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Department of Engineering Science and Mechanics
Virginia Polytechnic Institute and State University
Intuition tells us that two or more jets of the same fluid impinging into each other will readily coalesce to form a single mass of fluid. Fluid chains, sheets and fish-bone structures resulting from oblique collision of fluid jets are well studied phenomena [1, 2]. Here, we report the non-coalescence and rebounding of fluid jets off each other- something that completely defies common intuition.
A sample picture (Figure 1) shows two jets of silicone oil (viscosity 10 cSt at 25 °C) with diameter roughly equal to 500 µm, impinging obliquely onto a vertical jet of same fluid and same diameter. We observe that instead of coalescing, the jets from the sides rebound off the middle jet. This is due to lubrication effect of a thin film of air maintained between the jets. The motion of the jets keeps replenishing the air resulting in indefinitely sustained non-coalescence of the jets of same fluid . Similar phenomenon can also be observed in the interaction between a jet and drops of the same fluid, an example of which is shown in Figure 2.
In this case we observed that the drops plunged into the jet from two sides without coalescing into it, causing it to bend at two locations.
 J. W. M. Bush and A. E. Hasha, J. Fluid Mech. 511, 285 (2004).
 G. Taylor, Proc. R. Soc. A 259, 1 (1960).
 P. DellAversana, V. Tontodonato, and L. Carotenuto, Phys. Fluids 9, 2475 (1997).
These images may be used with the permission of BIF lab in the department of Engineering Science and Mechanics at Virginia Tech. Please credit the source.