Increasing flow speed transforms pure periodic tones into noisy turbulence

Evidence

Five stages of fluid flow around a cylinder. At the upper left, laminar, unseparated flow smoothly creeps around the cylinder at low velocities. To its right, at higher velocities, a pair of Föppl vortices form and remain behind the cylinder. Next, at higher wind speeds, these vortices begin to wag back and forth, and alternately suffer pinching off and separation, generating a von Kármán vortex street of alternating separated vortices. At still higher velocities, the general pattern is maintained, but the flow lines and vortices become turbulent (bottom left). At even higher velocities, vortex street formation ceases and a more random turbulence develops behind the cylinder (lower right). Not shown, at very high velocities, a form of turbulent vortex streets return. Sound is generated by the last three cases shown: first, at the upper right, a periodic tone with period equal to one complete vortex cycle is emitted from the vicinity of the back side of the cylinder. That tone remains but becomes somewhat noisy at the lower left. And last, for fully developed turbulence, there is nonperiodic noise with a spectrum that depends on the velocity of the wind. — Eric J. Heller, Why You Hear What You Hear- An…, 1285

Categorization

• DEFINE: Maps the five flow regimes around a cylinder, showing how each generates a distinct acoustic character from pure tone to noise.