Interactions between particles and quantized vortices in superfluid helium

We present a numerical, computational, and physical analysis of particle-vortex collisions in thermal superfluids. Our method allows fully self-consistent, dynamic computation of particle-vortex collisions within the vortex dynamical formalism. The algorithm is described in detail and is shown to be both accurate and efficient. The method is applied to the collision of a solid particle with a straight vortex at finite temperature. It predicts that the smallest velocity that the approaching particle must have in order to escape the vortex after being captured by it increases as the temperature approaches the superfluid transition temperature. A comparative study of particle-vortex collisions at various temperatures reveals the contributions of viscous damping, inertial, and boundary-induced effects on the dynamics of the system, as well as different particle-vortex interaction behaviors. The findings corroborate the possibility of direct measurement of the normal fluid velocity in thermal superfluids via appropriately designed particle image velocimetry experiments.