Abstract:
A core for forming a cooling microcircuit has at least one row of metering/tripping features configured to form at least one row of protrusions in the cooling microcircuit, a plurality of teardrop features configured to form a plurality of fluid passageways in the cooling microcircuit, and a terminal edge. The plurality of teardrop features includes a central teardrop feature having a trailing edge which is spaced from the terminal edge and a first teardrop feature located on a first side of and spaced from the central teardrop feature. The first teardrop feature has a longitudinal axis and is non-symmetrical about the longitudinal axis. A process of using the core and a turbine engine component formed thereby are described.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The Government of the United States of America may have rights in the present invention as a result of Contract No. N00019-02-C-3003 awarded by the Department of the Navy. 
    
    
     BACKGROUND 
     The present disclosure relates to a core which may be used to form a cooling microcircuit in an airfoil portion of a turbine engine component, which core is configured to allow the formation of a central fluid outlet which has a converging/diverging configuration and to a process of utilizing the core. 
     The fabrication of certain turbine engine components requires the use of a thin core. The thin core may be placed between a ceramic core which is used to form a central cooling fluid passageway in an airfoil portion of the turbine engine component and a region where an external wall of the airfoil portion will be created. The use of such a core creates a cooling circuit configuration which allows for film cooling. The thin cores can be made of either ceramic or a refractory metal material. 
     While highly useful, there exists the reality that the cores are a product of the dies used to fabricate them. Initially, dies are made with a theorized wear factor. For example, the cores are artificially made small in order to account for the fact that as the rough material forming the core is injected into the die time and again, the cores would effectively grow. Often, this fluctuation is not as expected and the dies need to be replaced sooner to prevent the formation of cores which do not meet desired specifications. Further, as the dies wear and cores which do not meet the specifications are formed, it becomes difficult to control the outflow from the turbine engine component whose cooling microcircuit(s) are formed using the core. 
     To date, these problems have not been fully addressed. 
     SUMMARY 
     In accordance with the instant disclosure, there is provided a core for forming a cooling microcircuit which broadly comprises at least one row of metering/tripping features configured to form at least one row of protrusions in said cooling microcircuit, a plurality of teardrop features configured to form a plurality of fluid passageways in said cooling microcircuit, a terminal edge, said plurality of teardrop features including a central teardrop feature having a trailing edge which is spaced from said terminal edge, and said plurality of teardrop features including a first teardrop feature located on a first side of and spaced from said central teardrop feature, said first teardrop feature having a longitudinal axis and being non-symmetrical about said longitudinal axis. 
     Further, there is provided a process for providing cooling microcircuits in an airfoil portion of a turbine engine component comprising the steps of: positioning at least one first core having at least one row of metering/tripping features configured to form at least one row of protrusions in said cooling microcircuit, and a plurality of teardrop features configured to form a plurality of fluid passageways in said cooling microcircuit, said plurality of teardrop features including a central teardrop feature having a trailing edge, a first teardrop feature located on a first side of and spaced from said central teardrop feature, said first teardrop feature having a longitudinal axis and being non-symmetrical about said longitudinal axis, and a second teardrop feature located on a second side of and spaced from said central teardrop feature, said second teardrop feature having a longitudinal axis and being non-symmetrical about said longitudinal axis; joining said at least one core to at least one ceramic core; forming said turbine engine component; removing said at least one core to form a cooling microcircuit having a plurality of fluid outlets; and drilling a central portion of said cooling microcircuit so as to form a cooling fluid outlet having a converging/diverging configuration. 
     Also, there is provided a turbine engine component having an airfoil portion and at least one cooling microcircuit located within a wall of said airfoil portion, each said cooling microcircuit having a plurality of fluid outlets with a central one of said fluid outlets having a converging/diverging configuration. 
     Other details of the drill to flow mini core described herein are set forth in the following detailed description and the accompanying drawings wherein like reference numerals depict like elements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an array of cores to be used to form an array of cooling circuits; 
         FIG. 2  illustrates a first embodiment of a core for forming a cooling circuit; 
         FIG. 3  is an end view of the core of  FIG. 2 ; 
         FIG. 4  illustrates a second embodiment of a core for forming a cooling circuit; 
         FIG. 5  illustrates an airfoil portion of a turbine engine component with film cooling holes; 
         FIG. 6  illustrates a process for forming a turbine engine component; and 
         FIG. 7  illustrates a turbine engine component. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an array  10  of cores  12  and  14  which may be used to form an array of cooling circuits in an airfoil portion of a turbine engine component. The array  10  includes a plurality of cores  12  having the design shown in  FIGS. 2 and 3  and a plurality of cores  14  having the design shown in  FIG. 4 . The figure also shows a ceramic core  80  which is used to form one or more internal cavities. 
     Referring now to  FIGS. 2 and 3 , there is shown one of the cores  12  to be used for forming a cooling circuit within the walls of the airfoil portion of the turbine engine component. The core  12  has an array of metering/tripping features  16  in the form of rows of shaped slots. The metering/tripping features  16  form a plurality of protrusions in the cooling microcircuit, which protrusions create turbulence in the cooling air flow. 
     The core  12  further includes a plurality of teardrop features  18  also in the form of slots having a teardrop or near teardrop shape. Each of the teardrop features  18  has a longitudinal axis  20  and is symmetrical about the longitudinal axis  20 . Further, each of the teardrop features  18  has a trailing edge  22  which ends a distance from a line or terminal edge  24  where the core  12  meets an airfoil wall. Each of the teardrop features  18  has a converging wall portion  25 . The space between the teardrop features  18  forms a series of outlet passages  29  having diverging walls, which outlet passages terminate in a series of film cooling holes  31  (see  FIG. 5 ). 
