Patent Application
20120102963
The present disclosure relates generally to a gas turbine combustor, and more particularly, to a gas turbine combustor with mounting for Helmholtz resonators.
In combustion chambers (called combustors) of turbine engines, acoustic vibrations can occur during the combustion process under certain conditions due to instabilities in the combustion process. In the industry, these high frequency acoustic vibrations are sometimes referred to as oscillations. Oscillations have been found to interfere with optimal operation of the turbine engine. Once oscillations occur, they can continue until the source of energy causing the oscillations is removed, or until system variables are changed, to shift the operation of the turbine engine to a non-oscillations operational range. However, the mechanics of how the operational characteristics interact to produce oscillations is not well understood. Therefore, changing the operational characteristics of the turbine engine to eliminate oscillations may be difficult since it is difficult to predict oscillations in a system with sufficient accuracy. Therefore, a positive structural means, such as a Helmholtz resonator, may be designed into the combustor to damp the high frequency acoustic vibrations.
A Helmholtz resonator, in its simplest form, consists of an enclosed volume (cavity) containing air connected to the combustion chamber with an opening. Due to a pressure wave resulting from the combustion process, air is forced into the cavity increasing the pressure within the cavity. Once the external driver that forced the air into the cavity is gone, the higher pressure in the cavity will push a small volume of air (plug of air) near the opening back into the combustion chamber to equalize the pressure. However, the inertia of the moving plug of air will force the plug into the combustion chamber by a small additional distance (beyond that needed to equalize the pressure), thereby rarifying the air inside the cavity. The low pressure within the cavity will now suck the plug of air back into the cavity, thereby increasing the pressure within the cavity again. Thus, the plug of air vibrates like a mass on a spring due to the springiness of the air inside the cavity. The magnitude of this vibrating plug of air progressively decreases due to damping and frictional losses. The energy of the pressure wave generated within the combustor is thus dissipated by resonance within the Helmholtz resonator. Energy dissipation is optimized by matching the resonance frequency of the Helmholtz resonator to the acoustic mode of the combustor. Typically, frequency matching (or “tuning”) of a Helmholtz resonator is accomplished by changing the dimensions of the Helmholtz cavity and the opening.
An array of Helmholtz resonators can be constructed using an empty space between interior and exterior liners of a double walled combustor. However, in such double walled combustors, the space between the liners is used to supply cooling air to the combustor walls. Therefore, locating the Helmholtz resonators in this space makes them a part of the cooling system. Helmholtz resonators being a part of the cooling system, reduces the ability to tune the Helmholtz resonators by changing the cavity and opening dimensions, without impacting the cooling of the combustor. This limitation reduces the effectiveness of the Helmholtz resonators in controlling oscillations. It is therefore desirable to locate the Helmholtz resonators close to the heat release zone of the combustor, but independent of the combustion chamber cooling system.
One implementation of a Helmholtz resonator in a gas turbine combustion chamber is described in U.S. Pat. No. 7,104,065 (the '065 patent) issued to Benz et al. on Sep. 12, 2006. In the '065 patent, Helmholtz resonators are located outside the outer liner of a double walled combustor. A throat section that penetrates through the inner and outer liner fluidly couples the resonator cavity with the combustor volume within the inner liner. In the '065 patent, a welded joint is used between the throat section of the resonator and the wall of the combustor to ensure a gas tight seal. By locating the Helmholtz resonator outside the space between the inner and outer liner, the '065 patent separates the resonator cavity from the cooling air path between the inner and outer liner.
Although the Helmholtz resonator of the '065 patent may be tuned without affecting the gap between the inner and the outer liner, the combustor of the '065 patent may have other drawbacks. For instance, the Helmholtz resonators on the outer liner may affect the cooling air flow into the space between the inner and the outer liner. Furthermore, thermo-mechanical stresses may develop at the welded joints between the throat and the liner due to thermal expansion mismatch between these parts. These thermo-mechanical stresses may eventually lead to cracks in the welded joints (or the attached parts) that compromise the reliability of the combustor.
