An experimental study of a starting plume on a mountain

Transient natural convection is commonly present on a mountain owing to sun radiation. In this study, a starting plume rising from the mountain is experimentally investigated. Shadowgraph technology is employed to visualize transient natural convection flows on a heated copper mountain model in a water tank for a range of Rayleigh numbers from Ra = 7.2 × 106 to 6.44 × 107. Transient flows on the mountain model can be characterized by a thermal boundary layer in the conduction stage and by the starting plume in the transition to a quasi-steady state. A very simple scaling analysis is used to discuss the dynamics of transient natural convection flows on the mountain model. The scaling relations of the thickness and the velocity of the thermal boundary layer and the starting plume on the mountain are obtained, some of which, for example, the velocity of the starting plume in the head velocity increase stage, vP ~ κ2tRa/h3(1 + A−2)1/3, are validated by the experimental data. Additionally, the breaking of the plume head is described and quantified, and the flapping of the plume stem is also discussed.