Thermocapillary convection in a differentially heated two-layer annular system with and without rotation

Thermocapillary convection in a differentially heated bilayer annular pool consisting of 5cS silicone oil and HT-70 is investigated by a series of three-dimensional numerical simulations. Both systems with and without rotation are considered. The results indicate that the thermocapillary convection is steady and axisymmetric when the Marangoni number is small. The system rotation suppresses the radial flow in the lower layer. Once the Marangoni number exceeds a threshold value, three-dimensional oscillatory flow occurs in both layers simultaneously. The stability diagram reveals that weak rotation destabilizes the axisymmetric flow, while stronger rotation retards the onset of oscillatory flow. The wave patterns for oscillatory flow appear in the form of blade-like waves propagating outward. The surface oscillation and the interface oscillation always share a common frequency but have about a half-period phase lag. In the rotating pool, single group of curved hydrothermal waves propagates in the azimuthal direction opposite to the pool rotation. As the rotation rate increases, the wave number increases while the oscillation frequency decreases.