Abstract:
A shroud for turbine engines. The shroud has an integrated anti-rotation device that prevents circumferential movement of the shroud during normal engine operation, and which allows for circumferential installation in split annular case designs. Since the anti-rotation device is an integral part of the shroud and/or annular split turbine case, no additional parts are necessary for assembly or disassembly. Moreover, existing annular split turbine cases can be reworked to accept the anti-rotation device and yet still be backwards compatible with original shroud designs.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The field of the invention relates to turbine engines generally, and more particularly to certain new and useful advances in anti-rotation features for turbine shrouds, of which the following is a specification, reference being had to the drawings accompanying and forming a part of the same. 
         [0003]    2. Description of Related Art 
         [0004]    Turbine engines comprise an airfoil attached to a rotor that rotates about a predetermined axis of rotation. An annular shroud is circumferentially positioned about and spaced apart from the airfoil. An annular split turbine case is circumferentially positioned about and coupled with the shroud. Additionally, an anti-rotation device is added and coupled with the shroud to prevent the shroud from rotating during normal engine operations. However, this anti-rotation device is an extra part that must be installed, disassembled and/or maintained in addition to other components of the turbine engine. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    The present disclosure describes embodiments of an improved shroud for turbine engines with 180 degree split turbine casings. The shroud has an integrated anti-rotation device that prevents circumferential movement of the shroud during normal engine operation, and which allows for circumferential installation. Since the anti-rotation device is an integral part of the shroud, no additional parts are necessary for assembly or disassembly. Moreover, existing turbine cases can be reworked to accept the anti-rotation device and yet still be backwards compatible with original shroud designs. 
         [0006]    Other features and advantages of the disclosure will become apparent by reference to the following description taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0007]    Reference is now made briefly to the accompanying drawings, in which: 
           [0008]      FIG. 1  is a perspective view of a portion of an improved turbine shroud configured for use in a turbine engine; 
           [0009]      FIG. 2  is a partial, close-up view of an anti-rotation device integrally formed with the improved turbine shroud of  FIG. 1 ; 
           [0010]      FIG. 3  is another partial, close-up view of the anti-rotation device of  FIG. 2 ; 
           [0011]      FIG. 4  is a plan view of an interior surface of the improved turbine shroud of  FIG. 1 ; 
           [0012]      FIG. 4A  is an end view of the improved turbine shroud of  FIGS. 1 and 4 ; 
           [0013]      FIG. 4B  is a forward side view of the improved turbine shroud of  FIGS. 1 and 4 ; 
           [0014]      FIG. 4C  is another end view of the improved turbine shroud of  FIGS. 1 and 4 ; 
           [0015]      FIG. 4D  is an aft side view of the improved turbine shroud of  FIGS. 1 and 4 ; 
           [0016]      FIG. 4E  is a plan view of a back surface of the improved turbine shroud of  FIGS. 1 and 4 ; 
           [0017]      FIG. 5  is a perspective view of a section of an improved turbine case that is configured to couple with the improved turbine shroud of  FIGS. 1 ,  4 ,  4 A,  4 B,  4 C,  4 D, and  4 E; 
           [0018]      FIG. 6  is a perspective view of a section of the improved turbine case of  FIG. 5  illustrating its coupling with the improved turbine shroud of  FIGS. 1 ,  4 ,  4 A,  4 B,  4 C,  4 D and  4 E and a second stage nozzle, a portion of which overlaps an anti-rotation device integrally formed with the improved turbine shroud; 
           [0019]      FIGS. 7 ,  8  and  9  are diagrams illustrating assembly of an embodiment of the improved turbine shroud of  FIGS. 1 ,  4 ,  4 A,  4 B,  4 C,  4 D and  4 E and engagement of the integrally formed anti-rotation device with a channel formed in an improved turbine case. 
