以實驗方法分析在低雷諾數下三角翼流場

Abstract

本實驗以展弦比4的三角翼，使用粒子顯影，染料顯影、並配合升阻力量測，討論非狹長三角翼前緣渦的發展以及結構。本實驗的工作流體為甘油和水的混合物，以雷諾數150、300配合15、30、45度攻角瞬間起動，並進行平移運動。使用六軸力規紀錄升阻力隨時間的變化，並觀察不同角度下升阻比的變化。流場觀測方面，藉由釋放顯影粒子，配合PIV方法計算流場的速度場及渦度。流場顯影方面，由翼板前縁釋放食用染料，並在其上方及側方處架設攝影機以觀察流場變化。 由量力結果發現翼板在較低攻角狀態下飛行會有較小的升阻力，但卻有較大的升阻比。而在PIV觀察前緣渦發展中，發現在雷諾數150下前緣渦以較對稱且集中的形式出現，然而在雷諾數300下前緣渦出現了較不對稱的現象且渦度較為散亂。流場顯影方面則觀察到在雷諾數300下，流場出現了回流的現象。

Flow over impulsive started delta wing of aspect ratio 4 at Re=150 and 300 are investigated to analysis the development and structures of vortex by PIV(particle image velocimetry),flow visualization and measurement of force with the AoA varying at 15, 30 and 45 degrees. We use the force sensor to record the lift and drag forces as time develop. Therefore, we observe the variation of the ratio of lift and drag coefficient beyond different angles. In addition to the observation of flow field, we release particles and use PIV method to calculate the associated velocity field and vorticity. With respect to flow visulization, we release dye from the leading-edge of delta wing, and set cameras to observe the flow. Results of measurement of force show that delta wings have smaller drag and lift force, but have larger ratio of lift to drag in smaller AoA. In PIV measurement, leading-edge vortices are symmetrical and concentrated at Re=150. However, leading-edge vortices are asymmetric and diffused at Re=300. In addition, the phenomena of flow reversal in flow visualization are observed to appear when Re=300.