Abstract
Amongst the multitude of approaches available in literature to reduce spurious velocities in Volume of Fluid approach, the Sharp Surface Force (SSF) model is increasingly being used due to its relative ease to implement. The SSF approach relies on a user-defined parameter, the sharpening coefficient, which determines the extent of the smeared nature of interface used to determine the surface tension force. In this paper, we use the SSF model implemented in OpenFOAM® to investigate the effect of this sharpening coefficient on spurious velocities and accuracy of dynamic, i.e., capillary rise, and static bubble simulations. Results show that increasing the sharpening coefficient generally reduces the spurious velocities in both static and dynamic cases. Although static millimeter sized bubbles were simulated with the whole range of sharpening coefficients, sub-millimeter sized bubbles show nonphysical behavior for values larger than 0.3. The accuracy of the capillary rise simulations has been observed to change non-linearly with the sharpening coefficient. This work illustrates the importance of using an optimized value of the sharpening coefficient with respect to spurious velocities and accuracy of the simulation.
Highlights
Modelling surface tension dominant multiphase flows is relevant in a multitude of industrial processes like lab-on-chip, atomization, and boiling
In the VOF approach used in interFoam, the volume fraction field is used to determine curvature and corresponding surface tension force based on models like the widely used Continuum Surface Force (CSF) approach (Brackbill et al, 1992)
We investigate the effect of the sharpening coefficient used in the Sharp Surface Force (SSF) model, as developed on OpenFOAM® 6 by Vachaparambil and Einarsrud (2019a), to model two dimensional dynamic cases like capillary rise and static cases like millimeter and sub-millimeter bubbles
Summary
Modelling surface tension dominant multiphase flows is relevant in a multitude of industrial processes like lab-on-chip, atomization, and boiling. The Sharp Surface Force model, developed by Raeini et al (2012), estimates surface tension based on a smoothed interface curvature and a sharpened interface region defined using a user defined sharpening coefficient (Csh). This model, which is relatively simple to implement compared to height function based approach (Pavuluri et al, 2018), has been shown to reduce spurious velocities in comparison to commonly used CSF model (Pavuluri et al, 2018; Vachaparambil and Einarsrud, 2019a). All the simulations discussed in this work use the sharpening coefficient typically used in simulating practical flow scenarios, i.e., 0 ≤ Csh ≤ 0.5 (based on the values used in Raeini et al (2012), Soh et al (2016), Maes and Soulaine (2018), Pavuluri et al (2018), Vachaparambil and Einarsrud (2019a), Vachaparambil and Einarsrud (2020))
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