           [0020]      FIG. 10  is a plan view of an interior surface of a second embodiment of an improved turbine shroud; 
           [0021]      FIG. 11  is a plan view of a back surface of the second embodiment of the improved turbine shroud of  FIG. 10 ; 
           [0022]      FIG. 12  is a perspective view of a section of another improved turbine case that is configured to couple with the improved turbine shroud of  FIGS. 10 and 11 ; 
           [0023]      FIG. 13  is a cross-sectional view of a portion of the improved turbine case of  FIG. 12 , taken along the line A-A′ in  FIG. 12 ; and 
           [0024]      FIG. 14  is a perspective view of a section of the improved turbine case of  FIG. 12  illustrating its coupling with the improved turbine shroud of  FIGS. 10 and 11  and a second stage nozzle, a portion of which overlaps an anti-rotation device integrally formed with the improved turbine shroud. 
       
    
    
       [0025]    Like reference characters designate identical or corresponding components and units throughout the several views, which are not to scale unless otherwise indicated. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    As used herein, an element or function recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or functions, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the claimed invention should not be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
         [0027]      FIG. 1  is a perspective view of a portion of an improved turbine shroud  100  configured for use in a turbine engine.  FIG. 2  is a partial, close-up view of an anti-rotation device  140  integrally formed with the improved turbine shroud  100  of  FIG. 1 .  FIG. 3  is another partial, close-up view of the anti-rotation device  140  of  FIG. 2 .  FIG. 4  is a plan view illustrating an interior surface  142  of the improved turbine shroud  100  of  FIG. 1 .  FIG. 4A  is an end view of the improved turbine shroud  100  of FIGS.  1  and  4 .  FIG. 4B  is a forward side view of the improved turbine shroud  100  of  FIGS. 1 and 4 .  FIG. 4C  is another end view of the improved turbine shroud  100  of  FIGS. 1 and 4 .  FIG. 4D  is an aft side view of the improved turbine shroud  100  of  FIGS. 1 and 4 .  FIG. 4E  is a plan view illustrating shroud backing surface  141  of the improved turbine shroud  100  of  FIGS. 1 and 4 . 
         [0028]    Referring to  FIGS. 1 ,  2 ,  3 ,  4 ,  4 A,  4 B,  4 C,  4 D, and  4 E, the improved turbine shroud  100  (hereinafter “shroud  100 ”) has an annular shape, although only a portion thereof is shown in the Figures for ease of illustration and description. As persons skilled in the aircraft engine and power generation fields will appreciate, the improved turbine shroud  100  is a component of a turbine engine. When installed in a turbine engine, the improved turbine shroud is spaced slightly apart from and positioned coaxially around an airfoil that is attached to a rotor. When the rotor rotates at a high speed about a predetermined central axis of rotation, the airfoil spins at high speeds within the annulus formed by the assemblage of the improved turbine shroud, which is supported by a split annular turbine case that is positioned coaxially around it. 
         [0029]    The shroud  100  comprises several sections: a body  130  and two rails connected therewith—an aft rail  131  and a forward rail  133 . As used herein, the term “aft” refers to a downstream portion of a turbine engine, and the term “forward” (also, “fwd”) refers to an upstream portion of a turbine engine. The aft rail  131  has an aft edge  105 . The forward rail  133  has a forward edge  107 . As shown in  FIGS. 1 ,  4 A and  4 C, the body  130  has a cavity  135  on its interior surface  142 . The cavity  135  is an indented portion of the body  130  between sidewalls  143  that connect the aft rail  131  and the forward rail  133  with the body  130 . Consequently, the shroud backing surface  141  of the body  130  occupies a different plane than the aft rail  131  and the forward rail  133 . The cavity  135  is configured to contain an open-faced honeycomb core  103 . The honeycomb core is comprised of corrugated sheet metal ribbon which is formed into hexagonal (6 sided) cells of a uniform size arranged in a staggered formation, where each cell is surrounded by 6 adjacent cells that share a common wall with one another. The honeycomb core  103  is connected to cavity  135  through a metal braze operation. This honeycomb structure provides a dual function; the first is to provide a sacrificial material to prevent damage to the turbine airfoil in the event of rub/contact/incursion between the rotating and static components of the engine during operation; and second to maintain a small tip clearance between the static and rotating components thus improving the engine performance by reducing flowpath air leakage around the tip of the airfoil. 
