Abstract
The noise reduction potential of different active noise control (ANC) configurations and control algorithms for the application to aircraft engines were studied. The work was done within the framework of the Brite/Euram research project RANNTAC (Reduction of Aircraft Noise by Nacelle Treatment and Active Control). ANC was applied to a fan model of 0.47m-diamete r in the SNECMA test facility in Villaroche, France. Loudspeakers mounted flush with the inner wall of the inlet duct were used as secondary acoustic sources. CNRS and EADS implemented various algorithms for active control using microphones as error sensors which are mounted (1) in the inlet duct and (2) in the free field upstream of the fan intake. DLR performed an acoustic mode analysis of the sound field in the inlet duct for the cases with and without ANC. For this purpose DLR designed and constructed a special duct section with 96 ports for wall-flush mounting of precision microphones and developed an appropriate analysis technique. Decomposition of the sound field into azimuthal and radial mode components provided detailed information on the effectiveness of the various active noise control techniques used. The sound power reductions achieved with ANC in the upstream far field were documented by microphoneantenna measurements conducted by SNECMA and served for further validation of the experimental findings.
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