Experimental studies of multi-layer flows using a visco-plastic lubricant

Static wall layers in plane channel displacement flows

“…For example, if the displaced fluid is also injected into the duct we can achieve stable multi-layer flows, such as those studied in [18][19][20]. Gas displacement of visco-plastic fluids has also been studied by various authors, typically in capillary tubes, e.g.…”

The critical wall velocity for stabilization of plane Couette–Poiseuille flow of viscoelastic fluids

“…Our interest is sparked by the study of parallel multi-layer Poiseuille flows with viscoplastic fluids, which have been found to be interfacially stable in certain regimes; see [1][2][3]. In an effort to extend this type of stability result to both viscoelastic fluids and to further practical flow configurations, PCP flows arise naturally and understanding their stability is a necessary step towards studying the multi-layer stability.…”

Stable two-layer flows at all Re; visco-plastic lubrication of shear-thinning and viscoelastic fluids

“…The two-layer configuration here, with stationary walls, effectively results in a PCP flow for the upper layer. Our experiments with core-annular flows [25] suggest that these flows could be robustly established experimentally. Thus, potentially we might experimentally study a single fluid flow through an easier two-fluid flow.…”

“…Although we have not conducted experiments in the configuration considered, those in [25] utilised Xanthan and Carbopol solutions in a core-annular configuration and observed no disruption of the interface until the onset of shear instabilities in the core fluid. Current experimental work is focused at a PEO-Carbopol system in the same apparatus.…”

“…The base linear stability of such flows is therefore determined by the underlying shear flow instability, not by interfacial modes, and such flows may indeed be more stable than the corresponding single fluid flow. In [24] it was shown that this interfacial stability in fact carries over to bounded non-linear perturbations and in [25] these stable multi-layer flows were demonstrated experimentally. This flow methodology has been termed visco-plastic lubrication.…”