Rafael Gabler Gontijo

University of Brasília | UnB · Engenharia Mecânica

This work describes a numerical model to compute the translational and rotational motion of N spherical magnetic particles settling in a quiescent viscous fluid under creeping flow condition. The motion of the particles may be produced by the action of gravitational forces, Brownian thermal fluctuations, magnetic dipole-dipole interactions, externa...

This work presents a numerical study of the relative trajectories of two magnetic particles interacting in a dilute suspension. The suspension is composed of magnetic spherical particles of different radius and density immersed in a Newtonian fluid. The particles settle relative to one another under the action of gravity and, when in close proximit...

This paper presents experimental results on thermo-magnetic convection inside cavities. We examine the flow induced by convective currents inside a cavity with aspect ratio near the unity and the heat transfer rates measurements inside a thin cavity with aspect ratio equal to twelve. The convective unstable currents are formed when a magnetic suspe...

Open source numerical research code written in FORTRAN designed to simulate the behaviour of magnetic particles in suspension.

SIMMSUS is an opensource research code written in FORTRAN that simulates the motion of a system of interacting particles. These particles can be simulated in different scenarios and may interact through different physical mechanisms. The code was initially developed for studying the physics of magnetic spherical particles in suspensions in order to...

The effect of a rotating magnetic field on heat dissipation due to magnetic hyperthermia is investigated numerically. A robust and validated in-house code based on Langevin Dynamics is used. High order asymptotic solutions of the temperature rate are used to validate the numerical approach. Comparisons between a rotating and an oscillatory excitati...

In this work, computational fluid dynamics simulations of a ferrofluid plane Poiseuille flow in the presence of a constant applied magnetic field are performed. The orientation of the field is perpendicular to the direction of the flow. An original numerical methodology for calculating magnetic and hydrodynamic fields is proposed, including an impo...

This work investigates the effects of an applied magnetic field on the laminar flow of a ferrofluid over a backward-facing step. Both constitutive equation and global magnetization equation for a ferrofluid are considered. The resulting formulation consists in a coupled magnetic-hydrodynamic problem. Computational simulations are carried out in ord...

This work aims to reconstruct a continuous magnetization profile of a ferrofluid channel flow by using a discrete Langevin dynamics approach for the fluid’s micro structure. The continuous magnetization field is obtained through the coupled solution of 2D Ferrohydrodynamics equations in a CFD approach using a numerical code developed by the authors...

In this work, we perform Langevin dynamics simulations to examine microstructure-macroscopic related properties of magnetic fluids in an attempt to understand the influence of the long range viscous hydrodynamic and dipolar interparticle interactions on the complex susceptibility response of a magnetic suspension undergoing an oscillatory magnetic...

This work presents a theoretical, numerical and experimental investigation on the shape and vertical displacement of a free surface formed in the interface between a magnetic fluid and a non-magnetic one. The magnetic fluid is confined between two parallel vertical flat plates. The presence of an external magnetic field applied by a permanent magne...

This work presents important additional discussions regarding our recent publication: Heat transfer increase for a laminar pipe flow of a magnetic fluid subjected to constant heat flux: an initial theoretical approach. In our first paper we proposed a theoretical law to predict the mean Nusselt number for a laminar pipe flow of a magnetic fluid sub...

This work presents a theoretical law to predict the mean Nusselt number for a laminar pipe flow of a magnetic fluid subjected to an uniform magnetic field. The intensity of the field, the magnetic susceptibility of the fluid and the orientation angle formed between the magnet and the direction of the flow appear explicitly in the final expression o...

The motion of a spherical bubble in a ferrofluid subjected to an acoustic pressure field and a magnetic field is examined. The continuous fluid here is a colloidal suspension composed of ferromagnetic particles dispersed in a Newtonian carrier liquid. The constitutive equation for the fluid is based on the standard Maxwell tensor for a symmetric or...

Short presentation on the 70th Annual Meeting of the APS Division of Fluid Dynamics discussing the interplay between long range hydrodynamic and magnetic particle interactions in suspensions of solid magnetic particles immersed in a Newtonian carrier liquid. In this short talk I discussed how the dispersive nature of hydrodynamic interactions could...

This work consists of performing a theoretical, numerical and experimental study to determine both the shape and vertical displacement of a free surface formed on the interface between a ferrofluid and a non-magnetic fluid between two parallel vertical flat plates, under the influence of an external magnetic field applied by a permanent magnet arbi...

This work presents theoretical and experimental analyses on the kinematics-wave motion of suspended active particles in a biological fluid. The fluid is an active suspension of nematodes immersed in a gel-like biological structure, moving at a low Reynolds number. The nematode chosen for the study is Caenorhabditis elegans. Its motion is subjected...

This work explores the physics of an ordered set of interacting spheres immersed in a carrier liquid. We present numerical simulations that compute the translational and rotational motion of NN interacting spheres based on classical principles of Stokesian dynamics. The spheres are assumed to be made of a magnetizable material, subjected to magneti...

