Open Rotor Noise Prediction Using the time Domain Formulations of Farassat

Abstract

During his career at the NASA Langley Research Center (LaRC), Feridoun (Feri) Farassat (1944–2011) made significant contributions to the understanding of open rotor (OR) noise generating mechanisms and to the development of OR aeroacoustic prediction technology. His time domain solutions of the Ffowcs Williams and Hawkings equation for surfaces in arbitrary motion are valid over all flight speeds ranging from subsonic through transonic to supersonic, and have led to the creation of several open rotor noise prediction programs. Two of these solutions, known as Formulation 1A and Formulation 3, are described here and have been implemented in the open rotor noise prediction codes ASSPIN (Advanced Subsonic and Supersonic Propeller Induced Noise) and ASSPIN2. Validation studies comparing noise predictions made with these codes to measured noise data are presented for a full-scale, single-rotation propfan at cruise conditions and for sub-scale, contra-rotating rotors at take-off conditions. In his later years, Farassat collaborated with the authors on the development of level 1 (non-CFD) blade aerodynamics codes for providing low-cost, time domain, blade surface pressure data for ASSPIN2 input. Use of the level 1 aerodynamics codes and their interaction with ASSPIN2 are demonstrated with noise radiation studies for a model SR7 open rotor at take-off and cruise conditions.