Method of damping aerofoil structure vibrations

Abstract

The method described herein includes providing an aerofoil structure having a root portion and an aerofoil portion, wherein the aerofoil portion has a tip remote from the root portion. In certain aspects, the tip of the aerofoil structure can be substantially surrounded by a casing with a clearance gap between the tip and the casing. In certain aspects, the method described herein includes disposing the aerofoil structure relative to the casing such that an oscillation of the aerofoil structure from an unperturbed position in a first direction reduces the clearance gap and that an oscillation from the unperturbed position in a second direction increases the clearance gap. In certain aspects, the method further includes disposing the aerofoil structure such that the frequency of the clearance gap variation is equivalent to the frequency of the aerofoil structure vibration and permits a flow through the clearance gap in which the flow tends to dampen the aerofoil structure vibrations.

1 . A method of damping aerofoil structure vibrations, the method comprising:
 providing an aerofoil structure having a root portion and an aerofoil portion, wherein the aerofoil portion has a tip remote from the root portion, the tip of the aerofoil structure being substantially surrounded by a casing with a clearance gap between the tip and the casing;   disposing the aerofoil structure relative to the casing such that an oscillation of the aerofoil structure from an unperturbed position in a first direction reduces the clearance gap and that an oscillation from the unperturbed position in a second direction increases the clearance gap;   further disposing the aerofoil structure such that the frequency of the clearance gap variation is equivalent to the frequency of the aerofoil structure vibration; and   permitting a flow through the clearance gap, the flow tending to damp the aerofoil structure vibrations.   
     
     
         2 . A method of damping aerofoil structure vibrations as claimed in  claim 1 , the method further comprising:
 limiting the aerofoil structure from vibrating beyond a minimum in the clearance gap when moving in the first direction.   
     
     
         3 . A method of damping aerofoil structure vibrations as claimed in  claim 1 , the method further comprising:
 providing a change in the curvature of the aerofoil portion of the aerofoil structure such that the tip of the aerofoil structure is displaced from the point of minimum clearance gap when in the unperturbed position.   
     
     
         4 . A method of damping aerofoil structure vibrations as claimed in  claim 1 , the method further comprising:
 angling the root portion of the aerofoil structure such that the tip of the aerofoil structure is displaced from the point of minimum clearance gap when in the unperturbed position.   
     
     
         5 . A method of damping aerofoil structure vibrations as claimed in  claim 1 , the method further comprising:
 angling the aerofoil portion with respect to the root portion such that the tip of the aerofoil structure is displaced from the point of minimum clearance gap when in the unperturbed position.   
     
     
         6 . An aerofoil structure configured to damp vibrations in the aerofoil structure, the aerofoil structure comprising a root portion and an aerofoil portion, wherein the aerofoil portion has a tip remote from the root portion, the tip of the aerofoil structure being substantially surrounded by a casing with a clearance gap between the tip and the casing;
 wherein the aerofoil structure is disposed relative to the casing such that an oscillation of the aerofoil structure from an unperturbed position in a first direction reduces the clearance gap and that an oscillation from the unperturbed position in a second direction increases the clearance gap; the aerofoil structure being further disposed such that the frequency of the clearance gap variation is equivalent to the frequency of the aerofoil structure vibration; and   wherein a flow through the clearance gap tends to damp the aerofoil structure vibrations.   
     
     
         7 . An aerofoil structure as claimed in  claim 6 , wherein the aerofoil structure is further disposed such that the aerofoil structure is limited from vibrating beyond a minimum in the clearance gap when moving in the first direction. 
     
     
         8 . An aerofoil structure as claimed in  claim 6 , wherein the aerofoil portion of the aerofoil structure comprises a change in the curvature such that the tip of the aerofoil structure is displaced from the point of minimum clearance gap when in the unperturbed position. 
     
     
         9 . An aerofoil structure as claimed in  claim 6 , wherein the root portion of the aerofoil structure is angled such that the tip of the aerofoil structure is displaced from the point of minimum clearance gap when in the unperturbed position. 
     
     
         10 . An aerofoil structure as claimed in  claim 6 , wherein the aerofoil portion is angled with respect to the root portion such that the tip of the aerofoil structure is displaced from the point of minimum clearance gap when in the unperturbed position. 
     
     
         11 . An aerofoil structure as claimed in  claim 6 , wherein the aerofoil structure comprises a suction surface and a pressure surface disposed either side of the aerofoil portion, the suction and pressure surfaces being arranged such that the flow through the clearance gap tends to move the aerofoil structure in the first direction. 
     
     
         12 . An aerofoil structure as claimed in  claim 6 , wherein the aerofoil structure is a fan blade. 
     
     
         13 . A turbomachine comprising the aerofoil structure of  claim 6 . 
     
     
         14 . A gas turbine comprising the aerofoil structure of  claim 6 . 
     
     
         15 . (canceled) 
     
     
         16 . (canceled)