There are few empirical measurements of velocity, shear velocity, sand transport, morphological change on the windward slopes of dunes.This thesis compares field measurements on a barchan dune in Oman with calculations using a mathematical model (FLOWSTAR) and measurements in a wind tunnel. All three techniques demonstrate similar patterns of velocity, confirming the acceleration of flow up the windward slope, deceleration between the crest and brink and significant flow deceleration upwind of and at the toe of the dune. The FLOWSTAR model is unable accurately to predict airflow at the brink and its predictions near the surface are highly susceptible to small-scale terrain irregularities. The measurements of shear velocity in the field and those predicted by the FLOWSTAR model reflect observations of previous studies including the widely reported upwind reduction in shear velocity. Such a reduction in shear velocity upwind of the dune should result in a reduction in sand transport and sand deposition. This is not observed in the field. Wind tunnel modelling using a near-surface pulse-wire probe suggests that the field and FLOWSTAR methods of shear velocity derivation are inadequate. The wind tunnel results exhibit no reduction in shear velocity upwind of or at the toe of the dune. This maintenance of upwind shear stress may be caused by concave (unstable) streamline curvature, which is not taken into account by the field and FLOWSTAR techniques. From this hypothesis, a new model of dune dynamics is developed relying on the establishment of an equilibrium between windward slope morphology, streamline curvature and streamwise acceleration.

Recent research has revealed that quasi-instantaneous turbulent Reynolds stresses (RS, -u’w’) and decomposed ‘quadrant’ activity (e.g., ejections and sweeps) over dunes in fluvial and wind tunnel studies has shown that turbulent stresses at the toe of a dune often exceed time-averaged, streamwise shear stress (u*2) estimates. It is believed that semi-coherent turbulent structures are conveyed toward the bed along concave streamlines in this region, and these activities cause fluctuations in local surface stresses that assist in grain entrainment. This study focuses on event-based landform scale interactions between turbulent airflow and sediment transport over a vegetated foredune through the assessment of two different experiments that took place at Greenwich Dunes, Prince Edward Island National Park, P.E.I., Canada. Reynolds decomposition of quasi-instantaneous fluctuating u’ and w’ signals into quadrant (Q) activity (i.e., Q1 outward interactions: u’>0, w’>0; Q2 ejections: u’<0, w’>0; Q3 inward interactions: u’<0, w’<0; Q4 sweeps: u’>0, w’<0) is explored to identify patterns of Reynolds stress signal distributions over the dune. Over flat surfaces, Q2 ejections and Q4 sweeps often dominate RS signals, whereas Q1 outward and Q3 inward interactions are less frequent and contribute negatively to RS generation. Over dunes, however, topographically forced streamline curvature effects alter quadrant activity distributions and, hence, near-surface RS generation by enhancing (at the toe) or inhibiting (at the crest) turbulent motions. This results in Q2 ejection and Q4 sweep activity dominating stress generation on the beach, dune toe, and lower stoss slope, whereas, toward the crest, there is a shift toward Q1 outward and Q3 inward interactions. A flow 'exuberance effect' was identified that explains the contribution of positive to negative contributing activities that varies over the dune and helps explain the spatial pattern in RS. RS generation and sand transport depend on location over the dune (via topographic forcing effects on streamline curvature and flow stagnation/acceleration) and on incident flow direction via topographic steering effects that alter the apparent ‘steepness’ of the dune to flow streamlines. Transport on the lower portion of the dune was driven predominantly by ejection and sweep activity, while toward the crest it became dominated by outward and inward interactions, likely due to increased frequency of streamwise gusts (+u’) and vertical lift (+w’) in topographically compressed flow. / Graduate

