Patent Publication Number: US-2013236301-A1

Title: Apparatus And System For Directing Hot Gas

Description:
TECHNICAL FIELD 
     The subject matter disclosed herein relates generally to combustion systems and more specifically hot gas flow. 
     BACKGROUND 
     A typical gas turbine includes a plurality of combustors. The combustors receive a combustible fuel from a fuel supply and compressed air from a compressor that is driven by a shaft. For each combustor, the fuel is combusted in the compressed air within a combustion chamber defined by a combustor liner to produce hot combustion gas that is expanded through a turbine to produce work for driving a shaft. The hot combustion gas is conveyed from the combustor liner to the turbine by a transition piece or duct. The hot combustion gas flowing through the transition piece subjects the duct structure to very high temperatures. Hot gases circulated back towards the transition piece aft frame can cause damage, such as cracking. 
     The fielded product life cycle of the transition piece has been limited by the cracking observed in the aft frame. The cracking may impart significant repair costs and reduce the overall cycle life of the part. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Disclosed herein are apparatuses and systems for directing the flow hot gas exiting a transition piece. In an embodiment, an apparatus at the aft exit of the transition piece has a face with an airfoil shape. In another embodiment, a transition piece aft exit has an airfoil shape. In yet another embodiment, a system comprises a first aft frame with an airfoil shape on the exit face and a second aft frame in proximity to the first aft frame, wherein the second aft frame has an airfoil shape on the exit face. 
     This Brief Description of the Invention is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Brief Description of the Invention is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to limitations that solve any or all disadvantages noted in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present subject matter will become better understood when the following detailed description is read with reference to the accompanying drawings, wherein: 
         FIG. 1  is a side view of a gas turbine transition piece; 
         FIG. 2  is a perspective view a transition piece aft frame; 
         FIG. 3  is a perspective cut view of an airfoil shape aft frame exit; 
         FIG. 4  is a front view of an aft frame; 
         FIG. 5  is a cross section taken along the line  401 - 401 ; 
         FIG. 6  is a front view of adjacent transition pieces with the aft looking forward; 
         FIG. 7  is a cross section taken along the  601 - 601 ; 
         FIG. 8  is a cross section of adjacent aft frames; 
         FIG. 9  is an exemplary hot gas flow off of adjacent aft frames with a blunt face; 
         FIG. 10  is an exemplary hot gas flow off of adjacent aft frames with an airfoil shape; 
         FIG. 11  is an exemplary hot gas flow off of adjacent aft frames with an airfoil shape; 
         FIG. 12  is a cross section of adjacent aft frames; 
         FIG. 13  is a front view of an aft frame; 
         FIG. 14  is a cross section taken along the line  1301 - 1301 ; 
         FIG. 15  is a cross section taken along the line  1302 - 1302 ; 
         FIG. 16  is a partial a cross section of an airfoil shaped aft frame with a cooling hole; 
         FIG. 17  is a cross section of adjacent aft frames with an airfoil shape; and 
         FIG. 18  is a cross section of adjacent aft frames with a spoiler. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
       FIG. 1  shows an exemplary transition piece. Transition piece  100  may be coupled at an upstream end to a combustor and at a downstream or aft end to a turbine. The transition piece  100  carries hot gas flow from the combustor to the turbine. The aft frame  105  is a component which is located at the exit or aft end of the transition piece and thus acts as an interface between the transition piece  100  and the stage  1  nozzle. The aft frame  105  is exposed to hot gases flowing into the stage  1  nozzle. 
       FIG. 2  is an exemplary, prior art embodiment of an aft frame. Aft frame  200  has an aft face  212  and inside wall  210 . Inside wall  210  intersects with face  212  at a sharp, approximate  90  degree, angle. Aft frame  200  has a top rail  205  and bottom rail  215  as well as a left side rail  207  and right side rail  220 . 
     A potential cause of thermal distress of prior art aft frame side rails may be due to ingestion of hot gas exiting the transition piece, trapping the hot gas and recirculating it between the stage one nozzle vane and aft face of the aft frame. 
     For example, with reference to  FIG. 2 , as typical in the prior art, the aforementioned ingestion may be deflected back towards the aft face  212  of the transition piece aft frame  200  because of the circumferential proximity of the stage one nozzle vane to the aft frame  200  and the blunt body effects of the aft face  212 , which is normal to the aft frame inner wall  210  in the direction of transition piece exit flow. As disclosed herein, the shape of the aft frame side rails (or the entire perimeter of the aft frame) may be altered to minimize hot gas recirculation. 
     In an embodiment, the prior art shape of the transition piece aft frame face and the normal aft frame inner wall may be changed to create an airfoil shape on each of the aft frame side rails.  FIG. 3  is an exemplary cut corner perspective view of an aft frame with a contoured or rounded airfoil face.  FIG. 4  is an exemplary front view of an aft frame  400  with a contoured aft face.  FIG. 5  is a cross section taken along line  401 - 401  of  FIG. 4 . 
