Abstract:
The invention provides for a simple and inexpensive fabrication to provide radial position retention to minimize the problems associated with single lobe attachment radial slop.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to turbo machinery rotor construction and, more particularly, to a structure for radially retaining the rotor blades with respect to the rotor disk of a turbo machine.  
           [0002]    Turbo machinery such as high performance gas turbine engines have a compressor and turbine, each of which includes one or more annular banks or rows of fixed stator vanes that are positioned between rows of rotatable rotor blades. Each rotor blade is formed with a rotor tip, an airfoil and a dovetail-shaped base or root that is mounted within a mating slot. The dovetail attachment of the turbine blade to the rotor may be defined as a single lobe attachment or a multi-lobe attachment. A dovetail attachment inherently results in an assembly having a measure of radial play to allow axial sliding placement of the turbine blades. The radial play is referred to as radial slop.  
           [0003]    Turbine blades with multi-lobe attachments have little radial slop by the inherent nature of the design. The left illustration of FIG. 1 shows a multi-lobe attachment in the running position with the turbine blade loaded radially outwardly. The right illustration of FIG. 1 shows the same blade  10  in the installed position, loaded radially in. As noted, there is a radial position shift delta or slop D m  relative to the rotor or hub disk  12 .  
           [0004]    In contrast, turbine blades with single lobe attachment inherently have a large amount of radial slop. Referring to FIG. 2, on the left a single lobe turbine blade  14  is illustrated in its running position, loaded radially outwardly. The same turbine blade  14  in its installed position, loaded radially inwardly, is illustrated on the right in FIG. 2. As shown, turbine blades with single lobe attachments have significant radial position shift or delta slop D s  relative to the rotor disk or hub  16  due to the design. As illustrated in FIG. 3, the radial slop of the turbine blades having single-lobe attachment results in radial mismatch between blades. Radial slop combined with single lobe dovetail creates large platform gaps between blades allowing seals and dampers to fall out. Also, the radial mismatch between adjacent blades causes issues with feather seal slot-alignment and platform damper alignment. Moreover, as illustrated in FIG. 4, the radial slop of the single lobe configuration permits blades to rock when not seated on the pressure face.  
         SUMMARY OF THE INVENTION  
         [0005]    The invention provides for a simple and inexpensive fabrication to provide radial position retention to minimize the problems associated with single lobe attachment radial slop.  
           [0006]    Thus, the invention may be embodied in a blade retention system for a rotating machine comprising: a hub having a plurality of shaped, generally axially extending, radially open slots at circumferentially spaced positions about the hub; a blade having complimentary shaped base portion axially received in a said slot and extending radially outwardly therefrom; and a radial retainer for spacing a radially inner end of said blade from a bottom surface of said slot, said retainer including a main body and a resilient component for resiliently urging the blade radially outwardly of said slot.  
           [0007]    In an exemplary embodiment, the invention is embodied in a radial retainer for spacing a radially inner end of a turbine blade from a bottom surface of a respective slot, comprising: a generally planer main body including a base portion and a frame portion; and a resilient component, said resilient component being coupled to and extending from said base portion.  
           [0008]    The invention may also be embodied in a method of radially retaining a turbine blade in a turbine blade slot, comprising: providing a hub having a plurality of shaped, generally axially extending, radially open slots at circumferentially spaced positions about the hub; engaging a blade having complimentary shaped base portion with a said slot so that said base of said blade is axially slidably disposed in said slot and said blade extends radially outwardly therefrom; and inserting a radial retainer between a radially inner end of said blade and a bottom surface of said slot, said radial retainer including a main body and a resilient component for resiliently urging the blade radially outwardly of said slot. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0009]    These and other objects and advantages of this invention will be more completely understood and appreciated by careful study of the following more detailed description of the presently preferred exemplary embodiments of the invention, taken in conjunction with the accompanying drawings, in which:  
         [0010]    [0010]FIG. 1 is a schematic axial view comparing a turbine blade to disk multi-lobe attachment during running and in the installed, non-running position;  
         [0011]    [0011]FIG. 2 is a schematic axial view comparing a turbine blade to disk single-lobe attachment during running and in the installed, non-running position;  
         [0012]    [0012]FIG. 3 is a schematic axial view of a plurality of circumferentially adjacent turbine blades;  
         [0013]    [0013]FIG. 4 is a schematic axial view of an installed single lobe turbine blade;  
         [0014]    [0014]FIG. 5 is a schematic perspective view of a radial retainer embodying the invention;  
         [0015]    [0015]FIG. 6 is a schematic axial view of a single lobe turbine blade radially retained with a radial retainer structure provided as an embodiment of the invention; and  
         [0016]    [0016]FIG. 7 is a side-elevational view showing the free-state and installed positions of a retainer embodying the invention.  
