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低雷諾數下三維有限翼分離泡特性與遲滯現象實驗探討
An Experimental Investigation on 3D Separation Bubble and Hysteresis Loop
摘要
風洞量測及表面油流視察技術被用於探討低雷諾數下三維機翼層流分離泡之型態，及遲滯現象發生時同一攻角不同氣動力表現所相對應之表面流態。本研究採用之實驗模型其翼剖面?NACA0015展弦比4之有限矩形翼，以弦長??考長度之雷諾數?6×104。由實驗結果顯示三維機翼分離泡受下洗作用及翼尖渦流影響，造成越靠近翼尖邊界層層流分離點越靠近機翼後面而分離氣泡重回點卻越靠近機翼前面，形成三維氣泡在機翼中間寬在機翼兩側窄之現象。另外藉由遲滯現象發生攻角範圍外與範圍內之表面流態之對比，發現遲滯現象發生之時同一攻角存在兩個不同的流態，以何種流態出現流場，取決於機翼進入新攻角時，一開始所感受之邊界層擾動型態。
並列摘要
The lift and drag characteristics and associated oil-flow visualization over the suction surface of an NACA 0015 airfoil with an aspect ratio of 4.0 are obtained at a Reynolds number of 60000. Oil flow visualization results show that the downwash effect and the existence of tip vortice make three dimensional laminar separation bubbles with largest width in the middle span and shrink into a point near the wing tips. Within hysteresis loop, two different surface flow types of the same angle of attack are observed in the present experiment. In the hysteresis loop, the final state of surface flow type is highly correlated with that of previous angle of attack. It means that the premier disturbances, sensed by the boundary layer, determine the final state of surface flow type at the angle of attack within the hysteresis loop.