Abstract:
The present invention discloses a novel apparatus and way for controlling combustion dynamics in a premix combustion system. The apparatus comprises a hemispherical dome assembly with a plurality of dome dampers having a predetermined damper volume and air supply with the damper in fluid communication with the combustion chamber. The dome dampers are pressurized with a volume of air to dampen pressure waves received from the combustion chamber. One or more combustor frequencies can be targeted through use of the present invention.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       TECHNICAL FIELD 
       [0002]    The present invention relates generally to an apparatus and method for controlling the combustion dynamics in a gas turbine combustion system. More specifically, a combustion system is provided having a combustor dome and a plurality of dome damper mechanisms for reducing the pressure fluctuations within the combustion system. 
       BACKGROUND OF THE INVENTION 
       [0003]    In an effort to reduce the amount of pollution emissions from gas-powered turbines, governmental agencies have enacted numerous regulations requiring reductions in the amount of oxides of nitrogen (NOx) and carbon monoxide (CO). Lower combustion emissions can often be attributed to a more efficient combustion process, with specific regard to fuel injector location, airflow rates, and mixing effectiveness. 
         [0004]    Early combustion systems utilized diffusion type nozzles, where fuel is mixed with air external to the fuel nozzle by diffusion, proximate the flame zone. Diffusion type nozzles historically produce relatively high emissions due to the fact that the fuel and air burn essentially upon interaction, without mixing, and stoichiometrically at high temperature to maintain adequate combustor stability and low combustion dynamics. 
         [0005]    An enhancement in combustion technology is the concept of premixing fuel and air prior to combustion to form a homogeneous mixture that burns at a lower temperature than a diffusion type flame and thereby produces lower NOx emissions. Premixing can occur either internal to the fuel nozzle or external thereto, as long as it is upstream of the combustion zone. An example of a premixing combustor has a plurality of fuel nozzles, each injecting fuel into a premix chamber where fuel mixes with compressed air from a plenum before entering a combustion chamber. Premixing fuel and air together before combustion allows for the fuel and air to form a more homogeneous mixture, which, when ignited will burn more completely, resulting in lower emissions. However, due to the mixing and combustion processes inherent in a premixing combustor, the pressures within the combustion system will fluctuate and varying pressure fluctuations can cause damage to the combustion hardware if not adequately controlled. 
       SUMMARY 
       [0006]    The present invention discloses an apparatus and method for reducing the combustion dynamics in a multi-staged premix gas turbine combustor. More specifically, in an embodiment of the present invention, a dome assembly for a gas turbine combustor is provided having a dome plate with a generally hemispherical cross section, a plurality of openings in the dome plate, and a plurality of dome dampers, each encompassing a respective opening. The dome dampers comprise a damper body having a cavity, a removable coverplate secured to the end of a damper, and a plurality of pure holes located about the damper body. 
         [0007]    In an alternate embodiment of the present invention, a gas turbine combustion system is disclosed comprising a generally cylindrical combustion liner located radially within a flow sleeve, and a set of main fuel injectors positioned radially outward of the combustion for directing a flow of fuel to mix with air to enter the combustion liner. A combustor dome assembly encompasses the inlet end of the combustion liner and has a dome plate with a generally hemispherical cross section, a plurality of openings in the dome plate, and a plurality of dome dampers, each encompassing a respective opening. Each of the dampers has a damper body and a removable coverplate secured thereto to form a damper volume and purge holes located in the damper body. 
         [0008]    In yet another embodiment of the present invention, a method of regulating combustion dynamics in a gas turbine combustor is provided. The method comprises providing a combustion system having a combustor dome in which a plurality of openings are present, each of the openings surrounded by a dome damper. One or more of the desired frequencies to control is determined and a volume required to target the one or more desired combustion frequencies is then determined. A desired amount of purge air flow to pass into the plurality of dampers is determined and a coverplate is secured to an end of each dome damper where the coverplate helps to form a desired volume within each damper, where the desired volume is sufficient in size to adequately dampen pressure fluctuations in the combustion system. 
         [0009]    In a further embodiment of the present invention, a dome assembly for a gas turbine combustor is provided having a dome plate with a generally hemispherically-shaped cross section, an adapter plate positioned adjacent to the dome plate, one or more resonator boxes, extending from the adapter plate and a plurality of dome dampers. 
