Les nuages de convection restreinte sont omniprésents au-dessus de l'Océan Tropical et durant l'été dans la couche limite des latitudes moyennes . Ils ont un impact sur la structure thermodynamique de la basse atmosphère et, par le biais de leur interaction avec la radiation solaire, ils influencent le budget énergétique à la surface. Dans ce projet, nous introduisons un paramétrage des nuages de convection restreinte dans le Modèle Régional Canadien du Climat (MRCC). Ce paramétrage est couplé au schéma de convection, qui est celui de Bechtold-Kain-Fritsch. La représentation de ces nuages ainsi que du MRCC avec ce paramétrage est évalué au-dessus du Pacific selon le protocole du GEWEX Pacific Cross-section Intercomparaison (GPCI). ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Convection restreinte, Paramétrage de la couverture nuageuse, Modèles régionaux du climat.

In recent years the U. S. and Canada have seen a steady increase in energy consumption. The U. S. in particular uses 25% more energy than it did 20 years ago. With declining natural resources and an increase in fuel costs, it has become important to find methods of reducing energy consumption, in which energy conservation in space heating and cooling has become a widely researched area. One method that has been identified to reduce the energy required for space heating is the use of radiant panels. Radiant panels are beneficial because the temperature set points in a room can be lowered without sacrificing occupant comfort. They have therefore become very popular in the market. Further research, however, is required to optimize the performance of these panels so energy savings can be realized. <br /><br /> An analytical model has been developed to predict the panel temperature and heat output for perimeter radiant panel systems with a known inlet temperature and flow rate, based on a flat plate solar collector (RSC) model. As radiative and convective heat transfer coefficients were required to run the model, an analytical analysis of the radiative heat transfer was performed, and a numerical model was developed to predict the convective heat transfer coefficient. Using the conventional radiative heat exchange method assuming a three-surface enclosure, the radiative heat transfer could be determined. Numerically, a correlation was developed to predict the natural convective heat transfer. <br /><br /> To validate the analytical model, an experimental analysis was performed on radiant panels. A 4m by 4m by 3m test chamber was constructed in which the surrounding walls and floor were maintained at a constant temperature and the heat output from an installed radiant panel was measured. Two radiant panels were tested; a 0. 61m wide panel with 4 passes and a 0. 61m wide panel with 8 passes. The panels were tested at 5 different inlet water temperatures ranging from 50°C to 100°C. <br /><br /> The RSC model panel temperature and heat output predictions were in good agreement with the experimental results. The RSC model followed the same trends as that in the experimental results, and the panel temperature and panel heat output were within experimental uncertainty, concluding that the RSC model is a viable, simple algorithm which could be used to predict panel performance.

The steady problem of free convective heat transfer from an isothermal inclined elliptic cylinder and its stability is investigated. The cylinder is inclined at an arbitrary angle with the horizontal and immersed in an unbounded, viscous, incompressible fluid. It is assumed that the flow is laminar and two-dimensional and that the Boussinesq approximation is valid. The full steady Navier-Stokes and thermal energy equations are transformed to elliptical co-ordinates and an asymptotic analysis is used to find appropriate far-field conditions. A numerical scheme based on finite differences is then used to obtain numerical solutions. Results are found for small to moderate Grashof and Prandtl numbers, and varying ellipse inclinations and aspect ratios. <br /><br /> A linear stability analysis is performed to determine the critical Grashof number at which the flow loses stability. Comparisons are made with long-time unsteady solutions.

