Detection of Non-Stationary Aeroacoustic Sources by Time-Domain Imaging Methods
20th AIAA/CEAS Aeroacoustics Conference, 2014
ABSTRACT Imaging methods like beamforming are widely used to localize and identify aeroacoustic s... more ABSTRACT Imaging methods like beamforming are widely used to localize and identify aeroacoustic sources. However, so far, existing applications in aeroacoustics have mostly been performed in the frequency domain. To tackle the characterization of non-stationary sources (for example, intermittent sources), time-domain imaging methods are more appropriate. Indeed, the spatio-temporal reconstruction of the acoustic �fields allows studying the source structure in "real-time". In this paper, two aeroacoustic problems are investigated with the help of time-domain inverse methods. First, simulated data of the acoustic radiation by a 2D mixing layer are studied through a time-reversal numerical method based on the Linearized Euler Equations. Using the reconstructed acoustic �fields, the spatio-temporal maxima of the acoustic energy are detected. These are assumed to correspond to wave focusing and, hence, to be related to the presence of a source. Finally, the vorticity fi�elds are observed at those times for which spatio-temporal maxima are found. A conditional average of the flow �fields, assuming large acoustic emission, is thus possible in principle. The global structure of the source is found to be quadripolar and each kind of detected peak corresponds to a fi�xed vortical structure. Second, experimental data of the noise produced by a forward-facing step in a wind-tunnel flow are analysed by using the time-domain beamforming technique. The detection of spatio-temporal maxima highlights that the wide band noise source produced by the step can be seen as a succession of short duration events scattered around the step edge.
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Papers by Cyril Nana