Acoustic Streaming near a Heated Cylinder

A photographic study employing smoke as the indicating medium has shown the existence of a new type of streaming near a heated horizontal cylinder in the presence of a horizontal transverse sound field. This phenomenon, called “thermoacoustic streaming,” is characterized by the development of two vortices above the cylinder; the fluid pattern resembles vortex shedding behind a cylinder in forced flow normal to its axis. In the presence of sound waves whose half-wavelength is six or more times greater than the diameter of the heated cylinder, the formation of the vortex flow is a function of the sound intensity only; for such wavelengths the vortices begin to appear at 140 db (re 0.0002 μbar) and become fully developed at 146 db. This type of streaming is a flow phenomenon which is much stronger than isothermal streaming for the same geometry and sound intensity. It appears that thermoacoustic streaming will have important practical applications, particularly in the field of heat transfer.