Search

The present work is dedicated to numerically study problems involving the Liquid Resin Infusion (LRI) process in thick composites. This technique uses fibers to obtain polymeric composites that can be applied in various lines of the industry and engineering. In this way, there is a great interest in improving this process to obtain a final product with physical and mechanical properties that meet the requirements of the current market. This study aims to analyze the flow of the resin inside the mold and to optimize the geometry, from the length of the flux mesh and the relationship between the permeabilities Kxx/Kzz. The flow mesh is a high permeability fabric and is employed during the LRI molding process to facilitate infiltration of the resin through the fibrous area. Numerical simulations were performed in OpenFOAM free software and the creation of the geometry and the mesh in the GMSH. The finite volume formulation of OpenFOAM was used for the discretization of the transport equations describing the resin flow inside the mold and the treatment of the interface between the two fluids (resin-air) is solved by the Volume of Fluid (VOF) method. In this paper, results for a Kxx/Kzz ratio and different flow mesh lengths were presented. By the presented results, one can find a way to generalize the study, and thus, to obtain the ideal size of the flow mesh for any length of mold., O presente trabalho é dedicado a estudar numericamente problemas envolvendo o processo de Infusão de Resina Líquida (LRI) em compósitos espessos. Esta técnica se utiliza de fibras para obtenção de compósitos poliméricos que podem ser aplicados em diversos ramos das indústrias e da engenharia. Nesse sentido, há um grande interesse em aprimorar este processo para obter um produto final com propriedades físicas e mecânicas que atendam às exigências do mercado atual. Esse estudo tem por objetivo analisar o escoamento da resina dentro do molde e otimizar a geometria, a partir do comprimento da malha de fluxo e a relação entre as permeabilidades Kxx/Kzz. A malha de fluxo é um tecido de alta permeabilidade e é empregada durante o processo de moldagem por LRI para facilitar a infiltração da resina através do meio fibroso. As simulações numéricas foram realizadas no software livre OpenFOAM e a criação da geometria e da malha no GMSH. A formulação de volumes finitos do OpenFOAM foi utilizada para a discretização das equações de transporte que descrevem o escoamento de resina dentro do molde e o tratamento da interface entre os dois fluidos (resina-ar) é resolvido pelo Método Volume of Fluid (VOF). Neste artigo, apresentou-se resultados para uma relação de Kxx/Kzz e diferentes comprimentos de malha de fluxo. Por meio dos resultados apresentados, pode-se encontrar uma maneira de generalizar o estudo, e assim, obter o tamanho ideal da malha de fluxo para qualquer comprimento de molde.

A study regarding the interaction between two consecutive Taylor drops flowing in a heavier liquid in a vertical tube is reported. Under certain conditions, due to the wake of the leading drop, the trailing drop accelerates, leading to coalescence of the two drops. This study was developed using a numerical model based in the Volume of Fluid method in an axisymmetric geometry. The simulations reported in the present work had to fulfill two conditions: axisymmetry (due to the numerical model) and a high enough drop Reynolds number (which is related to the disturbances in the wake of an isolated drop, and thus to the tendency to drop interaction). Relevant dimensionless numbers are used to assess the effect of the acting forces. Detailed flow patterns and drop shapes are provided. Furthermore, the approaching velocity acquired by the trailing drop is analyzed and velocity profiles between the leading and the trailing drop are also reported. In general, the trailing drop shows an accelerating region, followed by a deceleration near the leading drop. The increase of Eotvos number promotes higher accelerations, while the increase in Morton number and viscosity ratio has the opposite effect. By comparison to literature gas-liquid studies, it was also found that interfacial forces promote the shape stability of the drops.

