(237h) A VoF-LPT Solver for 3D Numerical Simulation of Aerated Slug Flow and Closure Law Development

The ultimate goal of our work consists in the derivation of closure relations for mono-dimensional models that aim at predicting aerated slug flow in (almost) horizontal pipes. Such mono-dimensional models are often used in the chemical and petroleum industry to describe multiphase flow in long pipes.

Our study is motivated by the fact that existing mono-dimensional closure laws (i) are often not suitable for general pipe configurations, and (ii) their range applicability is often limited to some particular flow rates. Thus, there is a lack of generally-valid closures for mono-dimensional slug flow models. The core idea of the present contribution is to use results from 3D numerical simulations to supply data for the development of closure laws.

To numerically simulate aerated slug flow in great detail, a coupled Volume of Fluid-Lagrangian Particle Tracking (VoF-LPT) solver was developed in OpenFOAM^® . Therefore, a new Lagrangian library was integrated in the available solver 'interFoam'. The latter describes the interface between the continuous gas and liquid phases using the VoF method. The dispersed bubbles motion in the continuous liquid phase was handled by a Lagrangian particle tracking approach (bubble-bubble collisions were not considered in this study). This new solver was developed since the VoF method alone does not allow the description of many (resolved) gas bubbles at a reasonable computational costs. The approach used in the present study is similar to what has been proposed by Tomar et al. (2010) in the field of primary atomization of liquid jets. Most important, our new solver accounts also for the possibility of bubble deposition into the continuous gas phase: when a bubble reaches the (VoF-resolved) gas-liquid interface, its volume is transferred to the continuous gas phase, and the bubble is removed from the LPT-based computation. The correct implementation of our new solver was verified with a simple test case, and a qualitative validation study was performed considering a more complex configuration.

Finally, our solver was coupled with the toolbox 'CPPPO' (Municchi et al, 2016) in order to compute filtered values of relevant fields (velocities, volume fractions...). Hence, filtered flow quantities can be extracted from our VoF-LPT simulations, and correlated with, e.g., bubble deposition rates. Ultimately, such correlations, together with a mechanistic understanding of the flow, can be used to develop closure relations for mono-dimensional models of pipe flow. Our present contribution will focus on both (i) the theory and numerics behind the new VoF-LPT solver, as well as (ii) first results for a rigorous closure to predict bubble deposition rates in aerated slug flow.

References

Municchi F., Goniva C., Radl S., Highly efficient spatial data filtering in parallel using the opensource library CPPPO, Computer Physics Communications 207, (2016) 400-414

Tomar G., Fuster D., Zaleski S., Popinet S., Multiscale simulations of primary atomization, Computer & Fluids 39, (2010) 1864-1874