Patent Application
20110061393
Not applicable.
Not applicable.
This invention relates to a transition duct for a gas turbine engine, specifically to a novel and improved profile for a transition duct that results in lower operating stresses and extended component life.
In a typical can annular gas turbine engine, a plurality of combustors are arranged in a generally annular array about the engine. The combustors receive pressurized air from the engine's compressor, adds fuel to create a fuel/air mixture, and combusts that mixture to produce hot gases. The hot gases exiting the combustors are utilized to turn a turbine, which is coupled to a shaft that drives a generator for generating electricity.
The hot gases are transferred from the combustor to the turbine by a transition duct. Due to the position of the combustors relative to the turbine inlet, the transition duct must change cross-sectional shape from a generally cylindrical shape at the combustor exit to a generally rectangular arc-like shape at the turbine inlet. In addition, the transition duct undergoes a change in radial position, since the combustors are typically mounted outboard of the turbine. Extreme care must be taken with respect to the design of these ducts in order to avoid sharp geometric changes, otherwise regions of high stress and stress concentrations can occur. The combination of complex geometry changes as well as extreme mechanical and thermal loading seen by the transition duct can create a harsh operating environment that can lead to premature deterioration, requiring repair and replacement of the transition ducts. To withstand the hot temperatures from the combustor gases, transition ducts are cooled or a surface coating is applied to the transition duct. A variety of methods are available to provide cooling such as through internal channels, impingement cooling, or effusion cooling.
Severe cracking, resulting in component failure and forcing engine shutdown, has been known to occur in transition ducts having extremely sharp geometry changes and internal air-cooled channels. In such an incident, the engine requires transition duct replacement or repair prior to returning to operational status. The present invention seeks to overcome the shortfalls of these prior art designs.
The present invention is defined by the claims below. Embodiments of the present invention solve at least the above problems by providing a transition duct having a geometric profile that results in lower operating stresses and improved component life while coupled to a low emissions combustor.
In an aspect of the present invention, a transition duct is provided having an inlet ring, an aft frame, and a panel assembly having an internal profile defined by a series of X, Y, and Z Cartesian coordinates taken along a sweep angle Θ that extends from the inlet to the outlet of the transition duct.
A novel and improved transition duct having an enhanced profile for improved performance and durability is provided. The internal flowpath geometry of the transition duct has been configured to remove areas of sharp geometric change. The sharp geometric changes, in combination with high thermal and mechanical loading, caused regions of high steady and vibratory stresses and local stress concentrations in prior art ducts that often lead to cracking and premature failure. Furthermore, due to a rounder profile, certain natural frequencies of the transition duct are raised to avoid potential vibratory issues.
A variety of cooling methods can be used in combination with the enhanced profile of the present invention transition duct. In an embodiment, a plurality of cooling holes are located in the walls of the transition duct for directing a cooling fluid, such as air, through the holes. The cooling holes are located in the panel assembly and are oriented at an angle relative to the panel assembly surface.
In an embodiment of the present invention, there is provided a transition duct with a panel assembly having an inlet end of generally circular cross section and an outlet end having a generally rectangular arc-like cross section with an uncoated internal profile substantially in accordance with the coordinate values Θ, X, Y, and Z as set forth in Table 1. The origin of the coordinate system is positioned at the center of the panel assembly inlet end along a centerline axis. It will be appreciated that the coordinate values given are for manufacturing purposes, in a room temperature condition. The coordinate values X, Y, and Z in Table 1 are standard Cartesian coordinates, and correspond to a specific sweep angle Θ, which together, define a cross section of the panel assembly. Each cross section is joined smoothly with adjacent cross sections to define a panel assembly for the transition duct. It will also be appreciated that as the transition duct transfers hot combustion gases from a combustor to the turbine inlet, the transition duct absorbs heat, and therefore the coordinates provided in Table 1 do not necessarily correspond to the panel assembly position when in operation at an elevated temperature.
