FIELD OF THE INVENTION

Aspects of the invention are related to turbine engines, and more particularly, to an interface between a combustor basket and a transition assembly of a can-annular gas turbine engine.

BACKGROUND OF THE INVENTION FIG. 1 is a cross-sectional view of a conventional combustor assembly 10 for a can-annular gas turbine engine 5, including an interface 1 1 between a combustion basket ring 12 and a transition assembly including a transition duct 14 and a transition inlet ring 20. A liner within the combustion basket ring 12 confines an exothermic reaction of combustion reactants and produces hot combustion gas 16. The transition duct 14 provides a flow path for the hot combustion gas 16 from an inlet at the combustion basket ring 12 to an outlet at a turbine inlet annulus 18.

FIG. 2 is a cross-sectional view of the interface 1 1 between the combustion basket ring 12 and the transition assembly 13. At the interface 1 1 , the combustion basket ring 12 is inserted within the transition inlet ring 20. The transition inlet ring 20 is used to enhance the mechanical integrity of the transition duct 14, to provide support for the transition duct 14 at the interface 1 1 and to provide a sealing surface at the interface 1 1 . A circumferential gap 22 is provided between an inner diameter of the combustion basket ring 12 and an inner diameter of the transition inlet ring 20, to provide space for an array of spring clips 24. The spring clips 24 are attached to the combustion basket ring 12 and pressure seated onto the transition inlet ring 20 to form a circumferential seal at the interface 1 1 .

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in the following description in view of the drawings that show:

FIG. 1 is a cross-sectional view of a conventional combustor assembly for a can- annular gas turbine engine; FIG. 2 is a cross-sectional view of an interface between a combustion basket ring and a transition assembly in the conventional combustor assembly of FIG. 1 ;

FIG. 3 is a cross-sectional view of an interface between a combustion basket ring and a transition assembly in a can-annular gas turbine engine;

FIG. 4 is a closer cross-sectional view of the conical structure of the interface of

FIG. 3;

FIG. 5 are respective plots of a flow area of the transition duct in FIG. 1 and FIG. 3 over a length of the transition duct; and

FIG. 6 is a cross-sectional view of a downstream edge of the combustion basket ring at the interface of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors have recognized several limitations of the conventional interface design used between the combustion basket ring 12 and the transition assembly 13 of the can-annular gas turbine engine 5. The circumferential gap 22 is provided between the combustion basket ring 12 and transition inlet ring 20 to provide space for the array of spring clips 24. As illustrated in FIG. 2, this circumferential gap 22 introduces a radial step or gap in a flow path across the interface 1 1 , which in turn causes a region of local recirculation 25 as the combustion gas flow path expands proximate the radial gap. The present inventors recognized several drawbacks of the hot gas flow expansion, including unwanted recirculation 25, oxidization of the downstream edge of the combustion basket ring 12 and heating of a weld 26 between the transition inlet ring 20 and transition duct 14. Accordingly, the present inventors designed an interface between the combustion basket ring and the transition assembly which minimizes this radial gap experienced by the flow path across the interface, and thus minimizes these noted drawbacks.

The present inventors also recognized that the conventional interface design includes various structural features in an attempt to mitigate effects of the hot gas recirculation 25. For example, a thermal barrier coating (TBC) 28 is provided along a cold side of the combustion basket ring 12, to minimize the thermal impact of the hot gas recirculation 25. In another example, an array of cooling passages 36 are provided within the combustion basket ring 12, to cool an outer surface of the combustion basket ring 12 from hot stagnant air between the combustion basket ring 12 and the transition inlet ring 20. As illustrated in FIG. 2, each cooling passage 36 includes an outlet 34 that discharges the cool air into the hot gas recirculation 25. The present inventors developed an improved interface between the combustion basket ring and the transition assembly, which minimizes the hot gas recirculation 25 and thus eliminates the need for the TBC 28. Additionally, the present inventors recognized that since the improved interface minimizes the hot gas recirculation 25, the cool air discharged from the outlets 34 need no longer be wasted in purging the hot gas recirculation 25 and can instead be directed along an inner surface of the transition duct to form an impinging laminar cooling film.

