Broad-Band Noise Generation in Turbofan Engines

At the exhaust flow velocities typical of current turbofan engines, a number of source mechanisms for broad-band noise generation can be postulated. These sources exist within the engine and act in addition to the more classical sources of jet noise that arise in the turbulent exhaust stream. Data are presented from laboratory studies that illustrate the importance and identify the mechanisms and parametric dependence of some of these sources. These sources, it is suggested, play a particularly significant rôle in the turbine and fan exhaust ducts of an engine—a rôle that may be augmented rather than diminished by current techniques of engine quieting. There is much to be learned about these sources before their significance in current and projected engine designs can be properly understood. Some suggestions are presented for future studies on real engines and laboratory systems.