The present disclosure is directed at overcoming one or more of the shortcomings set forth above.
In one aspect, a combustor liner is disclosed. The combustor liner may include an annular inner liner and an annular outer liner with a plurality of air holes thereon. The outer liner may be positioned circumferentially around the inner liner such that an annular cooling space is defined between the inner and the outer liner. The combustor liner may also include at least one resonator coupled to the outer liner such that a base of the resonator is separated from the outer liner to form a gap with an external surface of the outer liner. The combustor liner may also include a throat extending from the base of the resonator penetrating the inner liner and the outer liner. The combustor liner may further include a grommet assembly that allows for relative thermal expansion between the inner liner and the outer liner proximate the throat.
In another aspect, a resonator assembly for a gas turbine engine is disclosed. The resonator assembly may include a circumferential first support band including an array of perforations thereon. The first support band may include a shape resembling a frustum of a cone. The resonator assembly may also include a substantially cylindrical second support band coupled to the first support band to form a raised mounting structure for a resonator. The resonator assembly may also include at least one resonator mounted on the second support band, and a resonator throat coupled to the at least one resonator extending through the raised mounting structure. The resonator throat may be configured to fluidly couple the at least one resonator to the gas turbine engine.
In a further aspect, a method of operating a turbine engine is disclosed. The turbine engine may include a double walled combustor with an inner liner, an outer liner, and an annular cooling space between the inner and the outer liners. The outer liner may include a plurality of air holes that allow air flow into the cooling space. The method may include damping acoustic vibrations in the combustor using at least one resonator. The at least one resonator may be coupled to the outer liner such that a base of the least one resonator is positioned proud of an external surface of the outer liner. The method may also include allowing differential thermal expansion between the inner liner and the outer liner in the vicinity of a throat of the resonator by a grommet assembly. The grommet assembly may be configured to couple the throat to the combustor while allowing differential thermal expansion between the inner liner and the outer liner proximate the throat.
The combustion of fuel-air mixture within combustor volume 58 heats the combustor walls (80a and 80b). For increased reliability and performance, it is desirable to cool these walls. The outer combustor wall 80a includes an inner liner 82 and an outer liner 84, and the inner combustor wall 80b includes an inner liner 92 and an outer liner 94. The inner liners 82, 92 and the outer liners 84, 94 define cooling spaces 74, 75 between them. The outer liners 84, 94 include a plurality of air holes 83, 85 that direct high pressure air from enclosure 72 to impinge on, and cool the inner liners 82, 92. This technology of impingement cooling the combustor walls is referred to in the industry as Augmented Backside Cooled (ABC) technology. It is known that the use of ABC technology decreases the emission of pollutants into the atmosphere.
The combustion in the combustor volume 58 may also create instabilities manifested by pressure and acoustic oscillations (pressure waves) within combustor volume 58. When the frequency of these oscillations couple with the acoustic mode of the combustor 50, the resulting structural vibrations may damage GTE 100. Therefore, an annular array of Helmholtz resonators 40 (“resonators 40”) are provided in combustor 50 to damp these oscillations. These resonators 40 may be adapted to dampen the oscillations that occur at frequencies close to the acoustic modes of combustor 50. For improved damping characteristics, these resonators 40 may be positioned at the upstream end of combustor 50 (that is, in the combustion zone of combustor volume 58). The array of resonators 40 are coupled to the outer liner 84 of the outer combustor wall 80a and are adapted to be fluidly coupled to the combustor volume 58. Any type of resonator known in the art may be used as resonators 40. In some embodiments, resonators 40 may include purge holes (not shown) to allow cooling air flow into the resonators 40.
