過去研究指出鳥類有特殊構造-小翼羽 (alula)，可以在飛行時防止流體分離及延遲失速，其功能類似於渦流產生器 (vortex generator)。為了解渦流產生器在鳥類滑翔及拍撲兩種運動下的空氣動力效應，本研究以定翼 (滑翔) 及旋翼 (拍撲) 作為實驗模型，探討渦流產生器在不同攻角下 (α = 10°、25°、45°) 之效應，翅膀以展弦比(AR=b/c) = 4的薄型平板做為模型，渦流產生器的尺寸則參考小翼羽的概念，貼齊在翼前緣處。在定翼模型上使用壓力感測塗料和粒子影像測速儀進行表面壓力量測及流場量測，放置三個不同渦流產生器高度，了解不同渦流產生器高度 (h*= h/c) 在三個攻角下，翼上表面的壓力分佈及升力係數變化，接著透過觀測流場並驗證。旋翼模型使用粒子影像測速儀進行流場量測，改變渦流產生器離翼根的距離，了解不同渦流產生器位置 (Lw* = Lw/b) 在三個攻角下的流場變化，計算環流量及分析升力趨勢的變化。從定翼實驗結果得知，渦流產生器會提供流向及展向之動能防止流體分離產生，並增加低壓區的面積及升力，其效能與渦流產生器高度相關，在h*=11%時，在各個攻角下均有最佳提高升力之效果，若其高度過高時，會產生額外阻力。從旋翼實驗可知拍撲動作本身的展向效應與渦流產生器所產生之流向及展向動能之耦合情形，當渦流產生器安裝在靠近翼根處時(Lw* = 0.25)，因近翼根處之旋轉效應相比於靠翼尖處時較弱，渦流產生器提供之流向及展向動能可以給予額外環流量以提高升力。在Lw* = 0.5，因靠近翼尖處時之渦流強度已達近飽和狀態，故渦流產生器提供之額外流向及展向動能在 α = 45° 時，對於環流量並無明顯提升。透過本研究之成果可以更了解小翼羽結構於鳥在飛行過程中所提供的空氣動力特性，此實驗成果將可供未來微飛行器機翼設計與性能提升之參考。

The alula is a small structure of feather that can prevent birds from stalling and flow separation. The function of alula is similar to a vortex generator. This study uses pressure-sensitive paint (PSP) and particle image velocimetry (PIV) to determine the effect of an alula-like vortex generator under two flight conditions, gliding (fixed wing) and flapping (revolving wing), at three angles of attacks (α = 10°、25°、45°). For a thin-flat wing of AR = 4, PSP determines the surface pressure pattern on the suction surface and PIV characterizes the incoherent vortices in flow field. An alula-like vortex generator is positioned at the leading edge of the wing. The effectiveness of a vortex generator depends on the height (h*), the position (Lw*) and the angle of attack of a wing. The PSP results show that the low-pressure region is extended due to a vortical structure induced by a vortex generator, especially when h*=11%. In revolving wing, the interaction between revolving motion and the presence of a vortex generator is determined using PIV. Additional spanwise and chordwise momentums which are induced by a vortex generator energize the circulation of leading-edge vortex (LEV) and result in bursting of vortex in outer spanwise region. The effectiveness of a vortex generator is more significant when it is positioned near the wing root (Lw* = 0.25) than that the near the wing tip (Lw* = 0.5). These findings advance the understanding of wing-alula interactions in bird’s flying motions and are useful for a conceptual aerodynamic design of MAV.

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