Oscillatory instability caused by the interplay of Soret effect and cross-diffusion

We show that a subtle coupling between the thermal and solutal gradients driven by the thermodiffusion, cross-diffusion, and buoyancy force can lead to oscillatory dynamic behavior of a ternary mixture in the thermogravitational column. The potentially unstable stratification results from the interplay of mass fluxes of the two heaviest components where the leading role belongs to one of them. Our experiments and numerical analysis not only evidence the presence of oscillatory instability but also demonstrate the emergence of the secondary instability in the form of swinging pattern in addition to the large-scale standing wave. We suggest that the region, where oscillatory instability occurs, is characterized by opposite signs of Soret S T 1 ′ and thermodiffusion D T 1 ′ coefficients due to large cross-diffusion contribution.