Abstract:
A device for damping of vibratory energy in the blades of rotor assemblies during operation where the blades have a shroud attached thereto with at least one sealing rail extending radially outward from the shroud to an outer diameter surface. A damper element is attached to the turbine blade sealing rail extending radially inward from the rail outer diameter surface along rail sides to maintain the damper element out of the flow of gas and positioned at a radial location on the blade for damping.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This is a continuation of U.S. patent application Ser. No. 13/279,473, entitled “TURBINE BLADE RAIL DAMPER”, filed Oct. 24, 2011. 
    
    
     BACKGROUND 
     This invention relates to rotor blades and specifically to the mechanical damping of vibratory energy in the blades of rotor assemblies during operation. Rotor assemblies are used in a variety of turbo-machines, such as turbines and compressors. During operation, fluid forces induce vibratory stresses on the blades, resulting in high cycle fatigue and potential failure of the blades. Dampers, commonly frictional dampers, are utilized to reduce the magnitude of these dynamic stresses, thereby increasing operational life of the blades. 
     Typically the most effective frictional dampers are located on the turbine blade shroud. The shroud is located at the radial tip of the rotor blade adjacent the stationary housing. During operation, centrifugal forces urge the damper into frictional contact with its adjacent blade shroud. This contact reduces the relative motion between the adjacent blades, thereby reducing the vibratory stresses on the blades during operation. Frictional damping is effective so long as relative motion exists between the damper and the blade. When the rotor speed becomes high, typical flat plate shroud dampers become too heavy and the frictional damper sticks to the shroud due to friction thereby reducing its effectiveness. Typical lighter weight damper designs consist of loss fitting rivets. These rivets are hard to form due to the many tight tolerance features required and they are exposed to the main gas flow. 
     Other efforts to reduce vibrational damage not only are structurally deficient in affecting the clearances of the shroud, they are subject to fatigue that further reduces their effectiveness. 
     Conventional shrouds typically include one or more sealing rails that extend radially outward from the shroud in close proximity to the stationary housing and typically extend continuously across the top surface of the shroud between first and second circumferential sides. Typical previous shroud frictional dampers are retained by extra features added to the shroud. These added features are located on the shroud at the furthest distance from blade which increases the shroud overhung weight. These added features increase the centrifugal induced bending stress in the shroud which may result in potential failure of the rotor assembly due to high cycle fatigue. To counteract this, the shroud thickness must be increased. This increase in shroud thickness also results in higher centrifugal stress in the blade at the blade&#39;s two critical locations, the blade shank and firtree. 
     What is needed is a way to place any damper out of the main gas flow of turbo-machines without adversely affecting the function of the shroud. 
     SUMMARY 
     The present invention relates to a damper arrangement on the sealing rail of turbo-machine shrouds where the damper in the rail is outside of the main gas flow. This invention uses the existing rail and requires no modification to the shroud to retain the damper. The rail damper comprises a shim stock having its ends oriented to function with specific shroud rail configurations. The present invention does not require any special retainment features. Retainment features add weight to the shroud and result in lower shroud and blade safety factors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating one embodiment of the present invention in a rotor assembly used in turbo-machines, showing turbine blades having shrouds with rails and damper elements. 
         FIG. 2 a    is a perspective view of the embodiment in a shroud rail. 
         FIG. 2 b    is an enlarged perspective view of the damper used in  FIG. 1 . 
         FIG. 2 c    is an enlarged perspective view of the slot in the shroud and rail in  FIG. 2   a.    
         FIG. 2 d    is an end view of the damper in the slot of  FIG. 2   c.    
         FIG. 3 a    perspective view of another embodiment of this invention in a shroud rail. 
         FIG. 3 b    is an enlarged perspective view of the damper used in  FIG. 3   a.    
         FIG. 3 c    is an enlarged perspective view of the slot in the shroud and rail in FIG.  3   a.    
         FIG. 3 d    is an end view of the damper in the slot of  FIG. 3   c.    
         FIG. 4 a    perspective view of another embodiment of this invention in a shroud rail. 
         FIG. 4 b    is an enlarged perspective view of the damper used in  FIG. 4   a.    
