Nathalie Vriend (Cambridge)
Granular and particle-laden flows: Novel approaches to characterize avalanches and dunes across scales
Flowing granular materials arise everywhere around us, in industry from pharmaceutical processes to bulk good transport lines, and in nature from snow avalanches to captivating dune fields. An interesting length-scale separation exists between the particle and system-scale. At the micro-scale, collisions between individual particles are directly influenced by the particle size. In contrast, large desert dunes are composed of the same particles, but the effect of particle size may disappear entirely when analysing entire dunes. In this talk, we will illustrate this length-scale separation with two examples of our experimental work on granular flows.
At the macro-scale, we present a unique, recirculating, laboratory experiment in which we create and trace aqueous dunes over long times. We examine the interaction between two dunes of different sizes, and present a phase-space diagram with interaction outcomes. Furthermore, we explore the feedback mechanism between a bedform and the flow providing the forcing, and identify a repulsion mechanism that ensures that bedforms do not coarsen without limit.
At the micro-scale, we discover stress distributions in 2D granular avalanches, visualized with bespoke, superior-quality birefringent photoelastic particles. This technique gives us for the first time access to the full velocity, density and stress fields inside of a dynamic avalanche, and allows us to experimentally validate granular rheological models.
About this Series:
The PAOC Colloquium [PAOCC] is a weekly interdisciplinary seminar series that brings together the whole PAOC community. Seminar topics include all research concerning the physics, chemistry, and biology of the atmospheres, oceans and climate, but also talks about e.g. societal impacts of climatic processes. The seminars take place on Monday from 12-1pm. Besides the seminar, individual meetings with professors, post-docs, and students are arranged. Contact: email@example.com.