Fast air jets are inherently unstable and inevitably produce sound

Evidence

We now know why a certain amount of jet noise is inevitable: fast air jets are inherently unstable and cannot be controlled, and that instability leads to puffs of air “punching” out at nearby stiller air, resulting inexorably in sound production. — Eric J. Heller, Why You Hear What You Hear- An…, 1345

Categorization

• XREF: The inevitability of jet noise on every scale links to the scale-invariance point in the fricative/Apollo passage.