Institute of Mechanics, Chinese Academy of Sciences, Photo by Jing Wang

It’s warm and romantic for a couple to fly over the mountains and the seas to afar. When this scene appears in front of the aerodynamicists, what ignites in their hearts is another feeling, or it can be considered as a passion for creation. They are looking forward to sending the couple from the Eastern Hemisphere to the Western Hemisphere within 2 hours. This is their dream or more likely an innovative battle. The National Key Laboratory of High Temperature Aerodynamics, Institute of Mechanics, CAS, is a team that is passionately pursuing to make their dream come true.

If you have the opportunity to walk into the experimental base, they will tell you that the current general flight speed of a civil airliner is about 0.8 Mach, which is about 900 km/h; the fighter can reach 2-3 Mach, equivalent to 2000-3500 km/h; and the hypersonic aerospace vehicle exceeds 5,400 km/h and even reaches 10,000 km/h. Since the White Brothers first made the air-powered aircraft for more than a hundred years in 1903, aerodynamics have entered the supersonic era from the subsonic era. Today, hypersonic flight has become a new goal pursued by aerodynamicists: that is a speed at which a couple can be sent from the Eastern Hemisphere to the Western Hemisphere within two hours.

However, for 60 years, aerodynamicists have struggled to achieve this goal.

Three Major Problems

“Wind tunnel experiment has been conducted before any aircraft is launched. Three major problems will be expected when an aircraft flies at a hypersonic speed. ” they explained.

When an aircraft is flying at the hypersonic speed, the air encountered will undergo a thermochemical reaction. This phenomenon is beyond the theoretical scope of the classical aerodynamics, subverting the similar simulation criteria of traditional wind tunnel experiments, so it is necessary to develop wind tunnel experimental techniques that can reproduce these flight conditions. The shock tunnel is a typical pulse device with the potential to reproduce flight conditions, but it needs to solve the problems of weak wind turbine driving ability, small flow field scale, short experimental time and low measurement accuracy.

To this end, the United States has developed the world's most advanced shock tunnel (LENS II) for heating and compressing light gases, and the experimental test time is about 30ms. Japan has built the world's largest free piston shock tunnel (HIEST), and the experimental test time is about 2-3ms. How does China perform in this field of research?

It is reported that as early as the mid-20th century, Xuesen Qian once put forward an argument, that is: in the future, with the help of rockets, It can arrive in about 20 minutes from the eastern to western United States. The New York Times used a half layout to report it.

In 1950s, Yonghuai Guo, a researcher at the Institute of Mechanics of CAS, foresaw the importance of pulsed wind tunnel equipment, and supported his student Hongru Yu to conduct research. Since then, the Institute of Mechanics of CAS has promoted the development of shock tube and shock tunnel technology in China, the era of the development of spacecraft began, and gradually formed a basic research team for high temperature gas aerodynamics.

As a latecomer to Xuesen Qian and Yonghuai Guo, the National Key Laboratory of High Temperature Aerodynamics has been developing shock tunnel with performance indicators exceeding the most advanced levels in Europe and the United States since 2000. In 2008, in order to implement the important measures of the National Medium- and Long-Term Science and Technology Development Plan (2006-2020), the Ministry of Finance and CAS jointly supported eight National Major Scientific Research Equipment Development Projects, aiming to break through the traditional major scientific research equipment introduction and imitation modes in China; explore ways to independent innovation and development of China's major scientific research equipment. Reproducing the hypersonic conditions shock tunnel" project (JF12 shock tunnel) has became one of the eight pilot projects .

China Set New Milestone

The senior and young scientists in the laboratory did an excellent job. They have successively developed three aspects including high-power shock tunnel driving technology, long experimental time shock tunnel technology, and reappearance wind tunnel measurement technology, and nine specific contents which constitute the main body of reappearance flight condition shock tunnel experimental technology, have obtained a number of invention patents and published a series of papers. In 2012, the world’s first reappearance hypersonic flight conditions shock tunnel (JF12) was built.

During the construction of the hypersonic flight condition shock tunnel (JF12), the high-power shock tunnel detonation drive technology, which uses detonation high-speed release chemical energy instead of mechanical energy, has solved the problems of detonation, high-quality gas source generation and safety applications, etc. and achieved the controllable and adjustable detonation drive capability, becoming a new drive mode for hypersonic wind tunnels.

Their long experimental time shock tunnel technology integrates the detonation-driven shock tunnel suture operation, the vacuum system start shock wave reflection interference control and the shock/boundary layer interference test gas pollution suppression technology, which makes the effective test time of the JF12 reappearance tunnel reach 130ms, achieving an order-of-magnitude increase.

Reappearance flight conditions cause large impact loads, strong airflow erosion, and high temperature thermal environments, making some sensors difficult to survive, and measurement technology faces great challenges. They proposed the high-frequency large-range force measurement system integrated design, the balance interference signal wave system adaptive separation and high-precision thermocouple technology, which improved the accuracy of the high-shock shock wave wind tunnel by an order of magnitude and doubled the heat measurement accuracy. 

In this way, they groped for progress and improvement, integrated innovation into their daily work, and pursued consistently, making the achievement of each goal a milestone in the field.

Confidence and Pride of Asian　　

Although the research progress of this team is rarely mentioned in front of the Chinese public, it has been continuously followed and tracked by American Aerospace from American Aerospace Academy. Zonglin Jiang, the team leader, was invited to make an invitation report at the 2014 AAIA SciTech Conference. In 2015, he was awarded the honor of the American Aerospace Association. On June 14, 2016, The AIAA Ground Testing Award was given to Zonglin Jiang by the American Academy of Aeronautics and Astronautics for his outstanding leadership in the design, development and operation of the world's largest reappearance hypersonic flight condition shock wind tunnel. Zonglin Jiang has thus become the first Chinese scholar to win this award in 41 years of this prize setting, and it is the first time that an Asian scientist has won this honor.

The 265-meter reappearance hypersonic flight condition wind tunnel (JF12) is now quietly lying in the Xuesen Qian National Engineering Science Experimental Base by the Yanqi Lake in Huairou, Beijing. It is by far the largest and most advanced shock tunnel in the world, and a precedent for China to independently develop large-scale and advanced scientific research equipment.

The research team achieved the leap from simulation to reapperance by the entire process including research of innovation concept, key technology verification, engineering integration development, equipment installation and commissioning, and wind tunnel experiment research. It played an irreplaceable role in the national major task implementation and the frontier exploration of the high temperature and pneumatic discipline. Not long ago, this important achievement of enhancing the self-confidence and pride of the Chinese people won the 2016 China Academy of Sciences Outstanding Achievement Award and also won the second prize of the 2016 National Technology Invention.