         [0010]    Additional advantages and features of the present invention will be set forth in part in a description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned from practice of the invention. The instant invention will now be described with particular reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0011]    The present invention is described in detail below with reference to the attached drawing figures, wherein: 
           [0012]      FIG. 1  is a cross section of a gas turbine combustion system in accordance with an embodiment of the present invention. 
           [0013]      FIG. 2  is a perspective view of a portion of a gas turbine combustor in accordance with an embodiment of the present invention. 
           [0014]      FIG. 3  is an alternate perspective of the portion of the gas turbine combustor of  FIG. 2  in accordance with an embodiment of the present invention. 
           [0015]      FIG. 4  is an end view of a portion of the gas turbine combustor of  FIG. 2  in accordance with an embodiment of the present invention. 
           [0016]      FIG. 5  is an opposing end view of the gas turbine combustor of  FIG. 2  in accordance with an alternate embodiment of the present invention. 
           [0017]      FIG. 6  is a cross section taken through the portion of the gas turbine combustor depicted in  FIG. 2  in accordance with an embodiment of the present invention. 
           [0018]      FIG. 7  is a detailed cross section view of a portion of the gas turbine combustor of  FIG. 6  in accordance with an embodiment of the present invention. 
           [0019]      FIG. 8  is a detailed cross section view of a damper portion of the gas turbine combustor of  FIG. 6  in accordance with an embodiment of the present invention. 
           [0020]      FIG. 9  is an alternate cross section taken through a portion of the gas turbine combustor depicted in  FIG. 2  in accordance with an embodiment of the present invention. 
           [0021]      FIG. 10  is a perspective view of a portion of a gas turbine combustor in accordance with an alternate embodiment of the present invention. 
           [0022]      FIG. 11  is an alternate perspective view of a portion of the gas turbine combustor in accordance with the alternate embodiment of the present invention of  FIG. 10 . 
           [0023]      FIG. 12  an end view of a portion of the gas turbine combustor of  FIG. 10  in accordance with an alternate embodiment of the present invention. 
           [0024]      FIG. 13  is an opposing end view of the gas turbine combustor of  FIG. 10  in accordance with an alternate embodiment of the present invention. 
           [0025]      FIG. 14  is a cross section of the gas turbine combustor of  FIG. 10  in accordance with an alternate embodiment of the present invention. 
           [0026]      FIG. 15  is a detailed cross section view of a damper portion of the portion of the gas turbine combustor of  FIG. 14  in accordance with an alternate embodiment of the present invention. 
           [0027]      FIG. 16  is a detailed cross section view of a damper portion of the gas turbine combustor in accordance with yet another alternate embodiment. 
           [0028]      FIG. 17  is a partial perspective view of a damper portion and dome plate region of the gas turbine combustor of  FIG. 16  in accordance with yet another alternate embodiment. 
           [0029]      FIG. 18  is a detailed cross section view of a damper portion of the gas turbine combustor in accordance with an additional embodiment. 
           [0030]      FIG. 19  is a partial perspective view of a damper portion and dome plate region of the gas turbine combustor of  FIG. 18  in accordance with an additional embodiment. 
           [0031]      FIG. 20  is a perspective view of a portion of a gas turbine combustor in accordance with an alternate damper support configuration of the present invention. 
           [0032]      FIG. 21  is a perspective view of a portion of the gas turbine combustor configuration of  FIG. 20 . 
           [0033]      FIG. 22  is a detailed perspective view of the damper portion of the gas turbine combustor of  FIG. 21 . 
           [0034]      FIG. 23  is a cross section view of the damper portion of the gas turbine combustor of  FIG. 21 . 
           [0035]      FIG. 24  is a perspective view of a forward face of an adapter plate in accordance with an embodiment of the present invention. 
           [0036]      FIG. 25  is a perspective view of an aft face of the adapter plate of  FIG. 24  in accordance with an embodiment of the present invention. 
           [0037]      FIG. 26  is a flow diagram outlining a method of regulating combustor dynamics in accordance with yet another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0038]    The present invention discloses a dome assembly for gas turbine combustion system for use in a premix combustion system to help reduce combustion dynamics and is shown in detail in  FIGS. 1-26 . As one skilled in the art understands, a gas turbine engine typically incorporates a plurality of combustors. Generally, for the purpose of discussion, the gas turbine engine may include low emission combustors such as those disclosed herein and may be arranged in a can-annular configuration about the gas turbine engine. One type of gas turbine engine (e.g., heavy duty gas turbine engines) may be typically provided with, but not limited to, six to eighteen individual combustors, each of them fitted with the components outlined above. Accordingly, based on the type of gas turbine engine, there may be several different fuel circuits utilized for operating the gas turbine engine. 
