Catálogo de publicaciones - libros

The rising velocity of a spherical bubble in contaminated water can be less than a half of that in pure water. This is explained in terms of the Marangoni effect caused by the adsorption of surfactants in liquid phase on bubble surface. In this study, we conduct a numerical simulation with different surfactant species and bulk concentrations, and the dependence of their properties on the rising velocity of a bubble is analyzed through comparison with experiments. The simulation results show good agreement with the experimental ones, and the surface velocity and the concentrations are estimated. We also develop a simulation method for solving bubble deformation in the presence of a surfactant. We succeed in reproducing the conglobation effect of a bubble in surfactant solutions.

To investigate the two-way interaction between solid particles and fluid turbulence, a homogeneous flow field including more than 2000 spherical particles was directly simulated. Since flow around each particle is approximately resolved, no models were used for particle motion or fluid turbulence. A particle settles under gravity with the Reynolds number ranging from 50 to 300, based on diameter and slip velocity. When particle clusters are formed due to the wake attraction, the average settling velocity increases. Thus particular attention was focused on the distribution of particles. The influence of Reynolds number and loading ratio are assessed. It is found that the rotation of particle dominates the cluster dynamics.

Large-Eddy Simulation is used for the investigation of the breaking of steep water waves on a beach of constant bed slope. The method is built within a multi-fluid flow solver, in which the free surface is tracked using a Volume-of-Fluid method featuring piecewise planar interface reconstructions on a twice-as-fine mesh. The Smagorinsky sub-grid scale model is used for explicit under-resolved turbulence closure, coupled with a new scheme for turbulence decay treatment on the air-side of massively deformable free surfaces. The simulations were conducted for shear Reynolds numbers ≈≈400, based on the mean water depth. The Large-Eddy Simulation formulation in the interface tracking, single-fluid formulation is introduced for this purpose. The approach is demonstrated as a powerful tool for exploring large-scale, interfacial turbulent flows. The discussion focuses on coherent structures formation, the free surface flow effects at breaking, and form drag evolution with the surface.

We present an explicit finite-difference scheme for direct simulation of the motion of solid particles in a fluid. The method is based on a second-order MacCormack finitedifference solver for the flow, and Newton’s equations for the particles. The fluid is modeled with fully compressible mass and momentum balances; the technique is intended to be used at moderate particle Reynolds number. Several examples are shown, including a single stationary circular particle in a uniform flow between two moving walls, a particle dropped in a stationary fluid at particle Reynolds number of 20, the drafting, kissing, and tumbling of two particles, and 100 particles falling in a closed box.

Although much research has been performed on the motion of contact lines on solid surfaces, many questions remain. This paper presents results obtained with molecular dynamics (“MD”) simulations that address some of these questions. Of specific interest is the nature of the frictional resistance to contact line motion.

The effect of subgrid scales on the dispersion of heavy particles could be significant especially when the subgrid energy content is not negligible and/or the particle time constant is small. In this work, a modified Langevin type equation is used to reconstruct the instantaneous velocity of the seen fluid particle which is needed in the particle momentum equation. To assess the model, a decaying isotropic turbulence is studied via test. A good agreement between the model and DNS results is observed.

Recent measurements of bubble-phase velocity, volume fraction, and velocity variance, and liquid velocity profiles for flows of bubbly liquids in a vertical pipe are shown to be in good agreement with the predictions based on averaged equations.

In this work we address the effect of particle inertia in particulate density currents. First we introduce a novel tow-fluid model based on the equilibrium Eulerian approach [6]. The resulting model captures very important physics of two-phase flows, such as preferential concentration and migration of particles down turbulence gradients (turbophoresis), which modify substantially the structure and dynamics of the flow. We solve the mathematical model with a highly accurate spectral code, capturing all the length and time scales of the flow. We present two-dimensional simulations in planar configuration for Grashof =1.5×10. In the simulation results we observe the particles to migrate from the core of Kelvin—Helmholtz vortices shed from the front of the current and to accumulate in the current head, which affects the propagation speed of the front.

Large-Eddy Simulation is used for the investigation of the breaking of steep water waves on a beach of constant bed slope. The method is built within a multi-fluid flow solver, in which the free surface is tracked using a Volume-of-Fluid method featuring piecewise planar interface reconstructions on a twice-as-fine mesh. The Smagorinsky sub-grid scale model is used for explicit under-resolved turbulence closure, coupled with a new scheme for turbulence decay treatment on the air-side of massively deformable free surfaces. The simulations were conducted for shear Reynolds numbers ≈≈400, based on the mean water depth. The Large-Eddy Simulation formulation in the interface tracking, single-fluid formulation is introduced for this purpose. The approach is demonstrated as a powerful tool for exploring large-scale, interfacial turbulent flows. The discussion focuses on coherent structures formation, the free surface flow effects at breaking, and form drag evolution with the surface.

Large-Eddy Simulation is used for the investigation of the breaking of steep water waves on a beach of constant bed slope. The method is built within a multi-fluid flow solver, in which the free surface is tracked using a Volume-of-Fluid method featuring piecewise planar interface reconstructions on a twice-as-fine mesh. The Smagorinsky sub-grid scale model is used for explicit under-resolved turbulence closure, coupled with a new scheme for turbulence decay treatment on the air-side of massively deformable free surfaces. The simulations were conducted for shear Reynolds numbers ≈≈400, based on the mean water depth. The Large-Eddy Simulation formulation in the interface tracking, single-fluid formulation is introduced for this purpose. The approach is demonstrated as a powerful tool for exploring large-scale, interfacial turbulent flows. The discussion focuses on coherent structures formation, the free surface flow effects at breaking, and form drag evolution with the surface.