Patent Application
20100011576
The present invention relates to a method and apparatus for reducing vibration induced deflections in a gas turbine transition duct.
A conventional combustible gas turbine engine includes a compressor, a combustor, including a plurality of combustor units, and a turbine. The compressor compresses ambient air. The combustor units combine the compressed air with a fuel and ignite the mixture creating combustion products defining a working gas. The working gases are routed to the turbine inside a plurality of transition ducts. Within the turbine are a series of rows of stationary vanes and rotating blades. The rotating blades are coupled to a shaft and disc assembly. As the working gases expand through the turbine, the working gases cause the blades, and therefore the disc assembly, to rotate.
The transition ducts are positioned adjacent the combustor units and route the working gases into the turbine. Each transition duct may comprise a panel structure and a frame coupled to an exit of the panel structure. The working gases produced by the combustor units are hot and under a pulsating pressure. The transition ducts are exposed to these high temperature gases and pulsating pressures, and vibrations can cause deflections in various locations of the duct panels and duct frames. Failure of a duct panel structure can result due to these unwanted vibration induced deflections.
U.S. Pat. No. 6,442,946 B1 to Kraft et al. discloses a system for mounting a gas turbine transition duct to a turbine inlet housing. The mounting system allows rotational movement between the transition duct and the turbine inlet housing.
In accordance with a first aspect of the present invention, a method is provided for coupling a first portion of a gas turbine transition duct to a second portion of the gas turbine transition duct to reduce vibratory deflection. The method may comprise: coupling at least one first support structure to the transition duct first portion; coupling at least one second support structure to the transition duct second portion; and coupling the at least one first support structure to the at least one second support structure such that a substantial amount of thermal expansion induced sliding movement between the at least one first support structure and the at least one second support structure is permitted while a substantial amount of vibration induced sliding movement is prevented.
Coupling the at least one first support structure to the at least one second support structure may comprise creating at least one linear sliding joint between the at least one first support structure and the at least one second support structure.
Creating at least one linear sliding joint between the at least one first support structure and the at least one second support structure may comprise applying a desired compressive force to the at least one first support structure and the at least one second support structure.
Applying a desired compressive force to the at least one first support structure and the at least one second support structure may comprise providing at least one bolt, at least one nut and at least one biasing device to compress the at least one first support structure and the at least one second support structure together at the desired compressive force.
The at least one biasing device may comprise at least one Belleville spring washer.
Creating at least one linear sliding joint between the at least one first support structure and the at least one second support structure may further comprise providing a wearing element configured to wear as the at least one first support structure moves relative to the at least one second support structure while preventing wearing of the at least one first support structure and the at least one second support structure.
The wearing element may comprise at least one washer having a wear coating on at least one side.
The desired compressive force may be within a range of about 1600 Newtons to about 3200 Newtons.
The gas turbine transition duct first portion may comprise a gas turbine transition duct panel structure and the gas turbine transition duct second portion may comprise a gas turbine transition duct frame. The at least one linear sliding joint may permit a first linear sliding movement in a first direction substantially perpendicular to a section of the duct frame to which the at least one support structure is coupled and a second, greater linear sliding movement in a second direction substantially parallel to the duct frame section.
In accordance with a second aspect of the present invention, an apparatus is provided for coupling a first portion of a gas turbine transition duct to a second portion of a gas turbine transition duct to reduce vibratory deflection. The apparatus may comprise: at least one first support structure attached to the gas turbine transition duct first portion; at least one second support structure attached to the gas turbine transition duct second portion; and at least one coupling mechanism. configured to couple the at least one first support structure to the at least one second support structure so as to allow sliding movement between the at least one first support structure and the at least one second support structure when a movement force of at least one of the at least one first support structure and the at least one second support structure exceeds a predefined frictional force threshold value.
The at least one coupling mechanism may comprise at least one attaching device associated with the at least one first support structure and the at least one second support structure for applying a compressive force to the at least one first support structure and the at least one second support structure.
The at least one coupling mechanism may further comprise at least one biasing device associated with the at least one attaching device, the at least one first support structure, and the at least one second support structure configured to apply, with the attaching device, a desired compressive force to the at least one first support structure and the at least one second support structure.
The at least one attaching device may comprise at least one bolt and at least one nut.
The at least one biasing device may comprise at least one Belleville spring washer.
