Néstor Balcázar

A level-set method for thermal motion of bubbles and droplets

A conservative level-set model for direct simulation of two-phase flows with thermocapillary effects at dynamically deformable interface is presented. The Navier-Stokes equations coupled with the energy conservation equation are solved by means of a finite-volume/level-set method. Some numerical examples including thermocapillary motion of single and multiple fluid particles are computed by means of the present method. The results are compared with analytical solutions and numerical results from the literature as validations of the proposed model.

DNS of the wall effect on the motion of bubble swarms

Abstract This paper presents a numerical study of the gravity-driven motion of single bubbles and bubble swarms through a vertical channel, using High-Performance Computing (HPC) and Direct Numerical Simulation (DNS) of the Navier-Stokes equations. A systematic study of the wall effect on the motion of single deformable bubbles is carried out for confinement ratios CR = {2,4,6} in both circular and square channels, for a broad range of flow conditions. Then, the rising motion of a swarm of deformable bubbles in a vertical channel is researched, for void fractions α = {8.3%, 10.4%, 12.5%} and CR = {4, 6}. These simulations are carried out in the framework of a novel multiple marker interface capturing approach, where a conservative level-set function is used to represent each bubble. This method avoids the numerical and potentially unphysical coalescence of the bubbles, allowing for the collision of the fluid particles as well as long time simulations of bubbly flows. Present simulations are performed in a periodic vertical domain discretized by 2 × 106 control volumes (CVs) up to 16.6 × 106 CVs, distributed in 128 up to 2048 processors. The collective and individual behavior of the bubbles are analyzed in detail.

On the solution of the problem of a drop falling against a plane by using a level set - moving mesh - immersed boundary method

A coupled Conservative Level Set – Moving Mesh – Immersed Boundary method is formulated and validated against the three-dimensional gravity-driven falling drop problem. First, by employing Conservative Level-Set (CLS) method, the multiphase domain can be successfully handled, while the mass conservation is controlled. Then, by using an Arbitrary Lagrangian-Eulerian formulation (i.e. a moving mesh), the simulation domain can be optimized by reducing the domain size and by allowing an improved mesh, resulting in a computational resources saving. Finally, the use of an Immersed Boundary (IB) method allows to deal with intricate geometries. All these functionalities result in a versatile and robustness method to simulate bubbles/drops problems in complex geometries. The mentioned method was successfully used to thoroughly study the falling of a drop against a plane surface, providing detailed results including velocity evolution, mesh independence study, evolution of the vertical position of the drop, streamlines and vorticity fields, and profiles evolution.

DNS of the Rising Motion of a Swarm of Bubbles in a Confined Vertical Channel

The motion of bubbles and droplets is ubiquitous in a variety of natural processes and technological applications, such as boiling heat transfer, steam generators of nuclear power plants, unit operations of the chemical engineering (e.g. distillation, absorption columns, bubble reactors), micro-devices, among others [8].

DNS OF FALLING DROPLETS IN A VERTICAL CHANNEL

This paper presents Direct Numerical Simulation (DNS) of the falling motion of single and multiple deformable drops in a vertical channel. A systematic study of the wall effect on the motion of single drop is performed for Eötvös number (0.5≤Eo≤5), Morton number (10−3≤M≤10-8), and confinement ratio CR = 2. Second, the gravity-driven motion of multiple drops and their interactions are studied in a periodic vertical channel for CR = 4. These simulations are performed using a multiple marker level-set methodology, integrated in a finite-volume framework on a collocated unstructured grid. Each droplet is described by a level-set function, which allows capturing multiple interfaces in the same control volume, avoiding the numerical merging of the droplets. Numerical algorithms for fluid motion and interface capturing have been developed in the context of the finite-volume and level-set methodology, surface tension is modeled by means of the continuous surface force approach, and the pressure-velocity coupling is solved using a fractional-step projection method. DNS of single drop shows that they migrate to the symmetry axis of the channel when the Reynolds number is low, following a monotonic approach or damped oscillations according to the dimensionless parameters. If Eötvös number increases, stronger oscillations around the symmetry axis are observed. Simulations of multiple drops show that the collision of two drops follows the drafting-kissing tumbling (DKT) phenomenon. Deformable drops do not collide with the wall, whereas DKT phenomenon in the droplet swarm leads to the formation of groups which move through the center of the channel.

NUMERICAL STUDY OF AN IMPULSE WAVE GENERATED BY A SLIDING MASS

In this work, a numerical framework for the direct numerical simulation of tsunami waves generated by landslide events is proposed. The method, implemented on the TermoFluids numerical platform, adopts a free surface model for the simulation of momentum equations; thus, considering the effect of air on the flow physics negligible. The effect of the solid motion on the flow is taken into account by means of a direct forcing immersed boundary method (IBM). The method is available for 3-D unstructured meshes; however, it can be integrated with an adaptive mesh refinement (AMR) tool to dynamically increase the local definition of the mesh in the vicinity of the interfaces, which separate the phases or in the presence of vortical structures. The method is firstly validated by simulating the entrance of objects into still water surfaces for 2-D and 3-D configurations. Next, the case of tsunami generation from a subaerial landslide is studied and the results are validated by comparison to experimental and numerical measurements. Overall, the model demonstrates its efficiency in the simulation of this type of physics, and a wide versatility in the choice of the domain discretization.

On the solution of the full three-dimensional Taylor bubble problem by using a coupled Conservative Level Set - Moving Mesh method

Published under licence in Journal of Physics: Conference Series by IOP Publishing Ltd. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.