Feasibility of hovering small-scale low Reynolds number rotor-beam source localization by microphone array measurements
Résumé
The radiation of a small-scale low Reynolds number two-bladed rotor of 0, 2 diameter
with NACA0012 blade profile in interaction with cylindrical beams at different locations is
measured in anechoic room by an array of 45 microphones. Source localization algorithms
are used to localize tonal noise sources associated to blade passing frequency (BPF) harmonics
that are increased by the presence of the beam in order to better understand noise source
generation mechanisms. A first set of BPF harmonics, consisting of a hump centered around
5 ∗ BPF , appears to be localized above the rotor near the blade tip, whereas a second set of
BPF harmonics, consisting of a hump centered around 20 − 25 ∗ BPF , seems to have its origin
just below the beam in most cases and at ∼ 85% of the blade radius. The increase of rotational
speed, beam diameter and the decrease of rotor-beam distance leads to an increase of the
first BPF harmonics hump sound levels with similar source locations, except for the noisier
rotor-beam configuration for which both humps are located near the blade tip. As this was not
consistent with numerical simulations performed on the same configuration which showed that
first BPF harmonics levels were associated to unsteady loading on the beam, new simulations
were performed to obtain wave fronts between the rotor-beam setup and the array. This allows
to explain source locations on maps and to identify which sources were associated to the beam.
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