Patent Publication Number: US-2015064020-A1

Title: Turbine blade or vane with separate endwall

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of, and claims priority from, co-pending U.S. patent application Ser. No. 13/171,678, filed Jun. 29, 2011, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to turbine engines and, more particularly, to endwall structures for turbine engine&#39;vanes or blades. 
     BACKGROUND OF THE INVENTION 
     A gas turbine engine typically includes a compressor section, a combustor, and a turbine section. The compressor section compresses ambient air that enters an inlet. The combustor combines the compressed air with a fuel and ignites the mixture creating combustion products defining a working fluid. The working fluid travels to the turbine section where it is expanded to produce a work output. Within the turbine section are rows of stationary vanes directing the working fluid to rows of rotating blades coupled to a rotor. Each pair of a row of vanes and a row of blades form a stage in the turbine section. 
     Advanced gas turbines with high performance requirements attempt to reduce the aerodynamic losses as much as possible in the turbine section. This in turn results in improvement of the overall thermal efficiency and power output of the engine. One possible way to reduce aerodynamic losses is to incorporate endwall contouring on the blade and vane shrouds in the turbine section. Endwall contouring when optimized can result in a significant reduction in secondary flow vortices which may contribute to losses in the turbine stage. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the invention, a turbine engine airfoil structure is provided comprising an airfoil adapted to be supported to extend across a gas passage for a hot working gas in a turbine engine, the airfoil including sidewalls comprising radially extending pressure and suction sides. The airfoil structure further comprises a platform structure located at one end of the airfoil and positioned at a location forming a boundary of the gas passage. The platform structure includes a platform member including a gas side surface extending generally perpendicular from the airfoil at a junction with the airfoil, and providing a structural connection to the airfoil. The platform structure further includes a separately formed platform cover attached to the platform member at the gas side surface. The platform cover extends from a location radially displaced from the gas side surface and in contact with one of the sidewalls of the airfoil, and includes an outer surface located for contact with the hot working gas passing through the gas passage. An intersection between the platform cover and the airfoil includes a depressed trough and forms an acute angle between the outer surface of the platform cover and the sidewall of the airfoil. 
     In accordance with another aspect of the invention, a turbine engine airfoil structure is provided comprising an airfoil adapted to be supported to extend across a gas passage for a hot working gas in a turbine engine, the airfoil including sidewalls comprising radially extending pressure and suction sides. The airfoil structure further comprises a platform structure located at one end of the airfoil and positioned at a location forming a boundary of the gas passage. The platform structure includes a platform member including a gas side surface extending generally perpendicular from the airfoil at a junction with the airfoil, and providing a structural connection to the airfoil. The junction between the platform member and the airfoil forms a fillet joint. The platform structure further includes a separately formed platform cover attached to the platform member at the gas side surface. The platform cover includes an outer surface located for contact with the hot working gas passing through the gas passage, and the outer surface comprises a contoured endwall surface having a first edge located adjacent to one of the sidewalls. The first edge is located in engagement with the sidewall, with the contoured surface providing a varying contour defined at an intersection of the outer surface with the sidewall and extending in an axial direction between a leading edge and a trailing edge of the airfoil. 
