Patent Publication Number: US-11041625-B2

Title: Fuel nozzle with narrow-band acoustic damper

Description:
FIELD 
     The present invention generally involves a bundled tube type fuel nozzle assembly for a gas turbine combustor. More specifically, the invention relates to a bundled tube type fuel nozzle assembly with a narrow-band acoustic damper incorporated therein. 
     BACKGROUND 
     Particular combustion systems for gas turbine engines utilize combustors which burn a gaseous or liquid fuel mixed with compressed air. Generally, a combustor includes a fuel nozzle assembly including multiple fuel nozzles which extend downstream from an end cover of the combustor and which provide a mixture of fuel and compressed air to a primary combustion zone or chamber. A combustor may have bundled tube type fuel nozzles for premixing a fuel with compressed air upstream from the combustion zone. A bundled tube type fuel nozzle assembly generally includes multiple tubes that extend through a fuel plenum body which is at least partially defined by a forward plate, an aft plate and an outer sleeve. Compressed air flows into an inlet portion of each tube. Fuel from the fuel plenum is injected into each tube where it premixes with the compressed air before it is routed into the combustion zone. 
     During operation, various operating parameters such as fuel temperature, fuel composition, ambient operating conditions and/or operational load on the gas turbine may result in combustion dynamics or pressure pulses within the combustor. The combustion dynamics may cause oscillation of various combustor hardware components such as the liner and/or the fuel nozzle which may result in undesirable wear of those components. Alternately, or in addition, high frequencies of combustion dynamics may produce pressure pulses inside the premixer tubes and/or combustion chamber that affect the stability of the combustion flame, reduce the design margins for flashback or flame holding, and/or increase undesirable emissions. 
     BRIEF DESCRIPTION 
     Aspects and advantages are set forth below in the following description, or may be obvious from the description, or may be learned through practice. 
     One embodiment of the present disclosure is a bundled tube fuel nozzle assembly. The fuel nozzle assembly includes a fuel plenum body including a forward plate extending in a radial direction, an aft plate axially spaced from the forward plate and extending in a radial direction, an outer sleeve extending in an axial direction between the forward plate and the aft plate, and a fuel plenum defined by the forward plate, the aft plate and the outer sleeve. A fuel conduit is in fluid communication with the fuel plenum. The fuel nozzle assembly further includes a plurality of mixing tubes extending through the fuel plenum body. Each of the mixing tubes includes an air inlet, a fuel port in fluid communication with the fuel plenum, and an outlet downstream of the aft plate. The fuel nozzle assembly also includes a cap plate axially spaced from the aft plate with an air plenum defined between the aft plate and the cap plate, the cap plate being upstream of a combustion zone and including a hot surface facing the combustion zone. The fuel nozzle assembly also includes a narrow-band acoustic damper located within the air plenum. 
     Another embodiment of the present disclosure is a gas turbine including a compressor, a turbine, and a combustor disposed downstream from the compressor and upstream from the turbine. The combustor includes an end cover coupled to an outer casing and a bundled tube fuel nozzle assembly disposed within the outer casing and coupled to the end cover, the bundled tube fuel nozzle assembly being located upstream of a combustion zone. The bundled tube fuel nozzle assembly includes a fuel plenum body including a forward plate extending in a radial direction, an aft plate axially spaced from the forward plate and extending in a radial direction, an outer sleeve extending in an axial direction between the forward plate and the aft plate, and a fuel plenum defined by the forward plate, the aft plate and the outer sleeve. A fuel conduit is in fluid communication with the fuel plenum. The fuel nozzle assembly also includes a cap plate axially spaced from the aft plate with an air plenum defined between the aft plate and the cap plate, the cap plate including a hot surface facing the combustion zone. The fuel nozzle assembly further includes a plurality of mixing tubes extending through the fuel plenum body. Each of the mixing tubes includes an air inlet, an outlet downstream of the aft plate, and a fuel port in fluid communication with the fuel plenum. The fuel nozzle assembly also includes a narrow-band acoustic damper located within the air plenum. 
     Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the of various embodiments, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which: 
         FIG. 1  is a functional block diagram of an exemplary gas turbine that may incorporate various embodiments of the present disclosure; 
         FIG. 2  is a simplified longitudinal section view of an exemplary combustor as may incorporate various embodiments of the present disclosure; 
         FIG. 3  is a longitudinal section view of a portion of an exemplary bundled tube type fuel nozzle assembly as shown in  FIG. 2 , according to at least one embodiment of the present disclosure; 
         FIG. 4  is a perspective view of a portion of an exemplary fuel nozzle assembly, according to at least one embodiment of the present disclosure; 
         FIG. 5  is a longitudinal section view of the portion of the exemplary fuel nozzle assembly of  FIG. 4 , according to at least one embodiment of the present disclosure; 
         FIG. 6  is an end view of an exemplary bundled tube type fuel nozzle assembly, according to at least one embodiment of the present disclosure; 
         FIG. 7  is an end view of an exemplary bundled tube type fuel nozzle assembly, according to at least one embodiment of the present disclosure; 
         FIG. 8  is an end view of an exemplary bundled tube type fuel nozzle assembly, according to at least one embodiment of the present disclosure; 
         FIG. 9  is an end view of an exemplary fuel nozzle assembly, according to at least one embodiment of the present disclosure; 
         FIG. 10  is an end view of an exemplary fuel nozzle assembly, according to at least one embodiment of the present disclosure; and 
         FIG. 11  is a graph of an exemplary wave pattern and resultant wave according to at least one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to present embodiments of the disclosure, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the disclosure. 
     As used herein, the terms “first,” “second,” and “third” may be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components. The terms “upstream” and “downstream” refer to the relative direction with respect to fluid flow in a fluid pathway. For example, “upstream” refers to the direction from which the fluid flows, and “downstream” refers to the direction to which the fluid flows. The term “radially” refers to the relative direction that is substantially perpendicular to an axial centerline of a particular component, the term “axially” refers to the relative direction that is substantially parallel and/or coaxially aligned to an axial centerline of a particular component, and the term “circumferentially” refers to the relative direction that extends around the axial centerline of a particular component. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Each example is provided by way of explanation, not limitation. In fact, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present disclosure covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     Although exemplary embodiments of the present disclosure will be described generally in the context of a fuel nozzle assembly for a land based power generating gas turbine combustor for purposes of illustration, one of ordinary skill in the art will readily appreciate that embodiments of the present disclosure may be applied to any style or type of combustor for a turbomachine and are not limited to combustors or combustion systems for land based power generating gas turbines unless specifically recited. 
     Referring now to the drawings,  FIG. 1  illustrates a schematic diagram of an exemplary gas turbine  10 . The gas turbine  10  generally includes an inlet section  12 , a compressor  14  disposed downstream of the inlet section  12 , at least one combustor  16  disposed downstream of the compressor  14 , a turbine  18  disposed downstream of the combustor  16  and an exhaust section  20  disposed downstream of the turbine  18 . Additionally, the gas turbine  10  may include one or more shafts  22  that couple the compressor  14  to the turbine  18 . 
     During operation, air  24  flows through the inlet section  12  and into the compressor  14  where the air  24  is progressively compressed, thus providing compressed air  26  to the combustor  16 . At least a portion of the compressed air  26  is mixed with a fuel  28  within the combustor  16  and burned to produce combustion gases  30 . The combustion gases  30  flow from the combustor  16  into the turbine  18 , wherein energy (kinetic and/or thermal) is transferred from the combustion gases  30  to rotor blades (not shown), thus causing shaft  22  to rotate. The mechanical rotational energy may then be used for various purposes such as to power the compressor  14  and/or to generate electricity. The combustion gases  30  exiting the turbine  18  may then be exhausted from the gas turbine  10  via the exhaust section  20 . 
     As shown in  FIG. 2 , the combustor  16  may be at least partially surrounded by an outer casing  32  such as a compressor discharge casing. The outer casing  32  may at least partially define a high pressure plenum  34  that at least partially surrounds various components of the combustor  16 . The high pressure plenum  34  may be in fluid communication with the compressor  14  ( FIG. 1 ) so as to receive compressed air  26  therefrom. An end cover  36  may be coupled to the outer casing  32 . In particular embodiments, the outer casing  32  and the end cover  36  may at least partially define a head end volume or portion  38  of the combustor  16 . 
