This experimental investigation into the nature of free-surface flows was to study the
effects of surfactants on the wake of a surface-piercing cylinder. A better understanding
of the process of vorticity generation and conversion at a free surface due to the
absence or presence of surfactants has been gained. Surfactants, or surface contaminants,
have the tendency to reduce the surface tension proportionally to the respective
concentration at the free surface. Thus when surfactant concentration varies across
a free surface, surface tension gradients occur and this results in shear stresses, thus
altering the boundary condition at the free surface. A low Reynolds number wake
behind a surface-piercing cylinder was chosen as the field of study, using digital
particle image velocimetry (DPIV) to map the velocity and vorticity field for three
orthogonal cross-sections of the flow. Reynolds numbers ranged from 350 to 460 and
the Froude number was kept below 1.0. In addition, a new technique was used to
simultaneously map the free surface deformation. Shadowgraph imaging of the free
surface was also used to gain a better understanding of the flow. It was found that,
depending on the surface condition, the connection of the shedding vortex filaments
in the wake of the cylinder was greatly altered with the propensity for surface tension
gradients to redirect the vorticity near the free surface to that of the surface-parallel
component. This result has an impact on the understanding of turbulent flows in the
vicinity of a free surface with varying surface conditions.