Structural changes of a radially symmetric thermocapillary flow in the shallow cavity partially covered by a solid film

Numerical study is devoted to the spatial transformations of a radially symmetric flow in the liquid, filling a shallow cylindrical cavity covered partially by a solid non-deformable film. The upper part of liquid has a free surface in the center of which a beam of light produces the hot dot. The heating generates a divergent thermocapillary motion along the free surface after that the liquid flows under the immovable solid film. The edge of this film induces the perturbations into the current. At definite values of heat generation these perturbations begin to increase and cause the radial flow symmetry breakdown that visually leads to the origin of the vorticity in azimuthal plane. Three-dimensional calculations have been fulfilled on the base of interfacial hydrodynamics equations using mathematical package “Comsol Multiphysics”. The motion in azimuthal direction becomes more evident with the growth of heating intensity. There is a predominantly radial flow in the region with the free surface. At the same time, the vortices with azimuthal component of velocity are observed under the film. As in experiment, the proportion of free surface area to the covered one determines the number of vortices in azimuthal plane.