Enzo Dari

Centro Atómico Bariloche · Division of Applied Research

In the present work Direct Numerical Simulation of heat transfer in a spatial laminar-turbulent transitional channel flow is carried out to investigate the effects of the transitional phenomenon in the temperature field. The configuration is a spatially developing channel flow with two thermal boundary conditions: Uniform Wall Temperature (UWT) and...

In this work a temporal laminar-turbulent K-type transition at a subcritical Reynolds number (Re = 5000) is simulated employing Direct Numerical Simulation (DNS). The configuration is a temporal developing channel flow driven by a constant flow rate. The study focuses in the description of flow features before and after the time that corresponds to...

This study presents DNS results of the laminar-turbulent spatial transition in a plane channel flow. The transition is achieved imposing at the inlet the most unstable modes of the associated Orr–Sommerfeld and Squire eigenvalue problems. First, a study of the dependence of the transition on the intensity of the perturbations is presented. For Re=5...

Purpose The purpose of this paper is to present applications of the topological optimization method dealing with fluid dynamic problems in two- and three dimensions. The main goal is to develop a tool package able to optimize topology in realistic devices (e.g. inlet manifolds) considering the non-linear terms on Navier–Stokes equations. Design/me...

The aim of this work is to validate a numerical model used to simulate the natural convection in a distribution transformer. The transformer of interest is of the oil natural air natural (ONAN) type and the model seeks to obtain the temperature and velocity fields in the oil volume. The simulation domain reproduces a slice model developed for a pre...

RESUMEN La generación de flujo secundario en ductos rectos de sección rectangular se debe exclusivamente a la turbulencia. En muchos flujos ambientales existen efectos de estratificación que afectan la turbulencia y pueden modificar el flujo secundario. En las corrientes de turbidez, por ejemplo, en la escala microscópica la estratificación modula...

The aim of this work is to obtain experimental information on the thermal and fluid dynamics of a distribution transformer. The transformer of interest is of the oil natural – air natural type and our interest is centered in the natural circulation that is produced in the oil volume. An experimental device was built to simulate a representative sli...

Gravity currents are flows generated by the action of gravity on fluids with different densities. In some geophysical applications, modeling such flows makes it necessary to account for rotating effects, modifying the dynamics of the flow. While previous works on rotating stratified flows focused on currents of large Coriolis number, the present wo...

A three-dimensional (3D) computational fluid dynamics (CFD) model is presented for the Second Shutdown System (SSS) of the experimental nuclear reactor RA-10 under design and construction by the Argentinian National Commission of Atomic Energy (CNEA). The RA-10 SSS consists on the drainage of the reflector tank surrounding the reactor core through...

Resumen. Los análisis de ingeniería actuales exigen estudios en sistemas cada vez más complejos. És-tos, a su vez, involucran subsistemas de características disímiles: principalmente diferentes tamaños y parámetros característicos. Por ejemplo, en los sistemas termohidráulicos es posible identificar distintos regímenes de flujo en tanques o en cañe...

A three-dimensional multiscale numerical model is presented in order to describe the fluid dynamics associated to the Second Shutdown System (SSS) of an experimental nuclear reactor. Detailed computational fluid dynamics simulations were performed in a RA-10 SSS Mockup similar to the RA-10 SSS. The main component of the SSS is the reflector tank wh...

In this work we present a novel approach tailored to approximate the Navier-Stokes equations to simulate fluid flow in three-dimensional tubular domains of arbitrary cross-sectional shape. The proposed methodology is aimed at filling the gap between (cheap) one-dimensional and (expensive) three-dimensional models, featuring descriptive capabilities...

Las corrientes de gravedad son flujos generados por gradientes de presión horizontales resultantes del efecto de la gravedad sobre fluidos de diferente densidad. Cuando ocurren en la naturaleza, estas corrientes tienen un fuerte comportamiento no lineal y presentan un amplio rango de escalas temporales y espaciales. Adicionalmente, la rotación de l...

Development of blood flow distribution criteria is a mandatory step toward developing computational models and numerical simulations of the systemic circulation. In the present work, we (i) present a systematic approach based on anatomical and physiological considerations to distribute the blood flow in a 1D anatomically detailed model of the arter...

