<p>We study the effect of minute perturbations by using blowing jets at upstream and bio-inspired micro denticles on turbulence large-scale motions which are observed to be crucial in controlling heat transfer, noise and drag reduction. This work is divided into two phases. In first phase, we studied the effect of blowing perturbations at upstream on large-scale motions and associated co?herent vortical structures which are crucial in enhancing heat transfer by promoting mixing. The second phase is focused on impact of flow dynamics in preventing the biofouling using micro bioinspired structures and the importance of flow regime in designing the antifouling coating us?ing bioinspired structures is demonstrated, and subsequently, separation bubble dynamics and its characterization is carried out for a transonic channel imposed with pressure gradient to further expand our thesis outcomes to utilize micro bioinspired structures in aerospace applications, noise reduction, and to delay separation.</p> <p><br></p> <p>Extensive studies were focused on the importance of large-scale motions (LSM) and their con?tribution to TKE and turbulence mixing. Although there are studies focusing on the λ2 coherent vortical structures and large-scale motions separately, there are no studies addressing the control?ling using upstream perturbations on the large-scale motions and their associated λ2 vortices. In the first phase of our studies, we used the DNS data of channel flow for Reτ = 394 generated using in-house code. In these simulations, we created blowing perturbations using spanwise jets of low blowing ratio, 0.2, placed at upstream. The spatial large-scale motions are extracted using a a novel 3D adaptive Gaussian filtering technique developed based on Lee and Sung [1] for turbulent pipe flows. POD is used to extract the energetic large-scale motions and coherent vortical structures are extracted using λ2-criterion for its efficiency in educing coherent structures in cross flow jets. The results show that the upstream perturbations enhance streamwise heat flux via energetic LSM and also create a secondary peak of scalar production in the log-layer showing that the perturbations alter LSMs to enhance the heat transfer. Filtered large-scale field from Gaussian filtering technique have an integral length scale greater than 2h (where h is channel half-height) are used to obtain λ2 vortices. The resulted λ2 vortices are of ring-type and have higher signature of temperature than their counterpart. The pre-multiplied spectra shows that the upstream perturbations can excite the large-scale wave-numbers which are in the same order as the jet diameter and spacing between them. Simulations show the presence of secondary peak in the log-layer and increased turbulence production which are eminent of large-scales. Furthermore, our results suggest that jet spacing and diameter are crucial in exciting large-scale field to control turbulent flows.</p> <p><br></p> <p>Evans, Hamed, Gorumlu, et al. [2] modeled the denticles present on Mako shark skin into a diverging micro-pillars. They conducted experimental studies in a water tunnel using these on the back of airfoil exposed to an adverse pressure gradient flow. They observed that presence of these pillars reduced the re-circulation bubble (form drag) by 50%. They proposed a blowing and suction type mechanism by which the micro pillars interact with the boundary layer. However, the details of underlying interfacial mechanism is not completely understood. The unique impact of flow conditions on anti-biofouling and the corresponding mechanisms for the first time is illustrated. We employed commercially available bioinspired structures as micro-diverging pillars making it feasible to apply in real life. We demonstrated the underlying mechanism by which bio?inspired structures are responsible for anti-biofouling. To study the pressure gradient effects on the separation under transonic conditions, we performed direct numerical simulations (DNS) in a non?equilibrium flow created by a sinsuoidal contraction and also, we quantified the separation length,</p> <p>detachment, and attachment points of separation bubble imposed with various pressure gradients and their variation in the transonic and subsonic regimes. We noticed that the resultant shear at the attachement led to the enhancement of coherent structures which are extended into the outer layer under transonic flow which is quite different than the subsonic flow.</p>

The presence of vegetation in open channel flow has a significant influence on flow resistance, turbulence structures and sediment transport. This study will evaluate flow resistance and scale velocity profile in depth limited flow conditions, specifically investigating the impact of vegetation on the flow resistance under submerged flow conditions. The resistance induced by vegetation in open channel flows has been interpreted differently in literature, largely due to different definitions of friction factors or drag coefficients and the different Reynolds numbers. The methods utilized in this study are based on analytical and numerical models to investigate the effects of vegetation presence on flow resistance in open channel flows. The performing strategy approach was applied by three-dimensional computational fluid dynamics (CFD) simulations, using artificial cylinders for the velocity profile. This is to estimate the average flow velocity and resistance coefficients for flexible vegetation, which results in more accurate flow rate predictions, particularly for the case of low Reynolds number. This thesis shows different formulas from previous studies under certain conditions for a length scale metric, which normalises velocity profiles of depth limited open channel flows with submerged vegetation, using both calculated and simulated model work. It considers the submerged vegetation case in shallow flows, when the flow depth remains no greater than twice the vegetation height. The proposed scaling has been compared and developed upon work that have been influenced by logarithmic and power laws to present velocity profiles, in order to illustrate the variety of flow and vegetation configurations.

