Abstract:
A combustor assembly includes an inner and an outer liner defining a combustion chamber. The inner and outer liner includes a plurality of cooling holes that are spaced a specified distance apart. The cooling holes include a specified inclination angle and circumferential angle. A first group of cooling holes is spaced apart according to a uniform geometric pattern and density. A second group disposed between the first group and some structural feature within the liner assembly is disposed at a non-uniform pattern and a hole density equal to the density of the first group of cooling holes. The non-uniform cooling hole arrangement increases cooling flow effectiveness to accommodate local disturbances and thermal properties.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to a combustor liner for a gas turbine engine. More particularly, this invention is a cooling hole configuration for providing a desired cooling airflow proximate to cooling airflow disrupting features of a combustor liner.  
         [0002]     Typically, a combustor module for a gas turbine engine includes an outer casing and an inner liner. The liner and the casing are radially spaced apart to form a passage for compressed air. The liner forms a combustion chamber within which compressed air mixes with fuel and is ignited. The liner includes a hot side exposed to hot combustion gases and a cold side facing the passage formed between the liner and the casing. Liners can be single-wall or double-wall construction, single-piece construction or segmented construction in the form of discrete heat shields, panels or tiles.  
         [0003]     Typically, a plurality of cooling holes supply a thin layer of cooling air that insulates the hot side of the liner from extreme combustion temperatures. The liner also includes other openings much larger than the cooling holes that provide for the introduction of compressed air to feed the combustion process. The thin layer of cooling air can be disrupted by flow around the larger openings potentially resulting in elevated liner temperatures adjacent the larger openings. Further, the liner includes other structural features such as seams and rails that disrupt cooling airflow causing elevated temperatures. Elevated or uneven temperature distributions within the liner can promote undesired oxidation of the liner material, coating-failure or thermally-induced stresses that degrade the effectiveness, integrity and life of the liner.  
         [0004]     It is known to arrange cooling holes in a different grouping densities around larger openings or other features that may disrupt cooling airflow. The increased number of cooling holes around larger openings and other features increase airflow preferentially in these areas and are somewhat effective in maintaining the desired cooling airflow.  
         [0005]     Disadvantageously, the greater cooling airflow provided around such openings and other disrupting configurations, utilizes a large portion of the limited quantity of cooling air provided to the combustor liner. The increased demand for cooling airflow in the localized areas around larger opening and disruptions reduces the overall cooling airflow that is available for the remaining portions of the liner assembly. The amount of cooling airflow is limited by the design of the combustor liner and increases in cooling airflow requirements can impact other design and performance requirements.  
         [0006]     Accordingly, it is desirable to develop a combustor liner that improves cooling layer properties around cooling airflow disrupting structures to eliminate uneven temperature distributions or undesirable temperature levels without substantially increasing cooling airflow requirements.  
       SUMMARY OF THE INVENTION  
       [0007]     An example combustor assembly according to this invention includes a plurality of cooling holes for providing film cooling of a combustor liner that are preferentially oriented relative to a flow-disrupting structure.  
         [0008]     A combustor liner according to this invention utilizes groups of cooling holes that are provided in a generally uniform density with changes to the circumferential angle of some cooling holes to accommodate specific structural features that create disruptions in cooling airflow. The example combustor liner assembly includes a first plurality of cooling holes within the combustor liner that are angled through the liner at a first compound angle to provide a flow and layer of cooling air. The compound angle for each cooling hole includes a first circumferential angle component and a first inclination angle component. The first group of cooling holes is distributed throughout the combustor liner in regions spaced apart from structural features affecting cooling airflow. Each of the first group of cooling holes includes a common compound angle with substantially common circumferential and inclination angle components.  
         [0009]     A second group of cooling holes is disposed adjacent to structural features that affect cooling airflow at a second compound angle relative to the structural features. The second group of cooling holes includes a second circumferential direction corresponding to the proximate structural feature. Each of the cooling holes in the second group also includes an inclination angle that is substantially the same as that of the first group of cooling holes. The second group of cooling holes surrounds the structural formations within the liner assembly to provide a non-uniform and structural feature specific arrangement of cooling holes to provide the cooling airflow that maintains desired wall temperatures and increases cooling film effectiveness without significantly increasing the amount of cooling airflow required.  
