Abstract:
A seal having a first seal mechanism adapted for insertion between a first structure and a second structure, wherein the first structure is in communication with a first medium and the second structure is in communication with a second medium. The seal also includes a second seal mechanism, which is pressuringly biasable against the first seal mechanism and against the second structure by the second medium. In certain embodiments, a system has a first structure in communication with a first medium and a second structure houses a seal assembly between the first and second structures. The seal assembly includes an interface seal disposed against the first structure and a flexible seal pressuringly biased against the second structure and the interface seal by a second medium.

Description:
BACKGROUND 
   The present invention relates generally to methods and structures for sealing and, more particularly, a hybrid seal for sealing adjacent components of a turbine engine. 
   A number of applications have sealing arrangements between adjacent components. In some applications, seals enable relative motion between the adjacent components, while substantially minimizing fluid leakage between such components. These seals often vary in construction depending upon the environment, the fluids, the pressure ranges, and the temperature ranges. 
   For example, turbine engines generally have seals between stationary components, such as inner shrouds or outer shrouds. In these turbine engines, the inner shrouds are generally subjected to hot combustion gases, whereas the outer shrouds are subjected to cool purge gases used to cool outer and inner shrouds. It is therefore important to seal the inner and outer shrouds to prevent flows of the hot combustion gases into the outer shrouds and to prevent leakage of the cold purge gases into the inner shrouds. For example, leakage of the hot combustion gases into the outer shrouds could damage or adversely affect life of the turbine engine components. 
   Traditionally, the inner and outer shrouds are metallic. Therefore, existing seals include metal splines positioned against the inner shroud at locations of hot combustion gases, such that the splines reduce leakage of the hot combustion gases into the outer metallic components. Metal cloth seals also may be employed at such locations. In operation, these metallic seals may accommodate different thermal growths, non-uniformity or transient motion between adjacent components during operation of the turbine engine. Unfortunately, these metallic seals are prone to oxidation or chemical reaction by the hot combustion gases which limits their use as the operating temperatures in the turbine increase. 
   As a result, metallic sealing structures, such as metal splines and metal cloth seals, are not particularly well suited for higher operating temperatures. For example, higher temperature portions or stages of turbine engines may have temperature ranges approximately 100 to 200 degrees higher than current operating temperatures. Accordingly, higher temperature designs of turbine engines generally have inner shrouds made of materials suitable for these higher temperature ranges. For example, certain higher temperature turbine engines have inner shrouds made of a high temperature resistant ceramic material, such as a Ceramic Matrix Composite (CMC). The components surrounding the inner shroud, such as the outer shroud, are generally metallic in composition. Unfortunately, CMC components are difficult to machine, thereby making it difficult to mechanically capture the metallic seals in the locations of hot combustion gases. High-temperature interface seals, such as rope seals or ceramic block seals, are resistant to chemical reaction with the hot combustion gases, yet these seals do not provide the desired flexibility during periods of dissimilar thermal growth between the inner and outer shrouds. 
   In such applications as mentioned above, a spring-loaded seal may be employed to facilitate sealing of these CMC components. For example, a spring-loaded seal may have a rope seal with a central core of fibers, a surrounding resilient spring member supporting the core, and at least one layer of braided sheath fibers tightly packed together overlying the spring member. However, such a sealing mechanism, while having an improved resiliency and load bearing capacity, is likely to lose its resiliency when repeatedly loaded at high temperatures. 
   Therefore, a need exists for a system and method for effectively sealing components in applications, such as turbine engines. 
   BRIEF DESCRIPTION 
   A seal having a first seal mechanism adapted for insertion between a first structure and a second structure, wherein the first structure is in communication with a first medium and the second structure is in communication with a second medium. The seal also includes a second seal mechanism, which is pressuringly biasable against the first seal mechanism and against the second structure by the second medium. 
   In certain embodiments, a system having a first structure in communication with a first medium and a second structure housing a seal assembly between the first and second structures. The seal assembly includes an interface seal disposed against the first structure and a flexible seal pressuringly biased against the second structure and the interface seal by a second medium. 