     In accordance with a further aspect of the invention, a turbine engine airfoil structure is provided comprising an airfoil adapted to be supported to extend across a gas passage for a hot working gas in a turbine engine, the airfoil including sidewalls comprising radially extending pressure and suction sides. The airfoil structure further comprises a platform structure located at one end of the airfoil and positioned at a location forming a boundary of the gas passage. The platform structure includes a platform member including a gas side surface extending generally perpendicular from the airfoil at a junction with the airfoil, and providing a structural connection to the airfoil. The junction between the platform member and the airfoil forms a fillet joint. The platform structure further includes a separately formed platform cover attached to the platform member at the gas side surface. The platform cover includes an outer surface located for contact with the hot working gas passing through the gas passage and an inner surface opposite the outer surface. The platform cover extends in a generally circumferential direction between a first edge located adjacent to one of the sidewalls and a second edge opposite the first edge. The platform cover also extends in a generally axial direction between an upstream edge and a downstream edge of the platform member. A platform cover thickness, which is defined between the outer surface and the inner surface, varies in at least, one of the axial direction and the circumferential direction. The platform cover further includes at least one cooling fluid channel defined between the gas side surface of the platform member and the inner surface of the platform cover. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein: 
         FIG. 1  is a partial cross-sectional view of a gas turbine engine incorporating an airfoil structure formed in accordance with aspects of the present invention; 
         FIG. 2  is a perspective view of an airfoil structure illustrating aspects in accordance with the present invention; 
         FIG. 3  is a plan view of the airfoil structure of  FIG. 1 ; 
         FIG. 4  is a cross sectional view taken along line  4 - 4  in  FIG. 3 ; and 
         FIG. 5  is a view similar to  FIG. 4  illustrating further aspects of the airfoil structure in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, a specific preferred embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention. 
     In  FIG. 1 , a gas turbine engine  10  is illustrated, including a compressor section  12 , a combustor  14 , and a turbine section  16 . The compressor section  12  compresses ambient air  18  that enters an inlet  20 . The combustor  14  combines the compressed air with a fuel and ignites the mixture creating combustion products comprising a hot working gas defining a working fluid. The working fluid travels to the turbine section  16 . Within the turbine section  16  are rows of stationary vanes  22  and rows of rotating blades  24  coupled to a rotor  26 , each pair of rows of vanes  22  and blades  24  forming a stage in the turbine section  16 . The rows of vanes  22  and rows of blades  24  extend radially into an axial flow path  28  extending through the turbine section  16 . The working fluid expands through the turbine section  16  and causes the blades  24 , and therefore the rotor  26 , to rotate. The rotor  26  extends into and through the compressor  12  and may provide power to the compressor  12  and output power to a generator (not shown). 
     Referring to  FIG. 2 , an airfoil structure  30  comprising one of the blades of the row of blades  24  is illustrated for the purpose of describing aspects of the present invention. However, it should be understood that the following description is not limited to implementation on an airfoil structure comprising a blade, and the described aspects of the invention may be implemented on other airfoil structures, such as may be implemented on a vane of the row of vanes  22 . 
     Further, it should be understood that the terms “inner”, “outer”, “radial”, “axial”, “circumferential”, and the like, as used herein, are not intended to be limiting with regard to an orientation or particular use of the elements recited for aspects of the present invention. 
     The airfoil structure  30  includes an airfoil  32  adapted to be supported to extend radially across the flow path  28 . The airfoil  32  includes a generally concave sidewall  34  defining a pressure side of the airfoil  32 , and includes an opposing generally convex sidewall  36  defining a suction side of the airfoil  32 . The sidewalls  34 ,  36  extend radially outwardly from a shroud or platform structure  38 , and extend generally axially in a chordal direction between a leading edge  40  and a trailing edge  42  of the airfoil  32 . The platform structure  38  is located at one end of the airfoil  32  and is positioned at a location where the platform structure  38  forms a boundary, i.e., an inner boundary, defining a portion of the flow path  28  for the working fluid. In addition, the airfoil structure  30  may include a root  39  extending radially inwardly from the airfoil  32  and platform structure  38  for retaining the airfoil structure  30  to the rotor  26  (see  FIG. 1 ). 
