We examine the form of the free surface flows resulting from the
collision of equal jets at an oblique angle. Glycerol-water solutions
with viscosities of 15-50 cS were pumped at flow rates of 10-40 cc/s
through circular outlets with diameter 2 mm. Characteristic flow
speeds are 1-3 m/s. Figures 3-9 were obtained through strobe
illumination at frequencies in the range 2.5-10 kHz.
Figure 1: At low flow rates, the resulting stream takes the
form of a steady fluid chain, a succession of mutually orthogonal fluid
links, each comprised of a thin oval sheet bound by relatively
thick fluid rims. The influence of viscosity
serves to decrease the size of successive links,
and the chain ultimately coalesces into a cylindrical stream.
As the flow rate is increased, waves are
excited on the sheet, and the fluid rims become unstable. The rim appears
blurred to the naked eye (Figure 2); however, strobe illumination reveals
a remarkably regular and striking flow instability ( Figures 3-6).
from the sheet rims but remain attached to the fluid sheet by tendrils
of fluid that thin and eventually break. The resulting flow takes
the form of fluid fishbones, with the fluid sheet being
the fish head and the tendrils its bones. Increasing the flow
rate serves to broaden the fishbones.
Figures 7-9: In the wake of the fluid fish, a regular array
of drops obtains, the number and spacing of which is determined by
the pinch-off of the fishbones.
Some of these photos have appeared in
& Bush (2002, Phys. Fluids, Gallery of Fluid Motion).
A combined theoretical and investigation of fluid chains and fishbones
is presented in
& Hasha, JFM (2004).
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