Patent Publication Number: US-8523529-B2

Title: Locking spacer assembly for a circumferential entry airfoil attachment system

Description:
FIELD OF THE INVENTION 
     The present subject matter relates generally to circumferential entry airfoil attachment systems and, more particularly, to a locking spacer assembly for use in such a system. 
     BACKGROUND OF THE INVENTION 
     A conventional gas turbine includes a rotor with various rotor blades and turbine buckets mounted to discs in the compressor and turbine sections thereof. Each blade or bucket includes an airfoil over which pressurized air or fluid flows, and a platform at the base of the airfoil that defines the radially inner boundary for the air or fluid flow. The blades and buckets are typically removable, and therefore include a suitable root, such as a T-type root, configured to engage a complementary attachment slot in the perimeter of the disc. The roots may either be axial-entry roots or circumferential-entry roots that engage corresponding axial or circumferential slots formed in the disc perimeter. A typical root includes a neck of minimum cross sectional area and protrusions extending from the root into a pair of lateral recesses located within the attachment slot. 
     For circumferential roots, a single attachment slot is formed between forward and aft continuous circumferential posts and extends circumferentially around the entire perimeter of the disc. The cross-sectional shape of the circumferential attachment slot includes lateral recesses defined by forward and aft rotor disc posts that cooperate with the root protrusions to radially retain the individual blades or buckets against centrifugal force during turbine operation. 
     In the compressor section of a gas turbine, for example, rotor blades (specifically the root component) are inserted into and around the circumferential slot and rotated approximately ninety degrees to bring the root protrusions into contact with the lateral recesses to define a complete stage of rotor blades around the circumference of the rotor discs. The blades include platforms at the airfoil base that may be in abutting engagement around the slot. In other embodiments, spacers may be installed in the circumferential slot between adjacent compressor blade platforms. Once all of the blades (and spacers) have been installed, a final remaining space(s) in the slot is typically filled with a specifically designed spacer assembly, as generally known in the art. 
     A common technique used to facilitate the insertion of the final spacer assembly into the circumferential slot is to include a non-axi symmetric loading slot in the rotor disc. However, loading slots are costly to manufacture and the inclusion of such a slot creates a location of high stress. Various conventional spacer assemblies have been designed to eliminate the need for a loading slot in a rotor disc but include complicated multi-component devices. These conventional assemblies are generally difficult to assemble, and are prone to coming apart during operation of the turbine, for example, if either side of the device develops clearance relative to adjacent components (i.e., the rotor discs or platforms). Accordingly, there is a need for a final spacer assembly that it relatively easy to assemble within the final space between platforms of adjacent airfoils of rotor blades or turbine buckets located within a circumferential entry attachment slot. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the present subject matter will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the present subject matter. 
     In one aspect, the present subject matter provides a unique locking spacer assembly for use in a circumferential attachment slot between platforms of adjacent airfoils. The assembly includes two end pieces configured to fit into a space between the platforms, with each end piece comprising an outer surface and an inner surface. An actuator is movable between the inner surfaces and a spacer bock is configured to be inserted between the inner surfaces. The spacer block includes a cavity configured to receive the actuator. A fastener is also included and is configured to secure the spacer block to the actuator. Finally, the actuator is configured to engage the inner surfaces such that the end pieces move toward each other and lock the assembly within the attachment slot. 
     In another aspect, the present subject matter encompasses a rotor assembly having a rotor with a rotor disc. Forward and aft post components of the disc define a continuous circumferentially extending attachment slot. The rotor assembly also includes a plurality of airfoils, with each airfoil extending from a platform. Each platform is secured to the attachment slot by an inwardly extending root. A locking spacer assembly is installed in a space between at least two of the platforms. The locking spacer assembly may be configured as discussed above and described in greater detail herein. 
