Abstract:
An example blade outer air seal assembly may consist of a blade outer air seal containing channels that communicate cooling air through at least some of the blade outer air seal. The blade outer air seal has at least one circumferentially extending barrier separating the leading channel into a forward portion and an aft portion. Cooling air outlets from the leading channel are exclusively coupled to the aft portion.

Description:
BACKGROUND 
       [0001]    This disclosure relates to a blade outer air seal (BOAS) and, more particularly, to a multi-channel blade outer air seal (BOAS). 
         [0002]    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. 
         [0003]    An outer case, including a multiple of blade outer air seals (BOAS), provides an outer radial flow path boundary. A multiple of BOAS are typically provided 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 then through cooling channels within the BOAS for temperature control. The cooling channels used to communicate the cooling air through the blade outer air seal can provide entry points for hot gas ingestion if the back flow margin is not high enough. 
       SUMMARY 
       [0004]    An example blade outer air seal assembly may consist of a blade outer air seal containing channels that communicate cooling air through at least some of the blade outer air seal. The blade outer air seal has at least one circumferentially extending barrier separating the leading channel into a forward portion and an aft portion. Cooling air outlets from the leading channel are exclusively coupled to the aft portion. 
         [0005]    An example blade outer air seal casting core includes a core having a first open area configured to establish a corresponding axially extending barrier within a channel of a blade outer air seal, and a second open area configured to establish a corresponding circumferentially extending barrier within the channel of the blade outer air seal. The first open area may be positioned near a circumferential midpoint of the core. 
         [0006]    A blade outer air seal cooling method including introducing cooling air to a leading channel established in a blade outer air seal, and communicating cooling air away from the leading channel using, exclusively, one or more outlets coupled with an aft portion of the leading channel. 
         [0007]    These and other features of the disclosed examples can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0008]      FIG. 1  shows a cross-section of an example turbomachine. 
           [0009]      FIG. 2  shows a perspective view of an example blade outer air seal from the  FIG. 1  turbomachine. 
           [0010]      FIG. 3  shows a perspective view of the  FIG. 2  blade outer air seal at a radial cross-section through the cooling channels. 
           [0011]      FIG. 4  shows an inwardly facing surface of a core used to form a leading channel in the  FIG. 2  blade outer air seal. 
           [0012]      FIG. 5  shows a section view at line  5 - 5  in  FIG. 4 . 
           [0013]      FIG. 6  shows a simplified view of flow through the leading channel in the  FIG. 2  blade outer air seal. 
           [0014]      FIG. 7  shows a simplified view of flow through the leading channel in a PRIOR ART blade outer air seal. 
           [0015]      FIG. 8  graphically shows example pressures at different axial locations along the  FIG. 2  blade outer air seal. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Referring to  FIG. 1 , an example turbomachine, such as a gas turbine engine  10 , is circumferentially disposed about an axis  12 . The gas turbine engine  10  includes a fan section  14 , a low-pressure compressor section  16 , a high-pressure compressor section  18 , a combustion section  20 , a high-pressure turbine section  22 , and a low-pressure turbine section  24 . Other example turbomachines may include more or fewer sections. 
         [0017]    During operation, air is compressed in the low-pressure compressor section  16  and the high-pressure compressor section  18 . The compressed air is then mixed with fuel and burned in the combustion section  20 . The products of combustion are expanded across the high-pressure turbine section  22  and the low-pressure turbine section  24 . 
         [0018]    The high-pressure compressor section  18  includes a rotor  32 . The low-pressure compressor section  16  includes a rotor  34 . The rotors  32  and  34  are configured to rotate about the axis  12 . The example rotors  32  and  34  include alternating rows of rotatable airfoils or rotatable blades  36  and static airfoils or static blades  38 . 
         [0019]    The high-pressure turbine section  22  includes a rotor  40  that is rotatably coupled to the rotor  32 . The low-pressure turbine section  24  includes a rotor  42  that is rotatably coupled to the rotor  34 . The rotors  40  and  42  are configured to rotate about the axis  12  in response to expansion to drive the high-pressure compressor section  18  and the low-pressure compressor section  16 . The example rotors  40  and  42  include alternating rows of rotatable airfoils or rotatable blades  44  and static airfoils or static vanes  46 . 
