A volume-of-fluid method for interface-resolved simulations of phase-changing two-fluid flows

Abstract

We present a numerical method for interface-resolved simulations of evaporating two-fluid flows based on the volume-of-fluid (VoF) method. The method has been implemented in an efficient FFT-based two-fluid Navier-Stokes solver, using an algebraic VoF method for the interface representation, and extended with the transport equations of thermal energy and vaporized liquid mass for the single-component evaporating liquid in an inert gas. The conservation of vaporizing liquid and computation of the interfacial mass flux are performed with the aid of a reconstructed signed-distance field, which enables the use of well-established methods for phase change solvers based on level-set methods.The interface velocity is computed with a novel approach that ensures accurate mass conservation, by constructing a divergence-free extension of the liquid velocity field onto the entire domain. The resulting approach does not depend on the type of interface reconstruction (i.e. can be employed in both algebraic and geometrical VoF methods). We extensively verified and validated the overall method against several benchmark cases, and demonstrated its excellent mass conservation and good overall performance for simulating evaporating two-fluid flows in two and three dimensions. mechanisms drives phase change: (1) large temperatures, when phase change is triggered by a prescribed interface saturation temperature -boiling, and (2) 30 species concentration gradients near the interface, with phase change induced by a prescribed non-uniform interface concentration -evaporation. Front-tracking (FT) methods have been used to study boiling flows, with application to film boiling; see e.g. [9], [10] and [11]. Recent studies have extended this framework to evaporating two-fluid flows in two dimensions [12], 35 also in presence of chemical reactions [13]. Despite the successes of FT methods for phase change, highly scalable parallel implementations are challenging and remain scarce [14]. Such a feature is crucial for simulating e.g. turbulent gasliquid flows, which may require massive simulations with O(10 8 − 10 9 ) Eulerian grid cells [15]. 40As regards interface-capturing methods, the first study of interface-resolved simulations of phase change two-fluid flows used a level-set method, applied to film boiling [16]. Several studies have followed, aiming to incorporate interphasecoupling jump conditions with the so-called ghost-fluid method, which provides a sharp representation of the jump at the discrete level. These methods have 45 been employed for boiling [17,18,19], evaporation [20] and the combination of the two [21]. Despite the proven successes of the level-set methods for phase change problems, these are not mass-preserving by construction. Machineprecision mass conservation is desirable for numerical simulations of several systems, e.g. in multiphase turbulent flows, where the flow statistics should be 50 collected over periods of time long enough that mass loss becomes significant.Recent studies have dealt with this problem of lev...

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