NUMERICAL STUDY ON INTERACTIVE LAMINAR NATURAL CONVECTION FROM A PAIR OF VERTICALLY SEPARATED HORIZONTAL CYLINDERS

Abstract

Interactive natural convection heat transfer from a pair of vertically separated horizontal circular cylinders of equal diameter was studied by solving the Navier-Stokes and the energy equations numerically. The flow was assumed to be laminar, and each cylinder was kept isothermal. To handle the present complex flow domain, zone-dependent grid systems were successfully employed with grid overlapping in between. Results are presented for Pr = 0.7 and 10⁴ ≤ Ra ≤ 10⁵, where the Rayleigh number is based on the data of the upper cylinder. The effect of the cylinder-to-cylinder spacing (2 ≤ S/D ≤ 4) and the temperature imbalance ratio between the two cylinders {(δT)₁₂ = 1 and 2] was investigated. It is shown that the thermal performance of the upper cylinder is strongly influenced by the presence of the lower cylinder, while the lower cylinder remains virtually uninfluenced by the upper one for the given conditions. Comparison with earlier experimental results is good. A separation bubble, very unusual in natural convection about smooth bodies, was found on the top of the upper cylinder.