The use of induction fans for face ventilation in room and pillar mines has proved to be an efficient, flexible, and viable technique. In addition to their merits over conventional systems, induction fans enable remote controlled mine operations with low maintenance requirements. Theoretical investigations were conducted initially to verify the potential of free air jets in mine ventilation. A laboratory model using water as the fluid medium was designed to study the flow characteristics of a jet fan in a blind entry. The model was tested in a variety of brattice curtain and nozzle combinations to investigate the ventilating efficiency of jet fans. A jet fan was selected and tested in a full scale model and in a coal mine. Experiments were conducted to evaluate the laboratory flow models. Flow quantities and velocities in the entry were measured using state-of-the-art instrumentation to quantify various parameters. Air velocities near the face were found to be satisfactory to dilute contaminants from the face. A model for the axial velocity profile of the jet was suggested. Beyond 25m distance from the jet fan exit the jet tended to move away from the wall to the opposite wall. Carbon dioxide was used as a tracer gas to measure the effective ventilating air quantity near the face and re-circulation in various tests. The re-circulation involved in the system was found to be less than 40% in all the experiments. It was also found that the use of line curtains in combination with a jet a fan can eliminate any type of re-circulation. Numerical modeling of a jet fan in a typical coal mine heading was conducted to obtain details of the flow. The results of the simulation using computational fluid dynamics were similar to the flow patterns observed in the experiments. It was found that a jet fan can effectively ventilate an entry as deep as 40m. Fan positioning, airway geometry, airway surface properties, and mine layout severely affect its performance. It is therefore necessary to understand the flow mechanics of a jet fan in a mine heading before applying the technique for a particular situation. / Ph. D.

Jet noise has been a growing concern in recent years due to the costs associated with hearing loss of United States service members. Jet noise is also becoming more of a concern due to the rise of civilian complaints regarding the noise of jets near civilian and military air stations. One source of noise generation is from packets of air called eddies, which move with a convection velocity Uc. The current work seeks to expand upon the understanding of jet noise by collecting data using Time-resolved Doppler global velocimetry (TR-DGV) from regions of the jet known to produce high levels of acoustic radiation. Past experiments in studying convection velocity are reviewed based on the technique for obtaining the velocities. To add to these experiments, the current work analyzes data obtained using TR-DGV applied to a perfectly expanded Mach 1.65 flow with total temperature ratio (TTR) equal to 1. Additional measurements were obtained on a Mach 1.5 nozzle operated at a slightly over expanded condition and at TTR = 2. The cold jet flow is compared to the past experiments on unheated jets and demonstrates good agreement with respect to normalized convection velocities based on the jet exit speed. The data is then compared to past experiments conducted on the same nozzle at heated conditions. Shadowgraph imaging is used as a qualitative tool to locate shock cells within the jet plume. TR-DGV data from near the lipline (r = 0.5D) is axially aligned with the shadowgraph images to demonstrate that the shock structure within the potential core causes detectable variations in the scalar convective velocity. Additionally, it is shown that in the heated and unheated Mach 1.65 jet and the over expanded heated Mach 1.48 jet that the convection velocity does increase beyond the potential core. The Mach 1.48 jet is also compared to mean velocities obtained using Particle Image Velocimetry and found that the convective and mean velocities were only similar in some regions of the jet. A discussion is provided on suggestions of future work on where to obtain data within the jet plume and how to collect the data using current capabilities. Suggestions are also provided for improving data quality in future experiments, as well as ideas for future investigations into convection velocity along the length of the jet plume using TR-DGV. / Master of Science / Jet noise has been a growing concern in recent year due to the costs associated with hearing loss of United States service members. Additionally, many civilians complain about the noise of aircraft flying both out of military facilities and commercial airports. One source of noise generation is from packets of air called eddies which move with a convection velocity. Researchers have identified that by affecting the convection velocities of these eddies, there is a larger benefit than other traditional methods such as engine chevrons. The current work summarizes techniques used to investigate convective velocity as well as to provide evidence for other unconfirmed theories. This study focuses on using a laser-based technique to obtain data within the flow of an unheated supersonic jet. An unheated jet is studied to allow for easy comparison to other experiments that have used different diagnostic techniques. Additionally, this case is studied to complete a set of experiments that were previously conducted on the same nozzle so that there is a true base-line or “control” case for future work. Later in this paper, analysis will be done to show how shocks within the jet affect the convective velocity. A combination of both quantitative and qualitative efforts are performed to accomplish this. Additionally, it will be shown that after the potential core of the jet breaks down, there is an increase in the local convective velocity in this region immediately after the potential core. Finally, a brief summary will be given and suggestions for future work will be presented.

