Fan noise sources and passive reduction methodlogies in high bypass turbofan engines

Increasing air traffic and more stringent aircraft noise regulations continue to increase requirements on community noise prediction capabilities for conventional and unconventional aircraft configurations. For engines with a high bypass ratio, fan noise is a major noise source. The main established technologies for fan reduction and those currently under evaluation are scarf inlets, forward swept fans, swept and leaned stators, fan trailing edge blowing, acoustic treatment placed over the fan and acoustic liners. Acoustic liners have desirable acoustic attenuation properties and thus are commonly used to reduce noise in jet engines. The liners typically are placed upstream and downstream of the rotors (fans) to absorb sound before it propagates out of the inlet and exhaust ducts. This paper focusses on about the main fan noise sources in new modern turbofan engines.