Sound, usually in the band
of audible frequencies, associated with wake-eddy, vortex- produced pressure
fluctuations resulting from air flow around obstacles, such as wires and twigs.
Although many such sounds are irregular noises, other familiar sounds involve fairly clear musical notes or humming sounds. The latter sounds were called aeolian tones by Rayleigh. Their pitch
is controlled by the frequency
with which eddies
are formed and detached in the wake
region on the lee side of the obstacle. The tones produced by wind
flowing over a cylinder, including stretched wire, were shown by Strouhal in 1878 to be of frequency (pitch) f
is the cross-axis wind velocity (m s-1
) and d
is the cylinder diameter (m).
Lord Rayleigh 1878. The Theory of Sound. Vol. II, . 412–413.
Humphreys, W. J. 1940. Physics of the Air. 3d ed., . 442–448.
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