Numerical Simulation of Biofuels Injection

The use of alternative biofuels in the co-generation of electricity and heat, as well as in the transportation sector, presents major benefits, such as the conservation of the environment due to their renewable origin, the reduction of fossil fuels use or the conservation of agricultural activity in regions where the food production is being reduced. [...]Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

Numerical study of spray dispersion in a premixing chamber for Low-NOx engines

The present work describes a numerical study of a confined two-phase flow under high-pressure conditions, typical of gas turbine combustors. An Eulerian frame was used for the gas phase together with a Lagrangian approach to describe the dispersed phase. The computational method was extended to high-pressure environments, which are more representative of the practical gas turbine operating conditions. The results are compared with experimental data, and revealed the ability of the model to increase the knowledge of the turbulent dispersion phenomena for this type of practical conditions (high pressure and confined flow).Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

Spray impingement modelling: Evaluation of the dissipative energy loss and influence of an enhanced near-wall treatment

The goal of the present research is to contribute to improve the knowledge about the spray impingement topic through a numerical study that is aimed at investigating the impact of using the dissipative energy terms that are available in the literature when they are embedded into a specific dispersion model. Comparing all the numerical approaches, a non-negligible disagreement is observed between the relationship proposed in the original model and the other ones drawn from the literature. This fact evidences the influence of the energy dissipated term on the secondary atomization outcome. The present work also provides a comprehensive study on the estimation of the energy dissipated during the splash event. This is a major contribution to the permanent literature since the few works found only addressed the spread regime. In addition, this paper gives an in-depth analysis on the influence that an enhanced treatment of the boundary layer in the region close to the wall may have in the simulation of such flows. The work revealed that this near-wall droplets tracking method provides an alternative way to increase the accuracy of the dispersed phase and achieve more consistent results without the necessity of a direct mesh refinement.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

Turbulence Quantification in Supercritical Nitrogen Injection: An Analysis of Turbulence Models

In Liquid Rocket Engines, higher combustion efficiencies come at the cost of the propellants exceeding their critical point conditions and entering the supercritical domain. The term fluid is used because, under these conditions, there is no longer a clear distinction between a liquid and a gas phase. The non-conventional behavior  of thermophysical properties makes the modeling of supercritical fluid flows a most challenging task. In the present work, a RANS computational method following an incompressible but variable density approach is devised on which the performance of several turbulence models is compared in conjunction with a high accuracy multi-parameter equation of state. Also, a suitable methodology to describe transport properties accounting for dense fluid corrections is applied. The results are validated against experimental data, becoming clear that there is no trend between turbulence model complexity and the quality of the produced results. For several instances, one- and two- equation turbulence models produce similar and better results than those  of Large Eddy Simulation (LES). Finally, considerations about the applicability of the tested turbulence models in supercritical simulations are given based on the results and the structural nature of each model. Keywords: Supercritial fluids, RANS turbulence modeling, Liquid rocket engine

Comparison of Commercial and Open-Source CFD Solvers on Surface Tension Dominated Flows

Problems involving multiphase flows require a physical understanding of how the phenomenadevelop and the specific interactions they manifest. For surface tension relevant flows, suchas bubbles and droplets, the importance of modelling and predicting small-scale behaviouris crucial in accurately defining the liquid-gas interface and complex interactions that may takeplace. Axisymmetric numerical simulations of single droplets impacting onto thin liquid films areperformed using commercial and open-source CFD codes. ANSYS Fluent®is the commercialsoftware employed, whereas Basilisk is the open-source CFD solver adopted. The incompress-ible Navier-Stokes equations are coupled and handled differently throughout each software.A solution-adaptive mesh refinement tool is adopted to reduce computational cost. Softwarecomparison is based on quantitative and qualitative analysis, namely crown height and outerdiameter measurements, and the crown curvature and occurrence of splashing, respectively.Results show that Basilisk simulations are in good agreement with the experimental data. Fluent follows the tendency for the crown outer diameter however, in terms of height, the modelunder-predicts its growth and collapses at later stages of the impact for lower thicknessesFundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

Influence of the Spread/Splash Transition Criteria in the Spray Impingement Modeling

The present paper reports a numerical study of a spray impinging on a surface through a crossflow. This work is intended to study the influence of the spread/splash transition criteria in the modeling of the spray impingement phenomenon. Several experimental correlations available in the literature are inserted in the same base model and the results are tested against experimental data. It can be concluded that the employment of an accurate transition criteria can improve the quality of the results.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

