B. Gehlhar, W. Dobrzynski

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. This leads to different azimuthal noise directivities for (a) the acoustic interference between both rotors and (b) the unsteady interaction noise component. In contrast to the polar noise directivity of a single rotating propeller (with maximum noise radiation near the plane of rotation), counter rotating propellers exhibit distinct level maxima in the front and the rear arc. The levels of unsteady wake / rotor-interaction related noise increase with helical blade tip Mach number, less steep however than single-propeller noise levels. Initial acoustic test data obtained from the CRISP ("Counter Rotating Integrated Shrouded Propfan" Simulator of MTU) exhibit the same behavior.

Eurpean Propulsion Forum, 1990, Köln

Conference Paper

englisch

21,0 x 29,7 cm, 9 Seiten

DGLR-Bericht, 1990, 1990-01, Eurpean Propulsion Forum: Future Civil Engines and the Protection of the Atmosphere - Proceedings; S.97-105; 1990; Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V., Bonn

NA

Bestellbar

1990