Animations showing the effect of Marangoni forces on air-water heat transfer driven by evaporative surface cooling

DNS calculations have been performed of a fully-developed Rayleigh-Bénard-Marangoni flow at a fixed Rayleigh number and various Marangoni numbers (please refer to our manuscript Herlina & Wissink, J. Fluid Mech., 1025:A43, 2025). The animations illustrate the effect of Marangoni forces on the heat exchange between the (evaporatively) cooled water surface and the warmer bottom boundary of the computational domain. For zero and nonzero Marangoni numbers, sequences are shown of snapshots of temperature isosurfaces, where red and blue indicate relatively high and low temperatures. In the background, the domain boundaries show contour plots of the instantaneous temperature. Both animations show a small number of large buoyant plumes of similar size that rise quasi-periodically from the bottom of the computational domain. Without Marangoni forces, the shape of the periodically emerging large plumes at the surface mirrors the situation at the bottom. Contrastingly, with Marangoni forces the shape of these plumes as well as the mechanism by which they form changes markedly due to the entrainment of small-scale near-surface structures that significantly enhance interfacial heat and mass transfer and are characteristic for Marangoni-dominated convection.