Liquid film dynamic on the spray impingement modelling

The present paper addresses a liquid film sub-model included into a computational model that aims at reproducing the spray impingement phenomena. This numerical extension incorporates the spread of the liquid film over the neighbouring nodes due to the dynamic motion induced by the film inertia but also the exchange of mass between the liquid layer and the incident and splashing particles. Moreover, the dimensionless film thickness parameter is introduced into the sub-model by mean of an experimentally-deduced correlation that can be fitted and updated to specified conditions. In order to realize how the model behaves with different influencing parameters, a thorough investigation is performed: the results that are obtained with and without the liquid film sub-model are compared against the experimental data for two crossflow rates. The integration of the computational extension with the spread/splash transition criterion is also evaluated by considering two types of transition criteria: one that takes into account the effect of the film thickness and one that does not. The results show that the latter option in combination with the sub-model do not distinctly enhance the simulation results, contrary to what happens using the transition criterion that considers the film thickness as an influencing parameter. In this case, the model with the computational extension reveals better prediction results than the one without it, which indicates the necessity of considering the liquid film formation for spray impingement simulations but also a splash threshold that takes into account the influence of the film thickness.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

Graffiti nas edificações: identificação e resolução do problema

Trabalho final de Mestrado para obtenção do grau de Mestre em Engenharia Civil na Área de Especialização em EdificaçõesEste trabalho concentra-se no problema de vandalismo em propriedades mais frequente na actualidade, os graffiti. Uma propriedade coberta de graffiti está ligada à degradação e ao abandono, criando um clima de insegurança e de possível violência em toda a área. De tal modo que para além dos proprietários, as câmaras municipais e empresas com os seus negócios nas áreas afectadas procuram resolver o problema que se torna bastante dispendioso. Para solucionar a anomalia relacionada com os graffiti e os problemas daí associados terá de se executar uma intervenção eficiente e sem falhas para não agravar ainda mais os problemas com as edificações, enquanto uma política tolerante aos graffiti poderá levar a que os custos de reabilitação de toda a área sejam cada vez maiores. Com base em todos estes pressupostos, este trabalho apresenta-se como uma análise a uma adequada prevenção, que é essencial para evitar de todo a degradação e uma eventual reabilitação quer através da segurança, quer pelo conhecimento do problema e meios de o evitar. Apresenta-se, ainda, uma análise aos diversos tipos de graffiti que poderão surgir, à sua remoção de forma correcta segundo várias metodologias e avaliações das mesmas, bem como à protecção que poderá ser executada contra os graffiti, e por fim, uma forma original de prevenção automática desenvolvida pelo autor, propondo-se um sistema original que pretende facilitar as intervenções de remoção e até mesmo evitar que possa ser executado.Abstract: This study focuses on one of the most common property vandalism nowadays, graffiti. A property covered by graffiti is linked to degradation and abandonment, creating a climate of insecurity and possible violence in the entire area. So that in addition to the owners, local councils and companies with business in the affected areas seek to solve the problem that becomes a quite expensive one. To solve the anomaly relating to the graffiti and the associated problems, it will be important to run an efficient and flawless intervention, to avoid further worse problems with the buildings, while a tolerant policy to graffiti can lead to increasing costs for rehabilitation of the entire area. Based on all these assumptions, the present study is presented as an analysis of an adequate prevention, which is essential to avoid degradation and a further rehabilitation at all, by assuring security, knowledge of the problem and means to avoid it. It presents also an analysis to the different types of graffiti, correct removal according to various methodologies and their evaluation, as well as a protection that can be used against graffiti, and finally an original automatic prevention developed by the author, proposing a unique system that aims at making interventions to graffiti easier and even prevent it to be executed

An efficient muscle fatigue model for forward and inverse dynamic analysis of human movements

AbstractThe aim of this work is to present the integration of a simple and yet efficient dynamic muscle fatigue model in a multibody formulation with natural coordinates. The fatigue model considers the force production history of each muscle to estimate its fitness level by means of a three-compartment theory approach. The model is easily adapted to co-operate with standard Hill-type muscle models, allowing the simulation and analysis of the redundant muscle forces generated in the presence of muscular fatigue. This has particular relevance in the design of orthotic devices to support human locomotion and manipulation