Published in ASME Winter Annual Meeting: Anaheim, CA, December 1, 1986, pages 43-45. Copyright 1986 American Society of Mechanical Engineers (ASME). Publisher website: http://store.asme.org/.
NOTE: At the time of publication, the author William Durgin was not yet affiliated with Cal Poly.
High velocity flow past the junction of a side branch with a pipe can result in the excitation of depth-mode standing waves in the branch. The shear layer separating the main stream flow and the cavity provides coupling between the driving and the driven flow. Photographic evidence indicates that large scale vortex structures develop at the shear layer. The vortex formation process involves strongly non-linear instability of the shear layer and may be characterized as a non-linear fluid mechanical oscillator. The standing wave system formed in the cavity is essentially an acoustic wave system of nearly linear character. The principle interaction takes place through the excitation of a quarter wavelength standing wave in the cavity. Apparently, the shear layer oscillator drives the acoustic oscillator which, in turn, has the ability to drive the shear layer through a presently unknown feedback mechanism. The system exhibits bandwidth synchronization in that the shear layer frequency is captured by the depth-mode resonance of the cavity.