Flow Transitions in Rayleigh-BÉnard Convection: Influence of Heating Rate

Temporal evolution of the 3-D Rayleigh-Benard convection originated from different heating rates was obtained. The full 3-D governing equations for a Boussines fluid of Prandtl number P= 0.71 were solved inside a rectangular box of aspect ratios Tz= 1.25, Ty = 2 heated from below in the case of adiabatic and perfect conducting side walls. A final steady flow pattern, which consists of two counter rotating rolls with axes parallel to the shorter dimension of the box, is always found. However, the heating rate drives a flow transition for a wide range of Rayleigh numbers when perfect conducting side walls are considered. The flow transition consists of an abrupt change in the rotation sense of two counter rotating rolls and can be attributed to a thermal boundary condition competition. This transition agrees qualitatively with recent experimental results.