     These and other features, aspects and advantages of the present subject matter will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the present subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present subject matter, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
         FIG. 1  provides a partial sectional view of components in a compressor section of a conventional gas turbine configuration; 
         FIG. 2  provides a partial sectional view of an embodiment of a root and attachment slot configuration for circumferential entry rotor blades; 
         FIG. 3  is a partial perspective view of a rotor disc with final spaces between adjacent rotor blade platforms into which a locking spacer assembly may be inserted; 
         FIG. 4  is an exploded view of the components of an embodiment of the locking spacer assembly in accordance with aspects of the present subject matter; 
         FIG. 5 ,  FIG. 6 ,  FIG. 7 , and  FIG. 8  are sequential assembly views of an embodiment of a locking spacer assembly in accordance with aspects of the present subject matter; and 
         FIG. 9  is a sectional view of an assembled embodiment of a locking spacer assembly in accordance with aspects of the present subject matter indicating the locations of rotational loading. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference now will be made in detail to embodiments of the present subject matter, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the present subject matter, not limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present subject matter without departing from the scope or spirit of the present subject matter. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     Several components in a compressor section of a conventional gas turbine are illustrated, for example, in  FIG. 1  wherein a rotor  12  includes a plurality of rotor discs  20  disposed coaxially with the centerline axis  18  of the turbine. A plurality of circumferentially spaced rotor blades  22  is removably fixed to the disc and extends radially outward therefrom. Each blade  22  has a longitudinal centerline axis  24  and includes an airfoil section  26  having a leading edge  26   a  and a trailing edge  26   b  (in the direction of airflow over the blade  22 ). Additionally, each blade  22  has a platform  28  that provides a portion of the radially inner boundary for the airflow over the airfoils  26 , and an integral root  30  that extends radially inward from the platform  28 . The root  30  slides into and along a circumferentially extending attachment slot defined by forward and aft post components  34  ( FIG. 2 ) of the rotor disc  20 , as is generally known in the art. 
       FIG. 2  is a more detailed view of an embodiment of a T-type root and attachment slot configuration. The rotor blade  22  includes a platform  28  with an integrally formed root  30  extending therefrom into the attachment slot  36  defined by facing walls of forward and aft posts  34  of the rotor disc  20 . The root  30  includes protrusions  32  that are received into lateral recesses  38  in the attachment slot  30  defined by recessed portions of the post walls. It should be readily appreciated that the configuration of the root  30  and attachment slot  36  in  FIG. 2  is for illustrative purposes only, and that the root and slot configuration may vary widely within the scope and spirit of the present subject matter. 
       FIG. 3  is a partial perspective view of a portion of a rotor  12 , and particularly illustrates a plurality of rotor blades  22  configured in an attachment slot between forward and aft post components  34  of the rotor disc  20 . Each of the rotor blades  22  includes a platform  28 . Conventional spacers  40  may be disposed between the platforms  28  of adjacent blades  22 , as is generally known in the art. Final spaces  42 , having a horizontal width W between the rotor blade platforms  28 , can be filled by an embodiment of the locking spacer assembly  50 , which is described in greater detail below. However, it should be appreciated that the locking spacer assembly  50  can also be used to fill the final spaces between platforms of adjacent turbine buckets located within the turbine section of a conventional gas turbine. As such, the locking spacer assembly will be generally described below as being installed between platforms  28  of adjacent airfoils  26 , wherein the platforms  28  and airfoils  26  may be part of a rotor blade or a turbine bucket so as to fully encompass both applications. 
     Referring to  FIG. 4 , an embodiment of the locking spacer assembly  50  is illustrated in an exploded view. The assembly  50  includes a first end piece  52  and a second end piece  58  configured to fit into the final spaces  42  between platforms  28  of adjacent airfoils  26 . The end pieces  52 ,  58 , thus, have any dimensional configuration such that the width, length, thickness, or any other characteristics enables the end pieces  52 ,  58  to be inserted between the platforms  28 . For example, the end pieces  52 ,  58  may generally have a horizontal width W ( FIG. 3 ) in order to fit snugly between the platforms  28  of adjacent airfoils. 
     The first end piece  52  includes an inner surface  52   a  and an outer surface  52   b . Similarly, the second end piece  58  includes an inner surface  58   a  and an outer surface  58   b . Outer surfaces  52   b ,  58   b  have a profile generally adapted to project into the attachment slot  36 , as generally illustrated in  FIG. 5 . For example, the profile of the outer surfaces  52   b ,  58   b  may have a top portion that is substantially curved to mirror the curve of the post components  34 . Moreover, the profile may have a bottom portion that extends outwardly at the corner formed between the hoop components  34  and the lateral recesses  38  to project into the illustrated t-type attachment slot  36 . However, it should be readily appreciated that outer surfaces  52   b ,  58   b  can have any desired profile and need not have the particular profile illustrated in  FIG. 4  and  FIG. 5 . The profile of outer surfaces  52   b ,  58   b  will depend in large part on the particular shape and configuration of the attachment slot  36 . 
