The low-Reynolds number spreading of axisymmetric drops and gravity currents along a free surface

Experimental results are presented for the spreading of buoyant drops and gravity currents along a free surface. The spreading occurs at low Reynolds number, and no interfacial tension exists between the spreading and ambient fluid. Theoretical results suggest that distinct spreading rates occur in three regimes: l!@ ln(R/a)#a/R, a/R!l!R/a , and l@R/a , where l is the ratio of the spreading and ambient fluid viscosities and R/a is the aspect ratio of the drop or current. Experimentally measured spreading rates in these three regimes show agreement with the theoretical solutions for long-term spreading. © 1998 American Institute of Physics. @S1070-6631~98!00811-3#