Edge state in pipe flow experiments.

Recent numerical studies suggest that in pipe and related shear flows, the region of phase space separating laminar from turbulent motion is organized by a chaotic attractor, called an edge state, which mediates the transition process. We here confirm the existence of the edge state in laboratory experiments. We observe that it governs the dynamics during the decay of turbulence underlining its potential relevance for turbulence control. In addition we unveil two unstable traveling wave solutions underlying the experimental flow fields. This observation corroborates earlier suggestions that unstable solutions organize turbulence and its stability border.

Scaling properties of coating flows in rectangular channels.

We present an experimental study of the aspect-ratio dependence of two-phase displacement flows in channels of rectangular cross section. Above a buoyancy-dependent threshold Ca[over ;]_{t}, we find that the bulk features of the flow depend only on a modified capillary number Ca[over ;]=[1+0.12(alpha-1)+0.018(alpha-1);{2}]Ca, where Ca is the unmodified capillary number and alpha is the aspect ratio. This novel scaling has tremendous practical significance because it implies that the bulk features of the flows in any rectangular channel can be inferred from those in a square channel for Ca[over ;]>Ca[over ;]_{t}.