The at least one first support structure may comprise a support post fixedly coupled to the first portion of the gas turbine transition duct. The at least one second support structure may comprise a support tab fixedly coupled to a second portion of the gas turbine transition duct. The support post may have a substantially planar distal end provided with an oversized bore and the support tab may have a substantially planar distal end provided with an oversized bore. The distal end of the support post may be substantially parallel to and positioned adjacent to the distal end of the support tab.
The at least one bolt may comprise a first bolt extending through the bores in the distal ends of the support post and support tab and a bore in at least one Belleville spring washer. The at least one nut may comprise a first nut coupled to the first bolt.
The gas turbine transition duct first portion may comprise a gas turbine transition duct panel structure and the gas turbine transition duct second portion may comprise a gas turbine transition duct frame.
The oversized bore in the distal end of the support tab may be oversized at least in a direction substantially parallel to a section of the transition duct frame to which the support tab is coupled such that the coupling mechanism permits a first linear sliding movement in a first direction substantially perpendicular to the section of the duct frame to which the support tab is coupled and a second substantially greater linear sliding movement in a second direction substantially parallel to the duct frame section.
The predefined frictional force threshold value may fall within a range of from about 240 Newtons to about 1200 Newtons.
The at least one coupling mechanism may allow linear sliding movement between the at least one first support structure and the at least one second support structure when a movement force of at least one of the at least one first support structure and the at least one second support structure exceeds a predefined frictional force threshold value.
In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings that form a part hereof, and which is shown by way of illustration, and not by way of limitation, a specific preferred embodiment in which the invention may be utilized and that changes may be made without departing from the spirit and scope of the present invention.
Referring now to
A conventional combustible gas turbine engine (not shown) includes a compressor (not shown), a combustor (not shown), including a plurality of combustor units (not shown), and a turbine (not shown). The compressor compresses ambient air. The combustor units combine the compressed air with a fuel and ignite the mixture creating combustion products defining a working gas. The working gases are routed from the combustor units to the turbine inside a plurality of transition ducts 20, see
The plurality of transition ducts 20 provided in the engine may be constructed in the same manner, see
The transition duct 20A may comprise a substantially tubular duct panel structure 21 and a frame 22 coupled at an exit or aft-end 21A of the duct panel structure 21 via welds, see
The duct frame 22 is coupled such as by bolts to a turbine inlet structure TS, see
When the gas turbine engine is started from an ambient temperature condition, the transition duct 20 rapidly increases from ambient temperature to a much higher operating temperature. In the illustrated embodiment, upon engine start-up from the ambient temperature condition, it may take approximately 10 minutes for the duct panel structure 21 to fully reach an operating temperature. The corresponding thicker duct frame 22, located farther away from its corresponding combustor unit, may take approximately 30 minutes to fully reach an operating temperature.
When the engine is shut down from an operating steady state temperature condition, the transition duct 20 will return to ambient temperature. In the illustrated embodiment, during this cool-down period, the duct panel structure 21 will cool at a different rate than its corresponding thicker duct frame 22.
Because the duct panel structure 21 reaches its operating temperature more quickly than its corresponding duct frame 22 during engine start up and cools down to ambient temperature more quickly than the duct frame 22 after the engine has been shut down, the duct panel structure 21 thermally expands/contracts at a higher rate than the duct frame 22 during engine start up and cool down. The differences in the rates of thermal expansion/contraction of the duct panel structure 21 and its corresponding duct frame 22 during engine start up and shut down produces, for example, a first relative movement between a point 21D on the top panel 21B of the duct panel structure 21 and a point 22A on the duct frame 22 equal to the difference between the expansions/contractions of the duct panel structure 21 and the duct frame 22 as the panel structure 21 and duct frame 22 heat and cool, see
In accordance with the present invention, the coupling apparatus 10A is provided to minimize or eliminate vibration induced deflections of the top panel 21B of the duct panel structure 21 yet allow at least some thermal expansion induced movement between the top panel 21B and the duct frame 22 so as to prevent thermal cycle failure at one or more locations where the coupling apparatus 10A is coupled to the top panel 21B and the duct frame 22. While the coupling apparatus 10A minimizes or eliminates vibration induced deflections of the top panel 21B, high cycle vibrations in the top panel 21B, resulting from the pulsating pressures of the high temperature working gases passing through the duct panel structure 21, remain. However, as will be discussed below, most or a substantial amount of movement between the duct top panel 21B and the duct frame 22 caused by these vibrations is prevented. One or more further coupling apparatuses, not shown, constructed in the same manner as the coupling apparatus 10A coupled to panel 21B, may be provided and coupled between the bottom panel 21C of the panel structure 21 and the duct frame 22, a first side panel 21E of the panel structure 21 and the duct frame 22 and a second side panel 21F of the panel structure 21 and the duct frame 22.