Evaluating aerodynamic noise from aircraft engines is a design stage process, so that it conform to regulations at airports. Aerodynamic noise is also a principal source of structural vibration and internal noise in short/vertical take off and landing and rocket launches. Acoustic loads may be critical for the proper functioning of electronic and mechanical components. It is imperative to have tools with capability to predict noise generation from turbulent flows. Understanding the mechanism of noise generation is essential in identifying methods for noise reduction. Lighthill (1952) and Lighthill (1954) provided the first explanation for the mechanism of aerodynamic noise generation and a procedure to estimate the radiated sound field. Many such procedures, known as acoustic analogies are used for estimating the radiated sound field in terms of the turbulent fluid flow properties. In these methods, the governing equations of the fluid flow are rearranged into two parts, the acoustic sources and the propagation terms. The noise source terms and propagation terms are different in different approaches. A good description of the turbulent flow field and the noise sources is required to understand the mechanism of noise generation. Computational aeroacoustics (CAA) tools are used to calculate the radiated far field noise. The inputs to the CAA tools are results from CFD simulations which provide details of the turbulent flow field and noise sources. Reynolds-Averaged Navier Stokes (RANS) solutions can be used as inputs to CAA tools which require only time-averaged mean quantities. The output of such tools will also be mean quantities. While complete unsteady turbulent flow details can be obtained from Direct Numerical Simulation (DNS), the computation is limited to low or moderate Reynolds number flows. Large eddy simulations (LES) provide accurate description for the dynamics of a range of large scales. Most of the kinetic energy in a turbulent flow is accounted by the large-scale structures. It is also the large-scale structures which accounts for the maximum contribution towards the radiated sound field. The results from LES can be used as an input to a suitable CAA tool to calculate the sound field. Numerical prediction of turbulent flow field, the acoustic sources and the radiated sound field is at the focus of this study. LES based on explicit filtering method is used for the simulations. The method uses a low-pass compact filter to account for the sub-grid scale effects. A one-parameter fourth-order compact filter scheme from Lele (1992) is used for this purpose. LES has been carried out for four different flow situations: (i) round jet (ii) plane jet (iii) impinging round jet and (iv) impinging plane jet. LES has been used to calculate the unsteady flow evolution of these cases and the Lighthill’s acoustic sources. A compact difference scheme proposed by Hixon & Turkel (1998) which involves only bi-diagonal matrices are used for evaluating spatial derivatives. The scheme provides similar spectral resolution as standard tridiagonal compact schemes for the first spatial derivatives. The scheme is computationally less intensive as it involves only bi-diagonal matrices. Also, the scheme employs only a two-point stencil. To calculate the radiated sound field, the Helmholtz equation is solved using the Green’s function approach, in the form of the Kirchhoff-Helmholtz integral. The integral is performed over a surface which is present entirely in the linear region and covers the volume where acoustic sources are present. The time series data of pressure and the normal component of the pressure gradient on the surface are obtained from the CFD results. The Fourier transforms of the time series of pressure and pressure gradient are then calculated and are used as input for the Kirchhoff-Helmholtz integral. The flow evolution for free jets is characterised by the growth of the instability waves in the shear layer which then rolls up into large vortices. These large vortical structures then break down into smaller ones in a cascade which are convected downstream with the flow. The rms values of the Lighthill’s acoustic sources showed that the sources are located mainly at regions immediately downstream of jet break down. This corresponds to the large scale structures at break down. The radiated sound field from free jets contains two components of noise from the large scales and from the small scales. The large structures are the dominant source for the radiated sound field. The contribution from the large structures is directional, mainly at small angles to the downstream direction. To account for the difference in jet core length, the far field SPL are calculated at points suitably shifted based on the jet core length. The peak value for the radiated sound field occurs between 30°and 35°as reported in literature. Convection of acoustic sources causes the radiated sound field to be altered due to Doppler effect. Lighthills sources along the shear layer were examined in the form of (x, t) plots and phase velocity pattern in (ω, k) plots to analyse for their convective speeds. These revealed that there is no unique convective speeds for the acoustic sources. The median convective velocity Uc of the acoustic sources in the shear layer is proportional to the jet velocity Uj at the center of the nozzle as Uc ≈ 