Advanced Subsonic Aircraft Engine Noise Reduction Research

Abstract

Engine noise reduction research currently underway in the NASA Advanced Subsonic Technology Noise Reduction Program is described. Emphasis Is on noise reduction technology for high to ultra-high bypass ratio turbofan engines which will dominate the airline fleets early in the 21 st century. In terms of noise components, primary emphasis is on the fan with secondary effort on the jet for engines at the lower end of the bypass ratio range. The approach to fan noise prediction consists of modeling the chain of physical processes beginning with flow disturbances on fan blades and ending with far field sound levels. For the jet, CFD solutions for the nozzle geometries are couplele combined aeroacoustic source/radiation models. 0n the experimental side, realistic models at fans. nacelles, and nozzles are tested in aeroaooustic wind tunnel} Comparisons of predicted and measured noise levels are presented as indicators 01 progress toward developing improved low-noise design toois. The challenges of applying active control concepts to turbofan noise are discussed including both cancellation and source modification approaches.