In this study, the effects of submergence on local scour in a uniform cohesionless sediment bed by a plane turbulent wall jet and the resulting flow field were investigated experimentally. Here, submergence is defined as the ratio of the tailwater depth to the thickness of the jet at its origin. The main focus was to determine scour dimensions at an asymptotic state, examine whether there was similarity in the velocity profiles for the flow in the scour hole, and to determine the growth of the length scales and decay of the maximum velocity of the jet. Also examined were the relationships between the scales for the velocity field in the scour hole and the scour hole size.<p>In the experiments, the range of submergence was varied from 3-17.5, whereas the range of densimetric Froude number and the ratio of the boundary roughness to the gate opening (relative boundary roughness) were varied from 4.4-6.9 and 0.085-0.137 respectively. The velocity field in the scour hole at asymptotic state was measured using a SonTek 16-MHz MicroADV. Time development of the characteristic dimensions of the scour hole was also measured.<p>The dimensions of the scour hole were found to increase with increasing submergence for all experiments with a bed-jet flow regime. In the bed-jet flow regime, the jet remains near the bed throughout the scouring process. Further, the time development of the scour hole dimensions were observed to increase approximately linearly with the logarithm of time up to a certain time before the beginning of asymptotic state for experiments with either the bed-jet or surface-jet flow regimes.<p> The flow field results showed that the velocity profiles in the region of forward flow and the recirculating region above the jet were similar in shape up to about the location of the maximum scour depth. Relationships describing this velocity profile, including its velocity and length scales, were formulated. The decay rate of the maximum velocity, the growth of the jet half-width, and the boundary layer thickness were also studied. The decay and the growth rate of the jet length scales were found to be influenced by the submergence ratio, densimetric Froude number, and the relative boundary roughness.<p>Two distinct stages in the decay of the maximum streamwise velocity, with distance along the direction of flow, were observed for the jet flows having a bed-jet flow regime. The first stage of velocity decay was characterized by a curvilinear decay of velocity, which followed that of a wall jet on a smooth, rigid bed for streamwise distance approximately equal to 2L. For the surface-jet flow regime, the decay of velocity was observed to be similar to that of a free-jump on a smooth, rigid bed for a streamwise distance approximately equal to L. Here, L is defined as the streamwise distance measured from the end of the rigid apron to where the maximum streamwise velocity in the jet is half the velocity of the jet at the end of apron. The streamwise maximum velocity of the jet was then seen to increase in what was called the recovery zone.<p>A relationship for the streamwise decay of the maximum velocity within the scour hole is proposed. Moreover, other scales representing the flow inside the scour hole such as the streamwise distance from the end of the apron to where the streamwise maximum velocity starts to deviate from curvilinear to linear decay and the streamwise distance to where maximum streamwise velocity starts to increase are suggested. Some new results on the velocity distribution for the reverse flow for a bed-jet flow regime are also presented. Finally, some dimensionless empirical equations describing the relationship between the jet scales for the jet flow in a scour hole and the scour hole size are given.

Abstract The influence of rotating and cross flow effect on local heat transfer coefficient and flow visualization for a single confined air/water jet with jet-to-wall spacing from 5 to 11.4, jet Reynolds number from 6500 to 26000, rotational Reynolds number from 0 to 112000, curvature ratio from 150 to , ratio of crossflow massflux to jet mass flux from 0 to 2, and the heat flux from 1430 to 12890W/m2 were reported. The local heat transfer coefficient for air/water along the surface is measured and the effect of the rotation, the jet-to-wall spacing, the surface curvature, local and average Nusselt number, are presented and discussed. Furthermore, flow visualization was made in the present study. Based on the experimental result, it is found that the rotation will induce the centrifugal and coriolis force. It also shows that the heat transfer response will be decreased when the impinging direction parallel to the rotating direction, and increased when impinging direction perpendicular to the rotating direction. Crossflow effect will make Nusselt number decrease to 48% when M=2. Moreover, the roughen surface will increase the heat transfer coefficient up to 22% due to the secondary flow. The flow visualization is used to observe the transition of laminar to turbulence flow and to calculate the boundary layer thickness.

