I UNSTABLE NATURAL CONVECTION IN A VERTICAL CHANNEL WITH HOT-COLD WALL CONFIGURATION

The unstable phenomena induced by the natural convection in an open-ended vertical channel with a hot-cold wall configuration are investigated. The compressible solver combining absorbing and non-reflecting boundary conditions for extremely low Mach numbers is applied to eliminate the problem of requiring a priori knowledge of the flow rate. It is found that the existing empirical experience for the natural convection in a vertical channel cannot be applied to the current configuration. In order to better reflect the underlying physics, the turbulent behavior near the wall is investigated and the result shows that Grossmann-Lohse (GL) theory, originally proposed of horizontal (Rayleigh-Benard) convection, can be applied to describe the current flow behavior. From the correlation between the Rayleigh number and Nusselt number, it can be estimated that this kind of unstable phenomenon can enhance the heat transfer by around 10%.