La Commande prédictive ou Commande Optimale à Horizon Glissant (COHG) devient de plus en plus populaire dans de nombreuses applications pratiques en raison de ses avantages importants tels que la stabilisation et la prise en compte des contraintes. Elle a été bien étudiée pour des systèmes en dimension finie même dans le cas non linéaire. Cependant, son extension aux systèmes en dimension infinie n'a pas retenu beaucoup d'attention de la part des chercheurs. Ce travail de thèse apporte des contributions à l'application de cette approche aux systèmes de lois de conservation. Nous présentons tout d'abord une preuve de stabilité complète de la COHG pour certaines classes de systèmes en dimension infinie. Ce résultat est ensuite utilisé pour les systèmes hyperboliques 2x2 commandés aux frontières et appliqué à un problème de contrôle de canal d'irrigation. Nous proposons aussi l'extension de cette stratégie au cas de réseaux de systèmes hyperboliques 2x2 en cascade avec une application à un ensemble de canaux d'irrigation connectés. Nous étudions également les avantages de la COHG dans le contexte des systèmes non linéaires et semi-linéaires notamment vis-à-vis des chocs. Toutes les analyses théoriques sont validées par simulation afin d'illustrer l'efficacité de l'approche proposée. / The predictive control or Receding Horizon Optimal Control (RHOC) is becoming increasingly popular in many practical applications due to its significant advantages such as the stabilization and constraints handling. It has been well studied for finite dimensional systems even in the nonlinear case. However, its extension to infinite dimensional systems has not received much attention from researchers. This thesis proposes contributions on the application of this approach to systems of conservation laws. We present a complete proof of stability of RHOC for some classes of infinite dimensional systems. This result is then used for 2x2 hyperbolic systems with boundary control, and applied to an irrigation canal. We also propose the extension of this strategy to networks of cascaded 2x2 hyperbolic systems with an application to a set of connected irrigation canals. Furthermore, we study the benefits of RHOC in the context of nonlinear and semi-linear systems in particular with respect to the problem of shocks. All theoretical analyzes are validated by simulation in order to illustrate the effectiveness of the proposed approach.

