COLUMNAR VORTEX GENERATION AND INTERACTION WITH A CLEAN OR CONTAMINATED FREE-SURFACE

The interaction of a columnar vortex with a free surface is studied ex perimentally. The vortex is generated by a pair of corotating flaps an d is visualized by planar laser-induced fluorescence. When the surface is clean, the vortex is unaffected and remains essentially two dimens ional, However, when the surface is contaminated by a relatively visco us monomolecular layer, the vortex dynamics can be significantly alter ed, resulting in a downward axial flow followed by vortex breakdown. ( C) 1995 American Institute of Physics.