Patent Publication Number: US-11028709-B2

Title: Airfoil shroud assembly using tenon with externally threaded stud and nut

Description:
BACKGROUND OF THE INVENTION 
     The disclosure relates generally to turbomachines, and more particularly, to an airfoil shroud assembly including a tenon with an externally threaded stud for coupling airfoil shrouds to an airfoil in a turbomachine. 
     Turbomachines include one or more rows of airfoils, including stator vanes including stationary airfoils and rotor blades or buckets including rotating airfoils. Turbomachines can take a variety of forms such as gas turbines, jet engines, steam turbines and compressors. A gas turbine system, for example, may include an axial compressor at the front, one or more combustors around the middle, and a turbine at the rear. An axial compressor, for example, has a series of stages with each stage comprising a row of rotor blades followed by a row of stationary stator vanes. Accordingly, each stage generally comprises a set of rotor blades and stator vanes. In an axial compressor, the rotor blades increase the kinetic energy of a fluid that enters through an inlet and the stator vanes convert the increased kinetic energy of the fluid into static pressure through diffusion. Accordingly, both sets of airfoils play a vital role in increasing the pressure of the fluid. Similar dynamics are observed in other forms of turbomachines in which the kinetic energy of a working fluid that enters the turbomachine through an inlet is converted to rotational energy by the rotor blades as the stator vanes direct the kinetic energy of the working fluid into the rotor blades. In any system, the type of working fluid may vary depending on the type of turbomachine, e.g., air in a compressor, combustion gases in gas turbine, steam in a steam turbine, etc. 
     In the case of stator vanes, the set of airfoils is connected at the base of the airfoils to form the segment and may also be connected to the adjacent airfoils in the segment by an inner shroud. In many applications, it is not practical to manufacture an integral base, stator vane, and vane shroud. Thus, each stator vane in the segment may be produced independently, often including an integral base section, and assembled into the complete set. The shroud may be produced as one or more separate components that are attached to the inward facing ends of the stator vanes. In some embodiments, a single vane shroud is provided for each stator vane. In other embodiments, multiple adjacent stator vanes may be attached to a multi-vane shroud. Coupling of multiple adjacent stator vanes may help address vortex bursting or breakdown, which is an abrupt change in flow structure of swirling working fluid as the working fluid moves through the turbomachine that can cause undesirable vibrations in the machine. In some turbomachines, such as axial compressors, vortex bursting can present challenges for cantilevered stationary vanes because it can hinder operation at certain cold ambient temperatures and/or at part load conditions. 
     A stator vane, vane shroud, and one or more additional attachment components, such as bolts, bushings, washers, nut and other components may be referred to as a vane shroud assembly. The vane and shroud may each include features for engagement and attachment to each other. In some arrangements, the vane incorporates a tenon, or extension from the end of the airfoil, which extends into and/or through a compatible opening in the shroud, and a bushing is also inserted into the opening in the shroud and secured with an externally threaded bolt coupled to the tenon to attach the shroud to the vane. Assembling shrouds on stationary vanes with this type arrangement can pose a challenge on smaller turbomachines because space constraints prevent easy access. One current approach employs small externally threaded bolts that thread into internally threaded tenons on the stationary vanes to hold the shroud to the vanes. This approach is difficult to implement in the small spaces within smaller turbomachines, and presents concerns about durability. 
     BRIEF DESCRIPTION OF THE INVENTION 
     A first aspect of the disclosure provides an airfoil and shroud assembly, comprising: an airfoil including a root end, a free end and a tenon extending from the free end, the tenon including a base and an externally threaded stud extending from the base; a shroud including an opening configured to receive the base of the tenon; and a nut configured to be threadably couple to the externally threaded stud on the tenon on the airfoil to couple the shroud to the airfoil. 
     A second aspect of the disclosure provides a vane for a turbomachine, the vane comprising: an airfoil body including a free end and a root end, the root end configured to be mounted to an outer casing of the turbomachine; and a tenon extending from a free end of the airfoil body, the tenon including: a base configured to be received in an opening in a shroud and an externally threaded stud extending from the base. 
     A third aspect of the disclosure provides a turbomachine, comprising: an outer casing surrounding a rotor; a plurality of vanes, each vane including: an airfoil body having a radially outer end coupled to the outer casing and extending inwardly toward the rotor to a radially inner end, and a tenon extending from the radially inner end, the tenon including a base and an externally threaded stud extending from the base; a shroud including a plurality of openings to receive the base the tenon of each of a set of the plurality of vanes; and a nut threadably coupled to each of the externally threaded studs on the tenons for coupling the shroud to the set of the plurality of vanes. 