A design challenge of the transition assembly is the impact of combustion harmonics due to vibrational loading. Specifically, as illustrated in FIG. 2, transition inlet ring 20 parameters, including a length 30 and a thickness 32 are adjusted, to achieve a required stiffness of the transition assembly in order to tune harmonic responses of the transition assembly away from combustion components vibrations. The present invention includes a transition assembly having a flared, conical structure which increases the stiffness of the transition assembly and thus permits a reduction in the transition inlet ring thickness, while still achieving the required stiffness for the transition assembly.

FIG. 3 is a cross-sectional view of an interface 1 1 1 between a combustion basket ring 1 12 and a transition assembly 1 13 in a can-annular gas turbine engine according to one embodiment of the invention. The transition assembly 1 13 includes a transition inlet ring 120 and transition duct 1 14 connected at a joint weld 126. The interface 1 1 1 has a conical structure 1 15 that includes a flared inlet end 140 of the transition duct 1 14 connected to a flared outlet end 138 of the transition inlet ring 120 at the weld 126. Although the conical structure 1 15 depicted in FIG. 3 includes the flared inlet end 140 of the transition duct 1 14 and the flared outlet end 138 of the transition inlet ring 120, the conical structure 1 15 is not limited to this structural arrangement. In an example embodiment, the conical structure may include the flared inlet end 140 of the transition duct 1 14 connected to a non-flared outlet end of the transition inlet ring 120 at a joint weld. In another example embodiment, the conical structure may include the flared outlet end 138 of the transition inlet ring 120 connected to a non-flared inlet end of the transition duct 1 14 at a joint weld.

As illustrated in FIG. 3, the conical structure 1 1 5 of the interface 1 1 1 , including the flared inlet end 140 of the transition duct 1 14, translates the transition duct 1 14 gas path down to match the combustion basket ring 1 12 gas path, resulting in a radially uniform gas path 1 16 across the interface 1 1 1 . The flared inlet end 140 removes the circumferential gap 22 (FIG. 2) between the combustion basket ring 1 12 and the transition duct 1 14 at the interface 1 1 1 , and thus removes the radial offset of the gas flow and resulting hot gas recirculation 25 across the conventional interface 1 1 .

As illustrated in FIG. 3, the conical structure 1 15 positions the weld 126 outside the radially uniform gas path 1 16. By moving the weld 126 outside of the gas path 1 16, the conical structure 1 15 improves the mechanical durability of the transition assembly 1 13.

Additionally, the conical structure 1 15 increases the stiffness of the transition assembly 1 13, relative to the cylindrical structure of the conventional transition assembly 13. As previously discussed, the transition assembly 1 13 is designed with a minimum stiffness to tune harmonic responses of the transition assembly 1 13 away from resonance vibrations. Due to the increased stiffness of the conical structure 1 15, one or more stiffness parameters of the transition inlet ring 120 can be reduced, while still achieving the minimum stiffness. In an example embodiment, the thickness 132 of the transition inlet ring 120 is less than the thickness 32 of the conventional transition inlet ring 20. In an example embodiment, the thickness 132 is in a range of 30-40% lower than the thickness 32. However, in other embodiments, the thickness 132 of the transition inlet ring 120 is not limited to any specific range, such as being less than the thickness 32 of the conventional transition inlet ring 20.

The conical structure 1 15 of the interface 1 1 1 also includes the flared outlet end 138 of the transition inlet ring 120, which also removes the circumferential gap 22 to establish the radially uniform gas path 1 16 across the interface 1 1 1 . Additionally, an inlet end 137 of the transition inlet ring 120 opposite to the flared outlet end 138 is provided, to maintain the circumferential gap 122 between the inlet end 137 of the transition inlet ring 120 and the combustion basket ring 1 12, for positioning an array of spring clips 124 within the circumferential gap 122. Thus, the transition inlet ring 120 is simultaneously used to establish the radially uniform gas path 1 16 with the flared outlet end 138 and to establish the circumferential seal of the array of spring clips 124 with the inlet end 137.

