Abstract:
An exemplary turbomachine rotor assembly includes a pair of spaced rails that extend around a cylindrical surface to define a rotor hub. The rails define a space for receiving blades. Load slots are formed in one of the rails. A relief feature is formed in an opposite surface of an opposing rail. The load slots and relief feature utilized to move at least one of the blades into the space.

Description:
BACKGROUND 
       [0001]    This disclosure relates to a tangential compressor or turbine rotor having relief features formed on one of the two rails in the rotor and load slots formed on the other of the two rails in the rotor. 
         [0002]    Turbomachines, such as gas turbine engines, are known. Turbomachines typically include a compressor that compresses air and delivers it downstream into a combustion section. The compressed air is mixed with fuel and combusted. The products of combustion pass downstream through a turbine. The compressor and turbine include rotors. Arrays of removable blades are mounted to the rotors. 
         [0003]    When mounting the removable blades to the rotor, the removable blades are moved into load slots formed in the two opposed rails in the rotor. The load slots are formed at circumferentially spaced locations. Each of the load slots extend radially from radially inward facing surfaces of the rails to radially outward facing surfaces of the rails. During installation, the relatively wide root of each individual blade is moved into the load slots. The blades are then slid into a mount space between the rails, at locations that are circumferentially offset from the load slots. The blades are moved circumferentially until they fill the entire space. In addition, locks are positioned at several circumferentially spaced locations between the blades to take up remaining space and inhibit the blades from moving circumferentially relative to the rotor. 
         [0004]    In the prior art, circumferentially aligned pairs of load slots are formed in the opposing rails to accommodate the roots of the blades. Some prior art designs may utilize a single load slot formed in the rail that faces the compressor rather than a circumferentially aligned pair of load slots. The single load slot is much larger than each of the load slots in the circumferentially aligned pairs. The larger load slot may undesirably accelerate fatigue in the rail. 
       SUMMARY 
       [0005]    An exemplary turbomachine rotor assembly includes a pair of spaced rails that extend around a cylindrical surface to define a rotor hub. The rails define a space for receiving blades. Load slots are formed in one of the rails. A relief feature is formed in an opposite surface of an opposing rail. The load slots and relief feature are utilized to move at least one of the blades into the space. 
         [0006]    Another example turbomachine rotor assembly includes a pair of spaced rails that extend around a cylindrical surface to define a rotor hub. The rails define a space for receiving blades. Blade load slots are formed in one of the rails. The blade load slots extend from an outwardly facing surface of the one of the rails to an inwardly facing surface of the other of the rails. Relief features are formed on an underside of the opposed rail. The relief feature is circumferentially aligned with the blade load slots. The blades are moved into the space through the blade load slots and the relief feature. The blades are then moved circumferentially to be adjacent to other blades. 
         [0007]    A rotor assembly method includes moving a blade into a space between a pair of spaced rails that extend around a cylindrical surface to define a rotor hub. The method then moves the blade circumferentially to an installed position within the rotor hub. The blade moves through a blade load slot formed on one of the spaced rails, and through a relief feature formed on the other of the spaced rails. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the detailed description. The figures that accompany the detailed description can be briefly described as follows: 
           [0009]      FIG. 1  shows the mounting of a blade within a turbine rotor. 
           [0010]      FIG. 2  shows a portion of the  FIG. 1  turbine rotor and a blade insertion step. 
           [0011]      FIG. 3  shows a perspective view of a portion of the  FIG. 1  turbine rotor. 
           [0012]      FIG. 4  shows another perspective view of a portion of the  FIG. 1  turbine rotor. 
           [0013]      FIG. 5  shows yet another perspective view of a portion of the  FIG. 1  turbine rotor. 
           [0014]      FIG. 6  shows a portion of the  FIG. 1  turbine rotor and a blade insertion step that is earlier than the blade insertion step shown in  FIG. 2 . 
           [0015]      FIG. 7  shows lock members of the  FIG. 1  turbine rotor. 
           [0016]      FIG. 8  shows another feature of the lock members. 
           [0017]      FIG. 9  shows another detail of the lock member. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]      FIG. 1  schematically shows a turbine rotor  20  for use in a gas turbine engine or another type of turbomachine. The rotor  20  incorporates a rotor hub  22 , and an array of blades  24  spaced about the circumference of the rotor hub  22 . The rotor hub  22  is centered for rotation about a central axis X, as is known. While the example embodiments will be described with reference to a turbine rotor, other examples have application in a compressor rotor. 
         [0019]    As shown in  FIGS. 2-4 , a blade  26  in the array  24  is mounted between rear rail  34  and forward rail  38 , through a load slot  42 . The rear rail  34  and forward rail  38  together make up a pair of spaced rails. 