         [0030]    One or more supports  109 , or ship laps, are coupled with the shroud backing surface  141  of the body  130  and the aft rail  131 . Each support  109  has a base  137  configured to couple with the shroud backing surface  141  of the body  130  of the shroud  100 , a support sidewall  138  coupled with the base  137 , and a support rail  139  coupled with the support sidewall  138 . Each support  109  is formed of a nickel or cobalt based sheet metal and is coupled with the shroud  100  using tack-welds or alternate positioning techniques in preparation for metal braze operation to permanently bond/adhere each support  109  to the shroud backing surface  141 . Additionally, each support  109  functions to retain the shroud  100  radially within the casing assembly ensuring the shroud  100  is coaxial with the rotating airfoil. 
         [0031]    In one embodiment, the forward rail  133  of the shroud  100  has an anti-rotation device  140  integrally formed therein. The anti-rotation device  140  comprises a fixed base end  111 , a resilient portion  110 , and a free end  113  that comprises a tab  120 . A base gap  119  having a predetermined shape, width and length separates the base end  111  of the anti-rotation device  140  from a first portion of the forward rail  133  that adjoins the sidewall  143 . The base gap  119  serves to reduce the stresses at the base of the anti-rotation feature  140  to be within the material capability of the shroud  100 . A second gap  117  of predetermined length and width extends from the base gap  119 , substantially parallel a forward edge  107  of the forward rail  133 , and past an end surface  121  of the free end  113  of the resilient portion  110 . The second gap  117  separates the resilient portion  110  and free end  113  of the anti-rotation device  140  from a second portion of the forward rail  133  that adjoins the sidewall  143 . Consequently, the resilient portion  110  is flexible and biased to return the free end  113  to the position shown in  FIG. 1  if the free end  113  with the tab  120  and/or the resilient portion  110  are moved relative to the forward rail  133 . 
         [0032]    As shown in  FIGS. 1 ,  2 ,  3 ,  4  and  4 E, a third gap  115 , or cut-out, separates the end surface  121  of the free end  113  of the resilient portion  110  from an adjacent third portion of the forward rail  133 . The third gap  115  is dimensioned and configured to permit the free end  113  of the anti-rotation device  140  to move relative to the forward rail  133 . In one embodiment, the third gap  115  is orthogonal to the second gap  117 . 
         [0033]    Additionally, the tab  120  protrudes outwardly from the shroud backing surface  141  of the forward rail  133  a predetermined distance. The tab  120  has an end surface  121  of a height equal, or about equal, to a thickness of the forward rail  133 . Coupled with the end surface  121  is an angled surface  123 , which slopes at a predetermined angle towards the base end  111 . The angled surface  123  couples with a main surface  125 . In turn, the main surface  125  couples with an orthogonal, or nearly orthogonal, projection surface  127 , which couples with the resilient portion  110 . 