   
     DRAWINGS 
     These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
       FIG. 1  is a front cross sectional view of a turbine engine having a hybrid seal in accordance with embodiments of the present technique; 
       FIG. 2  is a partial cross sectional view of the turbine engine of  FIG. 1  illustrating a hybrid seal in accordance with embodiments of the present technique; 
       FIG. 3  is a partial cross sectional view of the turbine engine of  FIG. 1  illustrating a hybrid seal employing a C-seal and a rope seal according to one embodiment of the present technique; 
       FIG. 4  is a partial cross sectional view of the turbine engine of  FIG. 1  illustrating a hybrid seal employing a C-seal and a rope seal according to an embodiment of the present technique; 
       FIG. 5  is a partial cross sectional view of the turbine engine of  FIG. 1  illustrating a hybrid seal employing a U-seal and a rope seal according to one embodiment of the present technique; 
       FIG.6  is a partial cross sectional view of the turbine engine of  FIG. 1  illustrating a hybrid seal employing a U-seal and a rope seal according to an embodiment of the present technique; 
       FIG. 7  is a partial cross sectional view of the turbine engine of  FIG. 1  illustrating a hybrid seal employing a U-seal and a ceramic block seal according to an embodiment of the present technique; 
       FIG. 8  is a partial cross sectional view of the turbine engine of  FIG. 1  illustrating a hybrid seal employing a W-seal and a rope seal according to an embodiment of the present technique; 
       FIG. 9  is a partial cross sectional view of the turbine engine of  FIG. 1  illustrating a hybrid seal employing a C-seal and a ceramic coating according to an embodiment of the present technique; 
       FIG. 10  is a partial cross sectional view of the turbine engine of  FIG. 1  illustrating a hybrid seal employing a C-seal and a ceramic coating according to an alternate embodiment of the present technique; 
       FIG. 11  is a partial cross sectional view of the turbine engine of  FIG. 1  illustrating a hybrid seal employing a plurality of rope seal members according to one embodiment of the present technique; 
       FIG. 12  is a flowchart illustrating a method of operating a hybrid seal according to embodiments of the present technique; and 
       FIG. 13  is a flowchart illustrating a method of manufacturing a hybrid seal according to embodiments of the present technique. 
   

   DETAILED DESCRIPTION 
   As discussed in detail below, a variety of sealing mechanisms may employed to facilitate sealing between different structures and mediums, such as hot and cold gasses, which are separated by the structures. One such example is a turbine engine, which is subject to hot combustion gases and relatively cool purging air.  FIG. 1  is a partial cross-sectional view illustrating a turbine engine  10  having unique sealing mechanisms in accordance with embodiments of the present technique. As illustrated, the turbine engine  10  comprises a plurality of circumferentially spaced buckets or blades  14 , which rotate about an axis represented generally by point  12  (i.e., axis is perpendicular to the plane of  FIG. 1 ). At the outer periphery of these blades  14 , the turbine engine  10  comprises a shroud-like configuration or inner shroud  16  extending concentrically about the plurality of blades  14  in a ring-shaped configuration. The inner shroud  16  is stationary, and is surrounded by an outer shroud  18  extending concentrically about it. The hot combustion gas  22  generated by combustors (not shown) cause the plurality of blades  14  to rotate about the axis  12 . Between the inner and outer shrouds  16  and  18 , the turbine engine  10  also has a hybrid seal  20  in accordance with various embodiments described in further detail below. As recognized by one of ordinary skill in the art, hot combustion gases  22  in the turbine engine  10  pass between the rotational blades  14  and the stationary inner shroud  16 . Thus, the hybrid seal  20  facilitate sealing between the inner and outer shrouds  16  and  18  and the corresponding internal hot combustion gases  22  and external gases  23  (e.g., cool airflow). 
     FIG. 2  is a cross sectional view along an axial direction of the turbine engine  10  illustrating an exemplary hybrid seal  20  in accordance with embodiments of the present technique. The illustrated hybrid seal  20  is employed to seal an annular passage of the hot combustion gas  22  between the inner shroud  16  and the surrounding static outer shroud  18 . 
   In the illustrated embodiment, the inner shroud  16  comprises a ceramic material, such as Ceramic Matrix Composite (CMC), which is resistant to chemical reaction by the hot gas  22  even at substantially high temperatures. The illustrated outer shroud  18  comprises a metallic composition. 
