Abstract:
A sealing band for use in a turbomachine having a plurality of stages, each stage comprising a rotatable disk and blades carried thereby. At least one pair of adjacent rotatable disks define an annular gap therebetween and have respective opposing sealing band receiving slots aligned with the annular gap. The sealing band includes a plurality of seal strips located in series adjacent to one another, and adjacent seal strips include opposing end faces located in facing relationship adjacent to one another. An underlap portion is affixed adjacent to an end of at least one seal strip and extends past the end face of an adjacent seal strip, along a radially facing side of the adjacent seal strip.

Description:
FIELD OF THE INVENTION 
     This invention relates in general to seals for multistage turbomachines and, more particularly, to an optimized baffle seal provided between adjoining disks in a multistage turbomachine. 
     BACKGROUND OF THE INVENTION 
     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. Typically the opposing end faces may be provided with a slot for receiving a sealing band, known as a “baffle seal” or “belly band seal”, which bridges the gap between the end faces to prevent cooling air flowing through the cooling air cavity from leaking into the path for the hot combustion gases. The sealing band may be formed of plural segments, in the circumferential direction, that are typically interconnected at a sealing joint such as at a shiplap joint between the ends to prevent passage of gases past the joint. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the invention, a sealing band is provided for use in a turbomachine having a plurality of stages, each stage comprising a rotatable disk and blades carried thereby. At least one pair of adjacent rotatable disks define an annular gap therebetween and have respective opposing sealing band receiving slots aligned with the annular gap. The sealing band comprises a plurality of seal strips located in series adjacent to one another, and adjacent seal strips include opposing end faces located in facing relationship adjacent to one another. An underlap portion is affixed adjacent to an end of at least one seal strip and extends past the end face of an adjacent seal strip, along a radially facing side of the adjacent seal strip. 
     The underlap portion may have a width, extending across the gap, that is less than a width of the at least one seal strip. 
     The at least one seal strip may have a width greater than the annular gap, and the underlap portion may have a width no greater than the annular gap. 
     The underlap portion may have a width less than the annular gap. 
     The underlap portion may be attached in abutting relation to the end face of the at least one seal strip. 
     The underlap portion may extend radially away from a radially facing side of the at least one seal strip. 
     The radially facing side of both the at least one seal strip and the adjacent seal strip may face radially inwardly of the at least one pair of adjacent rotatable disks. 
     The underlap portion may extend radially beyond the sealing band receiving slots. 
     The adjacent disks may include opposing disk end faces defining the annular gap therebetween, and the underlap portion may include opposing sides extending adjacent and parallel to the opposing disk end faces. 
     In accordance with another aspect of the invention, a sealing band is provided in a turbomachine having a plurality of stages, each stage comprising a rotatable disk and blades carried thereby. At least one pair of adjacent rotatable disks define an annular gap therebetween and have respective opposing sealing band receiving slots aligned with the annular gap. The sealing band comprises a plurality of seal strips located in series adjacent to one another. Adjacent seal strips including opposing end faces located in facing relationship adjacent to one another, each seal strip including opposing radially outwardly and inwardly facing seal strip faces. An underlap portion is affixed adjacent to an end face of at least one seal strip and extends circumferentially past the end face of an adjacent seal strip, along the inwardly facing seal strip face of the adjacent seal strip. The underlap portion comprises opposing radially outwardly and inwardly facing underlap faces, wherein the outwardly facing underlap face is coplanar with the inwardly facing seal strip face. 
     The sealing band receiving slots may be formed in disk arms associated with each of the adjacent disks, the annular gap being defined between spaced disk arm faces formed on the disk arms, and the underlap portion having opposing sides, each underlap portion side may be located adjacent to a respective disk arm face. 
     The outwardly facing underlap face may form a planar surface between the underlap portion sides. 
     A distance between the underlap portion sides may be no greater than a distance between the disk arm faces. 
     The underlap portion may comprise a separate element attached to the end of the at least one seal strip. 
     A section of the underlap portion adjacent to the at least one seal strip has a width substantially equal to a width of the seal strip. 
