Flutter avoidance through control of texture and modulus of elasticity in adjacent fan blades

Abstract

A fan for a turbofan engine includes a plurality of blades and a disk, the plurality of blades constructed of an anisotropic material, the anisotropic material is a plate, sheet, or forging. A first blade type has a first crystallographic texture and a first natural frequency, and a second blade type has a second crystallographic texture and a second natural frequency. The first natural frequency is at least 4% greater than the second natural frequency, and the first blade type and the second blade type are attached to the disk in an alternating pattern to provide a flutter damping effect. The fan blades may be cut from a plate of the anisotropic material along orthogonal directions or forged from round bar oriented along a first direction and a second orthogonal direction, respectively.

We claim: 
     
         1 . A fan for a turbofan engine, comprising:
 a disk; and   a plurality of blades attached to the disk, the plurality of blades constructed of an anisotropic material, the anisotropic material comprising a plate, sheet, or forging;   wherein a first blade type has a first crystallographic texture and a first natural frequency, wherein a second blade type has a second crystallographic texture and a second natural frequency, wherein the first natural frequency is at least 4% greater than the second natural frequency, and wherein the first blade type and the second blade type are attached to the disk in a pattern to provide a flutter damping effect.   
     
     
         2 . The fan of  claim 1 , wherein the first blade type is cut from a plate, sheet or forging of the anisotropic material along a processing direction, and wherein the second blade type is cut from the plate, sheet, or forging of the anisotropic material along a transverse direction, wherein the transverse direction is orthogonal to the processing direction. 
     
     
         3 . The fan of  claim 2 , wherein the anisotropic material includes one or more alloys that exhibit changes in elastic modulus as a result of their crystallographic texture, the one or more alloys comprising at least one of titanium, aluminum, iron, nickel, and zinc. 
     
     
         4 . The fan of  claim 3 , wherein the blades are welded to the disk by linear friction welding. 
     
     
         5 . The system of  claim 2 , wherein the anisotropic material is a first titanium alloy and the disk is made of a second titanium alloy. 
     
     
         6 . The fan of  claim 5 , wherein the plurality of blades undergo superplastic forming. 
     
     
         7 . The fan of  claim 6 , wherein the first titanium alloy is Ti-6Al-4V. 
     
     
         8 . The fan of  claim 7 , wherein each of the plurality of blades comprises multiple layers. 
     
     
         9 . The fan of  claim 8 , wherein at least two of the layers are inflated by injecting the blade with a gas. 
     
     
         10 . A fan for a turbofan engine, comprising:
 a plurality of blades constructed of an anisotropic material, the plurality of blades attached to a disk; and   wherein a first blade type is obtained from a round bar of an anisotropic material and has a first crystallographic texture and a first natural frequency, wherein a second blade type has a second crystallographic texture and a second natural frequency, wherein the first natural frequency is at least 4% greater than the second natural frequency, and wherein the first blade type and the second blade type are attached to the disk in an arrangement to provide a flutter damping effect.   
     
     
         11 . The fan of  claim 10 , wherein the first blade type is forged from the round bar of the anisotropic material oriented in a first direction, and wherein the second blade type is forged from the round bar of the anisotropic material oriented in a second direction, wherein the first direction is orthogonal to the second direction. 
     
     
         12 . The fan of  claim 11 , wherein the anisotropic material includes one or more alloys that exhibit changes in elastic modulus as a result of their crystallographic texture, the one or more alloys comprising at least one of titanium, aluminum, iron, nickel, and zinc. 
     
     
         13 . The fan of  claim 12 , wherein the blades are welded to the disk by linear friction welding. 
     
     
         14 . The fan of  claim 13 , wherein the anisotropic material is a first titanium alloy and the disk is made of a second titanium alloy. 
     
     
         15 . The fan of  claim 14 , wherein the first titanium alloy is Ti-6Al-4V. 
     
     
         16 . The fan of  claim 15 , wherein each of the plurality of blades comprises at least two layers that are inflated by injecting a gas between the at least two layers. 
     
     
         17 . A method for producing a fan blade system for a turbofan engine, the method comprising:
 providing a sheet of anisotropic metal having a crystallographic texture, the sheet characterized by a processing direction and a transverse direction orthogonal to the processing direction;   cutting a plurality of first fan blades from the sheet along the processing direction;   cutting a plurality of second fan blades from the sheet along the transverse direction; and   mounting the first fan blades and second fan blades on a disk in an arrangement to provide a flutter damping effect.   
     
     
         18 . The method of  claim 17 , wherein the first fan blades have a first natural frequency and the second fan blades have a second natural frequency, and wherein the first natural frequency is at least 4% greater than the second natural frequency. 
     
     
         19 . The method of  claim 17 , wherein the anisotropic material is a titanium alloy. 
     
     
         20 . The method of  claim 19 , wherein the titanium alloy is Ti-6Al-4V.