Abstract:
The present application provides a stage of a gas turbine engine. The stage may include a bucket extending radially about a longitudinal axis of the gas turbine engine, a shroud facing the bucket, the shroud including a fore end portion including a radially inner surface spaced a first distance from the longitudinal axis, and a forward step honeycomb seal positioned on the shroud downstream of the fore end portion and facing the bucket. The forward step honeycomb seal may include a first linear portion including a radially inner surface spaced a second distance from the longitudinal axis, and a forward step portion positioned adjacent to and downstream of the first linear portion, the forward step portion including a radially inner surface spaced a third distance from the longitudinal axis, wherein the second distance is greater than the third distance, and wherein the third distance is greater than the first distance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of copending U.S. patent application Ser. No. 13/342,278, filed on Jan. 3, 2012, which is hereby incorporated by reference in its entirety herein. 
     
    
     TECHNICAL FIELD 
       [0002]    The present application and the resultant patent relate generally to gas turbine engines and more particularly relate to a forward step honeycomb seal for a turbine shroud with reduced leakage and reduced overall repair costs. 
       BACKGROUND OF THE INVENTION 
       [0003]    Generally described, a gas turbine engine includes a combustor to produce a flow of hot combustion gases. The hot combustion gases are directed towards a turbine. The hot combustion gases impart a rotational force on the turbine blades therein so as to create mechanical energy. The turbine blades include end portions that rotate in close proximity to a turbine casing and the like. The closer the tip portions of the turbine blades may be to the turbine casing, the lower the energy losses therein. Specifically, when clearances between the bucket tip rails and the turbine casing are relatively high, the high energy combustion gases may escape without producing useful work. Reducing the clearances therein ensures that a larger portion of the thermal energy of the combustion gases is converted to mechanical energy so as to provide increased output and overall efficiency. 
         [0004]    There is thus a desire for an improved seal for use in a gas turbine engine. Preferably, such an improved seal may provide increase efficiency and reduced leakage therethrough with fewer repairs and lower repair costs while also providing overall increased efficiency. 
       SUMMARY OF THE INVENTION 
       [0005]    The present application and the resultant patent thus provide a stage of a gas turbine engine. The stage may include a bucket, a shroud facing the bucket, and a forward step honeycomb seal on the shroud. The forward step honeycomb seal may include a forward step portion and one or more linear portions. 
         [0006]    The present application and the resultant patent further provide a method of retrofitting a turbine stage. The method may include the steps of removing a shroud with a number of projections thereon from the turbine stage, positioning a forward step honeycomb seal on a replacement shroud, positioning the replacement shroud in the turbine stage, and blocking an air gap between the shroud and a bucket with the forward step honeycomb seal. 
         [0007]    The present application and the resultant patent further provide a stage of a gas turbine engine. The stage may include a bucket, a shroud facing the bucket, and a forward step honeycomb seal on the shroud. The forward step honeycomb seal may include a forward step portion, a first linear portion, and a second linear portion with the forward step portion including an offset position. 
         [0008]    These and other features and improvements of the present application and the resultant patent will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the several drawings and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic diagram of a gas turbine engine showing a compressor, a combustor, and a turbine. 
           [0010]      FIG. 2  is a side view of portions of a turbine stage with a known honeycomb seal therein. 
           [0011]      FIG. 3  is a side view of portions of an example of a turbine stage with a forward step honeycomb seal as may be described herein. 
           [0012]      FIG. 4  is a side view of portions of a turbine stage with an example of an alternative embodiment of a forward step honeycomb seal as may be described herein. 
           [0013]      FIG. 5  is a side view of portions of a turbine stage with a further example of an alternative embodiment of a forward step honeycomb seal as may be described herein. 
           [0014]      FIG. 6  is a side view of portions of a turbine stage with a further example of an alternative embodiment of a forward step honeycomb seal as may be described herein. 
