Oscillatory Convection of a Colloidal Suspension in a Horizontal Cell

Numerical simulation of convection by the finite difference method has been performed for the inhomogeneously heated colloidal suspension (Hyflon MFA) filling a horizontal cell with a finite length. The cell has rigid and impermeable boundaries and is heated from below. A linear temperature distribution is maintained at the side walls. Owing to negative Soret coupling and gravitational sedimentation, a heavy impurity comprised of nanoparticles is accumulated at the hot lower boundary, while convection transfers it to the inside of the cell. The experimentally observed transient flows and stable oscillatory nonlinear convection regimes are analyzed. If the initial distribution of nanoparticles is uniform, then steady convection occurs in the cell. With accumulation of the concentration inhomogeneity, oscillatory perturbations begin to grow. A modulated traveling wave can appear in the layer. Stable oscillatory modes exist when the Rayleigh number exceeds critical value R-S, which depends, as calculations have shown, on the cell length. The spatial structure of the concentration field and the time evolution of the convective characteristics of the colloid suspension are determined. The numerical study results agree well with published experimental data. The behavior of the colloidal suspension in the modes of modulated traveling waves, including localized traveling waves and waves that change their direction, and transient flows near convection threshold R-S is simulated and clarified. Based on the results of analyzing the behavior of the vortex world lines and the impurity concentration field, the formation of defects in the form of vortex coalescence is established. It is found that the defect is formed as a result of merging two nearest vortices with the same direction of rotation.