<p>Disturbances introduced in wall-bounded flows can grow and lead to transition from laminar to turbulent flow. In order to reduce losses or enhance mixing in energy systems, a fundamental understanding of the flow stability and transition mechanism is important. In the present thesis, the stability, transition mechanism and early turbulent evolution of wall-bounded flows are studied. The stability is investigated by means of linear stability equations and the transition mechanism and turbulence are studied using direct numerical simulations. Three base flows are considered, the Falkner-Skan boundary layer, boundary layers subjected to wall suction and the Blasius wall jet. The stability with respect to the exponential growth of waves and the algebraic growth of optimal streaks is studied for the Falkner-Skan boundary layer. For the algebraic growth, the optimal initial location, where the optimal disturbance is introduced in the boundary layer, is found to move downstream with decreased pressure gradient. A unified transition prediction method incorporating the influences of pressure gradient and free-stream turbulence is suggested. The algebraic growth of streaks in boundary layers subjected to wall suction is calculated. It is found that the spatial analysis gives larger optimal growth than temporal theory. Furthermore, it is found that the optimal growth is larger if the suction begins a distance downstream of the leading edge. Thresholds for transition of periodic and localized disturbances as well as the spreading of turbulent spots in the asymptotic suction boundary layer are investigated for Reynolds number Re=500, 800 and 1200 based on the displacement thickness and the free-stream velocity. It is found that the threshold amplitude scales like Re^-1.05 for transition initiated by streamwise vortices and random noise, like Re^-1.3 for oblique transition and like Re^-1.5 for the localized disturbance. The turbulent spot is found to take a bullet-shaped form that becomes more distinct and increases its spreading rate for higher Reynolds number. The Blasius wall jet is matched to the measured flow in an experimental wall-jet facility. Both the linear and nonlinear regime of introduced waves and streaks are investigated and compared to measurements. It is demonstrated that the streaks play an important role in the breakdown process where they suppress pairing and enhance breakdown to turbulence. Furthermore, statistics from the early turbulent regime are analyzed and reveal a reasonable self-similar behavior, which is most pronounced with inner scaling in the near-wall region.</p>

A dual-axis fluidic thrust vectoring (FTV) system is proposed where the supersonic propulsive jet of an aircraft is exhausted over a scarfed (swept), curved surface to produce flight control moments in both the pitch and yaw axes. This work contributes towards practical dual-axis FTV through expansion of fundamental curved-wall jet (CWJ) understanding, development of the novel Superimposed Characteristics technique for supersonic nozzle design, and performance evaluation of an experimental scarfed curved wall FTV configuration. Previous work has suggested that the use of a sheared exhaust velocity profile improves the attachment of supersonic jets to curved surfaces; however, evidence to support this is limited. To address this, an inviscid numerical CWJ model was developed using the two-dimensional method of characteristics. A major outcome is improved understanding of the effect of exhaust velocity profile on CWJ wave structure and subsequent jet attachment. A sheared velocity exhaust is shown to generate a wave structure that diminishes adverse streamwise pressure gradients within a supersonic curved-wall jet. This reduces the likelihood of boundary layer separation and as a result, a sheared exhaust velocity CWJ is expected to be less readily separated compared to other exhaust velocity profiles. A novel method termed Superimposed Characteristics was developed for the low-order design of supersonic nozzles with rectangular exits. The technique is capable of generating 3D nozzle geometries based on independent exit plane orientation and exhaust velocity distribution requirements. The Superimposed Characteristics method was used to design scarfed rectangular exit nozzles with sheared velocity exhaust profiles. These nozzles were then evaluated using finite volume computational methods and experimental methods. From the analysis, the Superimposed Characteristics method is shown to be valid for preliminary nozzle design. Experimental methods were used to study the on- and off-design attachment qualities of uniform and sheared velocity exhaust jets for a FTV configuration with an external curved wall termination angle of 90 degrees and scarf angle of 30 degrees. Experiments at the on-design nozzle pressure ratio (NPR) of 3.3 demonstrated pitch and yaw jet deflection angles of 78 degrees and 23 degrees respectively for the uniform exhaust velocity CWJ. The sheared exhaust velocity CWJ achieved lower pitch and yaw deflection angles of 34 degrees and 14 degrees respectively at the same on-design NPR. The lower jet deflection angles observed for sheared exhaust velocity jets is inconsistent with the CWJ model prediction of reduced adverse streamwise pressure gradients; however, there was insufficient experimental instrumentation to identify the cause. In the off-design experiments, the uniform exhaust velocity CWJ was observed to detach at an NPR of 3.6, whilst the sheared exhaust velocity CWJ remained attached at NPRs in excess of 4. The capability of sheared exhaust velocity CWJs to remain attached at higher NPRs is consistent with the analytical theory and the CWJ model predictions. An actuation study was carried out to achieve controlled jet detachment using secondary blowing injected normal to the curved wall. Full separation of the wall jets was achieved downstream of the injection point. This provided vectoring angles of more than 20 degrees in pitch and 10 degrees in yaw, exceeding expected vectoring requirements for practical aircraft control. At the on-design NPR, the uniform and sheared exhaust velocity jets required secondary blowing mass flow rates of 2.1% and 3.8% of the primary mass flow respectively to achieve full separation.