         [0010]     Accordingly, the non-uniform cooling hole array in regions adjacent specific structural features of the liner assembly promote improved cooling airflow around specific structural features that increases cooling film effectiveness without increasing coolant air requirements.  
         [0011]     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a schematic view of a turbine engine assembly according to this invention.  
         [0013]      FIG. 2  is a schematic cross-sectional view of a combustor assembly according to this invention.  
         [0014]      FIG. 3  is a schematic view of a portion of an inner liner assembly according to this invention.  
         [0015]      FIG. 4   a  is a schematic view of a cooling hole angled within a liner wall according to this invention.  
         [0016]      FIG. 4   b  is a cooling hole angled in a circumferential direction within a liner wall according to this invention.  
         [0017]      FIG. 5  is a schematic representation of the effects of three-dimensional flow through openings within a liner wall according to this invention.  
         [0018]      FIG. 6  is another schematic representation of coolant airflow around a dilution hole according to this invention.  
         [0019]      FIG. 7  is a schematic representation of a portion of the liner assembly according to this invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]     Referring to  FIG. 1 , a turbine engine assembly  10  includes a fan, a compressor  12  that feeds compressed air to a combustor  14 . Compressed air is mixed with fuel and ignited within the combustor to produce hot gasses that are then driven past a turbine  16 . The schematic representation of the turbine engine assembly  10  is intended for descriptive purposes, as other turbine engine assembly configurations will also benefit from the disclosures of this invention.  
         [0021]     Referring to  FIG. 2 , the combustor assembly  14  includes a dual-wall liner assembly  15 . The liner assembly  15  includes an inner shell  22  and an outer shell  24 . The outer shell  24  and inner shell  22  are spaced radially apart from an inner heat shield  26  and an outer heat shield  28 . The inner shell  22  and outer shell  24  are spaced a radial distance apart to define an air passage  20  between the outer heat shield  28  and the inner heat shield  26 .  
         [0022]     The example combustor assembly illustrated is disposed annularly about the axis  18 . The radial space in between the shells  22 ,  24  and the heat shields  26 ,  28  define an air passage  20 . Cooling air  36  flows through the air passage  20  to provide cooling for the heat shields  26 ,  28 . The heat shields  26 , 28  are attached at a forward end by a dome plate or bulkhead assembly  25 . The combustion chamber  34  is defined by the heat shields  26 ,  28  and is open at an aft end  27  to allow the exhaust of combustion gasses.  
         [0023]     A layer of cooling air is supplied along a hot side surface  46 ,  42  of the heat shields  26 ,  28 . Cooling air  36  is communicated from a cold side  48 ,  44  through each of the heat shields  26 ,  28  to the hot side  46 ,  42  within the combustor chamber  34 . The layer of cooling air flows along the hot side surfaces  42 ,  46  toward the aft end  27  to provide insulation for the heat shields  26 ,  28 .  
         [0024]     Each of the heat shields  26 ,  28  includes a plurality of openings and other structural features. These openings include dilution air openings  32  and cooling air openings  30 . The cooling air openings  30  are disposed within the heat shields  26 ,  28  and are provided to communicate air that generates the insulating layer of cooling air. Other openings include the dilution openings  32  that provide air to aid the combustion process. The dilution openings  32  are much larger than the cooling air openings  30 . Airflow through the dilution holes  32  can disrupt the cooling airflow along the surfaces of the heat shields  28 ,  26 .  
         [0025]     Referring to  FIG. 3 , the inner heat shield  26  includes the hot side surface  42  and the cold side surface  44 . Cooling air  36  flows from the cold side surface  44  to the hot side surface  42 . The dilution opening  32  is much larger than the cooling openings  32 . Further, within the portion of the heat shield  26  are a rail assembly  38  and a seam  40 . The rail assembly  38  and the seam  40  are areas in the liner assembly of non-uniform material thickness that creates specific challenges to maintaining uniform temperatures of the heat shield  26 .  
