CISNE JÚNIOR, Roberto Lima da Costa. Transporte de Fluidos e Partículas em Meios Irregulares. 2014. 113 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2014. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-06-16T20:47:55Z No. of bitstreams: 1 2014_tese_rlccisnejunior.pdf: 4679198 bytes, checksum: 53ef0a18b5270d30f9e1fc7f5a1ad112 (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-06-18T18:22:45Z (GMT) No. of bitstreams: 1 2014_tese_rlccisnejunior.pdf: 4679198 bytes, checksum: 53ef0a18b5270d30f9e1fc7f5a1ad112 (MD5) / Made available in DSpace on 2015-06-18T18:22:45Z (GMT). No. of bitstreams: 1 2014_tese_rlccisnejunior.pdf: 4679198 bytes, checksum: 53ef0a18b5270d30f9e1fc7f5a1ad112 (MD5) Previous issue date: 2014 / O escoamento de fluidos no interior de estruturas irregulares apresenta certa complexidade. De início, investigamos o transporte de partículas no interior de uma estrutura ramificada tridimensional semelhante a um pulmão. Essas partículas são arrastadas por um fluido Newtoniano. Verificamos que a estrutura ramificada se comporta como um separador de partículas por tamanho, e que alguns parâmetros geométricos podem ser ajustados para controlar essa separação. Depois, estudamos o escoamento de um fluido Newtoniano e partículas pontuais no interior de canais catracas bidimensionais. Estes canais foram modelados de forma a permitir uma quebra de simetria espacial na direção do escoamento. No entanto, não encontramos mudanças significativas relacionadas ao perfil de escoamento do fluido. Já em relação às partículas ocorre uma grande assimetria no tempo médio de trânsito devido à existência de caminhos que se estabelecem próximos às paredes de perfil assimétrico. Assim, mostramos como obter um efeito catraca das partículas, podendo ocorrer uma seleção das mesmas em determinadas condições de escoamento. Finalmente, analisamos o escoamento de fluidos não-Newtonianos no interior de meios porosos bidimensionais. O fluido escolhido pode exibir dois principais regimes de escoamento: de altas viscosidades, quando em baixas tensões; e baixas viscosidades, quando em tensões mais elevadas. Para tal, utilizamos o modelo de Herschel-Bulkley usado em fluidos de Bingham (pseudoplásticos). Como resultado encontramos um regime de escoamento peculiar, apresentando uma forte canalização do fluido no interior do meio poroso.

Beside the traditional paradigm of "centralized" power generation, a new concept of "distributed" generation is emerging, in which the same user becomes pro-sumer. During this transition, the Energy Storage Systems (ESS) can provide multiple services and features, which are necessary for a higher quality of the electrical system and for the optimization of non-programmable Renewable Energy Source (RES) power plants. A ESS prototype was designed, developed and integrated into a renewable energy production system in order to create a smart microgrid and consequently manage in an efficient and intelligent way the energy flow as a function of the power demand. The produced energy can be introduced into the grid, supplied to the load directly or stored in batteries. The microgrid is composed by a 7 kW wind turbine (WT) and a 17 kW photovoltaic (PV) plant are part of. The load is given by electrical utilities of a cheese factory. The ESS is composed by the following two subsystems, a Battery Energy Storage System (BESS) and a Power Control System (PCS). With the aim of sizing the ESS, a Remote Grid Analyzer (RGA) was designed, realized and connected to the wind turbine, photovoltaic plant and the switchboard. Afterwards, different electrochemical storage technologies were studied, and taking into account the load requirements present in the cheese factory, the most suitable solution was identified in the high temperatures salt Na-NiCl2 battery technology. The data acquisition from all electrical utilities provided a detailed load analysis, indicating the optimal storage size equal to a 30 kW battery system. Moreover a container was designed and realized to locate the BESS and PCS, meeting all the requirements and safety conditions. Furthermore, a smart control system was implemented in order to handle the different applications of the ESS, such as peak shaving or load levelling.

