 , of which there can be several of these passages disposed about the periphery of the inner plenum  206  of the outer shroud  16 . Coolant that flows into the passages  104 ,  106  can be routed into the outer plenum  204  and can ultimately exhaust out of the vane  10  through the opening  90   a  in the outer plate  90 . Another portion of the coolant in the inner plenum  206  of the outer shroud  16  can be directed toward the inner plenum  202  of the inner shroud  14  by way of the cooling passage  108 , which can be one of a plurality of cooling passages that extend through the airfoil section  18 . Thus, cooling is provided to the airfoil section  18 . The coolant can flow out of the passage  108  and into the inner plenum  202  of the inner shroud  14 , at which point the coolant can turn and travel through passages  30 ,  32 . The coolant will ultimately exit the vane through the opening  90   a  in the outer plate  90 . 
     Some coolant entering the vane  10  through the duct  88  can take a different path from the above-described cooling circuit. For example, some coolant will not turn into the inner plenum  206  of the outer shroud  16 ; instead, the coolant can proceed through a cooling passage  34  in the airfoil  18  and flow into the outer plenum  200  of the inner shroud  14 , the duct  66  allowing the coolant to bypass the inner plenum  202  of the inner shroud  14 . The coolant can then flow through the plenum  200  generally transverse to the direction of elongation of the airfoil  18 . As it approaches the edges of the plenum  200 , the coolant can be directed into cooling passages  100 ,  102  that fluidly communicate with the inner plenum  202  of the inner shroud  14 . The shown cooling passages  100 ,  102  can actually be two of a plurality of cooling paths in the inner shroud  14 , the airfoil  18  and/or the junction  22  that connect the inner and outer plenums  200 ,  202  of the inner shroud  14 . 
     After exiting cooling passages  100 ,  102 , the coolant will flow into the inner plenum  74  of the inner shroud  14  and will flow generally transverse to the elongated direction of the airfoil  18 . The coolant can then exit the inner plenum  74  of the inner shroud  14  through the passages  30 ,  32  and ultimately exit the vane  10  through the opening  90   a  in the outer plate  90  of the outer shroud  16 . While the exit path as shown in  FIG. 4  includes two passages  30 ,  32 , there can be any number of passages such as a single passage or three or more. The two passages  30 ,  32  in this example may be the product of considerations during the casting process rather than dictated by cooling design. 
     Another cooling circuit of the turbine vane assembly provides generally for the trailing edge portion  56  including chamber  35  of the vane. Any coolant can be used to cool the trailing edge portion  56 , but air is preferred in the illustrated configuration. Coolant can enter through the two openings  92  in the supply tube  84 , which allows coolant to bypass the outer and inner plenums  204 ,  206  of the outer shroud  16  and directly enter a cooling chamber  35  generally around the trailing edge  56  of the airfoil section  18 . The chamber  35  is closed at the inner airfoil landing  38  by the plug  64 . 
     As the coolant enters the chamber  35 , it can interact with various structures provided in the chamber  35 . For example, a plurality of curved structures  110  are provided to guide coolant flow while the generally planar structures  112  assist in straightening the flow. Next, the coolant can encounter dual columns of oblong structures  114 ,  116 . The first column of oblong structures  114  is designed to restrict coolant flow; the second column  116  can be designed to effectuate impingement cooling of the airfoil  18 . Beyond the dual columns  114 ,  116 , the coolant can be guided by a plurality of structures  118  to exit the airfoil at its trailing edge  56  through a plurality of generally square window-like openings  120  ( FIG. 1 ) in a process known as “pressure side ejection.” 
     The above described vane is an example of an “open loop” system, which is characterized by providing one or more openings along the trailing edge of the vane to allow the coolant to exit the vane and join the working gas. Such a system can be disadvantageous, however, because it can reduce the usable energy of the working gas. 
     In contrast, a “closed loop” system allows a coolant to flow through the vane, cooling the vane and absorbing heat, and returning the coolant to be used elsewhere. For example, when the coolant is steam, cool steam is supplied to the vane assemblies and the heated steam may be directed to a steam turbine assembly which is coupled to the closed loop. One example of a closed loop system is disclosed in U.S. Pat. No. 6,454,526 (“the &#39;526 patent”). Aspects of the present invention can be applied to the closed loop system disclosed in the &#39;526 patent. For example, one skilled in the art would appreciate that outer end cap  10  and inner end cap  50  of the &#39;526 patent can be replaced in accordance with a plate assembly according to aspects of the present invention including, for example, at least a substantially flat inner plate and an outer plate. 
     It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the invention as defined in the following claims.