     The airfoil  32  is rigidly supported to a platform member  44  of the platform structure  38 . As may be further seen in  FIG. 4 , a gas side surface  48  of the platform member  44  extends generally perpendicular from a junction with the airfoil  32 . The gas side surface  48  extends axially between an upstream edge  50  and a downstream edge  52  of the platform member  44 , and extends in a circumferential direction between opposing mateface sides  54  and  56  of the platform member  44 . A junction structure, such as a fillet joint  46 , may be provided extending from one or both of the sidewalls  34 ,  36  to the gas side surface  48  of the platform member  44 . The fillet joint  46  provides a connection with a predetermined radius that may limit or reduce a stress concentration that may occur at the structural connection defined at the junction between the airfoil  32  and the platform member  44 , and thus may facilitate increasing the life of the airfoil structure  30 . 
     Referring to  FIG. 4 , the platform structure  38  further includes a platform cover  60  ( FIG. 2 ), which may comprise, for example, a pressure side platform cover  60   a  and a suction side platform cover  60   b . That is, the platform cover  60  may comprise two or more platform covers  60   a ,  60   b , or platform cover parts, such as to facilitate forming and mounting of the platform cover  60  on the platform member  44 , although the present invention is not intended to be limited to a construction requiring more than a single platform cover  60 . In the following description, particular reference is made to the pressure side platform cover  60   a , and it is to be understood that the suction side platform cover  60   b  may comprise a similar structure, in which elements of the suction side platform cover  60   b  corresponding to elements of the pressure side platform cover  60   a  are identified with the same reference numerals having a suffix “b”. 
     The platform cover  60   a  comprises an element or structure that is formed separately from the platform member  44  and, in particular, is formed separately from both the airfoil  32  and the platform member  44 . Hence, in accordance with an aspect of the invention, the airfoil  32  and platform member  44  may be formed as a unitary or integral structure, such as by casting the airfoil  32  and platform member  44  as a single member. Alternatively, the airfoil  32  may be joined integrally to the platform member  44 , such as by welding, and the platform cover  60   a  may subsequently be attached over the gas side surface  48  of the platform member  44  in a manner described below. 
     As may be further seen in  FIGS. 2 and 3 , the platform cover  60   a  includes an outer surface  62   a  extending generally circumferentially between a first or inner edge  64   a  and a second or outer edge  66   a , and extending generally axially between an upstream edge  68   a  and a downstream edge  70   a . The inner edge  64   a  may be located adjacent to or in engagement with the sidewall  34 , where the outer surface  62   a  intersects the sidewall  34  at a location that may be radially displaced from the gas side surface  48 . For example, the outer surface  62   a  may intersect the sidewall  34  at a location that is radially outwardly from the fillet joint  46 . The outer surface  62   a  is located for contact with the hot working gas, and substantially isolates the gas side surface  48  from contact with the hot working gas. 
     Referring to  FIG. 4 , the outer surface  62   a  may be formed with a contour defining a contoured endwall for the airfoil structure  30 . In particular, it may be desirable to provide the airfoil structure  30  with a contoured endwall, including contours such as one or more elevated ridges  72   a  and/or one or more depressed troughs  74   a  to minimize or reduce secondary flaw vortices that may form in the flow field at the endwall between adjacent airfoil structures  30 . 
     In accordance with an aspect of the platform cover  60   a , the inner edge  64   a  may be provided with a configuration or contour for providing an improved aerodynamic efficiency adjacent to the joint  46  between the sidewall  34  and the platform member  44  that in a conventional construction of the joint may not be desirable from a structural or component strength standpoint. In particular, an aerodynamically efficient intersection of the outer surface  62   a  with the sidewall  34  at the inner edge  64   a  may form a sharp corner or angle  76   a , and may comprise a corner defining an acute angle between the sidewall  34  and the outer surface  62   a . Since the junction forming the structural connection between the sidewall  34  and the platform member  44  member may comprise a structurally preferable fillet joint  46 , i.e., a curved or smooth transition, the separately formed platform cover  60   a  may enable provision of an aerodynamically efficient, non-structural shaped member while maintaining structural integrity of the airfoil structure  30 . The non-structural shaped member, as particularly defined at the inner edge  64   a , may extend along a length of the sidewall  34  and may define a varying contour along the length of the inner edge  64   a , see  FIG. 2 , to match the aerodynamic requirements at different locations along the airfoil  32 . Further, formation of a contoured outer surface  62   a  on a separate member, i.e., on the platform cover  60   a , distinct from the assembly of the airfoil  32  and platform member  44  may facilitate formation of particular contours, such as complex contours, that may be more difficult to manufacture with conventional techniques, such as by casting the contour directly on the gas side surface  48  of the platform member  44 . 