Questo lavoro di dottorato, svolto prevalentemente presso i laboratori hangar della Facoltà di Ing. Aerospaziale di Forlì, in collaborazione con AVIO S.P.A (Colleferro), ha come scopo quello di ricostruire alcune grandezze tipiche di un motore per razzi a propellente solido. In particolare è stato sviluppato un algoritmo in MatLab, successivamente "tradotto" in C++ per evidenti motivi di velocità computazionale, capace di prevedere la frazione volumetrica di un propellente bi-modale. Successivamente, sulla base di questo parametro, e utilizzando informazioni relative alla composizione completa del propellente stesso, si è andati a defnire un "Margine di Colabilità",capace di legare la viscosità cinematica del composto alla sua stessa composizione granulometrica. Infne si è cercato di fruttare queste informazioni per vedere come questi parametri, insieme all'orientazione e concentrazione delle particelle stesse, possono influenzare il proflo di pressione durante la fase di lancio, e cercare quindi di spiegare il così detto effetto HUMP (disuniformità della velocità di combustione internamente al grain) / This doctoral dissertation has been carried out in the laboratories based in the hangar of the Engineering Faculty of Forlì, University of Bolonia, in cooperation with AVIO S.P.A. (Colleferro). The aim of the thesis is to reconstruct some typical characteristics of a solid rocket motor. The work is particularly focused on the development of an algorithm - using MatLab - that has later been "translated" into C++ in order to reduce the computational load and to be able to predict the volume fraction of a bi-modal propellant. Later, using this parameter, as well as some informations concerning the full composition of the propellant, the "castability margin" has been defined, in order to link its cinematic viscosity to the related propellant formulation. Lastly, the informations collected has been exploited to figure out how these parameters, together with the particles' orientation and concentration, may influence the pressure profile during the launch phase. This data tries to explain the so-called HUMP effect (inhomogeneity of the combustion speed inside the grain)

Large Eddy Simulation (LES) represents nowadays one of the most promising techniques for the evaluation of the dynamics and evolution of turbulent structures characterizing Internal Combustion Engines (ICE). The demand for a high level of resolution accuracy as well as the need to evaluate different scenarios and system configurations lead to considerable computational and economic costs for both the hardware infrastructure and the licensing fees of commercial codes. In such context, the present Doctoral project has the objective to define the most suitable numerical methodology to perform LES analysis of ICE flows and to implement such methodology in an efficient, accurate and robust CFD code, based on open-source components. An evaluation of freely available CFD codes has led to the choice of the open-source CFD package OpenFOAM as the most suited code for the project’s objective. The LES modeling of interest for ICE applications has been then studied and three Sub-grid scale models particularly suited for such flows have been implemented and assessed into OpenFOAM. Moreover, Python scripts have been developed in order to automate and speed-up both pre-processing and post-processing phases. The CFD methodology has been then applied to a real world ICE systems such as a stationary flow bench, for which prior RANS simulations had shown some predictive deficiencies. The quality of the analyses has been assessed through specific LES quality estimators and the computational results have been validated against measurements, showing pretty good agreement. Finally, LES simulations have allowed the accurate investigation of the flow bench fluid-dynamic behavior and, thanks to the insights gained, an alternative RANS approach based on the Reynolds Stress Tensor Modeling has been proposed and tested in order to alleviate the aforementioned predictive deficiencies.

The Department of Mechanical and Civil Engineering (DIMeC) of the University of Modena and Reggio Emilia is developing a new type of small capacity HSDI 2-Stroke Diesel engine (called HSD2), featuring a specifically designed combustion system, aimed to reduce weight, size and manufacturing costs, and improving pollutant emissions at partial load. The present work is focused on the analysis of the combustion and the scavenging process, investigated by means of a version of the KIVA-3V code customized by the University of Chalmers and modified by DIMeC. The customization of the KIVA-3V code includes a detailed combustion chemistry approach, coupled with a comprehensive oxidation mechanism for diesel oil surrogate and the modeling of turbulence/chemistry interaction through the PaSR (Partially Stirred Reactor) model. A four stroke automobile Diesel engine featuring a very close bore size is taken as a reference, for both the numerical models calibration and for a comparison with the 2-Stroke engine. Analysis is carried out trough a comparison between HSD2 and FIAT 1300 MultiJet in several operating conditions, at full and partial load. Such a comparison clearly demonstrates the effectiveness of the two stroke concept in terms of emissions reduction and high power density. However, HSD2 is still a virtual engine, and experimental results are needed to assume the reliability of numerical results.