In the illustrated embodiment, the coupling apparatus 10A comprises first and second support structures 100 and 110 coupled to the top panel 21B of the panel structure 21, third and fourth support structures 120 and 130 coupled to the duct frame 22 and first and second coupling mechanisms 140 and 150 for compressively. coupling the first and third support structures 100 and 120 together and the second and fourth support structures 110 and 130 together, see
The third support structure 120 comprises a generally planar first support tab 122 having a distal end 122A provided with a generally oversized bore 222B, see
The first coupling mechanism 140 comprises a first attaching device 142 and a first biasing device 144. The first attaching device 142 comprises a first bolt 142A and a first nut 142B. The first biasing device 144 comprises one or more Belleville spring washers 144A. In the illustrated embodiment, two Belleville spring washers 144A made of Inconel 718 are provided. However less than two or more than two Belleville spring washers 144A may be provided. Further, the Belleville washers 144A may be made of materials different from Inconel 718. Also, devices, other than Belleville spring washers, such as helicoil springs, may be used instead as a biasing device.
The first coupling mechanism 140 further comprises first and second wearing elements 146 and 147, which in the illustrated embodiment, comprise first and second washers 146A and 147A provided with wear resistant coatings, see
The first bolt 142A has a diameter smaller than the size of the oversized bores 202B and 222B provided in the distal ends 102B and 122A of the first support post 102 and the first support tab 122. The bolt 142A passes through the oversized bores 202B and 222B, the Belleville spring washers 144A, the washers 146A and 147A and the first and second washers 148A-148B. The first nut 142B is coupled to the first bolt 142A such that the first coupling mechanism 140 applies a desired compressive force to the distal end 102B of the first support post 102 and the distal end 122A of the first support tab 122. As will be discussed in further detail below, the desired compressive force is selected so as to allow the distal end 102B of the first support post 102 and the distal end 122A of the first support tab 122 to frictionally slide relative to one another in response to thermal expansion differences between the top panel 21B and the frame 22 during engine start up and shut down.
In response to an increasing compressive force, the Belleville spring washers 144A will compress further from an initial relaxed state. Accordingly, a desired compressive force may be applied to the distal end 102B of the first support post 102 and the distal end 122A of the first support tab 122 by tightening the nut 142B on the bolt 142A to a torque corresponding to the desired compressive force.
The first and second washers 146A and 147A define sacrificial wearing elements to prevent the wearing of the distal end 102B of the first support post 102 and the distal end 122A of the first support tab 122 as they frictionally slide relative to one another during engine start up and shut down. The first and second washers 146A and 147A may be made from 1.5 Cr-0.5 Mo-1 Al alloy steel and the wear coatings may be formed via nitriding.
The second coupling mechanism 150 comprises a second attaching device 152 and a second biasing device 154, see
The second bolt 152A has a diameter smaller than the size of the oversized bores 204B and 232B provided in the distal ends 112B and 132A of the second support post 112 and the second support tab 132. The bolt 152A passes through the oversized bores 204B and 232B, the Belleville spring washers 154A, the washers 156A and 157A and the third and fourth washers 158A-158B. The second nut 152B is coupled to the second bolt 152A such that the second coupling mechanism 150 applies a desired compressive force to the distal end 112B of the second support post 112 and the distal end 132A of the second support tab 132. As will be discussed in further detail below, the desired compressive force is selected so as to allow the distal end 112B of the second support post 112 and the distal end 132A of the second support tab 132 to frictionally slide relative to one another in response to thermal expansion differences between the top panel 21B and the frame 22 during engine start up and shut down. A desired compressive force may be applied to the distal end 112B of the second support post 112 and the distal end 132A of the second support tab 132 by tightening the nut 152B on the bolt 152A to a torque corresponding to the desired compressive force.
The third and fourth washers 156A and 157A define sacrificial wearing elements to prevent the wearing of the distal end 112B of the second support post 112 and the distal end 132A of the second support tab 132 as they frictionally slide relative to one another during engine start up and shut down. The washers 156A and 157A may be made from 1.5 Cr-0.5 Mo-1 Al alloy steel and the wear coatings may be formed via nitriding.
