China has built the world’s largest free-piston-powered shock tunnel, enabling it to carry out wind tunnel tests for hypersonic research at relatively low cost and potentially widening its lead over the USA in the development of hypersonic weapons.
According to a report in the South China Morning Post, the Sichuan-based facility is capable of simulating extreme flight conditions up to Mach 33 (33 times the speed of sound), or 2.5–11.5 kilometres per second.
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Known as a Stalker tube – named after Australian space engineer Raymond Stalker, who invented the free-piston-driven tunnel during the 1960s – the X3 facility uses relatively cheap and inert high-pressure nitrogen gas to drive a piston to speeds of several hundred kilometres an hour.Compressed air bursts through several strong membranes to generate the sorts of extremely hot and fast shock waves that would be encountered by aircraft travelling at hypersonic speeds.
The testing tube reportedly has a diameter of 80 centimetres – twice as large as the previous largest piston-driven wind tunnel, the University of Queensland’s X3 Expansion Tube– and features an 840-kilogram piston, the heaviest piston ever utilised in a wind tunnel. The piston, which must be capable of withstanding crushing pressure from the compressed air equivalent to 10,000 times the force of gravity while travelling at a speed of up to 540 km/h, features a unique structural design and new materials, making it fully reusable and reducing operational costs.
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According to the research team, the piston has undergone numerous tests without suffering any damage. They also claimed that the X3 tunnel’s novel design, in which a high-pressure nitrogen tank is connected to the tube so that the two vibrate together as the piston moves, decreased the size and complexity of the entire facility but also significantly reduced the vibrations, which can compromise test results.
According to the South China Morning Post report, Chinese scientists hope to use the facility to carry out research in support of a number of missions, including sending Chinese astronauts to the Moon and developing a hypersonic scramjet-powered aircraft that could travel anywhere in the world in an hour.