Granular ripples under rotating flow: a new experimental technique for studying ripples in non-rotating, geophysical applications?

Micrometric granular ripple patterns in a capillary tube

The oscillatory motion of a fluid carrying micron-sized particles inside a capillary tube is investigated experimentally. It is found that initially uniformly distributed particles can segregate and accumulate to form regularly spaced micron-sized particle clusters. The wavelength of the microclusters is compared to data for macroscale sand-ripple patterns and found to obey the same universal scaling as these. A dimensional analysis is performed that confirms the universality of the experimentally observed scaling. The experimental data for the microripple clusters further suggest the existence of a minimum particle length scale for which patterns can form and below which the Brownian motion associated with the molecules of the matrix fluid inhibits pattern formation.

Geophysical granular and particle-laden flows: review of the field

An introduction is given to the title theme, in general, and the specific topics treated in detail in the articles of this theme issue of the Philosophical Transactions. They fit into the following broader subjects: (i) dense, dry and wet granular flows as avalanche and debris flow events, (ii) air-borne particle-laden turbulent flows in air over a granular base as exemplified in gravity currents, aeolian transport of sand, dust and snow and (iii) transport of a granular mass on a two-dimensional surface in ripple formations of estuaries and rivers and the motion of sea ice.