Patent Publication Number: US-6655147-B2

Title: Annular one-piece corrugated liner for combustor of a gas turbine engine

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to a liner for the combustor of a gas turbine engine and, in particular, to an annular one-piece corrugated liner of substantially sinusoidal cross-section where the amplitude of the corrugations and/or the wavelength between adjacent corrugations is varied from an upstream end to a downstream end. 
     Combustor liners are generally used in the combustion section of a gas turbine engine located between the compressor and turbine sections of the engine, although such liners may also be used in the exhaust sections of aircraft engines that employ afterburners. Combustors generally include an exterior casing and an interior combustor where fuel is burned to produce a hot gas at an intensely high temperature (e.g., 3000° F. or even higher). To prevent this intense heat from damaging the combustor case and the surrounding engine before it exits to a turbine, a heat shield or combustor liner is provided in the interior of the combustor. 
     One type of liner design includes a number of annular sheet metal bands which are joined by brazing, where each band is subject to piercing operations after forming to incorporate nugget cooling holes and shaped dilution holes. Each band is then tack welded and brazed to the adjacent band, with stiffeners known as “belly bands” being tack welded and brazed to the sheet metal bands. The fabrication of this liner has been found to be labor intensive and difficult, principally due to the inefficiency of brazing steps applied to the stiffeners and sheet metal bands. 
     In order to eliminate the plurality of individual sheet metal bands, an annular one-piece sheet metal liner design has been developed as disclosed in U.S. Pat. No. 5,181,379 to Wakeman et al., U.S. No. Pat. 5,233,828 to Napoli, U.S. No. Pat. 5,279,127 to Napoli, U.S. No. Pat. 5,465,572 to Nicoll et al., and U.S. No. Pat. 5,483,794 to Nicoll et al. While each of these patents is primarily concerned with various cooling aspects of the one-piece liner, it will be noted that alternative configurations for such liners are disclosed as being corrugated so as to form a wavy wall. In this way, the buckling resistance and restriction of liner deflection for such liners is improved. The corrugations preferably take on a shallow sine wave form, but the amplitude of each corrugation (wave) and the wavelength between adjacent corrugations (waves) is shown and described as being substantially uniform across the axial length of the liner. 
     It has been determined that the stiffness requirements for a one-piece sheet metal liner are likely to vary across the axial length thereof since certain points will be weaker than others. Thus, it would be desirable for an annular, one-piece corrugated liner to be developed for use with a gas turbine engine combustor which provides a variable amount of stiffness along its axial length as required by the liner. It would also be desirable for such a liner to be manufactured and assembled more easily, including the manner in which it is attached at its upstream and downstream ends. 
     BRIEF SUMMARY OF THE INVENTION 
     In a first exemplary embodiment of the invention, an annular one-piece liner for a combustor of a gas turbine engine is disclosed as including a first end adjacent to an upstream end of the combustor, a second end adjacent to a downstream end of the combustor, and a plurality of corrugations between the first and second ends, each corrugation having an amplitude and a wavelength between an adjacent corrugation, wherein the amplitude of the corrugations is variable from the first end to the second end. The wavelengths between adjacent corrugations may be either substantially equal or variable from the first end to the second end of the liner. 
     In a second exemplary embodiment of the invention, an annular one-piece liner for a combustor of a gas turbine engine is disclosed as including a first end adjacent to an upstream end of the combustor, a second end adjacent to a downstream end of the combustor, and a plurality of corrugations between the first and second ends, each corrugation having an amplitude and a wavelength between an adjacent corrugation, wherein the wavelength between adjacent corrugations is variable from the first end to the second end. The amplitudes of each corrugation may be either substantially equal or variable from the first end to the second end of the liner. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a gas turbine engine including a combustor liner in accordance with the present invention; 
     FIG. 2 is an enlarged, cross-sectional view of the combustor depicted in FIG. 1; 
     FIG. 3 is a partial perspective view of the outer liner for the combustor depicted in FIGS. 1 and 2 in accordance with the present invention; 
     FIG. 4 is an enlarged cross-sectional view of the outer liner depicted in FIGS. 1-3; 
     FIG. 5 is an enlarged, partial cross-sectional view of the outer liner depicted in FIG. 4, where the amplitude of the corrugations and the wavelength between adjacent corrugations is identified; 
     FIG. 6 is an enlarged, partial cross-sectional view of the middle section of the outer liner depicted in FIG. 4; 
     FIG. 7 is an enlarged, partial cross-sectional view of the upstream section of the outer liner depicted in FIG. 4; and, 
     FIG. 8 is an enlarged, partial cross-sectional view of the downstream section of the outer liner depicted in FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings in detail, wherein identical numerals indicate the same elements throughout the figures, FIG. 1 depicts an exemplary gas turbine engine  10  having in serial flow communication a low pressure compressor  12 , a high pressure compressor  14 , and a combustor  16 . Combustor  16  conventionally generates combustion gases that are discharged therefrom through a high pressure turbine nozzle assembly  18 , from which the combustion gases are channeled to a conventional high pressure turbine  20  and, in turn, to a conventional low pressure turbine  22 . High pressure turbine  20  drives high pressure compressor  14  through a suitable shaft  24 , while low pressure turbine  22  drives low pressure compressor  12  through another suitable shaft  26 , all disposed coaxially about a longitudinal or axial centerline axis  28 . 
