Teses / dissertações sobre o tema "Experimental Jetset"

Cette thèse porte sur l’étude d’un jet de plasma d'hélium à pression atmosphérique alimenté par des impulsions positives unipolaires à une fréquence de l’ordre du kHz. Des expériences sont effectuées pour caractériser la dynamique de propagation, la structure de l'écoulement et la température dans un jet en expansion libre, ainsi que l'influence d'une cible métallique sur le plasma.La spectroscopie à polarisation Stark indique un champ électrique axial d'environ 10 kV/cm dans le capillaire du jet et une augmentation jusqu'à 20 kV/cm dans le panache, qui est constante pour différentes amplitudes et durées de l'impulsion de tension appliquée. La diffusion Thomson et la diffusion Raman rotationnelle sont utilisées pour déterminer la densité électronique et la température électronique, à différentes positions axiales et radiales, ainsi que la température du gaz et la densité de N2 et O2 de l'air environnant qui sont mélangés dans le flux d’hélium.La comparaison quantitative de ces résultats expérimentaux avec les résultats d'un modèle fluide 2D montre une bonne concordance et permet une meilleure compréhension des résultats obtenus, à savoir que le champ électrique dans le front d'ionisation augmente avec la quantité d’air intégré au flux d’hélium au lond de la propagation. L'imagerie Schlieren révèle l'apparition de structures turbulentes à des débits élevés et lors de l'application des impulsions de tension. On constate que la température du gaz, mesurée par une sonde de température, augmente d'environ 12 C quand le plasma est allumé et d'environ 25 C lorsqu'une cible métallique est placée devant le jet
This thesis studies an atmospheric pressure helium plasma jet that is powered by positive, unipolar pulses at a kHz frequency. Experiments are performed that focus on the propagation dynamics, flow structure and temperature in a freely expanding jet, as well as the influence of a metallic target on the plasma.Stark polarization spectroscopy yields an axial electric field of around 10 kV/cm in the capillary of the jet and an increase up to 20 kV/cm in the plume, which is constant for different amplitudes and durations of the applied voltage pulse. Thomson and rotational Raman scattering are used to determine the electron density and electron temperature, at different axial and radial positions, as well as the gas temperature and the density of N2 and O2 that are mixed into the helium from the surrounding air.Quantitative comparison of these experimental results with results from a 2D fluid model show a good agreement and allow for a better understanding of the obtained results, namely that the electric field in the ionization front depends linearly on the flow composition at that location. Schlieren imaging shows the onset of turbulent structures at high applied flow rates and at the application of the voltage pulses. The gas temperature, as measured by a temperature probe, is found to increase by around 12 C when the plasma is ignited and by around 25 C when a metallic target is placed in front of the jet

This work is devoted to the visualization and characterization of twin air jet flow when impinging vertically to a solid surface, which is important to understand the phenomenon relevant to Vertical/Short Take-Of and Landing (V/STOL) type of aircraft when they are operating on short distances from the ground, landing or taking-off, and could be helpful to improve the performance and stability of this kind of aircrafts. The major concern of this work is characterizing the fountain upwash region, which is a distinctive fan-shape flow that is formed on the collision region. The parameters analysed on this work are the separation distance between the jets and the jet height. Have been observed significant changes in the flow pattern and properties in the fountain upwash region due to the changes in the parameter studied. To be possible the realization of this work an experimental facility has been built. The facility supports an adjustable mechanical system which can accommodate twin stainless steel barrels with different diameters, which are the jets. Within this mechanical system, the barrels horizontal distance and height can be independently adjusted. The working fluid is the air, and to be possible the flow visualization a seeding generator have been projected and built. The flow visualization has been supported by an algorithm developed on the “Image Processing toolbox of Matlab” software, where have been made the post processing of the images.
Este trabalho baseia-se na visualização e caracterização do escoamento desenvolvido por dois jactos paralelos e verticalmente disposto em relação a uma superfície sólida. Estes fenómenos estão associados com aeronaves de descolagem e aterragem vertical ou curta (V/STOL – vertical/short take-of and landing). Particularmente, interessa a caracterização da região conhecida como “fountain upwash”, que é uma forma característica do escoamento que se forma na região da colisão. Os parâmetros analisados neste trabalho foram a distância horizontal entre os jactos e a altura destes à superfície de impacto. Foram observados diferenças significativas no padrão e propriedades do escoamento na região de “fountain upwash” devido à variação dos parâmetros em estudo. Para a realização deste estudo foi construída uma instalação experimental. A instalação é ajustável mecanicamente, contendo dois tubos de aço, com diâmetro variável. O sistema mecânico permite o ajustamento, independentemente, a distância horizontal entre os jactos e a altura dos mesmos. Como neste trabalho se vai trabalhar com ar, para ser possível visualizar o escoamento é necessário marcar o escoamento. Nesse sentido foi desenvolvido um gerador de “seeding”. Para uma melhor e mais precisa visualização do escoamento foi desenvolvido um algoritmo no “Matlab” usando “Image Processing toolbox”, onde as imagens captadas foram pós processadas.

Les jets intracardiaques sont des jets turbulents. Ils peuvent etre analyses de multiples manieres mais leur structure hydraulique est mal connue. Les donnees disponibles sont soit imprecises soit lointaines car etablies en ecoulement continu. Ce travail a ete conduit pour recueillir experimentalement des champs de vitesses dans des simulations de ces jets grace a des velocimetres ultrasonores et un anemometre laser doppler. Les resultats montrent l'existence, au pic de vitesse, d'un cone central comparable a celui decrit en ecoulement continu. Il ne s'etablit que progressivement au cours de l'acceleration et le front d'onde progresse lentement. Ce n'est qu'en eliminant ce dephasage par l'extraction d'enveloppes que l'on retrouve la decroissance hyperbolique sur l'axe ou la normalisation gaussienne transversale. Toutes ces donnees sont alterees en cas de confinement. Dans la couche limite, on trouve des fluctuations rapides mais organisees de la vitesse. Ces donnees ont deja debouche sur des applications cliniques

Unconfined multiple interacting confluent round jets are interesting from a purely scientific point of view, as interaction between neighboring jets brings additional complexity to the flow field. Unconfined confluent round jets also exist in various engineering applications, such as ventilation supply devices, sewage disposal systems, combustion burners, chemical mixing or chimney stacks. Even so, little scientific attention has been paid to unconfined confluent round jets. The present work uses both advanced measurement techniques and computational models to provide deeper understanding of the turbulent flow field development of unconfined confluent round jets. Both Laser Doppler Anemometry (LDA) and Particle Image Velocimetry (PIV) have been used to measure mean velocity and turbulence properties within two setups, consisting of a single row of 1×6 jets and a square array of 6×6 confluent jets. Simulations using computational fluid dynamics (CFD) of the 6×6 setup were conducted using three different Reynolds Averaged Navier-Stokes (RANS) turbulence models: the standard k-ε, the RNG k-ε and the Reynolds Stress model (RSM). The results from the CFD simulations were compared with experimental data. The employed RANS turbulence models were all capable of accurately predicting mean velocities and turbulent properties in the investigated confluent jet array. In general the RSM and k-ε std. models provided smaller deviations between numerical and experimental results than the RNG k-ε model. In terms of mean velocity the second-order closure model (RSM) was not found to be superior to the less complex standard k-ε model. The validated CFD model was employed in a parametrical investigation, including five independent variables: inlet velocity, nozzle diameter, nozzle edge-to-edge spacing, nozzle height and the number of jets in the array. The parametrical investigations made use of statistical methods in the form of response surface methodology. The derived response surface models provided information on the principal influence and relative importance of the investigated parameters within the investigated design space. The positions of the jets within the array strongly influence both mean velocity and turbulence. In all investigated setups the jets experience merging and combining. Square arrays also include considerable jet convergence, which was not present in the 1×6 jet array. Due to the jet convergence in square arrays the turbulent flow field, especially for jets far away from the array center, is affected by mean flow curvature. Jets located along the sides of square jet arrays experience strong jet-to-jet interactions that result in considerable jet deformation, shorter potential core, higher turbulent kinetic energy and faster velocity decay compared to other jets. Jets located at the corners of the array do not interact as strongly with neighboring jets as do the jets along the sides. The locations of merging and combined points differ considerably between different jets and different jet configurations. As the jets combine a zone with uniform stream-wise velocity and low turbulence intensity forms in the center of square jet arrays. This zone has been called Confluent Core Zone (CCZ) due to its similarities with the potential core zone of a single jet. Within the CCZ the appropriate scaling length changes from nozzle diameter to the effective source diameter. The parametrical investigation showed that nozzle diameter and edge-to-edge nozzle spacing were the most important of the investigated parameters, reflecting a strong dependence on dimensionless jet spacing, S/d0. Higher S/d0 delays both merging and combining of the jets and leads to a CCZ with lower velocity and longer downstream extension. Increasing the array size leads to a reduced combined point distance, a stronger inwards displacement of jets in the outer part of the array, and reduced entrainment near the nozzles. A higher inlet velocity was found to increase the jet convergence in the investigated square confluent jet arrays. Nozzle height generally has minor impact on the investigated response variables.

This thesis presents the results of experiments to study the formation and dynamics of plasma jets in the laboratory, in particular their scaling to astrophysical jets. The experiments were performed on the MAGPIE generator, which delivered a peak current of 1 MA in 250 ns. A variety of plasma diagnostics allowed the dynamics of the jets to be studied and the conditions of the plasma to be determined. Radial wire array experiments were performed in which the mass of the wires and the magnitude of the toroidal magnetic field was varied. These results show that it is possible to control the time of formation and the expansion velocity of the magnetically driven jet that characterizes this configuration. In addition, the experiments allowed the introduction of a poloidal magnetic field into the radial wire array with the aim of studying its effect on the dynamics and stability of the plasma jet. The radial foil is introduced as a novel configuration to produce episodic magnetic-tower jets. Magnetic cavities were observed to emerge in timescales of ~ 30 ns, with increasing expansion velocities reaching ~ 300 km/s. The formation of episodic magnetically driven jets occurs due to reconnection of current at the base of the cavity, allowing 3-4 episodes to be produced per experiment. Results allowed the energy balance, the magnitude of the trapped toroidal magnetic field, and the characteristic temperatures in these outflows to be determined, as well as other plasma parameters. This experimental setup allowed the study of the interaction of episodic jets with an ambient medium by introducing a neutral gas above the foil. The dynamics of the formation of several shock structures at early times was studied, opening new possibilities for laboratory astrophysics experiments in the future.