This work explores, from a numerical perspective, the role of particle rotational inertia on the magnetization dynamics of ferrofluids. A robust numerical method is used for this purpose. The numerical research code is based on the use of a convergent long range dipolar interactions technique. These interactions are computed through a sophisticated...

This work provides an experimental investigation on the heat transfer rates exchanged between a heated device and a forced flow inside a channel. The focus of our approach is the evaluation of using turbulence promoters as a geometric alteration used to optimize the cooling process of electronic devices. The study is performed on a customized exper...

Poster presented at the CILAMCE 2016 – XXXVII Ibero-Latin American Congress on Computational Methods in Engineering by my undergraduate student Késsia Tayná. She is currently doing a scientific initiation program under my supervision.

In this work we use computational tools to model a monodisperse diluted colloidal suspension of permanently magnetized nanoparticles in carrier liquids that do not present magnetic properties. Three models are used to simulate repulsive forces acting on the particles, namely, the Screened-Coulomb potential based repulsive force, the classic Lennard...

Poster presented at the UnB Scientific Initiation congress by my former undergraduate student Arthur Campos.

This work focuses on a theoretical investigation of the shape and equilibrium height of a magnetic liquid–liquid interface formed between two vertical flat plates in response to vertical magnetic fields. The formulation is based on an extension of the so called Young–Laplace equation for an incompressible magnetic fluid forming a two-dimensional fr...

The main goal of this article is to study the oscillatory motion of a spherical gas bubble immersed in a Newtonian liquid subjected to a harmonic pressure excitation. We use the classical Rayleigh-Plesset equation to study the radial motion of the bubble undergoing a forcing acoustic pressure field. The second order nonlinear ordinary differential...

Poster presented by my undergraduate student, Ciro Fraga Alegretti, in the 3rd International Conference on Nanoscience, Nanotechnology and Nanobiotechnology.

The main goal of this article is to identify the vibrational patterns of an oscillating spherical bubble immersed in a ferrofluid using Neural Networks. The gas bubble is immersed on a magnetic fluid and subjected to an harmonic pressure excitation and an applied magnetic field. The classical Rayleigh-Plesset equation is modified and a magnetic ver...

This work explores the sedimentation process of an approximately initially spherical blob of dense particles immersed in a Newtonian fluid. We develop an experimental and numerical approach. For our experiments we designed a sedimentation column with super high viscosity silicon oil as the surrounding fluid. The particles are made of iron and sedim...

This work presents analytic and numerical results for a unidirectional flow in a circular capillary of a magnetic fluid. A condition that deviates from the standard equation of equilibrium magnetization due to the vorticity of the flow is considered. We show that the model of a magnetic symmetrical fluid with no-coupling between magnetization and f...

Accepted for presentation and publication on 23rd ABCM International Congress of Mechanical Engineering - December - 2015

Accepted for presentation and publication on 23rd ABCM International Congress of Mechanical Engineering - December - 2015

Accepted for presentation and publication on 23rd ABCM International Congress of Mechanical Engineering - December - 2015

PDF slides from the lecture I gave on the award cerimony of the ABCM PhD Thesis Prize in 2014. The videos presented on the slides can be seen at the link: https://www.youtube.com/user/rafaelgabler/videos?view=0&sort=dd&shelf_id=0

A new optimization algorithm based on a minimum residual technique is introduced to reduce the instability of numerical methods due to using wall functions to specify the boundary conditions for high Reynolds number flows. In the present article, four different models of the wall-function approximation are investigated for separated flow inside a t...

We study the relative trajectories of two magnetic spheres interacting in a dilute suspension in the presence of particle inertia and Brownian motion effect. The particles settle relative to one another under the action of gravity and when in close contact they exert on each other a magnetic force and torque due to a permanent magnetization. The ba...

The goal of this work is to propose a new methodology to simulate turbulent thermal wall flows using the classical κ − ε model. The focus of this approach is based on the manner used to implement heat flux boundary conditions on the solid walls. In order to explain and to validate this new algorithm, several test cases are presented, testing a grea...

The use of classical analogies between turbulent heat and momentum diffusion, employed to estimate the wall heat transfer rates in turbulent wall flows, is numerically modelated in this work. Some approaches are proposed in order to quantify the heat transfer rates in recirculation regions of turbulent flows and an algorithm, used to impose heat fl...

This works shows how some technicalities in the design of the diffuser can affect the turbulent boundary layer detachment. The behavior of a turbulent flow of air, inside a two dimensional asymmetric straight-walled diffuser, with an divergence angle of 9.97 degrees, is numerically simulated considering some aspects of the solid boundary geometry....

The temperature and velocity fields, for two turbulent flows generated by natural convection were investigated by numerical simulation. The analyzed flows are the natural convection provided by a heated vertical flat plate and the natural convection inside a tall cavity with side walls in different temperatures. The numerical algorithm applies a co...

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2009. O presente trabalho é um estudo numérico sobre o emprego de analogias entre difusão turbulenta de quantidade de movimento e de calor como metodologia para imposição de condição de contorno de fluxo de calor em escoamentos de camada l...