Thursday, January 11, 2001 - 4:30pm - 5:00pm
We present the results of a combined theoretical and experimental investigation of laminar vertical water jets impinging on a water reservoir. We consider the parameter regime where, in a pure system, the jet is characterized by a stationary field of capillary waves at its base. When surfactant is added to the reservoir, the reservoir-to-jet surface tension gradient transports the surfactant a finite distance up the jet surface until a balance is achieved between viscous and Marangoni stresses. The length of jet surface covered by surfactant is cylindrical and quiescent: water enters the reservoir as if through a rigid pipe. A theoretical description of the resulting fluid pipe is deduced by matching extensional flow upstream of the pipe onto entry pipe flow within it. Theoretical predictions for the pipe height are validated by an accompanying experimental study.