Transition of natural convection on a cooled circular surface with heated annular extension

Abstract

Transition of natural convection on a circular cooled surface with heated annular extension is investigated in the present study by numerical simulation. Flow features and regimes of natural convection on the surface are studied for which the cooling and heating Rayleigh numbers (Rac and Rah) vary from 1 to 106 with air as the working fluid (Prandtl number of 0.71) at a fixed geometrical aspect ratio of 1 (heating characteristic length/cooling characteristic length). Three steady states revealed by numerical results include steady plume flow, steady dome flow and steady crown flow, which are corresponding to different dynamic regimes: a positive buoyancy dominated regime, a transitional regime and a negative buoyancy dominated regime. Besides, the dynamics behaviors in those steady regimes are scaled and validated by numerical results. The transition route of natural convection on the cooled circular surface with heated annular extension to the unsteady flow is also characterized in the case of Rac/Rah = 1. It has been demonstrated that the steady regime is followed by the unsteady regime. The periodic puffing flow, quasi-periodic flow, and chaotic flow are present in the unsteady regime. In addition, heat transfer in different regime flows is quantified.