China could make submarines more stealthy and powerful with classified system that reduces noise 90%

Previous Chinese nuclear submarines made a lot of noise and were easily tracked by adversaries.
Baba Tamim
Stock Photo: Submarine in the sea, 3d rendered image.
Stock Photo: Submarine in the sea, 3d rendered image.

Pixel Stock/ iStock 

A Chinese research team claims to have created a new pump-jet propulsion system that can increase submarine thrust while minimizing obtrusive vibrations by more than 90 percent.

The team created a sealant that prevents water from entering a duct without hindering the rotation of the rotor. However, the precise nature of the system remains classified, South China Morning Post (SCMP) reported on Friday.

The new design could increase the thrust of a pump-jet at slower speeds while significantly reducing the noisy vibration "at most characteristic frequencies," said Hua Hongxing, the research lead, and professor of the State Key Laboratory of Mechanical System and Vibration at Shanghai Jiao Tong University, who conducted simulation experiments at a ground testing facility.

A shrouded propeller, which encloses the rotor in a duct to produce a water jet for propulsion, is sometimes utilized by modern submarines.

The distance between the rotor blades and the inner wall of the duct can be as little as one millimeter. Yet, it can still create a lot of turbulence or bubbles, slowing the submarine down and revealing its location.

The outside edge of the blades of the new pump-jet are driven into the duct wall by the rotor. The rotor tips do not contact water when moving, noted SCMP.

The Shanghai-based researchers claimed that they "had eliminated the gap," according to a study published in the peer-reviewed journal Chinese Journal of Ship Research on Monday.

The journal is run by Institute 701 in Wuhan- the country's major military ship designer.

What is a pump-jet?

A naval device that generates a jet of water for propulsion is known as a pump-jet, hydrojet, or water jet. The mechanical system could be an axial-flow pump, a centrifugal pump, or a mixed-flow pump that combines both axial and centrifugal designs.

Italian inventor Secondo Campini created the first contemporary ducted propeller in Venice in 1931. Pump-jet technology was first employed by the British navy in their Trafalgar-class submarine in the 1980s.

Currently, some of the most potent submarines in the world, notably the Seawolf, Virginia, and Columbia classes in the U.S. and the Triomphant class in France, use pump-jet propulsion.

Test results of the new pump-jet propulsion system

The ultimate fix, according to Hua's team, would be to do away with clearance altogether.

The team created a trench in the duct wall to allow the rotor tips to move freely within.

However, the new pump-jet needed a sealing substance that could keep water strictly outside the trench without obstructing the rotor's movement to function effectively.

The Chinese researchers claimed to have discovered the ideal substance and constructed a soft sealing structure consisting of fine fibers that could satisfy these specifications. The precise composition of the substance is classified.

The researchers also applied a coating to the rotor blade tips to lessen wear over an extended period of time.

One of the key concerns with the new technology is how well the pump-jet performs when the blade tips constantly rub the duct. The scientists placed the apparatus in a water tunnel and measured the thrust and vibration at various speeds.

They discovered that the clearance-free pump-jet was, in fact, somewhat less efficient than the conventional design at top speed.

But by minimizing the random turbulence that creates drag, the system might produce around 10 percent greater push at a lower speed. Additionally, it had fewer cavitation bubbles formed when the blades spin quickly.

According to the test results, the strength of loud vibrations was found to be between a tenth and a thirty-fifth of that of a conventional pump-jet in a wide range of frequencies.

Early Chinese nuclear submarines reportedly made a lot of noise, making it very simple for other nations to track their movements.

However, some military experts claim that the Chinese submarine fleet's more recent models have become faster and quieter as a result of the adoption of cutting-edge technologies like the pump-jet.

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