Extensive experimental data is available from previous research into the behaviour of buoyant jets released into an unstratified ambient. The experimental data has been the basis for theoretical and numerical modelling work, and currently several numerical models exist that are employed in the design of engineering structures built for the disposal of wastewater in the ocean. However there are still flow configurations with limited or no available experimental data, and hence confidence in the use of the models under some circumstances is limited. These circumstances include two-dimensional trajectory flows that are discharged at oblique angles to the ambient and buoyant jet flows with three-dimensional trajectories. As part of the current project an experimental investigation is conducted into the behaviour of discharges that have either two-dimensional or three-dimensional trajectories, focussing particularly on those configurations with currently limited available experimental data. A light attenuation technique is developed for the investigation of such flows, largely because it enables the behaviour of discharges with three-dimensional trajectories to be recorded with relative ease. However, this technique provides integrated views of the flow and hence the interpretation of the integrated concentration data is aided by assumed mean cross-sectional concentration profiles. In the strongly advected region (with the exception of the weak-jet) a double-Gaussian approximation is shown to provide a reasonable representation of mean concentration profiles. In the weakly advected regions and the weak-jet region, it is well- known that a single Gaussian adequately represents the mean flow structure. A new numerical model, the Momentum Model, is developed to assist in the design and to monitor the performance of the experimental investigation. Unlike other models, the behaviour of the flow is determined by the relative magnitudes of the initial excess momentum flux, the buoyancy-generated momentum flux and the entrained ambient momentum flux. It is shown that ratios of these momentum fluxes are equivalent to the length-scales traditionally employed for this task. Predictions from the Momentum Model are compared with data from the current and previous experimental investigations and, in addition, predictions from two representative numerical models, VisJet and CorJet. Predictions from the Momentum Model are shown to be consistent with data for a wide variety of discharge configurations. These predictions are also generally consistent with those of VisJet and CorJet. However, the experimental results from the II buoyant jet discharged in a moving ambient show that the spreading rates of the strongly advected flows (puffs and thermals) differ, and while this difference is incorporated into the Momentum Model, it is not evident in the VisJet and CorJet predictions. Numerical model predictions of negatively buoyant discharges are shown to be inadequate. This discharge configuration is investigated in some detail experimentally and additional analytical solutions of the flow behaviour are developed to aid in the interpretation of the flow behaviour. The experimental results show that buoyancy-induced instabilities on the inner side of the jets, which generate additional vertical mixing, significantly alter the form of the mean concentration profiles in this region. This results in considerably higher integrated dilutions along the flow centreline. Another significant difference between the newly developed Momentum Model and the existing numerical models (VisJet and CorJet), is the approach taken to dealing with oblique discharges in a cross-flow. Experimental results in combination with additional analytical solutions show that for initial discharge angles of 20° and less, an oblique discharge in a cross-flow becomes a weak-jet in the strongly advected region, and for angles of 40° and above, the flow becomes a puff. The strongly advected behaviour predicted by the Momentum Model changes abruptly at the transition angle, and is reasonably consistent with the data. The gradual change in strongly advected behaviour employed by VisJet and CorJet does not appear to be appropriate in the puff region. Finally a preliminary experimental investigation of discharges with three-dimensional trajectories shows that there are significant discrepancies between the predicted behaviour and the experimental data. This is surprising given the numerical models are, for the most part, able to predict the behaviour of flows with two-dimensional paths with reasonable accuracy. It is evident that flows with three-dimensional paths are modified more severely by the different directions of the initial, buoyancy-generated, and entrained ambient momentum fluxes than the current models suggest.

Thesis (Ph. D.) -- University of Maryland, College Park, 2004.
Thesis research directed by: Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

The velocity and mixing field of two turbulent jets configurations have been experimentally characterized by means of cold- and hot-wire anemometry in order to investigate the effects of the initial conditions on the flow development. In particular, experiments have been focused on the effect of the separation wall between the two streams on the flow field. The results of the experiments have pointed out that the wake behind a thick wall separating wall has a strong influence on the flow field evolution. For instance, for nearly unitary velocity ratios, a clear vortex shedding from the wall is observable. This phenomenon enhances the mixing between the inner and outer shear layer. This enhancement in the fluctuating activity is a consequence of a local absolute instability of the flow which, for a small range of velocity ratios, behaves as an hydrodynamic oscillator with no sensibility to external perturbations. It has been suggested indeed that this absolute instability can be used as a passive method to control the flow evolution. Finally, acoustic excitation has been applied to the near field in order to verify whether or not the observed vortex shedding behind the separating wall is due to a global oscillating mode as predicted by the theory. A new scaling relationship has been also proposed to determine the preferred frequency for nearly unitary velocity ratios. The proposed law takes into account both the Reynolds number and the velocity ratio dependence of this frequency and, therefore, improves all the previously proposed relationships.

The velocity and mixing field of two turbulent jets configurations have been experimentally characterized by means of cold- and hot-wire anemometry in order to investigate the effects of the initial conditions on the flow development. In particular, experiments have been focused on the effect of the separation wall between the two streams on the flow field. The results of the experiments have pointed out that the wake behind a thick wall separating wall has a strong influence on the flow field evolution. For instance, for nearly unitary velocity ratios, a clear vortex shedding from the wall is observable. This phenomenon enhances the mixing between the inner and outer shear layer. This enhancement in the fluctuating activity is a consequence of a local absolute instability of the flow which, for a small range of velocity ratios, behaves as an hydrodynamic oscillator with no sensibility to external perturbations. It has been suggested indeed that this absolute instability can be used as a passive method to control the flow evolution. Finally, acoustic excitation has been applied to the near field in order to verify whether or not the observed vortex shedding behind the separating wall is due to a global oscillating mode as predicted by the theory. A new scaling relationship has been also proposed to determine the preferred frequency for nearly unitary velocity ratios. The proposed law takes into account both the Reynolds number and the velocity ratio dependence of this frequency and, therefore, improves all the previously proposed relationships.

Onboard offshore platforms the wear imposed on pipes used for the transport of gases can be severe. The transport pipes potentially contain highly flammable and explosive hydrocarbon gases and hence the dangers that can be created by a leaking joint are serious. In these offshore installations, to minimise the danger created by a hydrocarbon gas leak, companies and government agencies proposing to commission oil or gas platforms often complete a safety study. This study includesd etailso f safetyp roceduresa nd the potentiale ffectsc reatedb y leaks. At present the methods used are based on the assumption that the leaks are all from more well known circular cross-sectional jets. This project was initiated to study leaking flange joints which are a typical source for gas leaks. Many leak geometries and a range of pipeline pressures up to a maximum of 410kPa were studied to consider their effect on the resulting gas leak jet. Laser light sheet imaging was used to obtain flow visualisation images, with total pressure probe measurements providing valuable time-averaged data. This alloweda two-dimensionasl liceo f the emergingle akj et to be studiedi n detail with two very differenta nalyticatl echniques. A steady core was observed at the point of exit of each gas jet studied. The core was shown to be a region in which the shear layers, initiated at the jet boundaries, grow towards a merging point on the jet centreline. At this location, the velocity decay rate was found to increase as the jet entered into a second flow regionWithin this region, the rate of velocity decay was shown to be similar to that typically observed in a planar jet. This is much slower than would develop in a roundj et. At the downstreamli mit of the experimentaml easurementsa, t hird flow region was observed. The centreline velocity within this region showed no tendencyt o a lineard ecayr ate as would be foundi n a round cross-sectionje t. Significant differences were noted between the spreading angle of a round jet and those included in the present study. A wide range of spreading angles were observed, which suggests that it is unrealistic for all flange joint leaks to be represented by the round jet assumption. More specifically, because of the effect of spreading angle, the round jet assumption is likely to show discrepancies in predicting the magnitude of important parameters, such as the gas concentration levelsa nde ntrainmenrta tes. As safetys tudiesa re at presentb asedo n circularc ross-sectiojne t data, the findings of this report indicate that the validity of those safety studies is probably being compromised

Flow control can lead to saving millions of dollars in fuel costs each year by making an aircraft more efficient. Synthetic jets, a device for active flow control, operate by introducing small amounts of energy locally to achieve non-local changes in the flow field with large performance gains. These devices consist of a cavity with an oscillating diaphragm that divides it, into active and passive sides. The active side has a small opening where a jet is formed, whereas and the passive side does not directly participate in the fluidic jet.Research has shown that the synthetic jet behavior is dependent on the diaphragm and the cavity design hence, the focus of this work. The performance of the synthetic jet is studied under various factors related to the diaphragm and the cavity geometry. Four diaphragms, manufactured from piezoelectric composites, were selected for this study, Bimorph, Thunder®, Lipca and RFD. The overall factors considered are the driving signals, voltage, frequency, cavity height, orifice size, and passive cavity pressure. Using the average maximum jet velocity as the response variable, these factors are individually studied for each actuator and statistical analysis tools were used to select the relevant factors in the response variable. For all diaphragms, the driving signal was found to be the most important factor, with the sawtooth signal producing significantly higher velocities than the sine signal. Cavity dimensions also proved to be relevant factors when considering the designing of a synthetic jet actuator. The cavities with the smaller orifice produced lower velocities than those with larger orifices and the cavities with smaller volumes followed the same trend. Although there exist a relationship between cavity height and orifice size, the orifice size appears as the dominant factor.Driving frequency of the diaphragm was the only common factor to all diaphragms studied that was not statistically significant having a small effect on jet velocity. However along with waveform, it had a combined effect on jet velocity for all actuators. With the sawtooth signal, the velocity remained constant after a particular low frequency, thus indicating that the synthetic jet cavity could be saturated and the flow choked. No such saturation point was reached with the sine signal, for the frequencies tested. Passive cavity pressure seemed to have a positive effect on the jet velocity up to a particular pressure characteristic of the diaphragm, beyond which the pressure had an adverse effect. For Thunder® and Lipca, the passive cavity pressure that produced a peak was measured at approximately 20 and 18kPa respectively independent of the waveform utilized. For a Bimorph and RFD, this effect was not observed.Linear models for all actuators with the factors found to be statistically significant were developed. These models should lead to further design improvements of synthetic jets.

An experimental investigation of collisions between supersonic plasma jets with metal foils and head-on collisions of two jets will be presented. The jets are produced by ablation of thin aluminium foils driven by 1.4MA, 250ns current pulse in a radial foil Z-pinch configuration. The jets propagate with velocity of 50-100km/s, showing a high degree of collimation (opening angle 2 [degrees] to 5 [degrees]) and are radiatively cooled (cooling time << hydrodynamic times). Collisions of the jets with foils, as well as inter-jet collisions, create a system of strong shocks both in the central dense part of the jet and in the lower density halo plasma which surrounds the jet and moves with the same speed. The formed shock features are sustained for 300ns, and are diagnosed with laser interferometry, optical and XUV imaging, and Thomson scattering diagnostics. Interpretation of the results indicates that dynamically significant magnetic fields are present in the system, balancing the ram pressure of the flow and supporting extended stationary shock structures. The results are relevant to the studies of astrophysical phenomena in the laboratory, in particular internal shocks in jets from young stars, accretion shocks, and for the understanding of magnetised high energy density plasma flows.

