Interaction of a vortex ring impinging on a flat surface*

Vortex rings are ubiquitous in both nature and engineering applications. Some examples in nature include marine animal locomotion, cardiovascular flows, and expiratory events like coughing, sneezing, and speaking. With respect to the COVID-19 pandemic, the fluid dynamic interactions of these vortex-laden expiratory events are paramount to understanding how infectious diseases spread. One strategy to reduce dispersion of expiratory aerosol adopted by essential businesses is the installation of barriers. In this study, the interaction of a vortex-laden expiratory flow with different flat surfaces is investigated via fluorescent dye flow visualization. A programmable syringe pump is used to generate a vortex ring that impinges on a flat surface in a water tank. Various configurations of the flat surfaces are studied to quantify the interaction mechanisms and the ability of the surface to reduce dispersion. It is observed that the generation of secondary and tertiary vorticity at the wall results in vortex-surface interactions that are vastly different from inviscid approximations. A better understanding of these vorticity interactions could lead to improved surface designs that reduce dispersion.