Heat shield   

The present application is a Continuation-in-Part Application of U.S. patent application Ser. No. 12/615,674, filed on Nov. 10, 2009.

FIELD OF THE INVENTION

The subject matter disclosed herein relates to hot gas path components such as airfoils, and more particularly to heat shields for hot gas path components.

BACKGROUND OF THE INVENTION

Airfoils (i.e., vanes and blades) are one embodiment of a hot gas path component typically disposed in hot gas paths of gas turbines. A blade, which can also be referred to as a “bucket” or “rotor”, can include an airfoil mounted to a wheel, disk or rotor, for rotation about a shaft. A vane, which can be referred to as a “nozzle” or “stator”, can include an airfoil mounted in a casing surrounding or covering the shaft about which the blade rotates. Typically, a series of blades are mounted about the wheel at a particular location along the shaft. A series of vanes can be mounted upstream (relative to a general flow direction) of the series of blades, such as for improving efficiency of a gas flow. Vanes succeeded by blades are referred to as a stage of the gas turbine. Stages in a compressor compress gas, for example, to be mixed and ignited with fuel, to be delivered to an inlet of the gas turbine. The gas turbine can include stages in order to extract work from the ignited gas and fuel. The addition of the fuel to the compressed gas may involve a contribution of energy to the combustive reaction. The product of this combustive reaction then flows through the gas turbine. In order to withstand high temperatures produced by combustion, the airfoils and other hot gas path components in the turbine need to be cooled. Insufficient cooling results in undue stress on the airfoils and hot gas path components, and over time this stress leads or contributes to fatigue and failure of the airfoil. To prevent failure of turbine blades in gas turbine engines resulting from operating temperatures, film cooling has been incorporated into hot gas path components, such as into airfoil blade designs. For example, in film cooling of an airfoil blade, cool air is bled from the compressor stage, ducted to the internal chambers of the turbine blades, and discharged through small holes in the blade walls. This air provides a thin, cool, insulating blanket along the external surface of the turbine blade. Film cooling can be inefficient because it can create non-uniform cooling, since close to the holes the film temperature is much cooler that farther away from the holes. Accordingly, a need exists for improved cooling of hot gas path components.

Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

According to one aspect of the invention, a heat shield is described. The heat shield may include a base layer and a spacer layer. The spacer layer may be coupled to the base layer. The spacer layer may define a plurality of flow channels. The base layer and the spacer layer may be configured to associate with a hot gas path component.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a gas turbine system 10 in which exemplary heat shields may be implemented.

FIG. 2 illustrates the turbine as illustrated in FIG. 1.

FIG. 3 illustrates a side perspective view of an exemplary heat shield.

FIG. 4 illustrates the airfoil of FIG. 2 including an exemplary heat shield.

FIG. 5 illustrates a top cross-sectional view of an airfoil having an exemplary heat shield.

FIG. 6 illustrates a top cross-sectional view of an airfoil having an exemplary heat shield in proximity of the airfoil.

FIG. 7 illustrates a cross-sectional view of an exemplary heat shield.

FIG. 8 illustrates one embodiment of the spacer layer of the heat shield, shown in isolation.

FIG. 9 illustrates an exemplary embodiment of the heat shield having a dovetail attachment arrangement.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

FIG. 1 illustrates a gas turbine system 10 in which exemplary heat shields may be implemented. The exemplary heat shields described herein have been described with respect to a gas turbine. In other exemplary embodiments, the heat shields described herein can be implemented with other systems in which heat shield protection is desirable such as, but not limited to, steam turbines and compressors. The gas turbine system 10 is illustrated circumferentially disposed about an engine centerline 12. The gas turbine system 10 can include, in serial flow relationship, a compressor 16, a combustion section 18 and a turbine 20. The combustion section 18 and the turbine 20 are often referred to as the hot section of gas turbine system 10. A rotor shaft 26 operatively couples the turbine 20 to the compressor 16. Fuel is burned in combustion section 18 producing a hot gas flow 28, for example, which can be in the range between about 3000 to about 3500 degrees Fahrenheit. The hot gas flow 28 is directed through the turbine 20 to power gas turbine system 10.

FIG. 2 illustrates the turbine 20 of FIG. 1. The turbine 20 can include a turbine vane 30 and a turbine blade 32. An airfoil 34 can be implemented for the vane 30. The airfoil 34 can be disposed in a portion of the compressor 16, a portion of the combustion section 18, or a portion of the turbine 20. The vane 30 has an outer wall 36 that is exposed to the hot gas flow 28. The turbine vanes 30 may be cooled by air routed from one or more stages of compressor 16 through a casing 38 of system 10. Furthermore, the outer wall 36 of the airfoil 34 can be fitted with an exemplary disposable heat shield as now described.