These resonators 40 are attached to the outer liner 84 such that the air holes 83 of the outer liner 84 in the attachment region are not blocked. Blocking these air holes 83 may prevent compressed air from entering the cooling space 74 and impinging on a region of the inner liner 82 in the vicinity of the blocked holes. Since the resonators 40 are located in the combustion zone of the combustor 50, blocking the air holes 83 in this region may unacceptably increase the temperature of the inner liner 82 in the combustion zone. To prevent blocking the air holes 83 in the attachment region, the resonators 40 are mounted proud of the exterior surface of the outer liner 84 such that a gap exists between the base 40a (shown in
First support band 64 (seen in
Second support band 68 is a component having a shape resembling a hollow cylinder, and may include a third end 68b that is attached to the second end 64c of first support band 64. Second support band 68 may also include an opposite fourth end 68c that extends along engine axis 98 by a length 68a. Fourth end 68c may be attached to the external surface of outer liner 84 using a plurality of brackets 66 such that an annular gap 62 exists between the second support band 68 and the external surface of the outer liner 84. Second support band 68 may have a diameter that is greater than the diameter of the external surface of the outer liner 84 by about twice the thickness of gap 62. The second support band 68 may provide a mounting surface for the resonators 40 that stands-off from the outer liner 84 by gap 62. Between third end 68b and fourth end 68c, second support band 68 may include openings (visible in
In general, first support band 64, second support band 68 and brackets 66 may include any material, such as stainless steel, nickel-based alloys, etc. In some embodiments, these components may include the same material as outer liner 84. It should be noted that the description of first support band 64, second support band 68 and brackets 66 are exemplary only, and many modifications can be made to these components without departing from the scope of the current disclosure. It should also be noted that although components of a specific mounting (that includes first support band 64, second support band 68 and brackets 66) are discussed here, resonators 40 may be attached to the combustor 50 using alternative mountings that do not block air flow into the cooling space 74 between the liners through the air holes 83 in the resonator attachment region. For instance, in some embodiments, the first support band 64, the second support band 68, and the brackets 66 may be combined to form one circumferential part that is attached to the outer liner 84.
The resonators 40 include a resonator cavity 42 that is fluidly coupled to the combustor volume 58 to dampen combustion induced oscillations that occur in the combustor volume 58. The general function of a resonator is well known in the art, and therefore will not be described in this disclosure. Resonator cavity 42 may be fluidly coupled to combustor volume 58 by a throat 44 of the resonator. Throat 44 may be a cylindrical conduit that extends from the base 40a of a resonator 40 to protrude through the inner and outer liners 82, 84 of outer combustor wall 80a. During operation of GTE 100, the temperature of the inner liner 82 proximate throat 44 will approximate the temperature of the flame in combustor volume 58, and the temperature of the outer liner 84 proximate throat 44 will approximate the temperature of the air in enclosure 72 (discharge temperature of compressor). Since there could be a large difference between these two temperatures, there could be a correspondingly large difference in thermal expansion between the inner and the outer liner 82, 84 proximate throat 44. Preventing the inner and the outer liners 82, 84 in this region to expand differently in response to the different temperatures may induce large thermo-mechanical stresses thereon. Since throat 44 penetrates through the two liners to fluidly couple the resonator cavity 42 to combustor volume 58, the throat 44 may pin a region of the outer core 84 (the region that the throat penetrates through) to a region of the inner core 82 (the region that the throat penetrates through) and restrict relative thermal expansion/contraction between these regions of the inner and the outer liner 82, 84. Restricting differential thermal expansion of the inner and the outer core, proximate the region where the throat 44 penetrates through, may induce large thermo-mechanical stresses in throat 44 and the inner and the outer liner 82, 84. To accommodate differential thermal expansion between the inner and outer liner 82, 84 without inducing large stresses in throat 44 and the combustor wall, sliding grommets 76, 86 are provided at the locations where the throat 44 penetrates the inner and outer liners 82, 84. Sliding grommets 76, 86 also provide for relative displacement between the throat 44 and the inner and outer liners 82, 84 in an axial direction (direction along the length of throat 44). This axial relative displacement allows the throat 44 to freely expand/contract in the axial direction (along the length of throat 44) in response to different temperatures at different regions of the throat 44. Additionally, this capability of axial relative displacement between the throat and the liners may allow the inner liner 82 to radially expand (or bulge) in response to an increase in pressure in combustor volume 58 without inducing stresses in the throat or the liners.