As previously discussed, a thermal barrier coating is provided along the outer surface of the conventional combustion basket ring 12 in the conventional interface 1 1 (FIG. 2) to minimize the effects of hot gas recirculation 25. Since the improved interface 1 1 1 removes the circumferential gap 22 and the corresponding hot gas recirculation 25, a protective coating is not required along the outer surface of the combustion basket ring 1 12.

FIG. 4 is a cross-sectional view of the conical structure 1 15 of the interface 1 1 1 of FIG. 3. In an example embodiment, the transition duct 1 14 is a welded fabrication of using a set of bonded panels including a portion 144 of the transition duct 1 14 with internal cooling passages 146. The flared inlet end 140 of the transition duct 1 14 excludes the portion 144 of the transition duct 1 14 with the cooling passages 146.

During the manufacturing which creates internal passages in the panels of the transition duct 1 14, grooves are created in a first plate and an inlet hole is drilled through the first plate at a first end of each groove. The grooves do not extend an entire length of the first plate, such that an inlet end and outlet end of the first plate excludes the grooves. A second plate is then bonded to the first plate, such that the grooves between the first and second plate form the internal cooling passages 146. The inlet end 140 (excluding grooves) of the bonded first and second plate is then flared using a tool appreciated by one skilled in the art, to be aligned at an angle 150

(discussed below). An outlet hole 147 is drilled through the second plate at a second end of each groove. During operation, cool air provided from a plenum of the gas turbine engine passes through the inlet holes and into the internal cooling passages 146. The cool air passes along the internal cooling passages 146, to cool the surface of the transition duct 1 14, after which the cool air is discharged from the outlet holes 147. Although the above example embodiment discusses a bonded panel transition duct 1 14, the transition duct 1 14 is not limited to this example embodiment and includes any combustion transition duct structure known to one skilled in the art where the inlet end can be flared to be aligned at the angle 150.

As depicted in FIG. 4, the flared inlet end 140 is oriented at the angle 150 with respect to a longitudinal axis 148 of the transition duct 1 14 or a combustion system axis. In an example embodiment, during engine operation, the combustion basket ring 1 12, transition inlet ring 120 and transition duct 1 14 share a common combustion system axis. In an example embodiment, during engine operation, the longitudinal axes of the combustion basket ring 1 12, transition inlet ring 120 and transition duct 1 14 are aligned with a common combustion system axis. In an example embodiment, the flared inlet end 140 is oriented at the angle 150 such that the flared inlet end 140 is aligned with a point 152 on the transition inlet ring 120 that is axially aligned with a downstream edge 154 of the combustion basket ring 1 12. In an example embodiment, the angle 150 is measured with respect to the point 152, to ensure a minimum radial gap is maintained between the combustion basket ring 1 12 and the transition inlet ring 120, to account for thermal growth between the combustion basket ring 1 12 and the transition inlet ring 120. In an example embodiment, the angle 150 is in a range of 45 ±15 degrees. In another example embodiment, the angle 150 is in a range of 45 ±10 degrees.

As further depicted in FIG. 4, the flared outlet end 138 of the transition inlet ring 120 is oriented at the same angle 150 as the flared inlet end 140 of the transition duct 1 14, with these two structures being joined at weld 126. In an example embodiment, the transition inlet ring 120 is manufactured using a process where the transition inlet ring 120 is shaped such that a flared outlet end 138 is oriented at the angle 150. Other embodiments may include a plurality of angles being formed in either or both of the transition inlet ring and/or transition duct in order to form a desired flared shape effective to eliminate axial offset of the combustion gas flow path through the combustor basket and transition duct interface region.

