China After five years of construction, the world's largest and fastest wind tunnel has opened in the suburbs of Beijing.
The JF-22 wind tunnel can simulate hypersonic speeds of Mach 30. Photo: SCMP
Located in the Huairou district of northern Beijing, the JF-22 wind tunnel is 4 meters in diameter and can generate air flows at speeds of up to 10 kilometers per second, according to a final assessment conducted on May 30. That makes it the world's largest and fastest wind tunnel, capable of simulating hypersonic flight conditions up to Mach 30 (37,044 km/h), according to the Institute of Mechanical Engineering, which manages the JF-22.
The tunnel will “support China’s research and development of hypersonic aircraft and space transportation systems,” the institute said in a statement on June 2. By comparison, the Mach 10 (7,650 mph) tunnel at NASA’s Langley Research Center in the United States, a key hypersonic test facility, has a test chamber diameter of nearly 2 feet. The larger chamber allows researchers to put large aircraft models and even entire weapons into the wind tunnel to collect more accurate flight data. Most intercontinental ballistic missiles are less than 13 feet in diameter.
The JF-22 is tied to a goal set by the Chinese government and is trying to achieve by 2035: deploying a fleet of hypersonic aircraft that can carry thousands of passengers into space each year, or anywhere on the planet within an hour. But such an aircraft must withstand the extreme temperatures and pressures of hypersonic flight, maintain a stable flight path, and provide a safe and comfortable environment for passengers.
At speeds of five times the speed of sound, the air molecules around the aircraft begin to compress and heat up, leading to molecular dissociation. The gas molecules break down into their constituent atoms, which can react with each other to form new chemicals. Understanding the complex physics of air flow and molecular dissociation is key to the development of supersonic aircraft.
By studying phenomena in experimental settings such as wind tunnels, scientists can explore how hypersonic vehicles interact with their environment and develop new technologies to improve performance and safety. Wind tunnel testing can help identify potential problems or design flaws before a vehicle is built and tested, reducing the risk of failure or accident.
By some estimates, simulating Mach 30 flight conditions inside a large wind tunnel would require the same amount of power as the Three Gorges Dam, which is practically impossible. So Professor Jiang Zonglin, the lead scientist on the JF-22 project, came up with an idea.
To generate the high-speed gas flow needed for hypersonic testing, Jiang proposed a new type of shock wave generator called a “direct-reflection shock wave engine.” In a conventional wind tunnel, the gas flow is generated by an expansion process in which high-pressure gas is rapidly discharged into a low-pressure chamber, creating a supersonic flow. However, this method has some limitations when it comes to generating the extremely high speeds and temperatures required for hypersonic testing.
Jiang's Reflective Shockwave Engine overcomes this limitation by using a series of precisely timed explosions to generate a series of shock waves that reflect off each other and converge at a single point. The resulting burst of intense energy is used to propel air through a wind tunnel at ultra-high speeds.
The innovation paves the way for many achievements by making hypersonic flight research more precise and efficient. Using explosives to generate energy in a wind tunnel has many disadvantages, including danger to both people and equipment, noise, and air pollution. However, because the energy source is generated by explosions rather than fixed mechanical systems, the intensity and duration of the explosions can be adjusted to create a variety of airflows for testing different types of vehicles or materials.
The National Natural Science Association of China sent 16 independent experts to evaluate the JF-22 in several key areas, including effective test time, total temperature, total pressure, and nozzle flow. They concluded that the JF-22 achieved world-leading performance. Together with the JF-12 tunnel, the JF-22 has become the only ground-based test facility that meets all aspects of near-space vehicles.
An Khang (According to SCMP )
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