Patent Publication Number: US-2004050058-A1

Title: Swirler assembly with improved vibrational response

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001] (Not Applicable)  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
       [0002] (Not Applicable)  
       FIELD OF THE INVENTION  
       [0003] The present invention relates in general to gas turbines and, more particularly, to swirler assemblies.  
       BACKGROUND OF THE INVENTION  
       [0004] Gas turbines generally comprise the following elements: a compressor for compressing air; a combustor for producing a hot gas by burning fuel in the presence of the compressed air produced by the compressor; and a turbine for expanding the hot gas produced by the combustor.  
       [0005] As shown in FIG. 1, an example of a prior art gas turbine combustor  10  comprises a nozzle housing  12  having a nozzle housing base  14 . A diffusion fuel pilot nozzle  16 , having a pilot fuel injection port  18 , extends through nozzle housing  12  and is attached to nozzle housing base  14 . In the shown configuration, main fuel nozzles  20 , each having at least one main fuel injection port  22 , extend substantially parallel to pilot nozzle  16  through nozzle housing  12  and are attached to nozzle housing base  14 . Fuel inlets  24  provide fuel  26  to main fuel nozzles  20 . A main combustion zone  28  is formed within a liner  30 . A pilot cone  32 , having a diverged end  34 , projects from the vicinity of pilot fuel injection port  18  of pilot nozzle  16 . Diverged end  34  is downstream of main fuel swirlers  36 . A pilot flame zone  38  is formed within pilot cone  32  adjacent to main combustion zone  28 .  
       [0006] Compressed air  40  from compressor  42  flows between support ribs  44  through main fuel swirlers  36 . Each main fuel swirler  36  is substantially parallel to pilot nozzle  16  and adjacent to main combustion zone  28 . Within each main fuel swirler  36 , a plurality of swirler vanes  46  generate air turbulence upstream of main fuel injection ports  22  to mix compressed air  40  with fuel  26  to form a fuel/air mixture  48 . Fuel/air mixture  48  is carried into main combustion zone  28  where it combusts. Compressed air  50  enters pilot flame zone  38  through a set of stationary turning vanes  52  located inside pilot swirler  54 . Compressed air  50  mixes with pilot fuel  56  within pilot cone  32  and is carried into pilot flame zone  38  where it combusts.  
       [0007]FIG. 2 shows a detailed view of an exemplary prior art fuel swirler  36 . As shown in FIG. 2, fuel swirler  36  is substantially cylindrical in shape, having a flared inlet end  58  and a tapered outlet end  60 . A plurality of swirler vanes  46  are disposed circumferentially around the inner perimeter  62  of fuel swirler  36  proximate flared end  58 . In the shown configuration, fuel swirler  36  surrounds main fuel nozzle  20  proximate main fuel injection ports  22 . Fuel swirler  36  is positioned with swirler vanes  46  upstream of main fuel injection ports  22  and tapered end  60  adjacent to main combustion zone  28 . Flared inlet end  58  is adapted to receive compressed air  40  and channel it into fuel swirler  36 . Tapered outlet end  60  is adapted to fit into sleeve  64 . Swirler vanes  46  are attached to a hub  66 . Hub  66  surrounds main fuel nozzle  20 .  
       [0008]FIG. 3 shows an upstream view of combustor  10 . Pilot nozzle  16  is surrounded by pilot swirler  54 . Pilot swirler  54  has a plurality of stationary turning vanes  52 . Pilot nozzle  16  is surrounded by a plurality of main fuel nozzles  20 . A main fuel swirler  36  surrounds each main fuel nozzle  20 . Each main fuel swirler  36  has a plurality of swirler vanes  46 . The diverged end  34  of pilot cone  32  forms an annulus  68  with liner  30 . Main fuel swirlers  36  are upstream of diverged end  34 . Fuel/air mixture  48  flows through annulus  68  (out of the page) into main combustion zone  28  (not shown in FIG. 3).  
       [0009] Fuel swirler  36  is attached to liner  30  via attachments  70  and swirler base  72 . With respect to the latter manner of attachment, the distal end of sleeve  74  is adjacent to the swirler base plate  72  as shown in FIG. 2. The distal end of sleeve  74  and the base plate  72  typically do not come into contact and are actually spaced approximately 10 mils apart. FIG. 3 shows a circular array of six swirlers, but other quantities, such as a series of eight swirlers, can be employed.  
       [0010] The other manner of attaching the swirler  36  to liner  30  is by way of attachments  70 . In initial designs, attachments  70  comprised dual straight pins, each pin being welded at one end to liner  30  and at the other end to the swirler  36 . This design, however, often fails due to fatigue induced cracking of the pins at the support casing. One prior design revision includes replacing the straight pin attachments with hourglass-shaped pins (as shown) to provide improved weld areas on both the swirler  36  and the liner  30 . However, this design also suffers from fatigue-related failures, primarily occurring at the weld joint between the hourglass-shaped pin attachments  70  and the swirler  36 .  