     In particular embodiments, the head end portion  38  is in fluid communication with the high pressure plenum  34  and/or the compressor  14 . One or more liners or ducts  40  may at least partially define a combustion chamber or zone  42  for combusting the fuel-air mixture and/or may at least partially define a hot gas path  44  through the combustor  16  for directing the combustion gases  30  towards an inlet to the turbine  18 . 
     In various embodiments, the combustor  16  includes at least one bundled tube type fuel nozzle assembly  100 . As shown in  FIG. 2 , the fuel nozzle assembly  100  is disposed within the outer casing  32  downstream from and/or axially spaced from the end cover  36  with respect to axial centerline  46  of the combustor  16  and upstream from the combustion chamber  42 . In particular embodiments, the fuel nozzle assembly  100  is in fluid communication with a fuel supply  48  via one or more fluid conduits  50 . In particular embodiments, the fluid conduit(s)  50  may be fluidly coupled and/or connected at one end to the end cover  36 . It should be understood that the fuel nozzle assemblies  100  and/or the fluid conduit(s) may be mounted to structures other than the end cover  36  (e.g., the outer casing  32 ). 
       FIG. 3  provides a longitudinal section view of a portion of an exemplary fuel nozzle assembly  100  as shown in  FIG. 2 , according to at least one embodiment of the present disclosure. As will be discussed in more detail below, various embodiments of the combustor  16  may include different arrangements of the fuel nozzle assembly  100  and is not limited to any particular arrangement unless otherwise specified. For example, in particular configurations as illustrated in  FIGS. 2 and 4 , the fuel nozzle assembly  100  includes multiple wedge shaped fuel nozzle segments annularly arranged about centerline  46 . In some embodiments, e.g., as illustrated in  FIGS. 4 and 8 , the fuel nozzle assembly  100  may further include a circular shaped fuel nozzle segment centered on the centerline  46 . In particular embodiments, the fuel nozzle assembly  100  may form an annulus or fuel nozzle passage about a center fuel nozzle  50 . Alternately, the fuel nozzle segments may be arranged in virtually any shape, such as circular (shown in  FIG. 7 ), triangular, square, or oval, and may be arranged in various geometries in the fuel nozzle assembly  100 . 
     In at least one embodiment, as shown in  FIG. 3 , the fuel nozzle assembly  100  and/or each fuel nozzle segment includes a fuel plenum body  102  having a forward or upstream plate  104 , an aft plate  106  axially spaced from the forward plate  104  and an outer band or sleeve  108  that extends axially between the forward plate  104  and the aft plate  106 . A fuel plenum  110  is defined within the fuel plenum body  102 . In particular embodiments, the forward plate  104 , the aft plate  106  and the outer sleeve  108  may at least partially define the fuel plenum  110 . In particular embodiments, the fluid conduit  50  may extend through the forward plate  104  to provide fuel to the fuel plenum  110 . In various embodiments, the fuel nozzle assembly  100  includes a cap plate  112  axially spaced from the aft plate  106 . An air plenum  111  is defined between the aft plate  106  and cap plate  112 . A hot side  114  of the cap plate  112  is generally disposed adjacent or proximate to the combustion chamber  42 . 
     As shown in  FIG. 3 , the fuel nozzle assembly  100  includes a tube bundle  116  comprising a plurality of tubes  118 . Each tube  118  extends through the forward plate  104 , the fuel plenum  110 , the aft plate  106 , the air plenum  111 , and the cap plate  112 . The tubes  118  are fixedly connected to and/or form a seal against the aft plate  106 . For example, the tubes  118  may be welded, brazed or otherwise connected to the aft plate  106 . Each tube  118  includes an air inlet  120  defined at an upstream end  122  of each respective tube  118  and an outlet  124  defined at a downstream end  126  of each respective tube  118 . The downstream end portion  126  extends through a corresponding tube opening in the cap plate  112 , the tube opening being sized to define a circumferentially continuous radial gap between an outer surface of the tube  118  and an inner surface of the corresponding tube opening. The circumferentially continuous radial gap permits compressed air  26  to flow around the tube from the air plenum  111  towards the combustion chamber  42 , thereby cooling the downstream end portions  126  of the tubes  118 . 