Transportation of unprocessed multiphase reservoir fluids from deep/ultra deep offshore through a long subsea tieback/pipeline is inevitable. This form of transportation is complex and requires accurate knowledge of critical transport velocity, flow pattern changes, phase velocity, pressure drop, particle drag & lift forces, sand/liquid/gas holdup, flow rate requirement and tieback sizing etc at the early design phase and during operation for process optimisation. This research investigated sand transport characteristics in multiphase, water‐oil‐gas‐sand flows in horizontal, inclined and vertical pipes. Two critical factors that influence the solid particle transport in the case of multiphase flow in pipes were identified; these are the transient phenomena of flow patterns and the characteristic drag & lift coefficients ( D C , L C ). Therefore, the equations for velocity profile were developed for key flow patterns such as dispersed bubble flow, stratified flow, slug flow and annular flow using a combination of analytical equations and numerical simulation tool (CFD). The existing correlations for D C & L C were modified with data acquired from multiphase experiment in order to account for different flow patterns. Minimum Transport Velocity (MTV) models for suspension and rolling were developed by combining the numerically developed particle velocity profile models with semi‐empirical models for solid particle transport. The models took into account the critical parameters that influence particle transport in pipe flow such as flow patterns and particle drag & lift coefficients, thus eliminate inaccuracies currently experienced with similar models in public domain. The predictions of the proposed MTV models for suspension and rolling in dispersed bubble, slug flow and annular flow show maximum average error margin of 12% when compared with experimental data. The improved models were validated using previously reported experimental data and were shown to have better predictions when compared with existing models in public domain. These models have the potential to solve the problems of pipe and equipment sizing, the risk of sand deposition and bed formation, elimination of costs of sand unloading, downtime and generally improve sand management strategies.

Understanding how swirl flows can be applied to processes in the oil and gas industry and how problems might hinder them, are the focus of this thesis. Three application areas were identified: wet gas metering, liquid loading in gas wells and erosion at pipe bends due to sand transport. For all three areas, Computational Fluid Dynamics (CFD) simulations were performed. Where available, experimental data were used to validate the CFD results. As a part of this project, a new test loop was conceived for the investigation of sand erosion in pipes. The results obtained from CFD simulations of two-phase (air-water) flow through a pipe with a swirl-inducing device show that generating swirl flow leads to separation of the phases and creates distinct flow patterns within the pipe. This effect can be used in each of the three application areas of interest. For the wet gas metering application, a chart was generated, which suggests the location of maximum liquid deposition downstream of the swirling device used in the ANUMET meter. This will allow taking pressure and phase fraction measurements (from which the liquid flow rate can be determined) where they are most representative of the flow pattern assumed for the ANUMET calculation algorithms. For the liquid loading application, which was taken as an upscaling of the dimensions investigated for the wet gas metering application, the main focus was on the liquid hold-up. This parameter is defined as the ratio of the flowing area occupied by liquid to the total area. Results obtained with CFD simulations showed that as the water rate increases, the liquid hold-up increases, implying a more effective liquid removal. Thus, it was concluded that the introduction of a swirler can help unload liquid from a gas well, although no investigation was carried out on the persistance of the swirl motion downstream of the device. For the third and final application, the erosion at pipe bends due to sand transport, the main focus was to check the erosion rate on the pipe wall with and without the introduction of a swirler. The erosion rate was predicted by CFD simulations. The flow that was investigated consisted of a liquid phase with solid particles suspended in it. The CFD results showed a significant reduction in erosion rate at the pipe walls when the swirler was introduced, which could translate into an extended working life for the pipe. An extensive literature review performed on this topic, complemented by the CFD simulations, showed the need for a dedicated multiphase test loop for the investigation of sand erosion in horizontal pipes and at bends. The design of a facility of this type is included in this thesis. The results obtained with this work are very encouraging and provide a broad perspective of applications of swirl flows and CFD for the oil and gas industry.