The study of problems dominated by natural convection through obstacles is of relevance in various fields of engineering. We may find examples where obstacles can be modeled explicitly (i.e. heat exchangers) and examples where it is convenient and practical to avoid this representation considering the obstacles as a porous medium (i.e. the cooling...

In this work we present HeMoLab (Hemodynamics Modeling Laboratory), a computational environment for modeling the Human Cardiovascular System. Its integrates novel computational tools, running from medical image processing to numerical simulation and visualization. As a simulation tool, it allows to accommodate complex physiological and/or pathophys...

A three-dimensional Lattice-Boltzmann fluid model with nineteen discrete velocities was implemented using NVIDIA Graphic Processing Unit (GPU) programing language "Compute Unified Device Architecture" (CUDA). Previous LBM CPU implementations required two steps to maximize memory bandwidth due to memory access restrictions of earlier versions of CUD...

We consider the approximation of eigenvalue problem for the Laplacian by the Crouzeix–Raviart non-conforming finite elements in two and three dimensions.Extending known techniques for source problems, we introduce a posteriori error estimators for eigenvectors and eigenvalues. We prove that the error estimator is equivalent to the energy norm of th...

Lattice Boltzmann Methods (LBM) was one of the first simulation models which successfully run on Graphic Processing Units. Earlier LBM implementations using NVIDIA Compute Unified Device Architecture programming language required two steps (collision-propagation and exchange) to maximize memory bandwidth. This article presents a parallel single-ste...

In this paper we describe and evaluate a geometric mass-preserving redistancing procedure for the level set function on general structured grids. The proposed algorithm is adapted from a recent finite element-based method and preserves the mass by means of a localized mass correction. A salient feature of the scheme is the absence of adjustable par...

There are many alternatives for treating the problem of a solid moving completely inside a fluid. One of them is using the fluid equations strictly in the space occupied by the fluid, and adjusting the mesh in each temporal step. If the displacements are limited a node-movement strategy without topology changes may be used to keep low the computati...

In the present work a model to tackle the fluid–solid interaction problem employing the concepts of immersed domains is derived from a well–known governing variational principle from the continuum mechanics. The goal of this work is to present a general formulation in which an augmented fluid, composed by the real fluid and a fictitious fluid that...

In this work, the theoretical bases to handle the fluid–solid interaction problem based on the conception of immersed domains are developed starting from a well-known governing variational principle from the continuum mechanics. The purpose of the present work is twofold. Firstly, a variational principle to model the interaction between a fluid and...

Though Computational Fluid Dynamics (CFD) is recognized as an emerging engineering tool, it is not infrequent that engineering projects make little or no use of it during the early design stages. CFD codes, if used at all, are left for the final stages in which an already finished design is tested to confirm its performance before construction. Sca...

dirección principal. Sin embargo, las tensiones cortantes "no newtonianas" son menores que las predichas por el modelo newtoniano en zonas de flujo estanco y por consiguiente de bajas tensiones cortantes. Es por esto último que decimos que, la predicción dada por el modelo newtoniano respecto a zonas de bajos esfuerzos de corte, es "optimista" resp...

A finite element simulation of flow and heat transfer in the moderator cell of a cold-neutron source (CNS), in which liquid deuterium subject to internal heat generation is flowing, is reported. The numerical scheme consists of a stabilized equal-order method. A time-accurate approach is adopted to resolve the large-scale eddies of the flow, with a...

The Level Set Method is becoming increasingly popular for the simulation of several problems that involve interfaces. The level set function is advected by some velocity field, with the zero-level set of the function defining the position of the interface.The advection distorts the initial shape of the level set function, which needs to be re-initi...

Laminar flow through a two-dimensional square cavity in which internal (volumetric) heat generation takes place is analyzed numerically. The inflow is a horizontal jet at the bottom of the cavity, and the outlet is at the top, in a centered position. As the internal heat generation rate is increased, several flow patterns appear, in particular peri...