         [0020]    The load slot  42  is formed in the “cold side” forward rail  38 , and is not formed in the “hot side” rear rail  34 . The “cold side” forward rail  38  may be further from a combustion section C than the “hot side” rear rail  34  when the rotor  20  is mounted within a gas turbine engine. While the “hot side” will typically face toward the combustion section, in certain applications, and at certain turbine stages, it is possible for the opposed “upstream” side of the turbine to be the hot side. Further, when the features of this disclosure are applied to a compressor rotor, the hot side may also be facing toward the combustion section, or away, depending on the particular application. 
         [0021]    As shown, the blade has a root section  46  having a forward ear  48 , which is received under the forward rail  38 , and a rear ear  50 , which moves through the load slot  42 . 
         [0022]    A relief feature  52  is formed in the underside of the rear rail  34 . The relief feature  52  facilitates movement of the root section  46 , and particularly the rear ear  50 , through the load slot  42 . 
         [0023]    Due to the relief feature  52 , the load slot  42  does not need to be as large. That is, the load slot  42  can be made shallower because of the relief feature  52  accommodating some of the root section  46  during installation. 
         [0024]    The load slot  42  is formed in the forward rail  38 , and there is no corresponding slot in the rear rail  34 . The relief feature  52 , however, does correspond to the circumferential location of the load slot  42 . In addition, as shown in  FIG. 2A , the forward rail  38  is formed with lock slots  56 , while the rear rail  34  does not have any such lock slots  56 . 
         [0025]    The rear rail  34  includes a radially outward facing surface  60  and a radially inward facing surface  62  that meet at an interface  64 . The example relief feature  52  is formed entirely within the radially inward facing surface  62  and does not extend past the interface  64 . That is, there is no portion of the relief feature  52  extending into the radially outward facing surface  60 . In this example, the radially outward facing surface  60  is continuous and uninterrupted about the entire circumference of the rear rail  34 . Also, in this example, the relief feature  52  is concave. 
         [0026]    The load slot  42 , in contrast to the relief feature  52 , does extend from an outwardly facing surface of the forward rail  38  to an inwardly facing surface of the forward rail  38 . 
         [0027]    As shown in  FIGS. 2 and 6 , when initially mounting the blade  26  within the rotor hub  22 , the forward ear  48  is rotated into the load slot  42  about a back edge  66  of the blade  26  in a direction P. The relief feature  52  provides room for the rear ear  50  of the root section  46 . The forward ear  48  may be “hooked” under a ladder seal (not shown) during installation. 
         [0028]    After the blade  26  is fully rotated into the load slot  42 , the blade  22  can be moved circumferentially, with the ears  48  and  50  remaining underneath portions of the forward rail  38  and rear rail  34 , such that the blades  26  can be aligned and positioned across the entire circumference of the rotor  20  (see  FIG. 1 ). In applications, there may be two load slots  42  spaced by 180° about the circumference of the rotor hub  22 . Essentially, the forward rail  38  and rear rail  34  define a space to receive and mount the blades  26 . 
         [0029]      FIG. 7  shows another detail, wherein blades  26  have been mounted between the forward rail  38  and rear rail  34 . In addition, other blades  26  are shown, which have a space to surround a lock member  70 . 
         [0030]    Lock members  70  are typically positioned on each side of a pair of blades  26  that sit circumferentially closest to the load slot  42  when the rotor  20  is fully assembled with blades  26 . In addition, other lock members  70  are provided at circumferentially spaced locations. 
         [0031]    In this example, there are a total of eight locks, spaced evenly about the circumference of the rotor  20 , but with two sets of locks secured on each side of the load slot  42 . 
         [0032]    As shown in  FIG. 8 , the locks  70  are received with a curved side  74  sitting in the lock slot  56 , and a relatively flat side  78  facing the rear rail  34 . 
         [0033]      FIG. 9  shows the lock member  70  having a flat side  78 , the curved side  74 , and receiving a lock pin, or set screw  82 , which is tightened to secure the lock member  70  within the rotor hub  22  once the rotor  20  is fully assembled. 
         [0034]    As shown, the curved (or barrel) side  74  is on one side of the lock member  70 , with the relatively flat side  78  on the opposite side. Flat side walls  86  extend between the curved side  74  and the flat side  78 . 
         [0035]    While the disclosed embodiment incorporates both blade and lock slots, rotors coming within the scope of this disclosure could use only one of the two in combination with the relief feature. 
         [0036]    Features of the disclosed examples include incorporating a relief feature on an aft rail to enable making the load slot on the forward rail shallower. The relief feature helps balance fatigue life between the two rails. Unlike the load slot, the relief feature does not penetrate the top of the aft rail, which keeps stress concentrations in a lower temperature and lower stress area. 
         [0037]    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.