As noted above, the coupling apparatus 10A minimizes or eliminates vibration induced deflections or large relative movements between the top panel 21B of the duct panel structure 21 and the duct frame 22; however, high cycle vibrations in the transition duct 20A, resulting from the pulsating pressures of the high temperature working gases passing through the transition duct 20A, remain and cause: the transition duct 20A as a whole to vibrate. This vibratory movement, however, does not cause large relative movements between the top panel 21B and the duct frame 22 due to the presence of the coupling apparatus 10A. It is believed that these vibrations create a vibration induced movement force in one or both of the distal end 102B of the first support post 102 and the distal end 122A of the first support tab 122. The vibration induced movement forces are three dimensional in nature and have components in a plane parallel to the plane of the interface between the distal ends 102B and 122A. For example, one component may extend in a direction substantially parallel to the duct frame section 22B. Likewise, it is believed that the high cycle vibrations in the transition duct 20A further create a vibration induced movement force in one or both of the distal end 112B of the second support post 112 and the distal end 132A of the second support tab 132. The vibration induced movement forces are three dimensional in nature and have components in a plane parallel to the plane of the interface between the distal ends 112B and 132A. For example, a component may extend in a direction substantially parallel to the duct frame section 22B. In the illustrated embodiment, the maximum vibration induced movement force transmitted by either the distal end 102B of the first support post 102 or the distal end 122A of the first support tab 122 may be 240 N, which may be determined by finite element vibrational analysis. Likewise, the maximum vibration induced movement force transmitted by either the distal end 112B of the second support post 112 or the distal end 132A of the second support tab 132 may be 240 N, which may be determined by finite element vibrational analysis.
As also noted above, the differences in the rates of thermal expansion/contraction of the duct panel structure 21 and its corresponding duct frame 22 during engine start up and shut down produce relative movement between the point 21D on the top panel 21B of the duct panel structure 21 and the point 22A on the duct frame 22. Hence, during engine start up and shut down, it is believed that thermally induced movement forces are created by the distal end 102B of the first support post 102 and/or the distal end 122A of the first support tab 122 in one or more planes parallel to the plane of the interface between them. Likewise, it is believed that thermally induced movement forces are created by the distal end 112B of the second support post 112 and/or the distal end 132A of the second support tab 132 in one or more planes parallel to the interface between them. In the illustrated embodiment, the maximum thermally induced movement forces created by the distal end 102B of the first support post 102 or by the distal end 122A of the first support tab 122 will be substantially greater than 240 N, for example, greater than about 5,000 N. Likewise, the maximum thermally induced movement force created by the distal end 112B of the second support post 112 or by the distal end 132A of the second support tab 132 will be substantially greater than 240 N, for example, greater than about 5,000.
The desired compressive force applied by the first coupling mechanism 140 to the distal end 102B of the first support post 102 and the distal end 122A of the first support tab 122 is selected so as to prevent vibration induced relative movement between the distal end 102B of the first support post 102 and the distal end 122A of the first support tab 122, yet allow the distal end 102B of the first support post 102 and the distal end 122A of the first support tab 122 to frictionally slide relative to one another at the interface between them in response to thermal expansion differences between the top panel 21B and the frame 22 during engine start up and shut down. Likewise, the desired compressive force applied by the second coupling mechanism 150 to the distal end 112B of the second support post 112 and the distal end 132A of the second support tab 132 is selected so as to prevent vibration induced relative movement between the distal end 112B of the second support post 112 and the distal end 132A of the second support tab 132, yet allow the distal end 112B of the second support post 112 and the distal end 132A of the second support tab 132 to frictionally slide relative to one another at the interface between them in response to thermal expansion differences between the top panel 21B and the frame 22 during engine start up and shut down.
Hence, in the illustrated embodiment, it is believed that the desired compressive force applied by the first coupling mechanism 140 to the distal end 102B of the first support post 102 and the distal end 122A of the first support tab 122 should be selected so that a frictional force applied by the distal end 102B of the first support post 102 to the distal end 122A of the first support tab 122 and vice versa is between about 240 N and about 1200 N and preferably between about 480 N and 960 N so as to prevent the vibration induced movement of the distal end 102B of the first support post 102 relative to the distal end 122A of the first support tab 122, yet allow the distal end 102B of the first support post 102 and the distal end 122A of the first support tab 122 to frictionally slide relative to one another in response to thermal expansion differences between the top panel 21B and the frame 22 during engine start up and shut down. Likewise, in the illustrated embodiment, it is believed that the desired compressive force applied by the second coupling mechanism 150 to the distal end 112B of the second support post 112 and the distal end 132A of the second support tab 132 should be selected so that a frictional force applied by the distal end 112B of the second support post 112 to the distal end 132A of the second support tab 132 and vice versa is between about 240 N and about 1200 N and preferably between about 480 N and 960 N so as to prevent the vibration induced movement of the distal end 112B of the second support post 112 relative to the distal end 132A of the second support tab 132, yet allow the distal end 112B of the second support post 112 and the distal end 132A of the second support tab 132 to frictionally slide relative to one another in response to thermal expansion differences between the top panel 21B and the frame 22 during engine start up and shut down.
