Hysteretic Phenomena in Transition from Forced Convection to Natural Convection around a Heated Cylinder

Abstract

Two-dimensional numerical computations have been conducted to investigate combined forced and natural convection around a cylinder in a cross flow. Reynolds number, Re, ranged between 75 and 150. Rayleigh number, Ra, was changed from 0 to 7×10⁵. Combined convective heat transfer characteristics cannot be expressed by a simple summation of forced and natural convective heat transfer characteristics. An abrupt decrease of mean Nusselt number, Nu_m, is observed in transition from forced convection to natural convection. A hysteresis occurs in the transition region and Nu_m has two different values which depend on initial conditions. This is attributed to subcritical bifurcation of flow behind the cylinder. Nu_m is higher for unsteady flows than for stcady flow in such a transition region.