Three dimensional nozzles and jet flows have attracted the attention of many researchers due to their potential application to many practical devices. Rectangular nozzles are considered for short/vertical take off and landing aircrafts for achieving powered lift. Axisymmetric nozzles with lobes, tabs or slots and elliptical nozzles are considered for noise reduction in aircrafts and mixing augmentation in airbreathing rockets. Interaction of supersonic jets with solid surface, as in the case of retro and ullage rockets in launch vehicles and interaction of multiple jets as in the case of launch vehicles with multiple booster rockets/multiple nozzle engines are of practical importance. Design of rockets and aircrafts employing these nozzles needs the understanding of the structure and behaviour of the complex three dimensional supersonic jets issuing from these nozzles. The problem is so complex that different investigators have addressed only some specific aspects of the problem and there is much more to be done to fully understand these flows. For example, in the case of rectangular nozzle with semi circular ends (known as elliptical nozzle), the investigations have been limited to a single nozzle of aspect ratio 3,0 and pressure ratio (ratio of the total pressure to ambient pressure) 3.0. Further, the measurements were made in the far field subsonic region beyond a distance of 20 times the equivalent nozzle radius (RJ. For the present study, the elliptical sonic nozzle of the type mentioned above was chosen, as it offered simplicity for manufacturing and carrying out computations, but has all the complex features associated with the three dimensional jets. A systematic study to understand the mean flow structure and the effect of important governing parameters like ratio and pressure ratio on the flow development process of the jet issuing from Navier-Stokes equations. The experimental study revealed many interesting flow features. It was found that the Underexpanded jet issuing from elliptical sonic nozzle spreads rapidly in the minor axis plane while it maintains almost constant width or contracts in the major axis plane. However, the gross spreading of this jet is much higher compared to the axisymmetric jet. The higher spreading rates experienced in the minor axis plane compared to the major axis plane of this 'et, results in the jet width in the minor axis plane to become higher than that in the major axis plane. The longitudinal location, where this occurs is called the axis switching location. This kind of axis switching phenomenon is known to exist for subsonic elliptical jets. However, for the present supersonic jets, the axis switching locations are much closer to the nozzle exit compared to the subsonic cases reported. It was further found that this location strongly depends on the pressure and aspect ratios. A critical pressure ratio was found to exist for each nozzle at which the axis switching location is the farthest. Above the critical pressure ratio, the axis switching location was observed to move upstream with the increase in the pressure ratio and is controlled by the complex interactions of shock and expansion waves near the nozzle exit. Below the critical pressure ratio, the axis switching location moves upstream with the decrease in pressure ratio and is controlled by some kind of instability in the minor axis plane. The shock structure present in the underexpanded jet from an elliptical nozzle was also observed to depend on both pressure and aspect ratios. For some aspect ratios and pressure ratios, the shock pattern observed in both the major and minor axis planes are similar to that of an axisymmetric jet, where the incident barrel shock and the Mach reflection (from the edges of the Mach disk) are present. But for all other cases, this shock continues to be seen only in the major axis plane. Whereas, in the minor axis plane, the incident shock is absent in the shock pattern. Detailed measurement in the jet cross sectional planes, for the case of aspect ratio 2.0 nozzle, shows that the cross sectional shape changes along the length and it becomes almost a circle at the axis switching location. Further downstream, the jet spreads rapidly in the minor axis plane whereas no significant change in the width of the jet in the major axis plane is observed. Far downstream, the jet boundary appears like a distorted ellipse with its major and minor dimensions lying respectively in the minor and major axis planes of the nozzle. The elongated shape of the jet cross sections at locations downstream of the axis switching point gives the impression that the entire flow in the major axis plane is turned towards the minor axis plane. This effect appears to be predominant at high pressure ratios. The computed near field shock structure in the planes of symmetry, pitot pressure distributions, cross sectional shape of the jet and the spreading pattern agree very well with the experimental results. In addition to this, the present computational method gives the detailed near field flow structure including the azimuthal extent of the incident shock, cross flow details and distributions of flow variables. It is shown that the present inviscid methodology can also predict the axis switching point accurately if it occurs before the formation of the Mach disk and it demonstrates that the jet growth phenomenon in the near field, atleast, is mainly controlled by the inviscid flow process. The computed results have shown that changes in the jet cross sectional shape in the near field is caused mainly by the interaction of compression and expansion waves with each other and with the constant pressure boundary. The inviscid method seems to be able to capture the complicated secondary cross flow structure (indicating presence of longitudinal vortices) of the elliptical jet. The complex mean flow structure in the near field region of the jet issuing from elliptical nozzles and the effect of nozzle aspect ratio and pressure ratio on the structure are brought out clearly in the present study. The mechanism governing the spreading and the axis switching characteristics are also brought out. Thus the present experimental and computational investigations give a comprehensive understanding of the mean flow structure of the underexpanded jets issuing from elliptical nozzles. Further studies are required to understand the other aspects of the elliptical jets as well as other three-dimensional jets. Some of these studies are identified for future work.

Three dimensional nozzles and jet flows have attracted the attention of many researchers due to their potential application to many practical devices. Rectangular nozzles are considered for short/vertical take off and landing aircrafts for achieving powered lift. Axisymmetric nozzles with lobes, tabs or slots and elliptical nozzles are considered for noise reduction in aircrafts and mixing augmentation in airbreathing rockets. Interaction of supersonic jets with solid surface, as in the case of retro and ullage rockets in launch vehicles and interaction of multiple jets as in the case of launch vehicles with multiple booster rockets/multiple nozzle engines are of practical importance. Design of rockets and aircrafts employing these nozzles needs the understanding of the structure and behaviour of the complex three dimensional supersonic jets issuing from these nozzles. The problem is so complex that different investigators have addressed only some specific aspects of the problem and there is much more to be done to fully understand these flows. For example, in the case of rectangular nozzle with semi circular ends (known as elliptical nozzle), the investigations have been limited to a single nozzle of aspect ratio 3,0 and pressure ratio (ratio of the total pressure to ambient pressure) 3.0. Further, the measurements were made in the far field subsonic region beyond a distance of 20 times the equivalent nozzle radius (RJ. For the present study, the elliptical sonic nozzle of the type mentioned above was chosen, as it offered simplicity for manufacturing and carrying out computations, but has all the complex features associated with the three dimensional jets. A systematic study to understand the mean flow structure and the effect of important governing parameters like ratio and pressure ratio on the flow development process of the jet issuing from Navier-Stokes equations. The experimental study revealed many interesting flow features. It was found that the Underexpanded jet issuing from elliptical sonic nozzle spreads rapidly in the minor axis plane while it maintains almost constant width or contracts in the major axis plane. However, the gross spreading of this jet is much higher compared to the axisymmetric jet. The higher spreading rates experienced in the minor axis plane compared to the major axis plane of this 'et, results in the jet width in the minor axis plane to become higher than that in the major axis plane. The longitudinal location, where this occurs is called the axis switching location. This kind of axis switching phenomenon is known to exist for subsonic elliptical jets. However, for the present supersonic jets, the axis switching locations are much closer to the nozzle exit compared to the subsonic cases reported. It was further found that this location strongly depends on the pressure and aspect ratios. A critical pressure ratio was found to exist for each nozzle at which the axis switching location is the farthest. Above the critical pressure ratio, the axis switching location was observed to move upstream with the increase in the pressure ratio and is controlled by the complex interactions of shock and expansion waves near the nozzle exit. Below the critical pressure ratio, the axis switching location moves upstream with the decrease in pressure ratio and is controlled by some kind of instability in the minor axis plane. The shock structure present in the underexpanded jet from an elliptical nozzle was also observed to depend on both pressure and aspect ratios. For some aspect ratios and pressure ratios, the shock pattern observed in both the major and minor axis planes are similar to that of an axisymmetric jet, where the incident barrel shock and the Mach reflection (from the edges of the Mach disk) are present. But for all other cases, this shock continues to be seen only in the major axis plane. Whereas, in the minor axis plane, the incident shock is absent in the shock pattern. Detailed measurement in the jet cross sectional planes, for the case of aspect ratio 2.0 nozzle, shows that the cross sectional shape changes along the length and it becomes almost a circle at the axis switching location. Further downstream, the jet spreads rapidly in the minor axis plane whereas no significant change in the width of the jet in the major axis plane is observed. Far downstream, the jet boundary appears like a distorted ellipse with its major and minor dimensions lying respectively in the minor and major axis planes of the nozzle. The elongated shape of the jet cross sections at locations downstream of the axis switching point gives the impression that the entire flow in the major axis plane is turned towards the minor axis plane. This effect appears to be predominant at high pressure ratios. The computed near field shock structure in the planes of symmetry, pitot pressure distributions, cross sectional shape of the jet and the spreading pattern agree very well with the experimental results. In addition to this, the present computational method gives the detailed near field flow structure including the azimuthal extent of the incident shock, cross flow details and distributions of flow variables. It is shown that the present inviscid methodology can also predict the axis switching point accurately if it occurs before the formation of the Mach disk and it demonstrates that the jet growth phenomenon in the near field, atleast, is mainly controlled by the inviscid flow process. The computed results have shown that changes in the jet cross sectional shape in the near field is caused mainly by the interaction of compression and expansion waves with each other and with the constant pressure boundary. The inviscid method seems to be able to capture the complicated secondary cross flow structure (indicating presence of longitudinal vortices) of the elliptical jet. The complex mean flow structure in the near field region of the jet issuing from elliptical nozzles and the effect of nozzle aspect ratio and pressure ratio on the structure are brought out clearly in the present study. The mechanism governing the spreading and the axis switching characteristics are also brought out. Thus the present experimental and computational investigations give a comprehensive understanding of the mean flow structure of the underexpanded jets issuing from elliptical nozzles. Further studies are required to understand the other aspects of the elliptical jets as well as other three-dimensional jets. Some of these studies are identified for future work.