         [0020]    The examples described in this disclosure is not limited to the two-spool gas turbine architecture described, and may be used in other architectures, such as a single-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. 
         [0021]    Referring to  FIGS. 2 and 3  with continuing reference to  FIG. 1 , an example blade outer air seal (BOAS)  50  is suspended from an outer casing of the gas turbine engine  10 . In this example, the BOAS  50  is located within the high-pressure turbine section  22  of the gas turbine engine  10 . During operation of the gas turbine engine  10 , an inwardly facing surface  52  of the example BOAS  50  interfaces and seals against tips of blades  40  in known manner. 
         [0022]    Attachment structures are used to secure the BOAS  50  within the engine  10 . The attachment structures in this example include a leading hook  55   a  and a trailing hook  55   b.    
         [0023]    The BOAS  50  is one of a group of several BOASs that circumscribe the rotor  42 . The BOAS  50  establishes an outer diameter of the core flow path through the engine  10 . Other areas of the engine  10  include other circumferential ring arrays of BOASs that circumscribe a particular blade stage of the engine  10 . 
         [0024]    Cooling air is moved through the BOAS  50  to communicate thermal energy away from the BOAS  50 . The cooling air moves from a cooling air supply  54  through apertures, such as inlet holes  56   a   1 - 56   e,  established in an outwardly facing surface  58  of the BOAS  50 . The cooling air supply  54  is located radially outboard from the BOAS  50 . 
         [0025]    Cooling air moves radially through the inlet holes  56   a   1 - 56   a   4  into a channel  66   a  established within the BOAS  50 . The inlet holes  56   a   1  and  56   a   2  are considered primary inlet holes, and the inlet holes  56   a   3  and  56   a   4  are secondary inlet holes (or optional resupply holes). Cooling air also moves radially through the inlet holes  56   b  into a cavity  66   b,  through the inlet holes  56   c  into a channel  66   c,  through the inlet holes  56   d  into a channel  66   d,  and through the inlet holes  56   e  into a channel  66   e.  Cooling air is not free to move between the cavities  66   a - 66   e  after entering the cavities  66   a - 66   e.    
         [0026]    The cooling air exits the BOAS  50  through apertures, such as outlet holes  68   a   1 - 68   e,  which are established in circumferential end portion  70   a  or a circumferential end portion  70   b  of the BOAS  50 . In this example, the outlet holes  68   a   1  and  68   a   2  communicate cooling air away from the channel  66   a  exclusively. Also, the outlet hole  68   b  communicates cooling air away from the channel  66   b,  the outlet hole  68   c  communicates cooling air away from the channel  66   c,  etc. 
         [0027]    The cooling air moves circumferentially as the cooling air exits the BOAS  50  through the outlet holes  68   a   1 - 68   e.  The cooling air moving from the outlet holes  68   a   1 - 68   e  contacts a circumferentially adjacent BOAS within the engine  10 . The BOAS  50  may interface with the circumferentially adjacent BOAS through a shiplapped joint, for example. 
         [0028]    The example BOAS  50  extends axially from a leading edge  72  to a trailing edge  74 . Notably, the outlet holes  68   a   1 - 68   e  in the example BOAS  50  are spaced from the leading edge  72 . The channel  66   a  is considered a leading channel as the channel  66   a  is the channel of BOAS that is closest to the leading edge  72 . 
         [0029]    Specifically, the outlet holes  68   a   1  through  68   e  are axially spaced from the leading edge  72 . 
         [0030]    The channel  66   a  closest to the leading edge  72  includes a front edge  75   a  and a rear edge  75   b.  The outlet holes  68   a   1  and  68   a   2  are each aft the front edge  75   a.  Also, each of the outlet holes  68   a   1  and  68   a   2  (in this example) is aft the leading hook  55   a.  The remaining channels  66   b - 66   e  (and their respective outlet holes  68   b - 68   e ) are aft of channel  66   a.  Thus, no cooling air moves from the BOAS  50  forward the front edge  75   a  or leading hook  55   a.    
