Viscoplastic, or yield-stress, fluids are involved in numerous geophysical and industrial applications. These materials have the property to behave either as fluids or solids, depending on the applied loading. Due to the coexistence in the flows of fluid and solid zones, whose respective boundaries are a priori unknown, simulating the propagation and deposition of free-surface viscoplastic surges remains challenging, in particular when the basal topography is complex. The objectives of this lab-course are (1) to perform well-controlled laboratory experiments in which viscoplastic, gravity-driven surges are generated over a complex topography; and (2) to compare the experimental results to the predictions of a hydraulic numerical model. Through this comparison, important assumptions concerning the treatment of viscoplastic rheology in the numerical model will be tested.
This lab course is well suited to M2 and PhD students with a background in fluid mechanics and / or materials science.
Experimental study of gravity driven viscoplastic surges
4 hrs session
The experiments will be performed in a dam-break configuration, using a model viscoplastic fluid (polymeric microgel). The rheological properties of the fluid will be measured independently with a laboratory rheometer. The basal topographies have been generated by 3D printing, to enable a precise comparison with the simulations. The propagation of the fluid and the final deposit will be monitored through optical stereoscopy techniques (fringe projection).
Numerical simulation and comparison of the results
4 hrs session
Experiments will be simulated using a hydraulic numerical model based on a depth-averaged approach. This type of models requires a good knowledge of the internal dynamics of the flow (internal velocity profile, basal slip condition, etc.). The influence of the assumptions made in the model will be tested and discussed.