Effect of local flow geometry on particle pair dispersion angle

Abstract: We combine experiments in a von K\'arm\'an flow with numerical simulations of Taylor-Green and homogeneous and isotropic turbulence to study the effect of the local flow geometry on particle pair dispersion. To characterize particle dispersion we use the pair dispersion angle, defined as the angle between the relative position and relative velocity of particle pairs. This angle was recently introduced as a means to more effectively identify the different dispersion regimes in finite-Reynolds-number flows. Our results show that, at a global scale, all flows considered show similar dispersion properties in terms of this metric, characterized by ballistic, super-diffusive, and diffusive regimes. Locally, however, these systems exhibit distinct behaviors, with anisotropies and local geometric features significantly influencing dispersion in both the von K\'arm\'an and Taylor-Green flows.