         [0034]      FIG. 5  is a perspective view of a section of an improved split line turbine case  200  (hereinafter, “case  200 ”) that is configured to couple with the improved turbine shroud  100  of  FIGS. 1 ,  4 ,  4 A,  4 B,  4 C,  4 D, and  4 E. Depending on the embodiment, the case  200  comprises a metal, a metal alloy, a composite material or a combination thereof. Referring to  FIG. 5 , although only a portion is shown for clarity and ease of illustration, the improved turbine case  200  is annular and is formed with at least 2 halves, of 180 degrees, where the axis of case  200  is collinear with the engine centerline and coaxial with the rotation of the airfoils. Additionally case  200  has a plurality of parallel grooves, channels and rails formed therein. For example, a first shroud groove  209 , e.g., a first stage shroud groove  209 , is formed adjacent and substantially parallel a forward edge  207  of the case  200 . In one embodiment, the shroud groove  209  comprises a first rail  225 , e.g., a forward rail  225 , and a second rail  227 , e.g., an aft rail  227 , that are spaced apart to form a cavity  231  therebetween. Additionally, first channels  229  are formed in corresponding upper portions of the forward rail  225  and the aft rail  227 . Additionally, the aft rail  227  comprises a second channel  233  formed in a lower portion thereof, below and on a side of the aft rail  227  opposite the first channels  229 . The case  200  further comprises a third rail  215 , e.g., a nozzle rail  215  that is positioned between and spaced apart from the aft rail  227  and a shroud ledge  223 . In other words, the nozzle rail  215  is spaced aft and apart from the aft rail  227  and also spaced apart from and forward of the shroud ledge  223 , as illustrated in  FIG. 5 . One or more notches  217  are formed in an upper portion of the nozzle rail  215 . Each notch  217  has a first surface  235  positioned opposite a second surface  237 . The first surface  235  is configured to engage at least the projection surface  127  of the tab  120  of the anti-rotation device  140  of  FIGS. 1 ,  2 ,  3 ,  4 ,  4 A,  4 B,  4 C,  4 D and  4 E. The second surface  237  is proximate, and may contact, the angled surface  123  of the tab  120  of the anti-rotation device  140  of  FIGS. 1 ,  2 ,  3 ,  4 ,  4 A,  4 B,  4 C,  4 D and  4 E during assembly and disassembly of a turbine engine. 
         [0035]    The space between the aft rail  227  and the nozzle rail  215  forms a nozzle groove  211 , for a second stage nozzle (not shown in  FIG. 5 ). The space between the nozzle rail  215  and the shroud ledge  223  forms a second shroud groove  213 , e.g., a second stage shroud groove  213 . The second shroud groove  213  has a surface  219  that is positioned below an upper surface of the nozzle rail  215  and an upper surface of the shroud ledge  223 . As illustrated, the shroud ledge  223  is adjacent and parallel to the aft portion  205  of the case  200 , and includes a ledge  221  along its top, forward edge. 
         [0036]      FIG. 6  is a perspective view of a section of the improved turbine case  200  of  FIG. 5  illustrating its coupling with the improved turbine shroud  100  of  FIGS. 1 ,  4 ,  4 A,  4 B,  4 C,  4 D and  4 E and a second stage nozzle  300 , a portion  301  of which overlaps an embodiment of an anti-rotation device  140  integrally formed with the improved turbine shroud  100 . The second stage nozzle  300  is positioned within the nozzle groove  211 . As shown, when installed, the shroud  100  occupies the second shroud groove  213  of the case  200 , with the shroud&#39;s aft rail  131  positioned proximate the aft portion  205  of the case  200  and the shroud&#39;s forward rail  133  positioned toward the forward portion  207  of the case  200 . In particular, the shroud&#39;s aft rail  131  contacts the shroud ledge  223 , and the shroud&#39;s forward rail  133  contacts the nozzle rail  215 . The base  137  of the shroud&#39;s support strip  109  does not contact the surface  219  of the second shroud groove  213  and forms a gap/clearance/cavity with said surface. Moreover, the support rail  139  of the support strip  109  maintains a clearance fit with the ledge  221  formed along an upper, forward edge of the shroud ledge  223 . 
         [0037]    The resilient portion  110  ( FIG. 1 ) is biased to mate, or couple, the tab  120  of the anti-rotation device  140  with the notch  217  formed in the nozzle rail  215  of the turbine case  200 . Once installed as shown, the forward rail  133  of the shroud  100 , including the anti-rotation device  140  ( FIG. 1 ) and all its components, are overlapped by a portion  301 , e.g. a nozzle overhang  301 , of a second stage nozzle  300 , which is positioned within the second stage nozzle groove  211 . By overlapping the anti-rotation device  140 , the nozzle overhang  301  prevents the tab  120  of the anti-rotation device  140  from disengaging the notch  217  formed in the nozzle rail  215 . Accordingly, the coupling between the tab  120  of the anti-rotation device  140  and the notch  217  formed in the nozzle rail  215  of the case  200  prevents the shroud  100  from rotating during engine operation. However, removal of the second stage nozzle  300  during disassembly of the engine, uncovers the forward rail  133  of the shroud  100 , including the anti-rotation device  140 . Thereafter, circumferential rotation of the shroud  100  in a direction opposite that of normal airfoil rotation causes the second surface  237  ( FIG. 5 ) of the notch  217  to contact the angled surface  123  ( FIG. 5 ) of the tab  120  of the anti-rotation device  140  and raise the tab  120  of the anti-rotation device  140  up and out of the notch  217 . 