         [0026]     The cooling holes  30  are distributed in a substantially uniform geometric pattern and density within the heat shield  26 . However, in locations proximate to the various structural features such as the dilution opening  32 , the rail assembly  38  and the seam  40 , the cooling holes  30  are distributed in a non-uniform matter to facilitate cooling air flow  36  adjacent these features of the liner assembly  15 .  
         [0027]     A first group  58  of cooling holes  30  is disposed in a generally uniform geometric pattern within a first region  60 . The first region  60  includes all of the regions within the heat shield  26  that are not disposed adjacent one of the structural features such as the rail  38  or the dilution opening  32 . A second region  64  is disposed between the first region  60  and the dilution opening  32 .  
         [0028]     Each of the cooling holes  30  is disposed at an angular orientation from the cold side  44  to the hot side  42  of the inner heat shield  26 . The angular orientation provides the directional flow of the cooling airflow  36 , thereby generating the insulating layer of air along the hot side  42 . Each of the cooling holes  30  is disposed at a compound angle including an inclination angle  54  and a circumferential angle  56 . The inclination angle  54  is disposed relative to a longitudinal axis  50  of the combustor assembly  14 . The circumferential angle  56  is disposed relative to a transverse or circumferential axis  52  disposed transverse to the to the axis  50 . Each cooling hole  30  is disposed within the heat shield  26  at the compound angle including components angled relative to the longitudinal axis  50  and the circumferential axis  52 . Tailoring of the inclination angle  54  and circumferential angle  56  provides for directing airflow over areas along the hot side surface  42 .  
         [0029]     Referring to  FIG. 4   a  a large schematic view of a cooling hole  30  disposed within the inner heat shield  26  is shown. The cooling hole  30  is disposed at the inclination angle indicated at  54 . Preferably, the inclination angle is within a range about 15 to 45 degrees. More preferably the inclination angle  54  is between 20 and 30 degrees. The specification inclination angle for the cooling holes  30  is maintained for each of the cooling holes  30  disposed within the liner assembly  15  according to this invention.  
         [0030]     Referring to  FIG. 4   b , each of the cooling holes  30  are also disposed at a circumferential or clock angle  56  that is transverse to the axis  18 . The clock angle  56  can vary by as much as 90 degrees relative to the axis  52 .  
         [0031]     The cooling holes  30  include a diameter of approximately 0.02-0.03 inches and are arranged with circumferential and axial spacing of between 2 to 10 hole diameters. Similar spacing both axially and circumferentially form a geometrically uniform pattern. The regular and repeatable cooling hole spacing works well in many regions of the liner assembly. However, in regions of the liner assembly that are located proximate to structural features such as the dilutions holes  32 , rails  38  and seams  40  that may suffer a loss of cooling film effectiveness require a different cooling hole angular orientation. A non-uniform cooling hole array in these regions is provided to control temperatures in the heat shield  26  proximate the dilution openings  32 , the rail assemblies  38  and the seams  40 .  
         [0032]     Referring to  FIG. 5  and  6 , compressed air flow flowing through larger openings such as the dilution opening  32  can generate three-dimensional airflows along the hot side surface  42 . Three-dimensional airflow schematically indicated at  37  disrupts cooling airflow  36  adjacent the surfaces of the inner and outer heat shield  26 ,  28 . Flow  37  through the dilution openings  32  causes the cooling airflow  36  to stagnate and generates three-dimensional or recirculating flows indicated at  39 . Three-dimensional recirculating flows drive cooling air  36  away from the surface areas in the vicinity of the larger dilution openings  32  and locally depress or siphon cooling airflow away from the cooling holes. These factors reduce cooling effectiveness around the cooling hole feature and dilution openings  32 . The upstream airflow migrates around the air flow  37  is at a significant momentum to produce complex gradients that reduces cooling effectiveness.  