0.6Uj. Simulations of the round jet at Mach number 0.9 were used for validating the LES approach. Five different cases of the round jet were used to understand the effect of Reynolds number and inflow perturbation on the flow, acoustic sources and the radiated sound field. Simulations were carried out for an Euler and LES at Reynolds number 3600 and 88000 at two different inflow perturbations. The LES results for the mean flow field, turbulence profiles and SPL directivity were compared with DNS of Freund (2001) and experimental data available in literature. The LES results showed that an increase in inflow forcing and higher Reynolds number caused the jet core length to reduce. The turbulent energy spectra showed that the energy content in smaller scale is higher for higher Reynolds number. LES of plane jets were carried out for two different cases, one with a co-flow and one without co-flow. LES of plane jets were carried out to understand the effect of co-flow on the sound field. The plane jets were of Mach number 0.5 and Reynolds number of 3000 based on center-line velocity excess at the nozzle. This is similar to the DNS by Stanley et al. (2002). It was identified that the co-flow leads to a reduction in turbulence levels. This was also corroborated by the turbulent energy spectrum plots. The far field radiation for the case without co-flow is higher over all angles. The contribution from the low frequencies is directional, mainly towards the downstream direction. The range of dominant convective velocities of the acoustic sources were different along shear layers and center-line. The plane jet results were also used to bring out a qualitative comparison of flow and the radiation characteristics with round jets. For the round jet, the center-line velocity decays linearly with the stream-wise distance. In the plane jet case, it is the square of the center-line velocity excess which decays linearly with the stream-wise distance. The turbulence levels at any section scales with the center-line stream-wise velocity. The decay of turbulence level is slower for the plane jet and hence the acoustic sources are present for longer distance along the downstream direction. Subsonic impinging jets are composed of four regions, the jet core, the fully developed jet, the impingement zone and the wall jet. The presence of the second region (fully developed free jet) depends on the distance of the wall from the nozzle and the length of the jet core. In impinging jets, reflection from the wall and the wall jet are additional sources of noise compared to the free jets. The results are analysed for the contribution of the different regions of the flow towards the radiated sound field. LES simulations of impinging round jets and impinging plane jet were carried out for this purpose. In addition, the results have been compared with equivalent free jets. The directivity plots showed that the SPL levels are significantly higher for the impinging jets at all angles. For free jets, a typical time scale for the acoustic sources is the ratio of the nozzle size to the jet velocity. This is ro/Uj for round jets and h/Uj for plane jets. For impinging jets, the non-dimensionlised rms of Lighthill’s source indicates that the time scale for acoustic sources is the ratio of the height of the nozzle from the wall to the jet velocity be L/Uj. LES of impinging round jets was carried out for two cases with different inflow perturbations. The jets were at Reynolds number of 88000 and Mach number of 0.9, same as the free jet cases. The impingement wall was at a distance L = 24ro from the nozzle exit. For impinging round jets, the SPL levels are found to be higher than the equivalent free jets. From the SPL levels and radiated noise spectra it was shown that the contribution from the large scale structures and its reflection from the wall is directional and at small angles to the wall normal. The difference in the range of angles where the radiation from the large scale structures were observed shows the significance of refraction of sound waves inside the flow. The rms values of the Lighthill’s sources indicate two dominant regions for the sources, just downstream of jet breakdown and in the impingement zone. The LES of impinging plane jet was done for a jet of Mach number 0.5 and Reynolds number of 6000. The impingement wall was at a distance L = 10h from the nozzle exit. The radiated sound field appears to emanate from this impingement zone. The directivity and the spectrum plots of the far field SPL indicate that there is no preferred direction of radiation from the impingement zone. The Lighthill’s sources are concentrated mainly in the impingement zone. The rms values of the sources indicate that the peak values occur in the impingement zone. The results from the different flow situations demonstrates the capability of LES with explicit filtering method in predicting the turbulent flow and radiated noise field. The method is robust and has been successfully used for moderate Reynolds number and an Euler simulation. An important feature is that LES can be used to identify acoustic sources and its convective speeds. It has been shown that the Lighthill source calculations, the calculated sound field and the observed radiation patterns agree well. An explanation for these based on the different turbulent flow structures has also been provided.

