The risk of dangerous shock waves when exiting tunnels has long been a challenge for high-speed rail systems. As the speed of maglev trains increases, this problem becomes more prominent and the need for effective solutions becomes greater. Now, researchers believe they have developed a mitigation method that could release compressed air from tunnels before it causes disturbance to humans or wildlife.
Researchers have developed a new method to reduce the "tunnel roar" effect caused by high-speed trains exiting tunnels, The Guardian reports. The technology may soon prove crucial as the next generation of maglev trains reach speeds exceeding 600 miles per hour.
Engineers have long known that when high-speed trains enter tunnels, they compress the air in front of them. This air is forced to the other end of the tunnel, where it collects. As the train exits, it disrupts the compressed air, creating a shock wave similar to the sonic boom produced when an airplane breaks the sound barrier.
Planes typically need to reach speeds of 762 miles per hour to create a sonic boom, while trains can create similar shock waves at much lower speeds. Such shock waves can not only cause harm to people and wildlife, but can also damage infrastructure.
Until now, tunnel shock waves have been a manageable problem because the fastest passenger trains currently in operation, which travel at just over 200 miles per hour, require tunnels at least 3.73 miles long to create shock waves. But China's recent maglev prototype has reached speeds of 600 kilometers per hour (about 590 kilometers per hour), shortening the tunnel length to just 1.2 miles (about 2.9 kilometers). Other tests have reached speeds in excess of 620 mph (about 990 km/h), faster than many aircraft.
Researchers say that installing a 100-meter-long porous sound buffer at the tunnel entrance and laying a porous coating inside the tunnel can reduce the intensity of tunnel roar by up to 96%. The material works by releasing compressed air before the train rushes out of the tunnel.
Maglev trains use magnetism and electromagnetism to levitate a few millimeters above the track. Because there is no physical contact with the track, speed is limited primarily by air resistance and passenger comfort, allowing extremely high speeds to be achieved.
The Shanghai Maglev Train Demonstration Line connecting Shanghai Longyang Road Station and Pudong Airport Station is the world's first commercially operated maglev train. It still holds the record for the fastest electric passenger train, with a speed of nearly 270 miles per hour after more than 20 years of operation.