     Each tube  118  defines a respective premix flow passage  128  through the fuel nozzle assembly  100 , for premixing the fuel  28  ( FIG. 1 ) with the compressed air  26  ( FIG. 1 ) within mixing tube  118  before it is directed into a combustion zone  42  defined downstream from the fuel nozzle assembly  100 . In particular embodiments, one or more tubes  118  of the plurality of tubes  118  is in fluid communication with the fuel plenum  110  via one or more fuel ports  130  defined within the respective tube(s)  118 , which openings  130  may be defined in a wall  138  of the mixing tube  118 . 
     As described above, the downstream end portions  126  of tubes  118  are not attached at the cap plate  112 . During operation, combustion dynamics may cause oscillations of the various parts of the combustor  16 , which in turn may impact one another. For example, the cantilevered tubes  118 , particularly the downstream end portion  126  of each tube  118 , may move radially with respect to a centerline of each respective tube  118  resulting in contact between the tubes  118  and the corresponding tube openings in the cap plate  112 . As another example, the fuel nozzle assembly  100  may impact the liner  40  of the combustor  16 . As yet another example, the fuel nozzle assembly  100  or other parts within the head end  38  may impact the outer casing  32  and/or the end cover  36 . Such impacts may cause undesirable wear on the various parts due to the physical force of the impact and/or increased thermal loading on upstream components of the combustor  16 . For example, the combustion gases  30  ( FIG. 1 ) may create an elevated temperature in the downstream end portion  126  of each tube  118  such that impact of the tubes  118  on the cap plate  112  may increase thermal loading of the cap plate  112 . 
     In various embodiments of the present disclosure, as shown in  FIG. 3 , the fuel nozzle assembly  100  includes one or more narrow-band acoustic dampers  200  disposed in air plenum  111  between the aft plate  106  and the cap plate  112 . In particular exemplary embodiments, the narrow-band acoustic dampers  200  may be provided as quarter-wave tubes  200 . In some embodiments, for example as illustrated in  FIG. 3 , the quarter-wave tube  200  may extend between an entrance  210  at an aft end  202  of the quarter-wave tube  200  and a reflective plane  220  at a forward end  204  of the quarter-wave tube  200  over a distance L ( FIG. 5 ). The length L of the quarter-wave tube  200  may be defined by the distance between the entrance  210  and the reflective plane  220 . In some embodiments, the quarter-wave tube  200  may extend generally along the axial direction. As such, the quarter-wave tube  200  may be generally aligned with the flow of fuel  28  and/or compressed air  26  through the fuel nozzle assembly  100 . In some embodiments, the quarter-wave tube  200  defines an internal volume  208  between the entrance  210  and the reflective plane  220  and bounded by wall(s)  206 . 
     In some embodiments, e.g., as illustrated in  FIG. 3 , the quarter-wave tube  200  may extend through the cap plate  112 . In exemplary embodiments, the quarter-wave tube  200  may extend through the cap plate  112  such that the entrance  210  of the quarter-wave tube  200  is flush with the hot surface  114  of the cap plate  112 . 
     The quarter-wave tube  200  may be tuned to dampen a particular frequency based on the internal volume and length of the quarter-wave tube  200  and, in some embodiments, purge flow through purge holes  230  ( FIG. 4 ). For example, the quarter-wave tube  200  may be tuned based on the relationship between the length L of the quarter-wave tube  200  and the wavelength λ, of the oscillation to be damped. The distance L between the entrance  210  and the reflective plane  220  may be around one quarter of the target wavelength (λ/4), such that an incident wave  300  entering the quarter-wave tube  200  at the entrance  210  travels from the entrance  210  to the reflective plane  220  over a distance of λ/4, and the reflected wave  400  travels from reflective plane  220  to entrance  210  over another distance of λ/4 for a total travel distance of λ/2. Thus, as illustrated in  FIG. 9 , the reflected wave  400  is shifted a total of λ/2 with respect to the incident wave  300 . In other words, the reflected wave  400  is one hundred eighty degrees (180°) or pi radians (π rad) out of phase with the incident wave  300 , effectively cancelling out the incident wave  300  (e.g., where the resultant wave from combining the incident wave  300  and the reflected wave  400  has an amplitude of about zero) and thus mitigating vibration at the selected frequency. 
