BUOYANCY-INDUCED SECONDARY VORTICES IN THE ENTRANCE SECTION OF A HORIZONTAL STRAIGHT TUBE

Abstract

Developing mixed connective flow in the entrance section of a horizontal straight lube is analyzed with special emphasis on the buoyancy-induced secondary vortices. The flow is subject to a constant wall temperature. Elliptic calculations on a half cross-section grid an performed for various Grashof numbers and two Prandtl numbers. It appears that for air (Pr = 0.7) the flow exhibits a two-vortex solution for all Grashof numbers and axial positions investigated, whereas for water (Pr = 5.0), secondary flow evolves from a two-vortex solution, via a four-vortex solution toward a six-vortex solution for increasing Grashof numbers and axial distances. Calculations on a full cross-section grid reveal that these solutions are insensitive to white noise perturbations in the “initial” flow field.