         FIG. 4 c    is an enlarged perspective view of the slot in the shroud and rail in  FIG. 4   a.    
         FIG. 4 d    is an end view of the damper in the slot of  FIG. 4   c.    
         FIG. 5 a    perspective view of another embodiment of this invention in a shroud rail. 
         FIG. 5 b    is an enlarged perspective view of the damper used in  FIG. 5   a.    
         FIG. 5 c    is an enlarged perspective view of the slot in the shroud and rail in  FIG. 5   a.    
         FIG. 5 d    is an end view of the damper in the slot of  FIG. 5   c.    
         FIG. 6 a    perspective view of another embodiment of this invention in a shroud rail. 
         FIG. 6 b    is an enlarged perspective view of the damper used in  FIG. 6   a.    
         FIG. 6 c    is an enlarged perspective view of the slot in the shroud and rail in  FIG. 6   a.    
         FIG. 6 d    is an end view of the damper in the slot of  FIG. 6   c.    
         FIG. 7 a    perspective view of another embodiment of this invention in a shroud rail. 
         FIG. 7 b    is an enlarged perspective view of the damper used in  FIG. 7   a.    
         FIG. 7 c    is an enlarged perspective view of the slot in the shroud and rail in  FIG. 7   a.    
         FIG. 7 d    is an end view of the damper in the slot of  FIG. 7   c.    
         FIG. 8 a    perspective view of another embodiment of this invention in a shroud rail. 
         FIG. 8 b    is an enlarged perspective view of the damper used in  FIG. 8   a.    
         FIG. 8 c    is an enlarged perspective view of the slot in the shroud and rail in  FIG. 8   a.    
         FIG. 8 d    is an end view of the damper in the slot of  FIG. 68   c.    
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a perspective view of an assembly  10 , generally, of a pair of turbine blades  14   a  and  14   b  of a turbo-machine such as a gas turbine engine. Blades  14   a  and  14   b  include firtrees  11   a  and  11   b , blade shanks  12   a  and  12   b , platforms  13   a  and  13   b , airfoils  15   a  and  15   b , shrouds  17   a  and  17   b , upstream rails  19   a  and  19   b , and downstream rails  20   a  and  20   b , respectively. Airfoils  15   a  and  15   b  extend radially out from platforms  13   a  and  13   b  to shrouds  17   a  and  17   b . Shrouds  17   a  and  17   b  include upstream rails  19   a  and  19   b  and downstream rails  20   a  and  20   b , which extend radially outward in close proximity to a stationary housing (of conventional design, not shown). Upstream rails  19   a  and  19   b  and downstream rails  20   a  and  20   b  typically extend continuously across the top surface of shrouds  17   a  and  17   b  between first and second radial faces. Rail damper  21  is placed on upstream rails  19   a  and  19   b  at a point remote from the main gas flow in the turbo-machine. Damper  21  is radially inward from the outer surface  19   c  of the upstream rail  19   a . Damper  21  is shown bridging the gap between successive upstream rail portions of  19   a  and  19   b  at junction  22 . 
       FIG. 1  shows two blades  14   a  and  14   b  to illustrate the positioning of damper  21  at junction  22 . Also shown is another damper  21  at the right end of rail  19   b  for positioning between rail  19   b  and a corresponding upstream rail of a blade that will be positioned adjacent blade  19   b.    
     Damper element  21  may be any shape that provides a fit on the rail, with a generally “U” shape being shown. The sides of the “U” shape may extend radially up or down, depending on the configuration of upstream rails  19   a  and  19   b . The use of the “U” shape allows for simple manufacture and installation. Damper  21  may be any material, such as steel or other metals, ceramics and other materials. Damper  21  material should be selected to have a light weight when possible. 
       FIG. 2 a    is an enlarged perspective view showing the details of the relationship between shrouds  17   a  and  17   b  and upstream rails  19   a  and  19   b . Damper  21  is seen in  FIG. 2 b    as having fully rounded end faces  21   d , a flat center portion  21   a , and side portions  21   b  and  21   c .  FIG. 2 c    shows damper slot  23  with a fully rounded end face  23   a  to accept and hold damper  21 .  FIG. 2 d    shows damper  21  in slot  23  in the operating position where side portions  21   b  and  21   c  extend up to engage upstream rail  19   b.    