     The present airfoil structure  30  may also facilitate formation of additional structure associated with an inner side  78   a  opposite from the outer side  62   a  of the platform cover  60   a . For example, the inner side  78   a  may comprise a channel wall  80   a  formed on the platform cover  60   a  and facing toward the gas side surface  48 . Further, support members  82   a  may extend from the channel wall  80   a  into engagement with the platform member  44 , and support the platform cover  60   a  with the channel wall  80   a  in spaced relation to the gas side surface  48  of the platform member  44 . 
     As may be seen in  FIGS. 3 and 4 , one or more cooling fluid channels  84   a  are defined in a space formed between the channel wall  80   a  and the gas side surface  48 , and between adjacent support members  82   a , permitting flow of cooling fluid. Hence, the platform cover  60   a  may facilitate provision of cooling channels  84   a  through the contoured surface, including additional cooling passages (not shown) that may be formed in or through the channel wall  80   a  and/or through the support members  82   a , to provide controlled amounts of cooling flow, such as to improve uniformity of cooling for the heat load at the outer surface  62   a . The construction of the airfoil structure  30  with a separately formed platform cover  60   a  may facilitate formation of the cooling channels  84   a , i.e., separately formed cooling channels  84   a , to customize the cooling provided to the varying thickness contours, while avoiding potentially complex manufacturing steps that may be required, such as complex core formations that may otherwise be required if similar cooling were to be provided by conventional methods of casting the cooling passages within the platform member  44 . 
     The cooling channels  84   a  may be provided with a cooling fluid, such as cooling air, via cooling fluid passages  88  extending through at least a portion of either or both of the airfoil  32  and the platform member  44 . The cooling fluid passages  88  receive cooling fluid from a cooling fluid source, such as a cooling fluid channel  90  extending radially outwardly from the root  39  through the airfoil  32 . The cooling fluid passages  88  discharge the cooling fluid into the cooling channels  84   a  through outlets at the gas side surface  48 . 
     The platform cover  60   a  illustrated in  FIG. 4  may be mounted or attached to the platform member  44  by a welding process, such as by braze welding distal ends  92   a  of the support members  82   a  to the gas side surface  48 . The platform cover  60   a  may be formed of the same material or a different material than the platform member  44 , such that the particular process forming the connection between the platform cover  60   a  and the platform member  44  may depend on the materials to be joined. Also, the material of the platform member  44  and the platform cover  60   a  may be selected such that the platform member  44  is formed of a higher strength material, while the material of the platform cover  60   a  may be optimized for desired thermal properties to withstand high temperatures. For example, and without limiting the invention, the platform member  44  may be formed of a conventional cast nickel-based alloy, while materials that may be used to form the platform cover  60   a  generally may include, but are not limited to, single crystal super alloys, powder metallurgy metals, ceramics, and other materials, including materials that may be readily preformed with contours and those which may provide thermal protection to the platform member  44 . 
     In accordance with one aspect of the platform cover of  FIG. 4 , the outer edge  66   a  of the platform cover  60   a  may define a planar surface that is generally aligned with the mateface side  54  of the platform member  44 , i.e., extending in a generally radial direction. The inner side  78   a  of the platform cover outer edge  66   a  is spaced from the gas side surface  48  to define a mateface seal slot  94   a , which may have an inner boundary defined by one of the support members  82   a . The mateface seal slot  94   a  may receive an edge of a mateface seal (not shown) for sealing a gap formed between the airfoil structure  30  and an adjacent airfoil structure (not shown). 