           [0015]      FIG. 7  is a side view of portions of a turbine stage with a further example of an alternative embodiment of a forward step honeycomb seal as may be described herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Referring now to the drawings, in which like numerals refer to like elements throughout the several views,  FIG. 1  shows a schematic view of gas turbine engine  10  as may be used herein. The gas turbine engine  10  may include a compressor  15 . The compressor  15  compresses an incoming flow of air  20 . The compressor  15  delivers the compressed flow of air  20  to a combustor  25 . The combustor  25  mixes the compressed flow of air  20  with a pressurized flow of fuel  30  and ignites the mixture to create a flow of combustion gases  35 . Although only a single combustor  25  is shown, the gas turbine engine  10  may include any number of combustors  25 . The flow of combustion gases  35  is in turn delivered to a turbine  40 . The flow of combustion gases  35  drives the turbine  40  so as to produce mechanical work. The mechanical work produced in the turbine  40  drives the compressor  15  via a shaft  45  and an external load  50  such as an electrical generator and the like. 
         [0017]    The gas turbine engine  10  may use natural gas, various types of syngas, and/or other types of fuels. The gas turbine engine  10  may be any one of a number of different gas turbine engines offered by General Electric Company of Schenectady, N. Y., including, but not limited to, those such as a 7 or a 9 series heavy duty gas turbine engine and the like. The gas turbine engine  10  may have different configurations and may use other types of components. Other types of gas turbine engines also may be used herein. Multiple gas turbine engines, other types of turbines, and other types of power generation equipment also may be used herein together. 
         [0018]      FIG. 2  shows a portion of a turbine stage  55 . The turbine stage  55  may be part of the turbine  40  described above and the like. In this example, the turbine stage  55  may be a second stage  60  of the turbine  40 . Other stages  55  may be used herein. The turbine stage  55  may include a number of buckets  65 . Each bucket  65  may include an airfoil  70 . The airfoil  70  ends at a tip shroud  75 . A pair of tip rails or projections may extend from the tip portion  75 . In this example, a first projection  80  and a second projection  85  may be used. Any number of projections may be used herein. The bucket  65  may be largely of conventional design. Other components and other configurations may be used herein. 
         [0019]    The bucket  65  may be enclosed within a shroud  90 . The shroud  90  may be in the form of a number of segments. Each of the segments of the shroud  90  also may include a number of projections extending toward the bucket  65 . In this example, three projections or labyrinth teeth are shown, a first projection  91 , a second projection  92 , and a third projection  93 . Any number of projections  91 ,  92 ,  93  may be used. The projections  91 ,  92 ,  93  of the shroud  90  and the projections  80 ,  85  of the bucket  65  serve to seal the leakage of hot combustion gases through a passage or a gap  94  between the bucket  65  and the shroud  90 . Other components and other configurations may be used herein. 
         [0020]    A honeycomb seal  95  also may be positioned on the shroud  90 . In this example, the honeycomb seal  95  may include a first honeycomb seal member  96  and a second honeycomb seal member  97 . Any number of honeycomb seal members  95  may be used herein. The first honeycomb seal member  96  may be positioned between the first projection  91  and the second projection  92  while the second honeycomb seal member  97  may be positioned between the second projection  92  and the third projection  93 . The honeycomb seal members  96 ,  97  may have a generally linear, uniform shape. The honeycomb seal members  96 ,  97  may be formed from a deformable material. The honeycomb seal members  96 ,  97  face the projections  80 ,  85  of the bucket  65  so as to reduce the gap  94  over the projections  80 ,  85  and thus reduce the leakage of the hot combustion gases over the bucket tip shroud  75 . Other components and other configurations may be used herein. 
         [0021]    The honeycomb seal  95  of the shroud  90  thus uses the projections  91 ,  92 ,  93  and the honeycomb seal members  96 ,  97  to seal the leakage over the bucket tip  75 . After an amount of time and extended operation, however, the projections  91 ,  92 ,  93  tend to oxidize and may fracture or otherwise begin to fail. As such, a leakage flow therethrough may increase such that the overall performance of the honeycomb seal  95  and the overall stage  55  may decrease. 
         [0022]      FIG. 3  shows a portion of a turbine stage  100  as may be described herein. As above, the turbine stage  100  may be used with the turbine  40  of the gas turbine engine  10  or otherwise. The turbine stage  100  may be a second stage  110 . Other stages  100  may be used herein. The turbine stage  110  may include a number of buckets  120  therein. Each of the buckets  120  may include an airfoil  130 . The airfoil  130  may have a tip portion  140  at one end thereof. The tip portion  140  may have a pair of labyrinth teeth or projections extending therefrom. In this example, a first projection  150  and a second projection  160  may be used. Any number of projections may be used herein. The bucket  120  may be largely of conventional design. Other components and other configurations may be used herein. 
