Abstract:
An apparatus and method are disclosed for reducing the operating stresses in a disk of a gas turbine engine while providing a seal plate to minimize leakage of a cooling fluid from the blades positioned in the disk. The seal plate is fastened to a tang of one or more of the blades. The seal plate configuration can be utilized with a newly manufactured disk and blades or with a modification to an existing disk and blades. The disk, blade, and seal plate configuration reduce operating stresses in the disk that are caused by mechanical loading on the disk by one or more rotating blades.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to the Provisional Patent Application having Ser. No. 61/012,475 and filed on Dec. 10, 2007. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to gas turbine engines. More particularly, embodiments of the present invention relate to an apparatus and method for reducing stress in a blade disk while minimizing leakage of cooling fluids directed towards one or more blades. 
       BACKGROUND OF THE INVENTION 
       [0003]    Gas turbine engines operate to produce mechanical work or thrust. Specifically, land-based gas turbine engines typically have a generator coupled thereto for the purposes of generating electricity. A gas turbine engine comprises a number of components including a compressor section which has a series of rotating compressor blades. The compressor, which receives air from an engine inlet, passes the air through the compressor, where the pressure of the air increases. The compressed air is then directed into one or more combustors where fuel is mixed with the compressed air and the mixture is ignited. The hot combustion gases are then directed into a turbine section, which is coupled by a shaft to the compressor section. The hot combustion gases pass through the turbine causing the turbine blades, which are attached to disks, to rotate, which also drives the compressor. Depending on the type of gas turbine engine, an electrical generator may also be coupled to the engine shaft for harnessing its mechanical output in order to generate electricity. 
         [0004]    Referring to  FIGS. 1 and 2 , a portion of a disk  100 , in accordance with a turbine of the prior art, is shown. The blades are typically held in the disk by a series of generally axially extending attachment surfaces  102 . These attachment surfaces are machined into an outer surface  104  of the disk  100 . The blades and disk have corresponding attachment surfaces such that when the disk rotates, the blade is held in place, in a radial direction, by the attachment surfaces. However, as the blades and disk rotate, the blades apply a substantial pulling load on the disk  100 . This is due to the weight of the blades, their radial position relative to the engine centerline, and rotational speed of the disk. For example, for a turbine blade installed in a prior art disk configuration, such as the disk  100 , with the disk rotating at approximately 3600 RPM, and the blade having a weight of approximately 17.5 lbs, a pulling load is created that results in a stress concentration of approximately 276 ksi in a corner between an attachment surface and a cooling channel of the disk. Such large stress concentrations have been known to exceed material capabilities at the disk operating temperatures and have led to cracking within the disk, failure of the disk, and engine failure. 
       SUMMARY 
       [0005]    Embodiments of the present invention are directed towards a system and method for, among other things, reducing stress levels in a disk assembly while providing a seal between a portion of the disk and one or more blades for a gas turbine engine. 
         [0006]    The present invention provides embodiments for a disk assembly of a gas turbine engine in which a seal plate is secured thereto in order to prevent leakage of cooling air that is directed to cool a blade installed in the disk. The assembly has a disk with generally axially extending slots for receiving one or more blades. In one embodiment, each blade in the disk has a tang that extends radially inward, and one or more seal plates positioned to receive and engage the tang. The tang of the blade is secured to a seal plate by a fastener. 
         [0007]    In an alternate embodiment of the present invention, a method of providing a sealing configuration between tangs of one or more blades and a disk is provided. This embodiment can be utilized in a variety of disk configurations, including modifying an existing turbine disk to remove areas of high concentrated stress. The method includes making alterations to the tang of the blade in order for it to mate with a seal plate. These alterations include machining a flat surface into a bottom of the tang and drilling a through hole in the tang. Once the blade is placed in the slot of the disk, the seal plate is placed around a portion of the tang such that a fastener can be placed through the seal plate and the tang, thereby joining the seal plate and tang together. 
         [0008]    In yet another embodiment, a seal plate capable of minimizing cooling fluid leakage between a disk and one or more blades is provided. In one embodiment, the seal plate has generally parallel first and second members that are connected by a leg with the first and second members each having through holes for receiving a fastener. The first and second members are spaced apart a distance sufficient to receive a blade tang therebetween. 
