PREDICTION OF TURBULENT THERMAL-CONVECTION IN CONCENTRIC AND ECCENTRIC HORIZONTAL ANNULI

Natural convection in horizontal concentric and eccentric annuli with heated inner cylinder has been studied using several variants of single-point closure models at the eddy-diffusivity and algebraic-flux level. The results showed that the application of the algebraic model for the turbulent heat flux <(theta u(i))over bar>, derived from the differential transport equation and closed with the low-Reynolds number form of transport equations for the kinetic energy k, its dissipation rate epsilon, and temperature variance <(theta(2))over bar>, reproduced well the experimental data for mean and turbulence properties and heat transfer over a range of Rayleigh numbers, for different overheatings and inner-to-outer diameter ratios. The application of the extended algebraic turbulence models proved to be crucial for predicting the flow pattern and wall heat transfer at transitional Rayleigh numbers, where substantial turbulence persists only in a narrow plume above the heated inner cylinder, with laminar flow, or even stagnant fluid, prevailing in the remainder of the annuli.