在無人飛行載具、微型飛行器與小型風力發電機的發展下，了解低展弦比機翼在低雷諾數下之流場結構可以進一步的提其空氣動力學的特性。大多數在低雷諾數區段的研究主要著重於二維或是半翼展模型的部分，對於三維的流場結構需要更進一步的探討。在這篇研究中透過力量測與流場可視化的實驗以及數值模擬的方法分別得到展弦比1之NACA0003機翼在雷諾數介於75,000和125,000間的空氣動力學特性以及流場結構之觀測結果。將有助於進而了解空氣動力學特性與流場結構之間的關係。
透過流場可視化之實驗與數值模擬的交叉驗證下發現本研究中的機翼在低雷諾數區間的流場結構包含翼前端分離、層流分離氣泡和翼尖端渦流結構。三維的渦流結構以及壓力梯度對於層流分離氣泡有顯著的影響。層流分離氣泡的發展受翼尖渦流結構的壓抑使得氣泡在翼中線的位置最大，隨著靠近翼尖端而縮小。這個現象在高功角的情形中更為明顯。而在表面油流視流與數值模擬的觀察下，當功角增大時分離氣泡的逐漸以螺旋線的方式旋轉至翼中線的位置，越靠近翼尖端的氣泡旋轉面與機翼上表面呈現非垂直狀態。此外，氣泡之長度擴展到整個翼弦長後氣泡的朝增大高度的方式繼續擴張。

For developing unmanned aerial vehicles (UAVs), micro air vehicles (MAV) and small-scale wind turbine blades, understanding the relationship between the flow structure and aerodynamic performance of NACA series wings is required. Most of the previous studies were focused on two dimensional cases, the clearly investigation of the flow structure of 3D wing still unclear. In this study, the three-dimensional aerodynamics characteristics and flow behaviors of a NACA0003 wing with an aspect ratio of 1 at Reynolds numbers of 75,000 100,000 and 125,000 have been investigated experimentally and numerically. Through the flow visualization, including the smoke and oil flow visualizations, the flow field is presented to identify the leading edge separation, laminar separation bubble and a pair of wing-tip vortex. The three dimensional vortex and Reynolds number have influence on the development of laminar separation bubble.
The size of laminar separation bubble decreases along with the spanwise of the wing from the middle section to the tip. This phenomena are more revealing at the higher angles of attack than the lower ones. As the angle of attack increases, the separation bubble which exists on the surface of wing tends to spread in such a way which is no longer perpendicular to the upper surface and is parallel to the chord line. After the length of the separation bubble expand to the chord length of the wing, the formation of bubble expand vertically.

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