         [0023]    A shroud  170  may enclose the bucket  120 . The shroud  170  may be in the form of a number of segments. The shroud  170  also may include a forward step honeycomb seal  200 . The forward step honeycomb seal  200  may have a first linear portion  210 , a forward step portion  220 , and a second linear portion  230 . The forward step portion  220  may have an offset position  240  such that a first length  250  of the first linear portion  210  may be less than a second length  260  of the second linear portion  230 . Likewise, the forward step  220  may be positioned closer to the first projection  150  as compared to the second projection  160  of the bucket  120 . (In other words, the forward step honeycomb seal  200  has the forward step portion  220  positioned about a forward end thereof and steps down into the air gap  195 .) The forward step portion  220  may be placed anywhere before the second projection  160 . The forward step honeycomb seal  200  may be attached to the shroud  170  via conventional means. 
         [0024]    The first linear portion  210 , the forward step portion  220 , and the second linear portion  230  may form a unitary element or the portions may be segmented. The forward step portion  220  may extend downward from the shroud  170  towards the tip portion  140  of the bucket  120  and into the air gap  195 . The relative size, shape, and configurations of the portions  210 ,  220 ,  230  may vary. The forward step honeycomb seal  200  may be made out of a deformable material  205 . Other components and other configurations may be used herein. 
         [0025]    In use, the flow of combustion gases  35  extends between the tip portion  140  of the bucket  120  and the forward step honeycomb seal  200  of the shroud  170  into the air gap  195 . The size, shape, configuration of the forward step honeycomb seal  200  and the projections  150 ,  160  of the tip portion  140  of the bucket  120  thus improves overall system and stage efficiency by sealing effectively the air gap  195 . Moreover, by the elimination of the projections  91 ,  92 ,  93 , of the shroud  90  described above, significant saving in terms of repair time and repair costs may be provided. Specifically, the use of the forward step honeycomb seal  200  eliminates the projections  91 ,  92 ,  93  and the associated repair time and costs. 
         [0026]    Although the turbine stage  100  has been described herein in terms of the second stage  110 , the forward step honeycomb seal  200  may be applicable to other stages and other locations as well. The forward step honeycomb seal  200  may be original equipment or part of a repair or a retrofit. Specifically, the shroud  90  with the projections  91 ,  92 ,  93  may be removed and replaced with the shroud  170  with the forward step honeycomb seal  200  as described herein. 
         [0027]      FIG. 4  shows a further example of an embodiment of a forward step honeycomb seal  270 . The forward step honeycomb seal  270  may be similar to that described above, but in this example, a forward step portion  280  may have a pair of angled sides  290 . The angled sides  290  may be angled away from the projections  150 ,  160 . The angles sides  290  may have any angle or shape. Other components and other configurations may be used herein. 
         [0028]      FIG. 5  shows a further example of an embodiment of a forward step honeycomb seal  300 . In this example, a first linear portion  310  and a second linear portion  320  both have a groove  330  positioned on both sides of a forward step portion  340 . The shape and size of the grooves  330  may vary. Other components and other configurations may be used herein. 
         [0029]      FIG. 6  shows a further example of an embodiment of a forward step honeycomb seal  350 . The forward step honeycomb seal  350  may be similar to that described above, but an aft end  360  of the shroud  170  may extend inwardly such that a second linear portion  370  may be truncated. The aft end  360  and the second linear portion  370  may be aligned with one another or the second linear portion  370  may protrude somewhat therefrom. Other components or other configurations may be used herein. 
         [0030]      FIG. 7  shows a further example of an embodiment of a forward step honeycomb seal  380  as may be described herein. The forward step honeycomb seal  380  may be similar to that described above, but a forward step portion  390  may extend along the aft length of the shroud  170 . In this example, a first projection  400  may be taller than a second projection  410  that extends underneath the extended forward step portion  390 . The size and shape of the projections  400 ,  410  may vary. Other components and other configurations may be used herein. 
         [0031]    It should be apparent that the foregoing relates only to certain embodiments of the present application and the resultant patent. Numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.