Active fan flutter control

Abstract

A flutter control system for a turbomachine fan includes a plurality of fan case sensors located at a fan case of the turbomachine and configured to sense passing of blade tips of a fan of the turbomachine. A controller is operably connected to the plurality of fan case sensors. A variable fan area nozzle actuator is operably connected to the controller, such that the variable fan area nozzle actuator urges a change in fan nozzle area in response to data from the plurality of fan case sensors indicating flutter or near flutter conditions. A method of flutter control for a turbomachine fan includes sensing a blade tip passing of a plurality of fan blades. Data from a plurality of fan case sensors is compared to a threshold and a fan exit area is changed based on the comparison to dampen flutter of the plurality of fan blades.

1 . A flutter control system for a turbomachine fan comprising:
 a plurality of fan case sensors disposed at a fan case of the turbomachine and configured to sense passing of blade tips of a fan of the turbomachine;   a controller operably connected to the plurality of fan case sensors; and   a variable fan area nozzle actuator operably connected to the controller, such that the variable fan area nozzle actuator urges a change in fan nozzle area in response to data from the plurality of fan case sensors indicating flutter or near flutter conditions.   
     
     
         2 . The system of  claim 1 , further comprising at least one blade sensor disposed on a blade of the fan. 
     
     
         3 . The system of  claim 2 , wherein the at least one blade sensor is operably communicative with the controller. 
     
     
         4 . The system of  claim 3 , further comprising a radio frequency identification tag disposed at the blade and at least one radio frequency sensor disposed at the fan case. 
     
     
         5 . The system of  claim 2 , wherein the at least one blade sensor is at least one strain gauge. 
     
     
         6 . The system of  claim 1 , wherein the plurality of fan case sensors is three fan case sensors. 
     
     
         7 . The system of  claim 1 , wherein the plurality of fan case sensors are a plurality of tip timing probes. 
     
     
         8 . The system of  claim 1 , wherein the controller is a full authority digital engine control (FADEC). 
     
     
         9 . A method of flutter control for a turbomachine fan comprising:
 sensing a blade tip passing of a plurality of fan blades via a plurality of fan case sensors disposed at a fan case of a turbomachine;   comparing data from the plurality of fan case sensors to a threshold; and   changing a fan exit area based on the comparison to dampen flutter of the plurality of fan blades.   
     
     
         10 . The method of  claim 9 , further comprising:
 communicating the data from the plurality of fan case sensors to a controller;   comparing the data to a threshold at the controller; and   sending a command from the controller to a variable fan area nozzle actuator to change the fan exit area.   
     
     
         11 . The method of  claim 10 , further comprising:
 collecting strain data via at least one fan blade sensor disposed at the plurality of fan blades;   communicating the strain data to the controller; and   comparing the strain data to a strain threshold.   
     
     
         12 . The method of  claim 11 , further comprising communicating the strain data to the controller via a radio frequency identification tag. 
     
     
         13 . The method of  claim 9 , further comprising:
 evaluating a twist of the plurality of fan blades via the plurality of fan case sensors; and   evaluating a flex of the plurality of fan blades via the plurality of fan case sensors.