The Noise of Counter Rotating Propfans: Initial Results of a Wind Tunnel Model Study.

Abstract

The advent of counter rotating propfans promises significant fuel savings for commercial aircraft. These engines exhibit, however, noise characteristics which are quite different from those of conventional ones. This is primarily a consequence of additional noise sources related to instationary aerodynamic interactions between both rotors.To further the understanding of the physical mechanisms involved, the noise characteristics of counter rotating model-scale propellers were investigated within an aeroacoustic wind tunnel study and the results evaluated against simplified aeroacoustic calculations. The results of the study indicate that unsteady wake/rotor-interaction related harmonic components predominantly contribute to the noise at high frequencies, while acoustic interference effects determine the shape of noise spectra at low frequencies.