La façade littorale du Grand Port Maritime de Dunkerque est une cellule sédimentaire quasi-fermée où les formes dunaires résultent de l’imbrication de facteurs humains et naturels. Ce littoral peut être divisé en deux parties : la partie Ouest est constituée d’un cordon bordier sur une longueur de 7 km (plage du Clipon) et le long de la partie Est, la plage est adossée à une digue en enrobé bitumineux de 6 km de long (digue du Braek) où des transferts sableux se produisent. L’objectif de cette étude est de (1) caractériser les formes dunaires et leur évolution sur un site artificiel, (2) quantifier le transport éolien sur le haut de plage, le versant externe de la dune bordière et la digue du Braek, et (3) proposer des mesures de gestion afin de remédier aux contraintes d’exploitation engendrées par les dépôts éoliens sur les infrastructures. A moyen terme (28 ans), l’analyse diachronique de photographies aériennes montre que les superficies dunaires ont fortement augmenté depuis 1983. A court terme (2 ans), des mesures topographiques révèlent que les dunes continuent de se développer aujourd’hui mais gardent la marque des interventions anthropiques passées. Sur la digue du Braek, des formes dunaires se sont naturellement constituées sur l’asphalte. Le sable a été colonisé par Ammophila arenaria qui s’est enraciné sous l’enrobé par l’intermédiaire de fissures. Une typologie de ces dunes de digue a été proposée. A l’Est, des dunes se développent en pied de digue en raison de l’interruption des transferts sédimentaires longitudinaux par une jetée. Des piégeages éoliens in situ ont montré que le transport éolien était essentiellement contrôlé par la vitesse du vent et la source de sable disponible. Par vents frontaux et obliques, les dunes de pied de digue constituent la principale source des envols, et le transport éolien est favorisé par une accélération du vent sur le versant exposé. Différents types de brise-vent ont été testés sur l’ensemble du site afin de trouver le meilleur mode de gestion souple de ces envols de sable. Ces analyses montrent que si la localisation des structures brise-vent a une grande influence sur leur efficacité, les systèmes habituellement utilisés sur les plages (ganivelles, filets synthétiques) peuvent aussi favoriser le développement de dunes sur une digue en asphalte. Les mesures de gestion envisagées sont la stabilisation des principales sources de sable en pied de digue ainsi que le renforcement de la dune bordière aux endroits les plus fragiles. / The coastline of Dunkirk seaport is a sedimentary cell where dune morphology is the result of both natural processes and human intervention. This shoreline can be divided in two parts: a western part of 7 km long, where a macrotidal beach is backed by naturally developing coastal dunes, and an eastern part consisting of a 6 km long asphalt dike overtopped in places by low elevated aeolian dunes. This study aims at (1) describing aeolian dunes and their evolution on a human-altered coast, (2) quantifying aeolian sand transport on the upper beach, the seaward slope of the foredune and the asphalt dike, and (3) suggesting management measures in order to solve windblown sand accumulation problems on harbour infrastructures. On the middle term (28 years), diachronic analysis of aerial photographs shows rapid development of dunes area since 1983. On the short term (2 years), topographic surveys reveal that dune development is still ongoing, although dune morphology keeps the marks of passed human interventions. Dunes have naturally developed on asphalt and their formation is initiated by Ammophila arenaria colonisation of numerous perpendicular cracks in the dike. A typology of these dunes is proposed. Dike toe dunes have developed at the beach/dike contact in the most eastern part of the site, where a jetty is interrupting net sediment transport. In situ field measurements revealed that aeolian sand transport is mainly controlled by wind speed and the source of sand available. Under oblique to direct onshore winds, dike toe dunes are the main source of windblown sand on the dike, and aeolian transport is enhanced by a wind speedup on the windward slope. Different kinds of windbreaks have been tested in order to solve uncontrolled aeolian sand transport problems on the dike, as well as to consolidate foredunes. It appeared from the topographic surveys carried out on the windbreaks that although their location seemed to play a major role on the amount of sand captured, fences and synthetic fabrics deployed on sandy surfaces were also able to trap windblown sand on a seaport dike. Management measures considered are a stabilisation of main sand sources at the dike toe and consolidation of foredunes with windbreaks.

