Variable thrust nozzle for quiet turbofan engine and method of operating same
AssigneeThe United States of America as represented by the Administrator of the National Aeronautics and Space Administration
InventorArthur P. Adamson
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Abstract
An improved method of operating a gas turbine engine is presented wherein engine-generated noise is maintained at a reduced level during reduced thrust operation. Fan speed is maintained at a constant level while fan nozzle area is increased. This maintains high inlet Mach numbers for reduced forward noise propagation and also permits reduced nozzle exhaust velocity for reduced shear noise. In another embodiment, airflow is increased by means of a fan blade pitch change or speed increase while the fan nozzle area is increased, yielding both a net reduction in engine thrust and noise.
Claims9
A method of operating an aircraft gas turbofan engine in a forward flight mode including the steps of:
- pressurizing air flowing through a stage of rotating fan blades disposed within an inlet duct;
- passing a portion of the air through an annular bypass duct of generally fixed geometry;
- discharging said portion through a nozzle of the type having a generally constant inlet area and variable exit area;
- and
- modulating the nozzle exit area from a first value associated with a flight cruise operating condition which is convergent with respect to the nozzle inlet to a second value which is at least five percent greater than the first value, thereby reducing engine thrust and noise;
- and wherein fan blade rotational speed is essentially constant.
A method of operating an aircraft gas turbofan engine in a forward flight mode including the steps of:
- pressurizing air flowing through a stage of rotating fan blades disposed within an inlet duct;
- passing a portion of the air through an annular bypass duct of generally fixed geometry;
- discharging said portion through a nozzle of the type having a generally constant inlet area and variable exit area;
- and
- modulating the nozzle exit area from a first value associated with a flight cruise operating condition which is convergent with respect to the nozzle inlet to a second value which is at least five percent greater than the first value, thereby reducing engine thrust and noise;
- and wherein the inlet duct Mach number is essentially constant.
A method of operating an aircraft gas turbofan engine in a forward flight mode including the steps of:
- pressurizing air flowing through a stage of rotating fan blades disposed within an inlet duct;
- passing a portion of the air through an annular bypass duct of generally fixed geometry;
- discharging said portion through a nozzle of the type having a generally constant inlet area and variable exit area;
- modulating the nozzle exit area from a first value associated with a flight cruise operating condition which is convergent with respect to the nozzle inlet to a second value which is at least five percent greater than the first value;
- and
- increasing the Mach number of the air flowing through the inlet duct, thereby reducing forward propagating noise.
A method of operating an aircraft gas turbofan engine in a forward flight mode including the steps of:
- pressurizing air flowing through a stage of rotating fan blades disposed within an inlet duct;
- passing a portion of the air through an annular bypass duct of generally fixed geometry;
- discharging said portion through a nozzle of the type having a generally constant inlet area and variable exit area;
- and
- modulating the nozzle exit area from a first value associated with a flight cruise operating condition which is convergent with respect to the nozzle inlet to a second value associated with a landing approach operating condition which is at least five percent greater than the first value, thereby reducing engine thrust and noise.
Dependencies are inferred from the claim text.