       FIG. 3 a    is an enlarged perspective view showing the details of an alternative relationship between shrouds  17   a  and  17   b  and upstream rails  19   a  and  19   b . Damper  21  is seen in  FIG. 3 b    as having fully rounded end faces  21   d , a flat center portion  21   a , and c-shaped side portions  21   b  and  21   c .  FIG. 3 c    shows damper slot  23  with an undercut end face  23   b  to accept and hold damper  21 .  FIG. 3 d    shows damper  21  in slot  23  in the operating position where side portions  21   b  and  21   c  engage upstream rail  19   b.    
       FIG. 4 a    is an enlarged perspective view showing the details of another alternative relationship between shrouds  17   a  and  17   b  and upstream rails  19   a  and  19   b . Damper  21  is seen in  FIG. 4 b    as having fully rounded end faces  21   d , a flat center portion  21   a , and side portions  21   b  and  21   c .  FIG. 4 c    shows damper slot  23  with an undercut end face  23   b  to accept and hold damper  21 .  FIG. 4 d    shows damper  21  in slot  23  in the operating position where side portions  21   b  and  21   c  engage upstream rail  19   b.    
       FIG. 5 a    is an enlarged perspective view showing the details of another alternative relationship between shrouds  17   a  and  17   b  and upstream rails  19   a  and  19   b . Damper  21  is seen in  FIG. 5 b    as having fully rounded end faces  21   d , a flat center portion  21   a , and side portions  21   b  and  21   c  having a size suitable to engage axial stops  19   d  and  19   e .  FIG. 5 c    shows damper slot  23  with an undercut end face  23   b  to accept and hold damper  21 .  FIG. 5 d    shows damper  21  in slot  23  in the operating position. 
       FIG. 6 a    is an enlarged perspective view showing the details of another alternative relationship between shrouds  17   a  and  17   b  and upstream rails  19   a  and  19   b . Damper  21  is seen in  FIG. 6 b    as having fully rounded end faces  21   d , a flat center portion  21   a  and both ends  21   b  and  21   c .  FIG. 6 c    shows damper slot  23  with a round end face  23   a  to accept and hold damper  21 .  FIG. 6 d    shows damper  21  in slot  23  in the operating position where damper ends  21   b  and  21   c  engage upstream rail  19   b.    
       FIG. 7 a    is an enlarged perspective view showing the details of another alternative relationship between shrouds  17   a  and  17   b  and upstream rails  19   a  and  19   b . Damper  21  is seen in  FIG. 7 b    as having fully rounded end faces  21   d , a flat center portion  21   a , and side portions  21   b  and  21   c .  FIG. 7 c    shows damper slot  23  with a fully rounded end face where portions of shroud  17   a  and  17   b  are relieved to accept and hold side portions  21   b  and  21   c .  FIG. 7 d    shows damper  21  in slot  23  in the operating position where side portions  21   b  and  21   c  extend downward to engage upstream rail  19   b.    
       FIG. 8 a    is an enlarged perspective view showing the details of another alternative relationship between shrouds  17   a  and  17   b  and upstream rails  19   a  and  19   b . Damper  21  is seen in  FIG. 8 b    as having fully rounded end faces, a flat center portion  21   a , and side portions  21   b  and  21   c .  FIG. 8 c    shows damper slot  23  wider to accept and hold side portions  21   b  and  21   c  without having any part of shrouds  17   a  and  17   b  being removed.  FIG. 8 d    shows damper  21  in slot  23  in the operating position where side portions  21   b  and  21   c  extend downward to engage upstream rail  19   b.    
     In all of the embodiments shown herein, the damper is designed to engage the sealing rail of a shroud facing inward from the rail outer surface to maintain the damper element out of the flow of gas and at the most effective radial location on the blade. Damping is affected without any lessening of the functionality of the rails or the shroud. Similar dampers may also be placed on downstream rails since alteration of the shroud is not needed. 
     The invention has been shown in association with a firtree bladed rotor. The invention is also suitable for use with other rotor configurations such as an integrally bladed rotor, for example. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.