Patent Publication Number: US-9845698-B2

Title: Belly band seal with anti-rotation structure

Description:
BACKGROUND 
     1. Field 
     The present invention relates in general to seals for multistage turbomachines. In particular, embodiments of the present invention relate to an anti-rotation structure for a belly band seal provided between adjoining disks in a multistage turbomachine, and to a method for assembling such a bellyband seal. 
     2. Description of the Related Art 
     In various multistage turbomachines used for energy conversion, such as turbines, a fluid is used to produce rotational motion. In a gas turbine, for example, a gas is compressed through successive stages in a compressor and mixed with fuel in a combustor. The combination of gas and fuel is then ignited for generating combustion gases that are directed to turbine stages to produce the rotational motion. The turbine stages and compressor stages typically have stationary or non-rotary components, e.g., vane structures, that cooperate with rotatable components, e.g., rotor blades, for compressing and expanding the operational gases. 
     The rotor blades are typically mounted to disks that are supported for rotation on a rotor shaft. Annular arms extend from opposed portions of adjoining disks to define paired annular arms. A cooling air cavity is formed on an inner side of the paired annular arms between the disks of mutually adjacent stages, and a labyrinth seal may be provided on the inner circumferential surface of the stationary vane structures for cooperating with the annular arms to effect a gas seal between a path for the hot combustion gases and the cooling air cavity. The paired annular arms extending from opposed portions of adjoining disks define opposing end faces located in spaced relation to each other. This space between the opposing end faces of the adjacent rotor disks is sealed by a seal structure commonly referred to as a “belly band seal”. The belly band seal includes a seal strip which bridges the gap between the opposing end faces of the adjoining rotor disks to prevent cooling air flowing through the cooling air cavity from leaking into the path for the hot combustion gases. The seal strip may be formed of multiple segments, in the circumferential direction, that are interconnected at lapped or stepped ends. 
     When the seal strip comprises plural segments positioned adjacent to each other, in the circumferential direction, under thermal load the seal strip may shift tangentially (i.e., along a circumferential direction) relative to each other. Shifting may cause one end of a seal strip segment to increase the overlap with an adjacent segment, while the opposite end of the seal strip segment will move out of engagement with an adjacent segment, opening a gap for passage of gases through the seal strip. In order to prevent rotation of the seal strip segments, the segments may be provided with anti-rotation structures to cooperate with an adjacent disk surface for holding the segments stationary relative to the disk. 
     Anti-rotation structures typically constrain the seal strip at the center of the seal strip segment. Known configurations for an anti-rotation structure includes a pin configuration, bend tab configuration, lock-block configuration, u-clip configuration and T-block configuration, among others. Among all of the above configurations, the pin configuration provides relatively high design life, typically about 18,000-50,000 hours. However, a belly band seal having an anti-rotation structure with a pin design can only be installed when the rotor is de-stacked. 
     SUMMARY 
     Briefly, aspects of the present invention provide a belly band seal with an anti-rotation structure for use in a turbomachine, a multi-stage turbomachine having a belly band seal with an anti-rotation structure, and a method for assembling a belly band seal having the illustrated anti-rotation structure. 
     According to a first aspect, a belly band seal for use in a turbomachine is provided. The turbomachine comprises a plurality of stages comprising plural rotor disks, and arms on opposed portions of adjoining rotor disks to define paired arms with a space therebetween, said paired arms comprising respective end faces including slots. The belly band seal comprises a seal strip for positioning in the space between the paired arms, the seal strip being in the shape of a segment of a ring having opposite edges for locating in respective slots of said paired arms and coaxial to the rotor disks. The bellyband seal further comprises an anti-rotation structure disposed on a radially inner surface of the seal strip. The anti-rotation structure is configured as a cantilever having a pivoted end fixed to the radially inner surface of the seal strip and a free end comprising a radially inwardly extending engagement member for removably positioning in a radial recess provided on one of the arms of the paired arms. The cantilever is configured so as to urge the engagement member toward the radial recess by spring action. The radial recess is configured to constrain a tangential movement of the engagement member upon being positioned therein. 
     According to a second aspect, a multi-stage turbomachine with the inventive belly band seal is provided. The multi-stage turbomachine includes a plurality of rotor disks, comprising arms on opposed portions of adjoining rotor disks that define paired arms with a space therebetween, said paired arms comprising respective end faces including slots. The belly band seal includes a seal strip positioned in the space between the paired arms. The seal strip being in the shape of a segment of a ring having opposite edges located in respective slots of said paired arms. The ring is coaxial to the rotor disks. The belly band seal includes an anti-rotation structure disposed on a radially inner surface of the seal strip. The anti-rotation structure is configured as a cantilever having a pivoted end fixed to the radially inner surface of the seal strip and a free end comprising a radially inwardly extending engagement member removably positioned in a radial recess provided on one of the arms of the paired arms. The cantilever is configured so as to urge the engagement member toward the radial recess by spring action. The radial recess is configured to constrain a tangential movement of the engagement member positioned therein. 