La recherche du boson de Higgs ainsi que celle de nouvelle physique auprès du LHC requiert une excellente compréhension des processus du Modèle Standard du fait de leurs signatures expérimentales similaires. La capacité de mesurer le plus précisément possible l'énergie des objets reconstruits dans les détecteurs est par ailleurs primordiale à la fois pour effectuer des mesures de précision et pour accroître la sensibilité des analyses à des signaux de physique au-delà du Modèle Standard. Les travaux présentés dans cette thèse s'attachent à ces deux points par l'étude d'événements contenant un ou plusieurs jets associés à un boson Z avec le détecteur ATLAS. D'une part, ces événements sont utilisés pour améliorer la calibration en énergie des jets de faible impulsion transverse, d'une importance capitale pour les analyses utilisant le dénombrement de jets ou leur veto. D'autre part la section efficace différentielle de production de ces événements est mesurée en fonction de nombreuses observables et comparée à diverses prédictions théoriques. Ces mesures pourront être utilisées pour améliorer les prédictions qui servent de modèles de bruit de fond dans des analyses sur le boson de Higgs et de recherche de physique au-delà du Modèle Standard. / The Higgs boson search as well as searches for new physics at the LHC require a very good understanding of Standard Model processes due to their similar experimental signatures. In addition, the ability to precisely measure the energies of reconstructed objects within the detectors is crucial in order to perform precision measurements and to improve the sensitivity to physics signals beyond the Standard Model. The results presented in this thesis address these two points by studying events containing one or several jets associated to a Z boson with the ATLAS detector. These events are used to improve the jet energy calibration in the low transverse momentum regime, which is important for analyses making use of jet counting or jet veto. The differential cross section for the production of such events is also measured as a function of several observables and compared to various theoretical predictions. These measurements will serve to improve the predictions used to model background contamination in Higgs analyses and searches for new phenomena.

Ce travail de thèse porte sur l’étude de l’effet des boîtes quantiques d’InAs sur l’efficacité de conversion des cellules solaires à simple jonction de GaAs crues par épitaxie par jets chimiques. Cette technique de croissance est particulièrement bien adaptée à la croissance de structures multicouches pour des applications photovoltaïques. Une partie importante de ce travail a été consacré à l’optimisation des conditions de croissance pour la réalisation des boîtes quantiques d’InAs et de structures à multicouches de boîtes quantiques d’InAs insérées dans une matrice de GaAs. L’optimisation des conditions de croissance des boîtes quantiques a été basée sur une étude morphologique réalisée à l’aide de mesures de microscopie à force atomique et sur une étude des propriétés optiques et électroniques effectuée à l’aide de mesures de photoluminescence en continu. Une optimisation de la quantité d’InAs déposée lors de la croissance des BQs d’InAs/GaAs a permis de montrer que les meilleures structures de BQs ont été obtenues pour une épaisseur nominale d’InAs comprise entre 2.07 et 2.47 monocouches atomiques avec une haute densité (8 × 10[indice supérieur 10] cm[indice supérieur −2]) et une énergie d’émission de 1.22 eV (λ= 1016 nm). La croissance des multicouches de boîtes quantiques, dans des conditions usuelles de maintien de la température lors de l’épitaxie des couches de barrière de GaAs, a montré des difficultés dues à l’accumulation de la contrainte dans la structure. Deux types d’amas d’InAs ont été observés : soit des boîtes quantiques cohérentes de petite taille (diamètre et hauteur typiques de 5 nm et 16 nm, respectivement) et des amas relaxés de grande taille (diamètre et hauteur de plus de 50 nm et 150 nm, respectivement). Dans ces conditions de croissance nos résultats ont montré que la formation des amas de grande taille est accompagnée par une diminution de la densité des boîtes quantiques au fur et à mesure que le nombre de couches de boîtes