         [0039]    Referring specifically to  FIG. 1 , a gas turbine combustion system  100  in accordance with an embodiment of the present invention is shown in cross section. The gas turbine combustion system  100  comprises a generally cylindrical combustion liner  102  having a central axis A-A and located coaxial to and radially within a flow sleeve  104 . The combustion liner  102  has an inlet end  106  and an opposing outlet end  108 . 
         [0040]    The gas turbine combustion system  100  also comprises a set of main fuel injectors  110  positioned radially outward of the combustion liner  102  and proximate an upstream end of the flow sleeve  104 . The combustion system  100  disclosed in  FIG. 1  is a multi-stage premixing combustion system comprising four stages of fuel injection based on the loading of the engine. However, it is envisioned that the specific fuel circuitry and associated control mechanisms could be modified to include fewer or additional fuel circuits. 
         [0041]    For the embodiment of the present invention shown in  FIG. 1 , the main fuel injectors  110  are located radially outward of the combustion liner  102  and spread in an annular array about the combustion liner  102 . The main fuel injectors  110  are divided into two stages with a first stage extending approximately  120  degrees about the combustion liner  102  and a second stage extending the remaining annular portion, or approximately  240  degrees, about the combustion liner  102 . The first stage of the main fuel injectors  110  are used to generate a Main  1  flame in combustion liner  102  while the second stage of the main fuel injectors  110  generate a Main  2  flame in the combustion liner. 
         [0042]    The gas turbine combustion system also comprises a combustor dome assembly  112  that encompasses the inlet end  106  of the combustion liner  102 . The combustor dome assembly  112  extends from proximate the set of main fuel injectors  110  to a dome plate  114 , where the dome plate  114  has a generally hemispherical-shaped cross section with the dome plate  114  positioned a distance forward of the inlet end  106  of the combustion liner  102  and turning to extend a distance into the combustion liner  102 . The shape of the combustor dome assembly can also be seen in  FIG. 6 . Referring now to  FIGS. 2-9 , the combustor dome assembly  112  comprises a plurality of openings  116  in the dome plate  114 , where each of the openings  116  has a diameter D and a neck length L. Preferably, the openings  116  have a circular cross section, but other shapes are also possible. The openings  116  are oriented in the dome plate  114  so as to preferably be parallel with a central axis A-A of the combustion system  100 . Extending away from the dome plate  114 , opposite of the combustion liner, is a plurality of dome dampers  118 . Referring to  FIG. 8 , each of the dome dampers  118  encompasses one of the openings  116  and comprises a damper body  120  having an opening located therein. Accordingly, for the dome plate  114 , the dome dampers  118  are oriented in an annular array about the central axis A-A of the combustion system  100 . A removable cover plate  122  is secured to an end of the damper body  120  opposite of the opening  116  to form a damper volume  124 . The damper body  120  also includes a plurality of purge holes  126 . 
         [0043]    The dome dampers  118  extend away from the combustion liner  102  in a way to establish predetermined volumes of air in order to provide a volume of air sufficient to dampen pressure fluctuations within the combustion liner  102 . The dome dampers  118  are supplied with compressed air by way of purge holes  126 , which, in an embodiment of the present invention are located along a side of the damper body  120  and are sized both in diameter and quantity to ensure a sufficient volume of compressed air is provided to the damper volume  124 . The exact location and spacing of the purge holes  126  can vary. That is, the purge holes  126  may be located about the damper body  120  or the cover plate  122 . 
         [0044]    In operation, a pressure wave from the combustor travels upstream towards the dome plate  114 , passes through the openings  116  in the dome plate  114 , and into the damper volume  124  formed by the damper body  120  and cover plate  122 . Once in the damper volume  124 , the wave then encounters the volume of compressed air. The extra volume of air serves to generate a wave that is out of phase with an incoming wave, similar to how a spring and shock operate to counteract the movement of a motor vehicle. That is, the volume of air in the damper counteracts the pressure wave traveling up through the combustor. 