No Litoral Norte do Rio Grande do Sul, ao norte do balneário Xangri-lá, a barreira holocênica encontra-se parcialmente coberta pela fase moderna e relativamente ativa de um campo de dunas transgressivo, enquanto que, ao sul deste balneário, o campo de dunas cobre completamente a barreira. Este trabalho contribuiu para o conhecimento acerca desse comportamento diferenciado de desenvolvimento da fase moderna do campo de dunas transgressivo sobre a barreira holocênica. Foram utilizadas séries temporais de vento (direção e velocidade) e precipitação de estações meteorológicas localizadas ao sul e ao norte de Xangri-lá, bem como foram realizadas medições simultâneas de vento, por meio de anemômetros portáteis, imediatamente ao norte e ao sul desse balneário. Potenciais de transporte de areia foram calculados para ambas as estações meteorológicas. Os registros históricos da estação de Tramandaí (mais ao sul) indicaram maiores velocidades de vento e menores de precipitação em relação à estação de Torres (mais ao norte). Devido a maior velocidade dos ventos em Tramandaí, o potencial de transporte de areia nessa localidade foi superior a Torres, indicando o favorecimento da migração das dunas em suas proximidades. O comportamento desigual de desenvolvimento da fase moderna do campo de dunas transgressivo pode então estar relacionado a maior velocidade e frequência dos ventos NNE, NE, ENE e E em Tramandaí (ou seja, ao sul de Xangri-lá), além da menor precipitação que também favorece um transporte de areia mais eficiente ao sul de Xangri-lá. / In the north coast of Rio Grande do Sul, to the north of Xangri-lá beach, the Holocene barrier is partially covered by the modern and relatively active phase of a transgressive dune field, while to the south of this balneario the dune field completely covers the barrier. This work contributed to the knowledge about this differentiated development behavior of the modern phase of the transgressive dune field on the holocene barrier. Time series of wind (direction and speed) and precipitation of meteorological stations located to the south and north of Xangri-lá were used, as well as simultaneous wind measurements using portable anemometers, immediately to the north and south of this balneario. Sand transport potentials were calculated for both meteorological stations. Historical records of the Tramandaí station (further south) indicated higher wind speeds and lower precipitation relative to the Torres station (further north). Due to the greater speed of the winds in Tramandaí, the potential of sand transport in this locality was higher than Torres, indicating the favor of the migration of the dunes in its proximities. The uneven developmental behavior of the modern phase of the transgressive dune field can then be related to the higher speed and frequency of the NNE, NE, ENE and E winds in Tramandaí (ie, south of Xangri-lá), as well as the lower precipitation also favors more efficient sand transportation south of Xangri-lá.

No Litoral Norte do Rio Grande do Sul, ao norte do balneário Xangri-lá, a barreira holocênica encontra-se parcialmente coberta pela fase moderna e relativamente ativa de um campo de dunas transgressivo, enquanto que, ao sul deste balneário, o campo de dunas cobre completamente a barreira. Este trabalho contribuiu para o conhecimento acerca desse comportamento diferenciado de desenvolvimento da fase moderna do campo de dunas transgressivo sobre a barreira holocênica. Foram utilizadas séries temporais de vento (direção e velocidade) e precipitação de estações meteorológicas localizadas ao sul e ao norte de Xangri-lá, bem como foram realizadas medições simultâneas de vento, por meio de anemômetros portáteis, imediatamente ao norte e ao sul desse balneário. Potenciais de transporte de areia foram calculados para ambas as estações meteorológicas. Os registros históricos da estação de Tramandaí (mais ao sul) indicaram maiores velocidades de vento e menores de precipitação em relação à estação de Torres (mais ao norte). Devido a maior velocidade dos ventos em Tramandaí, o potencial de transporte de areia nessa localidade foi superior a Torres, indicando o favorecimento da migração das dunas em suas proximidades. O comportamento desigual de desenvolvimento da fase moderna do campo de dunas transgressivo pode então estar relacionado a maior velocidade e frequência dos ventos NNE, NE, ENE e E em Tramandaí (ou seja, ao sul de Xangri-lá), além da menor precipitação que também favorece um transporte de areia mais eficiente ao sul de Xangri-lá. / In the north coast of Rio Grande do Sul, to the north of Xangri-lá beach, the Holocene barrier is partially covered by the modern and relatively active phase of a transgressive dune field, while to the south of this balneario the dune field completely covers the barrier. This work contributed to the knowledge about this differentiated development behavior of the modern phase of the transgressive dune field on the holocene barrier. Time series of wind (direction and speed) and precipitation of meteorological stations located to the south and north of Xangri-lá were used, as well as simultaneous wind measurements using portable anemometers, immediately to the north and south of this balneario. Sand transport potentials were calculated for both meteorological stations. Historical records of the Tramandaí station (further south) indicated higher wind speeds and lower precipitation relative to the Torres station (further north). Due to the greater speed of the winds in Tramandaí, the potential of sand transport in this locality was higher than Torres, indicating the favor of the migration of the dunes in its proximities. The uneven developmental behavior of the modern phase of the transgressive dune field can then be related to the higher speed and frequency of the NNE, NE, ENE and E winds in Tramandaí (ie, south of Xangri-lá), as well as the lower precipitation also favors more efficient sand transportation south of Xangri-lá.

