Efforts are made to delineate the dynamics of entrained gaseous cusps and flow of liquid films wrapped around a horizontal partially submerged rotating roller numerically. The solid roller is allowed to rotate across the gas–liquid interface with a fixed submergence ratio of 0.5 (equally immersed in both gaseous and liquid phases) and the gaseous phase is subjected to horizontal crossflow. The finite volume-based solver Gerris has been employed to track the interfacial configuration by using the volume of fluid (VOF) method. The combined influence of roller rotation (ω) and strength of crossflow (Reflow) on the wrapped film thickness and the structure of entrained cusp is demonstrated thoroughly for different gas–liquid pairs in order to understand the underlying physics. This study also includes the transient dynamics of liquid tip movement from the receding to advancing junction for various Reflow and gas–liquid pairs. Subsequently, the structure and rate of entrainment are also estimated, where the collapsible gaseous jet breaks into circular gaseous bubbles. Predictions are also made in order to establish the dependence of interfacial configuration on the Archimedes number (Ar). Finally, a theoretical model has been developed to elucidate both entrainment and wrapped film dynamics, which shows excellent agreement with the numerical results.

Entrainment of a gaseous cusp and wrapping dynamics of liquid film around the horizontal rotating roller have been studied in a stratified layer. Finite volume based simulations have been used for numerical prediction of the interface which has been tracked using volume of fluid (VOF) algorithm. After establishing the transient dynamics of the wrapping at receding front and entrainment at the advancing front, we showed the effect of liquid properties on interfacial dynamics. Mutual interplay between centrifugal force due to rotation of the cylinder and viscous damping generates different patterns of entrainment such as cusp formation, entrained air wrapping, ejection of bubble, and penetration of wrap inside entrainment. Variation of wrapped liquid thickness at the receding end is also studied for a wide range of Morton number and rotational speed. Finally, using scale analysis, we showed that viscosity plays a major role in deciding the azimuthal wrap thickness.

In this study, an attempt has been made to characterize the pattern of entrained air filament inside a liquid bath of high viscosity by employing a fully submerged horizontal rotating solid roller where the lighter phase is allowed to flow uniformly above the bath. The influence of roller rotational speed (ω), depth of submergence (h/D), strength of the crossflow (Re flow ), and fluid pair (Mo) on the entrainment profile has been established numerically to report the physical insights. An open-source Gerris solver has been employed to perform this computational work. We have also described the transient dynamics of the cusp tip for various input pertinent parameters. In addition, both departure of bubbles at the tip of the steady configured cusp and the entrainment rate are predicted for different gas−liquid pairs. Interfacial configurations are also obtained as a consequence of the effect of gravitational pull. Lastly, an analytical analysis predicted successfully the obtaining of the structure of the cusp, and the predictions are quite satisfactory compared to present numerical data.

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Collapse of a Taylor bubble inside a pipe at the free surface of a liquid is studied experimentally using speed imaging camera and illumination and subsequent image analysis. Three different fluids, water, glycerin, and silicone oil, are employed in the experiments. For all conditions studied herein, the bubble punctures at the free surface to form two thin films, i.e., one covering the cross-section of the tube near the free surface and one along the tube wall in the vertical direction. Surface tension acts to collapse the first film, which widens the punctured hole in the outward radial direction, thereby feeding the liquid in the vertical film. After the shrinking of the radial film, gravity causes the collapse of the vertical film, which generates a tiny jet of liquid at the end of collapse. Experiments with different fluids show a drastic change in shape and thickness of the vertical film that leads to higher drainage time. Analysis of time scale for the drainage of the horizontal film exhibits a favorable match with experiments. Finally, evolution of the vertical film is analyzed using a simple hydrodynamic model to estimate the order magnitude of time taken to collapse, which compares well with processed image data from experiments.