The Lattice Boltzmann Method: one single tool to address different sedimentation processes

The fluid dynamics of different sedimentological processes are often studied and interpreted by using models based on a combination of Newton dynamics and an empirical expression of the drag force in function of the drag coefficient. However, neither the expression of the drag force nor the value of the drag have a unique expression, depending on the state of the fluid (laminar, transitional, and turbulent) and on the shape and dimensions of the sediments. These (semi-) empirical models are often inaccurate, in particular in planetary sciences when gravity plays a determining role, like, for example, when calculating the terminal settling velocity of natural sediments on Mars. In this work, a numerical simulation code based on the Lattice Boltzmann Method (LBM) is used to study how settling velocity of some reference spherical particles changes at different gravity conditions, ranging from hyper to reduced gravity. LBM is a discrete computational method based on the kinetic Boltzmann equation that describes the dynamics of a fluid on a mesoscopic scale. This study shows that, despite the LB model has been calibrated and validated using only the set of experimental data collected during a parabolic flight, its validity goes beyond, being able to predict the correct terminal velocity of different particles, with different density and diameters. In addition, the same settings can be used to simulate other important processes that occur when sediments interact with each other and the fluid phase, such as hindered settling and the drafting, kissing, and tumbling phenomenon. This makes the Lattice Boltzmann method an ideal candidate for studying a wide range of sedimentological processes where a mesoscale accurate description is crucial to understand macroscale phenomena.