低雷诺数俯仰振荡翼型等离子体流动控制

PLASMA-BASED FLOWCONTROL ON PITCHING AIRFOIL AT LOWREYNOLDS NUMBER

针对低雷诺数翼型气动性能差的特点,通过介质阻挡放电(dielectric barrier discharge,DBD)等离子体激励控制的方法,提高翼型低雷诺数下的气动特性,改善其流场结构.采用二维准直接数值模拟方法求解非定常不可压Navier-Stokes方程,对具有俯仰运动的NACA0012翼型的低雷诺数流动展开数值模拟.同时将介质阻挡放电激励对流动的作用以彻体力源项的形式加入Navier-Stokes方程,通过数值模拟探究稳态DBD等离子体激励对俯仰振荡NACA0012翼型气动特性和流场特性的影响.为了进行流动控制,分别在上下表面的前缘和后缘处安装DBD等离子体激励器,并提出四种激励器的开环控制策略,通过对比研究了这些控制策略在不同雷诺数、不同减缩频率以及激励位置下的控制效果.通过流场结构和动态压强分析了等离子体进行流场控制的机理.结果表明,前缘DBD控制中控制策略B(负攻角时开启上表面激励器,正攻角时开启下表面激励器)效果最好,后缘DBD控制中控制策略C(逆时针旋转时开启上表面激励器,顺时针旋转时开启下表面激励器)效果最好,前缘DBD控制效果会随着减缩频率的增大而下降,同时会导致阻力增大.而后缘DBD控制可以减小压差阻力,优于前缘DBD控制,对于计算的所有减缩频率(5.01∼11.82)都有较好的增升减阻效果.在不同雷诺数下,DBD控制的增升效果较为稳定,而减阻效果随着雷诺数的降低而变差,这是由流体黏性效应增强导致的.

To improve the poor aerodynamic performance of pitching airfoils at low Reynolds number,the paper developed a control strategy based on the dielectric barrier discharge(DBD)plasma control.The 2D quasi direct numerical simulation method was applied to solve the unsteady incompressible Navier-Stokes equations around an oscillating NACA0012 airfoil at low Reynolds number.Equations for plasma flow control are added to the momentum equations in the Openfoam solver as a source term.The effects of steady DBD plasma actuation on the aerodynamic force characteristics of an oscillating NACA0012 airfoil are investigated.The DBD plasma actuators are located at the leading edge and trailing edge of the upper and lower airfoil surfaces,respectively.And four open-loop control strategies for the actuators were proposed.The flow control effects of these control strategies with different Reynold numbers,reduced frequency and the positions of plasma actuators are compared.The mechanisms of plasma flow control is analyzed by the flow field structures and dynamic pressure distribution.Results indicate the effect of control strategy B(switch on actuator located on the upper surface at negative angle of attack,and switch on actuator located on the lower surface at positive angle of attack)is best when the plasma actuators located at leading edge of airfoil,and control strategy C(switch on actuator mounted on the upper surface during counterclockwise rotation stage,switch on actuator mounted on the lower surface during clockwise rotation stage)has best effect when the plasma actuators located at the trailing edge of airfoil.When the plasma actuators located at leading edge,the flow control effect will decrease as the reduced frequency increases,and it also increase airfoil’s drag.For the trailing edge plasma cases,the pressure drag may decrease,which is better than the leading edge plasma cases.Meanwhile,the trailing edge DBD plasma control has good effect of enhancing lift and reducing drag for all the calculated reduced frequency ranges(5.01∼11.82).The lift enhancement effects of DBD flow control are good at different Reynolds numbers.However,due to the flow viscosity effect enhancement,the drag reduction effects of DBD flow control become worse with decreasing Reynolds numbers.