Abstract:
An attachment root of an airfoil is provided comprising a serration profile with a symmetry plane bisecting the serration profile. A first lobe of the serration profile has a first contact face angled 45 degrees from the symmetry plane. A second lobe of the serration profile has a second contact face angled 45 degrees from the symmetry plane. The first contact face may have a shorter length than the second contact face.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a nonprovisional of, and claims priority to, and the benefit of U.S. Provisional Application No. 62/092,038, entitled “TURBINE AIRFOIL ATTACHMENT WITH MULTI-RADIAL SERRATION PROFILE,” filed on Dec. 15, 2014, which is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The present disclosure relates to gas turbine engines, and, more specifically, to an airfoil attachment for rotating airfoils in a gas turbine engine. 
       BACKGROUND 
       [0003]    Airfoils that rotate in gas turbine engines may generally be attached to rotor disks. The rotor disks in turbine sections and compressor sections of a gas turbine engine may rotate at high angular velocities. The resulting centripetal force may place stress on contact points where the airfoil is connected to the rotor. The high stress levels combined with high temperatures may accelerate wear and tear on the airfoil. 
       SUMMARY 
       [0004]    An attachment root of an airfoil is provided comprising a serration profile with a symmetry plane bisecting the serration profile. A first lobe of the serration profile has a first contact face angled 45 degrees from the symmetry plane. A second lobe of the serration profile has a second contact face angled 45 degrees from the symmetry plane. The first contact face may have a shorter length than the second contact face. 
         [0005]    In various embodiments, the first lobe may comprise a first segment having a first radius of 0.055 to 0.065 inches. A second segment may follow the first segment and have a second radius of 0.115 to 0.125 inches. A third segment may follow the second segment with a third radius of 0.105 to 0.115 inches. The first contact face may follow the third segment with a fourth segment following the first contact face. The fourth segment may have a fourth radius of 0.055 to 0.065 inches. A fifth segment following the fourth segment and may have a fifth radius of 0.188 to 0.198 inches. A sixth segment may follow the fifth segment with a radius of 0.045 to 0.055 inches. A seventh segment may follow the sixth segment with a radius of 0.041 to 0.051 inches. 
         [0006]    In various embodiments, the second lobe may comprise an eighth segment following the seventh segment and having a radius of 0.115 to 0.125 inches. The proximal contact face may follow the eighth segment. A ninth segment following the proximal contact face may have a radius of 0.038 to 0.048 inches. A tenth segment may follow the ninth segment with a radius of 0.100 to 0.110 inches. 
         [0007]    In various embodiments, the first segment may be tangentially continuous with the second segment and the second segment may be tangentially continuous with the third segment. The serration profile may be tangentially continuous from the first segment to the tenth segment. The attachment root may also be symmetric about the symmetry plane. 
         [0008]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present disclosure, however, may best be obtained by referring to the detailed description and claims when considered in connection with the figures, wherein like numerals denote like elements. 
           [0010]      FIG. 1  illustrates a cross-sectional view of an exemplary gas turbine engine, in accordance with various embodiments; 
           [0011]      FIG. 2  illustrates a perspective view of an airfoil attachment root, in accordance with various embodiments; 
           [0012]      FIG. 3  illustrates a top view of an airfoil attachment root, in accordance with various embodiments; and 
           [0013]      FIG. 4  illustrates the serration profile of an airfoil attachment root, in accordance with various embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    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 the exemplary 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 disclosure 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. 
         [0015]    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. Surface shading lines may be used throughout the figures to denote different parts but not necessarily to denote the same or different materials. 
         [0016]    As used herein, “aft” refers to the direction associated with the tail (e.g., the back end) of an aircraft, or generally, to the direction of exhaust of the gas turbine. As used herein, “forward” refers to the direction associated with the nose (e.g., the front end) of an aircraft, or generally, to the direction of flight or motion. 
         [0017]    As used herein, “distal” refers to the direction radially outward, or generally, away from the axis of rotation of a turbine engine. As used herein, “proximal” refers to a direction radially inward, or generally, towards the axis of rotation of a turbine engine. 
