Acoustic streaming is a steady current in a fluid driven by the absorption of high amplitude acoustic oscillations. This phenomenon can be observed near sound emitters, or in the standing waves within a Kundt's tube. It is the less-known opposite of sound generation by a flow.
There are two situations where sound is absorbed in its medium of propagation:
- during propagation. The attenuation coefficient is, following Stokes' law (sound attenuation). This effect is more intense at elevated frequencies and is much greater in air (where attenuation occurs on a characteristic distance ~10 cm at 1 MHz) than in water (~100 m at 1 MHz). In air it is known as the Quartz wind.
- near a boundary. Either when sound reaches a boundary, or when a boundary is vibrating in a still medium. A wall vibrating parallel to itself generates a shear wave, of attenuated amplitude within the Stokes oscillating boundary layer. This effect is localised on an attenuation length of characteristic size whose order of magnitude is a few micrometres in both air and water at 1 MHz.
Read more about Acoustic Streaming: Origin: A Body Force Due To Acoustic Absorption in The Fluid, Order of Magnitude of Acoustic Streaming Velocities
Famous quotes containing the word streaming:
“Who wants to become a writer? And why? Because it’s the answer to everything. To “Why am I here?” To uselessness. It’s the streaming reason for living. To note, to pin down, to build up, to create, to be astonished at nothing, to cherish the oddities, to let nothing go down the drain, to make something, to make a great flower out of life, even if it’s a cactus.”
—Enid Bagnold (1889–1981)