Laminar natural convection heat transfer from sharp-edged horizontal bars with flow separation

Abstract

Laminar natural convection over a sharp-edged horizontal bar situated in an infinite fluid medium has been investigated numerically and experimentally. Finite-difference solutions to the two-dimensional Navier-Stokes and energy equations were obtained with a fixed Prandtl number of 0.7 for the two configurations: a flat plate of finite thickness and a square bar. The difficulty associated with the complex physical flow domain was overcome by using the body-fitted coordinates. In the numerical study we found no indication of flow separation for the flat plate, in the range ofRayleigh number 10 3 ⩽ Ra ⩽ 10 5. For the square bar, however, the boundary layer separated easily at the upper sharp edges for Ra ⩾ 5 × 10 3 and well-defined twin vortices were identified above the upper horizontal surface. A Mach-Zehnder interferometric study was concurrently carried out in air for the square bar to determine the local temperature and Nusselt number distributions in the Rayleigh number range 1.95 × 10 4 ⩽ Ra ⩽ 1.53 × 10 5. Comparison of the two results, the numerical and the experimental, offered good agreement.