Penlou B. auteur aut IRD Roche Olivier auteur aut IRD Manga M. auteur aut IRD van den Wildenberg S. auteur aut IRD text journalArticle eng text/pdf born digital access The dynamics of geophysical dilute turbulent gas-particles mixtures depends to a large extent on particle concentration, which in turn depends predominantly on the particle settling velocity. We experimentally investigate air-particle mixtures contained in a vertical pipe in which the velocity of an ascending air flux matches the settling velocity of glass particles. To obtain local particle concentrations in these mixtures, we use acoustic probing and air pressure measurements and show that these independent techniques yield similar results for a range of particle sizes and particle concentrations. Moreover, we find that in suspensions of small particles (78 mu m) the settling velocity increases with the local particle concentration due to the formation of particle clusters. These clusters settle with a velocity that is four times faster than the terminal settling velocity of single particles, and they double settling speeds of the suspensions. In contrast, in suspensions of larger particles (467 mu m) the settling velocity decreases with increasing particle concentration. Although particle clusters are still present in this case, the settling velocity is decreased by 30%, which is captured by a hindered settling model. These results suggest an interplay between hindered settling and cluster-induced enhanced settling, which in our experiments occur respectively at Stokes number O(100) and O(1). We discuss implications for volcanic plumes and pyroclastic currents. Our study suggests that clustering and related enhanced or hindered particle settling velocities should be considered in models of volcanic phenomena and that drag law corrections are needed for reliable predictions and hazard assessment. specialized gas-particle suspension particle settling clustering explosive volcanism turbulent flow acoustic probing CHILI LLAIMA 066 064 021 020 128 3 e2022JB025809 [16 p.] 2023 2169-9313 https://www.documentation.ird.fr/hor/fdi:010087478 10.1029/2022jb025809 2169-9313 [F B010087478] https://www.documentation.ird.fr/hor/fdi:010087478 https://www.documentation.ird.fr/intranet/publi/2023-04/010087478.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2023-04-14 2025-02-24 fdi:010087478 fre