A numerical study of natural convection across a window cavity with an insect screen was performed in order to investigate the effects of changing several variables on the heat transfer through the system. A two-dimensional, laminar model was created using the Computational Fluid Dynamics software FLUENT. The system was approximated by three rectangular zones, the largest representing the open room, a smaller area with an isothermal wall representing the window cavity and a thin area representing the insect screen, which connected the two other zones. The insect screen was assumed to be a porous media with a known pressure drop taken from experimentation and the Darcy-Forchheimer equation was applied to this zone. The factors that were changed in order to examine the effects were two window cavity heights and two widths, five different screen porosities and a variety of window, screen and ambient temperature combinations. The model was compared to analytical solutions for a vertical flat plate, as well as a qualitative analysis done through a simple flow visualization experiment for a midrange porosity of 0.5. It was found that the model matched the analytical solution very well and exhibited the same flow patterns as in the experiment. First a non-heated screen was used, simulating nighttime conditions. Velocity vector and temperature plots were created in order to see the changes in flow patterns as the porosity of the screen was decreased for the various geometries and as the temperature between the window and screen increased. Several flow patterns were observed. For small screen/window spacing, 0.0127m, the flow is fairly uniform for all porosities and follows the entire length of the cavity, slowing in velocity for decreasing porosities. For larger spacing, 0.0254m, there are recirculation zones present, one back up the screen, and one in the bottom corner which causes the flow to exit the cavity before it reaches the bottom. The results were then non-dimensionalized and the heat transfer rates were examined by comparing the local and average Nusselt and Rayleigh number for each model. The results showed the effects of the flow patterns on the heat transfer, with end effects jumping the Nusselt number as the flow navigates the bottom corner. These effects are lessened with decreasing porosity. The average Nusselt number also followed the same trend as flat plate correlations, but with less heat transfer. Finally, a methodology was proposed to approximate the heat transfer as resistor network in order to simplify the heat transfer calculations into a 1-D transfer analysis for building sciences applications. Each element of the system, the window, insect screen and open room, was reduced to an isothermal layer in order to describe the system solely by temperature differences in order to find the heat transfer rates. This final step was done in conjunction with ongoing research at the University of Waterloo Solar Thermal Research Lab.

In recent years the U. S. and Canada have seen a steady increase in energy consumption. The U. S. in particular uses 25% more energy than it did 20 years ago. With declining natural resources and an increase in fuel costs, it has become important to find methods of reducing energy consumption, in which energy conservation in space heating and cooling has become a widely researched area. One method that has been identified to reduce the energy required for space heating is the use of radiant panels. Radiant panels are beneficial because the temperature set points in a room can be lowered without sacrificing occupant comfort. They have therefore become very popular in the market. Further research, however, is required to optimize the performance of these panels so energy savings can be realized. <br /><br /> An analytical model has been developed to predict the panel temperature and heat output for perimeter radiant panel systems with a known inlet temperature and flow rate, based on a flat plate solar collector (RSC) model. As radiative and convective heat transfer coefficients were required to run the model, an analytical analysis of the radiative heat transfer was performed, and a numerical model was developed to predict the convective heat transfer coefficient. Using the conventional radiative heat exchange method assuming a three-surface enclosure, the radiative heat transfer could be determined. Numerically, a correlation was developed to predict the natural convective heat transfer. <br /><br /> To validate the analytical model, an experimental analysis was performed on radiant panels. A 4m by 4m by 3m test chamber was constructed in which the surrounding walls and floor were maintained at a constant temperature and the heat output from an installed radiant panel was measured. Two radiant panels were tested; a 0. 61m wide panel with 4 passes and a 0. 61m wide panel with 8 passes. The panels were tested at 5 different inlet water temperatures ranging from 50°C to 100°C. <br /><br /> The RSC model panel temperature and heat output predictions were in good agreement with the experimental results. The RSC model followed the same trends as that in the experimental results, and the panel temperature and panel heat output were within experimental uncertainty, concluding that the RSC model is a viable, simple algorithm which could be used to predict panel performance.

The steady problem of free convective heat transfer from an isothermal inclined elliptic cylinder and its stability is investigated. The cylinder is inclined at an arbitrary angle with the horizontal and immersed in an unbounded, viscous, incompressible fluid. It is assumed that the flow is laminar and two-dimensional and that the Boussinesq approximation is valid. The full steady Navier-Stokes and thermal energy equations are transformed to elliptical co-ordinates and an asymptotic analysis is used to find appropriate far-field conditions. A numerical scheme based on finite differences is then used to obtain numerical solutions. Results are found for small to moderate Grashof and Prandtl numbers, and varying ellipse inclinations and aspect ratios. <br /><br /> A linear stability analysis is performed to determine the critical Grashof number at which the flow loses stability. Comparisons are made with long-time unsteady solutions.

