Shear Laver Coupling with Side-branch Resonators

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 fl ow. Photographi c evi dence i ndi cates that 1arge 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 oscill ator. The standi ng wave system formed in the cavity is essenti ally an acousti c wave system of nearl y li near character. The principl e interacti on 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 synchroni­ zation in that the shear layer frequency is captured by the depth-mode resonance of the cavity.