     Referring to  FIG. 5 , alternative aspects are illustrated embodied in an airfoil structure  130 , where elements of the airfoil structure  130  corresponding to elements of the airfoil structure  30  of  FIG. 4  are identified with the same reference numeral increased by  100 . The airfoil structure  130  includes a separately formed endwall defined by pressure and suction side platform covers  160   a ,  160   b . As in the aspects discussed above with regard to the airfoil structure  30  of  FIG. 4 , the platform covers  160   a ,  160   b  comprise respective outer surfaces  162   a ,  162   b  that may include predetermined contours, such as elevated ridges  172   b  and one or more depressed troughs  174   b , as illustrated on the platform cover  160   b.    
     In accordance with one aspect illustrated in  FIG. 5 , and with reference to the platform cover  160   a , the distal ends  192   a  of the support members  182   a  include a form that may be captured in a corresponding form defined by recesses  193   a  in the platform member  144 . In the illustrated configuration for the support members  182   a , the form defined by the distal ends  192   a  and the cooperating recesses  193   a  for receiving the distal ends  192   a  comprise a dovetail, such as a dovetail configuration that may permit the dovetail distal end  192   a  to slide into position within the dovetail recess  193   a . That is, the enlarged dovetail ends  192   a  of the support members  182   a  define a form fit connection that may be effective to prevent movement of the platform cover  160   a  in a direction perpendicular to the gas side surface  148 , such as to resist a centrifugal force to the platform cover  160   a  during rotation of the rotor  26  ( FIG. 1 ). It should be understood that other form fit connections may be defined by the distal ends  192   a  and recesses  193   a  to retain the platform cover  160   a  in place. 
     The platform covers  160   a ,  160   b  may be slid into position in any direction, e.g., circumferentially, that is practical for assembling the platform covers to the platform member  144 . Further, the different platform covers  160   a ,  160   b  could be configured to slide in different directions as necessary to accommodate positioning of the platform covers  160   a ,  160   b  adjacent to the airfoil  32 . 
     As described above with regard to aspects of the airfoil structure  30  of  FIG. 4 , cooling channels  184   a  may be formed between an inner side  178   a  of the platform cover  160   a  and a gas side surface  148  of the platform member  144 . In accordance with a further aspect, cooling fluid passages  189  may extend through the platform member  144  to provide cooling fluid to the cooling channels  184   a  for discharging the cooling fluid to outlets at the gas side surface  148 . A cooling fluid, such as cooling air, passing through the cooling fluid passages  189  may be supplied from a disc cavity defined radially inwardly from the platform member  144 . Additionally, cooling fluid passages  188  may receive cooling fluid from a cooling fluid source, such as a cooling fluid channel  190  extending through the airfoil  132 , and discharge the cooling fluid through outlets at the gas side surface  148 , such as at locations adjacent to the fillet joints  146 . 
     In accordance with a further aspect illustrated in  FIG. 5 , a first or inner edge  164   a  of the platform cover  160   a  may be located adjacent to or in engagement with the sidewall  134 , where the outer surface  162   a  intersects the sidewall  134  at a location that may be radially displaced from the gas side surface  148 . A second or outer edge  166   a  may be located adjacent to an edge structure  165   a  of the platform member  144  that defines a mateface side  154 . The edge structure  165   a  defines a mateface seal slot  194   a  that may receive a mateface seal (not shown). A side of the edge structure  165   a  opposite from the mateface seal slot  194   a  comprises a generally radially extending wall  195   a  for engagement with the outer edge  166   a  of the platform cover  160   a . The second or outer edge  166   b  of the suction side platform cover  160   b  illustrates an alternative aspect in which an outer contour portion  167   b  of the platform cover  160   b  may extend circumferentially over at least a portion of the edge structure  165   b.    
     While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.