La dynamique sédimentaire des rivières, souvent modifiée par les aménagements, n'a pas été considérée comme un facteur significatif pour la qualité des environnements riverains et dans les stratégies de restauration. Les approches destinées à restaurer la charge sédimentaire d'une rivière afin qu'elle soit compatible avec les besoins environnementaux et humains, en termes de quantité de sédiments et de granulométrie, sont encore peu développées. De plus, les approches existantes telles que l'injection de sédiments sont souvent coûteuses et nécessitent une intervention humaine. Cette thèse porte sur l'érosion induite des berges, qui constitue une alternative plus durable pour l'environnement. Cette approche consiste à accroître le potentiel d'érosion en certains sites le long des berges d'une rivière chenalisée, en leur permettant d'être plus fortement érodés lors de crues. Deux approches, un modèle physique et des simulations numériques, ont été utilisées pour étudier un site localisé sur le Vieux-Rhin, en aval de Bâle (Suisse), où une modification des épis éxistents est prévue afin de favoriser l'érosion des berges. Dans un premier temps, différents scénarios de modification ont été testés sur une gamme de débits, au moyen d'un modèle physique à échelle de Froude non distordue avec un lit mobile. Dans ce modèle physique, un mélange de quatre classes granulométriques a été adopté afin de reproduire la courbe granulométrique mesurée en nature. Le modèle a été mis à l'échelle par une méthode spécifique qui représente avec précision le début du mouvement de chaque classe. Une stratégie efficace d'érosion des berges a été établie, qui libère des sédiments sans provoquer un retrait excessif des berges qui puisse compromettre la sécurité d'un chenal de navigation adjacent. Par la suite, l'aptitude du modèle numérique Telemac2D à modéliser l'érosion et les processus de rupture de berge a été évaluée. L'algorithme existant de rupture de berge a été modifié pour améliorer les résultats, et les développements implémentés ont été validés par des comparaisons sur des cas-tests de laboratoire. Enfin, les essais du modèle physique ont été simulés numériquement à la même échelle. Les simulations reproduisent les processus observés sur le modèle physique, et les volumes de sédiments érodés et déposés sont du même ordre de grandeur que ceux mesurés / Sediment transport dynamics, often heavily modified by river training, are not yet sufficiently considered as a significant factor in riparian environmental quality and river restoration strategies. Approaches for restoring a river's sediment in quantity and in grain size distribution, so that it is compatible with both ecological and human needs, are still under development. Furthermore, existing approaches such as direct sediment injection are often expensive and require human intervention. This thesis explores induced bank erosion, a more environmentally sustainable alternative. This approach involves increasing the potential for erosion at certain sites along the bank of a trained river, and allowing them to be eroded during high flow periods. Two modelling approaches, physical scaled models and numerical simulation, were used to study a site located on the Old Rhine downstream of Basle (Switzerland) where existing bank protection groynes will be modified to induce bank erosion. Firstly, different modification options were tested over a range of flow rates with a Froude-scaled undistorted movable-bed physical model. The physical model used a mixture of four grain sizes to reproduce the bank grain size distribution found at the site, and was scaled according to a specific method which accurately represents initiation of motion for each grain size. An effective bank erosion strategy was found that releases sediment without compromising the safety of an adjacent navigation channel through excessive bank retreat. Subsequently, the capability of the Telemac2D two-dimensional depth-averaged numerical modelling system to model bank erosion and failure processes was assessed, and the existing bank failure algorithm was modified in order to improve results. Algorithm developments were tested with two laboratory test cases. Then, the physical model tests were simulated at their same scale. Simulations reproduced the processes present in the physical model tests, and volumes of eroded and deposited sediment were of the same order of magnitude

