Settling of magnetic rods in quiescent fluid

The precise description of the motion of anisotropic particles in a flow rests on the understanding of the forces and torques acting on them. Here, we investigate experimentally magnetic rods settling at low Reynolds number when a homogeneous vertical magnetic field is applied. We show that the competition between the magnetic torque and the inertial torque from the fluid acting on the rod results in a bifurcation where the rod settle vertically for large magnetic fields while it settles with a steady oblique angle for moderate and small magnetic fields, until eventually reaching the classical horizontal settling regime for the non-magnetic case. Besides, we show that using magnetic rods offers a fantastic strategy to accurately measure the angular dependency of the inertial torque, which is a key ingredient for the understanding and modelling of small anisotropic particles transported by turbulence, with important applications to many natural and industrial multi-phase flows.