         [0038]      FIGS. 7 ,  8  and  9  are diagrams illustrating assembly of an embodiment of the improved turbine shroud  100  of  FIGS. 1 ,  4 ,  4 A,  4 B,  4 C,  4 D and  4 E and engagement of the integrally formed anti-rotation device  140  with a notch  217  formed in a nozzle rail  215  of an improved turbine case  200 . In these Figures, angled lines aft of the nozzle rail  215  represent honeycomb core  103 . Arrows  403  represent a direction of airfoil rotation during normal turbine engine operation. Arrow  400  indicates a direction of circumferential rotation of the shroud  100  during assembly and/or disassembly. Arrow  205  represents an aft portion of the turbine case  200 , and arrow  207  represents a forward portion of the turbine case  200 . In one embodiment, this direction of circumferential rotation  400  of the shroud  100  is opposite the direction of rotation  403  of the airfoil  401 . 
         [0039]    Beginning with  FIG. 7 , a turbine shroud  100  having a forward rail  133  that contacts a nozzle rail  215  of a turbine case  200  is circumferentially rotated in the direction of assembly represented by arrow  400  until, as shown in  FIG. 8 , the tab  120  of the anti-rotation device  140  fits within the notch  217  formed in the nozzle rail  215  and couples with a first surface  235  of the notch  217 . As shown in  FIG. 7 , the free end  113  of the anti-rotation device  140  initially rests on an upper surface of the nozzle rail  215  and is thus biased up and a way from the forward rail  133  and nozzle rail  215  to permit the main surface  125  and/or the angled surface  123  of the tab  120  of the anti-rotation device  140  to slide along the nozzle rail  215  in the turbine case  200  during assembly or disassembly. When the free end  113  of the anti-rotation device  140  is over the notch  217 , spring action of the biased resilient portion  110  ( FIG. 1 ) moves the tab  120  of the anti-rotation device  140  into the notch  217 . Since the projection surface  127 , e.g., load bearing surface  127 , of the tab  120  is in the same direction of the rotating airfoil, the shroud  100  is considered to be anti-rotated. Thereafter, the nozzle ( 300  in  FIG. 6 ) is assembled circumferentially after the shroud  100  is in place. An aft portion  301  of the nozzle  300  will overlap the flow path side of the anti-rotation device  140  thus preventing the tab  120  and/or the free end  113  of the anti-rotation device  140  from disengaging the notch  217 . 
         [0040]    When the tab  120  of the anti-rotation device  140  fits within the notch  217 , the anti-rotation device  140  is parallel, or substantially parallel, the plane of the forward rail  133  of the shroud  100  and ready to be overlapped by a portion  301  ( FIG. 6 ) of a nozzle  300  ( FIG. 6 ). As shown in  FIG. 9 , vibrations and forces caused by normal rotation of the airfoil  401  tend to drive at least the projection surface  127  of the tab  120  of the anti-rotation device  140  and the first surface  235  of the notch  217  closer together. However, once the tab  120  of the anti-rotation device  140  and the first surface  235  of the notch  217  engage, further circumferential movement of the shroud  100  in the direction of airfoil rotation  403  stops. 
         [0041]      FIG. 10  is a plan view of an interior surface of a second embodiment of an improved turbine shroud  100 .  FIG. 11  is a plan view of a back surface of the second embodiment of the improved turbine shroud of  FIG. 10 . Referring to  FIGS. 10 and 11 , this second embodiment is identical to that previously described above with respect to  FIGS. 1 ,  2 ,  3 ,  4 ,  4 A,  4 B,  4 C,  4 D and  4 E, except that the notch  217  that receives the tab  120  of the anti-rotation device  140  is formed in the forward rail  133 , instead of in the rail  215  ( FIG. 5 ) of the turbine case  200  ( FIG. 5 ). The aft rail  131 , support strips  109  and honeycomb  103  are the same as previously described. 
