Three-dimensional vortex and gas entrainment analysis in rotating liquid flow with a free surface

In nature and engineering, fluid movements involving swirling patterns, or vortices, are common occurrences. Some flows involve free-surface vortices that can potentially lead to a phenomenon termed gas entrainment (GE). There is no validated tool that can predict the free-surface profile of the gas core prior and subsequent to the GE. This study focuses on experimental and numerical investigation of flows with unsteady free-surface vortices that can potentially lead to gas entrainment. An extensive experimental work, performed in a dedicated experimental setup built in the present study, yields two main contributions. First, a new GE onset criterion, based on implementing dimensional analysis to the experimental results, is developed. The onset criterion is found to be suitable also for other experiments in the literature. Second, the experimental acquisition of the free-surface profiles, obtained with a high-speed camera, is used for validating the numerical approach. This three-dimensional numerical tool incorporates Large Eddy Simulation to capture turbulence, with Volume-of-Fluid approach to simulate free-surface profiles. The model predicts with high accuracy the free-surface profiles in cases with and without GE, observed experimentally. Then, the detailed simulation results for this type of flows are analyzed quantitatively for the first time in the available literature, using radial, axial, and tangential velocity components. The present study sheds new light on free-surface vortex flows, in general. The experimental and numerical achievements in this study can serve as a tool both to predict the free-surface flow profiles with high accuracy and to prevent gas entrainment in the engineering systems.