The present work proposes to extend the IMERSPEC methodology to solve two-phase flows. This methodology based on the coupling of Fourier psedospectral method (FPSM) and immersed boundary method (IBM). The main features of the FPSM are the high rate of numerical convergence, high numerical accuracy combined with high computational efficiency because it uses the Fast Fourier Transform algorithm, and beside that, in order to solve the Navier-Stokes equations, solving linear system for pressure-velocity coupling is not necessary. To deal with two-phase flows with moving and deformable geometry, two methods were coupled the IMERSPEC methodology: the Front-Tracking method (FT) and Volume of Fluid method (VOF). The FT method works with two domains, the Eulerian, where the equations for the fluid are evaluated and the Lagrangian for modeling the interfaces. In the FT, both domains are coupled by using interpolation and distribution process, with no restriction on the movement and deformation of the dispersed phase of the Lagrangian mesh over Eulerian domain. The disadvantages of the FT method are a possible mass loss and the need of a fragmentation and coalescence bubble model. The VOF method defines the surface by the volume fractions which allows the fragmentation and coalescence of bubbles without the requirement of implementing a specific model, however it may present numerical instabilities. The results obtained by evaluating the spurious currents, mass conservation and analysis through numerical experimentation of bubbles rise show that IMERSPEC-FT can be considered validated and promising, while the IMERSPEC-VOF presents promising results for cylindrical bubble regime. No presente trabalho propõe-se a extensão da metodologia IMERSPEC para resolver problemas de escoamentos bifásicos. Esta metodologia é baseada no acoplamento do método pseudoespectral de Fourier (MPEF) com o método da fronteira-imersa (MFI). As principais características desta metodologia são a alta taxa de convergência numérica e a alta acurácia aliadas a um baixo custo computacional devido ao algoritmo denominado Fast Fourier Transform (FFT) e, além disso, na resolução das equações de Navier-Stokes não é necessário resolver o sistema linear proveniente do acoplamento pressão-velocidade. Para tratar escoamentos bifásicos com geometria móvel e deformável, dois métodos foram acoplados á metodologia IMERSPEC: Front-Tracking(FT) e Volume of fluid (VOF). O método FT trabalha com dois domínios, sendo um euleriano, onde se resolvem as equações para o fluido e o outro, móvel, lagrangiano, utilizado para as interfaces entre dois fluidos. Para este método, ambos os domínios são acoplados pelo processo de interpolação e distribuição do campo de força lagrangiano e não apresentam restrição quanto ao movimento da malha lagrangiana sobre o domínio euleriano e quanto à deformação da mesma. As principais desvantagens do método Front-Tracking estão na possível perda de massa e na necessidade de implementar modelos para fragmentação e coalescência. O método VOF define a superfície através de frações de volume, o que permite fragmentação e coalescência de bolhas não requerendo modelos específicos. Entretanto apresenta instabilidades numéricas no cálculo da curvatura. Os resultados obtidos através da avaliação das correntes espúrias, conservação de massa e análise através de experimentação numérica de ascensão de bolhas mostram que a metodologia IMERSPEC-FT pode ser considerada validada, enquanto que a metodologia IMERSPEC-VOF apresentou resultados promissores para regime de bolha cilíndrica. Doutor em Engenharia Mecânica

The hydrocyclone is one of the most used classification equipment in industry, particularly in mineral processing. Maybe its main characteristic is to be a hydrodynamic separation equipment, whereby it has a high production capability and different levels of efficiency are depending on the geometrical configuration, operational parameters and the type of material to be processed. Nevertheless, there are a few successful studies regarding the modelling and simulation of its hydrodynamic principles, because the flow behavior inside is quite complex. Most of the current models are empirical and they are not applicable to all cases and types of minerals. One of the most important problems to be solved, besides the cut size and the effect of the physical properties of the particles, is the distribution of the flow inside the hydrocyclone, because if the work of the equipment is at low slurry densities, very clear for small hydrocyclones, its mechanic behavior is a consequence of the kind of liquid used as continuous phase, being water the most common liquid. This work shows the modelling and simulation of the hydrodynamic behavior of a suspension inside a hydrocyclone, including the air core effect, through the use of finite differences method. For the developing of the model, the Reynolds Stress Model (RSM) for the evaluation of turbulence, and the Volume of Fluid (VOF) to study the interaction between water and air were used. Finally, the model shows to be significant for experimental data, and for different conditions of an industrial plant.