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Published on: September 11, 2018
Low Air Drag Surface via Multilayer Hierarchical Riblets
ZiDan Zhou1, ShengKun Wang1, ZeXiang Yan1
1Key Laboratory of Micro/Nano Systems for Aerospace, Ministry of Education and Shaanxi Key Laboratory of Micro and Nano Electromechanical Systems, School of Mechanical Engineering, Northwestern Polytechnical University, Xi'an 710072, P. R. China.
Abstract:
Riblets inspired by shark skin exhibit a great air drag reduction potential in many industries, such as the aircraft, energy, and transportation industries. Many studies have reported that blade riblets attain the highest air drag reduction ability, with a current limit of ∼11%. Here, we propose multilayer hierarchical riblets (MLHRs) to further improve the air drag reduction ability. MLHRs were fabricated via a three-layer hybrid mask lithography method, and the air drag reduction ability was studied in a closed air channel. The experimental results indicated that the maximum air drag reduction achieved with MLHRs in the closed channel was 16.67%, which represents a 52% higher reduction than the highest previously reported. Conceptual models were proposed to explain the experiments from a microscopic perspective. MLHRs enhanced the stability of lifting and pinning vortices, while vortices gradually decelerated further, reducing the momentum exchange occurring near the wall. This verified that MLHRs overcome the current air drag reduction limit of riblets. The conceptual models lay a foundation to further improve the air drag reduction ability of riblets.
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