The present thesis deals with the fundamental aspects of turbulent mixingand non-premixed combustion in wall-jet flows. Direct numerical simulations(DNS) of compressible turbulent flows are performed in a wall-jet configura-tion, which has a close resemblance to many industrial combustion applica-tions. The triple ”turbulence-chemistry-wall” interactions are also present inthis flow set-up. These interactions have been addressed by first focusing onturbulent flow effects on the isothermal reaction, including the near-wall issues.Then, by adding heat-release to the simulations, it has been concentrated onheat-release effects on various phenomena that occur in the reacting turbulentwall-jet flow. In the computational domain, fuel and oxidizer enter separatelyin a non-premixed manner and the flow is fully turbulent and subsonic in allsimulations. In the first phase of this study, the case of a turbulent wall-jetincluding an isothermal reaction without heat release is addressed in order toisolate the near-wall effects and the mixing characteristics of the flow and thekey statistics for combustion are studied in the absence of thermal effects. Adeeper insight into three-dimensional mixing and reaction characteristics in aturbulent wall-jet has been gained through investigation of the probability den-sity functions, higher order moments of velocities and reacting scalars and thescalar dissipation rates of different species. In the second phase, DNS of turbu-lent reacting wall-jets including heat release is performed, where a single-stepglobal exothermic reaction with an Arrhenius-type reaction rate is considered.The main target was to identify the heat-release effects on different mixingscales of turbulent wall-jet flow. The scalar dissipation rates, time scale ratios,two-point correlations, one and two-dimensional premultiplied spectra are usedto illustrate the heat release induced modifications. It is observed that heatrelease effects delay the transition process in the chemically reacting cases andenlarge the fluctuation intensities of density and pressure, but have a dampingeffect on all velocity fluctuation intensities. Finer small mixing scales were ob-served in the isothermal simulations and larger vortical structures formed afteradding significant amounts of heat-release. Simulations with different Damk ̈h-  oler numbers, but comparable temperature-rise are performed and the expectedbehavior, a thinner flame with increasing Damk ̈hler number, is observed. Finally, some heat transfer related quantities are examined. The wall heat fluxand the corresponding Nusselt numbers are addressed. The near-wall reactioneffects on the skin friction coefficient are studied and further the reaction char-acteristics are investigated throughout the domain. / QC 20110908

Presented Ph.D. Thesis is focused on the use of the boron-doped diamond (BDD) electrodes for voltammetric and amperometric determination of selected nitrophenols: 2-nitrophenol (2NP), 4-nitrophenol (4NP), and 2,4-dinitrophenol (2,4DNP). These compounds are listed as "priority pollutants" by United States Environmental Protection Agency (US EPA) due to their negative impact on living organisms and are mainly used in agriculture as plant growth stimulators. BDD electrodes are used for determination of wide range of electrochemically both reducible and oxidisable organic compounds and have become a popular electrode material thanks to its commercial availability and excellent mechanical and electrochemical properties. A differential pulse voltammetric method was developed for the determination of 2NP, 4NP and 2,4DNP at a BDD film electrode using electrochemical reduction and of 4NP and 2,4DNP using electrochemical oxidation. The method was successfully applied for the direct determination of these compounds in drinking and river water in the concentration range from 4×10-7 to 2×10-5 mol.L-1 . To improve the limit of quantification, a preconcentration by solid phase extraction from 100 mL (drinking and river water) and 1000 mL (drinking water) of water samples was used with limit of determination...