     A fourth aspect of the disclosure relates to a vane and shroud assembly, comprising: a vane including an airfoil body including a root end, a free end and a tenon extending from the free end, wherein the root end is configured to be coupled to an outer casing of a turbomachine, and the free end extends radially inward toward a rotor of the turbomachine, and wherein the tenon includes a base and an externally threaded stud extending from the base; a shroud including an opening; a bushing having a first internal opening to receive the base of the tenon, a second internal opening allowing the externally threaded stud to pass therethrough, and an external surface configured to engage an inner surface of the opening in the shroud; and a nut configured to be threadably couple to the externally threaded stud on the tenon on the airfoil body to couple the shroud to the airfoil. 
     The illustrative aspects of the present disclosure are designed to solve the problems herein described and/or other problems not discussed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of this disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure taken in conjunction with the accompanying drawings that depict various embodiments of the disclosure, in which: 
         FIG. 1  is a schematic illustration of an illustrative turbomachine in the form of a gas turbine system. 
         FIG. 2  is a cross-section illustration of an illustrative compressor assembly that may be used with the gas turbine in  FIG. 1 . 
         FIG. 3  is a front view of an airfoil shroud assembly for a single airfoil body according to embodiments of the disclosure. 
         FIG. 4  is a front view of an airfoil shroud assembly for a multiple airfoil bodies according to embodiments of the disclosure. 
         FIG. 5  is an enlarged cross-sectional view of an airfoil shroud assembly according to embodiments of the disclosure. 
         FIG. 6  is an enlarged cross-sectional view of an airfoil shroud assembly according to another embodiment of the disclosure. 
         FIG. 7  is an enlarged cross-sectional view of an airfoil shroud assembly according to another embodiment of the disclosure. 
         FIG. 8  is an exploded perspective view of an airfoil shroud assembly for a multiple airfoil bodies according to embodiments of the disclosure. 
     
    
    
     It is noted that the drawings of the disclosure are not to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     As an initial matter, in order to clearly describe the current disclosure it will become necessary to select certain terminology when referring to and describing relevant machine components within a turbomachine. When doing this, if possible, common industry terminology will be used and employed in a manner consistent with its accepted meaning. Unless otherwise stated, such terminology should be given a broad interpretation consistent with the context of the present application and the scope of the appended claims. Those of ordinary skill in the art will appreciate that often a particular component may be referred to using several different or overlapping terms. What may be described herein as being a single part may include and be referenced in another context as consisting of multiple components. Alternatively, what may be described herein as including multiple components may be referred to elsewhere as a single part. 
     In addition, several descriptive terms may be used regularly herein, and it should prove helpful to define these terms at the onset of this section. These terms and their definitions, unless stated otherwise, are as follows. As used herein, “downstream” and “upstream” are terms that indicate a direction relative to the flow of a fluid, such as the working fluid through the turbine engine or, for example, the flow of air through a compressor. The term “downstream” corresponds to the direction of flow of the fluid, and the term “upstream” refers to the direction opposite to the flow. The terms “forward” and “aft,” without any further specificity, refer to directions, with “forward” referring to the front or compressor end of the engine, and “aft” referring to the rearward or turbine end of the engine. It is often required to describe parts that are at differing radial positions with regard to a center axis. The term “radial” refers to movement or position perpendicular to an axis. In cases such as this, if a first component resides closer to the axis than a second component, it will be stated herein that the first component is “radially inward” or “inboard” of the second component. If, on the other hand, the first component resides further from the axis than the second component, it may be stated herein that the first component is “radially outward” or “outboard” of the second component. The term “axial” refers to movement or position parallel to an axis. Finally, the term “circumferential” refers to movement or position around an axis. It will be appreciated that such terms may be applied in relation to the center axis of the turbine. 
     Where an element or layer is referred to as being “on,” “engaged to,” “disengaged from,” “connected to” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     As indicated above, the disclosure provides an airfoil and shroud assembly including an airfoil including a root end, a free end and a tenon extending from the free end. In contrast to conventional assemblies, the tenon includes a base and an externally threaded stud extending from the base. A shroud includes an opening configured to the base of the tenon. A nut is configured to be threadably coupled to the externally threaded stud on the tenon on the airfoil to couple the shroud to the airfoil. The airfoil and shroud assembly provides a stronger and more durable coupling. Further, the airfoil shroud assembly reduces vortex bursting and dampens response to secondary flow vibration, and reduces the impact of cold ambient or part load operations on certain turbomachines, such as an axial compressor. 
