Lubricated gravity currents of power-law fluids

TL;DR

This study experimentally investigates lubricated gravity currents of power-law fluids, revealing faster front evolution and distinct thickness profiles compared to non-lubricated flows, with implications for natural and industrial lubrication processes.

Contribution

It provides new experimental insights into the dynamics of lubricated gravity currents involving power-law fluids, highlighting differences in front speed and thickness distribution.

Findings

Lubricated GCs evolve faster than non-lubricated GCs.

The non-Newtonian fluid maintains a nearly uniform thickness.

Lubricated GCs remain axisymmetric under certain flux conditions.

Abstract

The motion of glaciers over their bedrock or drops of fluid along a solid surface can vary dramatically when these substrates are lubricated. We investigate the coupled flow of a gravity current (GC) of strain-rate softening fluid that is lubricated by a denser, lower-viscosity Newtonian fluid. We present a set of experiments in which such GCs are discharged axisymmetrically and at constant flux over a flat surface. Using imaging techniques we follow the front evolution of each fluid and their thickness field. We find that the two fronts of our lubricated GCs evolve faster than non-lubricated GCs, though with similar time exponents. In addition, the thickness of the non-Newtonian fluid is nearly uniform while that of the lubricating fluid is nonmonotonic with localised spikes. Nevertheless, lubricated GCs remain axisymmetric as long as the flux of the lubricating fluid is sufficiently smaller than the non-Newtonian fluid flux.