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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Atomisation et dispersion d'un jet liquide : approches numérique et expérimentale / Atomization and dispersion of a liquid jet : numerical and experimental approaches

Felis-Carrasco, Francisco 24 March 2017 (has links)
L'atomisation d'un jet circulaire d'eau typique des applications agricoles est présentée dans cette étude. Maîtriser la dispersion de l'eau à des fins d'irrigation ou de traitements phytosanitaires implique de réduire la consommation d’eau et la pollution de l'environnement. Un cas d'étude simplifié est construit : une buse ronde dn=1.2 mm et d'une longueur Ln=50dn y est considérée. La vitesse d'injection est fixée à UJ=35 m/s et alignée avec la gravité, plaçant le jet liquide dans un régime d'atomisation turbulent. L'écoulement est statistiquement axisymétrique. L'approche est à la fois expérimentale et numérique.Un modèle multiphasique Eulérien de mélange décrit l'écoulement constitué de deux phases. Plusieurs modèles de turbulence U-RANS sont utilisés: k-ε et RSM. Une attention particulière est alors portée à la modélisation des effets de masse volumique variable issus de la formulation du fluide de mélange. Un solveur numérique spécifique est développé à l'aide du code CFD OpenFOAM. Une série de cas d'étude est construite pour tester l'influence de la modélisation de la turbulence et des fermetures de premier/second-ordre des flux massiques turbulents.Les techniques optiques (LDV et DTV) sont déployées pour recueillir des informations statistiques des phases liquide et gazeuse du spray. La campagne expérimentale est réalisée de x/dn=0 jusqu'à x/dn=800. En ce qui concerne la LDV, des gouttelettes d'huile d'olive (~1 µm) permettent d'analyser la phase gazeuse. Une distinction entre les gouttes de liquide et ces traceurs est obtenue par une configuration spécifique de la source laser et le paramétrage de la détection des bouffées Doppler (Filtre-BP et le SNR). Dans la zone dispersée, les mesures par DTV permettent d'estimer les vitesses et les tailles des gouttes. Une attention particulière est portée à l'estimation de la profondeur de champ (DOF) afin d'obtenir une corrélation taille-vitesse des gouttes moins biaisée.Les résultats numériques et expérimentaux concordent pour le champ de vitesse moyenne. Une forte dépendance au modèle de turbulence est trouvée. Cependant, le modèle RSM ne simule pas le comportement du tenseur de Reynolds. En effet, ni l'anisotropie trouvée expérimentalement (R22/R11≈0.05), ni la vitesse de glissement liquide-gaz ne peuvent être reproduites; même avec une fermeture au 2nd-ordre des flux massiques turbulents. Le fort rapport de masse volumique (eau/air), la directionnalité de l'écoulement et la production d'énergie cinétique turbulente peuvent être à l'origine d'une faible dispersion et d'un faible mélange entre les deux fluides. Ce mécanisme n'est pas encore clarifié du point de vue de la modélisation RSM. / A typical water round-nozzle jet for agricultural applications is presented in this study. The dispersion of a liquid for irrigation or pesticides spraying is a key subject to both reduce water consumption and air pollution. A simplified study case is constructed to tackle both scenarios, where a round dn=1.2 mm nozzle of a length Ln=50dn is considered. The injection velocity is chosen to be UJ=35 m/s, aligned with gravity, placing the liquid jet in a turbulent atomization regime. The flow is considered statistically axisymmetric. Experimental and numerical approaches are considered.An Eulerian mixture multiphase model describes the original two-phase flow. Several U-RANS turbulence models are used: k-ε and RSM; where special attention is taken to the modelling of variable density effects from the mixture formulation. A custom numerical solver is implemented using the OpenFOAM CFD code. A series of study cases are constructed to test the influence of the turbulence modeling and first/second-order closures of the turbulent mass fluxes. LDV and DTV optical techniques are used to gather statistical information from both the liquid and the gas phases of the spray. The experimental campaign is carried out from x/dn=0 to x/dn=800. Concerning the LDV, small (~1 µm) olive-oil tracers are used to capture the gas phase, where a distinction between the liquid droplets and tracers is achieved by a specific set-up of the laser power source and the burst Doppler setting (BP-Filter and SNR). On the dispersed zone, DTV measurements are carried out to measure velocities and sizes of droplets. Special attention to the depth-of-field (DOF) estimation is taken in order to obtain a less biased droplet’s size-velocity correlation.Numerical and experimental results show good agreement on the mean velocity field. A strong dependence on the turbulence model is found. However, the RSM does not capture the same behaviour on the calculated Reynolds stresses. Indeed, neither the experimental anisotropy (R22/R11≈0.05), nor the liquid-gas slip-velocity can be reproduced, even with a second-order closure for the turbulent mass fluxes. The strong density ratio (water/air), flow’s directionality and production of turbulent kinetic energy may be the cause of a weak dispersion and mixing between the two fluids. This mechanism is not yet clarified from a RSM modeling point-of-view.
2

