Abstract:
The present invention provides an improved cooling circuit for a trailing edge of a turbine blade. The cooling circuit includes an inlet passage that receives a airflow and distributes the airflow through a feed passage. The feed passage primarily includes trip strips, at least one barrier including cross-over holes, teardrop shaped protrusions, and pockets disposed along a trailing edge. The geometry and positioning of both the cross-over holes and teardrop shaped protrusions downstream of the cross-over holes have been optimized to maximize cooling efficiency and reduce airflow. An improved transition between the inlet passage and the feed passage is also provided, which is arcuate and allows the airflow to maintain attachment and flow unimpeded from the inlet passage to the feed passage. The geometry of the pockets disposed along the trailing edge is optimized to improve cooling.

Description:
BACKGROUND OF THE INVENTION 
   This application relates generally to gas turbine engines and more specifically to a cooled turbine blade having a trailing edge cooling circuit with several unique features. 
   Conventional gas turbine engines include a compressor, a combustor and a turbine assembly that has a plurality of adjacent turbine blades disposed about a circumference of a turbine rotor. Each turbine blade typically includes a root that attaches to the rotor, a platform and an airfoil that extends radially outwardly from the rotor. 
   The compressor receives intake air. The intake air is compressed by the compressor and delivered primarily to the combustor where the compressed air and fuel are mixed and burned. A portion of the compressed air is bled from the compressor and fed to the turbine to cool the turbine blades. 
   The turbine blades are used to provide power in turbo machines by exerting a torque on a shaft that is rotating at a high speed. As such, the turbine blades are subjected to myriad mechanical stress factors. Further, because the turbine blades are located downstream of the combustor where fuel and air are mixed and burned, they are required to operate in an extremely harsh environment. 
   Hot burnt fuel-air mixture is expelled from the combustor and travels downstream to the turbine assembly, including the plurality of turbine blades. Each individual turbine blade includes a leading edge and a trailing edge, a pressure side and a suction side. The leading edge extends upwardly from the platform along the airfoil and is the first edge to contact the hot burnt fuel-air mixture as it travels through the turbine assembly. The trailing edge is substantially parallel to the leading edge and is located downstream of the leading edge. The pressure side is a concave surface that extends between the leading edge and the trailing edge. The pressure side directs the hot burnt fuel-air mixture along the turbine blade toward the trailing edge. The suction side is a convex surface, adjacent to the pressure side. The suction side also extends from the leading edge to the trailing edge. Various internal cooling circuits are disposed between the pressure side and the suction side. 
   As the hot burnt fuel-air mixture travels past the leading edge, along the pressure side, and past the trailing edge, a temperature associated with the individual turbine blades increases resulting in increased stress within the turbine blade. A cooling fluid, e.g. an airflow, is delivered to each individual turbine blade via the various internal cooling circuits sandwiched between the pressure side and the suction side of the turbine blade. The cooling circuits direct cooler compressed air bled from the compressor up through the root of the turbine blade and throughout the airfoil to cool the turbine blade. 
   One known cooling circuit technique directs airflow from the root radially outwardly toward the trailing edge. This cooling circuit receives an airflow from an opening disposed in the root of the turbine blade and feeds the airflow from an inlet passage radially outwardly through a feed passage. A known transition from the inlet passage to the feed passage includes a sharp corner that inhibits airflow from the inlet passage to a lower portion the feed passage. This may create a hot spot, i.e. an area of higher stress, within the turbine blade. 
   One known feed passage includes at least one barrier extending a length of the feed passage and a plurality of cross-over holes disposed along the length of the barrier. Known cross-over holes direct the airflow toward both a plurality of teardrop shaped protrusions downstream of the barrier and a plurality of openings disposed between each of the teardrop shaped protrusions. The plurality of teardrop shaped protrusions are disposed along the trailing edge of the turbine blade and direct airflow upward along the trailing edge and out of the turbine blade. 
