You can obviously hear wind. From everyday experience, the stronger the wind, the louder its sound. But this sound is always similar, and quite distinctive, noise-like. Can one compute the spectrum of the noise generated by the wind?

There is an inkling of an answer provided here: "Any way, once the wind starts doing non-linear things, it can generate periodic stresses, and from that you get the whistling or humming noise we all know and love." Could anyone expand on this, or provide references with more quantitative detail?

  • $\begingroup$ It depends what it's blowing through - trees, whatever. Anyway, it's "white" noise. $\endgroup$ – Mike Dunlavey Feb 25 '16 at 20:01
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    $\begingroup$ @MikeDunlavey it's quite definitely not white. That's why it sounds different depending on speed. $\endgroup$ – Carl Witthoft Feb 25 '16 at 20:36
  • $\begingroup$ @Carl: That's why I said "white" :) $\endgroup$ – Mike Dunlavey Feb 25 '16 at 21:34

I would recommend you to study Howe's Theory of Vortex Sound. Generally, an appearance of vorticity $\omega$ leads to conversion of a tiny part of flow kinetic energy in a pressure wave (really small part: proportional to $M^5$ in a free field). The main free field source is the divergence of the Lamb vector:

$$ \frac{1}{c_0^2}\frac{\partial^2 p}{\partial t^2}-\Delta p = \rho_0 \ \mathrm{div} (\omega \times v) $$

It's obvious that the maths is not very nice and complicated vorticity field in turbulent flows leads to noise-like perception of the generated sound.

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