         [0009]    Additional advantages and features of the present invention will be set forth in part in a description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned from practice of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0010]    The present invention is described in detail below with reference to the attached drawing figures, wherein: 
           [0011]      FIG. 1  depicts a perspective view of a portion of a disk in accordance with the prior art; 
           [0012]      FIG. 2  depicts a cross section view taken through a slot of the disk of  FIG. 1  in accordance with the prior art; 
           [0013]      FIG. 3  depicts a cross section view taken through a slot of the disk of  FIG. 1  in accordance with the prior art where a section of material to be removed is indicated; 
           [0014]      FIG. 4  depicts a perspective view of a portion of a disk assembly in accordance with an embodiment of the present invention; 
           [0015]      FIG. 5  depicts an elevation view of the disk assembly of  FIG. 4  in accordance with an embodiment of the present invention; 
           [0016]      FIG. 6  depicts an elevation view of a portion of a disk assembly in accordance with an alternate embodiment of the present invention; 
           [0017]      FIG. 7  depicts a cross section view of a seal plate taken through the disk assembly of  FIG. 5  in accordance with an embodiment of the present invention; 
           [0018]      FIG. 8  depicts an exploded assembly view of the disk assembly depicted in  FIG. 5  in accordance with an embodiment of the present invention; 
           [0019]      FIG. 9  depicts a perspective view of a seal plate in accordance with an embodiment of the present invention; 
           [0020]      FIG. 10  is a cross section view of the seal plate of  FIG. 9  in accordance with an embodiment of the present invention. 
           [0021]      FIG. 11  is a perspective view of a seal plate in accordance with an alternate embodiment of the present invention; 
           [0022]      FIG. 12  is an alternate perspective view of the seal plate of  FIG. 11 ; 
           [0023]      FIG. 13  is a cross section view of the seal plate depicted in  FIGS. 11 and 12  in accordance with an alternate embodiment of the present invention; 
           [0024]      FIG. 14  is a cross section view of a seal plate in accordance with yet another embodiment of the present invention; 
           [0025]      FIG. 15  is a detailed cross section view of the seal plate depicted in  FIG. 14 ; and, 
           [0026]      FIG. 16  is a perspective view of the seal plate depicted in  FIGS. 14 and 15 . 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    The subject matter of the present invention is described with specificity herein to meet statutory requirements. However, the description itself is not intended to limit the scope of this patent. Rather, the inventors have contemplated that the claimed subject matter might also be embodied in other ways, to include different components, combinations of components, steps, or combinations of steps similar to the ones described in this document, in conjunction with other present or future technologies. 
         [0028]    Referring initially to  FIG. 3 , a portion of a disk  300  is depicted in cross section. The disk  300  has an outer circumferentially extending surface  302  and a center axis A-A. In operation, the disk  300  rotates about the center axis A-A. Depending on the engine geometry, the disk  300  can vary in a thickness  304 . This thickness  304  can also vary for each stage of an engine. The disk  300  comprises a plurality of blade slots  306 , as shown in  FIGS. 4 and 5 , with the blade slots  306  having a slot length  308  that extends through the thickness  304  proximate the outer circumferentially extending surface  302 . The blade slots  306  are spaced generally equally about the outer circumferential extending surface  302 . 
         [0029]    One or more blades  310  are positioned within the blade slots  306  and extend radially outward from the disk  300 . Referring now to  FIGS. 4 ,  5 ,  7 , and  8 , the one or more blades  310  each comprise a root portion  312 , an airfoil portion  314 , and a tang  316 . More specifically, the root portion  312  has a root length  318  that may or may not be substantially similar to the slot length  308 . However, in order for the blade  310  to be secured within the disk  300  it is necessary for the root portion  312  to have a cross sectional profile that corresponds to the blade slot  306 . That is, the root portion  312  has a series of attachment surfaces  313 A that mate to attachment surfaces  313 B of the blade slot  306 . The cross sectional profile of the root portion  312  will be slightly undersized compared to the blade slot  306  to ensure that the blade  310  can slide into the blade slot  306 , as shown in  FIG. 5 . 
         [0030]    Referring to  FIG. 7 , the tang  316  is shown in greater detail. The tang  316  has a thickness  320  and extends radially inward opposite of the direction of the airfoil portion  314  and is spaced axially from the root portion  312  by a seal slot  322 . The tang  316  of the blade  310  also has a hole  324  that extends through the thickness of the tang  316 . 
         [0031]    Turning to  FIGS. 7-10 , the disk assembly also incorporates one or more seal plates  326  that are positioned to receive the tang  316  of the blade  310  in order to provide one or more sealing surfaces. Use of the seal plate  326  is especially critical for blades  310  that receive some type of internal cooling, as is commonly found in a turbine section of a gas turbine engine. Without adequate sealing, the cooling fluid, which is typically air or steam, can leak out of a cooling channel and not provide sufficient cooling to the blade, resulting in blade overheating and possible premature blade failure. 
