Transition to spatiotemporal chaos via spatially subharmonic oscillations of a periodic front.

An unusual sequence of bifurcations is documented in the flow of a viscious fluid inside a partially filled rotating horizontal cylinder. A periodic cellular pattern destabilizes to form a spatially subharmonic pattern that oscillates periodically in time. As the rotation rate is increased, the pattern evolves to spatiotemporal chaos. This state is characterized both by its correlation length and time, and by the fluctuating spatial phase of the pattern. The transition process is similar to that shown by a generalized Ginzburg-Landau model proposed by Daviaud et al. [Physica D 55, 287 (1992)].