The angle 150 of the flared inlet end 140 and flared outlet end 138 is determined based on an acceptable range of an axial gap 160 between the downstream edge 154 of the combustion basket ring 1 12 and the flared inlet end 140. If the angle 150 is too small, the axial gap 160 will become too large such that the gas path 1 16 will recirculate within the axial gap 160, resulting in hot gas entrainment onto the component surfaces. If the angle 1 50 is too large, the axial gap 160 will become too small resulting in mechanical interference when the downstream edge 1 54 of the combustion basket ring 1 12 (experiences thermal growth towards transition duct 1 14) and the flared end 140 (experiences thermal growth towards the downstream edge 154) make contact.

Additionally, the manufacturing of the flared inlet end 140 is impractical if the angle 150 is too large. In an example embodiment, the angle 150 of the flared inlet end 140 and flared outlet end 138 is adjusted such that the axial gap 160 is in a range of 7-12 millimeters (mm). However, the axial gap 160 is not limited to any specific numerical range, provided that hot gas recirculation within the axial gap 160 and mechanical interference between the combustion basket ring 1 12 and transition duct 1 14 are avoided.

The transition duct 1 14 includes a fillet 142 between the flared inlet end 140 and the portion 144 of the transition duct 1 14. In an example embodiment, the fillet 142 is a concave surface at a junction of the flared inlet end 140 and the portion 144 of the transition duct 1 14. The fillet 142 is the portion of the transition duct 1 14 over which an angle between the transition duct 1 14 and the longitudinal axis 148 increases from zero degrees to the angle 150 at the flared inlet end 140. In an example embodiment, the radius of curvature of the fillet 142 is in a range of 12-25 mm. However, the radius of curvature of the fillet 142 is not limited to any specific numerical range.

FIG. 4 illustrates that an inner diameter of the transition duct 1 14 is greater than an inner diameter of the combustion basket ring 1 12 by a threshold offset 162. The threshold offset 162 is adjusted to account for thermal growth of the transition duct 1 14 and the combustion basket ring 1 12. In an example embodiment, the threshold offset 162 is adjusted at the shaping of the transition duct 1 14 to provide a 0-3 mm step in the hot gas path 1 16. In an example embodiment, this step or gap is devised by stacking up the manufacturing tolerance average, thermal expansion and component misalignment tolerance. The threshold offset 162 ensures that a flow diameter of the gas path 1 16 in the transition duct 1 14 is not less than a flow diameter of the gas path 1 16 in the combustion basket ring 1 12, to avoid undesirable hot gas impingement of the gas path 1 16 on the inner surface of the transition duct 1 14. FIG. 5 shows respective plots 200, 201 of a flow area of the transition ducts 14, 1 14 of FIGs. 1 and 3 respectively over a length of the transition ducts 14, 1 14. The horizontal axis 204 is the length along the longitudinal axis 148 in a direction from a point 206 proximate a round-shaped inlet of the transition duct 14, 1 14 at the combustion basket ring 12, 1 12 outlet to a downstream point 208 more near a rectangular-shaped outlet of the transition duct 14, 1 14 at the turbine inlet annulus 18. The vertical axis 202 is the flow area within the transition duct 14, 1 14 at each respective length segment. As shown in the plot 200, the flow area within the prior art transition duct 14 rapidly rises at the inlet 206, as the combustion gas 16 (FIG. 2) expands across the circumferential gap 22, resulting in hot gas recirculation 25. The flow area of plot 200 then converges at a convergence rate toward point 208 of the transition duct 14. As shown in the plot 201 , the flow area of the inventive transition duct 1 14 at the inlet 206 does not rapidly rise, as in plot 200, and instead remains relatively constant. This is attributable to the conical structure 1 15 that translates the transition duct 1 14 gas path down to match the combustion basket ring 1 12 gas path, resulting in the radially uniform gas path 1 16. The flow area of plot 201 then converges at a smaller convergence rate (relative to the convergence rate in plot 200) to the flow area at point 208 of the transition duct 1 14.