       FIG. 1  is a schematic view of an illustrative turbomachine in the form of a gas turbine system  100 . System  100  includes a compressor  102  and a combustor  104 . Combustor  104  includes a combustion region  105  and a fuel nozzle assembly  106 . System  100  also includes a turbine  108  and a common compressor/turbine shaft  110  (sometimes referred to as rotor  110 ). In one embodiment, engine  100  is a MS7001FB engine, sometimes referred to as a 9FB engine, commercially available from General Electric Company, Greenville, S.C. The present disclosure is not limited to any one particular engine and may be implanted in connection with other gas turbines and turbomachines. 
     In operation, air flows through compressor  102  and compressed air is supplied to combustor  104 . Specifically, the compressed air is supplied to fuel nozzle assembly  106  that is integral to combustor  104 . Assembly  106  is in flow communication with combustion region  105 . Fuel nozzle assembly  106  is also in flow communication with a fuel source (not shown in  FIG. 1 ) and channels fuel and air to combustion region  105 . Combustor  104  ignites and combusts fuel. Combustor  104  is in flow communication with turbine  108  for which gas thermal energy is converted to mechanical rotational energy. Turbine  108  is rotatably coupled to and drives rotor  110 . Compressor  102  also is rotatably coupled to shaft  110 . 
       FIG. 2  shows a cross-section illustration of an illustrative compressor assembly  102  that may be used with gas turbine system  100  in  FIG. 1 . Compressor assembly  102  includes vanes  112  and rotor blades  114 . Each vane  112  is held in compressor assembly  108  fixed to an outer casing  116  by a radially outer, root end  118 , and includes a shroud  120  on a radially inner, free end  122 . Rotor blades  114  include a radially inner root end or base  124  fixed to rotor  110 , and free radially outer end  126 . Teachings of the disclosure will be described relative to an airfoil free end  122  in the form of a vane  112 . In this case, root end  118  is configured to be coupled to outer casing  116  of the turbomachine, and a free end  128  extends radially inward toward rotor  110  of the turbomachine. However, it is emphasized that teachings of the disclosure may be applicable to airfoils for rotor blades  114  also. Further, while teachings of the disclosure will be described relative to compressor assembly  108 , an airfoil shroud assembly  130  according to embodiments of the disclosure may be applied to a variety of turbomachines including, for example, a gas turbine assembly, a steam turbine, jet engine, etc. 
       FIGS. 3 and 4  show an example airfoil shroud assembly  130  in various views. Airfoil shroud assembly  130  includes various components that are assembled and attached to couple an airfoil(s) to a shroud and form the installed airfoil shroud assembly  130 .  FIG. 3  shows an airfoil shroud assembly  130  for a single airfoil body  132 , and  FIG. 4  shows an airfoil shroud assembly  130  for a number of airfoil bodies  132 . Each airfoil body  132  includes an integral root end or base  134  for fixed coupling, e.g., to an outer casing  116  ( FIG. 2 ). For simplicity, only a single airfoil shroud assembly  130 , including a single airfoil body  132  with integral root end or base  134  is shown in most figures without the ring, adjacent airfoils, and other turbomachine components with which it would be assembled in an actual installation. 
     As shown in the enlarged cross-sectional view of  FIG. 5 , airfoil shroud assembly  130  includes airfoil body  132  including root end  134  ( FIG. 3 ), free end  142  and tenon  150  extending from free end  142 . Tenon  150  includes a base  152  and, in contrast to conventional arrangements, an externally threaded stud  154  extending from base  152 . In one embodiment, shown in  FIG. 5 , shroud  140  includes an opening  156  configured to receive base  152  of tenon  150 , i.e., base  152  and/or externally threaded stud  154  therethrough. In this embodiment, base  152  may engage an inner surface  158  of opening  156 . Alternatively, as shown in  FIG. 6 , airfoil shroud assembly  130  may include a bushing  160  having a first internal opening  162  to receive base  152  of tenon  150 , and an external surface  164  configured to engage inner surface  158  of opening  156  in shroud  140 . Bushing  160  may also include a second internal opening  166  allowing externally threaded stud  154  to pass therethrough. Bushing  160  provides lateral spacing between the other components, and may include various configurations of lateral contact and non-contact surfaces between adjacent components. As shown best in  FIG. 8 , shroud  140  is installed on free end  142  by placement of opening  156  over base  152  of tenon  150  of airfoil body  132 . Where provided, bushing  160  can be positioned over tenon  150  to laterally (e.g., concentrically) position opening  156  about bushing  160  and base  152 . 
