Akkermans, R.A.D.

Delfs, J.W.

Ewert, R.

Lummer, M.

English

Institute of Transport Research:Publications

Aerodynamic and Acoustic Installation Effectson Open Rotor NoiseR.A.D. Akkermans, M. Lummer, R. Ewert, and J.W. DelfsDept. of Technical Acoustics, DLR, BraunschweigIn recent years, Counter Rotating Open Rotors (CROR) have received considerable attentionas the CROR concept promises a considerable reduction of fuel consumption over conventionalducted turbofan engines.However, the presence of a fuselage, wing, or pylon may significantly change noise charac-teristics of a CROR as compared to the isolated case. The two main installation effects are: (i)propeller blades operating in non-uniform flow influenced by wing/pylon (source effect), and(ii) propeller sound field interacting with e.g. fuselage, wing, and pylon flow field (propagationeffect).In this contribution the aerodynamic installation effect of CRORs will be investigated on thebasis of appropriate unsteady CFD simulations in combination with a porous Ffowcs-Williamsand Hawkings (FW-H) solver for the extrapolation of the sound into the far field. The resultsshow that an installed CROR leads to clear non-uniform azimuthal directivities, with increasedlevels in fuselage direction than towards the sideline. Ground noise polar directivities show theimportance of interaction tones for the up- and downstream noise emissions.Furthermore, aeroacoustic installation effects are studied via a Fast Multipole BEM (FMM)with a simplified noise source model in a quiescent flow. The latter constitutes of a ring sourcemodel to represent a CROR. The results show good agreement of this simplified noise sourcemodel of a CROR and CFD/CFD+FW-H data for frequencies below 700 Hz. Aeroacousticinstallation effects cause an increase in the footprint with respect to uninstalled case, as illus-trated in Fig. 1. The interaction tones exhibit a clearly changed directivity, with increased levelin the upstream direction.Figure 1: Footprint of loading noise 120m below aircraft for BPF of front rotor for isolatedCROR (left picture), installed at rear fuselage (middle), and installed underneath wing (right).

Aerodynamic and Acoustic Installation Effect on Open Rotor Noise

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Institute of Transport Research:Publications