La Cromodinàmica Quàntica (QCD) és la teoria de camps que descriu les interaccions fortes entre quarks i gluons. La signatura més destacada de QCD en col·lisionadors hadrúnics és la producció de jets col·limats d'hadrons. La mesura de la producció d'aquests jets associats amb un bosó vectorial, W o Z/gamma*, proporciona un test estricte dels càlculs pertorbatius de QCD (pQCD). A més a més, alguns processos de nova física en col·lisionadors hadrúnics, com ara la producciÓ del bosó de Higgs i partícules supersimètriques, poden ser molt semblants a la producció de bosons vectorial associats amb jets que constitueixen un fons irreductible en aquestes cerques. Per tant l'estudi i comprensió de processos Z/gamma*+jets és una part crucial del programa de física del col·lisionador Tevatron. Durant el Run I del Tevatron, protons i antiprotons col·lidien amb una energia en el centre de masses sqrt(s) de 1.8 TeV. La producciÓ de Z/gamma*+jets es va estudiar durant el Run I amb el detector CDF utilitzant 106 pb-1 de dades. Les mesures es van comparar amb les prediccions de l'ordre més baix en teoria de pertorbacions (LO) més parton shower d'alguns generadors de Monte Carlo. Les comparacions estaven dominades per les grans incerteses en les prediccions de LO. En el Run II, el Tevatron i el detector CDF es van millorar i, entre d'altres importants millores, sqrt(s) es va augmentar a 1.96 TeV. El bon funcionament de l'accelerador i del detector van proporcionar una quantitat més gran de dades que va fer possible mesures diferencials de gran precisió.
Aquesta tesi doctoral presenta la mesura de seccions eficaces inclusives de jets en esdeveniments amb Z/gamma*->ee utilitzant 1.7 fb-1 de dades obtingudes amb el detector CDF durant el Run II del Tevatron. L'algoritme de con Midpoint s'ha utilitzat per a buscar jets en els esdeveniments després d'haver identificat la presència d'un bosó Z/gamma* a través de la reconstrucció dels productes de la seva desintegració. Les mesures s'han comparat amb les prediccions del següent nivell (NLO) en pQCD per esdeveniments amb un o dos jets en l'estat final. Les prediccions pertorbatives s'han corregit per les contribucions de processos no-pertorbatius, com l'underlying event i la fragmentació dels partons en jets d'hadrons. Aquests processos no són descrits per la teoria de pertorbacions i s'han d'estimar amb models fenomenològics. En aquesta tesi, s'han realitzat un conjunt de mesures per a testejar diferents models d'underlying event i hadronització implementats en programes de Monte Carlo de LO més parton shower.
Quantum Chromodynamics (QCD) is the field theory that describes the strong interactions between quarks and gluons. The most prominent signature of QCD at hadron colliders is the production of collimated jets of hadrons. The measurement of the production of such jets in association with a vector boson, W or Z/gamma*, provides an stringent test of perturbative QCD (pQCD) calculations. Furthermore, some of new physics processes at hadron colliders, such as the production of Higgs bosons and supersymmetric particles, can be mimicked by the production of vector bosons in association with jets that constitute irreducible backgrounds to these searches. Therefore, the study and understanding of Z/gamma*+jets processes is a crucial part of the physics program of the Tevatron collider. At the Run I of the Tevatron, protons and antiprotons collided with an energy in the center-of-mass ps of 1.8 TeV. Z/gamma*+ jets production was studied during Run I with the CDF detector using 106 pb-1 of data. The measurements were compared to the predictions from leading order (LO) plus parton shower Monte Carlo generator programs. The comparisons were mainly dominated by the large scale uncertainties in the LO predictions. In Run II, the Tevatron and the CDF detector were upgraded and, among other important improvements, sqrt(s) was increased to 1.96 TeV. The good performance of the accelerator and the detector made available a larger amount of data, making possible precise differential measurements.
This Ph.D. thesis presents the measurement of inclusive jet cross sections in Z/gamma*(->ee) events using 1.7 fb-1 of data collected by the upgraded CDF detector during the Run II of the Tevatron. The Midpoint cone algorithm is used to search for jets in the events after identifying the presence of a Z/gamma* boson through the reconstruction of its decay products. The measurements are compared to next-to-LO (NLO) pQCD predictions for events with one and two jets in the final state. The perturbative predictions are corrected for the contributions of non-perturbative processes, like the underlying event and the fragmentation of the partons into jets of hadrons. These processes are not described by perturbation theory and must be estimated from phenomenological models. In this thesis, a number of measurements are performed to test different models of underlying event and hadronization implemented in LO plus parton shower Monte Carlo generator programs.

This study presents air distribution systems that are based on confluent jets; this system can be of interest for the establishment of indoor environments, to fulfill the goals of indoor climate and energy-efficient usage. The main objective of this study is to provide deeper understanding of the flow field development of a supply device that is designed based on wall confluent jets and to investigate the ventilation performance by experimental and numerical methods. In this study, the supply device can be described as an array of round jets on a flat surface attached to a side wall. Multiple round jets that issue from supply device apertures are combined at a certain distance downstream from the device and behave as a united jet or so-called confluent jets. Multiple round jets that are generated from the supply device move downward and are attached to the wall at the primary region, due to the Coanda effect, and then they become wall confluent jets until the floor wall is reached. A wall jet in a secondary region is formed along the floor after the stagnation region. The characteristics of the flow field and the ventilation performance of conventional wall confluent jets and modified wall confluent jets supply devices are investigated experimentally in an office test room. The study of the modified wall confluent jets is intended to improve the efficiency of the conventional one while maintaining acceptable thermal comfort in an office environment. The results show that the modified wall confluent jets supply device can provide acceptable thermal comfort for the occupant with lower airflow rate compared to the conventional wall confluent jets supply device. Numerical predictions using three turbulence models (renormalization group (RNG k– ε), realizable (Re k– ε), and shear stress transport (SST k– ω) are evaluated by measurement results. The computational box and nozzle plate models are used to model the inlet boundary conditions of the nozzle device. In the isothermal study, the wall confluent jets in the primary region and the wall jet in the secondary region, when predicted by the three turbulence models, are in good agreement with the measurements. The non-isothermal validation studies show that the SST k– ω model is slightly better at predicting the wall confluent jets than the other two models. The SST k– ω model is used to investigate the effects of the nozzle diameter, number of nozzles, nozzle array configuration, and inlet discharge height on the ventilation performance of the proposed wall confluent jets supply device. The nozzle diameter and number of nozzles play important roles in determining the airflow pattern, temperature field, and draught distribution. Increased temperature stratification and less draught distribution are achieved by increasing the nozzle diameter and number of nozzles. The supply device with smaller nozzle diameters and fewer nozzles yields rather uniform temperature distribution due to the dominant effect of mixing. The flow behavior is nearly independent of the inlet discharge height for the studied range. The proposed wall confluent jets supply device is compared with a mixing supply device, impinging supply device and displacement supply device. The results show that the proposed wall confluent jets supply device has the combined behavior of both mixing and stratification principles. The proposed wall confluent jets supply device provides better overall ventilation performance than the mixing and displacement supply devices used in this study. This study covers also another application of confluent jets that is based on impinging technology. The supply device under consideration has an array of round jets on a curve. Multiple jets issue from the supply device aperture, in which the supply device is positioned vertically and the jets are directed against a target wall. The flow behavior and ventilation performance of the impinging confluent jets supply device is studied experimentally in an industrial premise. The results show that the impinging confluent jets supply device maintains acceptable thermal comfort in the occupied zone by creating well-distributed airflow during cold and hot seasons.

An experimental study was designed to investigate the effect of different parameters on the development and structure of turbulent 3D offset jets. The present investigation considered the effects of offset height ratio, expansion ratio, surface roughness and rib placement on the flow dynamics of a turbulent 3D offset jet. The velocity measurements were performed using an acoustic Doppler velocimetry (ADV) and particle image velocimetry (PIV). Measurements were conducted within the symmetry and lateral planes. For the PIV technique, the measurements in the symmetry and lateral planes were conducted over a streamwise range of 0 ≤ x/bo ≤ 80 and 12 ≤ x/bo ≤ 60, respectively (where bo is the nozzle height). Likewise, velocity measurements using the ADV technique were conducted over a range of 4 ≤ x/bo ≤ 45 in both the symmetry and lateral planes. The velocity measurements were analyzed using both one-point and multi-point statistics. The one-point statistics included profiles of the mean velocities, Reynolds stresses and some of the budget terms in the turbulent kinetic energy transport equation. The quadrant analysis technique was used to investigate the dominant events that contribute towards the Reynolds shear stress. The two-point correlation analysis was used to investigate how the turbulence quantities are correlated. Information obtained from the two-point correlation analysis was also used to investigate the inclination of vortical structures within the inner and outer shear layers of the 3D offset jet. The direction of the positive mean shear gradient played an active role in the inclination of these vortical structures within the inner and outer shear layers. The reattachment process resulted in the breakdown of these structures within the developing region. Similarly, various length scales were estimated from these structures. The proper orthogonal decomposition was used to examine the distribution of the turbulent kinetic energy within the offset jet flow. Also, the dynamic role of the large scale structures towards the turbulent intensities, turbulent kinetic energy and Reynolds shear stress was investigated.
October 2016

In recent years, application of confluent jets for design of ventilation supply devices has been studied. Similarly, numerus studies have been made on the potential and application of variable air volume (VAV) in order to reduce the energy demand of ventilation systems. This study investigates the combination of supply devices based on confluent jets and VAV, both in terms of the nearfield flow behavior of the device and the impact on thermal comfort, indoor air quality and energy efficiency on a classroom-level space when the airflow rate is varied. The method used in this study is an experimental field study where the confluent jets-based supply devices were compared to the previously installed displacement ventilation. The field study evaluated the energy efficiency, thermal comfort and indoor air quality of the two systems. In the case of the confluent jets supply devices, airflow rate was varied in order to see what impact the variation had on the performance of the system for each airflow rate. Furthermore, the confluent jets supply devices were investigated both experimentally and numerically in a well insulated test room to get high resolution data on the particular flow characteristics for this type of supply device when the airflow rate is varied. The results from the field study show nearly uniform distribution of the local mean age of air in the occupied zone, even in the cases of relatively low airflow rates. The airflow rates have no significant effect on the degree of mixing. The thermal comfort in the classroom was increased when the airflow rate was adapted to the heat load compared to the displacement system. The results lead to the conclusion that the combination of supply devices based on confluent jets can reduce energy usage in the school while maintaining indoor air quality and increasing the thermal comfort in the occupied zone. The results from the experimental and numerical study show that the flow pattern and velocity in each nozzle is directly dependent on the total airflow rate. However, the flow pattern does not vary between the three different airflow rates. The numerical investigation shows that velocity profiles for each nozzle have the same pattern regardless of the airflow rate, but the magnitude of the velocity profile increases as the airflow increases. Thus, a supply device of this kind could be used for variable air volume and produce confluent jets for different airflow rates. The results from both studies show that the airflow rate does not affect the distribution of the airflow on both near-field and room level. The distribution of air is nearly uniform in the case of the near-field results and the room-level measurement shows a completely uniform degree of mixing and air quality in the occupied zone for each airflow rate. This means that there is potential for combining these two schemes for designing air distribution systems with high energy efficiency and high thermal comfort and indoor air quality.
Under senare tid har applikation av Confluent jets för design av tilluftsdon studerats. Många studier har även utförts över potentialen av att applicera variabelt luftflöde (VAV) för att minska energianvändningen i ventilationssystem. Denna studie undersöker möjligheten att kombinera Confluent jets-don med VAV, både med avseende på den lokala flödesbilden och dess påverkan på termisk komfort, luftkvalitet och energieffektivitet i en klassrumsmiljö där luftflödes varieras. Denna studie baseras dels på en experimentell fältstudie där tilluftsdon baserade på Confluents jets jämfördes med befintliga deplacerande tilluftsdon. Fältstudien utvärderade energieffektiviteten, den termiska komforten och luftkvaliteten för båda typerna av tillluftsdon. Confluent jets-donen testades under varierat luftflöde för att se påverkan av flödesvariationen på ventilationens prestation under de olika flödena. Utöver fältstudien testades Confluent jets-donen experimentellt och numeriskt i ett välisolerat test-rum för få den detaljerade flödeskarakteristiken för den här typen tilluftsdon vid varierat luftflöde. Resultaten från fältstudien visar på en jämn fördelning av den lokala luftsmedelåldern i vistelsezonen, även för fallen med relativt låga luftflöden. Luftflöden har ingen signifikant effekt på omblandningen. Den termiska komforten i klassrummet ökade när luftflödet anpassades efter värmelasten jämfört med de deplacerande donen. Slutsatsen från fältstudien är att kombinationen av VAV och Confluent jets-don kan användas för att minska energianvändningen på skolan och bevara luftkvaliteten och den termiska komforten i vistelsezonen. Resultaten från den experimental och numeriska studien visar luftflödet och lufthastigheten i varje enskild dysa är direkt beroende på det totala luftflödet genom donet. Dock är flödesfördelningen mellan dysorna oberoende av de tre olika luftflödena. Den numeriska undersökningen visar att flödesprofilen för varje dysa är konstant trots att flödet varieras, men amplituden för varje profil ökar med en höjning av luftflödet. Det betyder att tilluftsdon av den här typen kan användas med VAV för att producera Confluent jets för olika luftflöden. Resultaten från båda studierna visar att luftflöde inte påverkar fördelningen av luften vare sig längs luftdonen eller på rumsnivå. Fördelningen av luften är nästan helt jämn längs donen och på rumsnivå är omblandningen och luftkvalitet den samma för varje luftflöde. Det betyder att det finns potential för att kombinera det här två teknikerna för att designa luftdistribueringssystem med hög energieffektivitet och hög termisk komfort med god luftkvalitet.

