AN INVESTIGATION AND COMPARATIVE-ANALYSIS OF 2-DIMENSIONAL AND 3-DIMENSIONAL TURBULENT NATURAL-CONVECTION IN A HORIZONTAL ANNULUS

In the present study, simulation of turbulent buoyancy-driven flow in an annulus bounded by concentric, horizontal cylinders and adiabatic end walls has been carried out. Time-averaged equations of turbulent fluid motion and heat transfer were solved using a wall function approach coupled with the standard kappa-epsilon model. Discretization of the governing equations was achieved using a finite element scheme based on the Garlerkin method of weighted residuals. Using a two-dimensional analysis, results were obtained for Rayleigh numbers ranging from 10(6) to 10(9) and the effects of Prandtl number and radius ratio on the flow and heat transfer characteristics were thoroughly examined. A wide range of parameters (10(6) < Ra < 10(9), 0.01 < Pr < 5000, 1.5 < R < 11) was considered in the present study. A comprehensive comparative analysis establishing a unified treatment of previous experimental and computational results is presented. A good agreement was found between the results from this investigation and previous works. Results obtained from a three-dimensional model are also presented to describe more realistic three-dimensional flow characteristics. It is shown that, if the annulus is sufficiently long, there exists a core region over a substantial length of the cavity, which can be approximated by a two-dimensional model.