There are two coupled objectives for this study of buoyancy-driven turbulence. The first objective is to determine if the development of a Rayleigh-Taylor (RT) mixing layer can be manipulated experimentally by altering the initial condition of the experiment. The second objective is to evaluate the performance of the Besnard, Harlow, and Rauenzahn (BHR) turbulent transport model when initialized with experimentally measured initial conditions. An existing statistically steady water channel facility at Texas A&M University and existing experimental diagnostics developed for this facility have been used to measure the turbulent quantities of buoyancy-driven turbulence. A stationary, bi-planar grid with a high solidity ratio, σ, has been placed immediately downstream of the termination of the splitter plate, perpendicular to the flow direction, to generate a turbulent initial condition. The self-similar growth parameter, α , for the RT mixing layer has been measured using a visualization technique to determine if the initial conditions affect the development of the RT mixing layer. The self-similar growth parameter, α , decreased from a value of 0.072 ± 0.0003 with the fine grid to values of 0.063 ± 0.0003 and 0.060 ± 0.0003 with the medium and coarse grids, respectively. With the results from the first objective, a unique opportunity arose to evaluate the performance of the variable density, RANS-type, BHR turbulent transport model. Measurements of velocity statistics necessary to initialize the model accurately have been obtained using particle image velocimetry (PIV). The performance of the BHR model was evaluated through comparison of the experimentally measured and BHR modeled self-similar growth parameter, α , from the penetration height of the bubbles/spikes and the self-similar growth parameter, K α , of the turbulent kinetic energy at the centerline of the low Atwood RT driven turbulent mixing layer. When initialized with the experimentally measured initial conditions, the BHR model did agree with the experimental measurements of the penetration height growth parameter, α , as well as the centerline turbulent kinetic energy growth parameter, K α , in the self-similar portion of the flow.

Experiments and direct numerical simulations (DNS) have been performed to examine the e¤ects of initial conditions on the dynamics of a Rayleigh-Taylor unsta- ble mixing layer. Experiments were performed on a water channel facility to measure the interfacial and velocity perturbations initially present at the two-fluid interface in a small Atwood number mixing layer. The experimental measurements have been parameterized for use in numerical simulations of the experiment. Two- and three- dimensional DNS of the experiment have been performed using the parameterized initial conditions. It is shown that simulations implemented with initial velocity and density perturbations, rather than density perturbations alone, are required to match experimentally-measured statistics and spectra. Data acquired from both the exper- iment and numerical simulations are used to examine the role of initial conditions on the evolution of integral-scale, turbulence, and mixing statistics. Early-time turbu- lence and mixing statistics are shown to be strongly-dependent upon the early-time transition of the initial perturbation from a weakly-nonlinear to a strongly-nonlinear flow.

The effect of initial conditions in combined shear- and buoyancy- driven mixing was investigated through the use of an implicit large eddy simulation code under active development at Los Alamos National Laboratory and Texas A&M University. Alterations were done over several months both at Los Alamos National Laboratory and at the Texas A&M University campus, and include a transition from tilted rig to convective channel arrangement, introduction of an inertial reference frame, alteration of boundary conditions, etc. This work resulted in the development of a numerical framework with the capability to model various shear and Atwood number arrangements such as those seen in an inertial confinement fusion environment. In order to validate the code, it was compared to three published experiments, one with Atwood number 0.46 (White et al. 2010), one with high Atwood number 0.6 (Banerjee et al. 2010), and one with very low Atwood number 0.032 (Akula et al. 2012). Upon validating the code, pure Rayleigh-Taylor and pure Kelvin-Helmholtz instabilities were modeled along with five intermediate cases of increasing shear and constant density gradient. Plots of mixing width, Richardson number, growth parameter, and molecular mixing were compared in order to determine at what level of shear the minimum amount of mixing occurs. The results of height gradient and Reynolds number were to previous experiments and theory. The least amount of molecular mixing at the centerline was found to be when the system had a low Atwood number (0.032) and a multimode initial interface perturbation. While the increase in modes of the interface perturbation did not result in a significant change in the growth parameter, the level of molecular mixing at the centerline substantially decreased. As shear was increased in the system, the mixing width and molecular mixing subsequently increased. For this reason, the shear in the system should be eliminated, or at least minimized, if at possible so as to prevent any additional amalgamation in the system. Analysis of the Reynolds number revealed that with an increase in velocity difference between the fluid layers, the value consequently increased. This trend matches with theoretical results as the value is a function of the mixing width and velocity, thus further validating the code. Analysis of the transitional Richardson number revealed that it had a smaller value in the computational case over the experiment, but this fact can be attributed the difference in mixing width between the two methods. The development of the numerical framework with the capability to model various shear and Atwood number arrangements offers the platform for future study of hydrodynamic instabilities.