In an alternate embodiment, there is provided a transition duct with a panel assembly having an inlet end of generally circular cross section and outlet end having a generally rectangular arc-like cross section with an uncoated internal profile within an envelope of ±0.250 inches in a direction normal to any surface of the panel assembly substantially in accordance with the coordinate values Θ, X, Y, and Z as set forth in Table 1. The origin of the Cartesian coordinate system is positioned at the center of the panel assembly inlet end along a centerline axis. A distance of ±0.250 inches in a direction normal to any surface location along the panel assembly defines an envelope for this particular panel assembly and ensures that manufacturing tolerances are accommodated within the envelope of the panel assembly. As with the embodiment previously disclosed, it will be appreciated that the coordinate values given are for manufacturing purposes, in a room temperature condition. Each set of coordinate values X, Y, and Z in Table 1 is in standard Cartesian coordinates and corresponds to a specific sweep angle Θ, which, when taken together defines a cross section of the panel assembly. Each cross section is joined smoothly with adjacent cross sections to define a panel assembly for the transition duct. It will also be appreciated that as the transition duct transfers hot combustion gases from a combustor to the turbine inlet, the transition duct heats up and therefore the Cartesian coordinates for a given Θ value provided in Table 1 may not necessarily correspond to the panel assembly position when in operation at an elevated temperature.
The instant invention will now be described with particular reference to the accompanying drawings.
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. The instant invention will now be described with particular reference to the accompanying drawings.
The present invention is described in detail below with reference to the attached drawing figures, wherein:
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.
Embodiments of the present invention provide apparatus for a gas turbine transition duct that are configured geometrically to have lower operating stresses. Lower stresses, both mechanical and thermal result in improved component life.
Referring initially to
The present invention is shown in
The transition duct 300 further comprises an inlet ring 316 and an aft frame 318 fixed to the panel assembly 302. Because of the temperatures of the hot combustion gases passing through the transition duct, the panel assembly 302 is preferably formed from a high temperature nickel base alloy such as Haynes 230.
The panel assembly 302, formed from the first panel 308 and second panel 310, has an uncoated internal profile substantially in accordance with coordinate values X, Y, and Z as set forth in Table 1, carried only to three decimal places. Although the preferred unit of measure for the values given in Table 1 is inches, those skilled in the art will appreciate that the values of Table 1 for X, Y, and Z can be scaled up or down depending on the diameter of the particular of the particular combustion liner with which the present invention is to be used. This uncoated internal profile provides an optimized transition from a generally circular inlet end to a generally arc-like outlet end over the allowable axial and radial distance for a gas turbine engine, such that high steady stresses and stress concentrations in the transition duct 300 are minimized.
Referring to
Referring to
For the data listed in Table 1, a plurality of wireframe sections can be created when applying a best-fit curve to the section data for each sweep angle Θ. For example,
An additional feature of the transition duct 300 is a protective coating applied along the internal profile of the panel assembly 302 to protect the transition duct 300 from deterioration associated with prolonged exposure to elevated temperatures. For example, a two-layer air plasma sprayed coating can be applied comprising a MCrAlY bond coating, where M can be selected from Ni, Co, NiCo, or some other acceptable composition, applied directly to the panel assembly and a Yttra Stabilized Zirconia top coating applied over the bond coating. For one embodiment of the two-layer coating, the combined coating thickness is at least 0.019 inches. The coating is preferably applied once the panel assembly 302 has been formed and welded in accordance with the profile as defined in Table 1.
In an alternate embodiment of the present invention there is provided a transition duct similar to that of the preferred embodiment except for the uncoated internal profile of the panel assembly 302 is within an envelope of ±0.250 inches in a direction normal to any surface of the panel assembly substantially in accordance with the Cartesian coordinate values X, Y, and Z as set forth in Table 1. A distance of ±0.250 inches in a direction normal to any surface of the panel assembly thereby defines a profile envelope for this specific transition duct panel assembly. This envelope ensures that all reasonable manufacturing tolerances are accommodated within the profile.
The X,Y,Z Cartesian coordinate data and corresponding sweep angles Θ are summarized in the following Table 1.
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.
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.