     Such quarter-wave tubes  200  may be tuned to dampen any particular range of frequencies as needed. In one possible, non-limiting example, the quarter-wave tube  200  may be tuned to dampen a frequency range from about nine hundred Hertz (900 Hz) to about eleven hundred hertz (or 1.1 kHz). As used herein, “about” generally means within approximately ten percent (10%) more or less than a stated value. For example, about 1.1 kHz could include from 990 Hz to 1210 Hz. 
     As another example, an amplitude of about zero means that the amplitude of the resultant wave is significantly smaller than the incident wave  300 , such that it may be negligible as compared to the amplitude of incident wave  300 . In some embodiments, the amplitude of the resultant wave may be reduced sufficiently to avoid or minimize harmonic resonance in the combustor  16 , i.e., the narrow-band acoustic dampers  200  may be tuned to dampen a resonant frequency of the combustor  16 . For example, the length L of the quarter-wave tube  200  may correspond to one-quarter of the wavelength of the resonant frequency of the combustor  16  such that the quarter-wave tube  200  is tuned to dampen the resonant frequency. As such, the quarter-wave tube  200  may serve to avoid or minimize oscillations such as described above. 
     During operation, pressure waves  300  may form in the combustion chamber  42 , as shown in  FIG. 3 . Such waves  300  may propagate circumferentially around the combustor  16 , e.g., in a vertical direction in the view provided in  FIG. 3 . The quarter-wave tube  200  may be disposed tangential to the direction of travel of the wave  300 , and in some embodiments, may be orthogonal to the direction of travel of the wave  300 . When a pressure wave  300  travelling around the combustor  16  encounters the quarter-wave tube  200 , a portion of the wave  300  is diverted into the quarter-wave tube  200 , travels down quarter-wave tube  200 , and impedes on the reflective plane  220 , as described above, such that the frequency of the reflected wave  400  returning from the reflective plane  220  of the quarter-wave tube  200  is shifted as shown in  FIG. 9 . As a result, the pressure wave  300  may be damped by the quarter-wave tube  200 . 
     In some embodiments, for example as illustrated in  FIGS. 3 &amp; 5 , the entrance  210  of the quarter-wave tube  200  may be open and completely unobstructed. For example, no perforated plate or other flow control device may be provided in or near entrance  210  of the quarter-wave tube  200 . In such embodiments, the quarter-wave tube  200  is completely open to the combustion zone  42  to effectively damp the target frequency of combustion dynamics. Additionally, in at least one exemplary embodiment, the entrance  210  of the quarter-wave tube  200  permits unobstructed flow between the internal volume  208  and the combustion zone  42 . Further, in such embodiments, the quarter-wave tube  200  may be located upstream of the combustion zone  42  which may avoid or minimize exposure of the quarter-wave tube  200  to excessive thermal load. 
     As may be seen for example in  FIG. 3 , some embodiments include the quarter-wave tube  200  located on a “bald spot” of the cap plate  112  that is radially aligned with the fuel conduit  50  and axially aft of the fuel conduit  50 . Such location may be referred to as a “bald spot” in the cap plate  112  in that it is generally unoccupied by the mixing tubes  118 . In some embodiments, for example as shown in  FIGS. 3 and 5 , the quarter-wave tube  200  may be cantilevered from the cap plate  112 . In some embodiments, the quarter-wave tube  200  may be made from one-piece bar stock, which may reduce the mass overhung by the cantilevered construction. In other embodiments, the quarter-wave tube  200  may be integrally formed with cap plate  112 , such as by manufacturing both parts as one piece, e.g., using additive manufacturing techniques such as direct metal laser melting, selective laser sintering, or other suitable techniques. It is also possible within the scope of the present subject matter to form the quarter-wave tube  200  and attach it to the cap plate  112  by other suitable methods, such as welding or brazing a cast or fabricated quarter-wave tube  200  to the cap plate  112 . 