     A gas turbine configuration may allow for adjacent transition pieces and corresponding aft frames. With reference to  FIG. 6 , transition piece  600  and corresponding aft frame  605  may be adjacent to transition piece  607  and corresponding aft frame  610 .  FIG. 7  is an exemplary cross section taken along line  601 - 601  of  FIG. 6 . In  FIG. 7 ,  705  corresponds to aft frame  605  and  710  corresponds to aft frame  610 .  FIG. 8  is an exemplary cross section of adjacent aft frames from the prior art with inner walls normal to the aft frame front exit. 
     Transition piece aft frames configured as shown in  FIG. 8  may create a large bluff body with their side spans when assembled side by side within the gas turbine. As stated herein, this aft frame configuration may create a recirculation zone that when positioned upstream of a stage one nozzle can circulate hot gases back towards the transition piece aft frame and cause damage. Aft frames with an airfoil shape (e.g., a contour), as shown in  FIG. 7 , may reduce the recirculation zone.  FIGS. 9 and 10  are representations of computational flow dynamics contours.  FIG. 9  is an exemplary illustration of the wake of a flat aft frame face (e.g.,  FIGS. 2 and 8 ).  FIG. 10  is an exemplary illustration of a wake of contour shape aft frame face (e.g.,  FIGS. 3 and 7 ). The wake of the adjacent aft frames with a contoured aft frame face in  FIG. 10  is more stable than the wake of the flat face aft frame in  FIG. 9 .  FIG. 11  is an exemplary illustration of cross section of adjacent contoured aft frames and arrows showing an exemplary flow of cooling vectors. The cooling air pushes hot gases away from the cavities between hardware. 
       FIG. 12  is an exemplary embodiment of an asymmetrical air foil shape of a cross section of adjacent aft frames. To further optimize the flow field and minimize ingestion, the inner diameter of two adjacent side rails of adjacent aft frames may be tapered in the same direction (creating an asymmetric aft frame). The adjacent aft frame taper may be based on the taper of the stage one nozzle vane. 
       FIG. 13  is an exemplary illustration of a front view of an aft frame.  FIG. 14  is an exemplary cross section taken along line  1301 - 1301  of aft frame  1300 .  FIG. 15  is an exemplary cross section taken along line  1302 - 1302  of aft frame  1300 . The single aft frame  1300  may have asymmetric contours on the side rails as shown by cross section  1400  and cross section  1500 . The asymmetric contours of a single aft frame exit may be contoured in a manner that is oriented towards the stage one nozzle. 
     Currently, typical aft frame configurations incorporate cooling holes with circular cross sections in order to divert a portion of flow through an impingement sleeve (which surrounds the transition piece) into these holes to cool the aft frame. Embodiments of the aft frame face as discussed herein that use an airfoil shape of the aft frame exit provide an alternative method of reducing aft frame metal temperatures. Cooling holes on side rails may no longer be needed. Additional backside cooling of the aft frame airfoil may be added to protect the outer thermal barrier coating. Eliminating the flat aft frame face and creating an airfoil shape, may simplify fabrication processes. Cooling holes may be removed on the side rail which may eliminate a percentage of the electrical discharge machining (EDM) holes. In addition, thermal barrier coating (TBC) may be applied down the transition piece body and over the airfoil face to a side seal, which may now cover the entire transition piece surface exposed to hot gas.  FIG. 16  is an exemplary illustration of a cross section of an airfoil shaped aft frame. The combination of contour shape and cooling hole angle, as shown in  FIG. 16 , may produce a film cooling on the transition piece aft end. 
       FIG. 17  is an exemplary illustration of adjacent aft frames with an airfoil shape transition piece aft frame face that has a more angular shape.  FIG. 18  is an exemplary illustration of adjacent aft frames with aft frame side spans designed to spoil the effects of hot gas recirculation and ingestion. Spoiler  1801  of the aft frame exit may separate the flow and reduce the recirculation zone. In addition, cooling or purge holes can be added to the back side of the spoilers to further breakdown the recirculation zone. 
     Turbines and compressors designs may vary so design-of-experiments (DOE) methods for combining sets of computational fluid dynamics (CFD) and other analysis techniques may be used to optimize the various geometries (e.g., radius of contour of the aft frame) that maximize the results for the particular system. Although side rails of the aft frame are discussed, the entire perimeter of the aft frame face may have an airfoil shape. In addition, although an aft frame is discussed, the embodiments disclosed herein may apply to any apparatus separate from or integrated with the transition piece in a similar position as the aft frame at the transition piece aft end exit. 
     In describing preferred embodiments of the subject matter of the present disclosure, as illustrated in the Figures, specific terminology is employed for the sake of clarity. The claimed subject matter, however, is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.