quantiques augmente. L’application d’une étape appelée "indium-flush" (procédéd’évaporation d’indium sous atmosphère d’arsenic) pendant la croissance des couches de barrière de GaAs, qui encapsulent les boîtes quantiques, a montré une amélioration de la qualité cristalline de la structure globale. Les caractérisations morphologique et optique d’une série d’échantillons contenant 1, 5 et 10 plans de boîtes quantiques ont montré une préservation de la densité de boîtes quantiques et de leur distribution en taille. Les résultats montrent également que l’intensité intégrée de la photoluminescence des boîtes quantiques augmente linéairement en fonction du nombre de plans de boîtes quantiques. La structure finale optimisée est donc très prometteuse pour la réalisation de cellules solaires à boîtes quantiques à haute performance. L’étude de l’effet des boîtes quantiques et l’influence de leur hauteur sur l’efficacité des cellules solaires simple jonction de GaAs ont été analysés. Des mesures de l’efficacité quantique externe et des mesures I-V ont été effectuées pour caractériser ces cellules solaires. La technique de l’indium-flush a été utilisée pour contrôler la hauteur des boîtes quantiques. Une meilleure performance a été obtenue par la cellule solaire à boîtes quantiques tronquées à 2.5 nm de hauteur avec 5% d’amélioration de l’efficacité de conversion.

Active control of the flow over an airfoil is an area of heightened interest in the aerospace community. Previous research on flow control design processes heavily depended on trial and error and the designers knowledge and intuition. Such an approach cannot always meet the growing demands of higher design quality in less time. Successful application of computational fluid dynamics (CFD) to this kind of control problem critically depends on an efficient searching algorithm for design optimization. CFD in conjunction with Genetic Algorithms (GA) potentially offers an efficient and robust optimization method and is a promising solution for current flow control designs. But the traditional binary GA and its operators need to be transformed or re-defined to meet the requirements of real world engineering problems. Current research has combined different existing GA techniques and proposed a realcoded Explicit Adaptive Range Normal Distribution (EARND) genetic algorithm with diversity control to solve the convergence problems. First, a traditional binary-coded GA is replaced by a real-coded algorithm in which the corresponding design variables are encoded into a vector of real numbers that is conceptually closest to the real design space. Second, to address the convergence speed problem, an additional normal distribution scheme is added into the basic GA in order to monitor the global optimization process; meanwhile, design parameters boundaries are explicitly updated to eliminate unnecessary evaluations (computation) in un-promising areas to balance the workload between the global and local searching process. Third, during the initial 20% evolution (search process), the diversity of the individuals within each generation are controlled by a formula in order to conquer the problem of preliminary convergence to the local optimum. In order to better understand the two-jet control optimization results and process, at first, a single jet with a width of 2.5% the chord length is placed on a NACA 0012 airfoils upper surface simulating the blowing and suction control under Re=500,000 and angle of attack 18 degree. Nearly 300 numerical simulations are conducted over a range of parameters (jet location, amplitude and angle). The physical mechanisms that govern suction and blowing flow control are determined and analyzed, and the critical values of suction and blowing locations, amplitudes, and angles are discussed. Moreover, based on the results of single suction/blowing jet control on a NACA 0012 airfoil, the design parameters of a two-jet system are proposed. Our proposed algorithm is built on top of the CFD code, guiding the movement of two jets along the airfoils upper surface. The reasonable optimum control values are determined within the control parameter range. The current study of Genetic Algorithms on airfoil flow control has been demonstrated to be a successful optimization application.