Operações de produção de petróleo, que utilizam sistemas de bombeamento centrífugo submerso, constantemente encontram a presença de gás livre nos poços, o que pode gerar ou agravar problemas como cavitação e falhas dinâmicas, quando o gás é succionado pela bomba. O separador gravitacional do tipo shroud invertido é uma solução possível para este problema nos casos de operação em poços direcionais de petróleo. O trabalho tem como objetivo apresentar um estudo do diâmetro das bolhas que ocorrem no interior de um separador gravitacional gás-líquido do tipo shroud invertido. A finalidade é o aprimoramento de um modelo fenomenológico do funcionamento deste tipo de separador, aplicado à indústria petrolífera, sendo que o modelo fenomenológico garante total separação de gás, fornecidas determinadas condições. O modelo prevê, através do cálculo da energia cinética turbulenta, o tamanho médio das bolhas carregadas para o seio do líquido por aeração no duto anular. Partindo de estudos anteriores, uma verificação do modelo fenomenológico foi feita utilizando um aparato experimental com misturas bifásicas ar-água e ar-óleo em três diferentes inclinações. O aparato possui dimensões radiais reais de um poço de petróleo offshore. Foi utilizado um sensor 3D ORM para a medição do tamanho médio (sauter) das bolhas arrastadas pelo líquido até a entrada do tubo de produção, em diversas combinações de vazões da mistura água-ar. Esta medição permite o ajuste das correlações que regem o modelo fenomenológico, no que diz respeito às equações dependentes do diâmetro teórico de bolhas arrastadas pela fase líquida. As descobertas provenientes deste estudo foram implementadas em um código computacional que será utilizado pela PETROBRAS, financiadora do projeto, para suas operações de bombeamento. / Oil mining operations powered by centrifugal submersible pumping systems suffer constant setbacks due to the presence of free gas in wells. Decompression in the reservoir liberates this gas in the form of bubbles that, upon reaching the suction end of the pump, cause cavitation and dynamic failures resulting in production and equipment losses. The Inverted-shroud gravitational separator is a possible solution to this problem. This work presents a study on diameters of bubbles that occur inside this separator. The goal is the improvement of the understanding of this kind of separator as well as the enhancement of a previously reported phenomenological model, which ensures total gas separation when the separator is installed in directional wells and under specific operational conditions. Empirically adjusted correlations are used to ensure that all entrained bubbles do not reach the pump. The model was tested for two-phase flows of water-air and oil-air mixtures using three different inclinations. Tests were performed with an experimental apparatus that simulates a pilot-scale well casing with an inverted-shroud separator installed. A 3D ORM particle-size sensor was employed in order to measure the average (sauter) diameter of entrained bubbles that are dragged by the liquid flow towards the end of the production tube. This investigation will be used to improve the reliability of the phenomenological model and reduce its dependency on a theoretical prediction of the bubble size. The findings were incorporated to the final version of an in-house gas separator design software developed at the request of PETROBRAS, the project funder and Inverted-shroud patent holder, for usage on its oil mining operations.

Tidal bores are surge waves propagating upstream rivers as the tide rushes into estuaries. They induce large turbulences and mixing of the river and estuary flow of which effects remain scarcely studied. Herein, tidal bores are investigated experimentally and numerically with an idealised model of positive surges propagating upstream an initially steady flow. The experimental work estimated flow changes and typical turbulent length scale evolution induced by undular bores with and without breaking roller. The bore passage was associated with large free surface and flow velocity fluctuations, together with some variations of the integral turbulent scales. Coherent turbulent structures appeared in the wake of leading wave near the bed and moved upward into the water column during the bore propagation. The numerical simulations were based on previous experimental work on undular bores. Some test cases were realised to verify the accuracy of the numerical methods. The results gave access to the detailed flow evolution during the bore propagation. Large velocity reversals were observed close to the no-slip boundaries. In some configurations, coherent turbulent structures appeared against the walls in the wake of the bore front.

L'étude concerne les couches limites turbulentes dans le cas d'écoulements à surface libre sur fond rugueux homogène. Afin de réaliser cette étude, deux dispositifs de mesure PIV par stéréoscopie (PIV 2D-3C) ont été mis en place avec comme double objectif de fournir les lignes directrices au design d'un système stéréoscopique PIV in situ et d'étudier l'influence de la faible submersion des éléments rugueux sur la structure universelle de la couche limite sur fond rugueux, i.e. pour des submersions h/D comprises entre 0,33 et 0,66 (avec h la hauteur des rugosités et D la hauteur d'eau). Pour le premier objectif, le dispositif de mesure a permis un accès optique facilité par un point de vue incliné des caméras à la zone proche des rugosités dans des conditions naturelles d'écoulement (turbidité et éclairement naturels). Les mesures de