         [0042]      FIG. 12  is a perspective view of a section of another improved split turbine case  200  that is configured to couple with the improved turbine shroud  100  of  FIGS. 10 and 11 . This second embodiment is identical to that previously described above with respect to  FIG. 5 , except that a portion of the rail  215  has an anti-rotation device  140 , which includes the resilient portion  110 . The resilient portion  110  is separated from the rail  215  by gap  117 . The free end  113  of the resilient portion  110  includes the tab  120 , which has an angled surface  123  and a main surface  127 , as previously described. The aft portion  205 , forward portion  207 , aft rail  227 , first stage shroud groove  209 , second stage nozzle groove  211  and second stage shroud groove  213  are also as previously described. 
         [0043]      FIG. 13  is a cross-sectional view of a portion of the improved turbine case  200  of  FIG. 12 , taken along the line A-A′ in  FIG. 12 , that further illustrates the second embodiment of the anti-rotation device  140  formed in the rail  215  of the improved turbine case  200 . As shown in  FIG. 13 , the free end  113  of the resilient portion  110  includes the tab  120 . The tab  120  includes the projection surface  127 , which is coupled with the main surface  125 . The main surface  125  is coupled with the angled surface  123 . The angled surface  123  is coupled with the end surface  121 . The end surface  121  is separated from an opposite portion of the rail  215  by the gap  115 . 
         [0044]      FIG. 14  is a perspective view of a section of the improved split turbine case  200  of  FIG. 12  illustrating its coupling with the improved turbine shroud  100  of  FIGS. 10 and 11  and a second stage nozzle  300 , a portion  301  of which overlaps the anti-rotation device  140  integrally formed with the rail  215  of the improved split turbine case  200 . As shown, when installed, the shroud  100  occupies the second shroud groove  213  of the case  200 , with the shroud&#39;s aft rail  131  positioned proximate the aft portion  205  of the case  200  and the shroud&#39;s forward rail  133  positioned toward the forward portion  207  of the case  200 . In particular, the shroud&#39;s aft rail  131  contacts the shroud ledge  223 , and the shroud&#39;s forward rail  133  contacts the nozzle rail  215 . The base  137  of the shroud&#39;s support strip  109  does not contact the surface  219  of the second shroud groove  213  and forms a gap/clearance/cavity with said surface. Moreover, the support rail  139  of the support strip  109  maintains a clearance fit with the ledge  221  formed along an upper, forward edge of the shroud ledge  223 . 
         [0045]    The resilient portion  110  is biased to mate, or couple, the tab  120  of the anti-rotation device  140  with the notch  217  formed in the forward rail  133  of the shroud  100 . Once installed as shown, the forward rail  133  of the shroud  100 , including the anti-rotation device  140  ( FIG. 1 ) and all its components, are overlapped by a portion  301 , e.g. a nozzle overhang  301 , of a second stage nozzle  300 , which is positioned within the second stage nozzle groove  211 . By overlapping the anti-rotation device  140 , the nozzle overhang  301  prevents the tab  120  of the anti-rotation device  140  from disengaging the notch  217  formed in the forward rail  133  of the shroud  100 . Accordingly, the coupling between the tab  120  of the anti-rotation device  140  and the notch  217  prevents the shroud  100  from rotating during engine operation. However, removal of the second stage nozzle  300  during disassembly of the engine, uncovers the forward rail  133  of the shroud  100 , including the anti-rotation device  140 . Thereafter, circumferential rotation of the shroud  100  in a direction opposite that of normal airfoil rotation causes a surface of the notch  217  to contact the angled surface  123  of the tab  120  of the anti-rotation device  140  and move the tab  120  of the anti-rotation device  140  out of the notch  217 . 
         [0046]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 
         [0047]    Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. Other embodiments will occur to those skilled in the art and are within the scope of the following claims.