As is well known to those skilled in the art, the compressive force necessary to prevent sliding movement between two surfaces, called a normal force, may be determined by the equation:
Normal Force=Frictional Force/Coefficient of Friction.
As noted above with regard to the illustrated embodiment, the maximum vibration induced movement force created by either the distal end 102B of the first support post 102 or the distal end 122A of the first support tab 122 may be 240 N. Likewise in the illustrated embodiment, the maximum vibration induced movement force created by either the distal end 112B of the second support post 112 or the distal end 132A of the second support tab 132 may be 240 N. In the illustrated embodiment, the desired compressive force applied by the first coupling mechanism 140 is determined using the above equation and setting the value for “Frictional Force” equal to at least 240 N, which corresponds to a frictional force required to oppose the maximum vibration induced movement force created by either the distal end 102B of the first support post 102 or the distal end 122A of the first support tab 122 so as to prevent vibration induced movement of the distal ends 102B and 122A. It is contemplated that the “Frictional Force” value in the above equation may be set to a value greater than 240 N, such as 480 N, so as to include a design safety margin. The “Frictional Force” value of either 240 N or 480 N also corresponds to a threshold frictional force value. Hence, the distal end 102B of the first support post 102 and the distal end 122A of the first support tab 122 are permitted to move relative to one another when the thermally induced movement forces created by the distal end 102B of the first support post 102 and/or the distal end 122A of the first support tab 122 exceed the threshold frictional force value, which may occur during engine start up or shut down. In the illustrated embodiment, the value for the “Coefficient of Friction” used in the above equation was set equal to 0.3.
Further, the desired compressive force applied by the second coupling mechanism 150 is determined using the above equation and setting the value for “Frictional Force” equal to at least 240 N, which corresponds to a frictional force required to oppose the maximum vibration induced movement force created by either the distal end 112B of the second support post 112 or the distal end 132A of the second support tab 132 so as to prevent vibration induced movement of the distal ends 112B and 132A. It is contemplated that the “Frictional Force” value in the above equation may be set to a value greater than 240 N, such as 480 N, so as to include a design safety margin. The “Frictional Force” value of either 240 N or 480 N also corresponds to a threshold frictional force value. Hence, the distal end 112B of the second support post 112 and the distal end 132A of the second support tab 132 are permitted to move relative to one another when the thermally induced movement forces created by the distal end 112B of the second support post 112 and/or the distal end 132A of the second support tab 132 exceed the threshold frictional force value, which may occur during engine start up or shut down. In the illustrated embodiment, the value for the “Coefficient of Friction” was set equal to 0.3.
It is currently believed that the desired compressive force to be applied by the first coupling mechanism 140 to the distal end 102B of the first support post 102 and the distal end 122A of the first support tab 122 and by the second coupling mechanism 150 to the distal end 112B of the second support post 112 and the distal end 132A of the second support tab 132 should be between about 800 Newtons and about 4000 Newtons and preferably between about 1600 Newtons and about 3200 Newtons. Such a compressive force will prevent the vibration induced movement between the distal end 102B of the first support post 102 and the distal end 122A of the first support tab 122, yet allow the distal end 102B of the first support post 102 and the distal end 122A of the first support tab 122 to frictionally slide relative to one another in response to thermal expansion differences between the top panel 21B and the frame 22 during engine start up and shut down. Likewise, such a compressive force will prevent vibration induced movement between the distal end 112B of the second support post 112 and the distal end 132A of the second support tab 132, yet allow the distal end 112B of the second support post 112 and the distal end 132A of the second support tab 132 to frictionally slide relative to one another in response to thermal expansion differences between the top panel 21B and the frame 22 during engine start up and shut down.
While a particular embodiment of the present invention has been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.