Nella prima parte di questa tesi di dottorato sono presentate le attività svolte, di carattere numerico, ai fini della modellizzazione di macchine volumetriche ad ingranaggi esterni. In particolare viene dapprima presentato un modello a parametri concentrati utilizzato per l’analisi dei fenomeni che coinvolgono l’area di ingranamento della macchina; un codice di calcolo associato al modello è stato sviluppato ed utilizzato per la determinazione dell’influenza delle condizioni di funzionamento e delle caratteristiche geometriche della macchina sulle sovra-pressioni e sull’eventuale instaurarsi della cavitazione nei volumi tra i denti che si trovano nell’area di ingranamento. In seguito vengono presentati i risultati ottenuti dall’analisi del bilanciamento assiale di diverse unità commerciali, evidenziando l’influenza delle caratteristiche geometriche delle fiancate di bilanciamento; a questo proposito, viene presentato anche un semplice modello a parametri concentrati per valutare il rendimento volumetrico della macchina ad ingranaggi esterni, con l’intenzione di usare tale parametro quale indice qualitativo della bontà del bilanciamento assiale. Infine, viene presentato un modello completo della macchina ad ingranaggi esterni, realizzato in un software commerciale a parametri concentrati, che permette di analizzare nel dettaglio il funzionamento della macchina e di studiare anche l’interazione della stessa con il circuito idraulico in cui è inserita. Nella seconda parte della tesi si presentano le attività legate alla messa in funzione di due banchi prova idraulici per la caratterizzazione sperimentale di macchine volumetriche e componenti di regolazione, con particolare attenzione dedicata alla messa a punto del sistema di acquisizione e gestione dei dati sperimentali; si presentano infine i risultati di alcune prove eseguite su componenti di regolazione e macchine volumetriche. / In the first part of this thesis, the numerical modeling of external gear pumps and motors is described. Firstly a lumped parameter model of the meshing area is proposed and used to determine the pressure transient within the inter-teeth volumes; the influence of the machine operating parameters and of the geometrical parameters characterizing the gears and bearing blocks internal surfaces is then analyzed with reference to the pressure peaks and to cavitation arising within the meshing area. Successively, the bearing blocks axial balance is studied, by means of a numerical procedure, for different commercial units; the axial balance behavior of the machines is characterized with reference to the bearing blocks geometry and to the operating parameters. A lumped parameter model is then proposed to evaluate the volumetric efficiency, which is used as a parameter to determine the quality of the machine axial balance. Finally, the data collected by the previous analysis presented, have been used to create a model to study the dynamic behavior of an external gear machine, realized on a commercial lumped parameters software; the model allows also to determine the interaction between the gear machine and the hydraulic circuit supplied. In the second part of the thesis, the starting up of two test benches for hydraulic machines and valves characterization is described, with particular attention devoted to the experimental data acquisition hardware and software used. Then, some results obtained by the characterization of hydraulic machines and valves are presented and commented.

A wall film model has been implemented in a customized version of KIVA code developed at University of Bologna. Under the hypothesis of `thin laminar ow' the model simulates the dynamics of a liquid wall film generated by impinging sprays. Particular care has been taken in numerical implementation of the model. The major phenomena taken into account in the present model are: wall film formation by impinging spray; body forces, such as gravity or acceleration of the wall; shear stress at the interface with the gas and no slip condition on the wall; momentum contribution and dynamic pressure generated by the tangential and normal component of the impinging drops; film evaporation by heat exchange with wall and surrounding gas. The model doesn't consider the effect of the wavy film motion and suppose that all the impinging droplets adhere to the film. The governing equations have been integrated in space by using a finite volume approach with a first order upwind differencing scheme and they have been integrated in time with a fully explicit method. The model is validated using two different test cases reproducing PFI gasoline and DI Diesel engine wall film conditions.

No description available.

Increasingly stringent exhaust emission limits and higher fuel economy are the main drivers of the engine development process. As a consequence, the complexity of the propulsion units and its subsystems increase, due to the extensive use of sensors and actuators needed to obtain a precise control over the combustion phase. Since engine calibration process consumes most of the development time, new tools and methodologies are needed to shorten the development time and increase the performance attainable. Real time combustion analysis, based on the in-cylinder pressure signal, can significantly improve the calibration of the engine control strategies and the development of new algorithms, giving instantaneous feedback on the engine behavior. A complete combustion analysis and diagnosis system has been developed, capable of evaluating the most important indicators about the combustion process, such as indicated mean effective pressure, heat release, mass fraction burned and knock indexes. Such a tool is built on top of a flexible, modular and affordable hardware platform, capable of satisfying the requirements needed for accuracy and precision, but also enabling the use directly on-board the vehicle, due to its small form factor.

No description available.