vitesse ont été faites dans un canal hydraulique de petite dimension (12 m x 0,5 m x 0,25 m) rempli d'hémisphères positionnées en quinconce. Une étude paramétrique de l'influence de l'inclinaison des caméras ainsi que de la turbidité de l'eau sur la qualité des mesures de vitesse a été entreprise suivie par une nouvelle méthodologie basée sur l'analyse de l'intensité lumineuse dans le système. Il a été montré que l'écoulement est correctement résolu jusqu'à une turbidité d'environ 25 NTU avec un angle d'inclinaison par rapport au plan vertical de mesure de 25°. Pour le second objectif, les investigations expérimentales ont été réalisées dans une veine hydraulique de plus grande dimension (26 m x 1,10 m x 0,50 m), dont le fond rugueux est constitué par des cubes en PVC de 2 cm de côté comme dans l'étude de Florens et al. (2013). Les résultats mettent en évidence que l'étendue de la sous-couche rugueuse augmente avec la submersion pour finalement occuper toute la colonne d'eau dans le cas de la plus faible submersion (h/D=0,66). Malgré cela, une loi logarithmique est tout de même observée, et ce, quelle que soit la submersion étudiée. / This work deals with turbulent boundary layers in open-channel flows over rough homogeneous beds. The objectives of this work are, first, to provide some guidance for the design of an efficient in situ stereoscopic PIV measurements system (SPIV), and, second, to assess the effect of the relative submergence on the universal turbulent boundary layer structure for very high relative submergence ratios, i:e: 0.33 < h/D <0.66 (where h is the roughness height and D the water depth). For the first objective, a stereoscopic PIV configuration was set-up with steeply inclined camera viewpoints in order to improve the image quality and the optical access into the bed canopy under naturally occurring turbid conditions. Velocity measurements were undertaken in a 12 m x 0.5 m x 0.25 m open-channel flume filled with staggered hemispheres as surrogates for bed river peebles. A parametric study was then carried out to both analyze how the turbidity and camera angle impact the quality of PIV measurements. An innovative light intensity-based methodology was developed and applied to perform data analysis. The latter shows good PIV results up to 25 NTU with an optimal camera angle with respect to the vertical PIV measurements plane of 25. The SPIV measurements for the second objective were performed in a 26-m-long, 1.10-m-wide and 0.50-m-deep steep open channel filled with 2-cm cubes as in Florens et al. (2013). The results show that the extent of the roughness sublayer increases with the relative submergence to fill the entire water column for the highest relative submergence investigated. Despite this, the logarithmic law is still observed even for the highest relative submergence studied (h/D=0.66).

Common behavioral trends and characteristics of alluvial channels including rivers are extensively discussed in the literature. However, little is known about the hydrodynamic effects of seepage on alluvial channels. Factors like sand bed resistance, stream power of the channel, incipient motion of bed particles, and geometry of the channel cross section are significantly affected by seepage. This thesis presents the experimental investigations that are aimed to find out the quantitative effect of seepage, through a sand bed in downward (suction) direction, on the above mentioned factors. The problem in the sediment transport analysis is that the knowledge of complex interaction of several parameters with seepage cannot be fully obtained. In order to generalize the results, experiments are conducted in four rectangular smooth walled sand bed flumes under steady and fairly uniform flow conditions. Among the four, one is the Large Tilting Flume (LTF), which is 25 m long, 1.80 m wide and 1.00 m deep and with a seepage length of up to 20 m. This LTF is specially built at hydraulic laboratory, Indian Institute of Science exclusively for the present research work especially on alluvial channel regime. The experimental channels are designed to apply controlled amounts of uniform seepage flow in either direction in one flume (Flume-2), and only in downward direction to other three flumes (Flumes 1, 3 and 4). The application of seepage is perpendicular to the sand bed thickness over a sufficient length of the main channel. Appropriate instruments are used to accurately measure the basic experimental variables such as discharge in the main channel, seepage discharge, flow depth, water surface and bed slope, seepage gradients and cross sectional profiles. Experiments are carried out at different conditions (plane beds and curved shape channels) as explained below: Plane sediment beds Series – 1: Experiments to determine incipient motion of bed particles under no-seepage condition. Series – 2: Experiments on the non-transporting condition of the bed particles under both no-seepage and seepage condition. Series – 3: Experiments on the transporting