Method using secondary orientation to tune bucket natural frequency

Abstract

Tuning of turbine bucket torsional and stripe mode natural frequencies can be effected without altering any turbine bucket physical features, such as weight and/or shape, and without affecting flexure frequencies. The tuning of certain turbine bucket natural frequencies serves to avoid detrimental blade resonance, thus improving the reliability of a gas turbine. The method includes investment casting the turbine bucket with a single crystal alloy, and tuning the natural frequency of the turbine bucket without modifying physical features of the turbine bucket by placing a crystal seed along a desired direction according to a relative orientation of an engine axial direction.

What is claimed is:  
     
         1 . A method of manufacturing a turbine bucket comprising: 
 (a) investment casting the turbine bucket with a single crystal alloy; and    (b) tuning a natural frequency of the turbine bucket without modifying physical features of the turbine bucket.    
     
     
         2 . A method according to  claim 1 , wherein step (b) is practiced by tuning the natural frequency of the turbine bucket without affecting turbine bucket weight.  
     
     
         3 . A method according to  claim 1 , wherein step (b) is practiced by tuning the natural frequency of the turbine bucket without affecting turbine bucket shape.  
     
     
         4 . A method according to  claim 1 , wherein step (b) is practiced by tuning torsional and stripe mode frequencies without affecting flexure mode frequencies of the turbine bucket.  
     
     
         5 . A method according to  claim 1 , wherein step (b) is practiced by, prior to step (a), placing a crystal seed along a desired direction according to an orientation relative to an engine axial direction.  
     
     
         6 . A method of tuning turbine bucket natural frequency comprising: 
 (a) placing a crystal seed along a desired orientation relative to an engine axial direction; and    (b) investment casting the turbine bucket with a single crystal alloy, wherein the desired orientation is selected to tune torsional frequencies without affecting flexure frequencies.    
     
     
         7 . A method according to  claim 6 , comprising tuning the natural frequency of the turbine bucket without affecting turbine bucket weight.  
     
     
         8 . A method according to  claim 6 , comprising tuning the natural frequency of the turbine bucket without affecting turbine bucket shape.