         [0032]    Referring to  FIGS. 9 and 10 , the seal plate  326  comprises a first member  328  having a first thickness  330  and a second member  332  having a second thickness  334 . As it can be seen from  FIGS. 7 and 10 , the first member  328  is generally parallel to the second member  332 . In the embodiment shown, the first member  328  also has a height H 1  that is greater than a height H 2  of the second member  332 , but the second thickness  334  is greater than the first thickness  330 . Also, the first member  328  has one or more holes  336  that extends through the first thickness  330  and the second member  332  has one or more threaded holes  338  in the second thickness  332 . It is necessary, for the embodiment shown, that the second thickness  334  be greater than the first thickness  330 , since the hole  338  is threaded and a threaded hole requires additional thickness for the threads than does a through hole. The seal plate  326  also comprises a leg  333  that connects the first member  328  to the second member  332 . 
         [0033]    The disk  300  utilizes one or more fasteners  340  to secure the seal plate  326  to the tang  316  of the blade  310 . Fasteners  340  are placed through the one or more holes  336  in the first member  328 , through the hole  324  in the tang  316 , and engages a set of threads  342  of the one or more threaded holes  338  in the second member  332 . This arrangement is depicted in  FIG. 7 . When the threads of the fastener  340  engage corresponding threads  342  of the threaded hole  338 , at least the second member  332  of seal plate  326  is drawn into contact with the tang  316  to provide a seal. Also, upon rotation of the disk  300  having one or more blades  310 , angular momentum of the seal plate  326  causes a flat portion  344  of the leg  333  to move slightly radially outward and contact a corresponding flat surface  346  of the tang  316 . This contact provides an additional sealing region. 
         [0034]    As previously discussed, a sealing arrangement is required for blades which receive a supply of cooling fluid. While embodiments of this invention can be applied to a variety of blades and disk designs, including newly manufactured components, one particular embodiment in which this invention is applicable is with respect to a method of modifying an existing turbine disk having regions of excessive stress in an attachment area between a blade and the disk. For clarity purposes, the same figures will be used in describing this embodiment of the present invention that is directed towards modifying a turbine disk, as have been previously referenced. 
         [0035]    As previously discussed, the turbine disk  300  has a plurality of blade slots  306  for receiving blades along its outer circumferential surface  302 . However, this disk also contains a tangential cooling cavity  350  (see  FIG. 3 ). The intersection of the cooling cavity  350  and blade slots  306 , when combined with the radial pull associated with rotating blades  310 , can create excessive stress concentrations at these intersections. If not alleviated, the stress concentrations can exceed the allowable stress levels for a particular material and operating temperature resulting in failure of the disk. 
         [0036]    An alternate embodiment of the present invention applies the seal plate arrangement previously discussed to a modified blade disk, when the structure of the cooling cavity  350  adjacent to known high stress regions has been modified. Referring back to  FIG. 3 , a dashed line  352  indicates where a section of the disk, identified as  354 , is to be removed. An elliptical cut is made to reduce any remaining stress concentrations in the disk  300 . The blades  310  for that stage of the engine are also machined to place a flat surface  346  on the tang  316 . Then, a through hole is drilled into the tang  316  of the blade  310 . 
         [0037]    Once modifications have been made to the disk  300  and blade  310 , the blade  310  is then placed into the blade slot  306  of the now modified disk  300  and a seal plate  326  is slid at least partially around the tang  316  and into a seal slot  322  of the disk  300 . Referring to  FIG. 7 , the seal plate  326  is placed adjacent to the blade  310  and the disk  300  such that the first member  328 , which has a through hole  336 , is placed adjacent to a first side  316 A of the tang  316  while the second member  332 , which has a threaded hole  338 , is placed adjacent to a second side  316 B of the tang  316 . The second member  332  is placed into the seal slot  322  such that the through holes  336 ,  324 , and  338  are in alignment. During such an alignment, the flat surface  346  of the tang  316  may also contact the flat surface  344  of the seal plate  326 . 
         [0038]    Once the seal plate  326  is positioned around the tang  316 , a threaded fastener  340  is placed through the through hole  336  in the seal plate  326  and through the through hole  324  in the tang  316  such that the fastener  340  engages the threaded hole  338  in the second member  332  of the seal plate  326 . The fastener  340  is then secured to the first member  328  by a means such as tack welding so as to prevent the fastener  340  from backing out and coming loose during engine operation. 
