Xi'an, March 3 (Reporter Alena) The reporter learned from Northwestern Polytechnical University on the 27th that the university's aerospace micro-nano system innovation team has made breakthroughs in aircraft drag reduction. By imitating the tongue-shaped fractal sand ridge structure unique to the Kumtag Desert, the team designed a tongue-shaped multi-fractal drag reduction micro-nanostructure that imitates the sand ridge. The drag reduction rate of the structure has been increased by 27% compared with the best level reported internationally, and the resistance reduction wind direction disturbance angle has increased from 52° to 35°, and the drag reduction performance has exceeded the performance limit of small rib pneumatic drag reduction technology for half a century.
Design diagram of tongue-shaped fractal structure of imitation sand ridge. Photo courtesy of Northwestern Polytechnical University
According to reports, drag reduction is the focus of long-term attention in the aerospace field, which not only affects the aerodynamic shape design and layout optimization of aircraft, but also has important application value for aircraft energy saving, emission reduction and reduction of operating costs.
In recent years, different from the traditional means of reducing drag by changing the aerodynamic layout of aircraft, experts in related fields at home and abroad have conducted in-depth research on changing the surface microstructure of aircraft to achieve drag reduction. For example, Lufthansa Technik has developed an aircraft "film" through bionic "shark skin", which has been tested and applied to Boeing 747-400 aircraft, which can effectively reduce flight frictional resistance.
Shape characteristics of sand ridges in the Kumtag Desert. Photo courtesy of Northwestern Polytechnical University
However, the bionic "sharkskin" structure still has problems such as low aerodynamic drag reduction rate and poor wind direction robustness in practical applications, that is, it is difficult to continue to maintain the original aerodynamic drag reduction performance when the wind direction changes. To this end, Professor Yuan Weizheng, Director of the Key Laboratory of Aerospace Micro-Nano System of the Ministry of Education, and Professor He Yang's team, with the support of the National Natural Science Foundation of China, extracted the conditional features based on similar criteria after long-term comparison and analysis, and finally found a solution in the vast desert.
Talking about why he chose desert as the bionic object, He Yang said that sand grains naturally form sand ridges under the accumulation of wind, and form a geomorphological structure with certain undulating laws on the surface of the sand ridges. Nature follows the principle of least resistance, that is, all matter moves along the path of least resistance. This means that the wind has the least energy loss in the path formed by these geomorphological structures, which means that the surface of this sand ridge structure has the least resistance to the wind.
The team is conducting experiments. Photo courtesy of Northwestern Polytechnical University
Based on the scaling of dimensionless viscous length, the research team designed a fractalal micro-nanostructure of imitation sand ridge through modeling and simulation verification. Aiming at the problem that the existing micro-nano structure processing methods have low flexibility and are difficult to achieve complex configuration processing, the team creatively proposed a triple lithography method based on multiple masks, which effectively improved the processing accuracy and efficiency, and realized the accurate manufacturing of multi-layer high-depth heterogeneous composite microstructures.
In addition, the team independently developed, designed and built the world's first high-resolution micro-nano drag reduction measurement wind tunnel, providing an effective means for micro-nano structure flow measurement.
The laboratory has built a wind tunnel for micro-nano drag reduction. Photo courtesy of Northwestern Polytechnical University
After several rounds of testing and structural optimization, the final test report issued by the National Key Laboratory of Airfoil Grid Aerodynamics showed that "the micro-nano structure skin of imitation sand ridge has a significant drag reduction effect, which exceeds the highest known public report." The key project of the National Natural Science Foundation of China undertaken by the team - "Pneumatic Fractal Micro-nano Structure and Its Manufacturing Technology of Imitation Sand Ridge" also ended with "excellent", and the review experts spoke highly of the project as, "The research work has achieved outstanding results, and it is recommended to expand the engineering application." ”
"In the next step, we hope to put scientific research results into use in many fields such as large aircraft, high-speed rail, and wind power generation through the transformation of scientific and technological achievements, so as to provide new solutions for energy conservation and emission reduction and help achieve the goal of 'dual carbon'." Yuan Weizheng said. (End)