Design and Characterization of a Hybrid Acoustic Test Cell for 0.6×0.6-m Subsonic Recirculating Wind Tunnel
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Date
2023-05
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The Ohio State University
Abstract
The noise generated by air moving over passenger cars is becoming increasingly more pronounced to automotive manufacturers in designing future electric vehicles. Components such as front grilles are important for styling and marketability, but new designs can create undesirable flow-induced noise. To enable research into the physics of whistle tone generation on automotive components, an interchangeable acoustic test cell was pursued to support component-level studies in the Subsonic Recirculating Wind Tunnel at The Ohio State University Aerospace Research Center. By adding chambers lined with acoustic foam wedges to the upper and lower walls of the test section, sound waves are attenuated above the quarter-wavelength cut-off. A barrier of tensioned aramid fabric replaces two of the four hard-wall surfaces containing the tunnel stream, allowing sound waves to pass through the porous fabric to a microphone inside one chamber. The performance of acoustic chambers retrofitted to an existing smaller-scale wind tunnel, compared to larger hybrid anechoic test sections that have appeared in the past decade, was characterized in this work. Empty-tunnel noise spectra were measured with a microphone mounted inside the lower chamber at air speeds from 40 to 200 km/h. An overall reduction in sound pressure level for the hybrid acoustic test cell was obtained over the hard-wall baseline configuration. However, cross-correlation of the interior chamber microphone with an external microphone capturing the noise signature of the tunnel fan motor indicated strong coherence. Characterization of data quality and insight into potential methods to mitigate background noise are critical steps to guide future facility development and usage.
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Keywords
automotive aeroacoustics, anechoic wind tunnel, kevlar-walled wind tunnel, whistle tonal noise