Chinese scientists want to add wings to bullet trains to make them even faster
published : 24 Nov 2021 at 13:57
writer: South China Morning Post
HONG KONG: China wants even faster bullet trains, and a team of scientists in the southwest of the country have suggested a way to do it: add wings.
Their study found that adding five pairs of small wings on each train carriage would generate additional lift and reduce the weight of the train by nearly a third, taking the top speed to 450 kilometres per hour.
The research is part of a project launched by Beijing earlier this year named CR450, which aims to develop a new generation of high-speed trains that can travel at that speed.
China's high-speed rail network is currently the fastest in the world - its existing bullet trains can run at 350km/h. The CR450 project aims to have trains that run nearly 30% faster, meaning it would take only about three hours to travel from Beijing to Shanghai, or just five hours from Beijing to Guangzhou.
But "as the operating speed increases, the wear on the wheels will increase and inevitably shorten the repair cycle and service life of the wheels", according to a paper by the team from the Chengdu Fluid Dynamics Innovation Centre, led by research engineer Zhang Jun.
"The high-speed train with lift wings is a breakthrough in the traditional concept of high-speed train aerodynamic design, to reduce overall energy consumption and operating costs," they said in the paper published in peer-reviewed Chinese journal Acta Aerodynamica Sinica on Thursday.
The idea of putting wings on high-speed trains is not new - Japanese engineers came up with a proposal in the 1980s for a train with plane-like wings extending from the sides, eventually building a prototype two decades later.
While this early attempt proved that the wings gave aerodynamic efficiency, it failed in practical applications because the wings were too big and too wide for the train to run safely within the limited space of existing rail infrastructure like security fences and tunnels.
Zhang and his team have proposed something a little different. Instead of putting a pair of giant wings on the sides, they say an array of smaller wings on top of a train could generate sufficient force to lift it without the risk of hitting anything.
But they cautioned that the wings would need to be carefully designed and installed.
Travelling at 450km/h, the train's body would produce a high-speed airstream near the surface of the roof that could cause harmful turbulence if the wings were sitting too low, according to the paper.
And if a wing was too high above the train, it could run into currents generated by the wings in front and produce more drag than lift. The researchers estimated that the optimal range was for the wings to extend between 1.5 and 2 metres over the roof.
The biggest difference between their proposal and the Japanese one is that the Chinese train would work more like a cruise missile than an aircraft, according to Zhang and the team, who also work on the country's military research programme, including the development of hypersonic weapons.
Chen Yu, a research engineer with Tongji University in Shanghai who was not involved in the study, said there were some extremely challenging engineering issues to overcome to put wings on trains.
"For a train designer, the smoother the surface the better - every additional component is an additional issue," said Chen, who has studied the aerodynamic behaviours of high-speed trains in wind tunnels.
Wings would, for instance, inevitably increase noise in the cabin and reduce passenger comfort, he said. That would mean scientists and engineers would have to come up with ways to control the complex airstreams over the roof and absorb the increased noise with soundproofing materials or structures.
"But this will then increase the total weight of the train," Chen said.
High-speed trains draw electricity from overhead power lines via a pantograph that sits on top of the train, and he said additional measures would be needed to keep the pantograph in constant contact with the power lines given the disturbance generated by the wings.
The first CR450 trains will likely operate on a new 300km railway line between Chengdu and Chongqing, two big economic centres in the southwest, according to Chinese media reports. Construction on that line began in September and is expected to be finished in five years.
A nationwide research effort, the CR450 programme aims to solve technical issues ranging from automatic control and wheel design to the steering system, rail upgrades and safety measures, according to researchers involved in it.
Proponents of the wing solution believe it would be more economical and feasible for large-scale application than a maglev train with superconducting technology that travels at 600km/h. Two new maglev lines are being planned for cities in eastern China.