Oscillatory convection of a colloidal suspension in a horizontal cell

The finite difference numerical simulations performed are for convection of a non-uniformly heated colloidal suspension (Hyflon MFA) filling a horizontal cell of finite length. The cell has solid and impermeable boundaries and is heated from below. A linear temperature distribution is maintained at the side walls. Due to the negative effect of thermodiffusion (Soret) and gravity sedimentation, a heavy impurity is collected at the hot lower boundary, and convection transfers it inside the cell. The stable and transient oscillatory convection modes observed experimentally are analyzed. If the initial distribution of the concentration is uniform, then stationary convection occurs in the cell. As the concentration inhomogeneities accumulate, oscillatory perturbations begin to increase. A modulated traveling wave may form in the layer. Stable traveling waves are observed when the Rayleigh number exceeds a certain critical value, which depends on the cell length. There is a good agreement between the experimental data [1] and the results of numerical research. The spatial structure of the concentration field and the time evolution of the convective characteristics of the colloid suspension are determined. The behavior of the colloidal suspension in the regimes of modulated traveling waves and transient flows near the threshold of convection, including localized traveling waves and waves that change their direction, is simulated and elucidated. By analyzing the behavior of the world lines of the vortices and the concentration field, the mechanism of formation of defects in the form of vortex coalescence is clarified. In the process of defect formation, two vortices with the opposite direction of rotation are involved.