Patent Publication Number: US-8973365-B2

Title: Gas turbine combustor with mounting for Helmholtz resonators

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to a gas turbine combustor, and more particularly, to a gas turbine combustor with mounting for Helmholtz resonators. 
     BACKGROUND 
     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 &#39;065 patent) issued to Benz et al. on Sep. 12, 2006. In the &#39;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 &#39;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 &#39;065 patent separates the resonator cavity from the cooling air path between the inner and outer liner. 
     Although the Helmholtz resonator of the &#39;065 patent may be tuned without affecting the gap between the inner and the outer liner, the combustor of the &#39;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. 
     SUMMARY 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cutaway-view illustration of an exemplary disclosed turbine engine; 
         FIG. 2  is a cutaway-view illustration of an exemplary combustor system of the turbine engine of  FIG. 1 ; 
         FIGS. 3A and 3B  are external views of an exemplary combustor system of the turbine engine of  FIG. 1 ; 
         FIG. 4A  is cutaway-view illustration a Helmholtz resonator attached to the combustor of the turbine engine of  FIG. 1 ; and 
         FIG. 4B  is a cross-sectional view illustration of exemplary grommets attached to the combustor walls of the turbine engine of  FIG. 1   
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an exemplary gas turbine engine (GTE)  100 . GTE  100  may have, among other systems, a compressor system  10 , a combustor system  20 , a turbine system  70 , and an exhaust system  90  arranged lengthwise along an engine axis  98 . Compressor system  10  may compress air to a compressor discharge pressure and deliver the compressed air to an enclosure  72  of combustor system  20 . The compressed air may then be directed from enclosure  72  into one or more fuel injectors  30  positioned therein. The compressed air may be mixed with a fuel in fuel injector  30 , and the mixture may be directed to a combustor  50 . The fuel-air mixture may ignite and burn in combustor  50  to produce combustion gases at a high temperature and pressure. These combustion gases may be directed to turbine system  70 . Turbine system  70  may extract energy from these combustion gases, and direct the exhaust gases to the atmosphere through exhaust system  90 . The general layout of GTE  100  illustrated in  FIG. 1 , and described above, is only exemplary and the combustors of the current disclosure may be used with any configuration and layout of GTE  100 . 
       FIG. 2  is a cut-away view of combustor system  20  showing a plurality of fuel injectors  30  fluidly coupled to combustor  50 . In the embodiment of  FIG. 2 , combustor  50  is positioned within an outer casing  96  of combustor system  20 , and annularly disposed about engine axis  98 . Outer casing  96  and combustor  50  define the enclosure  72  between them. As discussed with reference to  FIG. 1 , enclosure  72  contains compressed air at compressor discharge pressure and temperature. Combustor  50  includes an outer combustor wall  80   a  and an inner combustor wall  80   b  annularly disposed about the engine axis  98 . The outer and the inner combustor walls ( 80   a ,  80   b ) are joined together at an upstream end by a dome assembly  52  to define a combustor volume  58  therebetween. Combustor volume  58  may be an annular space bounded by the inner and outer combustor walls ( 80   a ,  80   b ) that extend from dome assembly  52  to a downstream end along engine axis  98 . Combustor volume  58  is fluidly coupled to turbine system  70  at the downstream end. A plurality of fuel injectors  30 , positioned symmetrically about engine axis  98  on dome assembly  52 , direct a fuel-air mixture to combustor volume  58  for combustion. This fuel-air mixture burns in combustor volume  58 , proximate the upstream end (combustion zone), creating high pressure and high temperature combustion gases. These gases are directed to turbine system  70  through the downstream end of combustor  50 . It should be noted that the general configuration of combustor system  20  described here (and illustrated in  FIG. 2 ) is exemplary only, and that several variations are possible. Since these different configurations are well known in the art, for the sake of brevity, discussion of the different possible configurations is not provided here. 
