Treated and untreated liquid that is discharged from industrial and desalination plants is one of the main factors that break the ecological balance and destroys aquatic habitat in lakes, rivers and coastal areas where the effluent is discharged. Positively and negatively buoyant jets are two categories of outfalls which are generated because of the destiny difference between the effluent and ambient fluid. In order to ensure minimal impact of the effluent on the environment, it is necessary to estimate the dilution of the jet and compare it with environmental regulations on the level of required dilution to ensure that the concentration of the effluent is diluted quickly enough and the concentration of the effluent at different points does not exceed the allowed concentrations. This study investigated the positively buoyant jet, which happens near the coastal and near water area. For instance, cooling water that flows out from a power plant or factory, wasted water that is discharged from an industrial plant near river, submerged drainage from civil municipal sewer systems and treated water from desalination plant in coastal area. Density difference, velocity and inclined angle of the jet were considered as the main factors that contribute to the jet spreading and were compared to develop the best solution for its dilution. The jet was discharged inclined downward to allow for more mixing and dilution of the effluent with the ambient water. In order to simulate a positive jet, tap water was injected in saline ambient. A large number of experiments were conducted in the laboratory and using camera imaging. The jet trajectory was estimated from the images using image processing and the impact of various parameters such as Froude number and jet velocity were investigated. The opensource software OpenFOAM, was employed for numerical simulations which is a finite volume model ensures mass conservation and allows for flexible mesh size for further accuracy and optimization of computational cost. Using this Computational Fluid Dynamics (CFD) model, the numerical simulations were performed, and the results were compared with laboratory experiments. A Reynold-Averaged Navier-Stokes (RANS) approach was employed in the numerical simulations which offers a good balance between accuracy and computational cost. It was found that the numerical model in conjunction with the second order turbulence model called Launder-Reece- Rodi model (LRR) had a reasonable agreement with the experimental data.

INTRODUCTION: Non-extraction Class II malocclusion treatments often employ the use of maxillary dentition distalization mechanics. The rationale behind these mechanics is to treat the sagittal position of the maxillary dentition to the mandibular dentition. As anchorage loss may occur after distalization of molars, inter-arch mechanics are often used during comprehensive treatment that may manifest in the finish as a more protrusive lower dentition. OBJECTIVE: To evaluate the efficacy of several distalization modalities, used as part of comprehensive orthodontics, by measuring the overall effects on the dentition and soft tissue. MATERIALS AND METHODS: Four different modalities of distalization treatment of Class II malocclusion were compared regarding dental and soft tissue changes: Distal Jet (n=26), Horseshoe Jet (n=26), Pendulum (n=26), and the MGBM (Maino, Giannelly, Bernard, Mura) protocol (n=25). The Horseshoe Jet and MGBM methods use miniscrews supported anchorage while the Distal Jet and pendulum do not. The majority of the pendulum subjects (24 of 26) were prescribed headgear wear. For each of the groups, lateral cephalograms were taken before treatment and after comprehensive treatment. RESULTS: Minimal differences in soft tissue changes between the groups were found; however, significant (p≤0.05) differences in dental changes between groups for lower incisor, upper incisor, and upper first molar sagittal positions were found. Lower incisors showed significant protrusion and proclination for the Distal Jet experimental group (p<0.05). The upper incisor showed the greatest uprighting and retraction (p<0.05) in the pendulum group and the most proclination (p<0.01) in the Horseshoe Jet group. CONCLUSION: Three out of four experimental groups showed some amount of lower incisor protrusion and/or proclination. Bone anchored modalities had reduced side effects on the lower incisors, with the Horseshoe Jet showing less change than Distal Jet (p=0.05) and the MGBM group showing no significant change. The pendulum group had the greatest upper incisor retraction and showed negligible lower incisor proclination with only 1 out of 6 measurements showing significance.

Simulations of the circulation in the middle atmosphere during northern winter performed with a nonlinear, mechanistic, global circulation model show that the upper mesospheric jet is greatly overestimated and also the position with respect to latitude and height does not correspond to observations. Apart from that also the winter wind reversal in the mesopause region, evoked by breaking gravity waves (GWs), is located too low around 80km, but is observed to be usually around 100 km. These discrepancies are planned to be eliminated by modifying the distribution of GW amplitudes driving the GW parameterization. This distribution is currently based on potential GW energy data derived from GPS radio occultation measurements and has to be replaced by a distribution based on momentum flux estimates applying midfrequency approximation. The results show a weaker mesospheric jet more realistically tilted towards lower latitudes with height. Also the meridional circulation extending from the summer to the winter pole decelerates and less GWs are propagating into the mesosphere. By additionally varying the GW amplitudes in magnitude and time, the wind reversal is shifted upwards and the mesospheric jet is slowed down. / Simulationen der Zirkulation der mittleren Atmosphäre während des nordhemisphärischen Winters unter Verwendung eines nicht-linearen mechanistischen globalen Zirkulationsmodells ergaben beim Vergleich mit Messungen, dass der simulierte, mesosphärische Jet stark überschätzt wird und dessen Position von den Beobachtungen abweicht. Die in der Mesopausenregion einsetzende Windumkehr, hervorgerufen durch brechende Schwerewellen, befindet sich in etwa 80 km anstatt in 100 km. Diese Diskrepanzen sollen eliminiert werden. Hierfür wird die Verteilung der Schwerewellenamplituden, die die Schwerewellenparametrisierung innerhalb des Modells antreibt, am oberen Rand der Troposphäre modifiziert. Diese basiert derzeit auf global beobachteten, zonal gemittelten Daten der potentiellen Energie von Schwerewellen abgeleitet aus GPS Radiookkultationsmessungen und soll durch eine auf Impulsflüssen basierende Verteilung ersetzt werden. Das Modellexperiment zeigt, dass der mesosphärische Jet mit der Höhe in Richtung niedriger Breiten geneigt ist und abgebremst wird. Zudem schwächt die Meridionalzirkulation vom Sommer- zum Winterpol leicht ab und weniger Schwerewellen dringen bis in die Mesosphäre vor. Zusätzlich wird durch zeitliche und unterschiedlich starke Variation der Schwerewellenamplitude die Windumkehr verlagert und der mesosphärische Jet abgebremst.