   The illustrated hybrid seal  20  of  FIG. 2  comprises an interface seal  24  and a compliant seal or flexible seal  26 . The interface seal  24  is engaged against the inner shroud  16 . The flexible seal  26  is housed inside the outer shroud  18  and is disposed on the interface seal  24 . In operation, a relatively cool purge gas or air  30  flows through a passage  32  in the outer shroud  18  to cool outer metallic components, such as the outer shroud  18 . According to certain embodiments of the present technique, the purge gas or air  30  flows through the passage  32  at a relatively high pressure to pressure-load the flexible seal  26 , such that the flexible seal  26  is pneumatically biased against the interface seal  24  and also against an inner surface  28  of the outer shroud  18 . For example, the purge gas or air  30  may have a pressure range of approximately 700–1200 Kpa. Advantageously, the purge gas or air  30  also facilitates cooling of the flexible seal  26 . The flexible seal  26  surface provides a continuous loading surface for the purge air  30 , which leads to a uniform distribution of a high pressure even though the turbine engine  10  has a discrete number of purge air passages  32 , or purge holes, along the circumference of the outer shroud  18 . 
   The interface seal  24  can include one or more rope seals or block seals. For example, rope seals may comprise a high temperature metal alloy, such as oxide-dispersed strengthened alloy, amongst others, or ceramic fibers such as alumina, alumina-silica or silicon carbide. Other examples of a rope seals include a hybrid rope seal which has multiple layers of the above-mentioned fibers. By further example, block seals may comprise solid ceramic blocks. In operation, the interface seal  24  is exposed to the hot gas  22  and engages the inner shroud  16 . Accordingly, the interface seal  24  is desirably oxidation resistant, wear resistant, and resilient. The flexible seal  26  is generally a metallic seal having a C-shaped, U-shaped, or a W-shaped cross-section. The flexible seal  26  generally comprises a high temperature resistant metal alloy, such as nickel-based superalloys, oxide-dispersed strengthened alloys, amongst others. 
   As recognized by one of ordinary skill in the art, the foregoing hybrid seal  20  may have a variety of embodiments within the scope of the present technique. By further example,  FIGS. 3–11  illustrate various alternative embodiments of the hybrid seal  20  illustrated with reference to  FIGS. 1 and 2 . Referring now to  FIG. 3 , a partial cross-sectional view of the turbine engine  10  illustrates a sealing arrangement  34  having an interface seal or rope seal  38  and a C-shaped flexible seal or C-seal  36 . The illustrated C-seal  36  forms a hollow circular or elliptical structure having a C-shaped cross-section, which extends concave down within and against the inner surface  28  of the outer shroud  18 . The C-seal  36  also extends about an upper periphery of the rope seal  38 , which in turn engages the top of the inner shroud  16 . In operation, the purge gas or air  30  flows through the purge passages  32  to create a high pressure against the C-seal  36 . The upper surface of the C-seal  36  provides a continuous loading surface for the purge air  30  to facilitate uniform distribution of purge air  30  pressure over the C-seal  36 . Pressure exerted by the purge air  30  is in a direction substantially normal to the outer surface of the C-seal  36 . Advantageously, this pressure loading on the C-seal  36  and rope seal  38  biases the rope seal  38  into tighter and more sealed engagement with the inner shroud  16 , while also causing the rope seal  38  and the C-seal  36  to expand outwardly into tighter and more sealed engagement against the inner surface  28  of the outer shroud  18 . 
     FIG. 4  illustrates a partial cross-sectional view of the turbine engine  10  illustrating an alternative sealing arrangement  40  in accordance with embodiments of the present technique. As illustrated, the sealing arrangement  40  comprises a C-shaped flexible seal  36  having a convex configuration, which is open upwardly toward the air passage  30 . The C-shaped flexible seal  36  engages both the inner surface  28  of the outer shroud  18  and the upper surface of the rope seal  38 . Accordingly, as the purge gas or air  30  pressurably engages the C-shaped flexible seal  36 , the C-shaped flexible seal  36  expands outwardly against the inner surface  28  of the outer shroud  18  to provide a tighter and more sealed engagement with the outer shroud  18 . Simultaneously, the pressure loading against the C-shaped flexible seal  36  forces the rope seal  38  to expand outwardly against the inner shroud  16  to provide a tighter and more sealed engagement with the inner shroud  16 . In addition, the pressure loading may cause the rope seal  38  to expand outwardly against the inner surface  28  of the outer shroud  18 , thereby providing additional sealing between the inner and outer shroud  16  and  18 . Again, the relatively cool temperature of the purge gas or air  30  also facilitates cooling of the C-shaped flexible seal  36 . 
