*4.7. Plume Oscillation Period*

Comparing the previous data in terms of the POP at the di fferent values of the aspect ratio and gas volume flux, the simulation results obtained agree well with the predicted data of [16]. It was previously noted [22] that no POP occurred at a high flux and high aspect ratio. This conclusion is confirmed by the present simulations, with more detailed results provided. Figure 12 reveals that in some cases, plume oscillation is not observed. In other words, this means that at a high aspect ratio of 4 or 4.5, the bubbly flow does not oscillate at these high fluxes, and according to a particular flow path along the walls, the bubble plume is almost completely governed by the narrow width (and cannot fully develop). POP only happens under certain conditions.

**Figure 12.** Plume oscillation period (POP) statistics under the different conditions.