     According to a third aspect, a method is provided for assembling the inventive belly band seal in a multi-stage turbomachine. The method includes arranging the belly band seal to cover an annular space between a pair of arms formed by opposed portions of adjoining rotor disks of the multi-stage turbomachine by positioning the seal strip such that opposite edges of the seal strip are located in respective slots of said pair of arms. The method further includes moving the seal strip along the slots in a circumferential direction until a final assembly position is reached wherein the engagement member is aligned with a radial recess in one of the arms of the pair of arms, wherein during the movement of the seal strip, the free end of the cantilever is deflected and held in position by a temporary retaining structure to allow passage of the seal strip through the slots. The method further includes, upon reaching the final assembly position, releasing the free end of the cantilever such that the engagement member is urged towards the radial recess and held therein by spring action of the cantilever. The radial recess constrains a tangential movement of the engagement member positioned therein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is shown in more detail by help of figures. The figures show preferred configurations and do not limit the scope of the invention. 
         FIG. 1  is diagrammatic section view of a portion of a gas turbine engine, 
         FIG. 2  is a perspective view of a belly band seal with an anti-rotation structure according to a first embodiment, 
         FIG. 3  is a diagrammatic bottom end view of the belly band seal according to the first embodiment, 
         FIG. 4  is a diagrammatic cross-sectional view of the belly band seal along the plane IV-IV of  FIG. 3 , according to a first configuration of the verification pin, 
         FIG. 5  is a diagrammatic cross-sectional view of the belly band seal along the plane IV-IV of  FIG. 3 , according to a first configuration of the verification pin, 
         FIG. 6  is a perspective view of a belly band seal with an anti-rotation structure according to a second embodiment, 
         FIG. 7  is a diagrammatic bottom end view of the belly band seal according to the second embodiment, and 
         FIG. 8  is a diagrammatic cross-section view of the anti-rotation structure having a verification pin according to the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     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 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. 
     Referring to  FIG. 1 , a portion of a turbine engine  10  is illustrated diagrammatically. The turbine engine  10  has an engine axis  11  and includes adjoining stages  12 ,  14 . Each stage  12 ,  14  comprises at least one row of stationary vane assemblies  16  and at least one row of rotating blades  18 . The vane assemblies  16  and blades  18  are positioned circumferentially within the engine  10  with alternating arrays of vane assemblies  16  and blades  18  located in the axial direction of the turbine engine  10 . The blades  18  are supported on rotor disks  20  secured to adjacent disks with spindle bolts  22 . The vane assemblies  16  and blades  18  extend into an annular gas passage  24 , and hot gases directed through the gas passage  24  flow past the vane assemblies  16  and blades  18  to remaining rotating elements. 
     Disk cavities  26 ,  28  are located radially inwardly from the gas passage  24 . Purge air is preferably provided from cooling gas passing through internal passages in the vane assemblies  16  to the disk cavities  26 ,  28  to cool blades  18  and to provide a pressure to balance against the pressure of the hot gases in the gas passage  24 . In addition, interstage seals comprising labyrinth seals  32  are supported at the radially inner side of the vane assemblies  16  and are engaged with surfaces defined on paired annular disk arms  34 ,  36  extending axially from opposed portions of adjoining disks  20 . An annular cooling air cavity  38  is formed between the opposed portions of adjoining disks  20  on a radially inner side  37   a ,  37   b  of the respective paired annular disk arms  34 ,  36 . The annular cooling air cavity  38  receives cooling air passing through disk passages to cool the disks  20 . 
     The pair of arms  34 ,  36  of adjoining rotor disks  20  define an annular space or gap therebetween. This gap is bridged by a belly band seal  46 , which defines a seal for preventing or substantially limiting flow of gases between the cooling air cavity  38  and the disk cavities  26 ,  28 . The belly band seal  46  essentially includes a seal strip that is formed in the shape of a segment of a ring. Opposing edges of the seal strip are engaged with the arms  34  and  36  of the adjoining rotor disks  20  to seal the annular gap between them. Multiple such segments, typically four, are assembled circumferentially next to each other to form an annular-shaped belly band seal  46 . The turbine engine  10  typically includes multiple belly band seals  46  in a plurality of locations along its axis  11 , between rotor disks  20  of adjoining stages. 