         [0045]    As discussed above, the dome dampers  118  and corresponding damper volume  124  are sized to specifically target a particular resonance frequency for the damper in order to counteract a specific frequency or pressure oscillation in the combustion system. As one skilled in the art understands, the basic formula for resonance frequency of a damper is f res =c/2/π*sqrt(A neck /L neck,eff /V damper ), where f res  is the resonance frequency of the damper, c is the speed of sound, A neck  is the cross sectional area of the opening  116  connecting the damping volume to the combustor, L neck,eff  is the effective length L of the opening  116  and V damper  is volume of the damper. Therefore, altering the cross sectional area of opening  116 , its length L and the volume  124  can each affect the resonance frequency for the damper. For example, decreasing the volume of the damper increases the damper resonance frequency, while increasing the volume of the damper lowers the damper resonance frequency. Furthermore, the length L of the opening  116 , or “neck” of the opening, can also vary. That is, if the length L of the neck region is increased, the resonance frequency of the damper decreases and if the length L of the neck region is decreased, the resonance frequency of the damper increases. A final variable for determining the resonance frequency of the damper is the area of the opening  116 . If the area of opening  116  is increased, through a larger diameter D, the resonance frequency of the damper increases, whereas if the area of opening  116  is decreased, through a smaller diameter D, the resonance frequency of the damper decreases. Therefore, depending on the frequency one is trying to dampen, various elements on the damper can be modified to target one or more specific frequencies. 
         [0046]    As for the frequencies being targeted by a dome damper structure, in premix style combustions systems, such as that shown in  FIG. 1 , high frequencies (screech) in the range of 1-10 kHz are typically of high concern. However, lower frequencies, in the range of 50-500 Hz can also be targeted. When targeting screech, or high frequencies, typical damper dimensions include a neck length L of approximately 5 mm-25 mm and a neck diameter D of approximately 5 mm-15 mm. When targeting lower frequencies, a typical neck length L is longer, on the order of approximately 20 mm-200 mm while the neck diameter D is approximately 10 mm-100 mm. As such, one way to express these geometric requirements is through a ratio of diameter D to neck length L, which for an embodiment of the present invention is approximately 0.2 to 2.0. 
         [0047]    With respect to the purge holes  126 , the equivalent area of all of the purge holes  126  define the total mass flow through the damper, and therefore, the velocity in the neck, which in turn defines the damping properties. The total area of the purge holes  126  is generally small compared to the area of the opening  116 , or Aneck, such that the majority of the pressure drop across the damper is generated at the purge holes  126 . For example, the total area of all of the purge holes  126  are approximately 10% or less than the Aneck (or area of the opening  116 ). For the embodiment depicted in  FIGS. 1-9 , and specifically referring to  FIGS. 7-9 , each of the damper bodies  120  have six purge holes  126 . More purge holes  126  are typically required for higher velocity flow. 
         [0048]    As discussed above, there are three major variables which can be adjusted to adjust the resonance frequency of the damper—area of the neck (hence diameter D), length of the neck (length L) and volume of the damper. However, as a practical point, not all of these variables can be changed once the hardware has been manufactured in the event during operation, it is determined that a different frequency of the combustor should be dampened. For example, it is difficult to change the size of the openings  116  and the length L of the openings on completed combustion systems. However, one such variable that can be modified is the volume of the damper. For the configuration depicted in  FIGS. 2 ,  4 , and  6 - 8 , the damper volume  124  can be modified by way of a removable coverplate  122 , or plug-like plate. The removable coverplate  122  is secured to damper body  120  by a removable fastener  128 , such as a snap ring, clip, threaded body, or a bolt. This fastening mechanism provides an easy way to remove the coverplate  122  and replace it with a coverplate of a different size, resulting in a different damper volume  124 . In order to ease the process of exchanging coverplates  122 , each coverplate typically has a recess pocket  130  in which a tool can be placed to help remove the coverplate  122 . Thereafter a new coverplate  122  can be put in place and then secured to one or more of the damper bodies  120 . 
