蜻蜓翼三维流动结构的演变

为了与蜻蜓前后翼流动干扰的流动结构作比较,首先研究了悬停飞行状态下单个蜻蜓翼周围的三维流动结构,利用一套机电拍动翼运动模拟机构模拟了一个蜻蜓翼的拍动,使用数字体视粒子图像测速技术(DSPIV,Digital Stereo Particle Image Velocimetry)和多切面锁相技术分别测量了两个下拍拍动相位时刻(t=0.25T,0.375T)和两个上拍拍动相位时刻(t=0.75T,0.875T)蜻蜓翼周围的瞬时空间三维流场,运用局部涡识别准则中的λ_ci准则来识别和显示了流场中的三维涡结构,还展示了蜻蜓翼各个展向测量截面中的|ω_z|等值线、蜻蜓翼前缘涡的涡核线相对于蜻蜓翼上翼面的空间位置以及前缘涡在各个展向测量截面中的截面环量等.实验结果揭示了蜻蜓翼周围的三维流动结构在蜻蜓翼拍动时的演变历程.

Revolution of flow structures around model wing of dragonflies in hovering flight

To study the three dimensional flow structures around a single flapping wing of dragonflies in hovering flight for future experimental comparison with flow structures around a fore- or hind wing of dragonflies, an electromechanical flapping mechanism mounted with a model wing was used to simulate the flapping motion of a dragon wing in this experiment. Three dimensional instant flow fields around the flapping wing were measured respectively at two downstroke phases (t=0.25T,0.375T) and two upstroke phased (t=0.75T,0.875T) with the digital stereo particle image velocimetry (DSPIV) and the multi-slice phase-locked technique. Three dimensional vortex structures were visualized with the local vortex identification scheme. It also was presented that the contour lines of z component of vorticity in each spanwise measuring plane, the vortex core position of the leading edge vortex (LEV) with respect to the upper wing surface and LEV sectional circulation at each spanwise measuring position. The results show that the revolution of the three-dimensional flow structures around the dragonfly wing during its stroking.