     FIG. 5  illustrates a partial cross-sectional view of the turbine engine  10  illustrating an alternative sealing arrangement  42  in accordance with embodiments of the present technique. As illustrated, the sealing arrangement  42  comprises a U-shaped flexible seal or U-seal  44  and a rope seal  38 . As illustrated, the U-seal  44  has a concave middle section  43  and opposite convex outer sections  45 . Again, the U-seal  44  has the convex middle section  43  extending over a top periphery of the rope seal  38 , while also having the opposite convex outer sections  45  engaged against opposite internal surfaces  28  of the outer shroud  18 . In operation, the pressurized purge gas or air  30  forces the U-seal  44  downwardly against the rope seal  38  to facilitate sealing against the inner shroud  16 , while also causing the U-seal  44  and the rope seal  38  to expand outwardly toward the inner surface of the outer shroud  18 . As with the other rope seals, the downward pressure toward the inner shroud  16  causes the rope seal  38  to mushroom out, such that the rope seal  38  further biases the U-seal  36  toward the inner surface  28  of the outer shroud  18 . Accordingly, the sealing arrangement  42  facilitates substantially uniform sealing between the inner and outer shroud  16  and  18 . 
     FIG. 6  illustrates a partial cross-sectional view of the turbine engine  10  illustrating a sealing system  46  in accordance with embodiments of the present technique. In this embodiment, the U-shaped seal  44  has an upwardly open or convex configuration, which faces the purge gas or air passage  30 . Again, the pressurized purge gas or air  30  forces the U-seal  44  to expand outwardly toward the inner surface  28  of the outer shroud  18 , while simultaneously biasing the rope seal  38  downwardly toward the inner shroud  16 . 
     FIG. 7  illustrates a partial cross-sectional view of the turbine engine  10  illustrating a sealing arrangement  48  in accordance with embodiments of the present technique. In the illustrated embodiment, the sealing arrangement  48  has the U-seal  44  of  FIG. 6  with a block seal  50 , which is an alternative to the rope seal  38 . In operation, the pressurized purge gas or air  30  biases the U-seal  44  outwardly against the inner surface  28  of the outer shroud  18 , also forcing the block seal  50  downwardly against the inner shroud  16 . In certain embodiments, the block seal  50  may comprise of ceramic, ceramic-matrix composite, ceramic-coated metals or alloys, or high temperature metals (with or without coating). 
     FIG. 8  illustrates a partial cross-sectional view of the turbine engine  10  illustrating a sealing arrangement  52  in accordance with embodiments of the present technique. As illustrated, the sealing arrangement  52  includes a W-shaped flexible seal or W-seal  54  disposed against a rope seal  38 . Similar to the C-seal and U-seal discussed in detail above, the W-seal  54  is biased against the inner surface  28  of the outer shroud  18  by pressure from the purge air  30 , thereby providing a uniform loading surface for the purge air  30  against the rope seal  38 . In addition, the pressurized purge gas or air  30  forces the W-seal  54  to bias of the rope seal  38  downwardly against the inner shroud  16 . As a result, the sealing arrangement  52  is pressure-loaded against both the inner and outer shroud  16  and  18 , while also obtaining a cooling flow from the relatively cool temperature of the purge gas or air  30 . 
   According to a different embodiment, instead of having a rope seal or a block seal, the flexible interface seal (e.g., C-seal, U-seal, or W-seal) may comprise a coating of a ceramic material at one or more locations. For example, the flexible interface seal may comprise a metallic composition while the coating may comprise a ceramic composition. Referring to  FIG. 9 , a partial cross-sectional view of the turbine engine  10  illustrates a sealing arrangement  56  in accordance with embodiments of the present technique. As illustrated, the sealing arrangement  56  comprises a C-seal  36  and a ceramic coating  58 , which is disposed along a convex surface of the C-seal  36  and is engaged against the inner surface  28  of the outer shroud  18 . In operation, the pressurized purge gas or air  30  forces the C-seal  36  to expand outwardly against the inner surface  28  of the outer shroud  18 , while simultaneously forcing the C-seal  36  to seal downwardly against the inner shroud  16 . At these contact points with the inner and outer shrouds  16  and  18 , the ceramic coating  58  provides an interface that is more resistant to heat, oxidation, and other adverse affects of the hot combustion gases  22 . 
   In still another embodiment as shown in  FIG. 10 , a partial cross-sectional view of the turbine engine  10  illustrates a sealing arrangement  60  in accordance with embodiments of the present technique. Here, the sealing arrangement  60  comprises a C-seal  36 , which is engaged against a plurality of ceramic-coated surfaces  62  at the inner surface  28  of the outer shroud  18  and the top surface of the inner shroud  16 . As illustrated, these ceramic-coated surfaces  62  provide an interface between the C-seal  36  and the inner and outer shrouds  16  and  18 . Accordingly, these ceramic-coated surfaces  62  provide an interface that is more resistant to heat, oxidation, and other adverse affects of the hot combustion gases  22 . 