     The ends of each of the segments (seal strips) of the belly band seal may be ship-lapped. Under thermal load, the seal strips may shift tangentially (i.e., along a circumferential direction) relative to each other. Shifting may cause one end of a seal strip segment to increase the overlap with an adjacent segment, while the opposite end of the seal strip segment will move out of engagement with an adjacent segment, opening a gap for passage of gases through the seal strip. In order to prevent rotation of the seal strip segments, each of the segments or seal strips may be provided with an anti-rotation structure, located, for example near about the center of the seal strip, which would cooperate with an adjacent disk surface for holding the segments stationary relative to the disk. 
       FIG. 2  illustrates a perspective view of a belly band seal  46  according an example embodiment. The belly band seal  46  is made up of a number of seal strips  50 , only one of which is illustrated in the drawing. The seal strip  50  has the shape of a segment of a ring, such that when a plurality of such seal strips  50  are assembled circumferentially next to each other, an annular or ring-shaped belly band seal  46  is produced. The seal strip  50  has a radially outer surface  51  and a radially inner surface  52 . The surfaces  51  and  52  are delimited along an axial direction by opposite edges  53  and  54  that extend in a circumferential direction. 
     The illustrated belly band seal  46  comprises an anti-rotation structure  60 , located between the circumferential ends of the seal strip  50 . The anti-rotation structure  60  is disposed on the radially inner surface  52  of the seal strip  50  and essentially includes a cantilever  61  having a free end  62  and a pivoted end  63 , which is attached to the radially inner surface  52  of the seal strip  50 . In an exemplary embodiment, the anti-rotation structure  60  and the seal strip  50  are formed in one piece. For example, the anti-rotation structure  60  and the seal strip  50  may be machined out of a single metal bar, thus avoiding additional weight associated with welding or bolting. An exemplary machining process includes electro discharge machining (EDM). Alternately, the anti-rotation structure  60  may also be disposed on the radially inner surface  52  of the seal strip  50  by joining methods, such as by welding, brazing, bolting or combinations thereof. 
     The free end  62  of the cantilever  61  includes a radially inwardly extending engagement member  65 , which is meant to engage within a corresponding radial recess in one of the arms  34  of a rotor disk  20 , as illustrated hereinafter. In the embodiment of  FIG. 2 , the engagement member  65  is configured as a pin having a generally cylindrical shape. In one embodiment, the dimensions of the pin  65  (e.g., diameter) may correspond to that of a standard factory pin of a conventionally known type of anti-rotation structure. Such a feature provides easy adaptability of the inventive belly band seal to existing turbomachines having standard factory pin design of anti-rotation structures, resulting in minimal modification to its components, such as rotor disks. The factory pin design of the free end  62  of the cantilever  61  also provides high operational life of the belly band seal  46 . 
     In the illustrated embodiment, the pivoted end  63  of the cantilever  61  comprises a recess or a hole  66 . The recess or hole  66  provides a region of reduced mass, which results in a lighter weight of the rotating belly band seal  46 . 
     The cantilever  61  of the anti-rotation structure  60  is capable of being deflected, i.e., bent or rotated about a pivot axis  64 . In  FIG. 2 , the cantilever  61  is shown to be in a natural or un-deflected position. When deflected, i.e., bent or rotated about the pivot axis  64 , as illustrated in  FIG. 3 , the cantilever  61  tends to return to its natural position by spring action, resultant from the elasticity of the material of the cantilever  61 . 
     The assembly of the belly band seal  46  into the turbomachine  10  will now be illustrated referring generally to  FIG. 3-5 . 
       FIG. 3  illustrates a bottom view of the belly band seal  46  as seen along a direction III in  FIG. 2 . In the drawing, the cantilever  61  is shown in two states, namely a deflected state illustrated by dotted lines, and natural or free state illustrated in bold. During assembly of belly band seal  46 , the cantilever  61  of the anti-rotation structure is held in a deflected position. In this embodiment, a temporary retaining structure, such as a pin  70 , is used for holding the cantilever  61  in the deflected position during the assembly. To this end, the sealing strip  50  may be provided with a hole or a recess  79  to receive the pin  70  (see  FIG. 2 ). 
     The belly band seal  46  is arranged so as to to cover an annular space between the pair of arms  34 ,  36  formed by opposed portions of adjoining rotor disks  20  of the multi-stage turbomachine. During the assembly, the cantilever  61  is held in a deflected position by the temporary retaining structure, i.e., the pin  70 . The seal strip  50  is then positioned such that opposite edges  53 ,  54  of the seal strip  50  are located in respective circumferentially extending slots  81 ,  82  provided in the pair of arms  34 ,  36 . The seal strip  50  is then moved along the slots  81 ,  82  in a circumferential direction until a final assembly position is reached. During the movement of the seal strip  50 , the cantilever  61  remains in the deflected position so as to be located entirely the gap or clearance  71  between the pair of arms  34 ,  36  of the adjoining rotor disks, which allows the seal strip  50  to be moved unobstructed along the slots. 
