THERMOCAPILLARY FLOW OF A MODERATE- PRANDTL NUMBER FLUID IN ANNULAR POOLS WITH A HEAT INNER CYLINDER

In this paper, a set of direct numerical simulations on the thermocapillary flow of 2cSt silicone oil with Prandtl number of 28.01 in annular pools heated from inner cylinder were carried out. The critical Marangoni number of flow destabilization was determined, and the flow pattern evolution with Marangoni number was revealed when the aspect ratios of the annular pools were 0.375 and 0.75. It was found that the axisymmetric steady flow will transit into different types of oscillatory flows. The critical Marangoni number of flow destabilization depends on types of flow instability. At a small aspect ratio, the flow transits to the oscillatory concentric ring pattern firstly, then into the combination of the oscillatory concentric ring pattern and azimuthal non-uniform temperature fluctuation, and eventually into rotating wave, while it transits directly into the rotating wave at a large aspect ratio. With the increase of Marangoni number, the oscillation frequency of the oscillatory flow increases, and the wave number is almost unchanged. However, when the oscillatory flow pattern transition happens, there is always an abrupt drop of the oscillation frequency.