PREDICTION OF PROPFAN NOISE BY A FREQUENCY-DOMAIN SCHEME

The noise of single-rotating propfans is predicted from the solution of the Ffowcs Williams and Hawkings equation in the frequency domain. The computations under certification procedures are based on the concepts developed for conventional propellers because the flight speeds are low. Emphasis is put on noise computation on the fuselage outer wall at cruise speed. Since the helical tip velocities are then transonic, the previous codes must be completed to take into account the noncompactness of the acoustic sources and the blade twist. In addition, a method of estimation of near-field propeller sound levels is developed from the Euler three-dimensional equations. Finally, acoustic measurements on a 1-m model propfan in the S1-MA transonic wind tunnel of Modane-Avrieux are presented, and comparisons with theoretical results are given.