綠繡眼非對稱懸停飛行機制研究

The Mechanism of Asymmetrical Hovering Flight of Zosterops japonica

劉玠成(Chieh-Cheng Liu)

指導教授 ： 楊鏡堂 ； 葉孟考

國立清華大學/工學院/動力機械工程學系/碩士(2009年)

摘要

本文研究綠繡眼懸停飛行機制及高效率拍撲方式，並將此概念運用到仿生拍撲機構設計，實現並驗證高效率拍撲作動。利用粒子影像測速儀進行流場分析，本文揭示「翼前緣渦流」在綠繡眼非對稱懸停過程是重要的升力來源，證實綠繡眼懸停下拍階段，翅膀作動會在尾流區產生非穩態流場結構－翼前緣渦流（leading edge vortex）及翼尾緣渦流（trailing edge vortex），翼前緣渦流以往都主要被認為出現在昆蟲及蝙蝠飛行過程中，這是第一次被清楚記錄於鳥類非對稱懸停拍撲上。
綠繡眼懸停下拍階段，會出現升力產生機制轉變過程－由「翼前緣渦流升力機制」轉變為「拍合升力機制」。下拍前期，翼前緣渦流主導提供升力，下拍中期翼前緣渦流升力轉弱之際，拍合升力機制出現延緩升力衰減趨勢，此升力機制轉變讓整個下拍階段有足夠升力支持鳥體重。
本文利用仿翅機構模擬綠繡眼翅膀上拍階段的翼摺曲動作，流場分析結果表明：翼摺曲動作對於懸停飛行模式而言，具有減小上拍阻力之重要功能。本文定義上、下拍翼展比（span ratio）為一個表徵翼摺曲程度的無因次參數，並分析此參數之大小對巡航飛行之影響。實驗結果表明，span ratio會影響尾流區射流之作用方向，span ratio越大則射流之作用方向越貼近水平，表示產生大量推進力、少量升力；而span ratio越小則射流之作用方向越貼近垂直，表示產生大量升力、少量推進力，證實翼摺曲作動在巡航飛行亦有助於推進力之產生。
本文提出以下重要結論：綠繡眼拍撲作動，下拍前期升力主要來源為翼前緣渦流升力，中後期出現升力機制之轉變，改由拍合升力機制主導提供升力，此升力機制轉變讓整個下拍階段有足夠升力支持鳥體重；上拍階段翼摺曲作動在懸停模式有助於翅膀阻力減小、在巡航模式亦有助於推進力之產生，此謂高效率拍撲作動。

關鍵字

翼前緣渦流 ； 升力產生機制轉變過程 ； 翼前緣渦流升力機制 ； 拍合升力機制 ； 翼摺曲動作 ； 阻力 ； 推進力 ； 仿生拍撲機構 ； 高效率拍撲作動

並列摘要

There are two objectives in this thesis: investigate the asymmetrical hovering mechanism of Zosterops japonica; create biomimetic flapping machine to verify high-efficiency flapping mode. Using digital particle velocimetry, we demonstrated that Zosterops japonica was able to increase lift by using attached LEVs during hovering. Unsteady vortex structure- leading edge vortices (LEVs) and trailing edge vortices (TEVs) were created by flapping motion in the downstroke period during hovering. The use of unsteady aerodynamic mechanisms was limited to insects and bats in the past researches. It was the first time that LEVs appeared in bird’s asymmetrical hovering.
Lift mechanism transition enhance lift production in the downstroke period during hovering. It transferred from “leading edge vortex lift mechanism” to “clap lift mechanism”. LEVs dominated lift production in the beginning of downstroke. When LEVs were absent in the end of downstroke, clap lift mechanism would then appear to enhance lift. LEV lift mechanism and clap lift mechanism alternately provided sufficient lift during dowstroke period.
Flapping apparatus was created to imitate wing flexion of Zosterops japonica. The experimental results indicated that wing flexion would avoid excessive drag in hovering. Define span ratio R as one parameter that characterizes flexible geometry of bird wings and analyse the relationship between span ratio and cruising speed. From flow visualization data, increasing R would affect vortex jet inclined to horizontal axis. While jet inclined more horizontally, the resultant force was divided into greatly amount of thrust and limited amount of lift. While jet inclined more vertically, the resultant force was divided into greatly amount of lift and limited amount of thrust. With the experiment designed and analysis mentioned above, we illustrated that wing flexion could enhance thrust production during cruising flight.
To conclude, LEVs lift mechanism and clap lift mechanism alternately provide sufficient lift in the downstroke period during hovering. Wing flexion would avoid excessive drag in hovering and enhance thrust production in cruising flight. Zosterops japonica can maneuver the flight highly-efficient.

並列關鍵字

leading edge vortices (LEVs) ； lift mechanism transition ； LEV lift mechanism ； clap lift mechanism ； wing flexion ； drag ； thrust ； biomimetic flapping apparatus ； high-efficiency flapping mode

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