         [0018]    Referring to  FIG. 1 , a gas turbine engine  100  (such as a turbofan gas turbine engine) is illustrated according to various embodiments. Gas turbine engine  100  is disposed about axial centerline axis  120 , which may also be referred to as axis of rotation  120 . Gas turbine engine  100  may comprise a fan  140 , compressor sections  150  and  160 , a combustion section  180 , and a turbine section  190 . Air compressed in compressor sections  150 ,  160  may be mixed with fuel and burned in combustion section  180  and expanded across turbine section  190 . Turbine section  190  may include high-pressure rotors  192  and low-pressure rotors  194 , which rotate in response to the expansion. Turbine section  190  may comprise alternating rows of rotary airfoils or blades  196  and static airfoils or vanes  198 . Airfoils  196  may be inserted into high-pressure rotors  192  or low-pressure rotors  194  and retained be a root having a serration profile. A plurality of bearings  115  may support spools in the gas turbine engine  100 .  FIG. 1  provides a general understanding of the sections in a gas turbine engine, and is not intended to limit the disclosure. The present disclosure may extend to all types of turbine engines, including turbofan gas turbine engines, turbojet engines, and industrial gas turbine engines, for all types of applications. 
         [0019]    With reference to  FIG. 2 , an attachment root  200  for an airfoil (e.g., airfoil  196  of  FIG. 1 ) is shown, in accordance with various embodiments. Attachment root  200  comprises a serration profile  202  defining a boundary face  204  having a planar contour. Cross-sectional boundary  208  may be adjacent to boundary face  204  and serve as a radial boundary between attachment root  200  and an airfoil formed integrally to attachment root  200 . Cross-sectional boundary  208  may have a planar contour. A symmetry plane  206  may bisect the boundary face  204  and cross-sectional boundary  208 . In various embodiments, attachment root  200  may be formed by casting with serration profile  202  further refined by milling, electrochemical machining (ECM), or electrostatic discharge machining (EDM) as desired, for example. In that regard, the attachment root and airfoil may be made from a high performance austenitic nickel alloy (e.g., a nickel alloy available under the trademark INCONEL). 
         [0020]    In various embodiments, serration profile  202  may extend in the z direction (as shown in  FIG. 2 ) and define interface surface  210 . Interface surface  210  may comprise a proximal contact face  212  and distal contact face  214 . Each contact face may be substantially flat in the z direction. Serration profile  202  may be selected to fit into a retention groove formed in a rotor. In that regard, proximal contact face  212  and distal contact face  214  may be configured to contact a rotor and retain attachment root  200  in the rotor while limiting wear during use. Each contact face of interface surface  210  may be separated by a radial or multi-radial portion of interface surface  210 . Interface surface  210  may be bilaterally symmetric with respect to symmetry plane  206 . 
         [0021]    With reference to  FIG. 3 , an attachment root  200  is shown in a top view relative to engine center line  230  of a gas turbine engine (e.g., gas turbine engine  100  from  FIG. 1 ), in accordance with various embodiments. Attachment root  200  in  FIG. 3  is shown as viewed in the x-z plane (of  FIG. 2 ) passing through line A (of  FIG. 2 ). Attachment root  200  may have an angle θ with respect to engine center line  230 . For example, the angle between engine center line  230  and symmetry plane  206  may be approximately 5° when attachment root  200  is installed in a gas turbine engine. Axial boundary  232  and axial boundary  234  of cross-sectional boundary  208  may form a 90° angle with engine center line  230 . Similarly, an angle between the axial boundary  234  and boundary  238  may be approximately 95°, and an angle between axial boundary  234  and boundary  236  may be approximately 85°. In that regard, cross-sectional boundary  208  of attachment root  200  may have a parallelogram shape. 
         [0022]    With reference to  FIG. 4 , a serration profile  202  of an attachment root  200  is shown, in accordance with various embodiments. Serration profile  202  may be the cross-sectional profile of attachment root  200  taken through line B of  FIG. 3 . As described herein, serration profile  202  may be tangentially continuous between arcs and flat portions with discontinuities noted. Serration profile  202  may include distal contact face  214  and proximal contact face  212  with each defined by a different lobe of serration profile  202 . The radii R1-R10 defined herein may vary in a range as provided in table T1. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE T1 
               
