PERIODIC STATES IN INTERMITTENT PIPE FLOWS - EXPERIMENT AND MODEL

We report an experimental study of a transition to periodic intermitte ncy in pressure-driven pipe flows. The transition is preceded by a rap id increase of the intermittency factor with pressure. To model interm ittent pressure-driven flows, we introduce a general model, where a fi fth-order Ginzburg-Landau equation is coupled with a pressure-velocity relation that takes into account the frictional effect of the turbule nce on the flow velocity. We determine the phase diagram and show that the model gives a qualitative understanding of the transition to peri odic intermittency.