Drop formation at the tip of a vertical, circular capillary tube immer
sed in a second immiscible fluid is studied numerically for low-Reynol
ds-number flows using the boundary integral method. The evolution and
breakup of the drop fluid is considered to assess the influences of th
e viscosity ratio lambda, the Bond number B, and the capillary number
C for 10(-2)less than or equal to lambda less than or equal to 10, 10(
-2)less than or equal to C less than or equal to 1, and 0.1 less than
or equal to B less than or equal to 5. For very small lambda, breakup
occurs at shorter times, there is no detectable thread between the det
aching drop and the remaining pendant fluid column, and thus no large
satellite drops are formed. The distance to detachment increases monot
onically with lambda and changes substantially for lambda>1, but the v
olume of the primary drop varies only slightly with lambda. An additio
nal application of the numerical investigation is to consider the effe
ct of imposing a uniform flow in the ambient fluid [e.g., Oguz and Pro
speretti, J. Fluid Mech. 257, 111 (1993)], which is shown to lead to a
smaller primary drop volume and a longer detachment length, as has be
en previously demonstrated primarily for high-Reynolds-number flows. (
C) 1997 American Institute of Physics.