Massive stars play a key role in the evolution of the Galaxy; hence they are important objects of study in astrophysics. Although they are rare compared to low mass stars, they are the principal source of heavy elements and UV radiation, affecting the process of formation of stars and planets, and the physical, chemical, and morphological structure of galaxies. Star clusters form in dense "clumps" (~few parsecs in size) within giant molecular clouds, while individual stars form in cores (subparsec scale). An important step in the observational study of massive star formation is the identification and characterization of clumps. More detailed studies can then show how these clumps fragment into cores. Studies of clumps in our Galaxy will provide fundamental guidelines for the analysis of other galaxies, where individual clumps and cores cannot be resolved, and provide a catalog of interesting sources for observations of the Milky Way with a new generation of instruments, such as the Atacama Large Millimeter/Submillimeter Array. Large-scale blind surveys of the Galactic plane at millimeter and submillimeter wavelengths have recently been completed, allowing us to identify star forming clumps and improve our understanding of the early stages of massive stars. One of these studies, the Bolocam Galactic Plane Survey (BGPS), mapped the continuum emission at 1.1 mm over a large region of the northern Galactic plane at a resolution of 33'', identifying 8559 compact sources throughout the Galaxy. In this dissertation, I present observations of a sample of sources from the BGPS catalog, obtained with the Submillimeter High Angular Resolution Camera II (SHARC-II). I present in this work 107 continuum emission maps at 350 microns at high angular resolution (8.5'') toward clump-like sources and construct a catalog of BGPS substructures. I estimate clump properties such as temperatures and multiplicity of substructures, and compare my results with 350 microns continuum maps from the Hi-GAL survey. I also present a detailed analysis, using molecular line and dust continuum observations, of the region G331.5-0.1, one of the most luminous regions of massive star formation in the Milky Way, located at the tangent region of the Norma spiral arm. Molecular line and millimeter continuum emission maps reveal the presence of six compact and luminous molecular clumps, with physical properties consistent with values found toward other massive star forming sources. This work includes the discovery of one of the most energetic and luminous molecular outflows known in the Galaxy, G331.512-0.103. For this high-speed outflow, I present ALMA observations that reveal a very compact, extremely young bipolar outflow and a more symmetric outflowing shocked shell surrounding a very small region of ionized gas. The source is one of the youngest examples of massive molecular outflows associated with the formation of a high-mass star. / text

Negatively buoyant jets are turbulent flows that are frequently employed by the desalination industry to disperse reject brines into oceanic environments. Although such brines are characterised by elevated concentrations of the same elemental components as the discharge environment contains, there is significant potential for marine ecosystem damage if this waste is not diluted properly. Numerous workers have analysed the dilution and spatial characteristics of negatively buoyant jets, but published data demonstrates notable inconsistencies. An important reason for these discrepancies is the variety of bottom-boundary conditions employed. This complicates comparison with predictions by integral models typically employed for discharge design, as these generally have not been developed with consideration to boundary interaction. In the present study, negatively buoyant jet experimental data is collected where bottom boundary distances are sufficiently large to avoid boundary influence at the point where the discharge returns to its source height (the return point). Near-field centreline dilution data is measured under still ambient conditions, for the source inclinations of 15–75°. Considerable attention is paid to experimental data quality, and all relevant issues are mitigated where possible. In order to ensure the boundary has no influence, source heights in this study range between 2.33 d F0 and 8.07 d F0. A variety of time-averaged and temporal statistics are calculated, and these statistics are compared with published experimental data and predictions by integral models. Normalised trajectory and dilution data from the source through to the return point collapses well at each inclination. The attention to signal quality and the self-consistency of derived experimental results in this study suggest a high level of accuracy, and large distances to the bottom boundary ensure that results are not confused by boundary interaction. Data for dilution rate at the return point supports the use of higher source inclinations (60° and 75°) to maximise dilution capability. A new ‘forced jet’ model is developed that incorporates the concept of a reducing buoyancy flux as the flow rises to maximum height. While this model is not applicable above source inclinations of 60°, predictions at other inclinations are reasonable. Dilution predictions are notably improved when compared to those from existing integral models. Finally, CFD simulations of negatively buoyant jets are conducted using the k-ε turbulence model. Despite the sophistication of this model, the quality of spatial and dilution bulk flow predictions at the centreline maximum height are no better than those obtained from the forced jet model or analytical solutions of Kikkert et al. (2007).

