OpenFOAM hybrid - A Morphology Adaptive Multifield Two-fluid Model

The simulation of industrial multiphase flows is challenging, because these flows are typically characterized by coexisting morphologies. Modern simulation methods are well established for dispersed (e.g., Euler-Euler) or resolved (e.g., Volume-of-Fluid) interfacial structures. We propose a morphology adaptive multifield two-fluid model, which is able to handle dispersed and resolved interfacial structures coexisting in the computational domain with the same set of equations. The interfacial drag formulation of Štrubelj and Tiselj (Int J Numer Methods Eng, 2011, Vol. 85, 575-590) is used to describe large interfacial structures in a volume-of-fluid-like manner. For the dispersed structures, the HZDR baseline model is applied. The functionality of the framework is demonstrated by investigating a gas bubble, rising in a liquid, which is laden with micro gas bubbles, a 2D stagnant stratification of water and oil, sharing a large-scale interface, which is penetrated by micro gas bubbles, and an isothermal counter-current stratified flow case. For the latter the framework symmetric and asymmetric turbulence damping is used to account for turbulent flow conditions near an interface. Recent developments focus on the transition region, where bubbles are either over- or under-resolved for Euler-Euler or Volume-of-Fluid (Fig. 1). A drag model to allow tangential slip at an interface and a filtering technique are proposed for stable and robust handling interfacial structures in the transition region. Furthermore, a concept is presented for the transition of oversized dispersed bubbles into the resolved phase.