Saturated Nucleate Pool Boiling From Smooth/Plasma Coating Enhanced Tube Using LDV Method

ke, Chung-Guang 24 July 2001 (has links)
Pool boiling process is frequently encountered in a number of engineering applications. It is difficult to exactly predict the heat transfer coefficient. This is because the boiling phenomenon is rather complex and influenced by many factors, such as surface condition, heater size, geometry, material, arrangement of heated rods, and refrigerants, etc. The key boiling parameters (bubble dynamics data) such as bubble departure diameter, frequency, velocity and nucleation site density will be varied in such different heated surface resulting in the different effect of heat transfer. Furthermore, more fundamental of the physical phenomenon can be obtained. This study was performed experimentally. R-134a and R-600a were used as refrigerants. The surface condition will be changed with plasma spray coating. It is expected that the surface condition can affect the nucleate boiling heat transfer in certain degree. In addition, using the high speed digital vide camera and LDV to measure the bubble diameter and dynamics of R-600a and R-134a while growing. According of the results of experiments. The boiling curves in different situation were drawn and the influences of heat transfer coefficients by bubble velocity was also examinate. Finally, to broaden our basic understanding of different characteristics of refrigeration surface condition and heat transfer coefficient, thermal design data of a flooded type evaporator of high performance as well as more and further physical insight of the above-stated nucleate boiling heat transfer can be acquired. The results will hopefully be helpful not only for the academia but for the industry.
3

LDV Assisted Bubble Dynamic Parameter Measurements From Two Enhanced Tubes Boiling in Saturated R-134a

Lai, Wen-Chuan 23 July 2002 (has links)
Abstract Pool boiling process is frequently encountered in a number of engineering applications. It is difficult to exactly predict the heat transfer coefficient. This is because the boiling phenomenon is rather complex and influenced by many factors, such as surface condition, heater size, geometry, material, arrangement of heated rods, and refrigerants, etc. The key boiling parameters (bubble dynamics data) such as bubble departure diameter, frequency, velocity and nucleation site density will be varied in such different heated rod pitches resulting in the different effect of heat transfer. Furthermore, more fundamental of the physical phenomenon can be obtained. Pool boiling heat transfer of R-134a is investigated experimentally on twin tube arrangement. The tube pitch is 1.65 and 2.5. The surface condition was prepared with plasma spray coating. In addition, using the high-speed digital camera and LDV, the bubble diameter and dynamics of R-134a were measured while growing. The boiling curves in different twin-tube pitches were drawn and the influence of bubble velocity on heat transfer coefficients was also examined. Finally, to broaden our basic understanding of different arrangement of heated rods and heat transfer mechanisms, thermal design data of a flooded type evaporator of high performance as well as more and further physical insight of the above-stated nucleate boiling heat transfer can be acquired. The results would hopefully be helpful not only for the academia but also for the industry.
4

強乱流予混合火炎の流れ場と構造

山本, 和弘, YAMAMOTO, Kazuhiro, 西澤, 泰樹, NISHIZAWA, Yasuki 25 January 2002 (has links)
No description available.
5

Extracting the Rotational Degrees of Freedom From a Reconstructed Three-Dimensional Velocity Field Along With an Analytical Demonstraton and a Proposed Method for Experimental Verification

