China’s submarines can be quieter, more powerful with new pump-jet: scientists
- Shanghai research team says its new propulsion system can deliver higher thrust while reducing noisy vibrations by more than 90 per cent
- Scientists say they have identified a sealant to keep water outside duct without impeding rotor movement but the exact nature of material is classified
Some modern submarines used a shrouded propeller that puts the rotor in a duct to generate a jet of water for propulsion. Between rotor blades and the duct’s inner wall there is a clearance, sometimes as small as a millimetre wide, but it can produce a lot of turbulence or bubbles that can slow the submarine and give a hint of its location.
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The rotor in the new pump-jet sinks the outer edge of the blades into the duct wall. When moving, the rotor tips have no contact with water.
Simulation experiments conducted at a ground testing facility suggested the new design could increase the thrust of a pump-jet at slower speeds while reducing the noisy vibration significantly “at most characteristic frequencies”, said the team led by professor Hua Hongxing, of the State Key Laboratory of Mechanical System and Vibration at Shanghai Jiao Tong University.
The first modern ducted propeller was built by Italian inventor Secondo Campini in Venice in 1931. In the 1980s the British navy made the earliest use of pump-jet technology in its Trafalgar-class submarine. Now pump-jet propulsion can be found in some of the most powerful submarines in the world, including the Seawolf, Virginia and Columbia classes in the US and in France’s Triomphant class.
In theory, the pump-jet could suppress more noise and achieve higher energy efficiency with the duct than a fully exposed rotor.