Experimental investigation of a vortex ring in a polymer solution

Abstract

In this study, we experimentally investigated the kinematic characteristics of solitary vortex rings in polymer solutions. Two distinct experimental configurations are examined: (1) free downstream translation of the vortex ring and (2) vortex ring impingement onto a wall. Under the flow parameters in this study, the vortex ring maintains a laminar state throughout its evolution. Two-dimensional particle image velocimetry measurements of flow velocity fields were performed in the meridional plane of the vortex ring. Compared with its Newtonian fluid counterpart, the polymer solution vortex core exhibits a marked asymmetry in its vorticity distribution, with this disparity becoming more distinct at increased polymer concentrations. Nevertheless, normalized vorticity profiles demonstrate semi-self-similarity across different polymer concentrations. During its free downstream translation, both the translation speed and circulation of the vortex ring exhibit distinct power-law decay characteristics over time. These decay trends can be empirically described by separate scaling relationships. In wall impingement experiments, the azimuthal stretching of a vortex ring in a polymer solution is suppressed compared with its Newtonian counterpart when the inertial effect dominates. After colliding with the wall, a vortex ring in a polymer solution is less prone to develop secondary vortices compared to its Newtonian counterpart.