Using a supersonic process called supercavitation, Chinese scientists are one step closer to making a journey between eastern China and the western United States a lot faster.

Li Fengchen, professor of fluid machinery and engineering at the Harbin Institute of Technology's Complex Flow and Heat Transfer Lab announce he and his team had been able to create a bubble around a marine vehicle, allowing it to reach supersonic speeds underwater. The technology was first developed by Soviet scientists during the Cold War for high-speed torpedoes, and has since been researched not only in Russia and China, but also the United States and Iran.

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Current submarines have a limit to their speeds, a consequence of the drag caused by the surrounding water. A supercavitating device moves so fast that it splits the water around it into an oblong cavity or "bubble," leaving the majority of the vehicle surrounded by air. The Soviet prototype reached speeds of up to 370 kph (300 mph), but Chinese hope to push that number to beyond of the speed of sound - 1,225 kph (761.2 mph) - or even beyond. At those speeds, the entire width of the Pacific from west to east could be crossed in under two hours.

But supercavitation has practical hurdles: reaching the high speed required to create the bubble in the first place (around 100 kph/62 mph), and steering. The Soviet team found their prototype, powered by rockets, could not deviate from a straight line since its rudders were not in contact with water. That brings up the worry of missing a moving target, or even an impact with sea life or an iceberg drifting into the "flight path."

Li's team found ways around the first two problems. Using a rapidly spinning wheel submerged in water, Li used a man-made chemical "shower" to create a liquid membrane on the wheel's surface. Although the membrane is washed away by the passing water, it reduces the drag for the mechanism to reach a supercavitation state. By adjusting levels of the membrane's friction, the team found the device could be steered. 

"By combining liquid-membrane technology with supercavitation," Li observed, "we can significantly reduce the launch challenges and make cruising control easier." 

Supercavitiation has only been used on small devices. Larger vehicles meant for transport are still beyond the limits of Li's experiment, and he admits that practical application of the technology is still in the theoretical stage. 

However, he does see short-term benefits, such as the creation of a wetsuit capable of holding to itself a sheet of drag-reducing air bubbles. 

"If a swimsuit can create and hold many tiny bubbles in water, it can significantly reduce the water drag; swimming in water could be as effortless as flying in the sky," he said. 

Tagssupercavitation, submarine