Suspension plug in an oscillatory pipe flow: experiments and modeling

Non-colloidal particles under non-uniform shear can migrate across streamlines even at low Reynolds numbers, breaking the well-known reversibility of the Stokes flow. We conduct systematic experiments to study this phenomenon by oscillating a neutrally buoyant non-colloidal suspension plug with finite length inside a cylindrical tube. We visualize the particles on the central axial plane of the tube via refractive index matching and track the motion of individual particles. Our preliminary results qualitatively match the existing literature that shows the initial extension and plateauing of the suspension plug at a critical strain. In addition, we experimentally connect the macroscopic evolution of the plug with the trajectories of individual particles. Finally, we develop a simplified particle collision based model to understand the role of particle contact interactions in the plug evolution.