Main fan noise mitigation technologies in turbofan engines

Aircraft noise and emissions have been of concern since the beginning of commercial aviation. The continuing growth in air traffic and increasing public awareness have made environmental considerations one of the most critical aspects of commercial aviation today. To deal with this problem, aircraft manufacturers and public establishments are engaged in research on technical and theoretical approaches for noise reduction concepts that should be applied to new aircraft. While jet noise was the dominating contributor in the early jet engine designs, the noise emitted by the fan has become important with the reduction in jet speed and its control requiring an immense research effort. This paper concerns the main fan noise mitigation technologies in turbofan engines.