曲面附近的机翼地面效应和流场结构的实验研究

Experimental study on the ground effect and flow field structure of wing near the curved surface

该文介绍了机翼在正弦曲面地形上方运动的升/阻力特性和翼尖涡结构的拖曳水槽实验结果,其目的是研究地形周期性变化对机翼地面效应的影响。实验在拖曳水槽底部铺设正弦曲面地板,当机翼掠过地面时,由天平测量机翼载荷,同时采用时间分辨PIV(TR-PIV)系统测量翼尖涡速度分布及其时间演化过程,并且与相应实验条件下水平地面附近的地效翼的数据进行了对比,以分析曲面对机翼升/阻力、流场结构及其相位特性受地形影响的规律和特点。实验机翼模型采用NACA4412翼型,机翼弦长C=100 mm,雷诺数范围为2.0×105~3.0×105。与水平表面的地面效应相比,曲面地形对机翼受到的升/阻力产生了额外的周期性扰动,随着机翼远离地面该扰动减弱,相位特性表明当机翼前缘到达曲面地形波峰上方时升力也达到最大值;机翼飞行高度较低时曲面地形使翼尖涡提前发生耗散并产生明显的展向位移,同时不同波浪相位处产生的翼尖涡结构及强度不同,波峰处翼尖涡强度最弱。在较大攻角下周期性曲面引起的地面效应具有更高的增升减阻效率。

A towing water tank experimental study on the lift/drag forces and visualization of the wing tip vortices of a wing in adjacent to a sinusoidal wavy surface is introduced. The purpose of this paper is to study the influence of periodic terrain changes on ground effect of the wing. A sinusoidal curved floor is laid on the bottom of the towing tank. The wing load is measured by a balance. The velocity fields of the wing tip vortices and their time evolution process are measured using a time-resolved PIV(TR-PIV) system. The data is compared with those of a wing near the horizontal ground under the same experimental conditions, so as to analyze the influence of the curved surface to the lift/drag, flow field structure and its phase characteristics. The profile of the wing is NACA4412 airfoil, the chord length c=100 mm. The Reynolds number of experiment is 2.0×105. The curved terrain produces additional periodic disturbance to the lift and drag of the wing compared with the ground effect of a horizontal surface, and this disturbance decreases as the wing moves away from the ground. The phase characteristics indicate that the lift comes up to its maximum when the leading edge of the wing reaches above the peak of the curved terrain. At low flight height, the curved terrain causes the wing tip vortices to dissipate in advance and the structure to produce obvious spanwise displacement. It is different that the structure and strength of the wing tip vortices generated at different wave phases, and the wing tip vortex strength at the wave peak is the weakest. At a larger angle of attack, the ground effect caused by the periodic curved surface has a higher efficiency of increasing lift and reducing drag.