Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/2033
標題: 二維簡振機翼上方流場特性之探討
Investigations of Flowfield Characteristics Upon Two-Dimensional Airfoil Oscillating in Pitch
作者: 李夏吉
關鍵字: 二維簡振機翼;流場特性
出版社: 機械工程研究所
摘要: 
本研究是以實驗方法探討二維簡振機翼上方之非穩態流場特性。
實驗於封閉式循環水洞中進行,模型為NACA0012之對稱型機翼,弦長
120mm,翼展330mm;以機翼弦長為特微長度,自由流速(約16cm/sec)
為準的雷諾數約為2.7×104。流場觀察以氫氣泡法進行藉以定性地了
解非稱態流場之變化。並量測機翼上表面之平均壓力分佈。以雷射測
速儀系統進行速度場之量測。非穩態之流場條件為攻角α=15°,分
別以2Hz,3Hz之週期性俯仰運動產生。以此定性,定量的方法分別探
討機翼上方整體之流場特性及剪力流層沿下游之演化。經此方式可以
瞭解,機翼作小振幅(±1°)之俯仰運動時,若適當選取搖擺頻率fe
則由於剪力層受到特定頻率之激擾,於翼前緣釋出小渦旋;間接地促
使在前翼面之邊界層外緣產生局部加速之現象。進而因捲增之效應,
此一系列之小渦旋交互作用將引導剪力層向翼面發展;進而於下游合
併成一個較接近翼面的大渦旋,此經合併後而形成之大渦旋,將以較
低之速度向下游方向移動。在此過程中因大尺度渦旋結構較接近翼面
且有較長之時間滯流於翼面上方;因此,可以使機翼上方獲致一額外
升力,改善其空氣動力特性。

The flow structure over an NACA0012 airfoil oscillating sinusoidally in pitch will be investigated experimentally in a recirculation water channel. It is intended to understand the insight of hte flow physics and characteristics of the perturbed shear layer leading to higher lift at post-stall angle of attack. Flow visualizations are performed by hydrogen bubbles as well as the laser sheet methods; moreover, velocity informations are acquired by LDV system through phase-averaged technique.
The evolution of small scale vortices in perturbed shear layer leading to coalescence and formation of large scale vortex above but closer to the airfoil. Neverthless, appropriate perturbation at the leading edge would lead to the most effective separation control when the forcing frequency matched with the subharmonic of the Klevin-Helmholtz shear layer instability frequency. Consequently, the significant improvements of pressure distribution on the upper surface are achieved in the post-stall angle of attack.
URI: http://hdl.handle.net/11455/2033
Appears in Collections:機械工程學系所

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