         [0033]     Referring to  FIG. 7 , the liner assembly  15  includes a non-uniform grouping of cooling holes proximate to the structural features that can potentially disrupt cooling airflow. The first group  58  of cooling holes  30  is disposed within the first region  60 . The first region  60  is disposed in locations throughout the liner assembly and comprises the majority of cooling holes  30  within the heat shields  26 ,  28  that are not adjacent to structural features causing airflow disruption. In the first group  58 , in the first region  60 , the cooling holes  30  are disposed in a uniform repeating geometric pattern. Each of the cooling holes  30  within the first group  58  includes an identical inclination angle  54  and circumferential angle  56 .  
         [0034]     The inclination angle  54  and the circumferential  56  of the cooling holes  30  in the first group  58  provides the desired directional flow of cooling air along the hot side surface  42  of the heat shields  26 ,  28 .  
         [0035]     Between the first group  58  and structural features such as the rail  38  and flange  72  are a second group  62  of cooling holes  30 . The second group  62  is disposed in a second region  64  between the first region  60  and the dilution opening  32 . The dilution opening  32  is most often accompanied by a grommet  35  that increases the thickness proximate the dilution opening  32 . The grommet  35  provides an isolating chamber for the dilution flow, sealing of the chamber between the liner and heat shield and a standoff to maintain the gap between the liner and heat shield. In the second region  64 , the second group of cooling holes  30  include an inclination angle  54  equal to those of the inclination angle  54  of the first group  58 .  
         [0036]     The circumferential angle of the second group  62  differs from the circumferential angle of the first group  58 . The circumferential angle within the second group is preferably disposed such that each of the cooling holes is disposed in a tangential orientation relative to an outer perimeter  63  of the dilution opening  32 . The tangential orientation of the cooling openings  30  provides a directionally non-uniform or circumferential cooling airflow about the perimeter  63  of the dilution opening  32 . The directional flow of cooling air  36  proximate to the dilution opening  32  provides the desired accommodation for cooling airflow that provides uniform temperatures within the heat shield  26 .  
         [0037]     A third region  66  is disposed between the first region  60  and the rail  38 . The rail  38  is an area of increased thickness that also requires preferential and non-uniform cooling with respect and compared to the first group  60 . The third group  68  is disposed between the first group  60  and the rail assembly  38 . In the third group, the cooling holes  30  are disposed at a uniform circumferential angle along the rail  38 . The circumferential angle of the cooling holes  30  in the third group  68  is different than those in the first group  60 . The circumferential angle of the third group  68  of cooling holes is substantially parallel to the rail assembly  38  to direct cooling airflow  36  across the rail.  
         [0038]     A fourth group  72  is disposed within a fourth region  70  that is disposed between the first group  60  and the seam  40 . About the seam  40  each of the cooling holes  30  are alternately disposed at a circumferential angle different than an immediately adjacent cooling hole  30 . In the illustrative embodiment each of the cooling holes  30  are disposed at an angle that crosses at an outer boundary of the seam  40 . The cooling holes  30  are disposed with circumferential angles disposed in an opposing manner to the circumferential angle of cooling holes  30  disposed on an opposite side of the seam  40 . The alternating pattern of cooling hole  30  angles provides cooling airflow  36  longitudinally along the seam  40  with a hole density substantially equal to the density of the first group  58 . This provides the preferential direction of the cooling air required for the non-uniform thickness within the seam area  40 .  
         [0039]     Circumferential orientation and these non-uniform regions may vary by as much as 180 degrees with cooling holes  30  that are preferentially positioned. The inclination angle of these holes is similar to those of adjacent grouping and within a tolerance of +−5 degrees. The use of the same hole diameter and minimal changes to the inclination angle permits machining operations to be performed continually without requiring additional set up operations. This also provides for the increased cooling effectiveness that accommodates added mass proximate the rail  38  and seam  40  along with accommodating three dimensional flows produced by larger dilution openings  32 .  
         [0040]     Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.