仿蜻蜓褶皱翼滑翔与扑动气动特性的数值研究

Numerical investigation on aerodynamic characteristics of dragonfly corrugated airfoils in gliding and flapping flight

  • 摘要: 蜻蜓是自然界中飞行能力极为出色的一种扑翼昆虫,其翅膀上分布着明显的褶皱结构。为了探究不同的褶皱分布形式对翼型气动特性的影响,本文参考蜻蜓翅膀设计了前缘褶皱、后缘褶皱、全褶皱与平板四种翼型,采用计算流体力学方法,针对滑翔和扑动两种姿态分析了低雷诺数环境下(Re = 1000 ~ 2000)翼型的气动特性。结果表明:在滑翔时,褶皱回流区内会产生负摩擦阻力,前缘褶皱翼型具有更低的阻力,后缘褶皱翼型则具有更高的升力与升阻比,在迎角10°时,后缘褶皱相对平板翼型的时均升力系数提高了23.1%,时均升阻比提高了9.1%;在大迎角下,褶皱对升阻比几乎没有影响。流场分析显示,后缘褶皱增大了前缘涡的强度,提高了褶皱上游的表面压强差。在扑动时,后缘褶皱可以降低上扑冲程产生的负升力,从而提高周期平均升力。在此基础上,全褶皱翼型还由于上下冲程启动阶段更为明显的旋转环流机制而具有最大的周期平均升力。本研究表明,调整褶皱分布形式是实现翼型气动优化的有效方案。

     

    Abstract: Dragonfly is a kind of flapping insect with excellent flying ability in nature, and its wings are distributed with obvious corrugation. In this study, different types of corrugated airfoils, i.e. corrugation at the leading edge, corrugation at the trailing edge and corrugation along the whole chord are designed and compared with their smooth counterpart to investigate the effect of corrugation distribution on the aerodynamic characteristics of airfoils. Both gliding phase and flapping phase are simulated with the method of computational fluid dynamics (CFD). The chord Reynolds number (Re) based on the incoming velocity is varied from 1000to 2000. The results show that, in the gliding phase, the recirculation zones formed within the corrugation produce negative frictional drag. The leading-edge corrugated airfoil has lower drag while the trailing-edge corrugated airfoil has higher lift and lift-to-drag ratio. The time-averaged lift coefficient and lift-to-drag ratio of the trailing-edge corrugated airfoil are increased by 23.1% and 9.1% respectively compared with the flat airfoil at \alpha = 10^\circ . While at higher angles of attack, the aerodynamic characteristics of all airfoils are similar. Flow analysis shows that the trailing-edge corrugation increases the strength of leading-edge vortex (LEV) and the surface pressure difference upstream. In the flapping phase, the trailing-edge corrugation can decrease the negative lift generated in the upstroke, thereby increasing the cyclic-averaged lift. And the airfoil with corrugation along the whole chord has the highest cyclic-averaged lift because of stronger rotational circulation. This study suggests that it is an effective scheme to improve aerodynamic characteristics of airfoil by adjusting the corrugation distribution.

     

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