Convective heat transfer and drying processes are found in industrial applications from gas turbine blade cooling to drying of food products and paper. In many instances, these processes rely on either a single or an array of fluid jets which impinge onto a surface. Traditionally, non-swirling impinging jets have been used, but interest surrounds possible advantages from imposing swirl into these jets to further promote heat and mass transfer at the surface. The challenge of resolving this question is that including swirl further complicates fluid-surface interactions. Studies are faced with the complexity of flow behaviour, the need for intricate measurement techniques and jets which seamlessly transition from non-swirling to swirling with well-defined boundary conditions. To better understand the nature of turbulent jet impingement with, and without, swirl requires carefully designed experiments covering parameters believed to affect the magnitude and uniformity of heat transfer. This research investigated, experimentally and numerically, incompressible turbulent impinging air jets using aerodynamically derived swirl. The aim was to elucidate the effects of different parameters on fluid flow and surface heat transfer characteristics. Measurements of mean velocity and turbulence, surface pressure and temperatures were done using Constant Temperature Anemometry, integrating micro-manometer (pressure) tappings and steady-state heated thin foil technique via infrared thermography. Imaging for flow visualisations was also done. Numerical simulations were performed using ANSYS Fluent (version 14.5). Test conditions investigated encompassed a range of Reynolds numbers (Re = 11,600 – 35,000), swirl numbers (S = 0 – 1.05) and nozzle-to-plate distances (H = 1D – 6D). Results show that the use of low-to-medium swirl numbers (S = 0.27 – 0.45) is found to improve heat transfer (Nu) in the impingement region compared to non-swirling (S = 0) jets over H ≤ 4D, with little improvement in spatial Nu uniformity. When S further increases, significant enhancement in Nu occurs only at near-field impingement (H ≤ 2D), regardless of the impingement area (footprint). At H ≥ 4D, a significantly low but more uniform radial profile of Nu is obtained. Results conclude the effect of swirl on the heat transfer characteristics is a complex relationship, which depends on the Reynolds number and nozzleto- plate distance. Whilst high swirl can lead to significant improvements in heat transfer, this is not necessarily always the case. It appears that there exist a threshold impingement distance and a transitional swirl number (dependent on Re) over which the effect of swirl on field and turbulence at different swirl numbers and nozzle-to-plate distances, with flow recirculation in near-field impingement (H = 2D) and non-swirl like at far-field (H = 6D). The occurrence of peak heat transfers at different swirl numbers is largely correlated with swirl induced turbulence characteristics near the impingement surface. Increase in Reynolds number augments the magnitude of Cp and heat transfer. For a given S, flow field and heat transfer distributions are found to be largely independent of Re.

Cette thèse a été réalisée au sein du groupe D0 de l'Institut de Physique Nucléaire à Lyon. Le travail a porté sur l'étalonnage en énergie des jets pour l'expérience D0 située sur Tevatron, accélérateur proton-antiproton. Nous avons étudié la contribution de l'énergie sous-jacente sur l'énergie des jets. Nous avons également proposé une nouvelle méthode pour étalonner les jets issus de la fragmentation d'un quark b. Nous avons évalué la réponse de ces jets grâce à des événéments photons + b - jets.

El model estandar (ME) és actualment el marc teòric més complet que descriu la física de les partícules elementals. En ell s'hi descriuen les partícules de matèria (fermions) i les seves interaccions (bosons). Fins ara no s'ha trobat cap desviació significativa entre l'experiment i les prediccions del model. Així i tot, el ME no pot ser la teoria final que descriu la física de partícules perquè pateix dificultats teòriques importants a més altes energies. Una de les possibles extensions del ME amb més acceptació és la Supersimetria (SUSY) que relaciona masses i acoblaments entre bosons i fermions. D'aquesta forma, per cada bosó existent al ME ha d'existir una "super-parella" fermiònica i a l'inrevés. A més, una altra simetria anomenada "paritat R" s'hi acostuma a introduir per tal d'evitar la violació del nombre bariònic i leptònic. Si això és així, aquestes noves partícules, que apareixerien a l'escala energètica dels TeV, s'haurien de formar per parelles i no podrien desintegrar-se completament en partícules del ME. Això implica l'existència d'una partícula supersimètrica que sigui la més lleugera de totes (LSP), la qual serà estable i un candidat a explicar la presència de matèria fosca freda a l'univers.
Precisament l'escala energètica dels TeV és el rang d'energies accessible per al col·lisionador protó-antiprotó Tevatron (Fermilab). Tevatron i els seus dos experiments, els detectors CDF i D0 van ser preparats per l'anomenat "Run II" en el que les col·lisions se succeeixen cada 396 ns amb un centre de masses d'1.96 TeV. Degut a què les noves partícules són molt massives, es desintegren en cascades amb múltiples raigs de partícules (jets) d'alt moment transversal. Quan la paritat R es conserva, dos LSP són produïts que escapen del detector deixant un important desequilibri en el balanç energètic del succés.
Aquesta tesi tracta de la recerca de les super-parelles dels quarks (squarks) i gluons (gluinos) en múltiples jets i energia transversa mancant, amb les dades recollides amb el detector CDF durant gran part del Run II (371 pb-1 de lluminositat). Per aquest motiu, s'ha dut a terme un estudi curós de les condicions del feix i dels diferents processos del ME que tenen estats finals similars al senyal. Diferents talls per reduir la seva presència tot potenciant el possible senyal s'han estudiat i optimitzat. També s'han considerat les diferents fonts d'errors experimentals i teòrics per tal de fer una bona caracterització de les dades.
Observant les dades, no s'ha trobat cap desviació significativa de les prediccions del ME. Degut a aquests resultats, s'han posat límits inferiors a la massa squarks i gluinos (menor de 387 GeV/c2) en un determinat escenari del model teòric anomenat mSUGRA.
Aquest estudi és pioner al Run II de CDF i els resultats presenten millores significatives respecte a anteriors límits. En aquest sentit, el present treball constitueix la base i serà la referència per a futures extensions amb més dades.

Aquesta tesis presenta resultats sobre la recerca de nova física, usant 20.3 fb-1 de col·lisions protó-protó a una energia al centre de masses de √s = 8 TeV, enregistrades per l’experiment ATLAS a l’LHC. Per realitzar l’anàlisis, events de monojet han estat seleccionats, caracteritzats per la presència d’un jet molt energètic, alta energia transversa faltant (ET miss), un màxim de tres jets i cap leptó reconstruït. Per a tenir sensitivitat als diferents models de nova física estudiats, sis regions de senyal han estat definides, basades en diferents llindars de pT i ET miss, entre 280 GeV i 600 GeV. Els processos del Model Estàndard (SM) que superen les condicions de les regions de senyal estan dominats per l’irreduïble Z(νν)+jets, que representa més del 50% del background total. El segon procés de background més important és el W(τν)+jets, que entra a les regions de senyal quan el leptó τ decau hadrònicament. Les contribucions de W(ℓν)+jets i Z(ℓℓ)+jets també són importants, quan els leptons no són reconstruïts o són confosos per jets. Altres backgrounds minoritaris com els processos en què hi ha tops involucrats, o processos de dibosons, representen fins a un 6%, i són estimats directament per les simulacions de MC. Les contribucions de multijet i de non-collision background són negligibles en la majoria de les regions de senyal, i han estat estimades a partir de les dades. L’ús de regions de control permet extreure les normalitzacions dels diferents processos de W/Z+jets, així com també reduir de forma significativa la incertesa sistemàtica total, d’entre un 20% a un 30%, a valors entre un 3% i un 10%, per les diferents regions de senyal. Les estimacions dels processos del Model Estàndard concorden amb les dades. Els resultats s’han interpretat en termes de cotes superiors a la secció eficaç visible a un nivell de confiança (CL) del 95% independentment del model. Valors entre 96 fb i 5.2 fb han estat exclosos. Limits d’exclusió a un CL del 95% han estat calculats per models que involucren la producció de parelles d’squarks de tercera generació en escenaris comprimits. En particular, masses d’stops i sbottoms per sota de 260 GeV han estat excloses. També s’han calculat limits en la producció directa de parelles d’squarks de primera i segona generació, així com també de gluinos. Masses per squarks i gluinos per sota de 440 GeV i 600 GeV, respectivament, han estat excloses per escenaris comprimits. Els resultats d’aquest anàlisis també s’han interpretat en termes de models que involucren la producció directa de candidats a matèria fosca (DM). En particular, s’ha estudiat la producció directa de Weakly Interacting Massive Particles (WIMPs), gravitinos lleugers en escenaris supersimètrics mediats per interaccions de gauge, o producció directa d’electroweakinos. Finalment, els resultats s’han interpretat en termes del model ADD de dimensions extra.
This thesis presents results on the search for new phenomena using 20.3 fb-1 of proton-proton collision data at √s = 8 TeV, recorded with the ATLAS experiment at the LHC. Events with a very energetic jet, large missing transverse energy, a maximum of three reconstructed jets, and no reconstructed leptons are selected, leading to a monojet-like final state. Six signal regions with thresholds on the leading jet pT and ET miss ranging between 280 GeV and 600 GeV have been defined, in order to have sensitivity to a number of models. The Standard Model processes entering in the signal regions are dominated by the irreducible Z(νν)+jets, that accounts for more than 50% of the total background. The second most important background is the W(τν)+jets, which passes the signal region selection requirements when the τ-leptons decay hadronically. Contributions from W(ℓν)+jets and Z(ℓℓ)+jets processes are also important, when the leptons are not reconstructed or are misreconstructed as jets. Other minor backgrounds like the top and diboson contributions add up to about 6% and are estimated directly from MC simulations. The multijet and non-collision background contributions, negligible in most of the signal regions, are estimated with dedicated data-driven methods. The use of control regions, allows to extract the normalizations of the different W/Z+jets processes, and to significantly reduce the total systematic uncertainty, from 20% to 30%, to values between 3% and 10%, for the different signal regions. Good agreement is found between the data and the Standard Model background estimations. The results are interpreted in terms of model independent 95% confidence level (CL) upper limits on the visible cross section. Values in the range between 96 fb and 5.2 fb are excluded. Exclusion limits at 95% CL are set, for models involving the direct pair production of third generation squarks in very compressed scenarios. In particular, stop and sbottom masses below 260 GeV are excluded. Limits on the direct production of first and second generation squarks, or the direct production of gluinos, are also computed. Masses for squarks and gluinos below 440 GeV and 600 GeV are excluded for compressed scenarios, respectively. These limits extend the previous results from other dedicated searches. The results of this analysis are also interpreted in terms of models in which Dark Matter (DM) candidates are directly produced. Models involving Weakly Interacting Massive Particles (WIMPs), light gravitinos in Gauge Mediated Supersymmetric (GMSB) scenarios, or the direct production of electroweakinos, are studied. Finally, the monojet results are interpreted in terms of the ADD model of large extra dimensions