Numerical experiments for non-trivial flows, close to realistic situations in hæmodynamics, are described and interpreted. Two geometries have been selected: an axisymmetric corrugated tube (with periodic boundary conditions) and a 3D bifurcation with an obstructed end (anastomosis). Results concern sensitivity of errors associated to the time-step...

We report on the application of a parallel finite element program to the solution of the flow equations in blood vessels. We present some examples showing the capabilities of the solver to deal with problems with a high number of unknowns, and discuss some alternatives of formulations for the typical pulsatile flow involved in hemodynamic simulatio...

We report on the application of a parallel finite element program to the solution of the flow equations in blood vessels. We present some examples showing the capabilities of the solver to deal with problems with a high number of unknowns, and discuss some alternatives of formulations for the typical pulsatile flow involved in hemodynamic simulatio...

An application of “cluster computing” in finite element CFD is reported, demonstrating the feasibility of solving relevant 3D problems on low-cost architectures (PC’s connected by fast Ethernet network). The main ingredients of our implementation are described. The results concern the lift force on a solid particle in simple shear flow. It is shown...

. In this paper we dene an a posteriori error estimator for nite element approximations of 3-d elliptic problems. We prove that the estimator is equivalent, up to logarithmic factors of the meshsize, to the maximum norm of the error. The results are valid for an arbitrary polyhedral domain and rather general meshes. We also obtain analogous results...

Though the mathematical theory of classical linear elasticity is well established, there still lack some ingredients toward the numerical solution of real technological problems. In this paper we address one of these critical ingredients, namely the automatic construction of three-dimensional meshes in arbitrary geometries. Several methods exist fo...

On introduit deux «estimateurs» d'erreur a posteriori pour une approximation par une methode d'elements finis non conforme d'un probleme elliptique du second ordre. On montre que ces «estimateurs» sont equivalents a la norme d'energie de l'erreur. Finalement, on presente diverses experiences numeriques montrant le bon comportement de ces estimateur...

We discuss an optimization procedure for improving 3D finite element meshes. Our method can be effectively counted with any automatic mesh generator in order to obtain a triangulate without badly distorted elements. In this way, we are able to weaken the requirements on the generator, allowing it to produce singular elements, and post-process the r...

We define and analyze a posteriori error estimators for nonconforming approximations of the Stokes equations. We prove that these estimators are equivalent to an appropriate norm of the error. For the case of piecewise linear elements, we define two estimators. Both of them are easy to compute, but the second is simpler because it can be computed u...

We propose a new idea, based upon an optimization procedure, for improving three-dimensional finite element meshes. Our method can effectively be coupled with any automatic mesh generator in order to obtain a triangulation without badly distorted elements. In this way, we are able to weaken the requirements on the generator, allowing it to produce...

This paper is concerned with the implementation of Lagrange‐Galerkin finite element methods for the Navier‐Stokes equations. A scheme is developed to efficiently handle unstructed meshes with local refinement, using a quad‐tree‐based algorithm for the geometric search. Several difficulties that arise in the construction of the right‐hand side are d...

A transient decoupled method to treat viscoelastic flows is presented, using Lagrange-Galerkin techniques for velocities and the Lesaint-Raviart method for extra-stresses.An important point of our scheme is the linear interpolation employed for all fields: this allows for high Weissenberg numbers to be reached with no need for streamline upwinding...

The use of Object Oriented Programming (OOP) for automatic mesh generaton for Finite Element Analysis is presented in this paper. Aspects related to the geometry definition, meshing characteristics, triangular elements generation, data structures and implementation aspects are also discussed. Graphical examples generated by C++ code running on a PC...

An application of "cluster computing" in finite element CFD is reported, demonstrating the feasibility of solving relevant 3D problems on lowcost architectures (PC's connected by Fast Ethernet network). The main ingredients of our implementation are described. The results concern the lift force on a solid particle in simple shear flow. It is shown...

In this paper, we focus on numerical simulations of the wandering phenomenon in bubble plumes, obtained with a new comprehensive model. The theoretical model has been developed from the theory of multi-component fluids. We have implemented that model in a finite-element, parallel platform. After a brief discussion about the theoretical/numerical mo...