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...

We perform interface-resolved simulations of finite-size evaporating droplets in weakly compressible homogeneous shear turbulence. The study is conducted by varying three dimensionless physical parameters: the initial gas temperature over the critical temperature $T_{g,0}/T_c$, the initial droplet diameter over the Kolmogorov scale $d_0/\eta$ and the surface tension, i.e. the shear-based Weber number, $We_{\mathcal {S}}$. For the smallest $We_{\mathcal {S}}$, we first discuss the impact on the evaporation rate of the three thermodynamic models employed to evaluate the gas thermophysical properties: a constant property model and two variable-properties approaches where either the gas density or all the gas properties are allowed to vary. Taking this last approach as reference, the model assuming constant gas properties and evaluated with the ‘1/3’ rule is shown to predict the evaporation rate better than the model where the only variable property is the gas density. Moreover, we observe that the well-known Frössling/Ranz-Marshall correlation underpredicts the Sherwood number at low temperatures, $T_{g,0}/T_c=0.75$. Next, we show that the ratio between the actual evaporation rate in turbulence and the one computed in stagnant conditions is always much higher than one for weakly deformable droplets: it decreases with $T_{g,0}/T_c$ without approaching unity at the highest $T_{g,0}/T_c$ considered. This suggests an evaporation enhancement due to turbulence also in conditions typical of combustion applications. Finally, we examine the overall evaporation rate and the local interfacial mass flux at higher $We_{\mathcal {S}}$, showing a positive correlation between evaporation rate and interfacial curvature, especially at the lowest $T_{g,0}/T_c$.

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We present the Fluid Transport Accelerated Solver, FluTAS, a scalable GPU code for multiphase flows with thermal effects. The code solves the incompressible Navier-Stokes equation for two-fluid systems, with a direct FFTbased Poisson solver for the pressure equation. The interface between the two fluids is represented with the Volume of Fluid (VoF) method, which is mass conserving and well suited for complex flows thanks to its capacity of handling topological changes. The energy equation is explicitly solved and coupled with the momentum equation through the Boussinesq approximation. The code is conceived in a modular fashion so that different numerical methods can be used independently, the existing routines can be modified, and new ones can be included in a straightforward and sustainable manner. FluTAS is written in modern Fortran and parallelized using hybrid * M.C-E. and N.S. contributed equally to this work.

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