翅膀旋轉及拍翅相位對豆娘拍撲飛行之影響

Abstract

豆娘具有敏捷的操控性並能藉由調整雙翅的頻率、相位、攻角進行靈活的飛行，因此本文以兩種台灣常見的豆娘中華珈蟌(Psolodesmus mandarinus)及細胸珈蟌(Mnais tenuis)作為研究對象，研究豆娘在撲翼飛行時使用的正向旋轉機制，藉由實驗觀測與數值模擬的比對，結合流固耦合與動態網格技術，得到豆娘在飛行時能藉由翅膀旋轉增加升力，結果可以應用在仿生撲翼機構的設計上，提供飛行策略的設計概念。 實驗將豆娘放入壓克力箱中，藉由高速攝影機捕捉豆娘自由飛行時的拍翅動作，並利用二維PIV技術將流場可視化，藉由流場與動作分析，探討豆娘拍撲飛行時所採用的特殊機制與流場渦漩間的相互關係。流場分析得到，豆娘在下拍時雙翅皆能產生渦漩並由翼尖開始脫離翅膀表面，並藉由成對的渦漩產生射流提供飛行所需升力，此結果與數值模擬中得到之流場共同現象相吻合，藉此驗證模擬中之動作參數雖然皆以簡單函數逼近，但並不影響流場渦漩之趨勢。動作分析觀察到，兩種豆娘在自由飛行中皆採用翅膀由後向前的正向旋轉模式，因此將兩種不同的旋轉模式加入數值模擬中發現，在雙翅無相位差時，翅膀的旋轉改變了表面在水平及垂直方向上的投影量，因此加入旋轉動作後在一個上拍或下拍的衝程中的升力略微降低、阻力卻大幅上升，此結果看似對於拍撲飛行有著反效果但考慮完整一週期下之合力，正向旋轉能提供正值的升力與負值的阻力即推力。反向旋轉在上拍時產生的渦漩結構較完整，翅膀表面生成之低壓區也較大，進而產生強度更強的射流，然而其方向向上，反而造成負值的升力；而正向旋轉能減低上拍時產生的負升力值，使一週期之平均升力大幅提升，並在上拍時能產生一強大的推力，此結果說明了為何豆娘在拍撲飛行時皆使用正向旋轉而非反向旋轉。

This study is aimed to investigate the flapping fight of damselfly species Psolodesmus mandarinus and Mnais tenuis. By experimental observation and numerical simulation with fluid-structure interaction and dynamic mesh technique, we found out that damselfly can increase lift force by rotating their wing on flapping flight. The results can be applied on the design of biomimetic flapping mechanism and micro aerial vehicle. In the experiment, damselflies free-fly in acrylic chamber. High speed camera is used to capture the flapping motion and flow field while two dimensional PIV technique shows the interaction between the motion and vortex structure. In motion analysis, both species of damselflies utilize forward rotation, then adding this rotation motion into the numerical simulation. Comparing three kind of flapping motion, non-rotation, forward rotation, and backward rotation, while tandem wing has 0 degree phase lag. Results show that wing rotation changes wing surface area on horizontal and vertical direction. Flapping with rotation decrease lift force and increase drag force on each stroke but considering a whole flapping period, forward rotation can generate positive lift force and negative drag force which is thrust. Leading edge vortex and low pressure area on wing surface of backward rotation are stronger during up-stroke. It causes generating of negative lift force, however, forward rotation can decrease negative lift force during up-stroke. Therefore, It promote mean lift force greatly in a whole flapping period and can generate thrust during up-stroke. The result shows that why damselflies utilize forward rotation in stead of backward rotation on their flapping flight.