     A final assembly position is said to be reached when the radially inward extending engagement member  65  is aligned with a radial recess  83  in one of the arms, in this case the arm  34 . It is to be noted that in  FIG. 2 , the engagement member  65  extends perpendicularly outward from the plane of the paper. Upon reaching the final assembly position, the cantilever  61  is released from the deflected position by removing the pin  70 , upon which the cantilever  61  rotates (clockwise in this example) about the pivot axis  64  to assume its natural state. As a result, the engagement member  65  at the free end  62  of the cantilever  61  is pushed into the radial recess  83  in the arm  34  of the rotor disk and held in place therein by spring action. The radial recess  83  constrains tangential movement of the engagement member  65 , and thus prevents rotation of the seal strip  50 . 
       FIG. 4  illustrates a cross-sectional view of the belly band seal  46  in an assembled state. As shown, the seal strip  50  is positioned such that its opposite edges  53  and  54  are located in circumferentially extending slots  81 ,  82  provided on respective end faces  85 ,  86  of the arms  34 ,  36  of adjoining rotor disks. The slot  81  produces a forked structure of the arm  34  defined by a radially inner tongue  34   a  and a radially outer tongue  34   b . Likewise, the slot  82  of the arm  36  defines a radially inner tongue  36   a  and a radially outer tongue  36   b . The engagement member  65  of the anti-rotation structure is held in position in the radial recess  83 , which is formed through the radially inner tongue  34   a  of one of the arms  34 . 
     In the illustrated embodiment, the engagement member  65  further comprises a verification pin  67  that is configured to be located in a through-opening  68  extending from the radially inner surface  52  through the radially outer surface  51  of the seal strip  50 . The through opening  68  is so located on the seal strip  50  that the verification pin  67  snaps into the through-opening  68  when the engagement member is properly positioned in the radial recess  83  of the arm  34 . Further, in the illustrated embodiment, upon snapping into through-opening  68 , the verification pin protrudes outwardly from a radially outer surface  51  of the seal strip  50  to exhibit a protrusion  88 . 
     The illustrated design allows verification of proper assembly of the anti-rotation structure by visually inspecting the protrusion  88 . In an example embodiment, the verification pin  67  may be colored differently from the seal strip  50  to allow easy visual identification of the protrusion  88 . 
     In the embodiment of  FIG. 4 , the point of the protrusion  88  of the verification pin  67  is located within the slot  81  of the arm  34 . In this case, a bore-scope  90  may be used to provide visual access to the protrusion  88 . 
       FIG. 5  illustrates an alternate embodiment, which provides improved visual accessibility of the verification pin  67 . In this case, the engagement member  65  is designed to be wider so as to extend beyond the end face  85  of the arm  34 , allowing the verification pin  67  to be positioned in the engagement member  65  such that the protrusion  88  is located in the space between the paired arms  34  and  36 . The use of a bore-scope may be obviated in this example. 
     In the previously illustrated embodiments, the engagement member  65  had a generally cylindrical shape, similar to a conventionally used factory pin. However, the present invention is not limited by the shape and dimension of the engagement member.  FIG. 6-8  illustrate an alternate design of the engagement member.  FIG. 6  illustrates a perspective view of a belly band seal  46   a  according to this alternate embodiment.  FIG. 7  is a bottom view of the belly band seal  46   a  as seen along a direction VII in  FIG. 6 .  FIG. 8  is a cross-sectional view of the anti-rotation structure only along a section VIII-VIII in  FIG. 7 . As shown therein, the belly band seal  46   a  comprises an the engagement pin  65   a  with a bolted design having a hexagonal shape, preferably with a reduced height to minimize mass. The remaining elements, which are similar or equivalent to those in the embodiments of  FIG. 2-6 , are designated with like numerals. The description of such elements are not reiterated. 
     Embodiments of the invention illustrated herein provide a belly band seal with an anti-rotation structure that allows easy on-field assembly without having to de-stack the rotor, while at the same time ensuring that the operational life of the belly band seal is not compromised. Embodiments of the invention also do away with the requirement for welding, brazing or tightening of fasteners on the field. The illustrated embodiments also allow installation with existing field install machining of the turbine disk, and use of existing raw material bar. 
     While specific embodiments have been described in detail, those with ordinary skill in the art will appreciate that various modifications and alternative to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims, and any and all equivalents thereof.