Abstract:
A seal extending between adjacent slots of a gas turbine engine is disclosed. The seal comprises a plurality of generally planar members fixed together along a central axis. The outer member further comprises rounded ends that encompass the second and plurality of third generally planar members. The seal disclosed herein improves sealing capability by providing a more compliant seal over the prior art while reducing the mechanical loads experienced along the seal weld joint, thereby improving seal durability.

Description:
This application hereby claims the benefit of U.S. Provisional Patent Application Ser. No. 60/623,515, which was filed Oct. 29, 2004, entitled FLEXIBLE SEAL FOR A GAS TURBINE. 

   TECHNICAL FIELD 
   The present invention relates generally to a seal and more specifically towards a flexible seal for preventing the leakage of hot gases in a gas turbine engine. 
   BACKGROUND OF THE INVENTION 
   Gas turbine engines typically comprise a compressor, at least one combustor, and a turbine. The pressure of air passing through the compressor is raised through each stage of the compressor and is then directed towards the combustion system. Gas turbine combustion systems mix fuel with the compressed air and ignite this mixture to create hot combustion gases. The hot combustion gases are then directed towards a turbine, which produces work, typically for thrust, or shaft power if the engine shaft is connected to an electrical generator. 
   The turbine engine is comprised of numerous individual components that are fixed together in order to provide the path through which air and combustion gases pass while undergoing the process of generating the thrust or shaft power previously mentioned. It is imperative that all gaps between these individual components be controlled in order to minimize losses in compressor, combustion, or turbine efficiency due to undesirable leakages. Due to various thermal and mechanical loads on these individual components, often times the sealing region between mating components moves or twists. Therefore, it is imperative that any seal between mating components be compliant to such movement. While various fastening and sealing means are employed to control these leakages, one common means, especially in the turbine section, is the use of individual metallic seals. 
   Most common metallic seal designs have included individual strips of metal and a metallic cloth seal. Examples of these types of prior art seals are shown in  FIGS. 1-3 . Referring now to  FIGS. 1 and 2 , a metallic cloth seal in accordance with U.S. Pat. No. 5,934,687 is shown and hereby incorporated for reference. Metallic cloth seals have become common due to their sealing, wear resistance features, and ease of assembly with the turbine engine. As an example, seal  110  includes a center metal sheet  130  surrounded by cloth layer assemblages  132  and  134 . Cloth layers  132  and  134  are attached to metal sheet  130  by a plurality of spot welds  138 , which are located towards the outer edges of cloth layers  132  and  134 . While this seal design has shown improved resistance to wear, the seal has minimal flexibility, due especially to the locations of spot welds  138 . In operation, seal  110  must move and bend as required in order to maintain a seal between mating components. This seal movement imparts a high bending stress on spot welds  138  that has been known to cause the the weld to crack and the cloth layer  132  and  134  to separate from center metal sheet  130 . 
   An alternate prior art gas turbine engine seal is shown in  FIG. 3  and consists essentially of a plurality of thin slabs that are movable relative to one another as disclosed in U.S. Pat. No. 5,997,247 and incorporated for reference. The thin slabs  10  are designed to be free to slide and spread out laterally across slot  8  to seal gap  6 . However, this seal requires multiple thin slabs which can be an issue in ensuring the proper number of slabs have been installed in the slot. Too few slabs can result in an overly flexible seal that does not maintain an adequate seal and too many slabs can result in an overly stiff seal that does not move as necessary to maintain an adequate seal. 
   Therefore, in light of the requirements to provide a compliant seal to operate under high temperatures and mechanical loads, an improved seal is desired that overcomes the shortfalls of the prior art. 
   SUMMARY OF INVENTION 
   The present invention discloses a seal that extends between adjacent slots of a gas turbine engine. The seal comprises an outer sleeve having a first generally planar member including a length, a first end, a second end, a width extending therebetween, and a first thickness. A second generally planar member is positioned on the opposite side of the first generally planar member and has a raised portion. Extending from proximate the first end to proximate the second end and located in between the first and second generally planar members is a plurality of third generally planar members. The plurality of third generally planar members of the seal are arranged such that they are fixed to both the first and second generally planar members. The various planar members, which are preferably fabricated from relatively thin sections of sheet metal, are secured together by a means such as welding, where the welds are located generally along a centerline. The use of multiple planar members secured together along the seal centerline provides a device capable of sealing slots between adjacent engine components, that has the required flexibility to conform to mechanical and thermal loads, while having significantly lower stresses along the weld joint region. 
   In accordance with these and other objects, which will become apparent hereinafter, the instant invention will now be described with particular reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a perspective view of a portion of a prior art metallic seal for a gas turbine engine. 
       FIG. 2  is a cross section view of  FIG. 1  of a prior art metallic seal for a gas turbine engine. 
       FIG. 3  is a cross section view an alternate prior art metallic seal for a gas turbine engine. 
       FIG. 4  is an elevation view of a seal in accordance with the preferred embodiment of the present invention. 
       FIG. 5  is a cross section view of  FIG. 4  of a seal in accordance with the preferred embodiment of the present invention. 
