Phase-locking in a jet forced with two frequencies

This study investigates the effect of forcing a shear layer at more than one frequency. Multiple frequency forcing permits the phase and initial relative amplitudes among unstable waves to be manipulated. More control can be imposed on vortex merging and mixing. Various vortex merging modes were observed and explained by the relative strength of the instability waves and their phase alignment. The vortex phase and path jitterings present in single-frequency forcing cases are greatly reduced when forced at more than one frequency. The observed cycle-to-cycle variation was small. This enables phase-lock measurements to be performed more easily. The phase-lock data show excellent agreement with the flow visualization resutls even when averaged over only a few cycles. (Author)