     It may also be desirable to provide arcuate grooves  56 ,  62  on the outer surfaces  52   b ,  58   b , respectively. For example, the arcuate grooves  56 ,  62  may be included to provide a point of low stress or a location for stress relief on the end pieces  52 ,  58 . As illustrated, the arcuate grooves  56 ,  62  are located on the outer surfaces  52   b ,  58   b  at the corner formed between the hoop components  34  and the lateral recesses  38 . 
     In the illustrated embodiment, the inner surfaces  52   a ,  58   a  generally face towards each other when the end pieces  52 ,  58  are inserted into the attachment slot  36 , as is generally illustrated in  FIG. 6 . Preferably, planes  54 ,  60  form part of an indentation in the inner surfaces  52   a ,  58   a , respectively and are defined by an angle relative to radial. It should be appreciated that the angles and locations of planes  54 ,  60  on inner surfaces  52   a ,  58   a  can be varied depending on the configuration of the actuator  64 . In general, the angle of planes  54 ,  60  can range between 5° and 85°, such as from 20° to 70° or, more specifically, from 30° to 50°. 
     Additionally, rectangular recesses  57 ,  63  may be formed on the inner surfaces  52   a ,  58   a , respectively. As illustrated in  FIG. 4 , the rectangular recesses  57 ,  63  are formed in the inner surfaces  52   a ,  58   a  at the top of the end pieces  52 ,  58 . The rectangular recesses  57 ,  63  may be configured to receive complimentary rectangular collars  77  of the spacer bock, as will be discussed below. Thus, it should be appreciated that the shape, depth, and location of the rectangular recesses  57 ,  63  may vary depending on the configurations of the complimentary rectangular collars  77 . 
     The locking spacer assembly  50  also includes an actuator  64  movable between the inner surfaces  52   a ,  58   a  and configured to engage such inner surfaces  52   a ,  58   a . Preferably, the actuator  64  includes a projection  66  configured to engage the inner surfaces  52   a ,  58   a . In the illustrated embodiment, the projection  66  extends outward from the base of the actuator  64  in opposing directions such that the actuator is T-shaped. The projection  66  may include angled surfaces  68 ,  70 , which are defined by an angle relative to radial. Generally, the angled surfaces  68 ,  70  may have a shape and angle that conforms to the shape and angles of the planes  54 ,  60  forming part of the indentation in the inner surfaces  52   a ,  58   a.    
     Referring to  FIG. 4 ,  FIG. 8  and  FIG. 9 , the locking spacer assembly also includes a spacer block  72  and a fastener  84 . As illustrated, the spacer block  72  is configured to be inserted between the inner surfaces  52   a ,  58   a  and includes a cavity  74  (shown by hidden lines in  FIG. 4  and  FIG. 8 ) configured to receive the actuator  64 . Similar to the end pieces  52 ,  58 , the spacer block  72  is also configured to fit between the platforms  28  of adjacent airfoils  26 . Thus, the spacer block  72  may have any dimensional configuration such that the width, length, thickness, or any other characteristic enables the spacer block  72  to be inserted between the platforms  28  when disposed between inner surfaces  52   a ,  58   a . For example, the spacer block  72  may generally have a horizontal width W ( FIG. 3 ) in order to fit snugly between the platforms  28 . 
     The spacer block  72  may also include rectangular collars  77  extending laterally from the top of the spacer block  72 . The rectangular collars  77  may be configured to be received in the rectangular recesses  57 ,  63  formed in the inner surfaces  52   a ,  58   a . As illustrated in  FIG. 8 , the rectangular collars  77  slide into the rectangular recesses  57 ,  63  when the spacer block  72  is inserted between the inner surfaces  52   a ,  58   a , which can prevent the spacer block  72  from falling radially down in the attachment slot  36 . 
     The spacer block  72  may also include an opening  78  and a rectangular channel  82 . The opening  78  is defined in a top surface  76  of the spacer block  72  and is configured to receive the fastener  84 . For example, the fastener  84  may fit into opening  78  such that the fastener  84  is positioned generally flush with the platforms  28  when the locking spacer assembly  50  is locked within the attachment slot  36 . The rectangular channel  82  is defined in a bottom surface  80  of the spacer block  72  and is configured to receive a portion of the actuator  64 . Specifically, as illustrated in  FIG. 8 , the rectangular channel  82  slides over a portion of the projection  66  when locking spacer assembly  50  is assembled. It should be appreciated, however, that the opening  78  and rectangular channel  82  need not have the particular shape, depth or width as is generally illustrated. The shape, width and depth of the opening and rectangular channel may be varied to accommodate varying shapes and sizes of fasteners and actuators. 