       FIG. 6  is a cross section view of a slot region of a gas turbine engine utilizing a seal in accordance with the preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The preferred embodiment of the present invention is shown in detail in  FIGS. 4-6 .  FIG. 4  depicts an elevation view of seal  50  in accordance with the preferred embodiment of the present invention with  FIG. 5  taken as a cross section through the elevation view of  FIG. 4 . Seal  50  comprises an outer sleeve  51  having a first generally planar member  52  including length  53 , first rounded end  54 , second rounded end  55 , and width  56  extending therebetween. Outer sleeve  52  also has a first thickness  57 . Seal  50  further comprises a second generally planar member  58  that is opposite, yet substantially parallel to first generally planar member  51 , as is shown in  FIG. 5 . Second generally planar member  58  has a second thickness  59  and at least one step  60  thereby forming a raised portion  61  of second generally planar member  58 . 
   Located in between first generally planar member  52  and second generally planar member  58  is a plurality of third generally planar members  62  that each have a third thickness  63  and extend from proximate first end  54  to proximate second end  55 . Depending on the dimensions of the slot in which the seal is to be placed as well as the desired amount of seal movement, the number of third generally planar members can vary. However, in the preferred embodiment, three members are utilized in between first and second generally planar members as well as a shorter member that is located within the raised portion  61  of second generally planar member  58 . The more pliability desired will utilize fewer third generally planar members while a stiffer seal design will require more third generally planar members, for a given member thickness. In order to overcome the shortcomings of the prior art seal, in which multiple slabs can move relative to one another, the present invention fixes third generally planar members  62  to first and second generally planar members  52  and  58 , respectively. These planar members can be affixed by a variety of means, but the preferred means is through a plurality of spot welds  64 , as shown in  FIG. 4 . As one skilled in the art understands, in order to make a complete spot weld, there cannot be a gap between the raised portion  61 , the first generally planar member  52  opposite of the raised portion and the plurality of third generally planar members  62  located therebetween. Otherwise, the welding current cannot pass through all surfaces that are to be welded. 
   The preferred embodiment of the present invention further incorporates substantially rounded first and second ends,  54  and  55 , as shown in  FIG. 5 , such that a portion of second generally planar member  58  and plurality of third generally planar members are enclosed. Rounded ends to outer sleeve  51  have been incorporated for multiple reasons. First, the rounded ends provide a more compliant point of contact for the seal against the slot as shown in  FIG. 6 , which is beneficial during seal installation and engine operation. Second, the ends of various sheet members stacked in between the first and second generally planar members are protected from contacting adjacent hardware that could damage the assembled members by trying to pry the members apart. The rounded ends have, by nature, a height  66  when viewed in cross section, as shown in  FIG. 5 . The ends  54  and  55  are rounded completely on both the outer-most side of the seal and partially rounded on the inner side (the side closest to centerline A-A). As such, the height  66  of the rounded ends  54  and  55  is greater than the summation of thicknesses of first generally planar member  52 , second generally planar member  58 , and plurality of third generally planar members  62  (as indicated by thickness  57 ,  59 , and  63 , respectively). This can be seen in  FIG. 5 . These thicknesses, when stacked together and including any change in seal geometry. as shown in  FIG. 5 , have by nature a height  68 . The height  66  of the rounded ends  54  and  55  is greater than any height  68  along the width  56  of the seal. The seal must have this relative height configuration between the rounded ends  54  and  55  and the seal width  56  so as to comply with the operational requirement described above wherein the rounded ends serve as the point of contact for the seal (see  FIG. 6 ). As shown in  FIG. 6 , it is the rounded ends that provide the contact surfaces for the seal in a slot, not the generally planar members. 
   A further benefit of the rounded ends of outer sleeve  51  is with respect to the position of welds  64 . Seal  50  further comprises a centerline A-A, as shown in  FIG. 4 , that extends along length  53 . By positioning welds  64  along centerline A-A, a neutral axis is established allowing the seal ends, which are contacting the slot, to twist about centerline A-A, such that it is compliant to slot movement without overstressing the weld joints. One skilled in the art of sheet metal fabrication and welding will understand that the size and spacing of welds  64  depend on the material and thickness of that which is being welded. 
   Depending on the operating requirements, the seal material and respective member thickness can vary. However, it is preferred that seal  50  is fabricated from a high temperature alloy such as Haynes  188 . Furthermore, due to outer sleeve  51  serving as the outermost layer and generally the region of contact with an engine seal slot, it is preferred that first thickness  57  is greater than both second thickness  59  and third thickness  63 . Accordingly, outer sleeve  51  is fabricated from a sheet having a first thickness between 0.015 inches and 0.050 inches while second and third generally planar members  58  and  62  are fabricated from a sheet having a second and third thickness, respectively, of between 0.010 inches and 0.040 inches. 
   The configuration presented in the preferred embodiment of the present invention provides for a gas turbine seal fabricated from a plurality of generally planar members, preferably spot welded together along a neutral axis. As a result, the seal, which provides a seal to reduce or eliminate undesirable leakage resulting in engine performance loss, has improved shear and bending capability while reducing the stress loads applied to the weld joints. 
   While the invention has been described in what is known as presently the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment but, on the contrary, is intended to cover various modifications and equivalent arrangements within the scope of the following claims.