Development of a multiphase solver for numerical simulations of thermally driven marangoni flows

Thermocapillary flows, also known as thermal Marangoni flows, have extensive applications in a variety of different fields. Applications can be found in metal welding, growth of crystals and processing of alloys (both organic and metallic). They also have significant implications in the study of multilayer non-isothermal configurations, as well as microdroplet migration and coalescence. In this work we discuss the implementation of a non-isothermal multiphase solver based on Volume of Fluid (VOF) implemented within the open source toolbox OpenFOAM® for the numerical simulation of such flows. Interfacial tension gradients may appear consequently of a non-uniform temperature distribution along a free liquid-liquid or liquid-gas interface. The imbalance of tensile stresses, which derives from such circumstances, generates a fluid motion even in absence of any other force or external pressure gradients. The interfacial stresses are modelled via an additional body force term added to the momentum equation using a “Continuum Surface Force” (CSF) model (Brackbill et al. 1992). An energy transport equation is also solved in order to determine the temperature field evolution, which in turn influences the flow field through the Marangoni forces herein considered. To date, our solver has been tested in 2D configurations of thermally driven stratified flows. We compared our numerical simulations using a well-established code (Lappa, 2005) and good agreement was found in terms of velocity and temperature fields. Next, we aim to extend our simulations to more complex flow configurations and to consider the effect of the Marangoni stresses in non-Newtonian viscoelastic flows under non-isothermal conditions.