     
    
     DETAILED DESCRIPTION  
       [0017]    The invention provides a fabrication for determining a radial position of a turbine blade to minimize radial position delta and thereby avoid problems associated with radial slop and mismatch among adjacent turbine blades. The radial retainer is inserted between the bottom face or radially inner face of the turbine blade and the bottom of the respective disk slot to radially space the turbine bottom face from the disk slot bottom to dispose the turbine blade generally in its running position. Referring to FIG. 6, a turbine blade  22  is shown seated in one of a plurality of dovetail slots  1   8  defined circumferentially of a rotor disk or hub.  
         [0018]    In the illustrated embodiment, the radial retainer  20  resiliently urges the turbine blade  22  towards its running position and as such includes a main body  24  engaging the turbine blade  22  and a resilient component  26  for urging the turbine blade  22  and the disk bottom surface  28  in opposite directions. The main body  24  of the radial retainer distributes the urging force of the resilient component  26  to uniformly urge the turbine blade  22  radially outwardly. In the illustrated configuration, the bottom face  30  of the turbine blade  22  is generally flat to provide for generally contiguous contact between the radial retainer main body  24  and the turbine blade  22 .  
         [0019]    As schematically shown in FIGS. 6 and 7, a plurality of cooling passages  32 , 34  are typically defined radially through at least a portion of the turbine blade  22 . The radial retainer  20  of the illustrated embodiment advantageously provides a main body  24  configured to include a frame or perimeter band  42  for engaging the turbine blade  22  in surrounding relation to the cooling passage inlets  36 , 38  so that the radial retainer does not obstruct cooling air flow  40  into the turbine blade  22 . In the illustrated embodiment, the main body  24  of the radial retainer includes a base portion  44  from which the frame portion  42  extends. More specifically, the base portion  44  is secured to each end of the perimeter or frame  42 . The resilient component  26  is also coupled to the base portion  44  for urging the turbine blade and dovetail slot bottom surface  28  as mentioned hereinabove. A wire band is illustrated as an exemplary frame structure  42  to ensure that the retainer does not block the cooling passages in the blade, as mentioned above.  
         [0020]    In an exemplary embodiment, the resilient component  26  is configured as a resilient plate spring or tongue secured at its proximal end  46  to the base portion  44  of the main body  24  and resiliently projecting to a free distal end  48 . As illustrated e.g., in FIG. 7, the resilient tongue  26  is pre-formed to extend from a first plane including the main body  24  to a second plane including the free distal free end  48 , the second plane being spaced from and generally parallel to the first plane. The tongue  26  is secured to the base portion  44  so as to project from the main body  24  of the radial retainer a distance greater than a target gap between the dovetail slot bottom  28  and the turbine blade bottom face  30 . Accordingly, when the radial retainer  20  is disposed between the turbine blade  22  and the bottom surface  28  of the dovetail slot, the resilient tongue  26  is resiliently displaced towards the main body  24  of the retainer. It is the memory of the retainer sheet metal material, urging it to return to its free state from its installed position, that then resiliently urges the turbine blade  22  radially outwardly.  
         [0021]    As will be appreciated and understood, an advantage of the resilient retainer tongue is that it allows easy, sliding placement of the radial retainer  20  into the dovetail slot while providing the force necessary to maintain the desired blade radial position. Moreover, the curved configuration of the resilient tongue advantageously acts as a scoop to guide and direct the cooling air  40  into the cooling passages  32 , 34  to maximize cooling flow and effect.  
         [0022]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.