Patent Publication Number: US-10309255-B2

Title: Blade outer air seal cooling passage

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 61/918,249, which was filed on Dec. 19, 2013 and is incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with government support with the United States Air Force under Contract No.: FA8650-09-D-2923 0021. The government therefore has certain rights in this invention. 
    
    
     BACKGROUND 
     This disclosure relates to a blade outer air seal (BOAS) and, more particularly, to a cooling passage for a BOAS. 
     Gas turbine engines generally include fan, compressor, combustor and turbine sections along an engine axis of rotation. The fan, compressor, and turbine sections each include a series of stator and rotor blade assemblies. A rotor and an axially adjacent array of stator assemblies may be referred to as a stage. Each stator vane assembly increases efficiency through the direction of core gas flow into or out of the rotor assemblies. 
     An outer case supports multiple BOAS, which provide an outer radial flow path boundary. The BOAS are designed to accommodate thermal and dynamic variation typical in a high pressure turbine (HPT) section of the gas turbine engine. The BOAS are subjected to relatively high temperatures and receive a secondary cooling airflow for temperature control. The secondary cooling airflow is communicated into the BOAS through cooling channels within the BOAS for temperature control. 
     One type of BOAS includes multiple discrete cooling passages, each of which are fed cooling fluid through a single inlet hole in a backside of the BOAS. The cooling passages included chevron-shaped turbulators along the entire length of the cooling passage to improve cooling one the core gas flow side of the BOAS. 
     SUMMARY 
     In one exemplary embodiment, a gas turbine engine component includes a structure including a first wall and a second wall that provide a cooling passage. The cooling passage extends a length from a first end to a second end. A cluster of impingement inlet holes is provided in the second wall at the first end. An outlet is provided at the second end. 
     In a further embodiment of the above, the structure is a blade outer air seal. 
     In a further embodiment of any of the above, the cooling passage extends in a circumferential direction and is provided between lateral walls. The outlet is provided in one of the lateral walls. 
     In a further embodiment of any of the above, the structure includes multiple parallel cooling passages. 
     In a further embodiment of any of the above, the first wall includes a sealing surface. The second wall provides an outer wall that is configured to be in fluid communication with a cooling source. 
     In a further embodiment of any of the above, at least one of the first and second walls includes turbulators that are arranged downstream from the cluster of impingement inlet holes. 
     In a further embodiment of any of the above, the turbulators are chevrons. 
     In a further embodiment of any of the above, a first region is provided within the cooling passage beneath the cluster of impingement inlet holes. A second region includes the turbulators. 
     In a further embodiment of any of the above, the first region extends in the range of 25-65% of the length. 
     In a further embodiment of any of the above, the first region has lower fluid friction than the second region. 
     In another exemplary embodiment, a gas turbine engine component includes a structure that includes a first wall and a second wall that provide a cooling passage. The cooling passage extends a length from a first end to a second end. An impingement inlet hole is provided in the second wall at the first end. An outlet is provided at the second end. A first region is provided within the cooling passage beneath the impingement inlet hole. A second region includes turbulators. The first region extends in the range of 25-65% of the length. 
     In a further embodiment of the above, the structure is a blade outer air seal. 
     In a further embodiment of any of the above, the cooling passage extends in a circumferential direction and is provided between lateral walls. The outlet is provided in one of the lateral walls. 
     In a further embodiment of any of the above, the structure includes multiple parallel cooling passages. 
     In a further embodiment of any of the above, the first wall includes a sealing surface. The second wall provides an outer wall that is configured to be in fluid communication with a cooling source. 
     In a further embodiment of any of the above, at least one of the first and second walls includes turbulators that are arranged downstream from a cluster of inlet holes in the second wall. 
     In a further embodiment of any of the above, the turbulators are chevrons. 
     In a further embodiment of any of the above, the first region is provided within the cooling passage beneath the cluster of impingement inlet holes. 
     In a further embodiment of any of the above, the second region has a Darcy friction factor that is higher than a Darcy friction factor of the first region. 
     In a further embodiment of any of the above, the first region has a Darcy friction factor of around 1.0, and the second region has a Darcy friction factor of around 8.4. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1  is a highly schematic view of an example turbojet engine. 
         FIG. 2  is a schematic view of a turbine section of an example engine. 
         FIG. 3  is a schematic view of a blade outer air seal. 
         FIG. 4  is a cross-sectional view of a blade outer air seal taken along line  4 - 4  of  FIG. 5 . 
         FIG. 5  is a cross-sectional view of a blade outer air seal taken along line  5 - 5  of  FIG. 4 . 
     
