A combined experimental and numerical approach to study the hierarchy of multiscale structures arising from the stationary solutal Marangoni instability

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Mass transfer across liquid interfaces is frequently accompanied by solutal Marangoni convection with complex and irregular flow structures. This so-called interfacial turbulence, which can significantly enhance mass transfer rates, is of considerable importance in chemcial engineering, e.g. in liquid-liquid extraction processes. Interfacial turbulence is known to evolve progressively from small to large lengthscales by a cascade-like process, where larger and larger structures emerge on a background of smaller flow structures. This hierarchical evolution displays a characteristic sequence of flow structures before it is repeated on a significantly larger length scale. The details of this evolution and the characteristic properties of the various flow structures and their transformations are only poorly understood. These deficiencies will be addressed by the project through a combination of accurate experiments with novel techniques for optical flow measurement, and by highly resolved numerical simulations. The particular configuration to be studied is a liquid-liquid system, composed of two immiscible solvents separated by a plane interface. Solutes of different surfaceactivity together with a tuning of solvent system and container geometry will be used to select different hierarchy levels of the interfacial turbulence cascade. The mathematical model incorporates the ow in both liquid phases in connection with a separate transport equation of the interfacial concentration and takes a nonlinear sorption kinetics of the surfactant into account. Relevant data to the generic structures of interfacial turbulence at a plane interface will be provided to other projects of the priority programme in benchmark quality. In the second period, structures of higher order in the turbulence cascade will be addressed. Beside the potential to refine mass transfer models, the detailed understanding of interfacial turbulence will open important conceptual links to other areas of nonlinear dynamics such as reaction-diffusion systems.“