High-speed propeller noise prediction - A multidisciplinary approach

The prediction of noise produced by advanced propellers is a multidisciplinary subject which involves the aeroelasticity, aerodynamics, and aeroacoustics of rotating blades. As part of the PTA (Propfan Test Assess- ment) noise-prediction project of NASA Langley, state-of-the-art computational methods in these disciplines were combined to form a comprehensive propeller noise-prediction package. The primary function of the project was to assess current noise-prediction capability. This was accomplished by comparing predictions with the extensive noise data provided by the PTA flight tests of NASA Lewis. The emphasis of this paper is on free-field predictions, which correspond to boom microphone measurements, and conditions for which the inflow is approximately axial. Predictions made on the fuselage of the PTA aircraft and predictions correspond- ing to nonaxial inflow conditions form the subject matter of companion papers by the authors and co-workers. Excellent agreement in trends and generally good agreement in acoustic levels between free-field measured and predicted data were observed. A secondary goal of a the project was to study systematically the effect of blade deformation on propeller aerodynamics and acoustics. The twist and camber distributions of advanced pro- pellers are altered by centrifugal and aerodynamic forces. Consequently, blade surface pressure, power, and thrust are influenced by blade deformation. It was demonstrated that the impact of blade deformation on propeller noise can be significant and should be included.