Imagine a submarine that can travel from Shanghai to San Francisco in less than two hours.
That’s what Chinese scientists are working on.
Stephen Chen reports for Hong Kong’s South China Morning Post, Aug. 24, 2014, that a team of scientists at the Complex Flow and Heat Transfer Lab of the Harbin Institute of Technology in China have developed a new technology that will make it easier for a submarine or torpedo to travel at extremely high speeds underwater by creating the complicated air “bubble” required for rapid underwater travel.
Li Fengchen, professor of fluid machinery and engineering, said his team “are very excited by its potential.”
Water produces more friction, or drag, on an object than air, which means conventional submarines cannot travel as fast as an aircraft.
However, during the cold war, the Soviet military developed a technology called supercavitation, which involves enveloping a submerged vessel inside an air bubble to avoid problems caused by water drag.
A Soviet supercavitation torpedo called Shakval was able to reach a speed of 370km/h (230 mph) or more – much faster than any other conventional torpedoes.
In theory, a supercavitating vessel could reach the speed of sound underwater, or about 5,800km/h (3,604 mph), which would reduce the journey time for a transatlantic underwater cruise to less than an hour, and for a transpacific journey to about 100 minutes, according to a report by California Institute of Technology in 2001.
However, supercavitation technology has faced two major problems:
- The submerged vessel must be launched at high speeds, approaching 100km/h (62 mph), to generate and maintain the air bubble.
- It is extremely difficult – if not impossible – to steer the vessel using conventional mechanisms, such as a rudder, which are inside the bubble without any direct contact with water.
As a result, supercavitation’s application has been limited to unmanned vessels, such as torpedoes, but nearly all of these torpedoes were fired in a straight line because they had limited ability to turn.
Li said the team of Chinese scientists had found an innovative means of addressing both problems:
- Once in the water, the team’s supercavitation vessel would constantly “shower” a special liquid membrane on its own surface. Although this membrane would be worn off by water, in the meantime it could significantly reduce the water drag on the vessel at low speed.
- After its speed had reached 75km/h (46.6 mph) or more the vessel would enter the supercavitation state. The man-made liquid membrane on the vessel surface could help with steering because, with precise control, different levels of friction could be created on different parts of the vessel.
Li said, “Our method is different from any other approach, such as vector propulsion (or thrust created by an engine). By combining liquid-membrane technology with supercavitation, we can significantly reduce the launch challenges and make cruising control easier.”
However, many problems still needed to be solved before supersonic submarine travel became feasible. Besides the control issue, Li said a powerful underwater rocket engine still had to be developed to give the vessel a longer range. The effective range of the Russian supercavitation torpedoes, for example, was only between 11 km (6.8 mi) and 15 km (9.3 mi).
Li said the supercavitation technology was not limited only to military use. In future, it could benefit civilian underwater transport, or water sports such as swimming: “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.”
Besides Russia, countries such as Germany, Iran and the United States have been developing vessels or weapons using supercavitation technology.
Despite many scientists worldwide working on similar projects, the latest progress at the Harbin Institute of Technology remains unclear because they are regarded as military secrets.
Professor Wang Guoyu, the head of the Fluid Mechanics Laboratory at Beijing Institute of Technology and a member of the water armament committee of the China Society of Naval Architect and Marine Engineers, is leading another state-funded research project on supercavitation. He said even he had been kept in the dark about recent supercavitation developments in China because “The primary drive still comes from the military, so most research projects are shrouded in secrecy.”
H/t Yahoo News
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