condition of the bed particles under both no-seepage and seepage condition. Curved shape channels Series – A: Experiments to verify Lane’s (1953) geometric profile against higher discharge than prescribed by Lane (1953). Series – B: Experiments to verify the Lane’s (1953) geometric profile by allowing the discharge prescribed by Lane (1953). Series – C: Experiments to predict the final geometric profile by applying suction to Series – B experiments. A wide range of sediment particles are tested. Five different sized uniform sands (d50 = 1 mm, 0.56 mm, 0.65 mm, 1.00 mm and 1.77 mm) and gravel of size d50 = 8.00 mm are used for experimentation. Among the six sizes, three sizes (d50 = 0.56 mm, 0.65 mm, 2 mm) are used for seepage experimentation. The experimental data from the present experiments along with the available data from other sources on more sizes of sand are analyzed, thus covering a wide range of sand sizes. The following important results are obtained from the analysis. A new resistance equation has been developed for plane sediment beds (with little or no-transport) such that the average velocity in the channel depends on the shear velocity Reynolds number. A careful study has been done on incipient motion and concluded that incipient motion is better explained by critical stream power criterion for plane sediment beds. With the help of critical stream power criterion, a straightforward design procedure using design tables/design curves and analytical methods are presented to solve six possible design problems. For plane and non-transporting beds, in general, the stream power in the channel increases with suction and decreases with injection. The increase and decrease depend on the seepage power intensity parameter (NP), initial value of stream power (Ωbo), and critical stream power of the particles under no-seepage condition (Ωco). An expression relating all the influencing parameters is established to quantitatively estimate the stream power (Ωbs) variation with both the types of seepages, i.e., with suction and injection. It is found that the seepage has a significant influence in changing critical stream power for incipient motion of the bed material and the value is significantly different from the no-seepage critical value. An expression is established to quantitatively estimate the critical stream power with seepage (upward and downward) for a given critical stream power (Ωco) of the bed material under no-seepage conditions and initial stream power (Ωbo). It has been established that critical stream power curve used to define incipient motion is valid only for no-seepage condition of the bed and it cannot be used for sand beds under seepage condition, as seepage effects significantly alters the stream power. From the wide range of experimental data (including the observations from LTF) it is found that suction (downward seepage through the sand bed) enhances the transport or aids the incipient motion of bed particles which are initially at rest. Thus, suction reduces the stability and increases the erosion of bed particles when compared to no-seepage conditions. However, it is found that injection (upward seepage) affects in an opposite way, i.e., it can reduce the transport rate or even inhibit the incipient motion. Thus, injection increases the stability and reduces the erosion of bed particles when compared to no-seepage conditions. Therefore, it is concluded that suction increases the mobility of sand particles where as injection decreases their mobility. An expression to find the incipient motion with seepage (both suction and injection) is established in terms of stream power’s (Ωco, Ωbo and Ωbs) based on the present experimental data along with others' data. With the help of these expressions design procedure is developed for ten types of possible problems. A numerical model for spatially varied flow has been developed with the help of the seepage governing equations, developed in this thesis, to compute flow profiles along the channel length. A methodology of predicting the location of incipient motion section in sand bed channels affected by seepage is also presented. Channel geometry affected by seepage (suction) is established in the form of regression relationships for perimeter, flow depth and slope of the channel. Different combinations (bi-variate and tri-variate) of dimensional and non-dimensional regression relationships are developed. An approach to channel design has been developed based on the application of functional analysis of the salient variables that control the channel behavior. And also, it has been established that, Lane’s (1953) profile almost matches with experimental profile for no-seepage condition. The present investigation clearly shows the significance of seepage in altering the hydraulic and sediment transport behavior of sand bed channels. From the practicing engineer’s point of view it is hoped that present design procedures will be helpful in safe guarding the seepage affected channels.

