Variable displacement flutter damper for a turbofan engine

A gas turbine engine comprising:

• a nacelle;
• and
• a flutter damper secured to the nacelle, the flutter damper including:
• a chamber having an internal space;
• a movable diaphragm disposed at least partially within the chamber, the diaphragm separating the chamber into a first chamber and a second chamber, the second chamber forming an acoustic volume, wherein a size of the acoustic volume configures the chamber for peak acoustical energy absorption at a frequency range that is associated with one or more fan flutter modes;
• and
• a biasing member that moves the diaphragm responsive to a signal from an aircraft or engine electronic control (EEC) unit, wherein movement of the diaphragm increases or reduces the size of the acoustic volume of the second chamber;
• wherein
• the biasing member is an inflatable and deflatable bladder disposed in the first chamber, the diaphragm includes a parameter seal to fluidly seal the first chamber from the second chamber, and
• the flutter damper further includes:
• a pressurized fluid supply fluidly connected to the bladder and a first valve controlled by the electronic engine control to enable or prevent fluid from flowing to the bladder, the pressurized fluid being air;
• a vent and a second valve controlled by the electronic engine control to enable or prevent air from venting from the bladder;
• a sensor in electronic communication with the electronic engine control that detects the position of the diaphragm in the chamber;
• and
• a spring to counter-bias the diaphragm to an opened state that increases the acoustic volume.

A method of providing flutter damping to a gas turbine engine, comprising:

• determining with an electronic engine control that an acoustic volume in a chamber should change by being increased or decreased, wherein a size of the acoustic volume configures the chamber for peak acoustical energy absorption at a frequency range that is associated with one or more fan flutter modes;
• and
• actuating a biasing member to increase or decrease the acoustic volume,
• wherein,
• the biasing member is an inflatable and deflatable bladder, and the method includes:
• actuating a fluid vent valve to deflate a bladder in the chamber to move a diaphragm so as to increase the acoustic volume, or actuating a fluid supply valve to inflate the bladder in the chamber to move the diaphragm so as to decrease the acoustic volume;
• and
• the flutter damper includes a sensor in electronic communication with the electronic engine control that detects the position of the diaphragm in the chamber, and the chamber includes a spring to counter-bias the diaphragm to an opened state that increases the acoustic volume.