A Filtered-Interface Method for Simulations of Transcritical Multiphase Flows

In stark contrast to pure fluids, immiscible multi-species mixtures can retain sharp liquid-vapor interface with surface tension at pressures significantly higher than the critical points of the constituent species. Examples of such a system are commonly found in modern automotive and propulsion engines: the injection of low-temperature liquid fuel into a high-pressure, high-temperature gaseous environment. In this context, the thermodynamic state of the mixture can traverse both sub- and supercritical regimes temporally and spatially. In the past, modeling of the temporal transition requires an ad-hoc switching between a fitted-grid front-tracking two-fluid method for subcritical conditions and a single-fluid method for supercritical conditions. The complexity of this method limits its application to 1D domains. Meanwhile, modeling of the spatial transition from sub- to supercritical conditions is so far not possible. To address this, we introduce a newly developed Filtered-Interface Method (FIM). This single-fluid formulation can naturally describe both sub- and supercritical processes as well as the transition between them. After validation of the model against existing experiments and VOF simulations of subcritical interfacial behavior, we demonstrates the ability of FIM in resolving transcritical phenomena via a suite of transcritical configurations: droplet evaporation, droplet injection, and jet injection.