Résumé
Granular column collapse simulations are a benchmark in the study of transitional granular flows [1].The column collapse is a simplified version of occurring flows in highly varying scales, ranging innatural debris flows or industrial handling purposes. A characteristic among them is their occasionalsubmergence in a viscous fluid, resulting in strong grain-fluid interactions between particles ofdifferent sizes [2, 3, 4]. This work studies the effect of polydispersity in the runout of the collapse ofimmersed granular columns. For this purpose, we simulate a two-dimensional immersed granularcolumn employing a coupled discrete and finite element fluid model (DEM-FEM) [5]. In thisconfiguration, we study granular systems with different grain size distributions (GSD), varying theratio between the biggest and smallest particle from 1.2 to 10. We simulate dense granular columns,varying the initial column height H0 and initial column width L0 through three different aspect ratiosA = H0/L0 = (0.5, 1.0, 3.5). We show that the collapse mechanism and collapse duration stronglydepend on polydispersity. Increasing polydispersity reduces the kinematic energy of the collapse andreduces the final runout. For short columns A = (0.5, 1.0), the repose angle increases with thepolydispersity until it reaches a plateau near 17°. Our results highlight the effect on the final shape,flow mechanism, and fluid-grain interaction of increasing polydispersity in transitional immersedflows.