Dans le but d'étudier certains aspects dynamiques de la convection profonde atmosphérique, nous avons développé un modèle bidimensionnel axé sur le développement d'une cellule orageuse simple. Ce modèle considère des éléments de volume, où nous faisons l'hypothèse que les différents champs thermodynamiques sont homogènes. Ces volumes sont fixes dans l'espace et le temps et sont traversés par les flots d'air humide de sorte que leurs contenus varient au cours du temps. Durant ces évolutions l'eau subit des changements de phases. Ces phénomènes, simultanés dans la nature, sont représentés par un mécanisme à étapes successives dans le modèle. Une première étape se déroule en système ouvert: l'air circule pendant un pas de temps d'intégration entre les éléments de volume; l'air conserve ses propriétés pendant le déplacement. Les deux étapes suivantes se produisent dans chaque élément de volume considéré alors en système fermé et isolé: une première étape d'homogénéisation de l'air en pression et ensuite en température et enfin une étape de restauration de l'équilibre des phases de l'eau compte tenu de la nouvelle répartition des constituants et de leur état thermodynamique. Cette discrétisation du mécanisme d'évolution du contenu des éléments de volume nous permet d'utiliser les lois de la thermodynamique classique dans des systèmes ouverts. Ce mécanisme mène à une équation thermodynamique originale. Les autres équations du modèle sont les équations de l'hydrodynamique classique, les équations de la quantité de mouvement et de continuité. Pour l'intégration des équations, nous avons utilisé une méthode de filtrage numérique basée sur les transformations de Laplace, due à P. Lynch (1984) et adaptée à l'intégration par J. Van Isacker (1985). Au niveau du calcul, les champs de masse, de pression et des quantités de mouvement sont adaptés aux échanges de matières entre éléments de volume voisins à l'aide du processus d'intégration. Les équilibrages de phases interviennent comme ajustement du résultat de l'intégration. Ils modifient le défaut de balance hydrostatique qui sera minimisé au cours du pas d'intégration suivant grâce au filtrage de la méthode numérique. Les simulations réalisées à l'aide du modèle restituent de manière raisonnable les caractéristiques essentielles de la convection profonde atmosphérique. Nous avons utilisé le modèle pour étudier le développement d'un orage de masse d'air de manière plus approfondie. Ainsi, le développement initial, la croissance de la cellule convective, la formation de vortex ont été corrélés avec la structure de la flottabilité dans l'étude des mécanismes mis en oeuvre. Nous avons examiné les déplacements horizontaux et les accélérations verticales en termes de mélanges de masses d'air et des changements de phases qu'ils induisent. Dans l'étude de l'évolution des différentes formes d'énergie, cinétique, potentielle et interne et de leurs conversions, nous avons recherché les contributions dominantes à leurs variations et montré les rôles prépondérants joués par les processus de changement de phase et d'homogénéisation locale de la pression dans la variation de l'énergie interne. Dans l'examen de l'effet dynamique de la convection profonde sur le courant moyen, nous avons montré que, dans certains cas, nous avons non seulement transfert vertical d'énergie cinétique mais également création d'énergie cinétique du courant moyen. Le cumulonimbus peut dans certains cas agir comme moteur pour les mouvements atmosphériques à plus grande échelle.

The inner magnetosphere modeling is an important component of the magnetosphere simulation frameworks with significant implications for space weather and a. principle methodology to understand the magnetospheric response to changes in the solar wind. The thesis shows our efforts in constructing and validating the contemporary Rice Convection Model (RCM) code and its interface as a next-generation code to predict electric fields, field-aligned currents, and energetic particle fluxes in the inner magnetosphere and subauroral ionosphere during geomagnetic disturbed times. The RCM was used to simulate the geomagnetic storms with fixed boundary conditions of time-dependent Tsyganenko-Mukai boundary conditions. This work shows the results of two extremely- strong storm events with significant interchange motion. The ring current injection predicted by the RCM is shown to be overestimated, consistent with the previous results of overestimating particle fluxes by the RCM. This effect is magnified here since the southward component of interplanetary magnetic field is very strong reaching about 50 nT. Time-dependent Borovsky's boundary condition is implemented and used to alleviate the huge pressure and get better tendency of ring current energy calculated by the Dessler-Parker-Sckopke relation. This work also describes a new module of generalized Knight's relation to compute the parallel potential drops from the calculated field-aligned currents through Vasyliunas equation. It gives different ionospheric conductance and plasma drift signatures particularly around the midnight. The inclusion of parallel electric fields will replace the treatments of energy flux in the substorm simulations since that the Hardy normalization cannot perform the desired function during the substorm expansion phase and the energy flux floor gives arbitrary enhanced the precipitating energy flux and ionospheric conductances at high latitude especially for the westward clectrojet around the midnight. Since the original Knight's relation gives too large field-aligned potential drop, the modified Knight's relation is applied and implemented successfully into the RCM. Therefore, the RCM is capable of real time event simulation including strong geomagnetic storms and magnetospheric substorms, although full validation of model predictions with typical observations remains to be done.

