Lagrangian method to simultaneously characterize transport behaviour of liquid and solid phases: a feasibility study in a confined vortex ring

An experimental method was developed for the fully resolved, quasi-simultaneous measurement of the liquid and solid phases in a suspension (2% volume fraction). A Lagrangian measurement technique, Shake-The-Box (STB), was used to investigate suspended particle–vortex interactions in a confined vortex ring. The repeatability of the vortex-ring generator allowed liquid- and solid-phase tracers, which were tracked independently, to be combined into a quasi-simultaneous measurement pair. The liquid-phase results were first verified by particle image velocimetry (PIV), and vorticity field measurements of vortex-ring formation were found to be nearly identical with both techniques. The suspended particles (measured by STB) were seen to closely follow the liquid phase through the formation of a stable vortex ring. Furthermore, calculating the vorticity-history of each fluid parcel revealed the vortex entrainment process, laminar-to-turbulent transition, and instability of the vortex ring itself. Particle–wall interactions, such as large volumes of ambient particles being transported into the near-wall region, were observed by extending and labelling fluid parcels' pathlines based on their source. Finally, individual fluid-parcel trajectory and vorticity calculations allowed the interactions between coherent structures and suspended particles to be investigated. Graphic abstract:

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