     The combustion of fuel-air mixture within combustor volume  58  heats the combustor walls ( 80   a  and  80   b ). For increased reliability and performance, it is desirable to cool these walls. The outer combustor wall  80   a  includes an inner liner  82  and an outer liner  84 , and the inner combustor wall  80   b  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  80   a  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  40   a  (shown in  FIG. 4A ) of the resonators  40  and external surface of the outer liner  84 . 
       FIGS. 3A and 3B  show illustrations of the exterior surface of outer liner  84  with the array of resonators  40  attached thereon.  FIG. 3A  shows a view of the exterior surface with the compressor system  10  on the left and the turbine system  70  on the right, and  FIG. 3B  shows a view with the turbine system  70  on the left and the compressor system  10  on the right. As seen in  FIGS. 3A and 3B , the resonators  40  are mounted on combustor  50  such that a gap  62  exists between the base of the resonators  40  and the exterior surface of the outer liner  84 . Resonators  40  may be attached to the combustor  50  using a mounting that is configured to provide this gap  62  between the resonators  40  and outer liner  84 . In the embodiment illustrated in  FIGS. 3A and 3B , this mounting includes two circumferential support bands—a first support band  64  and a second support band  68 —disposed on the outer liner  84  to provide a raised mounting surface for the resonators  40 . These circumferential support bands may be attached to the outer liner  84  by welding or by any other attachment techniques known in the art. 
     First support band  64  (seen in  FIG. 3A ) is a component having a shape resembling a frustum of a hollow cone. First support band  64  may include a first end  64   b  having a diameter substantially equal to (or slightly greater than) the external diameter of the outer liner  84 . First support band  64  may also include an opposite second end  64   c  having a diameter that is larger than the diameter of the first end  64   b  by about twice the thickness of gap  62 . Between first end  64   b  and second end  64   c , first support band  64  includes a plurality of openings  64   a . These plurality of openings  64   a  may be annularly disposed around first support band  64 , and may be adapted to allow air flow therethrough. Openings  64   a  allow air from enclosure  72  to enter gap  62  between second support band  68  and outer liner  84 . From gap  62 , this cooling air may enter cooling space  74  through the unobstructed air holes  83  under the second support band  68 . This cooling air may impinge on and cool the inner liner  82  in the combustion zone. The thickness of gap  62 , and the number and size of the openings  64   a , may be configured to enable sufficient flow of cooling air into cooling space  74 . In the embodiment illustrated in  FIGS. 3A and 3B , the thickness of gap  62  may be between about ¼ inch (6.35 mm) and 1 inch (25.4 mm), the size of openings  64   a  may be between about ¼ inch (6.35 mm) and 1 inch (25.4 mm), and the number of openings  64   a  may be about 80. It is believed that openings  64   a  of this configuration allow for adequate cooling of the inner liner  82 . In general, about 20-150 of ¼ inch (6.35 mm) to 1 inch (25.4 mm) holes may be annularly disposed on first support band  64 . Second end  64   c  of first support band  64  may be attached to second support band  68 . 
     Second support band  68  is a component having a shape resembling a hollow cylinder, and may include a third end  68   b  that is attached to the second end  64   c  of first support band  64 . Second support band  68  may also include an opposite fourth end  68   c  that extends along engine axis  98  by a length  68   a . Fourth end  68   c  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  68   b  and fourth end  68   c , second support band  68  may include openings (visible in  FIG. 4A ) that allow the resonators  40  to be fluidly coupled to combustor volume  58 . In some embodiments, second support band  68  may also include additional openings that allow air from enclosure  72  to enter gap  62 . 
     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 . 
       FIG. 4A  illustrates a sectional view of resonator  40  attached to combustor  50 . As can be seen in  FIG. 4A , resonator  40  is mounted on the outer liner  84  in such a manner that gap  62  is provided between the base  40   a  of the resonator  40  and the external surface of the outer liner  84 . And, the openings  64   a  in the first support band  64  and the space between the brackets  66  allow compressed air from enclosure  72  to enter gap  62  between the resonator  40  and the outer liner  84 . This compressed air continues to flow into cooling space  74  through the air holes  83  to impinge on and cool the inner liner  82 . 
