展向流动分量对地面效应条件下组合翼气动特性的影响初探

THE INFLUENCE OF WING SPAN-WISE FLOW COMPONENT TO THE AERODYNAMIC CHARACTERISTICS OF A COMPOUND WING IN GROUND EFFECT

  • 摘要: 以地面效应条件下组合翼(compound wing)气动特性的风洞实验和翼尖涡PIV速度场的拖曳水槽实验结果为依据,总结了组合翼与平直翼升力和阻力差异的基本规律,并在分析翼尖涡流场演化特征的基础上,着重从展向机翼流动的观点初步探讨了气动力变化的机理。实验所采用的组合翼由中段平直翼和两侧外段带下反角的矩形翼组成。通常在自由空间中飞行时,下反角使机翼的横侧稳定性降低,滚转敏捷性提高,对机翼的气动性能影响并不大,但该实验结果表明,在地面效应条件下,下反角使机翼的升力和阻力均发生改变。越靠近地面,下反角大的组合翼升力增加的效果越明显,而PIV速度场测量的结果显示,组合翼的下反角结构能够抑制翼尖涡的生成和发展,有利于减小机翼的诱导阻力。此外,在特定工况下还发现翼尖涡流场中伴随有二次涡生成,诱导并耗散翼尖涡强度,从而削弱下洗运动,可进一步降低机翼的诱导阻力。

     

    Abstract: Based on the wind tunnel experiments on the aerodynamic characteristics of the combined wing in ground effect and the towing tank experimental results of the wingtip vortex PIV velocity field, the basic rules of the difference in lift and drag between the compound wing and the straight wing were summarized, and the wingtip vortex was analyzed. By analyzing the evolution of the tip vortex flow, the variation mechanism of the aerodynamics of the compound wing in ground effect was discussed from the view of wing span-wise flow component. The compound wing is composed of a straight middle section and a rectangular wing with anhedral angle on the outer sections on both sides. Generally, the negative-dihedral in free space reduces the lateral stability of the wing and improves the roll agility, but has little effect on the aerodynamic performance of the wing. However, the results of this experiment show that under ground effect conditions, the anhedral changes the lift and drag of the wing obviously. The closer to the ground, the more obvious the lift increase effect of the compound wing with large anhedral angle. And the results of PIV measurement show that the anhedral structure of the compound wing can weaken and inhibit the generation of wing tip vortex, which is beneficial to reducing the wing induced drag. In addition, under certain working conditions, it is found that the secondary vortex occurs in the wingtip vortex field, and dissipates the strength of the wingtip vortex, thereby weakening the downwash motion and further reducing the induced drag of the wing.

     

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