         [0049]    The damper bodies  120  shown in  FIGS. 1-9  are generally cylindrical and oriented in an annular array about a center axis, as shown in  FIGS. 2 and 4 . However, dampers are not limited to the cylindrical configuration, and in fact, can take on generally any shape and quantity, as required. An alternate embodiment of the present invention is shown in detail in  FIGS. 10-15 . In this alternate embodiment of the present invention, one or more resonator boxes  200  are secured over the dome plate and opening  202 . The size of opening  202  (diameter and neck length) is controlled by a threaded insert  203 , as shown in  FIGS. 14 and 15 . The neck length and diameter may be controlled by a single threaded insert. The resonator boxes  200  provide a larger volume than the smaller cylindrical-shaped dampers as depicted in  FIGS. 1-9 . For the similar combustion system of  FIGS. 1-9 , instead of twenty-four cylindrical dampers, there are instead six resonator boxes employed. However, it is envisioned that the number of cylindrical dampers and resonator boxes may be modified to include fewer or additional dampers or boxes. Similar to the cylindrical damper bodies  120 , the resonator boxes  200  also include purges holes  204  for supplying compressed air into the resonator box  200 . As discussed above, the placement of purge holes  204  can also vary about the resonator  200  and/or the coverplate  206 . Unlike the cylindrical damper body of the prior configuration, the coverplate  206  of the resonator box  200  is preferably fastened to the resonator box  200  by a means such as a bolt  208 . 
         [0050]    Similar to the cylindrical damper bodies, the three factors that can also change the resonator frequency of a resonator box  200  are the area of the neck (hence diameter D), length of the neck (length L) and volume of the resonator box. However, if during operation it is determined that a different frequency should be dampened, not all of these variables can be changed once the hardware has been manufactured. One variable that can be modified relatively easily, post-manufacturing, is the volume of the resonator box. The coverplate  206  can be removed and replaced with a different size coverplate that, due to its thickness, either increases or decreases the volume in the resonator box  200 . 
         [0051]    In an alternate embodiment of the present invention, various combinations of the damping mechanisms discussed above can be utilized together. For example, it is possible to employ a dome damper  118  positioned within a resonator box  200 . Alternatively, it is possible to use the resonator box  200  with a simple opening in the dome (i.e. no separate damper body). 
         [0052]    The damper bodies discussed above are depicted generally coaxial to the central axis A-A. However, the dome damper  118  and/or resonator box  200  can also be oriented at an angle relative to the central axis A-A. Where such damper bodies are angled, so are the corresponding openings  116  and  202 . An angled opening allows for damper airflow interaction with the combustion flame while providing an indirect interaction with the anchoring flame. 
         [0053]    In yet another embodiment of the present invention it is possible to target multiple critical frequencies in the combustion system through dampers configured to counteract more than one critical frequency. For example, a combustor can have a first set of dampers having a first opening diameter, area, volume and neck length directed towards targeting a first frequency, and a second set of dampers, having a second opening diameter, area, volume and neck length directed towards targeting a different frequency than the first set of dampers. The quantity of the first set of dampers and second set of dampers can vary as required. 
         [0054]    In the embodiments discussed above, a basic geometry for the damper was a single volume with one neck length and effective area are disclosed. However, it is envisioned that more complex geometries for the damper bodies can be utilized in the present invention. For example, in another embodiment, multiple frequencies can be targeted by way of a damper body having multiple volumes arranged in an axial series, where a series of volumes and necks form a multi-volume damper. 
         [0055]    As discussed above, without damper mechanisms in place on a premix combustor disclosed in  FIG. 1 , the operation of the premix combustor is limited. For example, for a combustion system similar to that of  FIG. 1 , normal combustion dynamics of 0.5 psi fluctuation could be tolerated by combustion hardware. By implementing a damper system disclosed herein, greater pressure fluctuations (increased combustion dynamics) can be tolerated, including pressure fluctuations upwards of approximately  1  psi. The damper system helps to reduce the adverse effects of the combustion dynamics by reducing the impact of critical vibration levels. 
         [0056]    Yet another embodiment of the present invention is disclosed in  FIGS. 16-25 . As discussed above, the plurality of damper bodies  120  and resonator boxes  200  are mounted to the dome plate  114 . However, the dome plate  114  has a curved surface, which can present difficulty when mounting this hardware. Furthermore, such combustor construction can also be quite costly to manufacture due to the complex geometries. 
         [0057]    An additional feature that may be included in an embodiment of the present invention is an adaptor plate  300  which is positioned between the resonator box  200  or dome dampers  118  and the dome plate  114 . The adapter plate  300  has the same general configuration and function, whether it is used in conjunction with a resonator box or a damper body—to provide an improved way of mounting and securing the dampers to the domeplate  114  of the combustor. 
         [0058]    Referring to  FIGS. 16-19 , the adaptor plate  300  is shown with respect to the embodiment of the present invention featuring a plurality of individual dome dampers  118 . The adapter plate  300  comprises a forward face  302  and an aft face  304  spaced a distance from the forward face  302  and parallel to the forward face  302 . The adapter plate  300  is secured to the dome plate  114  by a plurality of fasteners or can be permanently fixed to the domeplate  114  by way of welding or brazing. 