   Known barriers includes cross-over holes of varying size. A width between adjacent cross-over holes also varies along the length of the barrier. This variation in size and position of the cross-over holes can cause a non-uniform airflow through the feed passage. This may result in additional hot spots, i.e. areas of higher stress, within the turbine blade. Further, known positioning of the cross-over holes in relation to the teardrop shaped protrusions may also have a detrimental effect on the cooling efficiency of the airflow. 
   As such, it is desirable to provide a turbine blade including a trailing edge cooling circuit that is optimized to reduce the effects of the mechanical stress factors, improve air flow throughout the airfoil and maximize cooling efficiency. 
   SUMMARY OF THE INVENTION 
   The present invention provides an improved trailing edge cooling circuit for a turbine blade. The cooling circuit primarily includes an inlet passage that receives and distributes an airflow along a trailing edge via a feed passage. The feed passage includes trips strips, at least one barrier including cross-over holes, i.e. openings within the barrier that direct airflow through the barrier, teardrop shaped protrusions, and pockets disposed along the trailing edge. 
   In the present invention, the improved cooling circuit includes an inlet passage, which receives an airflow from an opening within the root, and a feed passage, which receives the airflow from the inlet passage and directs the airflow through the turbine blade. The airflow exits through pockets disposed along the trailing edge of the turbine blade. 
   The feed passage includes at least one barrier with cross-over holes optimized to maximize cooling efficiency and reduce an airflow. Further, the geometry and positioning of both the cross-over holes and teardrop shaped protrusions downstream of the cross-over holes have been optimized to maximize cooling efficiency and reduce airflow. 
   An improved transition between the inlet passage and the feed passage is also provided. The improved transition is arcuate, allowing the airflow to maintain attachment to an inside wall of the cooling circuit and flow unimpeded from the inlet passage to the feed passage. This prevents airflow starvation within a lower portion of the feed cavity and the trailing edge. 
   Finally, the geometry of the pockets disposed along the trailing edge has been optimized to improve cooling. 
   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 
       FIG. 1  is a schematic illustration of an example gas turbine engine; 
       FIG. 2  illustrates an example turbine blade; 
       FIG. 3  is a schematic illustration of a prior art airfoil; 
       FIG. 4  is a sectional view of a prior art airfoil illustrating example cooling circuits; 
       FIG. 5  is a sectional view of a trailing edge cooling circuit according to one embodiment of the present invention; 
       FIG. 6  is a cross-sectional illustration of the feed passage including the trailing edge cooling circuit encircled at B in  FIG. 5 ; 
       FIG. 7  is a schematic illustration of two protrusions according to one embodiment of the present invention; 
       FIG. 8  illustrates an airfoil including a plurality of pockets according to one embodiment of the present invention; 
       FIG. 8A  illustrates a single pocket according to one embodiment of the present invention; and 
       FIG. 8B  further illustrates a single pocket according to one embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  is a schematic illustration of an example gas turbine engine  10  circumferentially disposed about an engine centerline, or axial centerline axis  12 . The example gas turbine engine  10  includes a fan  14 , a compressor  16 , a combustor  18 , and a turbine assembly  20 . As is known, intake air from the fan  14  is compressed in the compressor  16 . The compressed air is mixed with fuel and burned in the combustor  18  and expanded in the turbine assembly  20 . The turbine assembly  20  includes rotors  22  and  24  that, in response to the expansion, rotate, driving the compressor  16  and the fan  14 . The turbine assembly  20  includes alternating rows of rotary blades  26  and static airfoils or vanes  28 , which are mounted to the rotors  22  and  24 . The example gas turbine engine  10  may, for example, be a gas turbine used for power generation or propulsion. However, this is not a limitation on the present invention, which may be employed on gas turbines used for electrical power generation, in aircraft, etc. 
     FIG. 2  illustrates an example turbine blade  30  having a platform  32 , with an airfoil  34  extending upward from the platform  32  and a root  36  extending below the platform  32 . While the present invention is being illustrated in a turbine blade, it should be understood that the invention would also be beneficial in a static structure such as a stator or a vane  28 . Further, while the inventive turbine blade  30  is designed for use in a first stage turbine assembly, the inventive turbine blade  30  may be used in any stage. 