         [0039]    Although this seal plate  326  has been described in use with a particular modification to a blade disk  300 , as shown in  FIG. 3 , similar modifications can be applied to a variety of disk configurations. Also, the seal plate  326  can take on a variety of configurations. One such alternate embodiment of the seal plate is depicted in  FIG. 6 . For clarity purposes, similar numerical identifiers are used in  FIG. 6  to denote similar features of other embodiments of the present invention. In this embodiment, the seal plate  626  extends circumferentially across a plurality of blades  610 . In this embodiment, the seal plate  626  extends across three blades  610 , but this alternate embodiment is not limited to spanning only three blades  610 . The seal plate  626  can span a larger or smaller quantity of blades  610  and can use a single fastener  640 , as depicted in  FIG. 6 , or multiple fasteners. 
         [0040]    Depending on the blade construction, the seal plate geometry can vary to include additional members similar to members  328  and  332 . Also, the spacing between the members  328  and  332  can vary and as a result, the length of the leg  333  will also vary. Furthermore, depending on the blade and disk configuration, it is possible that more than one seal plate  326  will be required. For example, multiple seal plates  326  can be used, with one at a forward end of a blade/disk assembly and another at an aft end of the blade/disk assembly. 
         [0041]    While the seal plate  326  and fastener  340  have been described with respect to a threaded engagement, this is but one type of coupling. Alternate forms of fastening the seal plate  326  and the blade tang  316  together are envisioned as such, slight modifications to the seal plate  326  and/or blade tang  316  may be required. For example, depending on the fastener type, the hole  338  may not be threaded, but instead may be a through hole or a tapered hole so as to engage an alternate form of the fastener  340 . 
         [0042]    Although the present invention has been described in terms of a threaded fastener, the fastener  340  is not limited to this configuration. In fact, alternate sealing arrangements between the seal plate  326  and the blade tang  316  can be utilized, such as a snap fit or trapping the seal plate  326  between the tang  316  and the disk  310 . Furthermore, the second member  332  may not have a hole  338 . In this embodiment, a fastener can pass through the first member and the tang and contact the second member  332   
         [0043]    An alternate embodiment of the present invention is shown in  FIGS. 11-16 . Referring initially to  FIGS. 11-13 , a first alternate embodiment of a seal plate  1100  is depicted. In this first alternate embodiment, a seal plate  1100  for minimizing a cooling fluid leakage between a portion of a disk  1102  and one or more blades  1104  is shown. The seal plate  1100  comprises a circumferentially extending base member  1106 , a first vertical member  1108  that extends radially outward from an end of the circumferentially extending base member  1106 . A second vertical member  1110  extends radially outward from the first vertical member  1108 . The first and second vertical members are connected by an axial member  1112 . 
         [0044]    The circumferentially-extending member  1106  also includes an angled surface  1114  that mates to an angled surface  1116  of the blade tang  1118 . During operation, as the blade  1104  rotates, the blade  1104  moves slightly radially outward away, from the disk  1102  due to the circumferential pull created by the blade weight and rotation. However, the blade  1102  is fixed in place radially by an attachment (not shown). The coverplate  1100 , is secured to a blade tang  1118  by one or more pins  1120  that pass through respective openings in the coverplate  1100  and tang  1118 . This securing means permits the coverplate  1100  to move slightly radially outward such that the angled surface  1114  of the coverplate comes into and maintains a line-on-line contact with the blade tang  1118 . 
         [0045]    Referring now to  FIGS. 14-16 , yet another alternate embodiment of the present invention is shown. The features of this alternate embodiment are similar to those described in  FIGS. 11-13  and carry similar identifiers where common, and as such, only new and/or different features of this embodiment are described in more detail below. 
         [0046]    In this alternate embodiment, the second vertical member  1110  further comprises a slot  1122  that contains a generally circumferentially-extending seal  1124  that has a circular cross section, such as a wire seal. The slot  1122  is formed from material removed or void from the radially outer portion of the second vertical member  1110 . The circumferentially-extending seal  1124  extends the circumference of the disk  1102  to provide a supplemental seal to the angled surfaces  1114  and  1116 . 
         [0047]    The present invention has been described in relation to particular embodiments, which are intended in all respects to be illustrative rather than restrictive. Alternative embodiments will become apparent to those of ordinary skill in the art to which the present invention pertains without departing from its scope. 
         [0048]    From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects set forth above, together with other advantages which are obvious and inherent to the system and method. It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and within the scope of the claims.