Foi construído um arranjo experimental para estudar o comportamento dos jatos evaporativos. Um injetor foi projetado para controlar e manter constantes a pressão e temperatura de reservatório durante a injeção. Um bocal cônico convergente de seção reta com diâmetro de saída de 0,30 mm e ângulo entre sua geratriz e seu eixo simetria igual à 10º forma o elemento principal do injetor. O jato é descarregado em uma câmara de baixa pressão de dimensões suficientemente grandes para manter a pressão constante durante o curto período de ensaio, igual à 1 s. Quando injetado, o líquido sofre uma repentina queda de pressão ocasionando sua evaporação. Os fluidos utilizados são os combustíveis querosene e óleo diesel, e a substância n-dodecano, os quais se caracterizam pela possibilidade de uma evaporação completa, de forma adiabática. Utilizou-se o método \"schlieren\" para a visualização do escoamento. A análise dos jatos é feita de forma qualitativa através dos registros fotográficos. Foram observados os seguintes tipos de jato: (1) contínuo, (2) pulverizante e (3) evaporação na superfície. O primeiro jato não implica em imediata mudança de fase tornando o jato de líquido emergente intacto. Com o aumento da temperatura de injeção, existe o espalhamento e a evaporação do jato, formando o segundo tipo de jato, onde é possível visualizar o campo do gradiente de densidade do escoamento e a formação de ondas de evaporação e de choque que pode ocorrer a uma distância proporcional a vários diâmetros à jusante. Em jatos com evaporação completa, foram constadas a formação de ondas de choque tanto de formas elipsóide como de esferóide para elevadas temperaturas. As fotografias digitais são submetidas à filtragem e processamento matemático para melhor destacar tais fenômenos do escoamento.
An experimental apparatus has been built to study the behaviour of flashing jets. An injector was designed to control and maintain the jet pressure and temperature at constant values during the injection process. A conical convergent nozzle whose main dimensions are 0,30 mm of exit diameter, 8 mm long, and a convergence half-angle of 10º is the central component of the injection system. The jet is discharged into a low-pressure chamber large enough to keep the reservoir pressure constant during the short test period of about 1 s. As the testing liquid expands in the nozzle it undergoes a sudden pressure drop causing its evaporation. The fluids are usual fuels, such as kerosene and diesel oil, and the substance ndodecane, which are distinguishable by the possibility of a complete evaporation in an isoentropic expansion process. The photographic method \"schlieren\" is used for flow visualisation. A qualitative analysis is made of the photographic documentation of the images obtained using a CCD camera. The images can be grouped into three categories of jets: (1) continuous, (2) shattering, and (3) with surface evaporation. The first regime has an undisturbed a liquid column, which remains more or less intact during the injection process. In the second type, the existing liquid jet is shattered by vapour nucleation and, in some cases, shock waves are clearly visible. It happens at higher temperature than the preceding evaporation mode. Finally, in special situations, the jet undergoes an evaporation at its surface and the two-phase mixture expands at a high speed followed by a shock wave before the mixture attains the pressure reservoir.

A series of experiments has been conducted for comparison with the results of a computer code called CHYMES. It is intended to calculate the coarse mixing of molten metal with water by solving the equations of the Separated Flow Model. These are derived by volume averaging and the terms that relate them to the particular case of participate flow are discussed. An experimental apparatus that is compatible with CHYMES and coarse mixing has been constructed which projects a jet of ball bearings into a thin tank of water. Experiments over a wide range of conditions were conducted at room temperature. Owing to practical difficulties only one, poorly controlled experiment with hot ball bearings was performed. Under nearly all sets of conditions an arrow-shaped plume was obtained. The speed of penetration of the plume varied little with changes in experimental conditions. The width of the plume was most strongly influenced by the widths of the tank and the jet. The individual paths of some particles were followed; it appeared that their motion was mostly dependent on their position in the plume. A model of the plume is proposed, based upon its front being impermeable to water in the vertical direction. Much of the detail of the experimental plumes was not present in the computational results and they responded differently to changes in conditions. It is proposed that this is a result of the different forms of the two sets of plumes. To rectify this an experimental plume was volume averaged. A method to determine a suitable averaging volume size is described. The process results in a plume similar to the computational ones. The length scales required for volume averaging to be successful are discussed and the possibility that this method is inappropriate for describing coarse mixing is admitted.

Definition des caracteristiquees du jet parietal. Historique du sujet. Theorie de glauert permettant l'existence d'une solution semblable selon laquelle la forme des profils de vitesse dans chaque section du jet reste inchangee le long du jet. Etude de la stabilite lineaire et non lineaire. Resolution de l'equation d'orr-sommerfeld en theorie temporelle et en theorie spatiale. Etude experimentale: mesure des vitesses en presence d'un corps bidimensionnel ou tridimensionnel, mesures de temperature