A numerical study of natural convection across a window cavity with an insect screen was performed in order to investigate the effects of changing several variables on the heat transfer through the system. A two-dimensional, laminar model was created using the Computational Fluid Dynamics software FLUENT. The system was approximated by three rectangular zones, the largest representing the open room, a smaller area with an isothermal wall representing the window cavity and a thin area representing the insect screen, which connected the two other zones. The insect screen was assumed to be a porous media with a known pressure drop taken from experimentation and the Darcy-Forchheimer equation was applied to this zone. The factors that were changed in order to examine the effects were two window cavity heights and two widths, five different screen porosities and a variety of window, screen and ambient temperature combinations. The model was compared to analytical solutions for a vertical flat plate, as well as a qualitative analysis done through a simple flow visualization experiment for a midrange porosity of 0.5. It was found that the model matched the analytical solution very well and exhibited the same flow patterns as in the experiment. First a non-heated screen was used, simulating nighttime conditions. Velocity vector and temperature plots were created in order to see the changes in flow patterns as the porosity of the screen was decreased for the various geometries and as the temperature between the window and screen increased. Several flow patterns were observed. For small screen/window spacing, 0.0127m, the flow is fairly uniform for all porosities and follows the entire length of the cavity, slowing in velocity for decreasing porosities. For larger spacing, 0.0254m, there are recirculation zones present, one back up the screen, and one in the bottom corner which causes the flow to exit the cavity before it reaches the bottom. The results were then non-dimensionalized and the heat transfer rates were examined by comparing the local and average Nusselt and Rayleigh number for each model. The results showed the effects of the flow patterns on the heat transfer, with end effects jumping the Nusselt number as the flow navigates the bottom corner. These effects are lessened with decreasing porosity. The average Nusselt number also followed the same trend as flat plate correlations, but with less heat transfer. Finally, a methodology was proposed to approximate the heat transfer as resistor network in order to simplify the heat transfer calculations into a 1-D transfer analysis for building sciences applications. Each element of the system, the window, insect screen and open room, was reduced to an isothermal layer in order to describe the system solely by temperature differences in order to find the heat transfer rates. This final step was done in conjunction with ongoing research at the University of Waterloo Solar Thermal Research Lab.

In this thesis, several aspects of the convection, magnetic, and optical auroral dynamics of the high-latitude ionosphere are investigated from multi-instrument observations. The spatial and temporal relationships between nightside radar flow enhancements (NRFEs) and auroral intensifications are studied in Chapter 3. The NRFEs on open field lines usually are associated with very little accompanying auroral and magnetic activity. The NRFEs on closed field lines are often accompanied by optical auroral activity, but there is not a definite one-to-one correspondence. Both the statistical investigation and event study showed that the NRFEs may occur nearly simultaneously with the auroral intensifications. Because existing models associating the tail reconnection process and near-geosynchronous onset of substorms do not explain these correlated radar and optical observations very well, we propose a new model to explain the nearly simultaneous onset of the NRFEs and the auroral intensifications. In Chapter 4 we describe a small postmidnight substorm event on October 9, 2000 during dominantly IMF By+ Bz+ conditions. A sequence of three optical auroral intensifications and Pi2 bursts were found. The first two activations were characteristic of pseudobreakups, while the last and strongest intensification corresponded to a substorm expansive phase (EP). The auroral, magnetic and radar signatures of the event are interpreted as the consequence of three successive drift-Alfven-ballooning (DAB) mode instabilities in the near-geosynchronous orbit plasma sheet (NGOPS). About 10 minutes after the EP onset, there was a second auroral brightening. The convection feature during this second auroral brightening was consistent with the scenario of a Stage-2 EP. We suggest that the first two pseudobreakups, the Stage-1 EP, and the Stage-2 EP are related, respectively, to loading-unloading, directly driven, and internal magnetotail processes. Finally, in Chapter 5, we make some comparisons between the ionospheric plasma convection vortex structure observed by SuperDARN and the associated equivalent current pattern derived from the magnetometer observations. The discrepancies between the equivalent convection (EQC) and the SuperDARN-observed convection (SDC) pattern are explained in terms of the effect of day-night photoionization conductance gradient, and the coupling between field-aligned currents (FACs) and ionospheric conductances. In particular, we found the agreement between the EQC and SDC patterns is rather poor for a counterclockwise convection vortex. We suggest the discrepancies are probably due to a downward FAC-conductance coupling process.

In our project we discuss a finite element time-relaxation method for high Reynolds number flows. The key idea consists of using local projections on polynomials defined on macro element of each pair of two elements sharing a face. We give the formulation for the scalar convection–diffusion equation and a numerical illustration.

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