Turbulent Flows With Drops and Bubbles: What Numerical Simulations Can Tell Us—Freeman Scholar Lecture

Soligo, Giovanni; Roccon, Alessio; Soldati, Alfredo

doi:10.1115/1.4050532

Cited by 30 publications

(25 citation statements)

References 273 publications

(490 reference statements)

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“…The numerical investigation of the multiphase flow is very attractive for the perspective of achieving a highly refined description of the flow field in both fluids, thus enabling a quantitative characterization of the exchange processes. Several models have been proposed in the last 25 years, and a comprehensive overview is reported in Mirjalili, Jain & Dodd (2017) and Soligo, Roccon & Soldati (2021). Both large-eddy simulations (e.g.…”

Section: Introductionmentioning

confidence: 99%

On coherent vortical structures in wave breaking

2022

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The flow generated by the breaking of free-surface waves in a periodic domain is simulated numerically with a gas–liquid Navier–Stokes solver. The solver relies on the volume-of-fluid method to account for different phases, and the interface tracking is carried out by using novel schemes based on a tailored total-variation-diminishing limiter. The numerical solver is proved to be characterized by a low numerical dissipation, thanks to the use of a scheme that guarantees energy conservation in the discrete form. Both two- and three-dimensional simulations have been performed, and the analysis is presented in terms of energy dissipation, air entrainment, bubble fragmentation, statistics and distribution. Particular attention is paid to the analysis of the mechanisms of viscous dissipation. To this purpose, coherent vortical structures, such as vortex tubes and vortex sheets, are identified, and the different behaviours of the vortex sheets and tubes at various Reynolds numbers are highlighted. The correlation between vortical structures and energy dissipation demonstrates clearly their close link both in the mixing zone and in the pure water domain, where the coherent structures propagate as a consequence of the downward transport. Notably, it is found that the dissipation is identified primarily by the vortex sheets, whereas the vortex tubes govern mainly the intermittency.

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Section: Introductionmentioning

confidence: 99%

On coherent vortical structures in wave breaking

2022

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“…As discussed in [15], there is now consensus that numerical methods suitable to perform interface-resolved simulations of multiphase flow should have the following properties: i) be able to enforce mass, momentum and kinetic energy conservation at discrete level, ii) allow mismatches in the material properties, whose magnitude depends on the application, and iii) handle complex and possibly arbitrary topological changes. Among the four groups of numerical methods for multiphase flows, Front-Tracking (FT) [16], Volume-of-Fluid (VoF) [17], Phase Field (PFM) [18], Level-set (LS) [19], it exists at least a variant of each which possesses the aforementioned numerical properties, giving some freedom to researchers and scientists on the choice of their preferred numerical tool (see [17,20,21] for a review).…”

Section: Introductionmentioning

confidence: 99%

FluTAS: A GPU-accelerated finite difference code for multiphase flows

Crialesi-Esposito¹,

Scapin²,

Demou³

et al. 2022

Preprint

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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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“…However, the issue of the appropriate velocity boundary condition will be shared between all of models based on single continuum description. A good recent classification of multiphase models can be found in work by Soligo, Roccon & Soldati (2021). It must be recognized that the hybrid models (Zhang et al.…”

Section: Discussionmentioning

confidence: 99%

Nanoscale sheared droplet: volume-of-fluid, phase-field and no-slip molecular dynamics

et al. 2022

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The motion of the three-phase contact line between two immiscible fluids and a solid surface arises in a variety of wetting phenomena and technological applications. One challenge in continuum theory is the effective representation of molecular motion close to the contact line. Here, we characterize the molecular processes of the moving contact line to assess the accuracy of two different continuum two-phase models. Specifically, molecular dynamics simulations of a two-dimensional droplet between two moving plates are used to create reference data for different capillary numbers and contact angles. We use a simple-point-charge/extended water model. This model provides a very small slip and a more realistic representation of the molecular physics than Lennard-Jones models. The Cahn–Hilliard phase-field model and the volume-of-fluid model are calibrated against the drop displacement from molecular dynamics reference data. It is shown that the calibrated continuum models can accurately capture droplet displacement and droplet break-up for different capillary numbers and contact angles. However, we also observe differences between continuum and atomistic simulations in describing the transient and unsteady droplet behaviour, in particular, close to dynamical wetting transitions. The molecular dynamics of the sheared droplet provide insight into the line friction experienced by the advancing and receding contact lines. The presented results will serve as a stepping stone towards developing accurate continuum models for nanoscale hydrodynamics.

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Turbulent Flows With Drops and Bubbles: What Numerical Simulations Can Tell Us—Freeman Scholar Lecture

Cited by 30 publications

References 273 publications

On coherent vortical structures in wave breaking

On coherent vortical structures in wave breaking

FluTAS: A GPU-accelerated finite difference code for multiphase flows

Nanoscale sheared droplet: volume-of-fluid, phase-field and no-slip molecular dynamics

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