Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/2740
標題: 三角翼具有尾緣襟翼的尾流結構研究
Experimental Study of Wake Structure Behind Delta Wing with Trailing Edge Flap
作者: 吳冠亨
Wu, Guan-Heng
關鍵字: trailing-edge flap;尾緣襟翼;vortex breakdown;characteristic frequency;渦漩潰散;特徵頻率
出版社: 機械工程學系
摘要: 
本文主旨在探討三角翼後方加裝尾緣襟翼(trailing-edge flap)後,下游尾流結構的變化情形。實驗於循環式的水槽中進行,先以流場可視化對上視(top view)方向及前視(front view)方向的流場結構作定性的瞭解,再使用雷射測速系統於機翼下游選定適當截面進行平均速度場之量測及流場中特徵頻率之分析。實驗之自由流速為8.1cm/s,機翼模型之根弦長為20.2cm,對應之雷諾數Re為1.9×104。實驗所用之半三角翼模型後掠角為75°,尾緣襟翼的偏角隨著實驗需要可作任意角度調整。
結果顯示:在攻角為30°之條件下,當襟翼偏角介於-30°到20°之間時,尾緣襟翼對渦漩潰散位置具有遲延的效果;而在這個偏角範圍以外,反而會使渦漩潰散位置提前發生。本實驗中經量測流場中長時間平均速度後得知:有尾緣襟翼之三角翼的下游流場中,主要受三種渦漩結構的影響。第一是翼面上方潰散後的主渦漩結構、第二是由機翼前緣尾緣交接處尖角引起的翼尖渦漩結構(tip vortex),以及第三自襟翼尾端分離的剪力層所形成往下游交替逸流的尾流渦漩結構。
經過頻譜分析之後,可得知各渦漩的速度擾動頻率,如:渦漩潰散的特徵頻率約為1Hz,翼尖渦漩特徵頻率則在2.2Hz附近。而自襟翼尾端分離剪力層形成的尾流渦漩之特徵頻率會隨著襟翼偏角不同而有所變動:當尾緣襟翼偏角 時,自襟翼尾端分離的剪力層因不穩定震盪造成的特徵頻率為3.1Hz。當尾緣襟翼偏角 時,由襟翼尾端分離的剪力層已形成交替逸流的尾流結構,其特徵頻率有兩組,分別為1.3Hz和1.6Hz。當尾緣襟翼偏角 時,襟翼尾端分離剪力層不穩定震盪特徵頻率為0.7Hz。

The purpose of this study is to understand the flow structure and characteristic frequency downstream of a delta wing with trailing-edge flap. The flow visualization is first employed to visualize the qualitative flow structure. Secondly, the quantitative results are performed by way of non-intrusive LDV system. Both the mean and spectrum of the fluctuating velocity field are analyzed to reveal the complex flow structure downstream of the delta wing. The Reynolds number, based on the root chord (20.2cm) and the free stream velocity (8.1cm/s), is around 1.9×104. The sweep angle of half delta wing model is 75°. Moreover, the flap deflection angle can be adjusted at any specific angle.
While the model is fixed at α=30°, the deflection angle of trailing-edge flap between -30°to 20°can delay the vortex breakdown location to a maximum amount 0.1C . While the deflection angle of the flap lies outside this range, breakdown location moves further upstream compared with the unperturbed case.
From the investigations on both the mean and the fluctuating velocity field, the flow structure downstream of the trailing-edge flap can be classified into three kinds of vortex structure. Namely, the breakdown state of the leading-edge vortex structure, the tip vortex structure, and the wake separated from trailing-edge flap. Different flow structures have different mean velocity profiles and different characteristic frequencies. In the condition studied herein, the characteristic frequency of vortex breakdown state is 1Hz, the characteristic frequency of tip vortex is about 2.2Hz. The characteristic frequency of wake separated from trailing-edge flap depends upon the flap deflecting angle. While the deflecting angle is 0°, the characteristic frequency of shear layer instability is 3.1Hz. As the deflecting angle becomes 30°, the shear layer instability wave has developed into an unsymmetrical wake structure with two slightly different frequencies, 1.3Hz and 1.6Hz. Further, when the deflecting angle is -50°, the shear layer instability frequency is around 0.7Hz.
URI: http://hdl.handle.net/11455/2740
Appears in Collections:機械工程學系所

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