At the Splash Lab, Hurd and his colleagues created an artificial male urethra on a 3D printer. The urethra a cylinder with a 8 mm x 3 mm elliptical channel running down the center was attached with tubing to a pressurized container, allowing it to deliver a steady stream of dyed water at 21 milliliters per second, the expected flow rate for a healthy, middle-aged male. High-speed cameras were used to visualize the flow as it struck both a solid surface (representing the porcelain back wall of most urinals) and a "free" surface (representing standing water); white paper was placed below the surfaces to track where splash droplets ended up.
Perhaps not surprisingly, the researchers found that it is indeed possible to use a urinal without splashing onto yourself or your own clothing. The key? Angle.
"For typical male urination, the stream breaks up into droplets before impacting the urinal wall or the water surface," he says. Significant splash-back occurs if that stream is angled perpendicular to the urinal wall, down to angles of about 45 degrees. But when this impact angle becomes very small, "it is much easier for the droplets to only slightly change direction, and slide along the porcelain surface without generating large splashes," says Hurd, who hopes to eventually create an optimization function to find the ideal approach for urinal usage.
"Although reducing the impact angle would also work in traditional toilets, these angles tend to only present themselves around the rim of the bowl, simultaneously increasing the chances of missing the bowl entirely," says Hurd. "I wouldn't recommend this approach to anyone but military snipers."
|Contact: Jason Socrates Bardi|
American Physical Society's Division of Fluid Dynamics