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University of Southern
Los Angeles, California
The Water spray pattern behind a rolling tire begins as a sheet of water. The thinner parts of the sheet rupture, forming holes. The smallest droplets are found along the edges of these holes. Thicker parts of the sheet become arc shaped ligaments, which pinch off to produce the largest drops.
Spray produced by motor vehicle tires rolling through water on a roadway is a familiar sight. Here we simulate that phenomenon in the laboratory by running a single-grooved tire (the upper one) against a smooth tire (the lower) simulating the road. Water is supplied from the left, flowing at a speed matched to the tire speed (6 m/s). The region immediately downstream of the tire contact patch is observed with high speed video.
As the water in the tire groove exits the contact patch it forms a thin sheet between the two tires. This sheet of water develops holes. As the margins of two neighboring holes collide, the margins break up, forming the very smallest droplets whose diameter is comparable to the sheet thickness, of the order of 100 microns. Much of the sheet remains intact, however, and begins to form thicker, more-or-less arc shaped structures or ligaments.
These ligaments are unstable (the Rayleigh instability) and pinch off to form the largest droplets whose diameter is roughly twice the diameter of the ligaments.
This work is funded in part by the U.S. Department of Energy and Michelin Americas Research and Development Corporation.
Reporters may freely use this image. Credit: Dennis Plocher, Fred Browand, and Charles Radovich (University of Southern California) (2010).