         [0031]    Regarding the channel  66   a,  the outlet holes  68   a   i  and  68   a   2 , are each closer to the rear edge  75   b  than the front edge  75   a.  The gas path pressure of the main flow path through the engine  10  is lower near the axially trailing edge  74  than the axially leading edge  72 . Thus, moving cooling air outlet holes  68   a  and  68   a   2  rearward increases back flow margin and lessens the likelihood of ingestion from the main flow path into the channel  66   a.    
         [0032]    Features of the BOAS  50  manipulate flow of cooling air through the channel  66   a.  Such features include axially extending barriers  76   a  and  76   b,  circumferentially extending barriers  78   a  and  78   b,  and trip strips  80 . In this example, the cavities  66   b - 66   e  also include trip strips  80 , but do not include axially or circumferentially extending barriers. 
         [0033]    The example axially extending barriers  76   a  and  76   b  project radially from an inner diameter surface  82  of the channel  66   a  and contact the outwardly facing surface  58 . The axially extending barrier  76   a  is a leading axial barrier. The axially extending barrier  76   b  is a trailing axial barrier. The example axially extending barriers  76   a  and  76   b  are positioned near a circumferential middle of the channel  66   a  and limit circumferential flow of cooling air through the channel  66   a.  The barriers  76   a  and  76   b  are axially aligned with the axis of rotation  12  ( FIG. 1 ). The barriers  76   a  and  76   b  are also perpendicular to the front edge  75   a.    
         [0034]    The example circumferentially extending barriers  78   a  and  78   b  also project radially from the inner diameter surface  82  of the channel  66  and contact the outwardly facing surface  58 . The example barriers  78   a  and  78   b  are designed to maximize heat transfer coefficients in the channel  66   a.  The example circumferentially extending barriers  78   a  and  78   b  are tapered relative to the front edge  75   a  and the rear edge  75   b,  which help focus flow of cooling air within the channel  66   a  and limits axial flow of cooling air through the channel  66   a.  The circumferentially extending barriers  78   a  and  78   b  are both tapered toward the axially extending barrier  76   a.    
         [0035]    The trip strips  80  project radially from the inner diameter surface  82  of the channel  66   a,  but do not contact the outwardly facing surface  58 . The trip strips  80  turbulate flow of cooling air within the channel  66   a,  which facilitates transfer of thermal energy from the BOAS  50  to the cooling air. 
         [0036]    Referring now to  FIGS. 4 and 5  with continuing reference to  FIGS. 2 and 3 , in this example, the channel  66   a  is formed within the BOAS  50  using an investment casting process. A ceramic core  90  can be used during the casting process to establish the channel  66   a  and the features within the channel  66   a.  Open areas  92  of the core  90  receive material that establishes the barriers  76   a,    76   b,    78   a,  and  78   b.  Grooves  98  in the core  90  establish the trip strips  80 . The other cavities  66   b - 66   e  are formed using other cores (not shown). 
         [0037]    Referring now to  FIG. 6  with continuing reference to  FIG. 2 , the circumferentially extending barriers  78   a  and  78   b  divide the channel  66   a  into a forward channel portion  100  and an aft channel portion  102 . During operation, cooling air entering the channel  66   a  through the primary inlet holes  56   a   1  moves generally along path P 1  and cooling air entering the channel  66  through primary inlet holes  56   a   2  moves generally along path P 2 . The paths P 1  and P 2  are both in the forward channel portion  100 . 
         [0038]    Cooling air moving along the paths P 1  and P 2  contacts the barrier  76   a,  which redirects cooling air moving along the paths P i  and P 2  through one or both of the openings  86  and  88 . The opening  86  is established between the barriers  76   b  and  78   a.  The opening  88  is established between the barriers  76   b  and  78   b.  The cooling air transitions from the forward channel portion  100  to the aft channel portion  102  as the cooling air moves through one of the openings  86  or  88 . 
