Patent Publication Number: US-2017362960-A1

Title: Turbine case boss

Description:
FIELD 
     The present disclosure relates to turbine cases and, more particularly, to bosses for turbine cases of gas turbine engines. 
     BACKGROUND 
     Turbine frame cases, such as a mid-turbine frame outer case, may contain bosses used to attach external parts. At some locations where no external parts are attached, the bosses may be in an unattached condition. Removing the boss from the case may create asymmetric stiffness. Accordingly, unused bosses may be left intact to maintain symmetric stiffness of the case. 
     SUMMARY 
     The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation thereof will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, the following description and drawings are intended to be exemplary in nature and non-limiting. 
     A stiffness boss for a turbine case of a gas turbine engine is disclosed. The stiffness boss includes a head portion disposed on an outer case surface of the turbine case, the head portion configured to provide rigidity in response to a transverse load being applied to the turbine case in a transverse direction. The stiffness boss also includes a leg portion disposed on the outer case surface of the turbine case and connected to the head portion, the leg portion configured to provide rigidity in response to an axial load being applied to the turbine case in an axial direction, such that deformation of the turbine case is resisted. 
     In any of the foregoing stiffness bosses, the head portion and the leg portion provide rigidity in response to a radial load being applied to the turbine case in a radially inward direction. 
     In any of the foregoing stiffness bosses, the head portion has a head length and head width determined to provide optimized rigidity and minimized weight. 
     In any of the foregoing stiffness bosses, the leg portion has a leg length and leg width determined to provide optimized rigidity and minimized weight. 
     In any of the foregoing stiffness bosses, the head portion is flat and is substantially parallel to an axis of the gas turbine engine. 
     In any of the foregoing stiffness bosses, the leg portion is flat and sloped radially inward. 
     In any of the foregoing stiffness bosses, the head portion and the leg portion are connected to the outer case surface by a filleted portion. 
     In any of the foregoing stiffness bosses, the filleted portion is curved radially inward. 
     A turbine case of a gas turbine engine is disclosed. The turbine case includes an outer case surface. The turbine case also includes a support member boss configured to secure support structures of the gas turbine engine. The turbine case also includes a stiffness boss disposed on the outer case surface and configured to provide rigidity in response to one or more loads applied to the turbine case, the stiffness boss being different from the support member boss. 
     In any of the foregoing turbine cases, the stiffness boss is a gusseted boss configured to provide rigidity in response to at least one of a transverse load, an axial load, or a radial load applied to the turbine case. 
     In any of the foregoing turbine cases, the stiffness boss comprises a head portion configured to provide rigidity in response to a transverse load being applied to the turbine case in a transverse direction, and a leg portion configured to provide rigidity in response to an axial load being applied to the turbine case in an axial direction, such that deformation of the outer case is resisted. 
     In any of the foregoing turbine cases, the head portion and the leg portion provide rigidity in response to a radial load being applied to the turbine case in a radially inward direction. 
     In any of the foregoing turbine cases, the head portion has a head length and head width determined to provide optimized rigidity and minimized weight. 
     In any of the foregoing turbine cases, the leg portion has a leg length and leg width determined to provide optimized rigidity and minimized weight. 
     In any of the foregoing turbine cases, the head portion is flat and is substantially parallel to an axis of the gas turbine engine. 
     In any of the foregoing turbine cases, the leg portion is flat and sloped radially inward. 
     In any of the foregoing turbine cases, the stiffness boss is at least one of welded, brazed, additively manufactured, machined, or cast on the outer case surface. 
     In any of the foregoing turbine cases, the stiffness boss and the turbine case are made of different materials. 
     A method of fabricating a turbine case is disclosed. The method includes disposing a head portion of a stiffness boss on an outer surface of the turbine case, the head portion configured to provide rigidity in response to a transverse load being applied to the turbine case. The method further includes disposing a leg portion of the stiffness boss on the outer surface of the turbine case, the leg portion configured to provide rigidity in response to an axial load being applied to the turbine case. 
