Techniques for Reducing Low-Frequency Fluctuations in Aeroacoustic Wind Tunnels

• Published in: Journal of Environment and Engineering Vol. 4; no. 2; pp. 289 - 301
• Main Authors: KUDO, Toshifumi, KOMATSU, Yoshinao, MAEDA, Kazuhiro, NISHIMURA, Masaharu
• Format: Journal Article
• Language: English
• Published: The Japan Society of Mechanical Engineers 2009
• Subjects: Acoustic Resonance; Aeroacoustic Wind Tunnel; Low-Frequency Fluctuation; Pulsation
• ISSN: 1880-988X; 1880-988X
• DOI: 10.1299/jee.4.289

Aeroacoustic wind tunnels, which consist of large measuring sections, such as anechoic rooms, and open jets, are generally applied as test facilities to measure aerodynamic noise generated around vehicles. In aeroacoustic wind tunnels, it is easy to generate flow-induced low-frequency fluctuations resulting in pressure fluctuations or velocity fluctuations associated with vortices or turbulence in the open jet. These low-frequency fluctuations are generated by various flow-induced phenomena, such as swaying that occurs in various elements of the circuit, fluctuations propagated from the shear layers or mixing layers of the open jet, and the acoustic resonances of the whole circuit, which often become serious problems, generally called pulsations, at particular wind speeds. Because these low-frequency fluctuations may affect the measured pressure and velocity of a flow around vehicles in measuring sections, we should aim to reduce or control them when designing aeroacoustic wind tunnels to ensure measurement with high reliability. In this study, we investigate the generating mechanisms and techniques for reducing these low-frequency fluctuations in aeroacoustic wind tunnels by performing experiments on a model wind tunnel. In particular, new techniques for reducing acoustic resonance components such as by installing an acoustic opening in the circuit are proposed and verified by simulations and experiments. Using these techniques for reducing low-frequency fluctuations, the fluctuations of pressure and velocity in the measuring section are markedly decreased over the entire wind speed range.