Breakthrough! "Exceeding the highest level known to be publicly reported"

author:Straits Network

Recently, the aerospace micro-nano system innovation team of Northwestern Polytechnical University has made breakthroughs in aircraft drag reduction. By imitating the tongue-shaped fractal sand ridge structure unique to the mainland Kumtag Desert, the team designed a tongue-shaped multi-fractal drag reduction micro-nano structure of imitating the sand ridge. The drag reduction rate of the structure has been increased by 52% compared with the best level reported by the previous international report, and the drag reduction wind direction disturbance angle has been increased from 35° to 60°, and the drag reduction performance has exceeded the performance limit of small rib pneumatic drag reduction technology for half a century.

Breakthrough! "Exceeding the highest level known to be publicly reported"

Imitation sand ridge tongue fractal structure film and structure display diagram

Why choose desert as a bionic object?

Professor He Yang of the research team introduced that sand grains naturally form sand ridges under the accumulation of wind transport, 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. In the past five years, the team has repeatedly carried out field investigations in the desert terrain of Xinjiang, Gansu and Inner Mongolia, analyzed the morphology of sand dunes, sand ridge structure, and sand grain characteristics, mastered a large number of first-hand data, and finally selected the Kumtag Desert as the research object.

Breakthrough! "Exceeding the highest level known to be publicly reported"

Shape characteristics of sand ridges in the Kumtag Desert

The Kumtag Desert lies between the Altun Mountains and Lop Nur, affected by the unique topography, the number of windy days above 8 accounts for nearly one-third of the year, and the direction of the wind is not fixed, so its sand ridge surface forms a unique "tongue-shaped fractal structure" in the world. This special wind direction condition and unusual structure inspired the team's research.

Knowing bionic objects≠ can make bionic objects

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. In view of 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 on the basis of mastering the advantages of MEMS (microelectromechanical system) chip manufacturing technology in the early stage, which effectively improved the processing accuracy and efficiency, and realized the accurate manufacturing of multi-layer high-depth heterogeneous composite microstructures.

Breakthrough! "Exceeding the highest level known to be publicly reported"

Design diagram of tongue-shaped fractal structure of imitation sand ridge

Test report: Drag reduction exceeds the highest known publicly reported level

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 total shear resolution of the system is accurate to 2.5×10-6N, which is comparable to the aerodynamic friction force acting on the surface of a business card by human breathing airflow, which is the best result for public reporting of international wind tunnel shear force measurement.

Breakthrough! "Exceeding the highest level known to be publicly reported"

The laboratory has built a wind tunnel for micro-nano drag reduction

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 reviewers spoke highly of the project as "outstanding results in research work and suggestions for expanding engineering applications".

Source: CCTV News Client