     FIG. 3  is a schematic overview illustration of a prior art airfoil  34 . The airfoil  34  includes a leading edge  37  and a trailing edge  38 . Cooling circuits  40  are provided through the airfoil  34 . The cooling circuits  40  receive an airflow from an air supply adjacent the platform  32  and direct the airflow radially outwardly through the airfoil  34 . 
   The airfoil  34  includes a pressure side  42  and a suction side  44 . A mean camber line MCL extends the length of the airfoil  34 , chordwisely from the leading edge  37  to the trailing edge  38  at a location midway between the pressure side  42  and the suction side  44 . 
     FIG. 4  is a sectional view of the prior art airfoil  34  through the Section A-A shown in  FIG. 3  along the MCL. A series of cooling circuits  40  and a trailing edge cooling circuit  41  are illustrated. A cooling fluid, typically an airflow, C TE  enters the trailing edge cooling circuit  41  through an inlet opening  50  and flows into an inlet passage  52 . The airflow C TE  from the inlet passage  52  attempts to flow around a transition  54  into a feed passage  56 . However, because the transition  54  is relatively sharp and angled towards the leading edge, much of the airflow C TE  maybe directed upwardly into an upper portion  56 B of the feed passage  56  to then exit the airfoil  34  through a trailing edge  58 . As such, a lower portion  56 A of the feed passage  56  can become starved of sufficient airflow resulting in hot spots and additional stress near the transition  54 . 
   A plurality of known cross-over holes  55  are also schematically illustrated along a barrier  57  in  FIG. 4 . A width W of each of the known cross-over holes  55  can vary along a length L of the barrier  57 . Further, a distance D between adjacent known cross-over holes  55  can also vary along the length L of the barrier  57 . The varying width W of each of the known cross-over holes  55  and the varying position of each the known cross-over holes  55  in relation to one another may result in a non-uniform flow of air through the barrier  57  resulting in uneven cooling along the trailing edge  58 . 
     FIG. 5  is a sectional view of a trailing edge cooling circuit  60  according to one embodiment of the present invention. A cooling fluid, typically an airflow, C TE  enters the trailing edge cooling circuit  60  through an inlet opening  62 . The airflow C TE  flows through an inlet passage  64  into a feed passage  66 , through the feed passage  66  and exits through a trailing edge  68 . 
   The airflow C TE  from the inlet passage  64  is directed to a lower portion  66 A of the feed passage  66  by a transition  70 , which is curved to maintain flow attachment. As such, a portion of the airflow C TE  flows unimpeded along the transition  70 , providing sufficient airflow to a lower portion  66 A of the feed passage  66  before exiting through the trailing edge  68 . Notably, the transition  70  extends toward the trailing edge  68 . 
   A remaining portion of the airflow C TE  is directed further upward from the lower portion  66 A of the feed passage  66  to an upper portion  66 B of the feed passage  66  by trips strips  72 , which are oriented angularly to improve convective cooling. The remaining portion of the airflow C TE , directed by the trips strips  72 , flows toward a first barrier  74  including a first plurality of cross-over holes  76 , which directs the airflow C TE  toward a second barrier  78  including a second plurality of cross-over holes  80 . 
   The airflow C TE  flows through the first plurality of cross-holes  76  associated with the first barrier  74  and through the second plurality of cross-over holes  80  associated with the second barrier  78 . The second plurality of cross-over holes  80  is sized to reduce air flow and maximize cooling efficiency. Each of the individual cross-over holes within the second plurality of cross-over holes  80  are spaced substantially equidistant from one another along a length L of the second barrier  78 . 
   The airflow C TE  exits the second plurality of cross-over holes  80 , which direct the airflow C TE  toward a plurality of protrusions  82  disposed along the trailing edge  68 . The plurality of protrusions  82  direct the airflow C TE  to a plurality of pockets  86  disposed along the trailing edge  68 , where the airflow C TE2  is dispersed by the plurality of pockets  86  and exits through the trailing edge  68 . 
