Séminaire IUSTI – 4 mars 2022 – 11h salle 250

Universality in pipes and landslides

Rory Cerbus – LOMA, Bordeaux

In this seminar I will describe my previous work on the transition to turbulence in pipe flow as well as my current work on landslides. In his seminal work over 130 years ago, Osborne Reynolds observed that as he gradually increased the flow speed of his initially laminar pipe, fluctuating irregular flow invaded the laminar flow creating a patchy combination of the two. These irregular patches have been the subject of intense study ever since, but their internal flow characteristics have largely been ignored. A thorough investigation of these patches has led to a partial solution to the problem of fluid friction in this transition regime, left unsolved by Reynolds, and has also addressed a hallmark of fully turbulent flow, the spatial energy distribution or energy spectrum treated by Kolmogorov. I will show that despite their outward differences, flashes possess the same universal friction laws and energy distributions as fully turbulent flows. Landslides are large mass movements that plague mountainous regions the world over. The feature of landslides of primary concern to both scientists and local inhabitants is the maximum runout distance. A classical result is that the runout correlates with fall height and landslide volume, but the correlation is noisy and the dependence on other parameters is difficult to determine. Using simple laboratory experiments with grains, we determined the runout’s systematic dependence on fall height, landslide size, and grain size, and determined an apparently universal scaling of the normalized runout which applies to both laboratory and natural data, showing that they are connected through their common granular nature.