Buildings in USA consume close to 40% of overall energy used and fenestration products (e.g. windows, doors, glazed-wall etc.) are the largest components of energy loss from buildings. Accurate evaluation of thermal performances of fenestration systems is critical in predicting the overall building energy use, and improving the product performance. Typically, two-dimensional (2-D) heat transfer analysis is used to evaluate their thermal performance as the 3-D analysis is highly complex process requiring significantly more time, effort, and cost compared to 2-D analysis. Another method of evaluation e.g. physical test in a hotbox is not possible for each product as they are too expensive. Heat transfer in fenestration products is a 3-D process and their effects on overall heat transfer need to be investigated. This thesis investigated 3-D heat transfer effects in fenestration systems in comparison to the 2-D results. No significant work has been done previously in terms of 3-D modeling of windows, which included all the three forms of heat transfer e.g. conduction, convection and radiation. Detailed 2-D and 3-D results were obtained for broad range of fenestration products in the market with a range of frame materials, spacers, insulated glass units (IGU), and sizes. All 2-D results were obtained with Therm5/Window5 (e.g. currently standard method of evaluating thermal performance) and GAMBIT/FLUENT while all 3-D results were obtained with GAMBIT/FLUENT. All the three modes of heat transfer mechanism were incorporated in the heat transfer modeling. The study showed that the overall 3-D heat transfer effects are relatively small (less than 3%) for present day framing and glazing systems. Though at individual component level (e.g. sill, head, Jamb) 3-D effects were quite significant (~10%) but they are cancelled by their opposite sign of variation when overall fenestration system effect is calculated. These 3-D heat transfer effects are higher for low conducting or more energy efficient glazing and framing systems and for smaller size products. The spacer systems did not have much impact on the 3-D effects on heat transfer. As the market transforms towards more insulating and higher performance fenestration products, 3-D effects on heat transfer would be an important factor to consider which it may require correlations to be applied to 2-D models, or may necessitate the development of dedicated 3-D fenestration heat transfer computer programs.

Turbulent mixed convection is a complicated flow where the buoyancy and shear forces compete with each other in affecting the flow dynamics. This thesis deals with the near wall dynamics in a turbulent mixed convection flow over an isothermal horizontal heated plate. We distinguish between two types of mixed convection ; low-speed mixed convection (LSM) and high-speed mixed convection (HSM). In LSM the entire boundary layer, including the near-wall region, is dominated by buoyancy; in HSM the near-wall region, is dominated by shear and the outer region by buoyancy. We show that the value of the parameter (* = ^ determines whether the flow is LSM or HSM. Here yr is the friction length scale and L is the Monin-Obukhov length scale. In the present thesis we proposed a model for the near-wall dynamics in LSM. We assume the coherent structure near-wall for low-speed mixed convection to be streamwise aligned periodic array of laminar plumes and give a 2d model for the near wall dynamics, Here the equation to solve for the streamwise velocity is linear with the vertical and spanwise velocities given by the free convection model of Theerthan and Arakeri [1]. We determine the profiles of streamwise velocity, Reynolds shear stress and RMS of the fluctuations of the three components of velocity. From the model we obtain the scaling for wall shear stress rw as rw oc (UooAT*), where Uoo is the free-stream velocity and AT is the temperature difference between the free-stream and the horizontal surface.A similar scaling for rw was obtained in the experiments of Ingersoll [5] and by Narasimha et al [11] in the atmospheric boundary layer under low wind speed conditions. We also derive a formula for boundary layer thickness 5(x) which predicts the boundary layer growth for the combination free-stream velocity Uoo and AT in the low-speed mixed convection regime.