In stead of assuming the starting observations as zero, the cointegration test statistic derived in this paper takes the initial conditions into consideration. The statistic helps us understand how the initial conditions affect the test and helps us recognize whether the cointegration relationship exists in the data generation process or not. Beside, with this statistic derived with the concept of discriminant function and residual based test, we can simulate our own critical value table in according to what starting observations we have in hand, what significant level we want and what value of rho we meet under H_1.

This thesis examines the effects of spatial location, Reynolds number and near exit flow modification on the development region of a round, free, turbulent jet. It is based on the publications generated by the author. The experiments were carried out over the range of Reynolds numbers between 10000 < ReD < 50000, where ReD is calculated based on the jet exit mean velocity and the nozzle exit diameter. The measurements were performed in the near- to intermediate-field region of a free jet defined between 0 ≤ x/D ≤ 30. In order to control the flow near the exit, two wire rings, with square cross-sections, of sides h = 1.5 mm, and outer diameter Dwire = 71.6 mm (positioned in the shear layer and called Rsl) and Dwire = 60 mm (positioned in the potential core and called Rpc) were placed at a stand-off distance downstream of the jet nozzle exit plane x/D = 0.03. Both stationary and flying hot wires were used to investigate the jet flow field. The results showed a considerable reduction in the jet spread rate and turbulence intensity using the passive rings. The reduction in the velocity decay rate was more obvious in the case of Rsl in lower Re; however, it was observed that as Re increases, the velocity decay rate became nearly the same for both cases of Rsl and Rpc. The axial velocity spectra showed the initial shear layer instability (shear layer mode) was suppressed while the jet preferred instability (preferred mode) remained active as the shear layer and potential core were modified. This shows the separation of these modes and is at variance with ideas that appeared in the literature that claimed the dependency of these two modes. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2012-04-27 16:06:31.03

Approved for public release; distribution in unlimited. / Numerical ocean modeling usually composes various initial- and boundary-value problems. It integrates hydrodynamic and thermodynamic equations numerically with atmospheric forcing and boundary conditions (lateral and vertical) from initial states of temperature, salinity and velocity. Past observations, historical datasets and climatological datasets of the ocean have contributed greatly to the knowledge of the data fields of initial condition, atmospheric forcing and boundary conditions. Change in either initial or boundary condition leads to a variety of model solutions. It is necessary to specify realistic initial and boundary conditions to achieve better understanding and prediction of the ocean behavior. However, uncertainty often exists in both initial and boundary conditions. Up to now, most studies on ocean predictability have usually been for one particular type of model input uncertainty within the three types of uncertainty (initial conditions, open boundary conditions, atmospheric forcing function). This thesis investigates the response of ocean model to the three types of model input uncertainty simultaneously using Princeton Ocean Model (POM) implemented for the Japan/East Sea (JES). / Lieutenant Commander, Taiwan, R.O.C. Navy