Lors d’une opération de forage, un certain nombre d’événements imprévus par rapport à l’écoulement du fluide de forage dans le puits, peuvent se produire assez rapidement. Des exemples de tels événements sont les afflux de pétrole ("kick") ainsi que les pertes de boue dans la formation. Un "kick" qui augmente en intensité peut entraîner, par ce que l’on nomme, un "blowout" (par exemple l’incident Deepwater Horizon en 2010). Les pertes et les gains sont habituellement détectés en contrôlant l’équilibre de la boue de forage dans le puits, en particulier en contrôlant le débit sortant du puits et en le comparant au débit entrant induit par les pompes. La plupart des méthodes de surveillance, de l’écoulement du puits en cours de forage, est d’utiliser un simple "paddle" (capteur qui mesure la hauteur du fluide de forage avec l’inclinaison d’une pagaie) dans la ligne d’écoulement de retour, ou d’utiliser un débitmètre de Coriolis (débitmètre connu pour sa précision, mais coûteux et nécessite une installation complexe en ajoutant un "by-pass"). Il y a un besoin évident d’un nouveau débitmètre précis, mais facile à installer et peu coûteux. Le canal Venturi a été utilisé comme débitmètre pendant des années dans l’industrie des eaux. Il apparaît comme une solution peu chère mais précise pour mesurer des débits importants. Beaucoup de personnes ont travaillé sur cette solution pour améliorer sa précision et élargir son champ d’application. Ils ont développé des modèles, sur la base d’un processus d’étalonnage, permettant de relier la hauteur en amont au débit. Cela signifie que les modèles actuels, comme ISO NORM 4359 [1], peuvent être uniquement utilisés pour l’écoulement d’eau et pour une géométrie bien spécifique. Comme nous le savons, les boues ont des comportement non- Newtonien, et donc ces modèles établis ne peuvent pas être utilisés avec ce type de fluides. Pour notre application, la forme trapézoïdale apparaît comme un bon compromis entre la précision et la portée des mesures de débit. Ainsi, nous avons développé un modèle capable de calculer le débit en prenant en compte les propriétés du fluide ainsi que les paramètres géométriques du canal. Ce modèle a été simplifié sous forme 1D en utilisant la théorie des eaux peux profondes, et a été complété par un modèle de friction tenant en compte de la variation des propriétés des fluides et de la géométrie du canal. Ce modèle a été validé par une série d’expériences avec les deux types de fluides: Newtonien et non-Newtonien, où nous avons mesuré le débit et la hauteur de l’écoulement à différents endroits le long du canal Venturi. Nous avons également réalisé des simulations 3D, en simulant des écoulements Newtoniens et non- Newtonien le long du canal. Pour généraliser cette étude, cette démarche a été étendue à une autre forme de Venturi plus adapté à un certain design de plate-forme pétrolière. Les corrélations et les modèles développés et validés expérimentalement au cours de cette étude peuvent être utilisés pour étendre l’utilisation des canaux Venturi à tous les fluides Newtonien mais aussi non-Newtonien. Il est maintenant l’occasion pour les industries de proposer une solution, peu chère mais précise pour mesurer les débits dans des canaux ouverts et pour tous types de fluides. / During a drilling operation, a certain number of unexpected events, related to the flow of drilling fluid in the well, may happen rather quickly. Examples of such events are formation fluid influx (kick) and mud loss to the formation. An uncontrolled kick that increases in intensity may result in what is known as a blowout (e.g. the Deepwater Horizon incident in 2010). Influxes and kicks are traditionally detected by monitoring the drilling mud balance in the well, in particular, by monitoring the flow out the well and comparing it to the incoming flow induced by the pumps. Most methods of monitoring the flow out of the well while drilling consists in using a simple paddle (sensor that measures the height of drilling fluid with the inclination of a paddle) in the return flow line, or in using a Coriolis flow meter (flow meter known for its accuracy but expensive and requires a complex installation by adding a bypass). There is a clear need of a new accurate flow meter, but easy to install and inexpensive. The Venturi flume has been used as flow meter for years in water industry. It appears as a cheap but accurate solution to measure large flow rates. Many people have worked on this solution to improve its accuracy and to expand its scope. They have developed models, based on a calibration process, to relate the upstream height to the flow rate. This means that current models, as ISO NORM 4359 [1], can be used only for water flow and specific geometry. As known, muds have non-Newtonian behavior and water models cannot be used with this kind of fluids. For our application, trapezoidal shape appears as a good compromise between accuracy and range of flow rate measurements. Thus, we built a model able to compute the flow rate with taking into account fluid properties and geometrical parameters. This model is simplified in 1D form by using the Shallow Water theory, and completed by a friction model taking into account the variation of fluid properties and geometry along the open channel. It have been validated by series of experiments with both Newtonian and non-Newtonian fluids, where we measured the flow rate and heights of the flow at different locations along the trapezoidal Venturi flume. It have been also completed by 3D CFD which has been simulated both Newtonian and non-Newtonian flows along the flume. To generalized this study, the work was extended to another shape of Venturi more suited to some rig design. The correlations and models developed and experimentally validated during this research can be used to extend the use of Venturi flume flow meters for any fluids : Newtonian and non- Newtonian. It is an opportunity for industries to propose a cheap but accurate solution to measure flow rates in open channels with any kind of fluids.

