An experimental and numerical investigation of natural convection in open ended annuli and its application to the cooling of an aircraft brake assembly

One of the main characteristics of buoyancy induced flows in open ended cavities is its basic geometry which reveals the interactions and the influence of the inner (inside the cavity) and outer (the open region) flow and temperature fields. These interactions are responsible for augmented heat transfer rates from the cavity. Apart from constituting a fundamental area of research in heat transfer, understanding these interactions allows better identification of the design parameters in a number of practical applications. Hence, there is a definitive need to understand the fundamental transport mechanisms associated with buoyancy induced flows in open ended structures.; An experimental and numerical analysis was carried out to develop an understanding of buoyancy induced flows in horizontal, annular cavities which communicate with the surrounding ambient air through one or both open ends. These basic geometries can be used to predict heat transfer rates from several applications of practical interest. The application studied here was the buoyancy induced cooling of an aircraft braking system.; Local and average heat transfer characteristics of the convective flow were obtained from the experimental investigation. Heat transfer correlations were obtained for the range of Rayleigh numbers considered in the experiments. In the numerical investigation, a finite element model was developed to simulate laminar and turbulent three-dimensional flow and temperature field around open annuli. An appropriate set of boundary conditions was proposed to account for the unknown conditions at the opening. Numerical results including the temperature distributions, heat transfer coefficients and flow field showing the interactions between the ambient air and cavity air agreed favorably with experimental results. The finite element numerical results were also found to be in good agreement with results obtained from a finite difference analysis. The effect of important geometrical and thermophysical parameters influencing the heat transfer rates from annular enclosures and open annular cavities was also studied.; Flow regimes ranging from steady state laminar conditions to the fully turbulent boundary layer regime were considered. The present work provides insight into the fundamental aspects of the fluid flow and heat transfer mechanisms associated with natural convection in open ended annuli.