     The underlap portion includes an underlap element having a width that is less than a width of the annular gap and defining the outwardly facing underlap face. 
     The underlap portion may extend radially inwardly beyond the sealing band receiving slots, and may define a seal spanning between the pair of adjacent disks and closing a gap between the end face of the at least one seal strip and the end face of the adjacent seal strip. 
    
    
     
       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 diagrammatic section view of a portion of a gas turbine engine including a seal strip assembly in accordance with the present invention; 
         FIG. 2  is an exploded perspective view illustrating aspects of the present invention; 
         FIG. 3  is a plan view of a pair of seal strips assembled extending between adjacent disk arms with an underlap portion forming a seal between end faces of the seal strips; 
         FIG. 4  is a cross-sectional view taken along line  4 - 4  in  FIG. 3 ; 
         FIG. 5A  is a plan view illustrating an underlap portion on a seal strip prior to movement into underlapping relation to an adjacent seal strip; 
         FIG. 5B  is a side view illustrating the underlapping portion in an assembled position, forming a seal between adjacent seal strips; and 
         FIG. 6  is a view similar to  FIG. 5B  illustrating an alternative structure providing an attachment of an underlap portion to a seal strip. 
     
    
    
     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. 
     Referring to  FIG. 1 , a portion of a turbine engine  10  is illustrated diagrammatically including adjoining stages  12 ,  14 , each stage  12 ,  14  comprising an array of stationary vane assemblies  16  and an array of rotating blades  18 , where 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 the 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 of the paired annular disk arms  34 ,  36 . The annular cooling air cavity  38  receives cooling air passing through disk passages to cool the disks  20 . 
     Referring further to  FIG. 2 , the disk arms of two adjoining disks  20  are illustrated for the purpose of describing the seal strip assembly  46  of the present invention, it being understood that the disks  20  and associated disk arms  34 ,  36  define an annular structure extending the full circumference about the rotor centerline. The disk arms  34 ,  36  define respective opposed disk end faces  48 ,  50  located in closely spaced relation to each other. A circumferentially extending sealing band receiving slot  52 ,  54  is formed in the respective disk end faces  48 ,  50 , wherein the slots  52 ,  54  are radially aligned with an annular gap  56  ( FIGS. 3 and 4 ) defined between the disk end faces  48 ,  50 . 
     As seen in  FIG. 4 , the seal strip assembly  46  includes a sealing band  60  forming a circumferentially extending belly band seal. The sealing band  60  includes opposing sealing band edges  62 ,  64  which are positioned within the respective slots  52 ,  54  defined in the opposed end faces  48 ,  50 . The sealing band  60  spans the annular gap  56  between the end faces  48 ,  50  and defines a seal for preventing or substantially limiting flow of gases between the cooling air cavity  38  and the disk cavities  26 ,  28 . Further, the sealing band  60  is comprised of a plurality of segments, typically four segments, referred to herein as seal strips  66  ( FIG. 3 ). 
     As seen in  FIGS. 2 and 3 , a first seal strip  66   a  and a second seal strip  66   b  are located adjacent to each other at respective seal strip end faces  66   a   1  and  66   b   2 . It may be understood that each seal strip  66  is formed as an elongated member extending circumferentially within the engine  10  and includes a first end face, e.g. first end  66   a   1  of seal strip  66   a , and a second end face, e.g., second end face  66   b   2  of seal strip  66   b . Referring to  FIG. 4 , the seal strips  66  also each include a radially outwardly facing seal strip face  68  (hereinafter “outer seal strip face  68 ”) and an opposing radially inwardly facing seal strip face  70  (hereinafter “inner seal strip face  70 ”). When positioned within the sealing band receiving slots  52 ,  54 , the outer seal strip face  68  is positioned adjacent a radially inwardly facing surface  74  in each of the slots  52 ,  54 , and the inner seal strip face  70  is positioned adjacent a radially outwardly facing surface  76  in each of the slots  52 ,  54 . The thickness of the seal strips  66  is selected such that the dimensional clearance between the seal strip faces  68 ,  70  and the slot surfaces  74 ,  76  is minimized to limit leakage past the sealing band  60 . 
