Leidenfrost flows: instabilities and symmetry breakings

Leidenfrost drops were recently found to host strong dynamics. In the present study, we investigate both experimentally and theoretically flow structures stability inside a water drop as it evaporates, starting with large puddle. As revealed by infrared mapping, base is warmer than its apex typically 10 $^{\circ }$ C, which likely trigger bulk thermobuoyant flows Marangoni surface flows. Tracer particles unveil complex that undergo successive symmetry breakings evaporates. We linear of in non-deformable, quasi-static, levitating induced thermobuoyancy effective thermocapillary stress, using only one adjustable parameter. The analysis nominally axisymmetric thermoconvective flows, parametrized radius $R$ , yields most unstable, thus, dominant, azimuthal modes (of wavenumber $m$ ). Our theory predicts well radii for mode transitions cascade decreasing from $m=3,\, m=2$ down $m=1$ (the eventual rolling entails propulsion) shrinks size. effect escaping vapour not taken into account here, may further destabilize inner couple liquid/vapour interface give rise motion (Bouillant et al. Nat. Phys. vol. 14 (12), 2018, pp. 1188–1192; Brandão & Schnitzer Physical Review Fluids 5 (9), 2020, 091601).