Natural Convection In A Top Cooled Section-triangular Cavity

Natural convection is driven by buoyancy generated by the difference of fluid density. It is of foundamental and practical significance. Natural convection in cavities has been paid conderable attention due to its prensence in nature and engineering application. Natural convection in a section-triangluar space is considered in building design; that is, attics of reasonable design may provide residents with thermal comfort and achieve energy conservation. This is also one of national long term sustainability plans. Accordingly, natural convection in a section-triangular cavity has attracted a number of investigators.In the thesis, the development of natural convection in the top cooled section-triangular cavity is argued using a scaling analysis. Some of the scaling relations obtained are validated by numerical results and there exists good agreement between scaling predictions and numerical results. Additionally, the dependence of flows and heat transfer in the cavity on governing parameters (such as the Rayleigh number, the Prandtl number and the aspect ratio) is characterized and quantified using three dimensional numerical results in comparison with previous experiments. Essential research progresses involve:(1) Dynamics and heat transfer of transient flows in a section-triangluar cavity are investigated using a scaling analysis. The thickness and velocity scales of the thermal boundary layer, the intrusion and the plume and the time scales of the transition from one dominance to the other are obtained. Possible flow regimes with different dominances of dynamics and heat transfer are presented in governing parameter space.(2) The three-dimensional numerical results demonstrate the presence of longitudinal rolls in the cavity. The mechanism responsible for the appearance of longitudinal rolls is discussed. The range of governing parameters for the existence of longitudinal rolls is given.(3) The three-dimensional numerical results show the bifurcation of multiple solutions. The flow structure of the solutions is described, and the bifurcation is presented in governing parameter space.Through studying flows and heat transfer induced by the coupled of the horizontal (from inclined walls) and vertical (from inclined and bottom walls) temperature gradients, gain further insights into dynamics and heat transfer of flows and transitions between different flow patterns.