The Effects of Surfactants on Free-Surface Flows

Citation

Warncke, Amy E. (1997) The Effects of Surfactants on Free-Surface Flows. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/1xg2-yy62. https://resolver.caltech.edu/CaltechETD:etd-01172008-092233

Abstract

This experimental investigation into the nature of free surface flows is to study the effects of surfactants on the boundary condition at the free surface and the resulting flow field. In particular, the flow field associated with a stationary Reynolds ridge was investigated as well as the wake behind a surface-piercing cylinder, where experimental techniques such as Digital Particle Image Velocimetry and a new surface slope measurement technique were utilized. Results show a large change in the flow field in the free-surface vicinity depending on the presence of surface tension gradients and thus shear stresses at the free surface. In particular, the boundary layer beneath a Reynolds ridge was measured and it is shown that the primary source of vorticity at the free surface can be attributed to the free surface deceleration at the ridge. Also, in the wake of the cylinder, depending on the surface condition, the connection of the shedding vortex filaments was found to be greatly altered with the propensity of surface tension gradients to redirect the vorticity near the free surface to that of the surface-parallel component. Thus it is shown that surfactants can dramatically alter the flow field due to the change in the free-surface boundary condition and resulting vorticity generation and conversion in the vicinity of the free surface.

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