     As seen in FIG. 2, combustor  16  further includes a combustion chamber  30  defined by an outer liner  32 , an inner liner  34 , and a dome  36  located at an upstream end thereof. It will be seen that a fuel/air mixer  38  is located within dome  36  so as to introduce a mixture of fuel and air into combustion chamber  30 , where it is ignited by an igniter (not shown) and combustion gases are formed which are utilized to drive high pressure turbine  20  and low pressure turbine  22 , respectively. 
     In accordance with the present invention, it will be noted from FIGS. 3 and 4 that outer liner  32  is annular in shape and preferably formed as a one-piece construction from a type of sheet metal. More specifically, outer liner  32  includes a first end  42  located adjacent to an upstream end of combustor  16 , where first end  42  is connected to a cowl  44  and dome  36  by means of a rivet band  40  (which is in turn connected to cowl  44  and dome  36  via a mechanical connection such as bolt  46  and nut  48 , a welded connection, or other similar form of attachment). Accordingly, it will be appreciated that outer liner  32  is preferably connected to rivet band  40  via rivets  41  and therefore eliminates the need for outer liner  32  to have a flange formed thereon at upstream end  42 . Starter slots  55  and  57  are preferably provided in rivet band  40  and upstream outer liner end  42 , respectively, to promote a cooling film along the hot side of outer liner  32 . Outer liner  32  also includes a second end  50  located adjacent to a downstream end of combustor  16 , where second end  50  is preferably connected to a seal assembly  52  by means of rivets  53 . In this way, outer liner  32  is able to move axially in accordance with any thermal growth and/or pressure fluctuations experienced. 
     Outer liner  32  further includes a plurality of corrugations, identified generally by reference numeral  54  (see FIG.  3 ), formed therein between first end  42  and second end  50 . It will be appreciated that corrugations  54  have a substantially sinusoidal shape when viewed in cross-section (see FIG.  4 ), as seen in accordance with a neutral axis  59  (see FIG. 5) extending therethrough. It will be appreciated from FIG. 5 that each corrugation  54  has a given amplitude  56 , as well as a given wavelength  58  between adjacent corrugations  54 . Contrary to the prior art, where the liners are disclosed as having corrugations with substantially the same amplitude and wavelength therebetween, corrugations  54  of outer liner  32  are configured so as to have a variable amplitude and/or a variable wavelength between adjacent corrugations. In this way, outer liner  32  is able to provide any degree of stiffness desired along various axial locations thereof without overdesigning outer liner  32  for its weakest points. 
     For example, it has been found that a middle section  60  of outer liner  32  is generally the weakest and most prone to buckling. Thus, an amplitude  62  for corrugations  64  located within middle section  60  (see FIG. 6) is preferably greater than an amplitude  66  for corrugations  68  located within an upstream section  70  (see FIG. 7) of outer liner  32  adjacent first outer liner end  42 . Similarly, amplitude  62  for corrugations  64  located within middle section  60  is preferably greater than an amplitude  72  for corrugations  74  located within a downstream section  76  (see FIG. 8) of outer liner  32  adjacent second outer liner end  50 . Since the fixed connection of outer liner  32  at first outer liner end  42  creates a slightly larger risk of buckling than at second outer liner end  50 , and the temperature at first outer liner end  42  is generally higher than the temperature at second outer liner end  50 , amplitude  66  for corrugations  68  is preferably equal to or greater than amplitude  72  for corrugations  74 . 
