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The paper presents guidelines for the optimal treatment of signals from microphone arrays that include continuously-scanning sensors. The signals from the scanning sensors are non-stationary due to the time-varying source-sensor distance and the traversing of an acoustic field with spatially-varying statistics. Quasi-stationarity has been sought in past studies by dividing the signals into blocks and applying a frequency-dependent window within each block. Optimal schedules versus frequency for block size and block overlap are proposed that enhance the spatial resolution while containing the computational cost. The guidelines are applied to the acoustic fields emitted by an impinging-jets source and a subsonic turbulent jet in isolation and integrated with a shielding plate. The noise source distributions are obtained through a direct spectral estimation approach in which the error between the modeled and measured far-field statistics is minimized. The ability of the continuous-scan paradigm, coupled with the proposed treatment of the signal, to provide high-definition noise source maps is demonstrated. • Overview of a direct spectral estimation method for acoustic source location. • Signal processing guidelines for continuous-scan phased microphone arrays. • High-resolution noise source maps of an impinging-jets rig. • High-resolution noise source maps of a subsonic jet. • Effect of a shielding plate on the noise emitted by a subsonic jet. • Far-field acoustic surveys of impinging-jets rig and subsonic jet. [ABSTRACT FROM AUTHOR]

The transmission of sound at normal incidence through perforated plates with bias flow is investigated experimentally and theoretically over a large parameter space. A specially designed experimental apparatus enabled the measurement of insertion loss with bias flow Mach number up to 0.25. A theoretical model for insertion loss was constructed based on inviscid, one-dimensional wave propagation with mean flow through a single contraction/expansion chamber. The mass end correction of the contraction is modified for hole interaction effects and mean flow. Hydrodynamic losses are modeled using a vena contracta coefficient dependent on both perforation geometry and Reynolds number. Losses in acoustic energy that occur in the mixing region downstream of the perforations are modeled as fluctuations in entropy. The proposed model was validated experimentally over a range of plate thickness, porosity, and hole size. The experimental results indicate an increase in insertion loss with increasing frequency, followed by saturation and decline as resonant conditions are established in the perforations. The insertion loss at low frequency increases with increasing Mach number through the perforation. The proposed model captures these trends and its predictions are shown to be more accurate than those of past models. [ABSTRACT FROM AUTHOR]