长耳鸮翼型气动及声学特性研究

Study on the aerodynamic and aeroacoustic performance of the long-eared owl airfoil

采用大涡模拟技术对长耳鸮翅膀展向20%、40%和60%截面处翼型的非定常湍流场进行数值模拟,并基于Lighthill声类比方法对非定常流场诱导的声场进行计算,研究上述仿生翼型的气动与声学性能。研究结果表明:三种仿生翼型均具有高升阻比特性,其中20%、40%截面处翼型的升力系数较高,5°攻角下分别为1.86和1.72;20%截面处翼型阻力系数最高,且在强烈的逆压梯度下,20%和40%截面处翼型气流在压力面前缘开始分离,在下游处自由剪切层产生了明显的不规则涡结构;翼型尾缘处,涡流脱落后在尾迹区发生涡结构破碎;60%截面处翼型载荷分布最均匀,附面层增长缓慢,因而该翼型流场的涡量相对较小,使得其诱导噪声较低。声学计算结果表明,三种仿生翼型的最大声压级分别为85.8、78.6和74.8 d B。

Numerical simulation of the unsteady turbulent flow field and its induced acoustic field of three bionic airfoils with the cross section of 20%,40%and 60%based on the long-eared owl wing was performed using large eddy simulation(LES)method and Lighthill acoustic analogy to get the aerodynamic and aeroacoustic performance.The results showed that these bionic airfoils had highlift-drag ratios.The lift coefficient of the airfoils with the cross section of 20%and 40%were higher,which were 1.86 and 1.72 at the attack angle of 5 degrees,respectively.The airfoil at the cross section of 20%had the highest drag coefficient.Under the strong adverse pressure gradient,the airflow separated from the suction surface of the airfoils with the cross section of 20%and 40%.The irregular vortexes were generated at the downstream of the free shear layer.At the airfoil tail region,the shedding vortexes broke in the wake region.The most uniform load distribution was the airfoil at the cross section of 60%.It grew slowly at the boundary layer.Therefore,the vorticity with this airfoil shape was relatively smaller,which resulted in the lowest noise.The results from the acoustic calculation showed that the maximum sound pressure level(SPL)of three bionic airfoils were 85.8,78.6 and 74.8 dB,respectively.