THE INFLUENCE OF SURFACE-FILMS ON NEAR-SURFACE VORTICAL FLOWS

An experimental apparatus was designed and constructed to generate rep roducible vortex rings in the laboratory. These rings were produced in a small test tank and were allowed to propagate upward where they the n interacted with an air/water interface. Tests were performed on the following surfaces: a clean free distilled water surface, a solid poly carbonate wall, and the surface of a 1 mu m solution of Triton X-100 i n distilled water. The vortex rings studied in the present investigati on ranged in Froude number from 0.042 to 0.164 and in Reynolds number from 1772 to 6785. Measurements of the two-dimensional near-surface fl ow field were made using the technique of particle image velocimetry ( PIV). Preliminary results show, (i) that the experimental set-up emplo yed in this study is able to generate repeatable vortex rings with var ying strengths and propagation speeds, (ii) that the PIV system used t o quantify the experimental observations is capable of resolving spati al velocity fields of the Bow accurately, and (iii) that the presence of the surface active Blm studied here profoundly affects the dynamics of the interaction between the vortex rings and the surface of the so lution. These effects were observed to manifest themselves in several ways which included vortex path modification, production of secondary and tertiary vortices, and a measured impact on total circulation and vorticity.