    
    
     The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an example turbojet engine  10 . The engine  10  generally includes a fan section  12 , a compressor section  14 , a combustor section  16 , a turbine section  18 , an augmentor section  19  and a nozzle section  20 . The compressor section  14 , combustor section  16  and turbine section  18  are generally referred to as the core engine. An axis A of the engine  10  extends longitudinally through the sections. An outer engine duct structure  22  and an inner cooling liner structure  24 , or exhaust liner, provide an annular secondary fan bypass flow path  26  around a primary exhaust flow path E. 
     While a military engine is shown, the disclosed blade outer air seal may be used in commercial and industrial gas turbine engines as well. The examples described in this disclosure is not limited to a single-spool gas turbine and may be used in other architectures, such as a two-spool axial design, a three-spool axial design, and still other architectures. That is, there are various types of gas turbine engines, and other turbomachines, that can benefit from the examples disclosed herein. 
     The example turbine section  18  includes multiple fixed stages  30   a ,  30   b  and multiple rotatable stages  32   a ,  32   b , schematically shown in  FIG. 2 . Fewer or greater number of fixed and/or rotating stages may be used than depicted, if desired. 
     One of the rotatable stages  32   a  includes a rotor  34  supporting a circumferential array of blades  36  for rotation about the axis A. Blade outer air seals (BOAS)  38 , which are typically provided by multiple arcuate segments, are supported by the static structure of the engine to provide an annular gas seal relative to core gas flow C through the blades  36 . 
     Referring to  FIG. 3 , the (BOAS)  38  includes forward and aft hooks  40 ,  42  used to secure the BOAS to the static structure. The BOAS  38  includes a first wall  44  providing a sealing surface that provides a gas seal relative to a tip  46  of the blade  36 . A second wall  48  is spaced from the first wall  44  and provides an outer wall that is in fluid communication with a cooling air supply  50 . The cooling air supply may be provided by an upstream stage, such as air from the compressor section. 
     One or more cooling passages  52  are provided in the BOAS  38  between the first and second walls  44 ,  48 . In the example, the multiple cooling passages are provided parallel to one another and arranged in a first or circumferential direction. In one example, around six to ten cooling passages  52  may be provided in a blade outer air seal  38 . 
     A cluster of impingement inlet holes  54  is provided in the second wall  48  and is in fluid communication with the cooling air supply  50  to supply the cooling air to the cooling passages  52 . The impingement holes  54  may be provided using a drilling or electro discharge machining process, for example. Outlets  56  are in fluid communication with the cooling passages  52  and may be provided in spaced apart lateral walls  53  that are next to circumferentially adjacent BOAS. The outlets  56  purge core gas flow from the gap between the adjacent BOAS. 
     Referring to  FIGS. 4 and 5 , the cooling passage  52  extends a length L from a first end  58  to a second end  60 . The outlet  56  is provided in the second end  60 . First and second regions  62 ,  64  are respectively arranged at the first and second ends  58 ,  60 . 
     The impingement holes  54  is arranged at the first end  58  such that cooling air impinges upon the first wall  48  in the first region  62 . In the example, the first region includes relatively smooth walls providing a Darcy friction factor of around 1.0. The first region extends along the cooling passage  52  a length L 1  in the range of 25-65%, and in one example, 30-60%. 
     Turbulators  66  are provided in the second region  64 , which is arranged downstream from the impingement holes  54 . In the example, the turbulators  66  are provided by an array of chevron-shaped protrusions extending from at least one of the first and second walls  44 ,  48 . In the example, the turbulators  66  are provided on the first wall  44 , which reduces the heat from the core gas flow path. In one example, the second region  64 , extending a length L 2 , has higher friction factor than in the first region  62 . In one example, the Darcy friction factor of the second region is around 8.4. 
     The disclosed blade outer air seal cooling scheme may also be used in a compressor section, if desired, as well as other gas turbine engine components, such as vanes, blades, exhaust liners, combustor liners, or augmenter liners. 
     The blade outer air seal reduces the friction losses within the cooling passages because first region  62  has lower fluid friction than in second region  64 , as compared to prior art blade outer air seals. The cooling passage also provides a higher inlet area and reduces the flow restriction into the cooling passage. As a result, a reduced amount of supply pressure is needed for the same amount of cooling as compared to prior art cooling passages. Using a lower pressure cooling fluid reduces leakage and increases the cooling capacity for the same amount of cooling fluid flow. 
     It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention. 
     Although the different examples have specific components shown in the illustrations, embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples. 
     Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.