       [0011] The fatigue failures stem from a swirler&#39;s exposure to vibrational forces generated during combustor operation. Combustion dynamics typically range from approximately 110-150 Hz, although variations outside this range are possible depending on the system design. Prior swirlers, when only adjacent to or abutting the base plate, generally had a natural frequency of approximately 145 Hz, falling within the typical vibrational range experienced during combustion dynamics. Consequently, when a swirler is subjected to such forces, the swirler will resonate, and repeated resonance of the swirler ultimately fatigues the weld joints of the support pins.  
       [0012] Thus, high cycle fatigue failures are a recurring problem with respect to swirlers and other turbo machinery components. The problem has been exacerbated by combustion design changes to reduce emissions and increase efficiency. These design changes have increased the severity of the combustion dynamics, requiring more robust swirler assemblies. Therefore, there is a continuing need for a swirler assembly that can avoid vibration-induced resonance and that can further enhance the inherent damping characteristics of the swirler to constrain any vibratory motion.  
       SUMMARY OF THE INVENTION  
       [0013] It is an object of the invention to provide a swirler assembly that is adapted to tolerate the severity of the dynamics of combustors designed for reduced emissions and greater efficiencies.  
       [0014] It is another object of the invention to provide a more robust swirler assembly that can accommodate changes due to thermal expansion.  
       [0015] These and other objects of the invention are achieved by a swirler assembly adapted to interface with a supporting base plate so as to raise the resonant frequency of the swirler assembly above the vibrational range of the combustion environment and to increase the damping of the swirler response to the combustion dynamics. The present invention applies particularly to a swirler assembly that includes a swirler, a generally cylindrical swirler sleeve and a plate. The swirler has an inlet and an outlet end. The sleeve has a proximal end and a distal end. The outlet end of the swirler extends into the sleeve through the proximal end. The plate has an opening that, due to manufacturing processes, is elongated into an elliptical shape.  
       [0016] According one aspect of the invention, the distal end of the sleeve extends into the plate opening and contacts the inner ring-like surface of the plate opening at least partially around its periphery so that portions of the sleeve contact the surface along the minor axis of the elliptical opening and transition to a clearance along the major axis. The contact areas between the sleeve and the plate stiffen the interface and increase the natural frequency of the swirler. For example, the natural frequency can be increased to 700 Hz, well above the operational combustion dynamics, in the neighborhood of 110-150 Hz. The contact areas also increase frictional forces to damp the vibrational response of the swirler.  
       [0017] The sleeve preferably tapers from a larger diameter outside the plate opening down to the diameter of the portion that extends into, and preferably through, the opening. The shape of the taper preferably substantially follows the profile of the plate into the opening. The matching profile increases the areas of contact between the sleeve and the plate, increasing the stiffness and the surface area for generating frictional damping forces.  
       [0018] The clearance in the region of the major axis of the elliptical plate opening accommodates thermal stresses that can arise from expansion of the sleeve in the high temperature environment of the combustor. Thus, the swirler assembly according to aspects of the invention avoids resonance and damps vibrational responses while providing for thermal expansion.  
       [0019] In another aspect, a turbo machinery assembly includes a turbo machinery component and a plate having an opening. The opening defines an inner surface. The turbo machinery component has a first end and a second end. The second end of the turbo machinery component has an outer profile that substantially follows the inner surface and substantially adjacent to at least a portion of the plate surrounding the opening. The outer profile contacts a portion of the inner surface while providing clearance in other regions along the opening periphery. The turbo machinery assembly has a natural frequency outside of the range of operational vibrational forces and further has increased damping capability.  
       [0020] In still another aspect, the present invention is directed to a method for altering the natural frequency and enhancing the damping characteristics of a swirler. The method includes the steps of: providing a plate having an opening, which defines an inner surface; providing a swirler having an inlet end and an outlet end; providing a sleeve having a first end and a second end, the second end having an outer surface substantially conforming to the inner annular surface and to a portion of the plate surrounding the opening; placing the outlet end of the swirler into a first end of a sleeve; and placing the second end of the sleeve into the opening such that the second end of the sleeve substantially contacts a portion of the inner surface of the opening and adjacent to the opening while providing clearance in other regions of the opening periphery.  
       [0021] In a further aspect of the invention, the stabilization provided by the sleeve engagement with the base plate can permit the use of a single pin for supporting the swirler from the surrounding shell. The single pin can be cast, providing further manufacturing savings.  