Sliding grommets 76, 86 may include first sliding grommet 76 between the throat 44 and the outer liner 84, and a second sliding grommet 86 between the throat 44 and the inner liner 82 respectively. First and second sliding grommets 76, 86 may include components that may together be adapted to accommodate a thermal expansion mismatch between the inner and the outer liners 82, 84 without inducing large stresses in throat 44 and the liners. These grommets may include materials that are the same as the materials of the liner or may include different materials.
To couple a resonator 40 with combustor 50, the resonator 40 may be positioned on second support band 68 such that the throat 44 of the resonator 40 extends into combustor volume 58 through openings 82a and 84a of inner and outer liner respectively. In this orientation, base 40a of the resonator 40 is rigidly attached to the surface of the second support band 68. When the resonator 40 is thus positioned, leg 276b of the second part 76b may slidably mate with leg 176a of the first part 76a of first sliding grommet 76, and leg 186b of the fourth part 86b may slidably mate with leg 176b of the second part 76b. An attachment cap 78a is secured over first part 76a and second part 76b of the first sliding grommet 76 to substantially gastightingly secure the components together. The attachment cap 78a may also include a substantially L-shaped cross-sectional shape. To couple first part 76a with second part 76b, one leg 278a of the attachment cap 78a may include attachment features, such as, for example, threads, that mate with corresponding attachment features on leg 276a on an outer surface of first part 76a. Second sliding grommet 86 may also include a similar attachment cap 88a that substantially gastightingly couples third part 86a and fourth part 86b of second sliding grommet 86 together. After attachment, legs 276b and 276a of the first sliding grommet 76 includes a first gap 76c, and legs 286b and 286a of the second sliding grommet 86 includes a second gap 86c that are adapted to accommodate a thermal expansion mismatch between the inner and the outer liner 82, 84 without inducing large stresses on throat 44 and the liners (inner liner 82 and outer liner 84). To accommodate the thermal expansion mismatch, the inner liner 82 may expand to increase or decrease the second gap 86c and the outer liner 84 may expand to increase or decrease the first gap 76c without inducing stresses in the components that are coupled together. Thus, the sliding grommets 76, 86 allow for relative thermal expansion between the inner liner and the outer liner proximate the throat. The slidable coupling of the throat to the liners also allow for axial relative displacement between the throat and the liners to accommodate changes in throat length due to a temperature gradient. Allowing these relative displacements prevent the introduction of thermo-mechanical stresses in the liners and the throat.
It should be noted that the structure of the first and second sliding grommets 76, 86 discussed herein is exemplary only, and other embodiments may include grommets having a different structure. In general any grommet that allows the inner and the outer liner 82, 84 to expand by different amounts without inducing significant amount of stresses in the resonator and the combustor wall components, while gastightingly coupling the resonator to the combustor, may be used to couple resonators 40 to outer liner 84.
The disclosed gas turbine combustor with mounting for Helmholtz resonators may be used in any application where Helmholtz resonators are applied without affecting the cooling of the combustor liners. The operation of a turbine engine with a disclosed combustor having mounting for Helmholtz resonators will now be explained.
An array of resonators 40 may be positioned on mounting (that includes first support band 64, second support band 68 and brackets 66) and fluidly coupled to combustor 50 such that a gap exists between the base of the resonators 40 and the external surface of the outer liner 84. During operation, air may be drawn into GTE 100 and compressed using compressor system 10 (See
Since the resonators 40 and the mounting of these resonators 40 do not block the air holes 83 in the outer liner 84, cooling of the combustor 40 remains unaffected due to the presence of the resonators 40. Also, since the attachment between the resonators 40 and the combustor wall 80a allows for differential thermal expansion between the layers of the combustor wall 80a, thermo-mechanical stresses induced in these components are minimized.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed combustor with mounting for Helmholtz resonators. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed combustor. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.