     The fastener  84  is configured to secure the spacer block  72  to the actuator  64 . Thus, the fastener  84  can be used to prevent the actuator  64  from falling radially down into the attachment slot  36 . It should be appreciated by one of ordinary skill in the art that the fastener  84  may generally comprise any locking mechanism that may be used to secure the spacer block  72  to the actuator  64 . In the illustrated embodiment, the fastener  84  has a threaded female end which can be screwed onto a threaded male end of the actuator  64 . 
       FIG. 5 ,  FIG. 6 ,  FIG. 7  and  FIG. 8  illustrate sequential assembly views of one embodiment of the locking spacer assembly  50 . Initially, the end pieces  52 ,  58  may be inserted into the attachment slot  36  and spaced apart such that the actuator  64  can be inserted between the inner surfaces  52   a ,  58   a . Once inserted between the inner surfaces  52   a ,  58   a , the actuator  64  is rotated ninety degrees so that the angled surfaces  68 ,  70  of the projection  66  generally face the angled planes  54 ,  60  of the inner surfaces  52   a ,  58   a . The spacer block  72  can then be inserted between the inner surfaces  52   a ,  58   a , with the rectangular collars  77  of the spacer block  72  being received into the complimentary rectangular recesses  57 ,  63  of the inner surfaces  52   a ,  58   a . The actuator  64  is then pulled radially outward (in direction Y) by hand until the angled surfaces  68 ,  70  engage the angled planes  54 ,  60  causing the end pieces  52 ,  58  to move toward each other and lock the assembly  50  together within the attachment slot  36 . The fastener  84  may then be applied to secure the actuator  64  to the spacer block  74  and prevent the actuator  64  from falling radially down. 
     Upon installation of the fastener  84 , the locking spacer assembly  50  remains locked together within the attachment slot  36 , albeit in a somewhat loose state. However, as the rotor disc  20  rotates during operation of the turbine engine, rotational loading on the assembly components cause the assembly  50  to lock together tightly within the attachment slot  36 . Specifically, the radial load on the actuator  64  caused by rotation of the rotor disc  20  is transferred through the end pieces  52 ,  58  to the rotor disc  20  to tightly lock the assembly within the attachment slot  36 . 
       FIG. 9  illustrates the locations of rotational loading on the various components of the locking spacer assembly  50  during operation of a conventional gas turbine. Upon rotation of the rotor disc  20 , end pieces  52 ,  58  load radially (in direction Y) on the post components  34  of the disc  20  at post locations  88 . Simultaneously, rotation of the rotor disc  20  causes rotational loading on the spacer block  72 , which is transmitted through the fastener  84  to the actuator  64 . Due to the rotational loading resulting from centrifugal forces, the actuator  64  moves radially outward engaging the end pieces  52 ,  58  at the projection locations  90 . Since the projection locations  90  are at an angle relative to radial, there is a component of the radial load which causes the end pieces  52 ,  58  to move towards each other, locking the assembly  50  tightly within the attachment slot  36 . 
     As illustrated in  FIG. 9 , the components of the locking spacer assembly  50 , once assembled, may have tolerance. However, it is desirable to have each component fit snugly within the attachment slot  36  such that the components of the locking spacer assembly  50  substantially fill the width of the attachment slot  36  between the post components  34 . For example, tight tolerances, resulting in a snug fit at the tolerance locations  92 , will ensure that only a minimal amount of translation is required for the end pieces  52 ,  58  to lock the locking spacer assembly  50  together within the attachment slot  36 . Additionally, tight tolerances can prevent significant rotation of the locking spacer assembly  50 , thereby creating an anti-rotation feature. 
     It should be appreciated that the present subject matter also encompasses a rotor assembly  100  ( FIG. 2 ) incorporating a locking spacer assembly  50  as described and embodied herein. The rotor assembly  100  includes a rotor  12  having a rotor disc  20  with forward and aft posts  34  defining a continuous circumferentially extending attachment slot  36 . The rotor assembly also includes a plurality of airfoils  26 , with each airfoil  26  extending from a platform  28 . The platform  28  is secured within the attachment slot  36  by an inwardly extending root  30 . At least one locking spacer assembly  50  in accordance with any of the embodiments illustrated or described herein is disposed in a space between two of the platforms  28 . It should be readily appreciated, as indicated above, that the rotor assembly  100  may be disposed in the compressor or turbine section of a gas turbine, with the platforms  28  and airfoils  26  being part of a complete stage of either rotor blades or turbine buckets. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.