Patent Publication Number: US-2020291803-A1

Title: Boas carrier with dovetail attachments

Description:
BACKGROUND 
     This application relates to a blade outer air seal carrier having dovetail attachments. 
     Gas turbine engines are known and typically include a compressor compressing air and delivering it into a combustor. The air is mixed with fuel in the combustor and ignited. Products of the combustion pass downstream over turbine rotors, driving them to rotate. 
     It is desirable to ensure that the bulk of the products of combustion pass over turbine blades on the turbine rotor. As such, it is known to provide blade outer air seals radially outwardly of the blades. Blade outer air seals have been proposed made of ceramic matrix composite fiber layers. 
     SUMMARY 
     In one exemplary embodiment, a blade outer air seal assembly includes a support structure. A blade outer air seal has a plurality of seal segments arranged circumferentially about an axis and mounted in the support structure by a carrier. The carrier has first and second hooks that extend radially outward from a platform along an axial length of the carrier. The first and second hooks are in engagement with the support structure. 
     In a further embodiment of the above, the first hook extends generally in a first circumferential direction. The second hook extends generally in a second circumferential direction opposite the first circumferential direction. 
     In a further embodiment of any of the above, the first and second hooks form a dovetail shape for engagement with the support structure. 
     In a further embodiment of any of the above, the dovetail shape has a ratio of a circumferential width to a radial height of about  3 . 
     In a further embodiment of any of the above, at least a portion of the platform is arranged within a passage of the seal segment. 
     In a further embodiment of any of the above, the carrier comprises a plurality of carrier segments. Each of the carrier segments are arranged between adjacent seal segments. 
     In a further embodiment of any of the above, a post extends radially outward from the platform and engages with an edge of the seal segment. 
     In a further embodiment of any of the above, the post is arranged circumferentially outward of the first and second hooks. 
     In a further embodiment of any of the above, a channel is arranged between the first and second hooks on the carrier. The channel is configured to accommodate an anti-rotation protrusion extending radially inward from the support structure. 
     In a further embodiment of any of the above, the channel extends partially through the carrier in an axial direction and terminates at a wall connecting the first and second hooks. 
     In a further embodiment of any of the above, the wall is near a trailing edge of the carrier. 
     In a further embodiment of any of the above, a notch is arranged in one of the first and second hooks. 
     In a further embodiment of any of the above, the notch is configured to permit cooling air to flow in a generally radial direction between the carrier and the segment. 
     In a further embodiment of any of the above, a tab extends from the platform in a generally radial direction and engages a portion of the seal segment. 
     In a further embodiment of any of the above, the blade outer air seal has first and second walls that extend from an inner platform and are joined at an outer wall to form a circumferentially extending passage. 
     In a further embodiment of any of the above, the blade outer air seal is a ceramic matrix composite material. 
     In a further embodiment of any of the above, the support structure is a metallic material. 
     In a further embodiment of any of the above, the carrier is a metallic material. 
     In another exemplary embodiment, a turbine section for a gas turbine engine includes a turbine blade that extends radially outwardly to a radially outer tip and for rotation about an axis of rotation. A blade outer air seal has a plurality of seal segments arranged circumferentially about the axis of rotation. Each of the segments are mounted in a support structure radially outward of the outer tip via a carrier. The carrier has a plurality of carrier segments. Each carrier segment has first and second hooks that extend radially outward from a platform to form a dovetail shape. The first and second hooks are in engagement with the support structure. The platform is arranged within a passage of the seal segment. 
     In a further embodiment of any of the above, the blade outer air seal is a ceramic matrix composite material. The carrier is a metallic material. 
     These and other features may be best understood from the following drawings and specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically shows a gas turbine engine. 
         FIG. 2  shows a portion of a turbine section. 
         FIG. 3  shows a view of an exemplary blade outer air seal assembly. 
         FIG. 4  shows a cross-section of the exemplary blade outer air seal assembly of  FIG. 3 . 
         FIG. 5  shows a portion of the exemplary blade outer air seal assembly. 
         FIG. 6  shows a portion of the blade outer air seal assembly. 
         FIG. 7  shows a portion of the exemplary blade outer air seal assembly. 
         FIG. 8  shows a portion of the exemplary blade outer air seal assembly. 