             
             
               
                   
               
               
                 Minimums and maximums for Radii R1-R10. 
               
             
          
           
               
                 Radius 
                 Min (inches) 
                 Max (inches) 
                 Min (mm) 
                 Max (mm) 
               
               
                   
               
               
                 R1 
                 0.055 
                 0.065 
                 1.397 
                 1.651 
               
               
                 R2 
                 0.115 
                 0.125 
                 2.921 
                 3.175 
               
               
                 R3 
                 0.105 
                 0.115 
                 2.667 
                 2.921 
               
               
                 R4 
                 0.055 
                 0.065 
                 1.397 
                 1.651 
               
               
                 R5 
                 0.188 
                 0.198 
                 4.775 
                 5.029 
               
               
                 R6 
                 0.045 
                 0.055 
                 1.143 
                 1.397 
               
               
                 R7 
                 0.041 
                 0.051 
                 1.041 
                 1.295 
               
               
                 R8 
                 0.115 
                 0.125 
                 2.921 
                 3.175 
               
               
                 R9 
                 0.038 
                 0.048 
                 0.965 
                 1.219 
               
               
                 R10 
                 0.100 
                 0.110 
                 2.540 
                 2.794 
               
               
                   
               
             
          
         
       
     
         [0023]    For example, serration profile  202  may have a distal lobe  252  starting at point P 1  with segment S 1 . Segment S 1  may be concave arc with radius R 1  of 0.055 to 0.065 inches (1.397 to 1.651 mm). Segment S 2  may be a concave arc following segment S 1 . Segment S 2  may have a radius R 2  of 0.115 to 0.125 inches (2.921 to 3.175 mm). Segment S 3  may be a concave arc following segment S 2 . Segment S 3  may have a radius R 3  of 0.105 to 0.115 inches (2.667 to 2.921 mm). Segment S 3  may be followed by distal contact face  214 . Distal contact face  214  may be a flat segment at substantially 45° relative to symmetry plane  206 . Segment S 4  may be a convex arc following distal contact face  214 . As used herein, substantially may refer to an angle in a +/−2° range. For example, an angle of substantially 45° may be in the range of 43° to 47° . Segment S 4  may have a radius R 4  of 0.055 to 0.065 inches (1.397 to 1.651 mm). Segment S 5  may be a convex arc following segment S 4 . Segment S 5  may have a radius R 5  of 0.188 to 0.198 inches (4.775 to 5.029 mm). Segment S 6  may have a radius R 6  of 0.045 to 0.055 inches (1.143 to 1.397 mm). Segment S 7  may be a concave arc following segment S 6 . Segment S 7  may have a radius R 7  of 0.041 to 0.051 inches (1.041 to 1.295 mm). A flat segment at approximately 85° from the symmetry plane may extend between S 6  and S 7 . The end of S 7  marks the end of distal lobe  252  and the beginning of proximal lobe  254 . 
         [0024]    In various embodiments, segment S 8  may be a concave arc following segment S 7 . 
         [0025]    Segment S 8  may have a radius R 8  of 0.115 to 0.125 inches (2.921 to 3.175 mm). Proximal contact face  212  may follow segment S 8  at an angle of substantially 45° from symmetry plane  206 . Proximal contact face  212  may have a shorter length than distal contact face  214 . Segment S 9  may follow proximal contact face  212 . Segment S 9  may be a convex arc with radius R 9  of 0.038 to 0.048 inches (0.965 to 1.219 mm). Segment S 10  may follow segment S 9 . Segment S 10  may be a concave arc having radius R 10  of 0.100 to 0.110 inches (2.540 to 2.794 mm). A tangential discontinuity or cusp may follow segment S 10  with a segment orthogonal to symmetry plane  206  extending to symmetry plane  206 . 
         [0026]    In various embodiments, the shape of serration profile  202  may improve the strength and wear characteristics of attachment root  200 . The lobes of serration profile  202  may be designed to withstand numerous start-up and shut-down sequences while resisting wear. As a result, turbine blades attached to a rotor by attachment root  200  with serration profile  202  may have a longer functional life before replacement. 
         [0027]    Benefits and other advantages 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, and any elements that may cause any benefit or advantage 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. 
         [0028]    Systems, methods and apparatus are provided herein. In the detailed description herein, references to “various embodiments”, “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. 
         [0029]    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 herein is to be construed under the provisions of 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.