Full two-dimensional velocity fields were measured by PIV in forced jets of
glycerin/water solution flowing into and pinching off in ambients of Dow C
orning 200 Series silicone fluid. The Reynolds, Froude, and Bond numbers co
mputed at the nozzle exit were 34, 0.20, and 6.1, respectively. Viscosity r
atios between the inner and outer fluids of 0.17 and 1.7 were examined in j
ets forced at a Strouhal number of 4.0. The experiments revealed that the v
iscosity ratio strongly affected the evolving jet flow, the pinch-off proce
ss, and the resulting droplet shapes. The higher viscosity ambient yielded
less gravitational acceleration within the jet fluid, a broader cone shape
upstream and a more rounded drop interface downstream of the pinch-off zone
, and eventually spheroidal droplets with weak oscillations in shape. The l
ower viscosity ambient yielded greater gravitational acceleration within th
e jet, a narrower cone shape upstream and flatter drop interface downstream
of the pinch-off zone, and eventually strong oscillations including invert
ed curvature within the droplets that formed. The difference in downstream
interface angles at pinch off could be explained by the velocity and vortic
ity distributions within the two flows. (C) 2001 Elsevier Science Ltd. All
rights reserved.