Rapid mixing is crucial for the efficient and environment-friendly operation of many industrial and propulsion devices involving jet flows. In this dissertation, two methodologies, self-excited nozzles and radially lobed nozzles, are studied and presented in order to enhance mixing in the near field of coflowing, subsonic, turbulent, free jet flows. The characteristics of the concentration field and the mixing performance are examined, mainly in quantitative manner. Two new parameters, mixing index and mixing efficiency index, are defined for free jets, allowing quantitative analysis of the mixing performance and efficiency. The flow fields are studied with hot wire anemometry, and with CFD simulation for some of the radially lobed nozzles. Due to the large vectoring angle of the jet flows from these nozzles, a new definition for the entrainment ratio is also adopted in order to take the large radial velocity component into consideration. Self-excited nozzles, rectangular and square shaped, are examined at Reynolds numbers of 17,000 and 31,000. The self-excited square jet has fastest mixing and highest mixing efficiency, with 400% higher mixing index at 4 diameters downstream than the unexcited square jet. The mixing is improved as the excitation frequency or coflow velocity increases. The study of flow field shows the presence of one pair of periodic, coherent array of large-scale, streamwise, counter-rotating inviscid vortices shedding from each of the two flaps which dominate the mean flow and the mixing process. The coflow is primarily entrained into the jet in the minor plane while the jet fluid vectors in the major plane. Significant increase in turbulent kinetic energy immediately downstream the nozzle exit improves small-scale mixing. Radially lobed nozzles, a cross-shaped and a clover-shaped with four lobes each, are analyzed in comparison to a conical nozzle. In addition, a few modified radially lobe nozzles, including a 6-lobe nozzle and an 8-lobe nozzle, two type of fully penetrating nozzles, and a cross-shaped nozzle with centerbody, are examined in order to achieve better mixing than the cross-shaped nozzle. At 4 diameters downstream, the mixing index of the cross-shaped nozzle is 650% higher than that of the conical nozzle. The cross-shaped nozzle with centerbody, the 6- lobe and 8-lobe nozzles have slower mixing and lower efficiency than the cross-shaped nozzle,but the fully-penetrating nozzles are generally better than the cross-shaped nozzle, especially at low coflow velocities and in the far field. The flow field study shows that parallel lobe walls and deep penetration of the coflow are importance factors responsible for the observed mixing enhancement. / Ph. D.

The flow of jets in confining enclosures has significant application in many engineering processes. In particular, two jet flows have been studied; the impingement of axisymmetric jets in a confined space and a turbulent inlet wall jet in a confining enclosure. The impingement of axisymmetric jets in a cavity has been examined using flow visualization, laser Doppler anemometry, and numerical simulations. When the flow field was examined under various geometrical and fluid parameters several flow regions were found, depending on the geometrical and fluid parameters. Initially, a steady flow field existed for all arrangements for Red < ~90 but subsequent increments in the fluid velocity caused an oscillating flow field to emerge. The onset of the oscillations and the upper limit of finite oscillations were found to be a function of the nozzle diameter to chamber dimension ratio. Although steady numerical simulations predicted the steady flow field well, steady simulations of the oscillating flow field over-predicted the peak axial velocities. The oscillating flow field is considered to be a class of self-sustaining oscillations where instabilities in the jet shear layer are amplified because of feed back from pressure disturbances in the impingement region. The turbulent wall jet in a cavity has been studied using flow visualization, laser Doppler anemometry (LDA), particle streak velocimetry (PSV) and numerical simulations. Instantaneous PSV measurements agreed well with time averaged LDA measurements. Two dimensional simulations using an algebraic stress turbulence model (ASM) were in better agreement with the experimental data than two and three dimensional simulations using a k - ε turbulence model in the wall jet region. A wall jet growth rate was found to be 54% higher than a wall jet in stagnant surroundings due to the enclosure boundaries. / Thesis / Doctor of Philosophy (PhD)

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published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

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