         [0039]    Cooling air that has moved through the opening  86  then moves generally in a direction P 3  to the corresponding outlet hole  68   a   2 . Cooling air that has moved through the opening  88  moves generally in a direction P 4  to the other one of the outlet holes  68   a   1 . Cooling air that has moved along the path P 1  and is redirected into the opening  86  thus flows in opposite circumferential directions within the channel  66   a.  Similarly, cooling air that has moved along path P 2  and is redirected into the opening  88  flows in opposite circumferential directions within the channel  66   a.  The outlet holes  68   a   1  and  68   a   2  are both within (or coupled to) the aft channel portion  102 . 
         [0040]    Additional cooling air may be introduced to the channel  66   a  though the resupply inlet holes  56   a   3 . This additional cooling air is combined with the cooling air that has moved through the opening  86  and is moving along the path P 3 . Additional cooling air may be introduced to the channel  66   a  though the resupply inlet hole  56   a   4 . This additional cooling air is combined with the cooling air that has moved through the opening  88  and is moving along the path P 4 . The resupply inlet holes  56   a   3  and  56   a   4  are optional. That is, the primary inlet holes  56   a  and  56   b  may be used exclusively to move air into the channel  66   a.    
         [0041]    As can be appreciated, tapering the barriers  78   a  and  78   b  focuses flow of cooling air toward the barrier  76   a  when the air moves along the paths P 1  and P 2 , and focuses flow of cooling air toward one of the outlet holes  68   a   1  and  68   a   2  when the air moves along the paths P 3  and P 4 . The example barriers  76   a,    76   b,    78   a,  and  78   b  do not extend across the entire channel  66   a.  Thus, the channel  66   a  is considered a single channel separate from the other cavities  66   b - 66   e.    
         [0042]    Referring now to  FIG. 7  with continuing reference to  FIG. 6 , leading edge cavities  200  and  204  in a prior art blade outer air seal  208  communicate air along a path P 5  or P 6  in a single circumferential direction. The air moving along path P 5  exits the channel  200  at an outlet  210 . The air moving along path P 6  exits the channel at an outlet  212 . 
         [0043]    Circulating cooling air flow circumferentially through only about half of the circumferential channel length of the BOAS  50 , means that the cooling air moving along paths P 1  and P 2  is cooler than the cooling air that has moved the full circumferential channel length, such as the air moving along paths P 5  and P 6 . The cooler air can be reused to cool by being moved along paths P 3  and P 4 . Reducing the cooling air requirement is desirable in jet engines. However, if more cooling air needs to move along paths P 3  and P 4 , the additional air can be fed through secondary inlet holes (resupply holes)  56   a   3  and  56   a   4 . 
         [0044]    Features of the disclosed embodiments include directing cooling air to exit farther axially aft of a BOAS leading edge into a lower gas path pressure. Communicating cooling air to a lower exit pressure reduces the chance of hot gas ingestion into the BOAS and helps to satisfy Back Flow Margin Requirements. The efficiency of the turbomachine is also improved because less cooling air is required than prior art designs. The leading edge of the BOAS is able to be maintained at a lower temperature. 
         [0045]    Another feature is more control over cooling flow at the leading edge of the blade outer air seal. For example, the disclosed embodiments provide more uniform circumferential cooling of the blade outer air seal. In the disclosed embodiments, the majority of the cooling air travels through about half of the blade outer air seal&#39;s circumferential length rather than the entire circumferential length, which provides more cooling if the leading edge is hot. 
         [0046]    Yet another feature is the ability to add more cooling flow if the leading edge of the blade outer air seal is a hot spot. For example, resupply holes can reduce the temperature of the cooling air after the cooling air has passed through the openings  86  and  88 . 
         [0047]    Still another feature is that, if film credit is take for Leading Edge Purge, (cooling air that dumps directly to the gas path between the first vane and first blade outer air seal), the cooling flow to the leading edge channel can be reduced (lower cooling air requirement results in higher efficiency for the engine). Alternatively, resupply holes can be added to reduce the cooling flow temperature before cooling the second row (which results in an increased heat transfer coefficient in the second row and a cooling blade outer air seal). 
         [0048]    The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. Thus, the scope of legal protection given to this disclosure can only be determined by studying the following claims.