Després de 20 anys de preparació, el LHC s'encendrà a finals del 2009, col.lisionant protons a energies de 14TeV, per recrear els primers moments del Big Bang. Les partícules s'acceleraran al llarg del túnel circular de 27 km de circumferència fins a velocitats properes a la de la llum. El túnel, situat prop de Ginebra, i els seus experiments formen un dels més grans esforços de la història per estudiar l'estructura fonamental de la matèria. S'espera que a aquestes altes energies de col.lisió nous fenòmens físics puguin esdevenir i siguin descoberts. Entre les restes resultants de les col.lisions entre protons, evidències de dimensions extres, de la misteriosa matèria fosca que inunda el nostre univers o de la partícula de Higgs que dona massa a les partícules elementals, podran ser observades.
ATLAS és un dels experiments del LHC. A més a més del descobriment de nova Física en el seu programa, també està inclosa la investigació de la Física ja coneguda. Un millor coneixement de la teoria pertorbativa de Quantum Chromodynamics és un dels objectius d'ATLAS. QCD és la teoria que descriu les interaccions fortes entre quarks i gluons. Aquesta teoria encara roman sense resoldre, ja que no exiteix un mètode d'aproximació vàlid per qualsevol escala d'energies. La teoria pertorbativa de QCD pot descriure un gran nombre d'interaccions a altes energies. El seu formalisme ha donat una eina molt valuosa dins l'estudi de les interaccions fortes.
La signatura més notable dels processos QCD en col.lisionadors d'hadrons és la producció de jets de partícules col.limats. La mesura d'aquests jets en associació amb un bosó vector, W o Z, proporciona un test estricte dels càlculs de la teoria pertorbativa de QCD. A més, alguns dels processos de la nova Física, com la producció del bosó Higgs o de partícules supersimètriques, poden ser imitats per la producció dels bosons vectros en associació amb jets, que constitueixen un background irreduïble a l'investigació d'aquests nous processos.
Aquesta tesi presenta la mesura de la "inclusive jet cross section" en events amb un bosó Z(e,e,) o Z(mu,mu), comparant les prediccions teòriques amb les dades "real", i.e. events Monte Carlo "fully-reconstructed", pel primer 1fb-1 de dades obtingudes amb el detector ATLAS. Les dades reconstruïdes i corregides es comparen amb les prediccions de la teoria pertorbativa de QCD a nivell NLO i LO. Aquestes prediccions pertorbatives es corregeixen amb les contribucions de processos no pertorbatius, com l'underlying event o la fragmentació dels partons dins dels jets d'hadrons. Aquests processos no poden ser descrits per la teoria pertorbativa, i s'estimen amb models fenomenològics. S'han utilitzat dos tipus diferents de dades reconstruides Monte Carlo, ALPGEN i PYHTIA. S'han estudiat les comparacions entre les prediccions d'ambdós generadors. Els processos background han estat estimats utilitzant diferents mètodes "data-driven". Per la recerca dels jets, s'ha utilitzat l'algoritme ATLAS Cone 0.4, després d'identificar la presència d'un bosó Z mitjançant la reconstrucció del seu decaiment (electrons o muons). Les dades reconstruides han estat corregides pels efectes del detector, utilitzant factors independents.
Aquest anàlisi ha estat realitzat abans que ATLAS recollís les primeres dades reals, abans de l'inici del LHC, per aquest motiu aquesta tesi es basa en dades simulades amb generadors Monte Carlo. Mentres dura la preparació d'un experiment de Física d'altes energies com ATLAS, aquestes simulacions són molt importants pel desenvolupament d'estratègies eficaces d'anàlisi de dades i reconstrucció d'objectes físics mesurats pel detector.
Después de 20 años de preparación, el LHC va a encenderse a finales del 2009, colisionando protones a una energia de 14 TeV, para recrear los primeros momentos después del Big Bang. Las partículas serán aceleradas a lo largo del tunel circular de 27 km de circumferencia hasta velocidades próximas a la de la luz. El túnel, situado cerca de Ginebra, y sus experimentos forman uno de los más grandes esfuerzos de la história para estudiar la estructura fundamental de la materia. Se espera que a estas elevadas energías de colisión, nuevos fenómenos físicos puedan ocurrir y sean descubiertos. Entre los resultantes escombros de las colisiones entre protones, evidencias de dimensiones extras, de la misteriosa materia oscura que inunda nuestro universo o de la partícula de Higgs que da masa a las partículas elementales serán observadas.
ATLAS es uno de los experimentos del LHC. Además del descubrimiento de nueva Fisica en su programa, también está la investigación de la Fisica ya descubierta. Un mejor conocimiento de la teoría perturbativa de Quantum Chromodynamics es uno de los objetivos de ATLAS. Quantum Chromodynamics es la teoria de campos que describe las interacciones fuertes entre quarks y gluones. Esta teoría todavia permanece sin resolver, ya que no existe un método de aproximación válido para cualquier escalada de energía. La teoría perturbativa de QCD puede describir un gran numero de interacciones a altas energías. Su formulismo ha dado una herramienta muy valiosa en el estudio de las interacciones fuertes.
La signatura más notable de procesos QCD en collisionadores de hadrones es la producción de jets colimados de hadrones. La medición de estos jets en asociación con un bosón vector, W o Z, proporciona un test severo de los cálculos de la teoría perturbativa de QCD. Además, algunos de los procesos de nueva Física en los colisionadores de hadrones, como la production del boson de Higgs o de partículas supersimétricas, pueden ser imitados por la producción de bosones vectores en asociación con jets, que constituyen un background irreducible a la investigación de estos nuevos procesos.
Esta tesis presenta la medida de la "inclusive jet cross section" en sucesos con un boson Z (ee) o Z(mu,mu), comparando las prediciones teoricas con los datos "reales", i.e. sucesos Monte Carlo "fully-reconstructed", para el primer 1fb-1 de datos obtenidos con el detector ATLAS. Los datos reconstruidos y corregidos son comparados a las predicciones de la teoria perturbativa de QCD a nivel NLO y LO. Estas predicciones perturbativas se corrigen con las contribuciones de procesos no perturbativos, como el underlying event o la fragmentación de los partones en jets de hadrones. Estos procesos no pueden ser descritos por la teoria perturbativa, y son estimados con modelos fenomenologicos. Se han ultilizado dos tipos distintos de datos reconstruidos Monte Carlo, ALPGEN y PYTHIA. Comparaciones entre las predicciones de ambos generadores Monte Carlo han sido estudiadas. Los procesos background han sido estimados usando distintos métodos "data-driven". Para la búsqueda de jets se ha usado el algoritmo ATLAS Cone 0.4 jet, después de identificar la presencia de un bosón Z a través de la reconstrucción de su decaimiento (electrones o muones). Los datos reconstruidos son corregidos por los efectors del detector, usando factores independientes.
Este analisis ha sido realizado antes que ATLAS recogiera los primeros datos reales, antes del inicio del LHC, por este motivo esta tesis esta basada en datos simulados con generadores Monte Carlo. Mientras dura la preparación de un experimento de fisica de altas energías como ATLAS, estas simulaciones son de vital importancia para el desarrollo de estrategias eficaces de analisis de datos y reconstrucción de objetos físicos medidos por el detector.
After 20 years of preparation, the Large Hadron Collider is going to be switched on in late 2009, smashing protons at an energy of 14 (10) TeV, to recreate the first moments after the Big Bang. Particles will whizz around a circular tunnel of 27 km in circumference at near light speed. The tunnel, built near Geneva, and its experiments constitute one of the largest coordinated efforts ever made to study the fundamental structure of nature. It is expected that at the energies reached in the proton-proton collisions at the LHC, unknown physical phenomena will have to occur and will be observable. Among the particle debris may lie evidence for extra dimensions, mysterious dark matter that pervades the universe or the Higgs boson, which gives mass to elementary particles.
ATLAS is one of the LHC experiments. Besides the new phenomena goals in its physics program, there is the understanding of the already known physics. The better understanding of perturbative Quantum Chromodynamics theory is one of the aims of ATLAS. Quantum Chromodynamics is the field theory which describes the strong interaction between quarks and gluons. It remains an "unsolved" theory, since no single approximation method can be used to all length scales. Perturbative QCD naturally describes a large set of high-energy, large-momentum-transfer cross sections and its formalism has provided an invaluable tool in the study of the strong interactions. The most prominent signature of QCD at hadron colliders is the production of collimated jets of hadrons. The measurement of the production of such jets in association with a vector boson, W or Z, provides a stringent test of perturbative QCD (pQCD) calculations. Furthermore, some of new physics processes at hadron colliders, such as the production of Higgs bosons and supersymmetric particles, can be mimicked by the production of vector bosons in association with jets that constitute irreducible backgrounds to these searches.
This PhD. thesis presents the measurement of the inclusive jet cross section in Z → e+e− and in Z → μ+μ− events, comparing theory predictions with "real data", i.e. Monte Carlo fully-reconstructed events, for the first 1fb−1 of data at the ATLAS detector. Reconstructed corrected data is compared to next-to-LO (NLO) and LO pQCD predictions. Perturbative predictions are corrected for the contributions of the non-perturbative processes, like the underlying event and the fragmentation of the partons into jets of hadrons. These processes are not described by perturbation theory and must be estimated using phenomenological models. Two different reconstructed data are used, PYTHIA and ALPGEN Monte Carlo data. Comparisons of both Monte Carlo predictions are studied. Background processes are estimated proposing different data-driven methods to be applied to real data. ATLAS Cone 0.4 algorithm is used to look for jets in the events after identifying the presence of a Z boson through the reconstruction of its decay (electrons or muons). Reconstructed data is corrected for detector effects, using independent factors.
As this work was carried out before the "physics-data" start of the LHC, the presented studies are based on Monte Carlo simulations. During the preparation of a high-energy collider experiment, such simulations are important to develop efficient strategies for data analysis and for the reconstruction of the physics objects observed with the detectors.

The basis of mixing ventilation is the airflow supply to the room by means of jets initiatedfrom the ventilation diffusers. To avoid the draught problem, the design of mixing ventilationmakes uses the throw term, which is defined as the distance to the supply air terminal inwhich the jet centreline mean velocity is decreased to a given value. Traditionally, the throw ismeasured by the supply air device manufacturer. The throw is applied by designers to estimatethe velocity levels in the occupied zone. A standard for determining the throw is the CENstandard CEN/TC156/WG4 N86 "Draft Standard. Air terminal Devices. AerodynamicsTesting And Rating For Mixed Flow Application".The measurement of the throw is very time consuming even with the free jets and theinfluence of the room (the effect of confinement) is not considered. The objective of thepresent study is to give a basis for modifying the existing design and testing method used topredict the velocities in the occupied zone during the design process. A new method whichmay probably be more easier than the existing methods and at the same time give a betterprecision by including the confinement effect.In this thesis two methodological systems of experiment and numerical simulations have beenused. The numerical predictions are used in comparison with the measurements. Thereasonable agreement of the above mentioned methods is implemented to numerical study ofthe other room configurations which are not experimentally studied. This examining methodallows the possibility of studying a lot of configurations and in this manner generalising of theresults. Although the experimental part was made for both model-scale and full-scale testrooms, a large amount of data was obtained for a new test room whose dimension aresystematically varied. All of studies have been made for the isothermal case and themeasurements of velocities and pressures conducted along the room perimeters. The effect ofshort and deep rooms on the properties of the jet ( velocities, pressure, integral scale, jetmomentum, the rate of spreading of jet and turbulence intensities) have been carried out.Some old and recent investigations have been examined. Specially the concept of correlationsfrom open to closed rooms is criticised. It is also shown that the flow field in a confined roomis affected by many other factors than the Reynolds number. The surface pressure on theperimeters was used to calculate the reaction forces at the corners which causes recirculatingbubbles at corners. A study of the turbulent axisymmetric jet which is the basic element inturbulent shear flows and some restrictions of the traditional measurement techniques at theregion of interest in ventilation applications are discussed. The jet momentum is measured byweighing on a balance. Also a study of jets which collide with a wall , that is impinging jet,the effect of walls and confinement on the jet momentum have experimentally andnumerically been carried out. A new momentum balance model was developed for both thefree jet and confined one. An empirical relation has been found for estimation of the room’srotation centre which is used for validation of CFD results.Finally, it is found that the jets in a ventilated room which are a combination of free jet, walljet and impinging jet differ from the traditional wall jets. The rate of spreading of the jet andthe maximum velocity decay in a ventilated room are also different depending on the roomsize and its confinement.

En este estudio se han construido dos diferentes instalaciones para investigar primero los chorros de gas horizontales y en segundo lugar los chorros verticales de agua que impactan sobre superficies libres de fluido, también se ha desarrollado un modelo numérico integral para predecir las trayectorias de estos jets y sus parámetros más importantes, validándose con los resultados experimentales obtenidos. En la primera parte de este trabajo, se han realizado experimentos para investigar el comportamiento de chorros de gas horizontales penetrando en agua. Los resultados experimentales indicaron que la longitud de penetración de los chorros de gas está fuertemente influenciada por el diámetro de la boquilla y el número de Froude, así como con el flujo de masa de de entrada y su momento. Aumentar el número de Froude y el diámetro del inyector lleva a aumentar la inestabilidad de jet. Además, la máxima ubicación antes de jet pinch-off se muestra que mantiene una relación logarítmica con el número de Froude para todos los diámetros de jet. Se han desarrollado correlaciones empíricas para predecir estos parámetros. Se ha desarrollado un modelo basado en la integración de las ecuaciones de conservación para que resulte útil en el diseño de aplicaciones en las que participen chorros horizontales así como para asistir a la investigación experimental. Las predicciones del modelo integral se comparan con los datos de los datos experimentales obtenidos con muy buenos resultados. En la segunda parte de este trabajo, se realizaron una serie de experimentos con de chorros de agua, inyectados verticalmente hacia abajo, a través de toberas circulares que impactan sobre una superficie de agua. Los resultados obtenidos mostraron que la profundidad de penetración de la burbuja disminuye con la longitud del chorro, pero que después de ciertas condiciones se mantiene casi constante. Además ésta aumenta con los diámetros de la boquilla y la velocidad del chorro. La velocidad de arrastre
Harby Mohamed Abd Alaal, K. (2012). Experimental and Theoretical Study of the Characteristics of Submerged Horizontal Gas Jets and Vertical Plunging Water Jets in Water Ambient [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/18065
Palancia

