Transient plumes from convective flow instability II horizontal cylinders

In this paper we report on a transient flow instability phenomenon in a horizontal cylinder whose wall is subjected to a step increase in temperature. Pertinent previous work on related subjects is reviewed, and the appropriate governing equations and their numerical simulation are discussed for the present problem. The flow is governed by the Rayleigh number Ra as the other parameters are kept fixed. Studies are carried out for 0 Ra 10⁶. The flowfield consists of two cells for Ra 10⁵. Boundary layers at the wall exhibit a filling box phenomenon, which leads to a vertical stable stratification of the interior temperature field. The two-cell mode is temporarily unstable at Ra = 10⁶, and a plume from a point source of buoyancy at the bottom of the cylinder evolves early in the transient. The downward motion of the stratification front suppresses the growth of the plume, and the flow is restabilized as the front approaches the bottom of the cylinder. The initial and final state in the system is a motionless fluid isothermal at the initial and new wall temperatures, respectively.