Numerical and experimental verification of a theoretical model of ripple   formation in ice growth under supercooled water film flow
  Little is known about morphological instability of a solidification front during the crystal growth of a thin film of flowing supercooled liquid with a free surface: for example, the ring-like ripples on the surface of icicles. The length scale of the ripples is nearly 1 cm. Two theoretical models for the ripple formation mechanism have been proposed. However, these models lead to quite different results because of differences in the boundary conditions at the solid-liquid interface and liquid-air surface. The validity of the assumption used in the two models is numerically investigated and some of the theoretical predictions are compared with experiments. 
K. Ueno, M. Farzaneh, S. Yamaguchi and H. Tsuji
physics.flu-dyn