带不同形状翼尖帆片的机翼地面效应实验研究

翼尖帆片将原型机翼集中的翼尖涡分散成多个小涡，加快翼尖涡的耗散，从而降低机翼诱导阻力。为进一步了解翼尖帆片对机翼在地面效应下流动特性的影响，分别对安装有3片椭圆形和梯形帆片的NACA4412机翼开展了风洞实验研究。测量了2种帆片机翼的气动力和翼尖涡结构，并通过比较流动结构，分析了2种机翼气动力产生差异的原因。机翼的升、阻力用六分量盒式风洞天平测量，翼尖涡速度分布用七孔探针扫描获得，以机翼弦线为特征长度的雷诺数为1.5×105。当远离地面时，梯形帆片与椭圆帆片的升、阻力差别较小，但随着机翼逐渐接近地面，梯形帆片的增升减阻效率逐渐高于椭圆帆片。而机翼升阻力的差异，主要是由于局部气流方向角对各帆片形成的有效迎角有所差别，使得帆片对主翼产生不同的增升和减阻贡献。

The influence of the tip sails shape on the wing aerodynamics in ground effect

The function of the wing tip sails is to scatter the concentrated tip vortices into several smaller scale vortex structures, and accelerate the dissipation of tip vortices, thereby reducing the induced drag. In order to study the influence of wing tip sails on the flow fields and aerodynamics of a wing in ground effect, wind tunnel experiment is conducted to measure aerodynamics and tip vortex structures of a NACA4412 wing fitted with three elliptic tip sails and three trapezoidal tip sails respectively, and the reason of the differences between the aerodynamic loads on the two wings is analyzed by comparing the flow fields of tip vortices. The lift and drag forces are measured using a 6-component balance, the velocity distribution of tip vortices is scanned by a 7-hole probe. The Reynolds number based on the chord length of the wing is 1.5×105. The experimental results show that the differences of lift and drag forces between the two wings increase as the wings get closer to the ground, and the trapezoidal tip sails is more efficient in lift augmentation-drag reduction than the elliptic tip sails. The local flow direction and local incidence of each sails are different for the two wings, which result in different contributions in increasing the lift and reducing the drag.