Numerical Study of Air Entrainment and Liquid Film Wrapping around a Rotating Cylinder

Abstract

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.

Numerical Simulation and Analytical Prediction on the Development of Entrained Air Filament Caused by the Combined Effect of Rotational Field and Free Stream Flow

“…Therefore, the numerical methodology employed in this study is compared with the existing studies. Figure 3a shows the comparison of the present work with those of Yu et al 29 and Rana et al 31 39 ). Panda et al 39 analyzed the entrainment of the air cusp in a liquid pool caused by a partially submerged roller, which was allowed to rotate across the gas−liquid interface, and the gaseous phase was subjected to a steady free stream flow above the free surface.…”

“…Therefore, the numerical methodology employed in this study is compared with the existing studies. Figure a shows the comparison of the present work with those of Yu et al and Rana et al by representing a plot between the width of the film ( h ) and the angular location (θ) for the case of a partly immersed rotary drum of diameter 15 cm and a rotational speed of 20 rad/s by employing an air–ink fluid pair (ρ air = 1.225 kg/m 3 , μ air = 1.789 × 10 –5 Pa·s, ρ ink = 1560 kg/m 3 , μ ink = 0.136 Pa·s, σ = 0.035 N/m). The rotary drum is equally immersed in air and ink.…”

“…Characterization of the complex pattern of the entrained gaseous cusp due to rotary solid cylinder(s) in a liquid bath was demonstrated by numerous researchers. 26,28,30,31,33,34 However, the influence of the continuous flow of the gaseous phase on the formation of the deviated cusp was not established in the existing investigation. In our recent attempt, 39 we had delineated the pattern of the cusp structure for a rotating roller that was partially submerged along with the horizontal crossflow of the gaseous phase.…”

“…(a) Comparison of the width of the film ( h ) with the findings of Yu et al and Rana et al . (b) Comparison of the width of the entrained cusp with that of Panda et al Copyright 2009, Elsevier, International Journal of Heat and Fluid Flow, Vol.…”

“…Peixinho et al 30 adopted experimental and numerical approaches to report the interfacial configurations inside the partly filled annular gap between a pair of concentric drums, with the inner drum being allowed to rotate. After a couple of years, Rana et al 31 investigated numerically to characterize the wrapping film and structure of gas entrainment when an equally immersed circular drum rotates across the phase boundary of various gas−liquid pairs. They noticed that the thicker film is coated around the cylinder with an increase of the Morton number (Mo) of the fluid pair.…”