A new shape dependent drag correlation formula for non-spherical rough particles. Experiments and results

A New One‐Equation Model of Fluid Drag for Irregularly Shaped Particles Valid Over a Wide Range of Reynolds Number

“…Dioguardi and Mele (2015) and the new drag law here presented (equation (14)) have the best performance, also at very low Re, which proved to be problematic for the other laws but crucial for volcanological applications like ash dispersion modeling. Going deeper into detail, it can be seen that (14) further improved the performance at very low Re and in the range 10-100, which is the most problematic for Dioguardi and Mele (2015); this was not surprising, since this range includes the critical value Re = 50 at which there is the switch between the two parts of the law (see equation (19)). (2005), Ganser (1993), Bagheri and Bonadonna (2016), Dioguardi and Mele (2015), and (14).…”

“…Bagheri and Bonadonna (2016) had the poorest performance after Dellino et al (2005), with a value of the slope of 1.261, meaning a general tendency to overestimate terminal velocities, which, in turn, is the result of the drag underestimation in the whole investigated Re range. Finally, Dioguardi and Mele (2015) and the new drag law ( (14) had the best performances, being a equal to 0.99 and 1, respectively. A closer inspection reveals that the new law better fit the points at terminal velocities between 0.01 and 0.1 m s À1 than Dioguardi and Mele (2015).…”

“…In order to find the new drag law here presented, we took into account and reviewed the database of experimental measurements presented in Dioguardi and Mele (2015). This database originally included 340 measurements of the aerodynamic drag C d,meas obtained by terminal velocity measurements of 143 irregular solid particles.…”

“…AERODYNAMIC DRAG OF IRREGULAR PARTICLES 144 Zhu et al, 2017), pyroclastic flows (e.g., Dellino et al, 2008;, eruptive columns (e.g., Cerminara et al, 2016;Folch et al, 2016), and distal ash clouds (e.g., Beckett et al, 2015;Bonadonna et al, 2012;Bonasia et al, 2010;Costa et al, 2012Costa et al, , 2006). Therefore, a major effort has been posed to find reliable shapedependent drag laws that work on the widest possible range of fluid dynamic regimes quantified by Re (Alfano et al, 2011;Bagheri & Bonadonna, 2016;Chhabra et al, 1999;Chien, 1994;Dellino et al, 2005;Dioguardi et al, 2017;Dioguardi & Mele, 2015;Ganser, 1993;Haider & Levenspiel, 1989;Hölzer & Sommerfeld, 2008;Loth, 2008;Pfeiffer et al, 2005;Swamee & Ojha, 1991;Tran-Cong et al, 2004;Wilson & Huang, 1979). These drag laws are a function of different shape descriptors, among which sphericity Φ is the most widely used.…”

“…In this law, particle shape is quantified by means of the shape factor Ψ first introduced by Dellino et al (2005) and later used in and Dioguardi and Mele (2015). The new drag law has the capability to work in a wide range of fluid dynamic regimes, almost covering all regimes that can be encountered in the aforementioned natural processes, and of particle shapes, from extremely irregular particles to perfect spheres.…”