         FIG. 9  shows a portion of the exemplary blade outer air seal assembly. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates a gas turbine engine  20 . The gas turbine engine  20  is disclosed herein as a two-spool turbofan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . The fan section  22  drives air along a bypass flow path B in a bypass duct defined within a nacelle  15 , and also drives air along a core flow path C for compression and communication into the combustor section  26  then expansion through the turbine section  28 . Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures. 
     The exemplary engine  20  generally includes a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine static structure  36  via several bearing systems  38 . It should be understood that various bearing systems  38  at various locations may alternatively or additionally be provided, and the location of bearing systems  38  may be varied as appropriate to the application. 
     The low speed spool  30  generally includes an inner shaft  40  that interconnects, a first (or low) pressure compressor  44  and a first (or low) pressure turbine  46 . The inner shaft  40  is connected to the fan  42  through a speed change mechanism, which in the exemplary gas turbine engine  20  is illustrated as a geared architecture  48  to drive a fan  42  at a lower speed than the low speed spool  30 . The high speed spool  32  includes an outer shaft  50  that interconnects a second (or high) pressure compressor  52  and a second (or high) pressure turbine  54 . A combustor  56  is arranged in the exemplary gas turbine engine  20  between the high pressure compressor  52  and the high pressure turbine  54 . A mid-turbine frame  57  of the engine static structure  36  may be arranged generally between the high pressure turbine  54  and the low pressure turbine  46 . The mid-turbine frame  57  further supports bearing systems  38  in the turbine section  28 . The inner shaft  40  and the outer shaft  50  are concentric and rotate via bearing systems  38  about the engine central longitudinal axis A which is collinear with their longitudinal axes. 
     The core airflow is compressed by the low pressure compressor  44  then the high pressure compressor  52 , mixed and burned with fuel in the combustor  56 , then expanded over the high pressure turbine  54  and low pressure turbine  46 . The mid-turbine frame  57  includes airfoils  59  which are in the core airflow path C. The turbines  46 ,  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. It will be appreciated that each of the positions of the fan section  22 , compressor section  24 , combustor section  26 , turbine section  28 , and fan drive gear system  48  may be varied. For example, gear system  48  may be located aft of the low pressure compressor, or aft of the combustor section  26  or even aft of turbine section  28 , and fan  42  may be positioned forward or aft of the location of gear system  48 . 
     The engine  20  in one example is a high-bypass geared aircraft engine. In a further example, the engine  20  bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10), the geared architecture  48  is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3 and the low pressure turbine  46  has a pressure ratio that is greater than about five. In one disclosed embodiment, the engine  20  bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor  44 , and the low pressure turbine  46  has a pressure ratio that is greater than about five (5:1). Low pressure turbine  46  pressure ratio is pressure measured prior to inlet of low pressure turbine  46  as related to the pressure at the outlet of the low pressure turbine  46  prior to an exhaust nozzle. The geared architecture  48  may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3:1 and less than about 5:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans. 
     A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section  22  of the engine  20  is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet (10,668 meters). The flight condition of 0.8 Mach and 35,000 ft (10,668 meters), with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram ° R)/(518.7° R)] 0.5 . The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second (350.5 meters/second). 
       FIG. 2  shows a cross section of a portion of an example turbine section  28 , which may be incorporated into a gas turbine engine such as the one shown in  FIG. 1 . However, it should be understood that the turbine section  28  could be utilized in other gas turbine engines, and even gas turbine engines not having a fan section at all. 
     A turbine blade  102  has a radially outer tip  103  that is spaced from a blade outer air seal (“BOAS”) assembly  104 . The BOAS assembly  104  may be made up of a plurality of seal segments  105  that are circumferentially arranged in an annulus about the central axis A of the engine  20 . The seal segments  105  have a leading edge  106  and a trailing edge  108 . The seal segments  105  may be monolithic bodies that are formed of a high thermal-resistance, low-toughness material, such as a ceramic matrix composite (“CMC”). In another embodiment, the seal segments  105  may be formed from another material, such as monolithic ceramic or a metallic alloy. The BOAS segments  105  are mounted to a BOAS support structure  110  via an intermediate carrier  112 . The support structure  110  may be mounted to an engine structure, such as engine static structure  36 . In some examples, the support structure  110  is integrated with engine static structure  36 . 
