Free falling and rising of spherical and angular particles
Résumé
Direct numerical simulations of freely falling and rising particles in an infinitelylong domain, with periodic lateral boundary conditions, are performed. The focusis on characterizing the free motion of cubical and tetrahedral particles for differentReynolds numbers, as an extension to the well-studied behaviour of freely falling andrising spherical bodies. The vortical structure of the wake, dynamics of particle movement,and the interaction of the particle with its wake are studied. The results revealmechanisms of path instabilities for angular particles, which are different from thosefor spherical ones. The rotation of the particle plays amore significant role in the transitionto chaos for angular particles. Following a framework similar to that of Mouginand Magnaudet [“Wake-induced forces and torques on a zigzagging/spiralling bubble,”J. Fluid Mech. 567, 185–194 (2006)], the balance of forces and torques actingon particles is discussed to gain more insight into the path instabilities of angularparticles.