     As noted above, a sealing joint, such as a shiplap joint, has typically been provided at the junction between segments of a sealing band. In accordance with an aspect of the invention, it has been observed that the reduced material thickness provided at shiplap joints, i.e., where the ends of the segments are reduced to about half thickness of the sealing band, is a potentially structurally weak location on the sealing band. The thinner material of the sealing band segments at the shiplap location may be subject to fracturing, which may form a breach in the seal with a resulting leakage of cooling air through the belly band. 
     Further in accordance with an aspect of the invention, an underlap seal  78  is provided to optimize sealing and facilitate durability at the junction between seal strips  66 . As may be best seen in  FIGS. 2 ,  3  and  5 A, the underlap seal  78  is formed by an underlap portion  80  comprising an elongated member that is affixed to the first seal strip  66   a  at or adjacent to the first seal strip end face  66   a   1 . It should be understood that the underlap portion  80  may be formed as a separate element that is attached to first seal strip  66   a  by welding or other attachment technique, or the underlap portion  80  may be formed integrally at the first end face  66   a   1  during a manufacturing process forming the first seal strip  66   a . Hence, the term “affixed” as used herein may reference either attachment of the underlap portion  80  provided as a separate element, or integral formation of the underlap portion  80  with the seal strip  66   a , such as may be provided during a manufacturing process forming the first end face  66   a   1 . 
     The underlap portion  80  described herein has a generally rectangular cross-section, as may be seen in  FIG. 4 , however other shapes that provide equivalent functional advantages as described herein are equally encompassed by the present description. As seen in  FIG. 5B , the underlap portion  80  includes a radially outwardly facing underlap face  82  (hereinafter “outer underlap face  82 ”) formed as a planar surface, and an opposing radially inwardly facing underlap face  84  (hereinafter “inner underlap face  84 ”), which may also be a planar surface. The outer and inner underlap faces  82 ,  84  are connected by opposing underlap portion sides  86 ,  88 . The underlap portion sides  86 ,  88  extend adjacent and parallel to the respective disk end faces  48 ,  50 . Hence, when the seal strip  66   a  is positioned within the slots  52 ,  54 , the underlapping portion  80  extends radially inwardly from the inner seal strip face  70 , i.e., radially inwardly from the slots  52 ,  54 , into the annular gap  56 . It may be noted that the underlap portion  80  may be formed with a radial thickness, i.e., the dimension between the outer and inner underlap faces  82 ,  84 , that is substantially equal to a radial thickness of the seal strips  66 , as measured between the outer and inner seal strip faces  68 ,  70 . 
     In the illustrated embodiment, the outer underlap face  82  is shown as being coplanar with or generally coplanar, i.e., generally lying in a common plane, with the inner seal strip face  70 . For example, the underlap portion  80  may be welded in position on the seal strip  66   a  with a portion of the outer underlap face  82  in contact with the inner seal strip face  70 , and with the remainder of the outer underlap face  82  extending outwardly from the first end face  66   a   1  of the seal strip  66   a.    
     As may be seen in  FIG. 4 , the width of the underlap portion  80  is less than the width of the seal strips  66 . Referring further to  FIG. 3 , the underlap portion  80  is dimensioned such that an axial width of the underlap portion  80 , as measured by the distance D 2  between the underlap portion sides  86 ,  88  is no greater that the axial width of the annular gap  56  as measured by the distance D 1  between the disk end faces  48 ,  50 . Preferably, the axial width D 2  of the underlap portion  80  is slightly less than the axial width D 1  of the annular gap  56  to accommodate variations in the axial width D 1  of the annular gap  56 , such as may be caused by relative axial movement of the adjoining disks  20 . 
     In a particular, non-limiting example of the seal strip assembly  46 , a nominal distance D 1  between the disk end faces  48 ,  50  may be about 12.7 mm, and a nominal width of the underlap portion  80  may be about 11 mm, such that a nominal gap of about 0.85 mm may be formed between the disk end faces  48 ,  50  and each of the respective sides  86 ,  88  of the underlap portion  80 . It may be understood that the exemplary dimensions described above may be measured when the components are cold, and that a dimension of the gap between the underlap portion  80  and the disk end faces  48 ,  50  may decrease when the components are at a higher or “hot” temperature, such as during operation of the engine  10 . 
