FLOW CHARACTERISTICS AND STRUCTURES OF THREE-DIMENSIONAL UNSTEADY THERMAL CONVECTION IN A CONTAINER

In this study, we numerically investigates the flow and thermal characteristics of the three-dimensional thermal convection in a cubic cavity heated below in the gravitational field, concerning about spatially-averaged kinetic energy (K) over bar, Nusselt number Nu and flow structure. We assume Prandtl number Pr = 7.1 (water) and Rayleigh number Ra = 1.0x10(4) - 3.5x10(5). As a result, we have specified two of three important values of the Rayleigh number which demarcate different flow bifurcations and are referred to as the second and third critical Rayleigh numbers Ra-c2 and Ra-c3. We have found that Ra-c2 and Ra-c3 are roughly 2.6x10(5) and 3.1x10(5), respectively. We have observed a histerisis effect upon the value of Ra-c2 with chaotic behaviour at Ra approximate to Ra-c2, and revealed flow structures. In addition, we investigate the relationship between Ra and the oscillatory-convection frequency. The increasing rate of the (K) over bar (mean) with increasing Re shows a different manner from that of Nu(inflow-ave, mean). That is, the former is progressive and the latter is asymptotic, as Re increases. Both the values of (K) over bar (mean) and Nu(inflow-ave, mean) in oscillatory flow tend to be smaller than those in steady flow, respectively. Then, there exist small jumps/drops of (K) over bar (mean) and Nuinflow-ave, mean at Ra = Ra-c2.