     The core  12  further has a portion  34  which forms entrances for allowing the cooling fluid to enter the cooling microcircuit. The core  12  has a portion  26  which forms a plenum area between the entrance forming portion  24  and the metering/tripping features  16 . 
     When the part is manufactured, cooling air flow from the main body core enters through a number of entrances formed by the portion  34  into the plenum area  26 . The cooling air flow then passes through a series of passageways formed by protrusions created by the metering/tripping features  16  and finally through the fluid passageways formed by the teardrop features  18  where the cooling air expands prior to exiting onto the external surface of the airfoil via film cooling holes  31 . 
     Referring now to  FIG. 4 , there is shown the core  14  which is different in several respects from the core  12 . As with core  12 , the core  14  has inlet forming features (not shown) which form one or more entrances to the cooling circuit passages and a plurality of metering/tripping features  16 ′. As before, the metering/tripping features take the form of one or more rows of shaped slots for forming a plurality of protrusions. The core  14  further has a plurality of teardrop features  18 ′ which have a longitudinal axis  20 ′ and are symmetrical about their respective longitudinal axis  20 ′. The teardrop features  18 ′ are the outermost ones of the teardrops. As before, the teardrop features have converging wall portions  25 ′ which form a series of diverging passageways  29 ′ which terminate in cooling holes  31 ′ (see  FIG. 5 ). 
     The core  14  differs from the core  12  in that it also has a central teardrop feature  40  and two asymmetrical teardrop features  42  adjacent to the central teardrop feature  40 . The central teardrop feature  40  is smaller in size than the teardrop features  18 ′. It has a trailing edge  43  which is spaced farther from the line or terminal edge  24 ′ than the trailing edges of the other teardrop features  18 ′ and  42 . Each of the teardrop features  42  has a longitudinal axis  46  and is asymmetric with respect to said axis  46 . Further, each of the teardrop features  42  has a trailing edge  44  which is formed by either a planar surface at an angle to the longitudinal axis  46  or an arcuate surface. The presence of the shorter central teardrop feature  40  creates a space  49  which is bordered by a portion  48  of the sidewalls  50  of the teardrop features  42 . The sidewall portions  48  together form a converging fluid passageway  52 . 
     The presence of the space  49  allows a final machining operation which cuts back the space  49  to form a diverging portion to the cooling fluid outlet  54  which enables the cooling flow to be increased as needed. For example, the cooling fluid outlet  54  may be formed using an EDM process. The farther the EDM electrode is pushed into the space  49 , the larger the exit of the cooling fluid outlet  54  will be. One of the results of using the core  14  is that the center of the core  14  will have more cooling fluid flow than the sides of the core  14  due to the presence of a cooling fluid outlet  54  which has a converging/diverging shape. The location of the throat portion in the converging/diverging outlet  54  determines the amount of fluid which will flow out of the outlet  54 . Further, given the presence of staggered cooling fluid outlets in the final part, extra air will be hitting in areas where the airfoil portion can be cooling challenged. 
     The cores  14  may be arrayed, as shown in  FIG. 1 , in a fan type configuration where each core is joined to the ceramic core(s)  80  which form the central cooling fluid passageway(s) in the final airfoil portion. 
     Each of the cores  12  and  14  may be formed from either a ceramic material or from a refractory metal material. 
     Referring now to  FIG. 5 , there is shown a portion of the airfoil portion  60  of the turbine engine component having a plurality of cooling microcircuits formed within at least one of its walls. As can be seen from this figure, there are two different types of cooling fluid outlet arrays formed by the cores  12  and  14 . The outermost array  62  of cooling fluid holes have film cooling holes  31  which are uniformly shaped and sized. The innermost array  64  of cooling fluid holes have a plurality of converging/diverging outlets  54  and a plurality of outer uniformly sized and diverging cooling holes  31 ′. 
     Referring now to  FIG. 6 , to form the turbine engine component, in step  100 , one forms the arrays  62  and  64  by positioning the cores  12  and  14  in a mold (not shown) in a desired pattern. Each of the cores  12  and  14  may be joined to the ceramic core(s)  80  which form the central cooling passageways in the interior of the airfoil portion  60 . In step  102 , after the cores  12  and  14  have been positioned in the mold, the turbine engine component with the airfoil portion  60  is formed by casting a metal or metal alloy. The casting technique which is used in step  102  may be any suitable casting technique known in the art. In step  104 , the cast material is allowed to solidify. In step  106 , following casting and solidification of the metal or metal alloy forming the turbine engine component, the cores  12  and  14  are removed. Removal of the cores may be carried out using any suitable process known in the art such as a chemical leaching process or a mechanical removing process. In step  108 , a suitable drilling process, such as EDM, is used to form the diverging portion of the converging/diverging outlets  54 . As discussed above, when using an electrode in an EDM technique, the further the electrode used to machine the outlet  54  is pushed into the cast turbine engine component, the larger the exit to the outlet  54  will be. 
       FIG. 7  illustrates a turbine engine component  90  having an airfoil portion  60  with the arrays  62  and  64 . 
     The technique described herein for forming the converging/diverging outlets  54  is desirable because it allows one to account for tolerances which occur as dies are used and experience wear and better control the flow of the cooling fluid. 
     While the converging/diverging outlet  54  has been described as being at the center of the outlet array, the converging/diverging outlet  54  may be offset from the center to create flow as needed. 
     There has been described in the instant disclosure a drill to flow mini core. While the drill to flow mini core has been described in the context of specific embodiments thereof, other unforeseen alternatives, modifications, and variations may become apparent to those skilled in the art having read the foregoing description. It is intended to embrace those alternatives, modifications, and variations as fall within the broad scope of the appended claims.