<p>Disturbances introduced in wall-bounded .ows can grow andlead to transition from laminar to turbulent .ow. In order toreduce losses or enhance mixing in energy systems, afundamental understanding of the .ow stability is important. Inlow disturbance environments, the typical path to transition isan exponential growth of modal waves. On the other hand, inlarge disturbance environments, such as in the presence of highlevels of free-stream turbulence or surface roughness,algebraic growth of non-modal streaks can lead to transition.In the present work, the stability of wall-bounded .ows isinvestigated by means of linear stability equations valid bothfor the exponential and algebraic growth scenario. Anadjoint-based optimization technique is used to optimize thealgebraic growth of streaks. The exponential growth of waves ismaximized in the sense that the envelope of the most ampli.edeigenmode is calculated. Two wall-bounded .ows areinvestigated, the Falkner–Skan boundary layer subject tofavorable, adverse and zero pressure gradients and the Blasiuswall jet. For the Falkner–Skan boundary layer, theoptimization is carried out over the initial streamwiselocation as well as the spanwise wave number and the angularfrequency. Furthermore, a uni.ed transition-prediction methodbased on available experimental data is suggested. The Blasiuswall jet is matched to the measured .ow in an experimentalwall-jet facility. Linear stability analysis with respect tothe growth of two-dimensional waves and streamwise streaks areperformed and compared to the experiments. The nonlinearinteraction of introduced waves and streaks and the .owstructures preceding the .ow breakdown are investigated bymeans of direct numerical simulations.</p><p>Descriptors: Boundary layer, wall jet, algebraic growth,exponential growth, lift-up e.ect, streamwise streaks,Tollmien-Schlichting waves, free-stream turbulence, roughnesselement, transition prediction, Parabolized StabilityEquations, Direct Numerical Simulation.</p>

Notre travail de thèse présente une contribution à l'étude du comportement d'un jet flottant horizontal, représentatif de la dispersion de rejets dans un milieu marin. Il consiste à modéliser ce type d'écoulement par une approche mathématique basée sur la résolution numérique moyennant la méthode des volumes finis, à valider le modèle numérique par des mesures à échelle réduite sur des maquettes expérimentales, et, enfin, à simuler la dispersion de polluants à grande échelle sur un cas réel. Trois cas d’étude ont été abordés:Le premier cas est relatif à l’étude numérique et expérimentale d'un jet flottant turbulent rond et "non-Boussinesq", injecté horizontalement dans un milieu statique et homogène. Les résultats ont permis de décrire la nature du jet et son comportement en fonction des conditions initiales d’éjection. La deuxième étude a concerné un autre cas représentatif des rejets des émissaires de stations d'épuration. Il s’agit d’un jet pariétal admettant l’approximation de Boussinesq en régime de convection mixte. L’objectif ici est d’étudier l'influence de l'effet combiné de la turbulence et de la présence de la paroi sur le comportement du jet. Dans le dernier cas d’étude, on a modélisé, en 2D et en 3D, à grande échelle un processus côtier de dispersion de rejets en surface libre appliqué sur le cas de la pollution de la baie de Tanger. Les résultats ont permis de visualiser le mécanisme de la dispersion et d’avoir des informations précieuses sur l’écoulement généré au voisinage des plages par l’interaction des rejets et des mouvements de flux et de reflux de la marée. / This work is a contribution to the study of horizontal buoyant jet behavior that presents the dispersion of discharges into the marine environment. It consists in the modeling of this flow by a mathematical approach based on numerical simulation by means of the finite volume method, the validation of a numerical model by measurements on experimental model at a small, and, finally, the simulation of pollutant dispersion on a large scale on a real case. Three cases of study were broached: The first case relates to the experimental and numerical study of horizontal round turbulent non-Boussinesq buoyant jet in a static homogeneous environment. The results were used to describe the nature and the behavior of the jet as a function of the initial conditions of ejection. The second study involved another case of discharges from outfalls. We investigated a numerical and experimental study about a horizontal buoyant wall turbulent jet in a static homogeneous environment. The aim was to analyze the influence the effect of both turbulence and wall boundary on the behavior of the jet. The latter case of study focused on numerical simulation in 2D and 3D of the coastal process of discharges dispersion on a free surface. This modeling dealt more precisely with the dispersion of discharges into a marine environment in the presence of cross flows. The bay of Tangier in Morocco was chosen as an application site. The results made it possible to visualize the dispersion mechanism and to gain valuable information on the flow generated by the interaction of discharges and high/low tide movements near the beaches of the bay.

