Desenvolvimento de um solver Navier-Stokes 3D combinado com o algoritimo de distância de Gilbert-Johnson-Keerthi para simulação de escoamento turbulento em geometrias complexas

Orientadores: Sávio Souza Venâncio Vianna, Rogério Gonçalves dos SantosTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia QuímicaResumo: Este trabalho tem como objetivo o desenvolvimento de um solver tridimensional de Navier- Stokes para análise de escoamentos turbulentos reativos em geometrias complexas. Os conceitos de Resistência Distribuída por Porosidade foram acoplados às técnicas de Flui- dodinâmica Computacional (CFD) e o algoritmo de distância de Gilbert-Johnson-Keerthi foi aplicado para descrever modelos geométricos como meios porosos. O solver foi desenvol- vido com base em um solver Euler compressível e bidimensional capaz e foi melhorado até se tornar um solver tridimensional capaz de resolver as equações de Navier-Stokes. A mo- delagem numérica foi conduzida dentro da abordagem tradicional de Reynolds-Averaged Navier Stokes (RANS) e o modelo de fechamento de turbulência foi abordado através da formulação de Boussinesq. O solver desenvolvido foi customizado para uma classe especí- fica de escoamentos turbulentos reativos, modelando o processo de combustão como uma explosão de gás. A abordagem demonstrou que pode manipular geometrias complexas dentro de um tempo computacional viável. Resultados numéricos para simulação de esco- amento não-reativos e reativos apresentaram as principais características previstas para o escoamento de fluidos e foi observado uma boa concordância com dados experimentais disponíveis na literaturaAbstract: This work proposes the development of a three-dimensional Navier-Stokes solver for anal- ysis of turbulent reacting flows in complex geometries. Concepts of Porosity Distributed Resistance were coupled with Computational Fluid Dynamics (CFD) techniques and the Gilbert-Johnson-Keerthi distance algorithm was applied in order to describe geometrical models as porous media. The solver was developed based on an initial two dimensional compressible Euler solver and have been improved until becomes a three-dimensional solver capable to compute the Navier-Stokes equations. The numerical modelling was conducted within the framework of traditional Reynolds-Averaged Navier Stokes (RANS) approach and the turbulence closure model was addressed via Boussinesq formulation. The developed solver was customized to a specific class of turbulent reacting flow by modelling combustion process as gas explosion. The approach has demonstrated that it can handle complex geometries within feasible computational time. Numerical findings for simulation of non-reacting flows and reacting flows present the main features of the fluid flow and good agreement with experimental data was observedDoutoradoEngenharia QuímicaDoutora em Engenharia Quimica140812/20148CNP

Desenvolvimento de um modelo matemático para prever o tamanho da nuvem de gás inflamável baseado em CFD e metodologia de superfície de resposta

Orientador: Sávio Souza Venâncio ViannaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia QuímicaResumo: Este trabalho tem como objetivo desenvolver um modelo matemático capaz de prever o tamanho de nuvem de gás inflamável formada em uma típica plataforma de petróleo considerando condições reais de ventilação e de operação de uma planta de processo. Para tanto, foi realizado um estudo de dispersão de gás inflamável (gás natural) na plataforma em questão utilizando Fluidodinâmica Computacional (CFD). Os resultados deste estudo de dispersão serviram como base para a construção do modelo matemático utilizando Metodologia de Superfície de Resposta. Tal modelo permite o cálculo do tamanho de nuvem de gás inflamável no ambiente estudado usando duas variáveis principais: a taxa não-dimensional de vazamento (que contabiliza a relação entre a taxa de vazamento de gás e a taxa de ventilação na plataforma) e a direção adimensional de vazamento (que computa a relação entre as direções de vazamento de gás e do vento). O modelo desenvolvido mostrou-se eficaz, pois foi capaz de prever com considerável grau de confiabilidade os tamanhos de nuvem de gás inflamável quando comparados aos valores fornecidos por simulações com CFDAbstract: This work proposes the development of a mathematical correlation for prediction of flammable gas cloud size in a typical offshore module. Real conditions regarding the ventilation and process plant operation were considered. A dispersion study of natural gas release in the module was conducted using Computational Fluid Dynamics (CFD) and the state of art as far as the gas dispersion modelling is concerned. A mathematical model was built based on the numerical results and Response Surface Methodology (RSM). The approach comprises into a single mathematical model the most relevant independent variables. The response surface curves calculate the flammable gas cloud volume as a function of the non-dimensional leak rate (that concerns the ventilation and the gas release rate) and the non-dimensional leak direction (which comprises the wind direction and the leak direction). The developed model had proved to be effective. It was able to predict flammable gas volume and good agreement with CFD results was observedMestradoSistemas de Processos Quimicos e InformaticaMestra em Engenharia Químic

The Nature of Flammable Cloud Volumes in Semi-confined Environment under the Influence of Flow of Air

PresentationIn the Explosion Risk Analysis (ERA), ventilation and dispersion calculations using Computational Fluid Dynamics (CFD) are usually considered when the level of confinement and congestion cannot be neglected. As far as the dispersion analysis is considered, alternative approaches are sought when a large number of simulations are required. Setting many scenarios and simulate them all is not always suitable within the timeframe of real engineering design. As a result, semi-empirical dispersion models and several procedures based on statistical approaches using CFD have been proposed to improve the robustness and the accuracy of prediction of the flammable gas cloud volume. In addition, notwithstanding the use of Response Surface Method (RSM) and Frozen Cloud Approach (FCA), it is convenient to address the problem on the basis of the physics underlying the dispersion of a scalar in the chemical process area. Following this line of reasoning, we propose a new dimensionless number balancing the transport of the flammable cloud and the accidental leak rate. Numerical experiments have shown that the dimensionless number is related to the angle of the wind direction as the angles in a circle are related to the phase angle in a sine wave, V ∼ sin (kφ/π+ β) , where V̂ is the nondimensional flammable cloud volume and φ the phase angle. The numerical findings suggest a periodic function comprising harmonically sinusoids in the same fashion put forward by Fourier and observed in the analytical solutions of diffusive transport equations

Collision of Convex Objects for Calculation of Porous

PresentationWe investigate the coupling of the flamelet combustion model with the collision distance algorithm for entertainment games. The collision algorithm is coded to calculate the porosity of the geometry based on the PDR (Porosity Distributed Resistance) approach for modelling of complex geometries. The turbulent field generated by the interaction of the flow with the porous objects is used to calculate the wrinkling length scale of the flame via the fluctuating velocities. The turbulent fluxes are amended in accordance with assigned porosities at the cell faces. The combustion and porosity models are implemented in the framework of an in house Fortran code that solves the full set of Navier-Stokes equations. Results are presented for non-reacting flows and reacting flows over a bluff body for Re=44,000 and Ka=1 (Reynolds and Karlovitz numbers, respectively). Numerical findings are compared with standard commercial CFD tools