I have read that because turbulence has a fractal structure then all frequencies are excited equally and that makes the familiar whistling noise.
Is this explanation correct?
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Turbulent air motion is excited by a fast train and hence acoustic power is radiated by that turbulent air as a "WHOOSH" sound. Because air has mass, elasticity and compliance, extremely low and extremely high frequencies might be missing from the actual sound spectrum of a fast train, but between those extremes all frequencies will be represented.