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Introduction Gasliquid multiphase flows are important in natural and industrial processes. Some examples include bubbles and droplets, free surfaces, liquid jets, sprays, boiling flows among others. This type of flows are usually called interfacial flows, since the contact of immiscible fluids or phases in motion produces a thin region that separates them called interface. In detail, interfacial flows are governed by the NavierStokes equations in the variabledensity incompressibility limit, as well as energy conservation equation and mass conservation equation for heat transfer and mass transfer processes. Additionally, they require the solution of a set of equations that describes the interface topology as it moves due to the velocity field. To accurately solve gasliquid multiphase flows, the NavierStokes equations are discretized to conserve mass, momentum, and energy. In detail, finitevolume schemes, suitable for 3D collocated unstructured meshes, adaptivemeshrefinement, and moving meshes, have been developed and implemented in the parallel CFD platform TermoFluids. These methodologies have been designed in the framework of interfacecapturing methods such as levelset method [1,3,5], volumeoffluid method [6,7], coupled levelset/volumeoffluid method [4] and multiple marker levelset approach [2,13,18,19], on threedimensional unstructured meshes. In this context, our research objectives are twofold: First, the development of finitevolume based numerical methods, for DNS of gasliquid multiphase flows on threedimensional unstructured meshes [1,2,4,5,6,7,18], and their coupling with adaptivemeshrefinement [22,10] and movingmesh [11,12] strategies. Second, these numerical models are used to research the hydrodynamics, heat transfer and mass transfer in bubbly flows [15,1112,13,1420,2226], gasliquid jets [8,9], and free surface flows [1,8,21,28]. 
1. Numerical methods and interface capturing Multiple methods have been developed in the last decades for DNS of twophase flows with sharp interfaces, e.g., levelset, volumeoffluid, fronttracking, among others. Although the idea behind these methods is similar, their numerical implementations may differ greatly. Each method has advantages and disadvantages, and it is difficult to select a single approach as the best for all the range of applications. As a consequence, the development and improvement of interface capturing methodologies, their extensions to threedimensional unstructured meshes, and their applications on the computation of gasliquid multiphase flows is an intense field of investigation over the last years. Our research group has been working on the development and implementation of levelset method [1,3,5], volumeoffluid method [6,7], coupled levelset/volumeoffluid method [4] and multiple marker levelset approaches [2,5], in the framework of threedimensional unstructured meshes and finitevolume discretizations on collocated meshes. As general remarks, our numerical approaches are based on the fractionalstep projection method (Chorin, 1967) to solve the pressurevelocity coupling, unstructured fluxlimiters schemes for the convective terms as introduced in [1,5,14], centraldifference schemes for diffusive terms, and leastsquares method for gradient evaluation. Surface tension force is solved in the framework of the Continuous surfaceforce model (Brackbill, 1992), extended to the multiple marker levelset approach [2] and variable surface tension [5,23]. In recent works, complex interfacial physics has been included, for instance thermocapillary [5,23], and interfacial heat and mass transfer [5,14,16]. 
2. DNS of gasliquid multiphase flows Bubbly flows 
Figure 1: DNS of gravitydriven bubbly flows [2,5,13,18,19,25] in a vertical channel. (a) Spherical bubbles. (b) Deformable bubbles. 
Figure 2: (a) Bubbly flow in a fullperiodic domain [14,16]. (b) Thermocapillarydriven motion of a swarm of droplets [5,23]. 

Figure 3: DNS of droplet collision with a fluidfluid interface without coalescence, by means of a multiple marker levelset method [1]. 

Figure 4: DNS of binary droplet collision with bouncing outcome, by means of a multiple marker levelset method [1]. 

Figure 5: Bouncing interaction of two deformable bubbles rising in a vertical channel [18]. 
Taylor bubbles, freesurfaces, and gasliquid jets Further efforts have been focused on the application of the numerical models to research the hydrodynamics of Taylor Bubbles [11,20], freesurfaces flows [8,21,28], gasliquid jets [10], the development of a numerical approach for binary droplet collisions in generalized Newtonian fluids [17], and the coupling of levelset method [1,3] with immersedboundary and movingmesh strategies to simulate bubbles and droplets in complex geometries [12]. 
Figure 6: Interfacial flow with topology changes. Oblique coalescence of two deformable bubbles, computed by means of the unstructured levelset method introduced in [1]. (a) Time evolution of the bubble shape, (b) Velocity field.

Figure 7: Interfacial flow with topology changes. Impact of a drop (water) fallen down into a liquid film (air as environment fluid), computed by means of the unstructured levelset method introduced in [1]. 

Figure 8: Free surface flow. Collapse of a liquid column (water) in a rectangular container (air as environment fluid), computed by means of the unstructured levelset method introduced in


Figure 9: Free surface flow. Oscillating water column (OWC) system (air as environment fluid), computed by means of the unstructured levelset method introduced in [1]. 

Figure 10: 3D dam break over a fixed obstacle, simulated by means of the freesurface flow solver (single phase model) on an unstructured mesh [8]. 

Figure 11: 3D sphere entry in water, presented in [21]. The interaction between the freesurface and the moving solid is considered by using a IBM technique.. 

Figure 12: Injection of high speed liquid and gas flows in 3D coaxial configuration at Re=10000 [10]. A notable application is the atomization of liquid propellants in combustion engines. 

Figure 13: Study of the Liquid Injection into stagnant air by means of CLSAMR strategy [10]. Phenomenological study for variable Re, We and Oh numbers. Case of Re=800, high Oh number. 

Figure 14: Binary droplet collision at high Weber number using a levelset with lamella stabilization model [17]. 

Figure 15: Binary droplet collision at high Weber number using a levelset with lamella stabilization model [17]. 
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