Membranous or hairly: fluid dynamics approach to the wing microstrucures

2023 Fiscal Year Final Research Report

• Project/Area Number: 22K20656
• Research Category: Grant-in-Aid for Research Activity Start-up
• Allocation Type: Multi-year Fund
• Review Section: 0702:Biology at cellular to organismal levels, and related fields
• Research Institution: Takushoku University
• Principal Investigator: Maeda Masateru 拓殖大学, 工学部, 准教授 (80795774)
• Project Period (FY): 2022-08-31 – 2024-03-31
• Keywords: 動物飛行 / 空気力学 / 羽根 / 羽毛 / 羽枝 / 小羽枝 / 微細構造 / 鳥

Outline of Final Research Achievements

We conducted an aerodynamics study on a feather considering the microstructure to elucidate the role of feather evolution in the evolution of powered flight in birds. We created a simple feather model possessing a shaft (rachis) and planar plate (vane). We then compared it with models with various gaps (slits) on its vane. We then conducted a series of steady laminar flow simulations on the feather models. The results showed that the lift-to-drag ratio, an index for flight efficiency, decreases with increasing the total gap area. Flow visualisation revealed that the high-pressure air on the ventral side of the feather vane flowed into the upper surface through the gaps. This flow neutralises the low surface pressure on the upper surface, the main contributor to the lift.

Free Research Field

生物流体力学

Academic Significance and Societal Importance of the Research Achievements

鳥の羽ばたき飛行の進化は樹上説・地上説・WAIR（坂の駆け上がり）等が議論されている一方、羽根の進化については「羽根の微細構造（羽枝・小羽枝）が密に結合しており風を通さないほどよい」とか「羽弁（板部分）が羽軸を挟んで前縁側（外弁）と後縁側（内弁）で非対称であることが必要」などとされるが、裏付けに乏しい。本研究はこの点を実証する第一歩として、微細構造を考慮した羽根の空気力学に取り組み、メカニズムの解明に近づけた。今後は引き続き羽根の空気力学を進めるとともに、毛でできた翼で飛翔する昆虫や植物との比較を行い、類似性の有無や、どのような条件のもとで収斂が起きているのかを明らかにしてきたい。