     In any of the foregoing methods, the method further includes determining a head length and a head width of the head portion by optimizing rigidity and minimizing weight and determining a leg length and a leg width of the leg portion by optimizing rigidity and minimizing weight. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various features will become apparent to those skilled in the art from the following detailed description of the disclosed, non-limiting, embodiments. The drawings that accompany the detailed description can be briefly described as follows: 
         FIG. 1  is a schematic cross-section of a gas turbine engine having a turbine case, in accordance with various embodiments; 
         FIG. 2  is a perspective view of an outer case, in accordance with various embodiments; 
         FIG. 3  is a portion of the outer case including a stiffness boss, in accordance with various embodiments; 
         FIG. 4  illustrates a cross-section of the stiffness boss from a first orientation, in accordance with various embodiments; and 
         FIG. 5  illustrates a cross-section of the stiffness boss from a second orientation opposite the first orientation across a circumferential axis, in accordance with various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice embodiments of the disclosure, it should be understood that other embodiments may be realized and that logical changes and adaptations in design and construction may be made in accordance with this invention and the teachings herein. Thus, the detailed description herein is presented for purposes of illustration only and not limitation. The scope of the disclosure is defined by the appended claims. For example, the steps recited in any of the method or process descriptions may be executed in any order and are not necessarily limited to the order presented. Furthermore, any reference to singular includes plural embodiments, and any reference to more than one component or step may include a singular embodiment or step. Also, any reference to attached, fixed, connected or the like may include permanent, removable, temporary, partial, full and/or any other possible attachment option. Additionally, any reference to without contact (or similar phrases) may also include reduced contact or minimal contact. As used herein, “approximately” or “substantially” may refer to a measurement or dimension within 10% of the corresponding measurement of the referenced object. For example, a length that is substantially or approximately equal to a length of 10 feet may be between 9 feet and 11 feet. 
     Furthermore, any reference to singular includes plural embodiments, and any reference to more than one component or step may include a singular embodiment or step. Surface shading lines may be used throughout the figures to denote different parts but not necessarily to denote the same or different materials. 
     As used herein, “aft” refers to the direction associated with the exhaust (e.g., the back end) of a gas turbine engine. As used herein, “forward” refers to the direction associated with the intake (e.g., the front end) of a gas turbine engine. 
     A first component that is “radially outward” of a second component means that a first component is positioned at a greater distance away from the engine central longitudinal axis, than the second component. A first component that is “radially inward” of a second component means that the first component is positioned closer to the engine central longitudinal axis, than the second component. In the case of components that rotate circumferentially about the engine central longitudinal axis, a first component that is radially inward of a second component rotates through a circumferentially shorter path than the second component. The terminology “radially outward” and “radially inward” may also be used relative to references other than the engine central longitudinal axis. 
     In various embodiments and with reference to  FIG. 1 , an exemplary gas turbine engine  2  is provided. Gas turbine engine  2  may be a two-spool turbofan that generally incorporates a fan section  4 , a compressor section  6 , a combustor section  8  and a turbine section  10 . Alternative engines may include, for example, an augmentor section among other systems or features. In operation, fan section  4  can drive air along a bypass flow-path B while compressor section  6  can drive air along a core flow-path C for compression and communication into combustor section  8  then expansion through turbine section  10 . Although depicted as a turbofan gas turbine engine  2  herein, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures. 
     Gas turbine engine  2  may generally comprise a low speed spool  12  and a high speed spool  14  mounted for rotation about an engine central longitudinal axis X-X′ relative to an engine static structure  16  via several bearing systems  18 - 1 ,  18 - 2 , and  18 - 3 . It should be understood that various bearing systems at various locations may alternatively or additionally be provided, including for example, bearing system  18 - 1 , bearing system  18 - 2 , and bearing system  18 - 3 . 