FIG. 3 illustrates a side perspective view of an exemplary heat shield 100. The heat shield 100 may be configured to associate with a hot gas path component 34, such as with an airfoil 34. For example, the airfoil 34 or any hot gas path component 34 may be at least partially disposed in a hot gas path, such as in the path of hot gas flow 28. The heat shield 100 may be disposed between the hot gas path component 34 and the hot gas path. In exemplary embodiments, the heat shield 100 can be a single integral piece that is configured to affix to the airfoil 34 as described above. As further discussed herein, the heat shield, although a single integral piece, can be a multi-layer design. In other exemplary embodiments, each layer of the heat shield 100 can be a separate piece, and the separate pieces can be configured to affix to the airfoil 34 as described above. It should be understood that the heat shield 100 is not limited to applications on airfoils, but can also be affixed to any portion of the gas turbine system 10 that needs heat protection, such as to other hot gas path components 34. Any discussion of airfoils and associations between heat shields and airfoils contained herein is merely illustrative of various embodiments of the present disclosure. In exemplary embodiments, the heat shield 100 is configured to be affixed and removed with minimal downtime to the gas turbine system 10 because the heat shield 100 is a modular part of the airfoil 34, and can be removed as described herein. In exemplary embodiments, the heat shield 100 can be frictionally affixed to the airfoil 34. As such, the heat shield 100 includes several frictional pieces. In exemplary embodiments, the heat shield 100 includes casing walls 105 (i.e., upper and lower) configured to mechanically engage the casing 38 of the gas turbine system 10. The casing 38 can include a variety of shapes and curvatures. As such, the casing walls 105 can include corresponding shapes and curvatures depending on the shape of the casing 38. The heat shield 100 can further include a wall 110 disposed between the casing walls 105. The wall 110 can be oriented perpendicular to the casing walls 105. Furthermore, the casing walls 105 include a cutout 106 having a curvature that matches a curvature of the airfoil 34. The cutout 106 further matches a curvature of the wall 110. The wall 110 may be configured to associate with the airfoil 34. For example, the curvature of the wall 110 may match the curvature of the airfoil 34. In one embodiment, the wall 110 may be a multi-layer design, and each layer may be configured to associate with the airfoil 34. In exemplary embodiments, the wall 110 further includes a leading edge 111 and a trailing edge 112. The leading edge 111 is an outer convex portion of the wall 110 that initially receives the hot gas flow 28 at various angles of attack. Those skilled in the art appreciate that the leading edge 111 covers a leading edge of the airfoil 34.

FIG. 4 illustrates the airfoil 34 of FIG. 2 including an exemplary heat shield 100. As described herein, the heat shield 100 is mechanically affixed to the airfoil 34 via frictional forces between the casing 38 and casing walls 105, and between the airfoil 34 and wall 110. In other exemplary embodiments, mechanical fasteners such as, but not limited to, bolts can be implemented to affix the heat shield 100 to the airfoil 34. In exemplary embodiments, a top plug 115 can further be affixed to a portion of the casing 38. The top plug 115 can include a series of prongs 116 disposed adjacent the airfoil 34. The heat shield 100 can be affixed over the prongs 116 when affixed to the airfoil 34, thereby increasing the frictional forces between the heat shield 100 and the airfoil 34. In exemplary embodiments, several other frictional surfaces and devices can be included on the airfoil 34 and the heat shield 100 to assist affixation and removal of the heat shield 100. For example, a series of mating dovetails can be disposed on the airfoil 34 and heat shield 100.

As discussed herein, the heat shield 100 can be in-field replaceable at combustion intervals. For example, the heat shield 100 may be detachably connected to the hot gas path component 34, such as to an airfoil 34. The slip-on heat shield 100 covers the leading edge of the inner side wall and outer side wall of the airfoil 34 as well as the majority of the pressure side and to the high camber point on the suction side. The heat shield 100 can be held on with a combination of pressure side trailing edge prongs 116 that interface with recesses on the nozzles and pins on the suction side high camber point. Although any type of positive detainment devices can be implemented, the series of curved dovetails can cover the inner side wall and/or outer side wall of the airfoil 34. The airfoil 34 can then match up with a mating series of dovetails on the heat shield 100. The dovetails can be curved in the direction of the nozzle to allow for the sliding-on nature of the replaceable heat shield 100. Furthermore, bolts can be placed above a transition piece seal (that interfaces with the combustion section 18) on the leading edge of the airfoil 34. Therefore, the heat shield 100 can be replaceable at just the combustion intervals when the transition piece of the combustion section 18 and liners are removed.