       [0022] Thus, the invention provides a swirler assembly that can more readily endure combustion dynamics and high temperature conditions while presenting opportunities for manufacturing economies.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0023]FIG. 1 is a cross-sectional view of a prior art gas turbine combustor.  
     [0024]FIG. 2 is a cross-sectional view of a prior art main fuel swirler.  
     [0025]FIG. 3 is an upstream view of a prior art gas turbine combustor.  
     [0026]FIG. 4 is a cross-sectional view a preferred embodiment of a swirler according to the present invention.  
     [0027]FIG. 5 is close-up view of FIG. 4, showing the engagement of the swirler and the base plate according to the present invention.  
     [0028]FIG. 6 is a sectional view taken along section line  6 - 6  in FIG. 5, showing the fit of the swirler sleeve into an elliptical opening of the base plate, exaggerated for clarity of illustration. 
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION  
     [0029] The present invention provides a more vibrationally tolerant swirler assembly and a method for making such a swirler assembly that has a natural frequency outside of the range of combustion-generated vibrational forces to preventing swirler resonance. In addition, the swirler according to aspects of the invention enhances the damping capability of the swirler assembly so as to subdue any vibrational forces acting on the system. The invention has application to various turbo machinery components. Features of the invention are, however, described with respect to fuel swirlers for use in a turbine combustor.  
     [0030] An embodiment of the swirler assembly  80  of the present invention is illustrated in FIGS. 4 and 5. In FIG. 4, an exemplary swirler  82  is shown, but the structure is not limited to swirlers and can actually be any turbo machinery component having first and second ends. Moreover, the swirler is not limited to any particular configuration, but it will generally have an inlet end  84  and an outlet end  86 . Preferably, the swirler  82  is generally cylindrical in shape, but the swirler may be any shape, such as rectangular or polygonal, as dictated by design considerations and performance requirements. In the shown embodiment, the swirler tapers from its flared inlet end  84  to its outlet end  86 . Like the other features of the swirler, the outer surface does not have to be tapered. For example, the swirler may have a generally uniform cross-sectional profile along its length.  
     [0031] The swirler  82  is supported by one or more pins  88 , which can be welded to the swirler  82  at one end and welded or otherwise secured to a combustor outer liner (not shown, see FIG. 5). The pins  88  can be hour-glass shaped in profile to provide expanded welding footprints, as is known in the art.  
     [0032] Preferably, the swirler assembly  80  includes a sleeve  90  having a proximal end  92  and distal end  94 . The sleeve  90  is preferably cylindrical in shape. However, the sleeve  90  need not be limited to a cylindrical configuration. The sleeve  90  can be made of stainless steel.  
     [0033] The outlet end  86  of the swirler  82  is positioned so as to extend into the proximal end  92  of the sleeve  90 . Once the swirler  82  is positioned inside of the sleeve  90 , the sleeve  90  and swirler  82  are welded  96  together, preferably peripherally or circumferentially in the case of a cylindrical swirler. The sleeve  90  may be a single cast component or it may be divided into first and second halves (not shown), with first half including a proximal end and a first joining end, and second half including a second joining end and a distal end, the joining ends abutted and welded circumferentially.  
     [0034] According to aspects of the invention, the sleeve decreases in diameter (or periphery) from its proximal end  92  to its distal end  94 . Beginning at its proximal end  92 , the sleeve  90  generally tapers until an area of greater thickness  96  is reached. In this area, the outer surface of the sleeve is substantially horizontal but then a second, sharper taper begins  98 . This tapered  98  region can be curved instead of being linearly tapered. Eventually the taper or curve  98  transitions into a second substantially horizontal portion  99  which continues until the extreme distal end  94  of the sleeve  90  is reached.  
     [0035] Referring to FIG. 5, a base plate  100  supports the swirler assembly  80  and attaches the swirler assembly  80  to the outer liner  102 . Commonly, the plate is made of an alloy, for example, Hastelloy X. The plate  100  is generally disposed between the swirler  82  and the combustion chamber  104 . The plate  100  can be anchored to the outer liner  102  by welds  106 . The plate  100  may be a single component such as a flat plate, or it may be a localized area of a larger structure.  
     [0036] An opening  108  is provided in the plate. The opening  108  may be a through hole or it may be, as shown, a product of bends in the plate  100 . Typically, the plate  100  is shaped from a metal sheet and the openings are drawn out from the sheet. The plate is welded in place to the liner. The manufacturing processes often result in an elongation of the plate opening  108  to a generally vertical elliptical shape, as discussed more fully below.  
     [0037] The opening  108  is defined by a ring-like inner surface  110  that is connected to the generally vertical face  112  of the plate  100  by a convex fillet region  114 . As used in this specification, the inner surface  110  is referred to as annular to describe the generally ring-like shaped of the surface. This terminology is not intended to connote that the surface is circular, when the shaped is more generally elliptical due to the elongation that occurs during manufacture.  