       FIG. 4  is a partial perspective view according to at least one exemplary embodiment of the cap plate  112  and at least a portion of the outer shroud  108 .  FIG. 5  is a section view of the cap plate  112 , the partial outer shroud  108 , and the quarter-wave tube  200  of  FIG. 4 . Other portions of the fuel nozzle assembly  100 , such as the mixing tubes  118 , are omitted for clarity of illustration in  FIGS. 4 and 5  for illustrative purposes only. As may be seen for example in  FIG. 4 , in some embodiments, the forward end  204  of the quarter-wave tube  200  may be provided with small purge holes  230  through the plate defining the reflective plane  220 . Purge holes  230  are defined in the forward end  204  of the quarter wave tube  200  and are configured to permit air from the air plenum  111  to flow through the quarter-wave tube  200 . As such, the purge holes  230  may provide a purge flow through the quarter-wave tube  200  from the forward end  204  to the aft end  202 . Additionally, the purge holes  230  may serve to cool the quarter-wave tube  200 . While shown as being located opposite the opening  210  of the quarter-wave tube  200 , it is contemplated herein that the purge holes  230  may be located in the wall  206  defining the tube  200 , additional to, or instead of, the plate defining the reflective plane  220 . 
     In some exemplary embodiments, the fuel nozzle assembly may include wedge-shaped segments arranged radially around the combustor centerline  46 , which may or may not include a central circular fuel nozzle segment. As illustrated in  FIG. 4 , five wedge-shaped segments may be arranged radially around a central circular segment. In this embodiment, five quarter-wave tubes  200  may be provided. That is, each wedge-shaped segment may have a quarter-wave tube  200  provided therein, e.g., in a location aligned with a fuel conduit  50  (not shown in  FIG. 4 , see, e.g.,  FIG. 3 ) associated with each respective wedge-shaped segment. Alternately, the number of quarter-wave tubes  200  may be greater than or less than the number of fuel nozzle segments. 
       FIGS. 6, 7, and 8  provide various end views of one or more exemplary fuel nozzle assemblies  100  looking upstream from the combustion chamber  42 . In some exemplary embodiments, e.g., as illustrated in  FIG. 6 , fuel nozzle assembly  100  may consist essentially of a single segment provided with the tubes  118  radially arranged across the entire cap plate  112 . As shown in  FIG. 6 , the outlets  124  appear as circles radially outward of the axial centerline of the nozzle assembly  100 . Also illustrated in  FIG. 6 , a single quarter-wave tube  200  may be provided, e.g., centered on centerline  46  of the combustor  16 . 
     In some exemplary embodiments, e.g., as illustrated in  FIG. 7 , the fuel nozzle segments be arranged as six fuel nozzle segments surrounding a single fuel nozzle segment, wherein all of the segments are circular or rounded. In some embodiments, such as the exemplary embodiment illustrated in  FIG. 7 , each segment may have a quarter wave tube  200  associated therewith.  FIG. 8  illustrates yet another exemplary embodiment including a combination of wedge-shaped and circular fuel nozzle segments. In some embodiments, for example as illustrated in  FIG. 8 , a single quarter-wave tube  200  may be provided in only one of the several segments. 
     One of ordinary skill in the art should understand that the present invention is not limited to any particular geometry of individual nozzles or nozzle arrangements or number of fuel nozzle segments, unless specifically recited. Additionally, various combinations of features from the illustrated example embodiments shown and described herein may be provided within the scope of the present subject matter. For example, different combinations of fuel segment shapes and the quarter-wave tubes  200  may be provided, e.g., some or all of the wedge-shaped segments of  FIG. 8  may have the quarter-wave tubes  200  such as is illustrated in  FIG. 4 . 
     In the illustrated exemplary embodiments, the quarter-wave tube  200  is cylindrical with a single continuous side wall  206  extending between the entrance  210  and a plate defining the reflective plane  220 . Additionally, in some embodiments, the cross-sectional shape of the quarter-wave tube  200  may vary, e.g., the quarter-wave tube  200  could be hexagonal, rectangular, oblong, annular, or any other suitable shape. For example, in some embodiments wherein the quarter-wave tube  200  is annular, the annular quarter-wave tube may extend around the fuel nozzle assembly  100  across multiple segments thereof. 
     Finally, while reference has been throughout the present disclosure to the application of quarter-wave tubes in bundled tube fuel nozzle assemblies, it should be understood that the present quarter-wave tubes may be similarly employed on cap plates  112  supporting other types of fuel nozzles. For example, as illustrated in  FIGS. 9 and 10 , the fuel nozzles may be swozzles (swirled nozzles)  100 . In this embodiment, the quarter-wave tubes  200  may be mounted between the fuel nozzles  100 , rather than being incorporated within the fuel nozzles, as described above. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.