An image of a 15-mph projectile at the point of impact with water from earlier tests. Credit: Bryan Schmidt/Case Western Reserve University.
Vaporization? Exotic ice? Light creation? These are all possible results when Bryan Schmidt fires an 18-millimeter-diameter projectile against a wall of water at 9,000 miles per hour this summer.
“Even today, the scientific community actually doesn’t know what exactly will happen to the water in that type of event,” says Schmidt, an assistant professor of mechanical and aerospace engineering at Case Western Reserve University. “But there's reason to believe it might do some really strange things—from creating ice to creating light.”
Sometime this summer, Schmidt and his team hope to record something no one has ever witnessed before. To conduct the experiments, Schmidt will use a 40-foot-long piece of equipment, known as a “two-stage light gas gun,” to propel an 18-millimeter projectile into an 8-foot-deep tank of water.
The devices, often used by scientists to propel objects to simulate meteorites hitting the atmosphere, have two different stages of propulsion, resulting in faster launch speeds—which means the impact, although dramatic, won’t be visible to the naked eye.
The experiments will be at a speed nearly twice as fast as anything in the published research and with far better recording equipment than when military research was first conducted in the 1940s to study what the shock waves from underwater explosions might do to boats or submarines.
Schmidt says he will chronicle the impact with a high-speed camera that can capture up to 200 million frames per second. For comparison, the human eye sees the equivalent of 30 frames per second; while a smartphone camera captures about 300 frames per second.
“We’re doing something no one else is doing right now,” Schmidt said. “What we learn will be very important to this country for being able to accurately predict things like the damage potential for ships close to high-yield underwater explosions, the flight of hypersonic vehicles or missiles through mist, rain, or sea spray, and damage potential of hypersonic projectiles.
Hypersonic weapons travel at speeds greater than Mach 5, or about 4,000 mph, making them hard to detect and intercept. The missiles can also maneuver and vary altitude, allowing them to evade missile-defense systems. Recently, the U.S. has launched hypersonic test rockets, while Russia and China claim they’ve already used them in conflicts.
Schmidt says what will occur in the instant of impact as well as the subsequent milliseconds is a mix of “knowns, unknowns and what-if’s.”
One prediction, hailing from research performed in the 1950s, is that “exotic ice” will form once the water is hit by the supersonic projectile. Exotic ice is any formation beyond the six-sided ice most common on Earth, and found mostly in space or the Earth’s mantle.
Another possibility is sonoluminescence, the creation of light when liquid collapses quickly as the result of a sound wave. The bubbles may also reach extremely high temperatures and pressures for brief periods of time, a phenomenon that has intrigued researchers for decades for its potential to possibly lead to a waste-free energy source.
For his part, Schmidt says he’s “dead certain” the team will see cavitation behind the projectile. Cavitation occurs when the formation of vapor bubbles within a liquid is accelerated to high velocities, such as when hit by a high-speed projectile.
The research by Schmidt and collaborators is supported by a pair of recent defense grants, totaling about $1 million: $750,000 from the Office of Naval Research and $300,000 from the Air Force Office of Scientific Research Instrumentation Program.
“Our experiments are timely and could have a…great impact for our country,” said Schmidt.