     [0038] According to the invention, the distal end  94  of the sleeve  90  extends into the opening  108 , and preferably extends through and past the annular surface  110  of the opening  108 . The second taper  98  is shaped to substantially follow the convex fillet  114  and the second substantially horizontal portion  99  substantially follows the inner annular surface  110  of the opening  108 .  
     [0039]FIG. 6 shows a cross section of the swirler sleeve distal end  94  as inserted in the opening  108  of the base plate  100 . The sleeve  90  engages the inner surface  110  of the base plate opening  108  along the minor axis  116  of the ellipse and transitions to a clearance fit  118  at along the major axis  120 . In this example, the major axis  120  of the elliptical opening  108  extends substantially through the top and bottom of the opening while the minor axis extends across the left and right sides. This orientation corresponds to the general tendency of the base plate opening  108  to elongate vertically during manufacture. The orientation can of course deviate from this example.  
     [0040] The degree of elongation and the percentage of the inner surface  110  that is contacted can vary. With tolerances of the preferably circular sleeve to an average of the elliptical dimensions, the percentage of surface contact is preferably around 70%.  
     [0041] The clearance  118  in the region of the elliptical major axis  120  is preferably in the range of 0-3 mils. The resonant frequency is directly related to the percentage of contact and inversely related the degree of clearance. Further, the clearance region  118  allows for thermal expansion of the sleeve  90 , thus reducing thermal stresses in the high temperature environment of a turbine combustor.  
     [0042] Referring again to FIG. 5, the area of contact not only serves to increase the resonant frequency outside the range of combustion dynamics, but also generates frictional forces that damp the vibrational response of the swirler. The areas of friction are further increased by the taper  98  of the sleeve  90  that substantially mimics the convex fillet  114  of the plate  100 . In the regions of contact of the inner surface  110 , there can be a corresponding contact along the convex fillet region  114 .  
     [0043] With the increase stability provided by the nested sleeve, the swirler can be supported by a single pin  88 , located generally centrally, instead of a pair of spaced pins. Moreover, the pins  88  can be cast as hollow members with the rest of the cast swirler, and increased in diameter to maintain proper strength in view of its hollow interior (not shown).  
     [0044] The pin  88 , whether a single or a pair can be reinforced at its junction with the swirler main body  82 . One approach is to thicken the body in the region of the pin.  
     [0045] The preferred embodiment of the swirler assembly  80  employs a sleeve  90 . Of course, a sleeve  90  may not be necessary in the assembly so long as the outlet end  86  of the swirler  82  or other turbo machinery component substantially follows the opening  108  in the plate  100  and substantially adjacent to a portion of the plate surrounding the opening to provide a hybrid contact and clearance fit with the surfaces in and around the opening.  
     [0046] The present invention is also directed to a method for altering the natural frequency and enhancing the damping characteristics of a swirler. Steps include, in no particular order, providing a plate  100  having an opening  108  that defines an inner annular surface  110 ; providing a swirler  82  having inlet  84  and outlet  86  ends; and providing a sleeve  90  having first  92  and second  94  ends. The second end  94  of the sleeve  90  has an outer surface substantially conforming to the inner annular surface  110  of the opening  108  and also to a portion of the plate  100  surrounding the opening  214  such that contact occurs in certain regions while other regions are spaced. The outlet end  86  of the swirler  82  is placed into the first end  92  of the sleeve  90 . Additionally, the swirler  82  may be secured to the sleeve  90  by, for example, welding. The second end  94  of the sleeve  90  is substantially matingly fitted into and at least partially beyond the inner annular surface  110  of the opening  108  and substantially adjacent to a portion of the plate  100  surrounding the opening  108 .  
     [0047] In operation, the swirler assembly  80  described above has a natural frequency out of the range of commonly experienced combustion dynamic vibrational forces. As noted earlier, combustion dynamics typically range from approximately 110 Hz to 150 Hz. Tests on a swirler assembly according to principles of the present invention reveal a natural frequency as high as approximately 700 Hz. The increased natural frequency can vary as a function of the percent of the swirler sleeve in contact with the inner surface of the base plate opening and the amount of clearance in the areas of separation, but the resonant frequency is nevertheless well above the operational frequency range of the combustion environment. Accordingly, the combustion dynamic vibration will not cause the swirler to resonate and ultimately cause some part or connection to fail due to fatigue. The surface areas of contact generate frictional forces to damp the vibrational response of the swirler, and the clearance regions permit the arrangement to thermally expand.  
     [0048] It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the invention as defined in the appended claims.