横摆振荡翼型动态气动掠效应试验研究

大型风力机设计对获取翼型更加全面、准确的动态载荷提出更高要求, 研究翼型横摆振荡动态气动特性具有重要意义. 借助"电子凸轮"技术和动态数据同步采集手段, 针对翼型动态“掠效应”首次开展了横摆振荡风洞试验研究, 研究表明: 横摆振荡翼型的气动曲线存在明显迟滞效应, 吸力面压力周期性波动是主要诱因, 且随着振荡频率、初始迎角和振幅的增大, 气动迟滞特性均增强; 升力和压差阻力随横摆角变化的迟滞回线呈"W"形, 俯仰力矩迟滞回线呈"M"形, 升力差量迟滞回线呈"$\infty$"形; 负行程下翼型气动力相对于正行程下的更高, 且负行程下翼型气动力随振荡频率的增大而略有增大, 正行程下则明显减小; 升力系数功率谱密度分布在振荡频率倍频处的能量集中的幅值随着振荡频率增大有增大趋势; 吸力面1.2%和40%弦长处压力的滞回特性较强, 是由于翼面剪切层涡和动态分离涡周期性发展、运动、破裂和重建; 振幅为$10^{\circ}$时, 升力迟滞曲线呈"$^{\wedge}$"形, 振幅为$30^{\circ}$ 时, 升力迟滞曲线呈"$^{\wedge\wedge\wedge}$"形. 

EXPERIMENTAL STUDY OF DYNAMIC AERODYNAMIC SWEPT EFFECT ON YAW OSCILLATING AIRFOIL1)

The design of large wind turbines has put forward higher requirements for obtaining more comprehensive and accurate dynamic loads of airfoil. It is of great significance to study the influence of yaw oscillation on the dynamic aerodynamic characteristics of airfoil. With the help of "electronic cam" technology and synchronous acquisition of dynamic data, the wind tunnel test of yaw oscillation was first carried out for the dynamic "sweep effect" of the airfoil in this paper. The study shows that the aerodynamic curve of the yaw oscillating airfoil has obvious hysteresis effect, the periodic pressure fluctuation of the airfoil suction surface is the main inducement, and the aerodynamic hysteresis characteristics are enhanced with the increase of the oscillation frequency, the initial angle of attack and the amplitude. The hysteresis loop of the lift and pressure difference drag changing with yaw angle is "W" type, the hysteresis loop of the pitching moment is "M" type, and the hysteresis loop of the lift difference is "$\infty$" type. The aerodynamic force of the airfoil under the negative stroke is higher than that under the positive stroke, and the aerodynamic coefficients of the airfoil under negative stroke increase slightly with the increase of the oscillation frequency, but decrease obviously under positive stroke with the increase of the oscillation frequency. The power spectral density (PSD) distribution of the airfoil lift coefficient has obvious energy concentration characteristics at the integer multiple of the oscillating frequency, and with the increase of the oscillation frequency, the amplitude of the energy concentration is obviously increased, which reflects the enhancement of the unsteady flow around the yaw motion airfoil. There is hysteresis effect of the pressure coefficient changing with the yaw angle on different suction surface position, in which the hysteresis areas of the pressure coefficient are larger on 1.2% chord position and 40% chord position, as the result of the periodic generation, development, movement, breakdown and reconstruction of the shear layer vortex and the dynamic separation vortex on the airfoil surface. When the amplitude of yaw oscillation $\beta_1=10^{\circ}$, the shape of $C_\text L-\beta$ curve is "$^\wedge$" type. When the amplitude of yaw oscillation $\beta_1=30^{\circ}$, the shape of $C_\text L-\beta$ curve is "$^{\wedge\wedge\wedge}$" type, that is, when the yaw angle $\beta>20^{\circ}$ or $\beta<-20^{\circ}$, the shape of the lift coefficient hysteresis loop of the airfoil presents "drooping" phenomenon.