     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  40   a  of a resonator  40  to protrude through the inner and outer liners  82 ,  84  of outer combustor wall  80   a . 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.  FIG. 4B  is a schematic that illustrates a cross-sectional view of the first and second sliding grommets  76 ,  86 . In the discussion that follows, reference will be made to both  FIGS. 4A and 4B . First sliding grommet  76  may include a first part  76   a , and the second sliding grommet  86  may include a third part  86   a  that are attached to the outer liner  84  and the inner liner  82 , respectively. First part  76   a  and third part  86   a  may include a ring shaped component having a substantially L-shaped cross-sectional shape. One leg  176   a  of the substantially L-shaped cross-section of the first part  76   a  may be attached to the outer liner  84  and the other leg  276   a  may extend substantially perpendicularly therefrom. Similarly, one leg  186   a  of the substantially L-shaped cross-section of the third part  86   a  may be attached to the inner liner  82  and the other leg  286   a  may extend substantially perpendicularly therefrom. First sliding grommet  76  may also include a substantially cylindrical second part  76   b  having a substantially L-shaped cross-sectional shape. One leg  176   b  of the second part  76   b  may be slidably attached to throat  44  and the other leg  276   b  may extend substantially perpendicularly therefrom. Second grommet  86  may include a ring shaped fourth part  86   b  having a substantially L-shaped cross-sectional shape. One leg  286   b  of the fourth part  86   b  may be slidably attached to the leg  186   a  of the third part  86   a  and the other leg may extend substantially perpendicularly therefrom. 
     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  82   a  and  84   a  of inner and outer liner respectively. In this orientation, base  40   a  of the resonator  40  is rigidly attached to the surface of the second support band  68 . When the resonator  40  is thus positioned, leg  276   b  of the second part  76   b  may slidably mate with leg  176   a  of the first part  76   a  of first sliding grommet  76 , and leg  186   b  of the fourth part  86   b  may slidably mate with leg  176   b  of the second part  76   b . An attachment cap  78   a  is secured over first part  76   a  and second part  76   b  of the first sliding grommet  76  to substantially gastightingly secure the components together. The attachment cap  78   a  may also include a substantially L-shaped cross-sectional shape. To couple first part  76   a  with second part  76   b , one leg  278   a  of the attachment cap  78   a  may include attachment features, such as, for example, threads, that mate with corresponding attachment features on leg  276   a  on an outer surface of first part  76   a . Second sliding grommet  86  may also include a similar attachment cap  88   a  that substantially gastightingly couples third part  86   a  and fourth part  86   b  of second sliding grommet  86  together. After attachment, legs  276   b  and  276   a  of the first sliding grommet  76  includes a first gap  76   c , and legs  286   b  and  286   a  of the second sliding grommet  86  includes a second gap  86   c  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  86   c  and the outer liner  84  may expand to increase or decrease the first gap  76   c  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 . 
     INDUSTRIAL APPLICABILITY 
     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  FIG. 1 ). This compressed air may be directed to enclosure  72 , and from there into combustor  50 , through fuel injectors  40  positioned therein. Air from enclosure  72  may also be directed into cooling space  74  between the inner and the outer liners  82 ,  84  of the combustor  50  to impinge on and cool the inner liner  82 . The mounting that couples the resonators  40  to the combustor  50  may be such that air flow into the cooling space  74  through air holes  83  of the outer liner  84  are not blocked. The resonators  40  may also be coupled to the combustor  50  such that grommets (first sliding grommet  76  and second sliding grommet  86 ) are provided between the throat  44  of the resonator  40  that penetrates the liners and the inner and the outer liner  82 ,  84 . These grommets allow the inner and the outer liner  82 ,  84  to expand differently without inducing significant stresses in the throat and the combustor liners, while gastightingly coupling the resonator to the combustor. 
     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  80   a  allows for differential thermal expansion between the layers of the combustor wall  80   a , 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.