High-fidelity large eddy simulation is carried out for the flow field around a NACA-0012 aerofoil at Reynolds number of 9 × 10 4 , Mach number of 0.4, and various angles of attack around the onset of stall. The laminar separation bubble is formed on the suction surface of the aerofoil and is constituted by the reattached shear layer. At these conditions, the laminar separation bubble is unstable and switches between a short bubble and an open bubble. The instability of the laminar separation bubble triggers a low-frequency flow oscillation. The aerodynamic coefficients oscillate accordingly at a low frequency. The lift and the drag coefficients compare very well to recent high-accuracy experimental data, and the lift leads the drag by a phase shift of π / 2 . The mean lift coefficient peaks at the angle of attack of 10.25 ° , in total agreement with the experimental data. The spectra of the lift coefficient does not show a significant low-frequency peak at angles of attack lower than or equal the stall angle of attack ( 10.25 ° ). At higher angles of attack, the spectra show two low-frequency peaks and the low-frequency flow oscillation is fully developed at the angle of attack of 11.0 ° . The behaviour of the flow-field and changes in the turbulent kinetic energy over one low-frequency flow oscillation cycle are described qualitatively.

中文翻译：

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失速开始时NACA-0012翼型低频流动振荡的数值研究

对NACA-0012翼型周围流场进行了高保真大涡模拟，雷诺数为9×10 4 ，马赫数为0.4，失速开始附近的各种攻角。层流分离气泡形成于翼型的吸力面上，由再附着的剪切层构成。在这些条件下，层流分离气泡不稳定并在短气泡和开放气泡之间切换。层流分离气泡的不稳定性触发低频流动振荡。空气动力系数相应地以低频振荡。升力和阻力系数与最近的高精度实验数据相比非常好，升力领先阻力 π / 2 的相移。平均升力系数在 10.25° 迎角处达到峰值，与实验数据完全一致。在迎角小于或等于失速迎角 (10.25°) 时，升力系数的频谱没有显示出明显的低频峰值。在更高的攻角处，频谱显示出两个低频峰值，并且在 11.0°的攻角处低频流动振荡充分发展。定性地描述了流场的行为和湍流动能在一个低频流动振荡周期内的变化。谱图显示出两个低频峰，在11°攻角处低频流动振荡充分发展。定性地描述了流场的行为和湍流动能在一个低频流动振荡周期内的变化。谱图显示出两个低频峰，在11°攻角处低频流动振荡充分发展。定性地描述了流场的行为和湍流动能在一个低频流动振荡周期内的变化。