       FIG. 3  shows an exemplary BOAS assembly  104 . The BOAS segment  105  is mounted to the engine  20  via the support structure  110  and intermediate carrier  112 . Each seal segment  105  has a platform  115  that defines radially inner and outer sides R 1 , R 2 , respectively, and first and second circumferential sides C 1 , C 2 , respectively. The radially inner side R 1  faces in a direction toward the engine central axis A. The radially inner side R 1  is thus the gas path side of the seal segment  105  that bounds a portion of the core flow path C. The leading edge  106  faces in a forward direction toward the front of the engine  20  (i.e., toward the fan  42 ), and the trailing edge  108  faces in an aft direction toward the rear of the engine  20  (i.e., toward the exhaust end). 
     The support structure  110  may be a unitary structure or a plurality of segments arranged circumferentially about the engine axis A. The support structure  110  has a plurality of hooks  116 ,  118  extending radially inward to engage with the intermediate carrier  112 . 
     The intermediate carrier  112  has a circumferentially extending platform  124  having several radial protrusions, such as hooks  120 ,  122 . Hooks  120 ,  122  extend radially outward from the platform  124  of the carrier  112  to engage the hooks  116 ,  118  of the support structure  110 . The hooks  120 ,  122  extend along the carrier  112  in the axial direction and hook in opposite circumferential directions to form a dovetail  121 . That is, hook  122  curves in a direction towards the first circumferential side C 1 , while hook  120  curves in a direction towards the second circumferential side C 2 . The dovetail  121  has a circumferential width W and a radial height H. The dovetail  121  may have an aspect ratio of width W to height H between about 2 and about 4, and in a further embodiment between about 2.5 and about 3.5. In one example, the dovetail  121  has an aspect ratio of the width W to the height H of about 3:1. 
     In the illustrated embodiment, the seal segment  105  is a loop BOAS segment. That is, the seal segment  105  generally has first and second walls  111 ,  113  extending radially outward from the platform  115  and joined by an outer wall  114  to form a circumferentially extending passage  130 . Edges  136 ,  137 ,  138  on the outer wall  114 , first wall  111 , and second wall  113 , respectively (shown in  FIGS. 5-6 ), provide surfaces for engagement with the carrier  112 . 
     In this embodiment, the seal segment  105  is formed of a ceramic matrix composite (“CMC”) material. The BOAS segment  105  is formed of a plurality of CMC laminate plies. The laminates may be silicon carbide fibers, formed into a woven fabric in each layer. The fibers may be coated by a boron nitride. In some embodiments it may be desirable to add additional material to make the laminates more stiff than their free woven fiber state. Thus, a process known as densification may be utilized to increase the density of the laminate material after assembly. Densification includes injecting material, such as a silicon carbide matrix material, into spaces between the fibers in the laminate plies. This may be utilized to provide 100% of the desired densification, or only some percentage. One hundred percent densification may be defined as the layers being completely saturated with the matrix and about the fibers. One hundred percent densification may be defined as the theoretical upper limit of layers being completely saturated with the matrix and about the fibers, such that no additional material may be deposited. In practice, 100% densification may be difficult to achieve. Although a CMC loop BOAS segment  105  is shown, other BOAS arrangements may be utilized within the scope of this disclosure. 
       FIG. 4  is a cross-sectional view of the blade outer air seal assembly of  FIG. 3  taken along line  4 - 4 . The platform  124  of the intermediate carrier  112  has a first end portion  126  and a second end portion  128 . The first and second end portions  126 ,  128  are configured to engage with the seal segment  105 . In this example, the seal segment  105  is a loop BOAS defining a circumferentially extending passage  130 . The end portions  126 ,  128  are inserted within the passage  130 . First and second posts  132 ,  134  are arranged on either side of the first and second hooks  120 ,  122  for engagement with the seal segment  105 . For example, the posts  132 ,  134  abut an edge  136  of the BOAS passage  130  when the carrier  112  is assembled with a seal segment  105 . The posts  132 ,  134  may help radially contain the carrier  112  and prevent rotation of the seal segment  105 . 
       FIG. 5  shows a view of the carrier  112  and BOAS segment  105 . An axially extending passage  140  is arranged between the first and second hooks  120 ,  122 . The passage  140  extends a portion of the axial length of the carrier  112  from the leading edge to a wall  142  near the trailing edge. The passage  140  provides weight reduction for the carrier  112 . The passage  140  also engages with anti-rotation tabs on the support structure  110  (shown in  FIGS. 8-9 ). The passage  140  may have a shoulder  144  for accommodating different anti-rotation features of the support structure  110 . 
