低雷诺数翼型分离流动的大涡模拟研究

采用高精度大涡模拟算法,对低雷诺数下的孤立翼型分离流动问题进行研究,计算了雷诺数为55000、马赫数0.2、来流5°攻角下的NACA-0025翼型,生成数值数据库,从时均流场、瞬态流场、频谱和高阶统计量等多个角度进行分析.研究结果表明:大涡模拟方法能够很好的描述低雷诺数翼型分离流动,其瞬态流场图画与实验结果吻合的很好;翼型上表面出现大尺度的开放式分离区,在Kelvin-Helmholtz(K-H)不稳定性作用下,自由剪切层失稳卷起展向涡,展向涡二次失稳发生旋涡配对现象;分离区流场的演化受大尺度涡结构控制,流场中高阶统计量的分布也与涡结构密切相关.

Large-eddy Simulation of Separated Flows on an Airfoil at Low Reynolds Number

A high accuracy large-eddy simulation（LES）solver was employed to simulate the separated flows on NACA-0025 airfoil at Reynolds number 55 000,Mach number 0.2and incidence 5degree.The numerical data were analyzed and presented from various aspects of time-averaged flow field,instantaneous flow field,frequency spectrum and high-order statistics.The results show that the LES methodology can well describe the separated flows of low Reynolds number airfoil and the instantaneous flow fields are in good agreement with the experimental results.A large open separation bubble appears on the upper surface of the airfoil,and due to the Kelvin-Helmholtz instability,the spanwise vortices roll up from the free shear layer,then the subharmonic instability leads to the formation of vortex pairing.The evolution of the separated flow field is dominated by the large scale vortex structures and the high-order statistics is also closely related to the vortices.