FIG. 6 is a cross-sectional view of the downstream edge 154 of the combustion basket ring 1 12 at the interface 1 1 1 of FIG. 3. The combustion basket ring 1 12 includes an interior cooling passage 136 that, like the cooling passage 36 in the conventional combustion basket ring 12, pass cool air within the combustion basket ring 1 12 to cool an outer surface 172 of the combustion basket ring 1 12 from hot stagnant air between the combustion basket ring 1 12 and the transition inlet ring 120. The cooling passage 136 features an outlet 134 that is radially aligned with the fillet 142 of the transition duct 1 14. The outlet 134 is radially aligned to provide a purge of cooling fluid 145 across the axial gap 160 between the downstream edge 154 and the flared inlet end 140 to prevent hot gas entrainment within the axial gap 160. Additionally, the cool air is discharged from the outlet 134 and forms a cooling film 143 along an inner surface of the fillet 142. The cooling film 143 along the inner surface of the fillet 142 continues along the inner surface of the transition duct 1 14. In an example embodiment, the threshold offset 162 (FIG. 4) in the inner diameter of the transition duct 1 14 relative to the inner diameter of the combustion basket ring 1 12 advantageously provides additional flow area for the cooling film 143 along the inner surface of the transition duct 1 14. In an example embodiment, the outlet 147 (FIG. 4) of the cooling passage 146 within the portion 144 of the transition duct 1 14 also discharges cool air, which forms a secondary cooling film along the inner surface of the transition duct 1 14, inside the cooling film 143 formed by the cool air from the cooling passage 136. Although FIG. 6 depicts a single interior cooling passage 136, the combustion basket ring 1 12 can include multiple spaced cooling passages 136. Although FIG. 6 depicts that the outlet 134 is radially aligned with the fillet 142 to form an impinging flow, the interface 1 1 1 is not limited to this structural arrangement. In an example embodiment, the outlet 134 can be radially aligned to impinge upon the flared inlet end 140 to form the cooling film 143 along the flared inlet end 140, after which the cooling film 143 passes along the fillet 142 and inner surface of the transition duct 1 14. In another example embodiment, the outlet 134 can be radially aligned with the inner surface of the transition ducti 14 without impinging the fillet 142 to form the cooling film 143 along the inner surface of the transition duct 1 14.

As further illustrated in FIG. 6, the downstream edge 154 of the combustion basket ring 1 12 includes a first chamfer 166 angled at a first angle 176 from an outer surface 172 of the combustion basket ring 1 12 to an interior portion 170 between the outer surface 172 and an inner surface 174 of the combustion basket ring 1 12. In an example embodiment, the first chamfer 1 66 is angled to match the angle 150 to be parallel to the flared inlet end 140 in order to maximize the axial gap 160 and consequently minimize the instance of mechanical interference between the combustion basket ring 1 12 and flared inlet end 140 due to thermal growth. In another example embodiment, the first angle 176 is 45 ±10 degrees.

Additionally, the downstream edge 154 of the combustion basket ring 1 12 includes a second chamfer 168 angled at a second angle 178 from the inner surface 174 to the interior portion 170 of the combustion basket ring 1 12. As further illustrated in FIG. 6, a thermal barrier coating (TBC) 179 is provided along the inner surface 174 of the combustion basket ring 1 12 but does not extend onto the chamfered end. This permits the combustion basket ring 1 12 to be rested vertically on a surface on its downstream edge 154 during assembly operations without the TBC 179 making contact with the surface, thereby minimizing the risk of damage to the TBC 179 due to contact with the surface. In an example embodiment, the second angle 178 is equal to the first angle 176. In another example embodiment, the second angle 178 is 45 ±10 degrees.

As further illustrated in FIG. 6, the interior cooling passage 136 is provided along the interior portion 170 of the combustion basket ring 1 12. In an example embodiment, the outlet 134 is provided at a junction of the first chamfer 166 and second chamfer 168.

While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.