Vortex shedding becomes audible sound despite wasting most energy as heat

Evidence

The Föppl vortices are a rotating pocket of air, but as they wag back and forth and are shed they push the surrounding air as surely as a solid object would, starting a propagating pressure wave. This we hear as sound if the frequency of vortex formation is in the audio range. Not much of the energy of a vortex ends up as sound—most of the energy is dissipated through internal friction of the air, or viscosity, eventually winding up as heat. But then, not much energy is needed to make even loud sounds, as we know. If the object is symmetrical, like a cylinder, the vortices are identical except for their leftand righthandedness. The vortex shedding pitch heard for a rigid obstacle is the frequency of formation of every righthanded (or equivalently every lefthanded) vortex—that is, the period for one complete oscillation, or “wagging” of air behind the object. — Eric J. Heller, Why You Hear What You Hear- An…, 1284

Categorization

• DEFINE: Clarifies the mechanism by which vortex shedding becomes audible sound — a pressure wave born from the wagging of the shed vortex pocket.
• corroborated: 2 independent passages support this claim — Eric J. Heller, Why You Hear What You Hear- An…, 1284