Dans cette étude, le comportement aérodynamique du jet pariétal (Re = 8000) cisaillé latéralement par un courant de perturbation externe (ELS) de profil de vitesse uniforme (Ulf) a été étudié et analysé. Les expérimentations ont été réalisées par PIV et LDV sur une maquette aéraulique isotherme à échelle réduite d’un meuble frigorifique de vente. L’étude est centrée sur la région du jet située à proximité de la section de soufflage (x/e < 10) qui correspond à la zone dans laquelle se développent les instabilités et le processus de transition vers la turbulence. L’analyse des résultats obtenus avec et sans perturbation a mis en évidence que la perturbation entraîne une diminution significative du pouvoir d’entraînement du jet, une forte décroissance de la vitesse moyenne maximale, un faible épanouissement du jet et une augmentation globale des valeurs des moments d’ordre deux de toutes les composantes des contraintes de Reynolds. L’analyse par PIV résolue en temps (10 kHz) montre une topologie déformée et allongée des structures de Kelvin-Helmholtz (K-H) pour (Ulf = 0,5 ms-1) et détachée pour (Ulf = 1 ms-1). Les résultats de l’interaction mutuelle ente les couches interne et externe indiquent que le courant ELS brise partiellement le mécanisme de formation des dipôles de vortex qui deviennent irréguliers et moins prédictifs, ce qui conduit à l’allongement de la zone de transition et retarde donc l’apparition de la zone auto-similaire du jet. D’après la technique POD, l’ELS engendre une redistribution énergétique entre les modes. Le courant ELS affecte également les instabilités K-H en perturbant leur organisation bidimensionnelle, leur topologie, leur alignement et leur fréquence de passage mettant en évidence l’effet inhibiteur exercé sur le développement des structures primaires. Les corrélations spatiales Rvv reflètent la diminution des échelles de longueur dans le cas d’un jet perturbé. / In this study, the aerodynamic behavior of the plane wall jet (Re = 8000) sheared laterally by an external lateral stream (ELS) of a uniform velocity profile (Ulf) was studied and analyzed. The experiments were carried out by PIV and LDV on a reduced-scale isothermal aeraulic model of a refrigerated display cabinet. The study focuses on the near-field region of the jet (x / e <10) which corresponds to the zone of transition to turbulence and onset and development of instabilities. The results obtained with and without perturbation showed a significant decrease in the entrainment rate, a strong decrease in the maximum velocity decay rate, a lower jet expansion and an overall increase in the values of second order moments of the Reynolds stress components. The time-resolved PIV analysis (10 kHz) shows a distorted and elongated topology of the Kelvin-Helmholtz (K-H) structures for (Ulf = 0,5 ms-1) and a detached topology for (Ulf = 1 ms-1). The results of the mutual interaction between the inner and outer layers indicate that the ELS partially breaks the vortex dipole formation mechanism which becomes irregular and less predictive, leading to the elongation of the transitional region and a lag effect in the beginning of the self-similarity region. POD technique reveals the role of the ELS in redistributing energy between the modes. The ELS also affects the K-H instabilities by disrupting their two-dimensional organization, topology, alignment and shedding frequency, highlighting the inhibitory effect exerted on the development of primary structures. The spatial correlations Rvv reflect the decrease of the length scales in the case of a perturbed jet.

The goal of this work is to experimentally assess the influence of limiting walls of Škoda Octavia 3 automobile cabin to the air jet flowing from the right-front situated automotive vent which is part of a car dashboard. The experiment is performed by the smoke visualization method. There is a single construction option measured for an experiment. The setup of the vanes direction and the air flow rate are modified for this option. The experiment is divided into two phases. In the first phase, the visualization of the free air flow is conducted. In the second phase, exit plates are constructed and consequently, the visualization of the wall-jet flow is conducted. The results of both are compared to each other. The results imply that the influence of the surrounding surfaces must be taken into account with the increasing flow rate for the vanes set in the direction of upper-right, middle-right, and middle-middle. There is a direct interaction between the flow and exit plates (the flow impact, the Coanda effect). The free flow does not contain the information about the mutual interaction between the flow and the exit plates, as it is in the case of the wall-jet flow. In the case of the wall-jet flow, the opening of the flow takes place due to the effect of the impact and the subsequential suction caused by the Coanda effect. The exit plates substituting the car dashboard and the front window contribute to the prevention of the air intake from surrounding space and consequently to earlier flow opening from the vent. The present work also contains the measurement methodology and the image evaluation, the comparison with previous free flow measurements (70% match) and the comparison to the measurement of hot-wire anemometry method.