The effect of one-sided confinement on nappe oscillations in free falling liquid sheet

Abstract

A thin liquid sheet flowing under the effect of gravity, subjected to one-sided confinement, generates considerable oscillations. These oscillations (called nappe oscillations) are incidental to the interaction of the liquid sheet with the air enclosure present within the confinement. In this regard, a numerical study is presented here involving parametric investigations to establish the effect of the proximity of the liquid sheet to the wall and surface tension on the instability of the liquid sheet. The present study demonstrates that the confinement is responsible for the perturbations near the inlet of the sheet, which then propagates the sheet into the non-linear regime. Moreover, the study on the effect of the proximity of the wall to the liquid sheet depicts that the wall and liquid sheet interact with each other with pressure in the air cushion acting as a liaison between the two. The sheet closer to the wall evolves into the non-linear regime at a preceding time instant due to the higher rate of pressure rise in the air cushion. The liquid sheet oscillations are stabilized for higher values of the surface tension coefficient. The visualization of vortical structures reveals that the vortices are clustered in the confined space, ascending toward the inlet due to higher values of baroclinicity as the sheet gets closer to the wall. On the other hand, the vortices are sparsely distributed in the domain for higher values of the surface tension coefficient.