     Airfoil shroud assembly  130  also includes a nut  170  configured to be threadably couple to externally threaded stud  154  on tenon  150  on airfoil body  132  to couple shroud  140  to airfoil body (or bodies)  132 . Nut  170  may include any member having an internally threaded opening  174  configured to mate with externally threaded stud  154 . In one embodiment, nut  170  includes an integral washer  172 ; however, as shown in  FIG. 7 , an integral washer is not necessary where nut  170  has sufficient diameter to compress against bushing  160  or shroud  140 . 
     The interaction of opening  156  and base  152  or bushing  160  are sized to allow for stress transmission through surface engagement. In one embodiment, shown in  FIG. 6 , bushing  160  has a radially outer surface  168  (relative to center of bushing) having a diameter D same as a diameter of integral washer  172  to provide uniform force distribution; however this is not necessary in all instances. 
     Referring to  FIG. 8 , as noted, shroud  140  may include a plurality of openings  156 , each opening  156  configured to receive a tenon  150  of a respective airfoil body  132 . While five openings  156  are shown in shroud  140 , any number can be employed. As understood in the art, a number of shrouds  140  can be configured to create a full ring about rotor  110  ( FIG. 2 ), and couple any desired number of individual airfoil bodies  132  into any number of sets of airfoil bodies  132 . 
     A turbomachine  100  according to embodiments of the disclosure may include outer casing  116  surrounding rotor  110 , and a plurality of vanes  112  ( FIG. 2 ) coupled to outer casing  116  ( FIG. 1 ) at a radially outer end  134  thereof and extending inwardly toward rotor  110  to a radially inner, free end  142  thereof. Each vane  112  includes: an airfoil body  132  having radially outer, root end  134  coupled to outer casing  116  and extending inwardly toward rotor to radially inner, free end  142 , and a tenon  150  extending from radially inner end  142 . As noted, tenon  150  includes base  152  and externally threaded stud  154  extending from the base. Shroud  140  includes a plurality of openings  156  to receive base  152  of tenon  150  of each of a set of the plurality of vanes  112 . As shown for example in  FIG. 6 , airfoil shroud assembly  130  may also include bushing  160  having internal opening  162  to receive base  152  of tenon  150 , and external surface  164  configured to engage inner surface  158  of opening  156  in shroud  140 . As shown in  FIG. 8 , shroud  140  is installed on free end  142  by placement of opening  156  over base  152  of tenon  150  of airfoil body  132 . Where provided, bushing  160  can be positioned over tenon  150  to laterally (e.g., concentrically) position opening  156  about bushing  160  and base  152 . A nut  170  threadably couples to each of externally threaded studs  154  on tenons  150  for coupling shroud  140  to the set of plurality of vanes  112 . Nut  170  may include integral washer  172 . 
     It will be appreciated that the surfaces of parts such as shroud  140 , tenon  150  including base  152  and stud  154 , may be angled in any direction desired for ease of installation and/or stress transmission through mating surfaces. Parts of airfoil shroud assembly  130  can be made of any material appropriate for their function, e.g., superalloys, alloys, etc. While tenon  150 , bushing  160  and opening  156  in shroud  140  have been shown generally circular, it is understood that the mating surfaces between any two of the components may have different mating shapes, e.g., polygonal: square, rectangular, hexagonal, etc.; oval or otherwise oblong; etc. Further, base  152  and mating first internal opening  162  of bushing  160  can be hexagonal as shown, or may have different mating shapes, e.g., polygonal: square, rectangular, hexagonal, etc.; oval or otherwise oblong; etc. 
     Embodiments of the disclosure provide an airfoil shroud assembly that can be used for small sized systems with sufficient durability and strength, and still reduce vortex bursting and dampen response due to secondary flow vibration. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not. 
     Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about,” “approximately” and “substantially,” are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. “Approximately” as applied to a particular value of a range applies to both values, and unless otherwise dependent on the precision of the instrument measuring the value, may indicate +/−10% of the stated value(s). 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiment was chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.