     Low speed spool  12  may generally comprise an inner shaft  20  that interconnects a fan  22 , a low pressure compressor section  24  (e.g., a first compressor section) and a low pressure turbine section  26  (e.g., a first turbine section). Inner shaft  20  may be connected to fan  22  through a geared architecture  28  that can drive the fan  22  at a lower speed than low speed spool  12 . Geared architecture  28  may comprise a gear assembly  42  enclosed within a gear housing  44 . Gear assembly  42  couples the inner shaft  20  to a rotating fan structure. High speed spool  14  may comprise an outer shaft  30  that interconnects a high pressure compressor section  32  (e.g., second compressor section) and high pressure turbine section  34  (e.g., second turbine section). A combustor  36  may be located between high pressure compressor section  32  and high pressure turbine section  34 . A mid-turbine frame  38  of engine static structure  16  may be located generally between high pressure turbine section  34  and low pressure turbine section  26 . Mid-turbine frame  38  may support one or more bearing systems  18  (such as  18 - 3 ) in turbine section  10 . Inner shaft  20  and outer shaft  30  may be concentric and rotate via bearing systems  18  about the engine central longitudinal axis X-X′, which is collinear with their longitudinal axes. As used herein, a “high pressure” compressor or turbine experiences a higher pressure than a corresponding “low pressure” compressor or turbine. 
     The core airflow C may be compressed by low pressure compressor section  24  then high pressure compressor section  32 , mixed and burned with fuel in combustor  36 , then expanded over high pressure turbine section  34  and low pressure turbine section  26 . Mid-turbine frame  38  includes airfoils  40 , which are in the core airflow path. Turbines  26 ,  34  rotationally drive the respective low speed spool  12  and high speed spool  14  in response to the expansion. 
     Gas turbine engine  2  may be, for example, a high-bypass geared aircraft engine. 
     In various embodiments, the bypass ratio of gas turbine engine  2  may be greater than about six (6). In various embodiments, the bypass ratio of gas turbine engine  2  may be greater than ten (10). In various embodiments, geared architecture  28  may be an epicyclic gear train, such as a star gear system (sun gear in meshing engagement with a plurality of star gears supported by a carrier and in meshing engagement with a ring gear) or other gear system. Geared architecture  28  may have a gear reduction ratio of greater than about 2.3 and low pressure turbine section  26  may have a pressure ratio that is greater than about 5. In various embodiments, the bypass ratio of gas turbine engine  2  is greater than about ten (10:1). In various embodiments, the diameter of fan  22  may be significantly larger than that of the low pressure compressor section  24 , and the low pressure turbine section  26  may have a pressure ratio that is greater than about 5:1. Low pressure turbine section  26  pressure ratio may be measured prior to inlet of low pressure turbine section  26  as related to the pressure at the outlet of low pressure turbine section  26  prior to an exhaust nozzle. It should be understood, however, that the above parameters are exemplary of various embodiments of a suitable geared architecture engine and that the present disclosure contemplates other turbine engines including direct drive turbofans. 
     In various embodiments, the next generation of turbofan engines may be designed for higher efficiency, which may be associated with higher pressure ratios and higher temperatures in the high speed spool  14 . These higher operating temperatures and pressure ratios may create operating environments that may cause thermal loads that are higher than thermal loads conventionally encountered, which may shorten the operational life of current components. In various embodiments, operating conditions in high pressure compressor section  32  may be approximately 1400° F. (approximately 760° C.) or more, and operating conditions in combustor  36  may be higher. 
     In various embodiments, combustor section  8  may comprise one or more combustor  36 . As mentioned, the core airflow C may be compressed, then mixed with fuel and ignited in the combustor  36  to produce high speed exhaust gases. 
     With reference to  FIG. 2 , a perspective view of outer case  70  is shown. Outer case  70  may be used in a mid-turbine frame  38 , discussed above with respect to  FIG. 1 , which in addition to outer case  70  includes airfoils  40  (shown in  FIG. 1 ). Although described with respect to mid-turbine frame  38 , stiffness bosses  102  may be used in any portion of the outer case in which rigidity control of the case is desired. An A-R-C axis is shown throughout the drawings to illustrate the axial, radial and circumferential (or transverse) directions. 