     As seen in  FIGS. 3 and 5B , in an assembled state of the sealing band  60 , the underlap portion  80  extends underneath, i.e., underlaps, the second seal strip  66   b . In particular, the underlap portion  80  extends past the second seal strip end face  66   b   2  and under the second seal strip  66   b  to position the outer underlap face  82  in engagement with the inner seal strip face  70  of the second seal strip  66   b . That is, in a final position of the seal strips  66 , a substantial portion of the length of the underlap portion  80  extending beyond the first seal strip end face  66   a   1  is located under the second seal strip  66   b , and a relatively smaller section of the underlap portion  80  spans a gap  90  that may be formed between the opposing seal strip end faces  66   a   1  and  66   b   2 . 
     It should be noted that the relative position between adjacent ones of the seal strips  66  may be maintained by anti-rotation structure associated with each of the seal strips  66 . For example, an anti-rotation structure such as is disclosed in U.S. Pat. No. 7,581,931 may be provided, which patent is incorporated herein by reference. The anti-rotation device provided to each seal strip  66  substantially limits circumferential movement of the seal strips  66  relative to the adjacent disks  20  and relative to each other. 
     As described above, the underlap portion  80  extends substantially the entire axial width D 1  of the annular gap  56 , and substantially prevents or limits passage of cooling air to the seal strips  66   a  and  66   b  at the location of the underlap portion  80 . In particular, the underlap portion sides  86 ,  88  extend radially inwardly from the inner seal strip face  70 , i.e., radially inwardly from the radially outwardly facing surface  76  of the slots  52 ,  54 , to form a seal with the adjacent disk end faces  34 ,  36  to prevent or limit passage of air around the underlap portion  80  at the circumferential location of the gap  90  between the seal strip end faces  66   a   1 ,  66   b   2 . 
     As noted above, although the underlap portion  80  is illustrated as a separate element attached to the seal strip  66   a , the underlap portion  80  may be formed as an integral feature on the seal strip  66   a , such as during manufacture of the seal strip  66   a . For example, the underlap portion  80  may be formed through use of a combination of forging and machining operations in which the end of the first seal strip  66   a  is shaped to configure the underlap portion  80  as an integral part of the seal strip  66   a.    
     Alternatively, as is illustrated in  FIG. 6 , an underlap portion  80 ′ may be provided that forms an end of the first seal strip  66   a . In particular, the underlap portion  80 ′ may comprises a seal strip end  81  having a width that is generally the same as an end face  66   a   1  of the first seal strip  66   a , and further includes an end face  66   a   1 ′ having the same width as the seal strip end  81 . The underlap portion  80 ′ includes an integrally formed underlap element  83  having a width that is generally the same as the axial width D 2  described above for the underlap portion  80 . 
     The underlap portion  80 ′ may be affixed to the end face  66   a   1  of the first seal strip  66   a  at a butt weld connection  85 , such that the underlap portion  80 ′ forms an extension of the seal strip  66   a  wherein the end face  66   a   1 ′ is located in opposing relation to the end face  66   b   2  of the second seal strip  66   b . The underlap element  83  defines a seal extending in underlapping relation to the second seal strip  66   b  in the same manner as described above for the underlap portion  80 . 
     It should be understood that, although various structures are described for providing an underlap portion, such as are described for the underlap portions  80 ,  80 ′, within the spirit and scope of the present invention, any manner of attachment or formation techniques may be implemented to provide an underlap portion  80 , as described herein, for sealing between adjacent seal strips  66 . 
     Further, although the underlap portion  80  is described with particular reference to the end of the first seal strip  66   a , it may be understood that in a practical embodiment of the invention, an underlap portion  80  may be provided to an end of each of the segments or seal strips  66  forming the sealing band for underlapping with an adjacent seal strip end. 
     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.