Functional Beamforming Applied to Imaging of Flyover Noise on Landing Aircraft

Comparing flyover noise measurements to full-scale nose landing gear wind tunnel experiments for regional aircraft

“…Functional beamforming [33,34] was selected in this case, as it provides better dynamic range and array spatial resolution than conventional frequency domain beamforming, and these features are very important for flyover measurements, due to the relatively large distance between source and observer [18,22,35].…”

“…The de-Dopplerized acoustic signals were employed and the movement of the source was taken into account in the beamforming formulation [18,24,36]. Removing the main diagonal of the CSM for this algorithm is prone to significant errors, since the method relies on the eigenvalue decomposition of the CSM [37].…”

“…The Doppler effect was corrected according to Howell et al [26] and the movement of the source was also later considered in the formulation of the beamforming algorithm [18,24]. Finally, the geometrical spreading and the the atmospheric absorption were also taken into account to obtain the L p at the source position [3].…”

“…According to Dobrzynski [5], prediction models based on wind-tunnel tests featuring scale models are prone to underestimate airframe noise levels compared to full-scale flight tests. On the other hand, field experiments with aircraft flyovers under operational conditions present different challenges, such as the inability to control the aircraft position, larger distances between the sound source and the observer, and less-controlled flow characteristics, but they fully represent the actual conditions experienced in reality [18,19], such as crosswind. Differences between both kinds of experiments typically occur, mostly due to lack of model fidelity, installation effects in the wind tunnel and discrepancies in the Reynolds number [20].…”

“…For both kind of experiments, a common approach is to employ microphone arrays and beamforming algorithms for estimating the locations and strengths of the sound sources [16,[21][22][23]. These devices require relatively shorter measurement times compared with other tools, such as acoustic mirrors, enabling cheaper and faster experiments, especially in wind tunnels [24].…”