| Popis: |
This article introduces a novel numerical framework designed to model the interplay between free-falling particles and their surrounding fluid in situations of high particle to fluid density ratio, typically exhibited by atmospheric particles. This method is designed to complement experimental studies in vertical wind tunnels to improve the understanding of the aerodynamic behavior of small atmospheric particles, such as the transport and sedimentation of volcanic particles, cloud ice crystals and other application areas. The solver is based on the lattice Boltzmann method and it addresses the numerical challenges, including the high density ratio and moderate to high Reynolds number, by using an immersed-boundary approach and a recursive-regularized collision model. A predictor-corrector scheme is applied for the robust time integration of the six-degrees-of-freedom (6DOF) rigid-body motion. Finally, the multi-scale nature arising from the long free-fall distances of a particle is addressed through a dynamic memory allocation scheme allowing for a virtually infinite falling distance. This tool allows for the simulation of particles of arbitrary shape represented by a triangularized surface. The framework is validated against the analytical and experimental data for falling spheres and ellipsoids, and is then applied to the case of an actual volcanic particle geometry, the shape of which is obtained from a 3D surface-contour scanning process. The physics of the free-fall of this particle is investigated and described, and its terminal velocity is compared against the experimental data measured with the 3D printed exemplars of the same particle. |