FIG. 5 illustrates a top cross-sectional view of an airfoil 34 having an exemplary heat shield 100. FIG. 6 illustrates a top cross-sectional view of an airfoil 34 having an exemplary heat shield 100 in proximity of the airfoil 34. FIGS. 5 and 6 illustrate that the heat shield 100 has a curvature that matches the curvature of the airfoil 34. As illustrated, the airfoil 34 can include a plurality of impingement holes 41. The impingement holes 41 may be configured to provide cooling air to the heat shield 100. As discussed herein, the impingement holes 41 can also be implemented for conventional film cooling. The airfoil 34 can further include gaps 42 formed between the airfoil 34 and the heat shield 100. The gaps 42 can receive cooling air for film cooling. As further described herein, the heat shield 100 includes a spacer layer 101, through which the cooling air can flow. The airfoil 34 can further include a recessed surface 43. The recessed surface 43 enables the affixation of the heat shield 100 onto the airfoil 34. The airfoil 34 can further include trailing edge cooling passages 44 that receive the cooling air. As further described herein, the spacer layer 101 of the heat shield 100 defines flow channels 49. In one embodiment, the flow channels 49 may provide cooling air to the gaps 42 and the trailing edge cooling passages 44.

In exemplary embodiments, the heat shield 100 includes multiple layers. For example, the heat shield 100 can include a spacer layer 101. The spacer layer 101 can define a plurality of flow channels 49. In one embodiment, the plurality of flow channels 49 may be in fluid communication with one another. In one embodiment, the spacer layer 101 can be a corrugated layer 101. The flow channels 49 receive cooling air from the impingement holes 41, and may provide the cooling air to the trailing edge cooling passages 44 and the gaps 42. The heat shield 100 can also include an outer (thermal) layer 103. The outer (thermal) layer 103 is a material with thermal resistance to the hot gas flow 28. For example, the outer (thermal) layer 103 may be a thermally insulating ceramic coating or thermal barrier coating (“TBC”), which can be sprayed on or affixed with a bond layer 104 as described further herein. The spacer layer 101 maintains an offset between the hot gas path component 34 and the heat shield 100 as well as adds rigidity to the heat shield 100 as well as defines a plurality of flow channels 49, as described herein.

FIG. 7 illustrates a cross-sectional view of an exemplary heat shield 100. FIG. 7 illustrates the airfoil 34 in mechanical contact with the heat shield 100, which can include a base layer 102 rigidly coupled to the spacer layer 101. The base layer 102 may comprises a first surface 121 and a second surface 122. The spacer layer 101 may be situated adjacent the first surface 121. The spacer layer 101 may be configured to allowing cooling air to flow between the airfoil 34 and the base layer 102. In exemplary embodiments, the base layer 102 can be a high temperature super-alloy that provides structural strength to the heat shield 100, and provides both an aerodynamic profile and a smooth, non-corrugated surface for an outer (thermal) layer 103 to be applied. FIG. 7 further illustrates the outer (thermal) layer 103, which may be situated adjacent the second surface 122 of the base layer 102. A bond layer 104 may be situated between the second surface 122 of the base layer 102 and the outer (thermal) layer 103. The bond layer 104 may be configured to bond the outer (thermal) layer 103 to the base layer 102. For example, the bond layer 104 may be any material that is capable of bonding the outer (thermal) layer 103 to the bond layer 104, such as, for example, an aluminide.

FIG. 8 illustrates the spacer layer 101 of the heat shield 100, shown in isolation in order to illustrate the flow channels 49. The base layer 102, bond layer 104, and thermal (outer) layer 103 are not shown for illustrative purposes. In exemplary embodiments, the spacer layer 101 includes spacer sections 107. The spacer sections 107 define the plurality of flow channels 49. The spacer sections 107 can have a wide variety of patterns. For example, in one embodiment, the spacer layer 101 may be a corrugated layer 101, and the spacer sections 107 may be corrugation sections 107 disposed in a corrugation pattern. It should be understood, however, that the spacer layer 101 and spacer sections 107 are not limited to a corrugated layer 101 and corrugation sections 107, but may be any layer 101 and sections 107 that define a plurality of flow channels 49. It should further be understood that the spacer layer may be formed using any forming process known in the art, including but not limited to stamping, punching, roll-forming, or embossing.

It should further be understood that the spacer sections 107 can be spaced on the spacer layer 101 at a wide variety of widths. For example, if there are identified areas of high structural stress on the heat shield 100, patterns of spacer sections 107 can be denser or spaced closely, while in identified areas of lower stress the density of spacer sections 107 can be lower, or spaced further apart. In addition, lower density and increased spacing of spacer sections 107 provides enhanced cooling in the heat shield 100 and thus the airfoil 34. In exemplary embodiments, the impingement holes 41 are arranged approximately orthogonal to the spacer sections 107. A first series 108 and a second series 109 of spacer sections 107 are illustrated. As described above, the first series 108 of spacer sections 107 may provide airflow to the gaps 42, and the second series 109 of spacer sections 107 may provide airflow to the trailing edge cooling passages 44. As shown in FIG. 8, the first series 108 may be arranged approximately orthogonally to the second series 109. In other exemplary embodiments, a variety of other configurations of spacer sections 107 are contemplated.

