China developing Supersonic Submarine

China has moved a step closer to creating a supersonic submarine. This submarine is capable to travel from Shanghai to San Francisco i.e. covering nearly 9,900 kms in less than two hours.

This new technology is being developed by a team of scientists at Harbin Institute of Technology's Complex Flow and Heat Transfer Lab.

Team's innovative approach meant they could now create the complicated air "bubble" required for rapid underwater travel.

This technology will make easier for a submarine or torpedo, to travel at extremely high speeds underwater.

How this Technology works?

• This technology has an innovative means to address problems like designing a submerged vessel to travel at high speeds to generate and maintain the air bubble with a rudder placed within it to avoid direct contact with water.
• In practical application this technology is so far limited to unmanned vessels, such as torpedoes. In practical working all of these torpedoes were fired in a straight line because they had limited ability to turn.
• Once in the water, this 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 75 km/hr 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.
• This technology will use vector propulsion or thrust created by an engine.
• By combining liquid-membrane technology with supercavitation, this technology will significantly reduce the launch challenges and make cruising control easier.
• However, many problems are still needed to be solved before supersonic submarine travel became feasible.
• For the control issue, 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 and 15 km.
• This supercavitation technology was not limited only to military use. In future, it could benefit civilian underwater transport, or water sports such as swimming.

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 remains unclear because they are regarded as military secrets.

What is Supercavitation?

• Supercavitation is the use of cavitation effects to create a bubble of gas inside a liquid large enough to encompass an object travelling through the liquid.
• It reduces the skin friction or drag on the object which enables to achieve very high speeds.
• Current applications are mainly limited to projectiles or very fast torpedoes, and some propellers, but in principle the technique could be extended to include entire vehicles.
• 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.
• The supercavitation, torpedo called Shakval was able to reach a speed of 370km or more - much faster than any other conventional torpedoes.

An object (black) encounters a liquid (blue) at high speed. The fluid pressure behind the object is lowered below the vapour pressure of the liquid, forming a bubble of vapour (a cavity) that encompasses the object.