Recent developments in aircraft engine noise reduction technology

Some of the more important developments and progress in jet and fan noise reduction and flight effects are reviewed. Experiments are reported which show that nonaxisymmetric coannular nozzles have the potential to reduce jet noise for conventional and inverted velocity profiles. It is shown that an improved understanding of suppressive linear behavior, coupled with the new understanding of fan source noise, will soon allow the joint optimization of acoustic liner and fan design for low noise. It is also shown that fan noise source reduction concepts are applicable to advanced turboprops. Advances in inflow control device design are reviewed that appear to offer an adequate approach to the ground simulation of inflight fan noise.