The acoustic characterization of fluid machines, e.g., internal combustion engines, compressors, or fans is of great importance when designing the connected duct systems and its silencers. For machines connected to large ducts where also the non-plane wave range is important, for instance large diesels and gas turbines, a suitable way to characterize the source is to determine the sound power under reflection free conditions. For the low frequency plane wave range in-duct sound power can be measured with the widely used two microphone method. The goal of this study is to investigate how, starting from the two-microphone approach, a suitable wall mounted microphone configuration can be defined and used to estimate the propagating in-duct sound power also beyond the plane wave range. For this purpose an acoustic source test-rig was built and numerical simulations were also conducted. The in-duct sound power from monopole, dipole, and quadrupole source types was determined using twelve wall mounted microphones and cross-spectra averaging methods. The in-duct results were compared against sound power measured using the reverberation room method (ISO 3741). Based on the simulations and the experimental results the best microphone positions and weighting factors were determined.
- Noise Control and Acoustics Division
Procedure to Estimate the In-Duct Sound Power in the High Frequency Range With Non-Plane Waves
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Hynninen, A, & Åbom, M. "Procedure to Estimate the In-Duct Sound Power in the High Frequency Range With Non-Plane Waves." Proceedings of the ASME 2012 Noise Control and Acoustics Division Conference at InterNoise 2012. ASME 2012 Noise Control and Acoustics Division Conference. New York City, New York, USA. August 19–22, 2012. pp. 181-191. ASME. https://doi.org/10.1115/NCAD2012-0531
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