     Outer case  70  includes outer flange  74  and inner flange  76  for connection to aft and forward case assemblies, respectively. Outer flange  74  has a greater diameter than inner flange  76  and inner flange  76  is located axially forward of outer flange  74 , in the positive A direction. This orientation results in outer case  70  having outer case surface  120 , which is between outer flange  74  and inner flange  76 , sloping radially inward (in the negative R direction and the positive A direction). Outer case  70  further includes multiple support member bosses  78  disposed circumferentially around outer case  70  for receiving and securing support structures such as struts or rods that communicate forces radially inward in the negative R direction. Additionally, multiple spoke bosses  80  are similarly disposed circumferentially around outer case  70  that allow for attachment of parts used in various functions of the outer case  70  and gas turbine engine  2 , in general. 
     In addition, multiple gusseted bosses  82  are disposed circumferentially around outer case  70 , and between support member bosses  78  and/or spoke bosses  80 . Gusseted bosses  82  provide system stiffness symmetry, thereby minimizing deformation of the outer case  70  and centerline shift. The interior of gusseted boss  82  may be hollow, which reduces the weight of outer case  70  without affecting the load bearing capability of outer case  70 . However, the process of fabricating the gusseted boss  82  may be time consuming, as it may be machined on both sides in order to achieve its hollow configuration. 
     Load applied at the support member bosses  78  and the spoke bosses  80  may be counteracted with reinforced, stiffened regions between the points of contact, such that the outer case  70  resists deformation. To this end, stiffness bosses  102  are fabricated to assist in resisting deformation of the outer case  70 . 
     Instead of fabricating more gusseted bosses  82  or unused spoke bosses  80 , stiffness bosses  102  may be used to reinforce rigidity of the outer case  70  and maintain the outer case  70  shape. In particular, the geometry of stiffness bosses  102 , and the placement of stiffness bosses  102  circumferentially around outer case  70 , provides additional stiffness to outer case  70  that resists or prevents deforming of outer case  70  in response to forces applied via support member bosses  78  and spoke bosses  80 . Stiffness bosses  102  may be manufactured on one side of the outer case  70 , making them less expensive to manufacture than gusseted bosses  82 , which may be machined from both sides. Stiffness bosses  102  may also be lighter and may use fewer materials to manufacture than unused spoke bosses  80 . In various embodiments, gusseted bosses may be a type of stiffness boss. Gusseted bosses may provide rigidity in response to a radial load applied to the outer case  70 . Gusseted bosses may also provide rigidity in response to an axial load applied to the outer case  70 . Gusseted bosses may also provide rigidity in response to a transverse load applied to the outer case  70 . 
     With reference to  FIG. 3 , a portion of outer case  70  is shown. As described herein, outer case  70  includes support member boss  78 , spoke boss  80 , gusseted boss  82 , and stiffness boss  102 . Stiffness boss  102  includes a head portion  104  and a leg portion  106 . The head portion  104  is flat and approximately parallel to the engine centerline axis X-X′, as shown in  FIGS. 4 and 5 . The head portion  104  has a head length  116  and a head width  114 . The leg portion  106  is also flat, but sloped downward and radially inward. The leg portion  106  has a leg length  112  and a leg width  110 . Head length  116 , head width  114 , leg length  112 , and leg width  110  may be determined such that rigidity provided by the stiffness boss  102  is optimized. Head length  116 , head width  114 , leg length  112 , and leg width  110  may also be determined such that rigidity provided by the stiffness boss  102  is optimized and weight of the stiffness boss  102  is minimized. The dimensions of the head portion  104  and the leg portion  106  may be optimized using virtual modeling of the turbine case, or may be optimized based on fabricating and testing the turbine case with stiffness bosses having various head portion  104  and leg portion  106  dimensions. 
     The leg portion  106  provides a primary source of rigidity in response to an axial load  302  being applied to the outer case  70  in the positive A direction. When a transverse load  304  is applied to the outer case  70  in the positive C direction, the head portion  104  provides a primary source of rigidity. When a radial load  306  is applied to the outer case  70  in a negative R direction, both the head portion  104  and the leg portion  106  provide rigidity. 
     The stiffness boss  102  may be made of a metal or metal alloys. In various embodiments, the stiffness boss  102  is made of a nickel superalloy such as an austenitic nickel-chromium-based alloy such as that sold under the trademark Inconel® which is available from Special Metals Corporation of New Hartford, N.Y., USA. The stiffness boss  102  may be made of the same material as the outer case  70 , or may be made of a different material from the outer case  70 . 