No Litoral Norte do Rio Grande do Sul, ao norte do balneário Xangri-lá, a barreira holocênica encontra-se parcialmente coberta pela fase moderna e relativamente ativa de um campo de dunas transgressivo, enquanto que, ao sul deste balneário, o campo de dunas cobre completamente a barreira. Este trabalho contribuiu para o conhecimento acerca desse comportamento diferenciado de desenvolvimento da fase moderna do campo de dunas transgressivo sobre a barreira holocênica. Foram utilizadas séries temporais de vento (direção e velocidade) e precipitação de estações meteorológicas localizadas ao sul e ao norte de Xangri-lá, bem como foram realizadas medições simultâneas de vento, por meio de anemômetros portáteis, imediatamente ao norte e ao sul desse balneário. Potenciais de transporte de areia foram calculados para ambas as estações meteorológicas. Os registros históricos da estação de Tramandaí (mais ao sul) indicaram maiores velocidades de vento e menores de precipitação em relação à estação de Torres (mais ao norte). Devido a maior velocidade dos ventos em Tramandaí, o potencial de transporte de areia nessa localidade foi superior a Torres, indicando o favorecimento da migração das dunas em suas proximidades. O comportamento desigual de desenvolvimento da fase moderna do campo de dunas transgressivo pode então estar relacionado a maior velocidade e frequência dos ventos NNE, NE, ENE e E em Tramandaí (ou seja, ao sul de Xangri-lá), além da menor precipitação que também favorece um transporte de areia mais eficiente ao sul de Xangri-lá. / In the north coast of Rio Grande do Sul, to the north of Xangri-lá beach, the Holocene barrier is partially covered by the modern and relatively active phase of a transgressive dune field, while to the south of this balneario the dune field completely covers the barrier. This work contributed to the knowledge about this differentiated development behavior of the modern phase of the transgressive dune field on the holocene barrier. Time series of wind (direction and speed) and precipitation of meteorological stations located to the south and north of Xangri-lá were used, as well as simultaneous wind measurements using portable anemometers, immediately to the north and south of this balneario. Sand transport potentials were calculated for both meteorological stations. Historical records of the Tramandaí station (further south) indicated higher wind speeds and lower precipitation relative to the Torres station (further north). Due to the greater speed of the winds in Tramandaí, the potential of sand transport in this locality was higher than Torres, indicating the favor of the migration of the dunes in its proximities. The uneven developmental behavior of the modern phase of the transgressive dune field can then be related to the higher speed and frequency of the NNE, NE, ENE and E winds in Tramandaí (ie, south of Xangri-lá), as well as the lower precipitation also favors more efficient sand transportation south of Xangri-lá.

