Instrumentation and signal analysis
Abstract
Methodologies employed in aeronautical acoustics research on noise reduction are outlined. Each problem involves assessment of current knowledge, formation of a hypothesis regarding the performance of available transducers, and selection of the signal processing routines. A fast Fourier transform (FFT) is normally applied when one transducer, i.e., a microphone, is deployed to measure far-field noise. With two transducers, located in the source volume and in the acoustic field, two-point correlations are possible. Determinations of the group convection velocities, coherence lengths and lifetimes, the causality relations, and the transfer functions are performed. A model for experimentally validating theoretical methods for rotor noise prediction is described. FFTs are also applied with three transducers, which sense far-field and source noise as well as fluctuations in order to calculate cross-spectral densities. Finally, array processors permit use of many transducers, and images of the acoustic field can then be generated by computer.
- Publication:
-
ONERA
- Pub Date:
- 1983
- Bibcode:
- 1983atyr.vkifQ....E
- Keywords:
-
- Aeroacoustics;
- Noise Reduction;
- Signal Analysis;
- Sound Transducers;
- Aircraft Noise;
- Fast Fourier Transformations;
- Mathematical Models;
- Noise Prediction (Aircraft);
- Rotors;
- Transfer Functions;
- Acoustics