Cette thèse est une contribution expérimentale à l’étude des résonances aéroacoustiques des jets sous-détendus : le Screech. Diverses méthodes expérimentales sont utilisées à ces fins, telles que la mesure de pression acoustique, la strioscopie et Vélocimétrie par Image des Particules, et associées à des techniques classiques de post-traitement comme les décompositions en mode de Fourier et aux valeurs propres. Ces Techniques permettent d’évaluer les effets d’épaisseur de la lèvre de la buse sur l’écoulement, et fournissent des informations sur les différences de comportement d’un même jet montrant des modes oscillatoires différents. Enfin, on entreprend d’étudier la présence de divers mécanismes de fermeture de la boucle de résonance pour divers modes de screech. La présence d’ondes intrinsèques du jet, se propageant vers l’aval pour les modes axisymétrique (A2) et hélicoïdal (C) suggèrent que ces ondes puissent jouer un rôle dans la résonance. La signature de ces ondes n’est en revanche pas attestée pour les modes battants (B). Ces résultats semblent donc indiquer que plusieurs mécanismes de rétroaction différents puissent être à l’oeuvre dans la résonance du jet sous-détendus
This work provides an experimental contribution to the study of the Screech phenomenon. Various experimental techniques such as microphones array, Schlieren and Particle Image Velocimetry (PIV) together with advanced post-processing techniques like azimuthal Fourier decomposition and Proper Orthogonal Decomposition (POD) are employed. These techniques enable the evaluation of the lip thickness effects on the jets generated by two different round nozzles. The differences on the flow aerodynamics and acoustics are discussed. Then, we carry out experiments to analyse the effects of the different dominant Screech modes (B and C) on the flow characteristics. No noticeable differences are found in the mean fields. However, the fluctuation fields shows the contrary: B mode has larger fluctuation. In the last part, we investigate the Screech closure mechanism. The signature of upstream jet waves is revealed in the axisymmetric (A2) and helical (C) mode. However, the mode B does not present evidence of this instability in the flow, indicating that its closure mechanism may be bonded to another kind of waves. The conclusion from the results is that the Screech phenomenon seems be driven by different closure mechanisms

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Com a rápida evolução da tecnologia, os dispositivos eletrônicos tornaram-se compactos e com o alto poder de processamento, aumentando a geração de calor. Mas devido à baixa eficiência de ventiladores e dissipadores utilizados atualmente, há a necessidade de desenvolver novas formas de resfriamento. O uso de jatos sintéticos no resfriamento de dispositivos eletrônicos ainda é incipiente. Estudos monstram que este método pode ser uma alternativa eficaz. Assim, neste trabalho foi desenvolvido um estudo experimental com jatos sintéticos onde foram analisadas diferentes configurações de jatos com orifício retangular. Um alto-falante foi utilizado como diafragma e excitado através de um gerador de sinais senoidais para produzir o jato. A frequência de ressonância era desconhecida e foi necessário analisá-la antes de iniciar o experimento. O sistema foi montado em um suporte móvel para que fosse possível variar a posição vertical do gerador de jatos. Foram analisadas as dimensões do orifício para diferentes diâmetros hidráulicos (4 – 8 mm) e razões de aspecto (2 – 4), como também a profundidade da cavidade (2 – 8 mm). Também se analisou a transferência de calor através do impacto de jatos sobre uma placa aquecida. Dentre os estudos, verificaram-se outros parâmetros como o número de Reynolds e o número de Strouhal a fim de calcular a frequência mais adequada para a produção de vórtices. Os resultados demonstraram que para orifícios retangulares, as configurações com diâmetro hidráulico maior e razão de aspecto menor, são as melhores opções para resfriamento dos dispositivos eletrônicos.
With the rapid evolution of technology, electronics have become more compact and with higher processing power, increasing heat generation. Thus, there is a need to develop new forms of cooling, due to the low efficiency of cooling fans and heatsinks used currently. Using synthetic jets for cooling electronic device is still incipient but studies show that this method is an effective alternative. Thus, this work was developed an experimental study with synthetic jets where different configurations were tested with rectangular orifice. A loudspeaker was used as diaphragm and it was excited by a sinusoidal signal generator to produce the jet. The previously unknown ressonant frequency was determined experimentaly as part of this study. The system was mounted on a vertical traverse to allow changes in the vertical position of the synthetic jet generator. Orifice dimensions were analyzed covering variations in hydraulic diameter (4-8 mm) and aspect ratio (2-4), as well as the depth of the cavity (2-8 mm). Also the heat transfer was examined through the jet impingement on a hot plate. Other parameters such as Reynolds and Strouhal number were also examined in order to calculate the best frequency for jet performance. Results show that for rectangular orifice, geometries with larger hydraulic diameter and aspect ratio smaller are the best options for electronic cooling devices.

This thesis describes the measurements of jet activity in the rapidity region between a dijet system formed in proton-proton collisions at a centre-of-mass energy of 7 TeV. The data used were collected by the ATLAS detector during 2010 at the Large Hadron Collider at CERN. A number of observables that probe additional quark and gluon radiation in the dijet topology are studied. The development and performance of the monitoring system for the ATLAS calorimeter high level trigger is described. The performance of the jet calibration and a study of the properties of jets in the forward calorimeter is also given. The fraction of events that survive a veto on jets with transverse momentum above a jet veto scale, Q0, in the rapidity region between the dijet system is measured for dijets with mean transverse momentum 50 < pT < 500 GeV and rapidity separation, ∆y, of up to six. The mean number of jets that have a transverse momentum above the jet veto scale in the rapidity region between the dijet system is also measured. These measurements are compared to state-of-the-art theoretical calculations from HEJ and POWHEG, and also compared to PYTHIA and HERWIG++ Monte Carlo generators. The results of a preliminary analysis of dijet events with a large rapidity separation are given. In this analysis azimuthal decorrelation variables are also been measured.

Esta tésis presenta búsquedas de nueva física en estados finales tt ̄ con jets adicionales pesados usando 20,3 fb-1 de datos provenientes de colisiones de pp a una energía de √s = 8 TeV, recogidos en el experimento ATLAS en el LHC. Haciendo uso de este estado final, tres análisis han sido realizados para investigar la inestabilidad de la masa del bosón de Higgs desde diferentes perspectivas. La mayor dificultad para los análisis es conseguir una predicción precisa del background, en concreto tt+bb. Dado que aún no se han realizados medidas de la producción de tt con jets adicionales pesados, los análisis basan la descripción de este proceso en simulación mediante Monte Carlo (MC). Avances recientes en la simulación de MC han conseguido mejorar la descripción del background, y se ha dedicado mucho trabajo a conseguir incluir estas mejoras en el análisis. Los sistemáticos debidos al modelado de tt+bb constituyen la mayor fuente de degradación de la sensiblidad de los análisis. A fin de reducir el impacto de los sistemáticos, el análisis usa un ajuste a los datos para constreñir in-situ los sistemáticos más importantes. Un análisis estadístico detallado es necesario para probar la existencia de una señal en los datos. El primero de los análisis estudia el proceso ttH para medir su producción, de lo cual se puede extraer el acoplo entre el quark top y el bosón de Higgs. Para distinguir la señal ttH del background se usan redes neuronales, y la variable más discriminante viene de aplicar el matrix element method. No se observa evidencia para el proceso ttH, y por tanto se pueden establecer limites con una confianza del 95 %, excluyendo una señal 3.6 veces más grande que la predicción del model estándar. Realizando un ajuste con la hipótesis de señal, el mejor valor para la normalización de la señal es: μ = 1,2 ± 1,3. También se ha realizado una búsqueda de quarks vectoriales emparejados con el top, para estudiar varios modelos que predicen esta señal. El análisis de eventos con un número alto de jets y b-jets, y al mismo tiempo varios objetos con alto pT permiten mejorar la sensibilidad de la búsqueda. No se observa un exceso sobre la predicción y se han fijado límites en varios modelos. El mismo análisis se ha usado también para establecer límites en modelos que predicen estados finales con cuatro quarks top. Se han establecido límites en la producción de cuatro tops en el model estándar, en un modelo efectivo con una interacción de contacto, la producción de pares de sgluons y producción de modos de Kaluza-Klein en un modelos con dos dimensiones extra. Por último, la tesis incluye también una búsqueda de tops bosónicos, o stops, a fin de estudiar modelos supersimétricos donde las búsquedas típicas no tienen sensibilidad. El análisis busca el stop pesado, t2, en modelos donde el t1 es ligero, y la diferencia de masas con el neutralino es parecida a la masa del quark top. No se observa un exceso sobre la predicción de eventos y se han establecido límites en el plano de masas mt2−mχ . Para valores concretos de la masa se han establecido también límites en función de la fracción de decaimiento del t2. Los análisis presentados en esta tesis constituyen los análisis más sensibles en los respectivos canales.
This dissertation presents searches in tt final states with additional heavy-flavor jets using 20.3 fb-1 of pp collision data at √s = 8 TeV, recorded with the ATLAS experiment at the LHC. Exploiting this final state, three analyses are presented that address the instability of the Higgs boson mass from different perspectives. The main challenge for the presented analyses lies in the precise modeling of the background, in particular tt+bb. Since no measurements have been performed yet on the tt production with additional heavy-flavor jets, the analyses have to rely on Monte Carlo (MC) simulation for the background. Recent developments in MC simulation have improved the description of the background, and a great effort is invested in porting the state-of-the-art predictions into the analyses. The systematic uncertainties on the modeling of the tt+bb background constitute the main source of sensitivity degradation. In order to reduce the impact of the systematic uncertainties, the analyses use a profile likelihood fit to reduce in-situ the leading uncertainties. A detailed statistical analysis is performed in order to test for the presence of a signal in the observed data. The first of the analyses aims to study the ttH process and to measure its production rate, from which the top Yukawa coupling can be extracted. Neural networks are used to discriminate the ttH signal from the background, where the most discriminant variable stems from the matrix element method. No evidence for the ttH process is found, and a 95% confidence level (CL) upper limit is set, excluding a signal 3.6 times larger than predicted by the SM. Performing a signal-plus-background fit the best fitted value for the signal strength is found to be: μ = 1.2±1.3. A search for vector-like top partners and four-top-quark production is presented, addressing several models that predict such signatures. The analysis of events with high jet and b-tag multiplicity, as well as multiple high-pT objects allows increasing the sensitivity of the search. No excess over the background expectation is found and 95% CL upper limits are set in different models. The same search is also used to establish limits on models predicting four-top-quark final states. Exclusion limits are set on SM tttt production, tttt production via an effective field theory model with a four-top contact interaction, sgluon pair production and Kaluza-Klein modes production. As last, a search for bosonic top partners, or stops, is presented, addressing supersymmetric models where traditional searches have little sensitivity. A search for the heavier stop, t2, is performed targeting models where the t1 is light and the mass difference to the neutralino is close to the top mass. No excess over the background expectation is found and 95 % CL upper limits are set for different masses in the mt2−mχ. For representative values of the masses exclusion limits are set as a function of the t2 branching ratios. The analyses presented constitute the most sensitive searches to date in their respective channels.