     The stiffness boss  102  may be welded, brazed, additively manufactured, machined, or cast on to the outer case  70  (and outer case surface  120 ). Also shown is filleted portion  108 , which curves radially inward from the outer case surface  120  to the head portion  104  and to the leg portion  106 . The filleted portion  108  may be a result of welding the head portion  104  and the leg portion  106  to the outer case  70  at outer case surface  120 . The filleted portion  108  may be part of the design of the stiffness boss  102 , which may be cast, additively manufactured, or machined. Filleted portion  108  may provide support for the head portion  104  and the leg portion  106 . Filleted portion  108  may also surround the perimeter of the head portion  104  and the leg portion  106 . 
     Stiffness boss  102  provides rigidity for the outer case  70  substantially similar to the rigidity provided by a spoke boss  80  that is not used as an attachment means. As such, stiffness boss  102  may be placed anywhere spoke boss  80  is located. For example,  FIG. 2  illustrates alternating between spoke boss  80  and stiffness boss  102  around the circumference of the outer case  70 . However, stiffness boss  102  may be located instead of any of the spoke bosses  80 , and rigidity of the outer case  70  may be maintained. 
     While the dimensions of the stiffness boss  102  may contribute to determining the amount of rigidity provided by the stiffness boss  102 , the location of the stiffness boss  102  on the outer case  70  may also contribute to the rigidity. Rigidity provided by stiffness boss  102  may vary based on its relative location to spoke boss  80  and support member boss  78 . 
       FIG. 4  illustrates a side view of the stiffness boss  102 . As described herein, head portion  104 , having head width  114 , is approximately parallel to axis X-X′. Shown is head portion surface plane  202  which is approximately parallel to axis X-X′. Also as described herein, outer case surface  120  is sloped radially inward (in the negative R direction and the positive A direction). Leg portion  106  is flat and has a leg length  112  and a leg surface length  118 . Filleted portion  108  is also shown, connecting the head portion  104  and the leg portion  106  to the outer case surface  120 . 
       FIG. 5  illustrates a side view of the stiffness boss  102  that is opposite on circumferential axis C of the side view shown in  FIG. 4 . As described herein, head portion  104 , having head width  114 , is approximately parallel to axis X-X′. Shown is head portion surface plane  202  which is approximately parallel to axis X-X′. Also as described herein, outer case surface  120  is sloped downward and in the axially forward direction. Leg portion  106  is flat and has a leg length  112  and a leg surface length  118 . Filleted portion  108  is also shown, connecting the head portion  104  and the leg portion  106  to the outer case surface  120 . 
     Referring to  FIGS. 2 and 3 , while stiffness bosses  102  with the head portion  104  being to the left of center of leg portion  106  are shown, the center of head portion  104  may be in a negative C direction of the center of leg portion  106 . Further, while stiffness bosses  102  with the head portion  104  being radially outward relative to the leg portion  106  are shown, the head portion  104  may be radially inward relative to the leg portion  106 . 
     While the disclosure is described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the disclosure. In addition, different modifications may be made to adapt the teachings of the disclosure to particular situations or materials, without departing from the essential scope thereof. The disclosure is thus not limited to the particular examples disclosed herein, but includes all embodiments falling within the scope of the appended claims. 
     Benefits, other advantages, and solutions to problems have been described herein with regard to specific embodiments. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical system. However, the benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the disclosure. The scope of the disclosure is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” Moreover, where a phrase similar to “at least one of A, B, or C” is used in the claims, it is intended that the phrase be interpreted to mean that A alone may be present in an embodiment, B alone may be present in an embodiment, C alone may be present in an embodiment, or that any combination of the elements A, B and C may be present in a single embodiment; for example, A and B, A and C, B and C, or A and B and C. Different cross-hatching is used throughout the figures to denote different parts but not necessarily to denote the same or different materials. 
     Systems, methods and apparatus are provided herein. In the detailed description herein, references to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the disclosure in alternative embodiments. 
     Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element is intended to invoke 35 U.S.C. 112(f) unless the element is expressly recited using the phrase “means for.” As used herein, the terms “comprises”, “comprising”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.