Le contexte économique et écologique difficile ainsi que la réglementation en matière d'émissions de CO2 poussent les industriels de l'automobile à améliorer les moteurs à allumage commandé. L'une des voies d'amélioration envisagées est l'admission de mélanges pauvres ou fortement dilués par des gaz d'échappement (EGR) dans la chambre de combustion. La difficulté de ce type de fonctionnement est l'initiation de l'allumage. Afin de pallier ce problème, les systèmes d'allumage sont étudiés et tout particulièrement l'étincelle. Cette décharge est à l'origine de l'apparition d'un plasma et la compréhension des mécanismes impliqués dans le transfert d'énergie entre ce plasma et le gaz réactif environnant est essentielle. Ce travail s'intéresse à la modélisation de l'étincelle dans sa phase d'arc électrique afin de pouvoir prédire le comportement hydrodynamique de l'arc et la propagation de l'onde de choc. Les modèles transitoires bidimensionnels ou tridimensionnels utilisés sont basés sur le logiciel @ANSYS Fluent couplé à des fonctions utilisateurs développées au sein de l'équipe AEPPT. Ils s'appuient dans un premier temps sur la littérature afin de comprendre le comportement général de la décharge, puis sur des configurations expérimentales utilisées dans le cadre du projet ANR FAMAC. Les simulations sont dans un premier temps et en majorité réalisées dans l'air sur des configurations simplifiées de type pointe-pointe afin de valider le modèle. Ensuite, une étude est faite dans une configuration de réacteur où l'arc est généré entre les bornes d'une bougie d'allumage. Le modèle permet de démontrer le rôle de chacun des paramètres initiaux des simulations ainsi que leur impact sur l'écoulement du plasma. L'influence de la prise en compte du champ magnétique est montrée dans le cadre d'un arc impulsionnel nanoseconde. Enfin, le modèle a permis de montrer le rôle d'un écoulement laminaire latéral en direction d'une décharge de type conventionnelle générée par une bobine d'allumage Audi. L'ensemble de ces résultats pourront être le point de départ d'une étude énergétique sur les systèmes d'allumage ainsi que d'une réflexion concernant la compréhension de l'initiation de la combustion. / The economic/ecological context and the CO2 regulation by the "euro" standards lead the automotive industry to improve the spark ignited engines. A way of improvement is the admission of a lean mixture or of a diluted mixture by recirculation of exhaust gases in the combustion chamber. The main difficulty in these conditions is to start the combustion. To overcome this problem, the ignition systems are studied and more particularly the spark. This discharge leads to the apparition of plasma and the understanding of the energy transfer mechanisms between this plasma and the reactive mixture is essential. This work is focus on the modeling of a spark during its electrical arc phase in order to predict the hydrodynamic behavior of the arc and the shock wave propagation. The 2D and 3D transient models are based on ANSYS Fluent coupled with user defined functions developed by the AEPPT team. First, the simulation is based on data from literature review in order to understand the general behavior of the discharge. Then, the model uses experimental configuration developed during the ANR FAMAC project. Simulations are mainly realized in air using simplified configurations (pin-to-pin configurations) in order to valid the model. Then, a study is done in a vessel configuration using real sparkplug geometry. This model allows us to show the role of each initial parameter as well as their impact on the plasma flow. The magnetic field influence is also determined for a nanosecond arc discharge. Finally, the model is used in order to determine the role of a cross flow on a discharge generated by a conventional Audi ignition coil. All these results could be the beginning of an energetic study on ignition systems and could lead to a discussion on the understanding of initiation of the combustion process.

The requirement for reduced jet noise in order to meet stringent noise legislation (civil aviation), and low infra-red observability and the use of unconventional exhaust nozzle configurations to improve aircraft survivability and performance (military aviation) is driving research to develop a better understanding of jet development and mixing mechanisms. One option open to the engineer is the use of small-scale model testing to investigate jets flows and provide valuable data for the validation of numerical models. Although more economical than large/full scale testing, additional factors that influence jet development may be present which would not be present at full scale and whose influence needs to be fully understood in order to allow small scale–large scale read-across. One such factor is the nozzle exit boundary layer. Although considerable data exist on the influence of nozzle exit boundary layers on low speed jet flows, current information on high speed jet flows is limited. It was, therefore, the aim of this thesis to extend the current understanding of nozzle exit boundary layers and their influence on the jet development for high speed jet flows through a combination of experimental and computational techniques. A combination of pneumatic probe measurements and Laser Doppler Anemometry (LDA) was used to investigate nozzle inlet and exit boundary layers of simple conical nozzles and the influence of adding a parallel extension piece. The measurements showed that the rapid acceleration of the boundary layer within the nozzle significantly reduced its momentum thickness Reynolds number and changed the state of the boundary layer from turbulent to laminar-like. The addition of a parallel extension to the nozzle exit returned the boundary layer to a fully turbulent state. A low Reynolds number RANS CFD approach was used to investigate the flow within the nozzle. Simulations using the Launder-Sharma low Reynolds number k–ε model revealed that the magnitude of the acceleration within the conical nozzles resulted in the boundary layer beginning to relaminarise. Full relaminarisation was not achieved due to the short axial distance over which the acceleration was sustained. The addition of a parallel extension provided a relaxation region in which the boundary layer could recover from the acceleration to become fully turbulent. Measurements of the jet plume originating from nozzles with laminar-like and turbulent boundary layers showed little influence of the boundary layer shape and thickness on shear layer spreading and jet centreline development.

