Aerodynamic and functional consequences of wing compliance
Experiments in Fluids
Volume 46, Number 5 / 2009年5月
愈來愈多證據指出大多數的昆蟲在飛行時會經歷某程度上的翅膀變形。由於翅膀基部不具肌肉末梢，昆蟲翅膀的瞬間形狀是由翅膀的週期性加速形成的空氣動力伴隨著慣性與彈力所造成。由於伴隨著快速往復拍擊翅膀而來的慣性力量負擔- 乘載高過平均空氣動力，翅的被動形變是許多昆蟲拍翅飛行不可避免的現象。雖然翅的順服涉及一些加強抬昇的機制(如：適合的弧度)，然而翅膀變形在直接的空氣動力上的結果仍未被解答。在本文中，作者針對菸草天蛾(Manduca sexta)翅膀的順服如何影響整體產生的氣流呈現新的研究資料。真正的蛾翅被置於自動裝置以其主要的旋轉平面及自然狀況下的振翅頻率25 Hz拍擊翅膀。作者使用數位質點影像測速儀的超高頻率解析以評估在此平均對流程度下之翅膀順服，憑藉翅膀僵硬程度在自然狀況下的變化以修改翅突然變形的程度(新鮮的翅較有彈性且比脫水的翅表現出較好的順服度)。作者發現有彈性的翅產生明顯強度較大的平均對流程度，且方向較乾硬的翅膀有利於抬昇。作者指出其結果確認翅膀的順服在飛行力量上瓣演著關鍵的角色。
A growing body of evidence indicates that a majority of insects experience some degree of wing deformation during flight. With no musculature distal to the wing base, the instantaneous shape of an insect wing is dictated by the interaction of aerodynamic forces with the inertial and elastic forces that arise from periodic accelerations of the wing. Passive wing deformation is an unavoidable feature of flapping flight for many insects due to the inertial loads that accompany rapid stroke reversals—loads that well exceed the mean aerodynamic force. Although wing compliance has been implicated in a few lift-enhancing mechanisms (e.g., favorable camber), the direct aerodynamic consequences of wing deformation remain generally unresolved. In this paper, we present new experimental data on how wing compliance may affect the overall induced flow in the hawkmoth, Manduca sexta. Real moth wings were subjected to robotic actuation in their dominant plane of rotation at a natural wing beat frequency of 25 Hz. We used digital particle image velocimetry at exceptionally high temporal resolution (2,100 fps) to assess the influence of wing compliance on the mean advective flows, relying on a natural variation in wing stiffness to alter the amount of emergent deformation (freshly extracted wings are flexible and exhibit greater compliance than those that are desiccated). We find that flexible wings yield mean advective flows with substantially greater magnitudes and orientations more beneficial to lift than those of stiff wings. Our results confirm that wing compliance plays a critical role in the production of flight forces.