Each of the spacer sections 107 may define a plurality of apertures 48. The apertures 48 may be configured to allow cooling air to enter the spacer layer 101 and flow between the plurality of flow channels 49. For example, various apertures 48 may allow cooling air to enter the spacer layer 101 from the impingement holes 41. Other apertures 48 may allow the cooling air in the spacer layer 101 to pass through the apertures 48 and between the flow channels 49. This may allow a layer of cooling air to be created in the spacer layer 101, between the hot gas path component 34 and the base layer 102, providing more efficient cooling of the hot gas path component 34, as discussed below.

FIG. 9 illustrates an exemplary embodiment of the heat shield 100 having a dovetail attachment arrangement. For illustrative purposes, only the spacer layer 101 and the base layer 102 of the heat shield 100 are illustrated. As described herein, although any type of positive detainment devices can be implemented, dovetails 113 can cover the inner side wall and/or outer side wall of the airfoil 34. The airfoil 34 dovetails 113 can match up with mating heat shield dovetails 117 on the heat shield 100. In exemplary embodiments, the heat shield dovetails 117 can be disposed on the base layer 102 adjacent spacer sections 107 on the spacer layer 101. In other exemplary embodiments, the heat shield dovetails 117 can be disposed on the spacer layer 101.

Technical effects include the rapid in-field repair of the hot gas path components 34 implementing the heat shields 100 described herein. For example, the heat shield 100 may be detachably connected to the hot gas path component 34. The heat shield 100 may be configured to shield the hot gas path component 34 from the hot gas path, such as from hot gas flow 28, allowing for relatively stress- and strain-free operation of the hot gas path component 34, as discussed below. When the heat shield 100 needs to be repaired, such as due to stress and strain to the heat shield 100 caused by large temperature gradients in the hot gas path, the heat shield 100 may be detached from the hot gas path component 34 and repaired or replaced, without the need to repair or replace the hot gas path component 34. Such in-field repair can occur at combustion intervals. One example in which the exemplary heat shield 100 can be implemented is in the first stage nozzle of a gas turbine, often referred to as S1N. The first stage nozzle of the gas turbine converges and accelerates the hot gas flow 28 after the combustion section 18, and as a result the first stage nozzle is tapered. As illustrated above, the heat shield 100 can cover the first stage nozzle airfoil 34 on the leading edge as well as on a majority of the pressure side of the airfoil 34, and the heat shield 100 can reach to a high camber point on the suction side of the airfoil 34. The heat shield 100 described herein in conjunction with the first stage nozzle allows the first stage nozzle to be a modular/replaceable system rather than a single part design as in conventional systems. Maintenance costs are thus reduced and the service life of the nozzle increased; when the heat shield 100 begins to wear, the heat shield 100 can be removed and replaced.

The multi-layer design of the heat shield 100 may significantly lower the bulk metal temperatures of hot gas path components 34. As described above, the heat shield 100 includes an outer (thermal) layer 103. The outer (thermal) layer 103 may be affixed though the bond layer 104 to the base layer 102 and the spacer layer 101. The spacer layer 101 may provide airflow and structure to the heat shield 100. The multi-layer design of the heat shield 100 traps the cooling air in the spacer layer 101, between the base layer 102 and the hot gas path component 34, thus cooling the hot gas path component 34. This method of cooling is much more efficient than film cooling because the coolant air is trapped between the two layers, rather than being mixed with the hot gas flow 28, which reduces the cooling efficiency as the film cooling air travels downstream from the hole exit. Thus, less cooling air is needed to cool the hot gas path component 34. The reduction in cooling air can be used to reduce the combustion temperature for the same output power, thereby reducing NOx creation and increasing gas turbine efficiency.

The multi-layer design of the heat shield 100 may allow for relatively stress- and strain-free operation of hot gas path component 34. For example, the heat shield 100 may be detachably connected to the hot gas path component 34. Further, the heat shield 100 may be movable relative to the hot gas path component 34. Thus, the heat shield 100 may be exposed to the high temperatures of the hot gas flow 28 passing through the hot gas path, and may expand and contract with changes in the temperature of the hot gas flow 28. The heat shield 100 may operate to protect the hot gas path component 34 from the high temperatures in the hot gas path, thus reducing stress and strain in the hot gas path components 34 by limiting the temperature gradients experienced by the hot gas path component 34. This may allow the hot gas path component 34 to operate relatively stress- and strain-free.

While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.