Bringing the "sky" to the ground, he "blasted" a new path for Chinese wind tunnels

"I think the country is so poor, can you spend a lot of money? To be able to do this kind of work, you must have the ability to save money," said 96-year-old Yu Hongru.

As the theoretical founder of my country's "detonation-driven high-enthalpy shock wave wind tunnel technology", Yu Hongru has devoted himself to this for more than 50 years, and has "blasted" a new path for my country's wind tunnel research. Today, when the arduous and extraordinary work half a century ago is unfolded frame by frame, and when people are moved by his "doing what others dare not do, and what others cannot do", he said: "I just helped a little."

Bringing the sky to the ground

Every generation of wind tunnel means every generation of aircraft.

Wind tunnels are the most reliable experimental means for the study of aerospace vehicles. Hypersonic wind tunnels artificially generate and control high-speed airflows, simulate the flow of gas around the vehicle, and obtain the aerodynamic characteristics of the vehicle, which is equivalent to artificially building a "flying sky" on the ground. The models of the "Shenzhou" series of spacecraft, "Dongfeng" series of missiles and other national heavy weapons that we are familiar with have all been tested in wind tunnels.

JF12 Recreates Hypersonic Flight Conditions in a Shock Wave Wind Tunnel

In the first half of 2023, my country's JF-22 hypersonic wind tunnel officially passed acceptance. As the cradle of a new generation of aircraft, the J-22 hypersonic wind tunnel can reproduce flight conditions at altitudes of 40 to 90 kilometers, equivalent to about 30 times the speed of sound.

Also in the Space Experiment Center of Qian Xuesen Experimental Base in Huairou, Beijing, there is a "predecessor" - the "shock wave wind tunnel for reproducing hypersonic flight conditions", the JF-12 reproducing wind tunnel. The JF-12 can reproduce hypersonic flight conditions at an altitude of 25 to 40 kilometers and 5 to 9 times the speed of sound. It can be said that the development of the JF-22 hypersonic wind tunnel is inseparable from the experience accumulated by the JF-12 reproducing wind tunnel. The emergence of these two wind tunnels also makes my country the only country in the field of hypersonics with the ability to cover all "flight corridors" experiments.

The success of the J-12 wind tunnel was achieved by applying Yu Hongru's detonation drive theory and technology. On this road, he considered himself to be a "spare piece" laid by Guo Yonghuai, but while concentrating on his work, he became a "wonderful piece" in my country's wind tunnel industry.

Do more with less

In 1956, after the establishment of the Institute of Mechanics of the Chinese Academy of Sciences, Qian Xuesen personally wrote a letter to Guo Yonghuai, who was still in the United States: "The Institute of Mechanics has been established. Please come back as soon as possible. There are many important things that need you to do."

Before Guo Yonghuai returned to China, Qian Xuesen and Qian Weichang had already recruited five graduate students in fluid mechanics and physical mechanics for him. Yu Hongru was one of them. "Mr. Guo designated a direction for me - to develop shock tube technology and shock wave wind tunnel."

In early 1958, the Institute of Mechanics of the Chinese Academy of Sciences established a shock tube group, and Yu Hongru was appointed as the group leader by Guo Yonghuai. At that time, he was a graduate student who had just joined the institute for less than 10 months. Yu Hongru was under great pressure when he took on the heavy responsibility. Simply put, the cost of building wind tunnels internationally is high, the process requirements are high, and a large amount of capital investment is required. But the biggest problem facing Yu Hongru was: no money!

Yu Hongru took a photo while conducting an experiment in the 1960s.

"With very little funding, it was impossible to have the advanced instruments and technical equipment used by foreign counterparts." Yu Hongru recalled several years later. This means that the path of imitation is not feasible. What should we do? "The most important thing in scientific research is people and innovation, not money. With innovation, no matter how poor you are, you can use your own methods to do unique work in the world. Without innovation, no matter how much money you have, no matter how many advanced technologies you imitate from abroad, they will still be fakes and you will not be able to produce truly valuable scientific results."

In order to save money, Yu Hongru chose to improve the shock tube method based on hydrogen-oxygen combustion. This method has a high accident rate and unstable performance, and is not recognized internationally. But at the time, Yu Hongru had no better choice. Guo Yonghuai only made one request: to prevent personal injury accidents.

"Later we had many accidents. The most serious one was when the laboratory building was blown up. It doesn't matter if the house was blown up. We will repair it for you immediately after the explosion," said Yu Hongru.

In this way, amid the sound of explosions, the "detonation drive" gradually took shape.

In 1958, Yu Hongru successfully developed my country's first generation of shock tubes. In the 1960s, they successfully developed the JF4 straight-through shock tunnel, the JF4A reflection shock tunnel and the JF8 shock tunnel. In the 1990s, they built the hydrogen-oxygen detonation-driven high-enthalpy shock tunnel (JF10), which became the world's first successfully operated detonation-driven shock tunnel, laying a solid foundation for my country's research on hypersonic wind tunnels.

In the 1970s, stainless steel was generally used for nozzles in international wind tunnel research. "A nozzle costs hundreds of thousands or even millions of yuan," Yu Hongru felt that he "could not afford it." After several studies, he used cast iron to improve it, which only cost tens of thousands of yuan. Before that, when he installed the JF8 shock wave wind tunnel, he also tried every means to use abandoned equipment and found a cheap and reliable factory, and completed the task at a processing fee of only 80,000 yuan. After that, the JF-12 not only has comparable advantages in indicators, but its test cost is also much lower than similar international wind tunnels.

Over the past few decades, "spending less to accomplish great things" has become a matter of course for Yu Hongru. In his view, "the country now has to save money even if it has money", after all, "the country is so big that it has to do everything".

Yu Hongru at work

Paving stones that can't be idle

"The country's scientific cause needs us to serve as stepping stones." This was Guo Yonghuai's teaching to Yu Hongru, and he always kept it in mind.

After entering his seventies, Yu Hongru set two constraints for himself: do not compete with the younger and more energetic people for projects that are suitable for them and that they particularly want to do; try to use as few resources as possible and choose projects with higher risks.

At the beginning of the 21st century, the world was very enthusiastic about developing hypersonic scramjet engines. Based on the needs of major national scientific and technological research and development, Yu Hongru actively paid attention to the research on "hyper-super" issues, and in 2006 formally proposed to the Chinese Academy of Sciences to build a pulse wind tunnel that reproduces hypersonic flight conditions. Two years later, the long test time detonation driven shock wind tunnel (JF-12) project was officially launched, and Yu Hongru once again joined the "battle" and illuminated this journey with his technical ideas. But in 2016, when the JF-12 shock wind tunnel won the second prize of the National Technological Invention Award, he took the initiative to put his name at the end to let more young people come to the front.

"Our generation built the wind tunnel and set up a stage. Whether the show will be good in the future will depend on the young people," said Yu Hongru. But even now, whenever the younger generation asks him questions, he will actively give suggestions. He is a paving stone that never sits idle.