扑动翼型的低雷诺数气动特性分析

通过求解引入拟压缩项的不可压Navier-Stokes方程,数值模拟了绕扑动翼型的低雷诺数非定常流动。针对厚度在4%-12%之间的NACA对称翼型,分析了翼型厚度等参数对扑动翼型气动特性的影响。在低雷诺数条件下,对于纯俯仰运动,随着翼型厚度的减小,平均阻力系数也变小。而对于纯沉浮运动,发现翼型厚度对气动特性的影响和俯仰运动有很大的差别,平均阻力系数随着翼型厚度的减小而变大。通过对沉浮运动一个周期流线图的分析,认为这是翼型前缘涡的影响造成的。由于前缘涡的影响,翼型厚度增加,平均压差阻力系数变小,甚至会出现负值。雷诺数的影响研究表明,随着雷诺数的增加,扑动翼型的阻力系数减小的趋势越缓慢。

Aerodynamic characteristics of flapping airfoils at low reynolds number

Unsteady flows around flapping airfoils are simulated at low Reynolds number,by solving incompressible Navier-Stokes based on pseudo compressibility method.The effect of maximum thickness variations is investigated using uncambered NACA four-digit airfoils range from 4% to 12% thickness.For pure pitching motion,the results show that average drag coefficient decreases as airfoil thickness is reduced.But for pure plunging motion,it was found that the thickness variations have a different effect on aerodynamic performance compared with that of pitching motion.Average drag coefficient increases as airfoil thickness is reduced.An analysis of periodic flow streamlines shows that it is probably due to the effect of leading edge vortex.As airfoil thickness is increased,the average pressure drag,affected by leading edge vortex is reduced even to be negative,and meanwhile friction has little increase.For Reynolds-number,as it increases,average drag coefficient is reduced slowly.The research work of this paper is expected to be useful for the design of flapping micro air vehicles.