Doctor of Philosophy / Department of Economics / E. Wayne Nafziger / This dissertation explores the relationships between three groups of variables in the transition economies of Central and Eastern Europe (CEE) and Commonwealth of Independent States (CIS), from 1989 to 2003. The first group consists of output level and output growth as measured by gross domestic product index (GDPI) and gross domestic product growth (GDPG). The second group consists of two categories of institutional development (INST), and the third group of variables is structural policy reforms (SPR), often known as liberalization policies. This dissertation’s theoretical and empirical framework explicitly account for the endogeneity between output performance variables, the measures of institutional development and SPR. Several empirical specification models of the theoretical simultaneous system of three equations are estimated. In the first group of specification models the dependent endogenous variables are GDPG, SPR and INST, while in the second group the dependant endogenous variables are GDPI, SPR and INST. Moreover, two datasets are used. The first dataset has data from 1989 to 2003, thus covering the whole transition period, while the second dataset is a subset of the first one, containing data for the recovery stage of transition only. The empirical methods used in this dissertation include panel data analysis, principal component analysis, two stages least squares approach and three stage least squares approach in the presence of a SUR modeling procedure. With respect to the output performance equation, the findings of this research indicate that institutional reform (INSTREF), and property rights and contract enforcement institutions (PCINST and ROLINST) are very important determinants of output levels when the whole transition period dataset is used, and very important determinants of both the output levels and output growth rates when the recovery stage dataset is used. While the effect of current SPR is ambiguous, the effect of lagged SPR on output and output growth is positive. Moreover, SPR continue to affect output performance via their indirect effect on institutional development. With respect to the institutional reforms, and property rights and contract enforcement institutions, two sets of determinants were found to be important. On the side of the demand factors, SPR, and especially lagged SPR is found to be an important determinant of both institutional reforms and property rights and contract enforcement institutions. On the side of supply factors, macroeconomic stabilization, a measure of the state’s capacity to implement institutional reform, resulted very important in explaining the variation in institutional reform and property rights and contract enforcement institutions. Political reform, in terms of a shift from the autarkic political regime to a democratic political regime, is found to positively affect institutional development in the recovery stage. With respect to the structural policy reforms’ equations, this dissertation’s main finding is that political reform positively affects SPR in both datasets. Moreover, lagged SPR is found to positively affect SPR, which is an indication of transition governments’ maintained commitment to a package of SPR-s.

Social innovation brings about sustainability which is regarded as a new paradigm for development. In order to bring about social innovation, cross-sector collaboration among different actors is required. However, it is known that establishing cross-sector collaboration is very complex, especially in a penta helix model where the public administration, business, academia, third sector and citizens are all involved. The research aims to investigate the initial conditions for establishing penta helix collaboration in the context of co-produced social innovation from the perspectives of core co-producers. Through a case study of ReTuren, a co-produced public platform for waste handling and prevention in Malmö, Sweden, the research finds out four themes of initial conditions, viz. environment, resources, relationships, and strategy. It is also discussed that the significance of these conditions to the collaboration establishment can depend on the development stage of the social innovation initiative. The research also provides new insights about the unclear boundary and the flexible role of each sector in the penta helix model. Based on the findings, an adapted model of initial conditions from Bryson et al. (2015) for penta helix collaboration in social innovation is created.