Turbine exhaust case assemblies include inner and outer rings that are spaced from one another by a plurality of radially extending struts. These struts are fixedly attached at both their inner and outer ends to the inner and outer rings. The outer ring defines the radially outer surface of the engine gas flow path downstream of the last stage of turbine blades of a gas turbine engine.
Due to the high temperature of the exhaust flow path, thermal protection systems are used to prevent damage to the turbine exhaust case. Thermal barrier coatings can be applied to the exhaust case. Furthermore, cooling air may be used to effect effusion cooling and/or impingement cooling. Common exhaust cases are formed of a metal alloy, then coated with a coating such as a thermal barrier coating. Effusion cooling holes are then formed in the case, often by laser ablation or electrical discharge machining Cooling air, such as bypass air, may then be routed from radially outside the turbine exhaust case through the effusion cooling holes and into the exhaust flow path, preferably forming an effusion film of cool bypass air along the surface of the case that would otherwise be exposed to hot core flow.
Cooling air may be routed into the exhaust flow path for other purposes than for the protection of the turbine exhaust case. For example, diffusion cooling holes may also be present in the turbine exhaust case that promote mixing of cooling air with exhaust gases to modify engine acoustics, exhaust temperature, or promote combustion in an augmentor or afterburner. Effusion cooling holes are distinct from diffusion cooling holes in that effusion air is routed along the surface of the turbine exhaust case, rather than into the exhaust gas flow. By arranging several effusion cooling holes together, an effusion cooling film is generated that protects the TEC from damage. In order to maximize the efficacy of the effusion film, effusion cooling hole spacing and orientation are selected based on expected exhaust gas temperature and velocity at each location.
An effusion-cooled component includes a base portion defining at least one oversized cooling hole preform. A coating is disposed on the base portion and at least partially covers the oversized cooling hole preform to define a cooling hole. The component may be repaired by removing the coating from a component, visually inspecting the resultant base, and re-coating the base with a coating that oversprays to at least partially fill the oversized cooling preforms to define a plurality of cooling holes.
In order to provide an effusion cooling film in a turbine exhaust case, cooling holes are defined in the case to permit the passage of relatively cooler bypass air through the case. Portions of the turbine exhaust case are made by creating a base portion with oversized cooling hole preforms, then coating the base—including cladding the oversized cooling hole preforms—with a coating. The deposition of the coating in the oversized cooling hole preforms creates cooling holes of the desired size. A turbine exhaust case made in this manner may be repaired by removing the coating and re-applying a new coating without having to create new cooling holes in the case.
TEC 10 is a component of a gas turbine engine. During normal operation, core flow C passes through a combustor (not shown), is routed through a turbine section (not shown), and then passes through TEC 10. The TEC can be fabricated using several methods. One such method is Laser Powder Deposition (LPD). In this method, either a portion of the TEC or the entire TEC can be built layer by layer which allows for various features to be included therein. Alternatively, TEC can be manufactured using casting or molding.
Core flow C passes through the region between outer ring 12 and inner ring 14. Core flow C may be sufficiently hot to cause damage to outer ring 12, inner ring 14, or struts 16. In the embodiment shown in
In some embodiments, base 20 may include a bond coat (not shown). Such bond coats may be used to promote adhesion between base 20 and an adjacent material, such as coating 22 (
Cooling hole structures 18 are defined by base 20 and coating 22. Base 20 is manufactured to define oversized cooling hole preforms 24. Base 20 may be made by additive manufacturing, such as direct metal laser sintering, laser powder deposition, or other additive methods. Oversized cooling hole preforms 24 can be included in base 20 as it is built. Alternatively, base 20 may be made by casting or molding, then oversized cooling hole preforms 24 may be created by electro-discharge machining (EDM), laser ablation, or other known subtractive manufacturing techniques.
Additive manufacturing may be used to define oversized cooling hole preforms 24 that have complex geometries not easily generated using laser ablation of EDM. Such geometries include tapered cooling holes, lobed cooling holes, or groups of cooling holes with non-uniform angles. In addition, additive manufacturing can easily form oversized cooling hole preforms 24 that are large enough that they would be expensive and/or time consuming to create using traditional subtractive manufacturing mechanisms. Various additive manufacturing mechanisms may be used, including direct metal laser sintering, laser powder deposition, selective laser sintering, and electron beam melting, among others. Additive manufacturing can be used to build up layers of a meltable, sinterable, or polymerizable material into a complex, multilayered structure.
Coating 22 is applied after base 20—including oversized cooling hole preforms 24—is completely formed, as described with respect to
Components with clad cooling holes prevent exposure of base 20 to external elements, ranging from thermal energy to radar waves. For example, coating 22 (
Effusion holes 26 include inlet 30 and outlet 32, which are apertures that allow ingress and egress of bypass air B, respectively, to cooling holes 26. Inlet 30 and outlet 32 are fluidically connected to permit fluid flow from bypass air B to effusion film E. In alternative embodiments, a bond coating, such as a bimetallic material, may be applied to base 20 prior to coating 22.
Surface 28 of coating 22 is exposed to core flow C. Surface 28 is protected from damage that could be caused by core flow C by effusion film E. Inlet 30 and outlet 32 are configured to optimize effusion film E. By changing the size, shape, or tapering of oversized cooling hole preform 24, various structures may be generated in surface 28, inlet 30, and/or outlet 32 that accelerate fluid flow in a desired direction to promote laminar flow in effusion film E.
Effusion film E may be directed in any desired direction to protect a portion of outer ring 12. In some embodiments, such as the one shown in
Oversized cooling hole preforms 24 allow for a cycle of repair or refurbishment. Prior art components are coated and then cooling holes are manufactured subtractively. Thus, if the coating were to be removed from a prior art component, and the component were then re-coated, the base would be filled by the coating to an unacceptable extent. In order to create acceptable cooling holes, such prior art components would have to be coated and then undergo a second round of subtractive manufacturing. This second round of subtractive manufacturing results in a second set of holes punched through the base. Unlike these prior art components, base 20 of
The following are non-exclusive descriptions of possible embodiments of the present invention.
According to one embodiment, an effusion-cooled component includes a base portion defining an oversized cooling hole preform. The component further includes a coating disposed on the base portion and at least partially covering the oversized cooling hole preform to define a cooling hole.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
Filing Document | Filing Date | Country | Kind |
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PCT/US2014/059099 | 10/3/2014 | WO | 00 |
Number | Date | Country | |
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61892886 | Oct 2013 | US |