Jet engines often operate under dirty conditions where large amounts of particulate matter can be ingested, especially, sand, ash and dirt. Particulate matter in different engine components can lead to degradation in performance. The objective of this dissertation is to investigate sand transport and deposition in the internal cooling passages of turbine blades. A simplified rectangular geometry is simulated to mimic the flow field, heat transfer and particle transport in a two pass internal cooling geometry. Two major challenges are identified while trying to simulate particle deposition. First, no reliable particle-wall collision model is available to calculate energy losses during a particle wall interaction. Second, available deposition models for particle deposition do not take into consideration all the impact parameters like impact velocity, impact angle, and particle temperature. These challenges led to the development of particle wall collision and deposition models in the current study. First a preliminary simulation is carried out to investigate sand transport and impingement patterns in the two pass geometry by using an idealized elastic collision model with the walls of the duct without any deposition. Wall Modeled Large Eddy Simulations (WMLES) are carried to calculate the flow field and a Lagrangian approach is used for particle transport. The outcome of these simulations was to get a qualitative comparison with experimental visualizations of the impingement patterns in the two pass geometry. The results showed good agreement with experimental distributions and identified surfaces most prone to deposition in the two pass geometry. The initial study is followed by the development of a particle-wall collision model based on elastic-plastic deformation and adhesion forces by building on available theories of deformation and adhesion for a spherical contact with a flat surface. The model calculates deformation losses and adhesion losses from particle-wall material properties and impact parameters and is broadly applicable to spherical particles undergoing oblique impact with a rigid wall. The model is shown to successfully predict the general trends observed in experiments. To address the issue of predicting deposition, an improved physical model based on the critical viscosity approach and energy losses during particle-wall collisions is developed to predict the sand deposition at high temperatures in gas turbine components. The model calculates a sticking or deposition probability based on the energy lost during particle collision and the proximity of the particle temperature to the softening temperature. For validation purposes, the deposition of sand particles is computed for particle laden jet impingement on a coupon and compared with experiments conducted at Virginia Tech. Large Eddy Simulations are used to calculate the flow field and heat transfer and particle dynamics is modeled using a Lagrangian approach. The results showed good agreement with the experiments for the range of jet temperatures investigated. Finally the two pass geometry is revisited with the developed particle-wall collision and deposition model. Sand transport and deposition is investigated in a two pass internal cooling geometry at realistic engine conditions. LES calculations are carried out for bulk Reynolds number of 25,000 to calculate flow and temperature field. Three different wall temperature boundary conditions of 950 oC, 1000 oC and 1050 oC are considered. Particle sizes in the range 5-25 microns are considered, with a mean particle diameter of 6 microns. Calculated impingement and deposition patterns are discussed for different exposed surfaces in the two pass geometry. It is evident from this study that at high temperatures, heavy deposition occurs in the bend region and in the region immediately downstream of the bend. The models and tools developed in this study have a wide range of applicability in assessing erosion and deposition in gas turbine components. / Ph. D.

River mouths are very active coastal regions. Continuous sediment supply by the river and the movement by wave action cause the shoreline to change in time and space. Modeling of shoreline changes is an essential step before the design of any coastal engineering project. This research aimed to develop a system of numerical models to present the shoreline changes around a river mouth. The system of numerical models has three components: 1) modeling of nearshore wave characteristics, 2) modeling of longshore sand transport rates using the results of the first component, 3) modeling of shoreline changes using the estimated sand transport rates. Thus, firstly, deep water wave characteristics including the annual wave rose affecting Manavgat River mouth have been obtained from the database of NATO TU-WAVES Project. Then REF/DIF1 and SWAN nearshore wave models have been used to find out nearshore wave conditions. Since the results obtained from REF/DIF1 wave model have been found to be more reasonable compared to SWAN&rsquo / s output, REF/DIF1 wave model has been used in preparing a time series nearshore reference wave file with three hours time interval. This reference file has been used to run GENESIS. Last step of the numerical shoreline change modelling of Manavgat River mouth was the calibration procedure in which the &ldquo / transport parameters&rdquo / k1 and k2 have been determined. As there is lack of measurements of shoreline positions that can be used in calibrating shoreline change model, k1 and k2 has been approximately found to be k1=0.516 and k2=0.9 by using an empirical sediment transport formula. As a future study, it is recommended that when the protection structure controlling the river mouth is finished, the measurements of shoreline position behind the structure should be used in verification of shoreline change model in order to get more accurate results.