Enhancing Aeroacoustic Wind Tunnel Studies through Massive Channel Upscaling with MEMS Microphones

TL;DR

The paper demonstrates a massively upscaled MEMS microphone array (6 m × 3 m, 7200 sensors) integrated with modular panels and FPGA-based data acquisition to enable flexible sub-array beamforming in open wind tunnels. By validating against a conventional DNW array and far-field microphones on a 1:9.5 aircraft half-model, it shows that with conventional beamforming and CLEAN-SC, source emission and directivity can be accurately estimated, and far-field predictions can be recovered from near-field data. A key contribution is the use of a frequency-dependent sub-array aperture (Fermat spiral) to compensate shear-layer decorrelation across frequencies, improving agreement with far-field spectra up to high frequencies. Overall, the study confirms that MEMS-based massive channel upscaling, combined with targeted processing, enables robust aeroacoustic source localization and directivity analysis in open wind tunnels, with practical implications for more detailed aeroacoustic testing and validation.

Abstract

This paper presents a large 6~m x 3~m aperture 7200 MEMS microphone array. The array is designed so that sub-arrays with optimized point spread functions can be used for beamforming and thus, enable the research of source directivity in wind tunnel facilities. The total array consists of modular 800 microphone panels, each consisting of four unique PCB board designs. This modular architecture allows for the time-synchronized measurement of an arbitrary number of panels and thus, aperture size and total number of sensors. The panels can be installed without a gap so that the array's microphone pattern avoids high sidelobes in the point spread function. The array's capabilities are evaluated on a 1:9.5 airframe half model in an open wind tunnel at DNW-NWB. The total source emission is quantified and the directivity is evaluated with beamforming. Additional far-field microphones are employed to validate the results.

Figures (19)

• Figure 1: Photo of the model and the array in the open test section.
• Figure 2: Sub-array with 50 MEMS microphones of size $250mm\times500mm$.
• Figure 3: Illustration of wind tunnel setup with nozzle, half-model and microphone array. The array is placed $d=3.39m$ away from the model.
• Figure 4: Frequency response of the DNW microphones and DLR MEMS.
• Figure 5: $(a)$, $(b)$, and $(c)$ show projections of the experimental setup with the DNW array, and close MEMS positions from the DLR array. Additionally, the positions of far-field microphones are shown. $(d)$ shows the distance between the DNW and MEMS array positions.