     The first and second hooks  120 ,  122  may have first and second notches  146 ,  148 , respectively. The first and second notches  146 ,  148  extend radially through the first and second hooks  120 ,  122 . The first and second notches  146 ,  148  may permit cooling air to flow radially inward to the seal segment  105 . The first and second notches  146 ,  148  may also provide tooling access to the platform  124  to form posts  132 ,  134 . In one example, the posts  132 ,  134  are milled into the carrier  112 , and the notches  146 ,  148  permit tooling to form the posts  132 ,  134 . 
       FIG. 6  shows another view of the carrier  112  and BOAS segment  105 . A tab  150  extends radially outward from the platform  124 . The tab  150  may be near the trailing edge  108  of the seal segment  105 . The tab  150  engages with an edge  138  of the seal segment  105 , and provides an axial load-bearing surface. The first and second hooks  120 ,  122  may engage with an edge  137  of the seal segment  105  to provide an axial load-bearing surface near the leading edge  106 . 
       FIG. 7  shows the support structure  110 . The first and second hooks  116 ,  118  are arranged to accept the dovetail shaped hooks  120 ,  122  of the carrier  112 . An anti-rotation tab  160  extends radially inward from the support structure  110  between the first and second hooks  116 ,  118 . The anti-rotation tab  160  provides the radially inner-most portion of the support structure  110 . The anti-rotation tab  160  is arranged toward the trailing edge of the support structure  110 . Protrusions  162 ,  164  may also extend radially inward from the support structure  110  between the first and second hooks  116 ,  118 . The protrusions  162 ,  164  extend in a radial direction for at least a portion of the axial length of the support structure  110 . 
     As shown in  FIG. 8 , the protrusions  162 ,  164  engage with the shoulder  144  of the passage  140 . A gap G in the radial direction may be formed between the support structure  110  and the carrier  112 . This gap G permits some movement in the radial direction. The posts  132 ,  134  may limit the amount of movement in the radial direction by contacting the first and second hooks  116 ,  118  of the support structure  110 . 
       FIG. 9  shows a cross-sectional view of a portion of the support structure  110  and carrier  112 . The anti-rotation tab  160  abuts the wall  142  of the carrier  112 , which prevents rotation of the carrier  112  relative to the support structure  110 . The anti-rotation tab  160  is centered between the hooks  120 ,  122  and thus is centered on each seal segment  105  in the circumferential direction. The anti-rotation tab  160  may further support radial loads from the BOAS segment  105  or the carrier  112 . The anti-rotation tab  160  also prevents the carrier  112  from being assembled incorrectly, such as backwards. 
     The disclosed support structure  110  and carrier  112  having a dovetail arrangement permits a greater hook solidity. Hook solidity refers the contact area of the hooks, and in particular to a ratio of the arc length of the hooks  120 ,  122  on the carrier  112  to the total arc length of the carrier  112 . For example, if a length of the carrier  112  in the circumferential direction is 10 inches (254 mm), and the combined hook arc length of the hooks  120 ,  122  is 4 inches (101.6 mm) (i.e., each hook  120 ,  122  is 2 inches (50.8 mm)), the carrier will have a hook solidity of 40%. Known axially assembled BOAS carriers may have a hook solidity of about 40% shared between rows of leading edge and trailing edge hooks. The disclosed axially extending dovetail hook arrangement permits a greater hook solidity, which provides a more stable assembly  104 . The example carrier  112  and support structure  110  arrangement provides a hook solidity of greater than 40%. In one embodiment, the hook solidity is between about 40% and about 70%. In a further embodiment, the carrier  112  and support structure  110  have a hook solidity of about 50%. 
     The dovetail arrangement of the support structure  110  and carrier  112  enables larger contact areas between the carrier  112  and the support structure  110  than known axially-facing hooks. This arrangement may improve BOAS carrier stability. The dovetail arrangement also permits axial assembly of the entire BOAS assembly. The carrier  112  and support structure  110  permit the use of a ceramic BOAS, which is not as ductile as metallic materials. The ability to use ceramic BOAS promotes a more stable assembly. 
     In this disclosure, “generally axially” means a direction having a vector component in the axial direction that is greater than a vector component in the circumferential direction, “generally radially” means a direction having a vector component in the radial direction that is greater than a vector component in the axial direction and “generally circumferentially” means a direction having a vector component in the circumferential direction that is greater than a vector component in the axial direction. 
     Although an 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 disclosure. For that reason, the following claims should be studied to determine the true scope and content of this disclosure.