     FIG. 6  is cross-sectional illustration of the feed passage  66  of the trailing edge cooling circuit  60  encircled at B in  FIG. 5 . An airflow C TE  flows upward into the feed passage  66  from the inlet passage  64  ( FIG. 5 ). Before exiting the feed passage  66  through the trailing edge  68 , a majority of the airflow C TE  flows through a first plurality of cross-over holes  76 , a second plurality of cross-over holes  80  and around a plurality of protrusions  82 . 
   An offset relationship exists between the first plurality of cross-over holes  76  and the second plurality of cross-over holes  80  such that an example airflow C TE1  flowing through a cross-over hole  76 A of the first plurality of cross-over holes  76  cannot follow a direct linear path from the cross-over hole  76 A through the second plurality of cross-over holes  80 . Instead, the example airflow C TE1  flows through the cross-over hole  76 A, which directs the example airflow C TE1  toward a wall portion  84 A disposed between a pair of cross-over holes  80 A and  80 B of the second plurality of cross-over holes  80 . 
   The wall portion  84 A redirects the example airflow C TE1  upwardly and diagonally to cross-over holes  80 A and  80 B. The example airflow C TE1  then flows linearly from the cross-over hole  80 A or  80 B toward a protrusion  82 A or  82 B of the plurality of protrusions  82 . The protrusions  82  direct the example airflow C TE1  upward around the protrusions  82  and into a pocket  86 A,  86 B of the plurality of pockets  86  disposed along the trailing edge  68  where the air is dispersed. This sequential redirection of the example airflow C TE1  prior to dispersion effectively reduces the velocity of the example airflow C TE1 . 
     FIG. 7  is a schematic illustration of two protrusions  82  according to one embodiment of the present invention. Each protrusion  82  has a first end  90  and a second end  92 . The protrusions  82  extend from the first end  90  located near trailing edge  68  to a second end  92  inward away from the trailing edge  68 . Each protrusion  82  has a teardrop shape that extends from a first thickness T 1  near the first end  90  to a second thickness T 2  near the second end  92 , which includes a convex surface. An axis C along a length of each of the protrusions  82  is substantially perpendicular to the trailing edge  68 . 
     FIG. 8  illustrates an example airfoil  100  according to one embodiment of the present invention including a plurality of pockets  86  disposed along trailing edge  68 . The airfoil  100  includes a first surface  102 , which is a pressure surface, and a second surface  104 , which is a suction surface. The plurality of pockets  86  are disposed along the trailing edge  68  and extend inward from the trailing edge  68  on the first surface  102 . The plurality of pockets  86  extend from a bottom edge  106  of the airfoil  100  to a top edge  108  of the airfoil  100 . Each of the plurality of pockets  86  include a cutout  87  on the first surface  102 , which controls dispersion of an airflow exiting the airfoil  100  from the feed passage (not shown). A depth D of each cutout  87  is a maximum depth in a first pocket  86  located nearest the bottom edge  106  of the airfoil  100  and decreases with each consecutive pocket upward along the trailing edge  68  to a minimum depth in a last pocket  86  nearest to the top edge  108 . 
     FIG. 8A  schematically illustrates a single pocket  86 A of the plurality of pockets  86  according to one embodiment of the present invention. The single pocket  86 A is formed in the first surface  102 . The single pocket  86 A includes a cutout  87  in the first surface  102  that has a depth D which extends from the trailing edge  68  to a cutout edge  89  of the cutout  87 . 
   As illustrated in  FIG. 8B , the single pocket  86 A has a first height H 1  between the first surface  102  and the second surface  104  that is greater than a second height H 2  between the first surface  102  and the second surface  104  within a feed passage  66 . As an airflow C TE  flows from the feed passage  66  and exits through the pocket  86 , the change in height from H 1  to H 2  in conjunction with the change in the depth D along the plurality of pockets  86  as discussed above operates to direct the airflow C TE  from the feed passage  66  upward along the trailing edge  68  to maximize cooling efficiency of the airflow along the trailing edge  68 . 
   Although preferred embodiments of this invention have 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.