Periodic states in intermittent pipe flows: Experiment and model

We report an experimental study of a transition to periodic intermittency in pressure-driven pipe flows. The transition is preceded by a rapid increase of the intermittency factor with pressure. To model intermittent pressure-driven flows, we introduce a general model, where a fifth-order Ginzburg-Landau equation is coupled with a pressure-velocity relation that takes into account the frictional effect of the turbulence on the flow velocity. We determine the phase diagram and show that the model gives a qualitative understanding of the transition to periodic intermittency.