DeVlaminck, James Raymond 26 July 2001 (has links)
A theoretical method for extracting the rotational degrees of freedom from a reconstructed three-dimensional velocity field has been developed. To extract the angular velocities the curl of the translational velocities must be performed. The three-dimensional velocity field is to be equally spaced so that the DFT-IDFT technique of taking partial derivatives of the translational velocities is used. A program was written in C along with MATLAB® which performed the theoretical calculations. Two proposed methods of experimentally verifying the angular velocity data is developed using a Kistler translational/angular piezobeam accelerometer to compare against the DFT-IDFT partial derivative technique for calculating the angular velocities. / Master of Science
6

Modelling, Simulation and Optimisation of Asymmetric Rotor Profiles in Twin-screw Superchargers

Ilie, Katherine-Rodica, Katherine.ilie@rmit.edu.au January 2007 (has links)
There is a growing recognition worldwide of the need for more powerful, smaller petrol engines, capable of delivering the higher picking power of larger engines, yet still being economical and environmentally friendly when used for day-to-day driving. An engineering solution for more efficient engines has been considered by research so far. It has been identified that superchargers can potentially improve the performance of automotive engines; therefore research has focused on developing superchargers and supercharger components with higher efficiency. Of particular interest to the research presented in this thesis has been the twin-screw supercharging compressor with design adapted for automotive use (the twin-screw supercharger). The performance of this supercharger type depends on the volume and total losses of the air flow through the supercharger rotors more than on any other aspects of its behaviour. To accurately predict the efficiency of the twin-screw su percharger for matching a particular engine system, accurate supercharger design is required. The main objective of this research was the investigation of the existing limitations of twin-screw superchargers, in particular leakage and reduced efficiency, leading to the development of optimal asymmetric rotor profiles. This research has been completed in four stages defining an innovative rotor design method. The parametric three-dimensional geometric model of twin-screw supercharger rotors of any aspect ratio was developed. For model validation through visualisation, CAD rotor models with scalable data were generated in commercial CAD software and calibrated experimentally by Laser Doppler Velocimetry (LDV) tests. Calibrated rotor profile data can be transferred into CAD-CFD interface for flow simulation and performance optimisation. Through the application of this new rotor design method, new opportunities are created for the twin-screw supercharger design practice, making it a part of the engineering solution for more efficient engines.
7

Experimental studies of the plane turbulent wall jet

Eriksson, Jan January 2003 (has links)
No description available.
8

Experimental studies of the plane turbulent wall jet

Eriksson, Jan January 2003 (has links)
No description available.
9

旋回噴流燃焼器を用いた強乱流予混合火炎の研究 (第3報, Slot-Correlation法による燃焼場の乱れスケールの計測)

山本, 和弘, YAMAMOTO, Kazuhiro, 西澤, 泰樹, NISHIZAWA, Yasuki, 小沼, 義昭, ONUMA, Yoshiaki 25 February 2002 (has links)
No description available.
10

Facility and Methodologies for Evaluation of Hydrogen-Air Mixer Performance

Norberg, Adam D. 19 October 2006 (has links)
Increased efficiency and reduced emissions from gas turbine (GT) engines are of consistently growing concern for the current gas turbine community and for the political environment. GT engines commonly produce undesirable emissions such as Carbon Monoxide (CO), Carbon Dioxide (CO₂), Nitric Oxides (NO<sub>x</sub>), and Unburned Hydrocarbons (UHC), which all pose various threats to the environment. Lean premixed combustion of hydrogen provides a potential solution to these concerns. A key component of successful lean hydrogen combustion is the fuel-air mixer. A facility and methodology for the evaluation of such a hydrogen-air mixer is developed and discussed in this thesis. The facility developed utilizes three experimental techniques: Mie scattering flow visualization, schlieren flow visualization, and Laser Doppler Velocimetry (LDV) to characterize and evaluate mixer performance. Results from the two flow visualization experiments illustrate the effectiveness of the established facility. The results from the Mie scattering experiment are post processed and overlaid on CFD predictions of mixer performance and many similarities are found. Capability of the LDV to measure two components of mean velocity is also demonstrated. / Master of Science

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