A fundamental study of two turbulent directly opposed impinging jets in a stagnant ambient fluid, unconfined or uninfluenced by walls is presented. By experimental investigation and numerical modeling, the main characteristics of direct impingement of two turbulent axisymmetric round jets under seven different geometrical and flow rate configurations (L*= L/d = { 5, 10, 20 }, where L is nozzle to nozzle separation distance and d is nozzle diameter, and Re = { 1500, 4500, 7500, 11000 }) are discussed. Flow visualization and velocity measurements performed using various laser based techniques have revealed the effects of Reynolds number, Re, and nozzle to nozzle separation, L, on the complex flow structure. Although locally valid, the classical analysis of turbulence is found unable to provide reliable results within the highly unstable and unsteady impingement region. When used to simulate the present flow, the assessment of the performance of three distinct k - epsilon turbulence models showed little disagreement between computed and experimental mean velocities and poor predictions as far as turbulence parameters are concerned.

This thesis contains a thorough investigation of the properties of freely decaying turbulence in a rotating shallow water layer on a sphere. A large number of simulations, covering an extensive range of Froude and Rossby numbers, have been carried out using a novel numerical algorithm that exploits the underly- ing properties of the flow. In general these flows develop coherent structures; vortices interact, merge and migrate polewards or equatorwards depending or their sign, leaving behind regions of homogenized potential vorticity separated by sharp zonal jets. In the first half of the thesis we investigate new ways of looking at these structures. In the second half of the thesis we examine the properties of the potential vorticity (PV) induced, balanced component and the residual, unbalanced component of the flows. Cyclone-anticyclone asymmetry has long been observed in atmospheric and oceanic data, laboratory experiments and numerical simulations. This asymmetry is usually seen to favour anticyclonic vorticity with the asymmetry becoming more pronounced at higher Froude numbers (e.g. Polvani et al. [1994a]). We find a similar result but note that the cyclones, although fewer, are significantly more intense and coherent. We present several ways of quantifying this across the parameter space. Potential vorticity homogenization is an important geophysical mechanism responsible for sharpening jets through the expulsion of PV gradients to the edge of flow structures or domains. Sharp gradients of PV are obvious in contour plots of this field as areas where the contours are bunched together. This suggests that we can estimate the number of zonal jets by performing a cluster analysis on the mean latitude of PV contours (this diagnostic is also examined by Dritschel and McIntyre [2007]). This provides an estimate rather than an exact count of the number of jets because the jets meander signficantly. We investigate the accuracy of the estimates provided by different clustering techniques. We find that the properties of the jets defy such simple classification and instead demand a more local examination. We achieve this by examining the palinstrophy field. This field, calculated by taking the gradient of the PV, highlights the regions where PV contours come closer together, exactly what we would expect in regions of strong jets. Plots of the palinstrophy field reveal the complex structure of these features. The potential vorticity field is even more central to the flow evolution than the strong link with jets suggests. From a knowledge of the spatial distribution of PV, it is possible to diagnose the balanced components of all other fields. These components will not contain inertia-gravity waves but will contain the dominant, large scale features of the flow. This inversion, or decomposition into balanced (vortical) and unbalanced (wave) components, is not unique and can be defined to varying orders of accuracy. We examine the results of four dfferent definitions of this decomposition, two based on truncations of the full equations and two based on an iterative procedure applied to the full equations. We find the iterative procedure to be more accurate in that it attributes more of the flow to the PV controlled, balanced motion. However, the truncated equations perform surprisingly well and do not appear to suffer in accuracy at the equator, despite the fact that the scaling on which they are based has been thought to break down there. We round off this study by considering the impact of the unbalanced motion on the flow. This is accomplished by splitting the integration time of the model into intervals τ < t < τ+dτ and comparing, at the end of each interval, the balanced components of the flow obtained by a) integrating the model from t = 0 and b) integrating the full equations, initialised at t = τ with the balanced components from a) at t = τ. We find that any impact of the unbalanced component of the flow is less than the numerical noise of the model.