     FIG. 11  illustrates a partial cross-sectional view of the turbine engine  10  illustrating a sealing arrangement  64  in accordance with embodiments of the present technique. In the illustrated embodiment, the sealing arrangement  64  includes a plurality of interface seals or rope seal members, such as outer rope seals  66  and central rope seal  68 . The sealing arrangement  64  also has a baseline seal or flexible W-seal  70 , which engages all three of the rope seals  66  and  68 . In operation, the pressurized purge gas or air  30  forces the flexible seal  70  to expand outwardly against the inner surfaces  28  of the outer shroud  18 , while also biasing each of the rope seals  66  and  68  the downwardly toward the inner shroud  16 . In this embodiment, the downward pressure against the rope seals  66  and  68  also forces the larger central rope seal  68  to fill the space between the outer rope seals  66 , thereby biasing the outer rope seals  66  outwardly toward the inner surface  28  of the outer shroud  18 . The sealing arrangement  64  also provides sealing redundancy if one or more rope seal members  66  and  68  fails on account of excessive chemical or mechanical degradation. 
   In certain embodiments, the rope seals  66  and  68  of  FIG. 11  may comprise fiber ropes of a ceramic material or a high temperature resistant metal. The smaller diameter rope seals  66  also may be coupled to the larger diameter rope seal  68  to provide a network of sealing fibers. The flexible seal  70  comprises a compliant material, for example, a high temperature resistant metal. The compliance of the flexible seal  70  can be varied by prescribing specific radii for the bend regions and specific angles for straight ligaments that comprise the W-shape. 
     FIG. 12  illustrates a process  72  of using the proposed hybrid seal in a turbine engine in accordance with embodiments of the present technique. As illustrated, the process  72  comprises engaging an interface seal against an inner shroud of the turbine engine (block  74 ). This step  74  may include engaging one or more rope seals or block seals, such as solid ceramic blocks, against the inner shroud  16  of the turbine engine  10  illustrated in  FIG. 1 . As discussed above, the inner shroud  16  may be subject to a hot gas  22 . At step  76 , a flexible metallic seal is engaged against the interface seal and housed in an outer shroud of the turbine. As discussed above, the outer shroud  18  may be in communication with a purge air  30  relatively colder than the hot gas  22 . Step  76  may comprise engaging a metallic C-seal, U-seal, or a W-seal in a desired orientation against the interface seal, as described in embodiments discussed earlier. At step  78 , the flexible seal is preloaded by the purge air to a desired pressure as prescribed by various flow parameters of the hot gas operating on the inner shroud. At step  80 , the purge air is continuously passed through a purge hole at a pressure uniformly onto the outer surface of the flexible seal. Thus, the pressure biases the flexible seal against the interface seal and against a lateral inner surface of the outer shroud, as discussed in detail above. Advantageously, this pressure-loaded engagement between the interface seal, the flexible metal seal, and the inner and outer shrouds provides a uniform and reliable seal between these different components and gases. 
     FIG. 13  illustrates an exemplary process  82  of manufacturing a hybrid seal for a turbine engine in accordance with embodiments of the present technique. The process  82  comprises providing an interface seal intermediate to an inner shroud and an outer shroud of a turbine engine (block  84 ). As discussed in detail above, the inner shroud is adapted to be in communication with a hot gas, while the outer shroud is adapted to be in communication with a relatively colder purge air. Step  84  includes providing a rope seal, a solid ceramic block, or a ceramic coating as described in various embodiments. At step  86 , the process  82  provides a flexible seal, which is disposed on the interface seal and also against a lateral inner surface of the outer shroud. Step  86  may include providing a metallic seal having a C-shaped, a U-shaped or a W-shaped cross-section. Moreover, the flexible seal may be composed of a high temperature resistant metal. 
   The aforementioned embodiments effectively incorporate the advantages of compliant metallic seals, and high temperature and oxidation resistant rope seals and ceramic blocks. The embodiments described employ a purge air to preload and bias the seal, eliminating the need for mechanical capture of the seal. Further, pneumatic biasing of the flexible seal against the lateral inner surface of the outer shroud provides a desired sealing against leakage of the cold purge air into the hot gas path. The techniques illustrated also provide for a uniform distribution of preloading and biasing pressures on the surface of the flexible seal. 
   While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.