     Either in conjunction with, or separately from, varying amplitudes  62 ,  66  and  72  for corrugations  64 ,  68  and  74  of middle section  60 , upstream section  70  and downstream section  76 , respectively, it has been found that varying the wavelengths between adjacent corrugations therein can also be utilized to tailor the stiffness of outer liner  32  at various axial locations. Accordingly, in the case where middle section  60  of outer liner  32  is considered to be most prone to buckling, a wavelength  78  between adjacent corrugations  64  is preferably less than a wavelength  80  between adjacent corrugations  68  of upstream section  70  and a wavelength  82  between adjacent corrugations  74  of downstream section  76 . Likewise, wavelength  80  between adjacent corrugations  68  of upstream section  70  is preferably equal to or less than wavelength  82  between adjacent corrugations  74  of downstream section  76  for the aforementioned reasons with regard to their respective amplitudes. 
     In order to provide at least the same degree of stiffness as in current outer liners, it has been determined that an overall buckling margin of outer liner  32  preferably be in a range of approximately 35-250 psi. A more preferable overall buckling margin range for outer liner  32  would be approximately 85-200 psi, while an optimal range for such overall buckling margin would be approximately 120-180 psi. 
     Various configurations for outer liner  32  have been tested and analyzed, including the number of corrugations  54  formed therein, the thickness  84  thereof (see FIG.  5 ), and the material utilized to form such outer liner  32 . It will be appreciated that the overall buckling margin discussed above is the overriding concern, but optimization of the other parameters involved is important since factors involving weight, cost, ability to form the material, and the like must be taken into account. Accordingly, it has been found that the total number of corrugations  54  (as defined by the total number of waves) formed in outer liner  32  preferably is approximately 6-12. The total number of corrugations  54  depicted within FIGS. 1-4 is 6½, which is shown only for exemplary purposes. The preferred thickness  84  for outer liner  32  preferably is approximately 0.030-0.080 inches when a sheet metal material (e.g., Hastelloy X, HS 188, HA 230, etc.) is utilized. In this way, the material can be easily formed with corrugations  54 , provide the necessary stiffness, and reduce cost over previous liners. 
     With regard to the generation of a cooling flow along the hot (radially inner) side of outer liner  32 , it is preferred that a multihole cooling pattern be formed therein like those described in U.S. No. Pat. 5,181,379, 5,233,828, and 5,465,572 be employed (i.e., regarding size, formation, etc.). It will be understood that the pattern of cooling holes may vary depending on their location with respect to a corrugation  54 , the axial position along outer liner  32 , the radial position along outer liner  32 , the amplitude  56  for such corrugation, and the wavelength  58  for such corrugation. More specifically, a more dense multihole cooling pattern (spacing between cooling holes having a diameter of approximately 20 mil being approximately five diameters therebetween) is preferably utilized in those axial locations where the amplitude for a corrugation  54  is increased and/or the wavelength between adjacent corrugations is decreased. This stems from the need for more cooling air to be provided within a pocket  88  that is steeper and therefore less susceptible to the cooling flow from upstream outer liner end  42 . A more dense multihole cooling pattern is also preferably provided on an upstream side  92  of corrugations  54  and adjacent the radial locations of fuel/air mixers  38 . By contrast, a less dense multihole cooling pattern (spacing between cooling holes having a diameter of approximately 20 mil being approximately seven and one-half diameters therebetween) is preferably provided in those axial locations of outer liner  32  where the amplitude for a corrugation  54  is decreased and/or the wavelength between adjacent corrugations is increased. The less dense multihole cooling pattern is further preferred on a downstream side  94  of corrugations  54  and radial locations between adjacent fuel/air mixers  38 . 
     Having shown and described the preferred embodiment of the present invention, further adaptations of outer liner  32  for combustor  16  can be accomplished by appropriate modifications by one of ordinary skill in the art without departing from the scope of the invention. In particular, it will be understood that the concepts described and claimed herein could be utilized in inner liner  34  and still be compatible with the present invention. While inner liner  34  typically will not require corrugations to be formed therein in order to satisfy stiffness requirements, it would be particularly useful for inner liner  34  to have a flangeless configuration that can be riveted at its upstream and downstream ends like that described for outer liner  32  as to simplify manufacturing and reduce cost.