         [0059]    The adapter plate  300  also comprises a first plurality of plate openings  306 . These openings  306  correspond to the openings  116  in the domeplate  114  such that the damper volume  124  is in communication with the combustor volume inside the domeplate  114 . Extending from the forward face  302  of the adapter plate  300  are a plurality of dome dampers  118 . The dome dampers  118  can be integral to the adapter plate  300  or separately attached, such as through braze or welding, to the adapter plate  300 . The dome dampers  118  can be mounted perpendicular to the adapter plate  300  as shown in  FIGS. 16 and 17  or the dome dampers  118  can be mounted at an angle relative to the dome dampers  118 , as shown in  FIGS. 18 and 19 . 
         [0060]    In another version of the present invention, the adapter plate  300  can take on a slightly different configuration as shown in  FIGS. 24 and 25 . More specifically, the adapter plate  300  has a front face  312  and an opposing aft face  314 . The aft face  314  includes a contoured portion  308  that is sized and shaped to mate to the curved profile of the domeplate  114 . 
         [0061]    The alternate version of the adapter plate  300  can be seen in use with an alternate dome damper configuration, the resonator box  200 , as shown in  FIGS. 20-23 . Referring to  FIGS. 20-23 , a combustor dome assembly incorporating the resonator boxes  200 , similar to that of  FIGS. 10-15  is disclosed. However, for the embodiment shown in  FIGS. 20-23 , the resonator boxes  200  are mounted to the domeplate  114  through the adapter plate  300 , previously discussed and shown in  FIGS. 24 and 25 . More specifically, the adapter plate  300  shown in  FIGS. 24 and 25  includes a first plurality of plate openings  310  through which the damper bodies/volume communicates with the combustor. The adapter plate  300  also includes a second plurality of plate openings  315 . The adapter plate  300  also includes a third plurality of openings  318  spaced in an annular array about the adapter plate  300 . The third plurality of openings  318  each include a fastener  320  secured to the adapter plate  300 , where the fastener  320  is used to secured the one or more resonator boxes  200  to the adaptor plate  300 , as shown in  FIG. 22 . 
         [0062]    The dome dampers  324  can extend generally perpendicular to the adapter plate  300 . Alternatively, and as shown in  FIGS. 22 and 23 , the dome dampers  324  can also be oriented at an angle relative to the adapter plate  300 . Whether resonator boxes  200  or dome dampers  118  are being used, the adaptor plate  300  provides an improved way of securing and locating damper configurations to the domeplate  114 . 
         [0063]    Referring to  FIG. 26 , an alternate embodiment of the present invention discloses a method  2600  of regulating combustion dynamics in a gas turbine combustor. In a step  2602 , a combustion system is provided having a combustor dome assembly comprising a dome plate with a plurality of openings in the dome plate, where each of the openings has a diameter and neck length. The combustion system also includes a plurality of dome dampers encompassing respective openings in the dome plate. In a step  2604 , one or more desired combustion frequencies to control is determined. As discussed above, the frequency to be controlled can be a high frequency, such as screech, or a lower frequency. In a step  2606  a desired volume for the dome dampers necessary to target the one or more frequencies identified in step  2604  is determined. Then, in a step  2608 , a desired amount of purge air to flow into the dome dampers is determined. In a step  2610 , a coverplate is secured to at least an end of the dome dampers where the coverplate is placed in a position to form the desired volume for the dampers determined in step  2606 . Then, in a step  2612 , a determination is made as to whether the desired volume of each damper determined in step  2606  is sufficient to alter the combustor frequency. Such a determination is typically made as a result of operating the combustion system. If the determination is made that the damper volume is insufficient, then in a step  2614 , one or more variables affecting the resonance frequency of the damper, such as neck length, opening diameter or damper volume are determined to be changed and the process returns to step  2606  to determine the desired damper volume. If a determination is made at step  2612  that the desired damper volume is sufficient to dampen the desired combustion frequency, then the process ends at a step  2616 . 
         [0064]    While the invention has been described in what is known as presently the preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment but, on the contrary, is intended to cover various modifications and equivalent arrangements within the scope of the following claims. The present invention has been described in relation to particular embodiments, which are intended in all respects to be illustrative rather than restrictive. 
         [0065]    From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects set forth above, together with other advantages which are obvious and inherent to the system and method. It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and within the scope of the claims.