Operações de produção de petróleo, que utilizam sistemas de bombeamento centrífugo submerso, constantemente encontram a presença de gás livre nos poços, o que pode gerar ou agravar problemas como cavitação e falhas dinâmicas, quando o gás é succionado pela bomba. O separador gravitacional do tipo shroud invertido é uma solução possível para este problema nos casos de operação em poços direcionais de petróleo. O trabalho tem como objetivo apresentar um estudo do diâmetro das bolhas que ocorrem no interior de um separador gravitacional gás-líquido do tipo shroud invertido. A finalidade é o aprimoramento de um modelo fenomenológico do funcionamento deste tipo de separador, aplicado à indústria petrolífera, sendo que o modelo fenomenológico garante total separação de gás, fornecidas determinadas condições. O modelo prevê, através do cálculo da energia cinética turbulenta, o tamanho médio das bolhas carregadas para o seio do líquido por aeração no duto anular. Partindo de estudos anteriores, uma verificação do modelo fenomenológico foi feita utilizando um aparato experimental com misturas bifásicas ar-água e ar-óleo em três diferentes inclinações. O aparato possui dimensões radiais reais de um poço de petróleo offshore. Foi utilizado um sensor 3D ORM para a medição do tamanho médio (sauter) das bolhas arrastadas pelo líquido até a entrada do tubo de produção, em diversas combinações de vazões da mistura água-ar. Esta medição permite o ajuste das correlações que regem o modelo fenomenológico, no que diz respeito às equações dependentes do diâmetro teórico de bolhas arrastadas pela fase líquida. As descobertas provenientes deste estudo foram implementadas em um código computacional que será utilizado pela PETROBRAS, financiadora do projeto, para suas operações de bombeamento. / Oil mining operations powered by centrifugal submersible pumping systems suffer constant setbacks due to the presence of free gas in wells. Decompression in the reservoir liberates this gas in the form of bubbles that, upon reaching the suction end of the pump, cause cavitation and dynamic failures resulting in production and equipment losses. The Inverted-shroud gravitational separator is a possible solution to this problem. This work presents a study on diameters of bubbles that occur inside this separator. The goal is the improvement of the understanding of this kind of separator as well as the enhancement of a previously reported phenomenological model, which ensures total gas separation when the separator is installed in directional wells and under specific operational conditions. Empirically adjusted correlations are used to ensure that all entrained bubbles do not reach the pump. The model was tested for two-phase flows of water-air and oil-air mixtures using three different inclinations. Tests were performed with an experimental apparatus that simulates a pilot-scale well casing with an inverted-shroud separator installed. A 3D ORM particle-size sensor was employed in order to measure the average (sauter) diameter of entrained bubbles that are dragged by the liquid flow towards the end of the production tube. This investigation will be used to improve the reliability of the phenomenological model and reduce its dependency on a theoretical prediction of the bubble size. The findings were incorporated to the final version of an in-house gas separator design software developed at the request of PETROBRAS, the project funder and Inverted-shroud patent holder, for usage on its oil mining operations.