Air (or water) jet as a vibrating diaphragm in aerial (or underwater) organ pipes.
Shigeru Yoshikawa · The Journal of the Acoustical Society of America · 1992
The jet works as not only an energygenerator to drive the resonant pipe but also an energycollector to maintain its wavelike vibration over the mouth. The jet may act virtually as a flexible thin diaphragm whether it bears the jet instability or not. Its overall lateral vibration then produces the acoustic mouth current, which must correspond to the feedback current collected by the jet in the jet-drive model [J. Acoust. Soc. Jpn. (E) 1, 175–191 (1980)]. Calculation of the acoustic impedance Z j’ of the jet as a vibrating diaphragm will help one understand how the jet vibration is sustained. Although the energy dissipation that occurred in the jet is much smaller than that in the pipe, the jet as well as the pipe should maintain its own oscillation according to the proper phase relation. In other words, the velocity of the jet diaphragm should be directed out of the mouth when the acoustic pressure is positive at the mouth. The question of whether the organ pipe sounds in water as well as in air was considered theoretically from the above viewpoint and was solved experimentally [J. Acoust. Soc. Jpn. (E) 5, 211–221 (1984)]. In spite of the great difference in fluid dynamical and acoustical properties between water and air, a small underwater organ pipe made of aluminum and driven by the water jet sounded at about 155 dB re: 1 μPa near 1 kHz. Similarities and differences between aerial and underwater organ pipes will also be discussed.