Forced or periodic vortex breakdown resulting from the instability of the impingement, in a vortex valve, of two equal and opposite jets is investigated. Experiments were conducted with a system consisting of a vortex chamber, two tangential jets, and two Helmholtz resonators. The results show that a periodic vortex breakdown is initiated when the velocities of the two opposing tangential jets acquire nearly identical values. The breakdown is accompanied by large pressure oscillations whose magnitude depends on the geometrical characteristics of the system and the magnitudes of the input flows. The major characteristics of the instability are theoretically predicted by a remarkably simple analysis by ignoring the viscous shear losses. The experimental results compare favorably well with those obtained theoretically.

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http://archive.org/details/forcedndperiodic1094540073

Lieutenant Commander, Royal Thai Navy