扰流片分离流动特性的数值研究

在非结构网格下,采用SIMPLE算法结合两层带状边界层模型求解雷诺平均N-S方程.研究了底部间隙对平板扰流片引起的分离再附流动结构的影响.结果表明带底部间隙扰流片的流动结构主要由顶部绕流和底部间隙射流影响.底部间隙的大小决定了射流的强度,最终决定了绕流的结构.随着底部间隙的增大,绕流经历了封闭单涡回流区、射流干扰回流区以及平板绕流3种流动结构.它们之间的分界点分别是用扰流片宽无量纲间隙g/h=0.2,0.4.底部间隙0.2＜g/h＜0.4,底板压力分布基本保持不变,因此不会影响其应用于飞机部件的静态气动特性.      

Gurney flap—Lift enhancement,mechanisms and applications

Since its invention by a race car driver Dan Gurney in 1960s, the Gurney flap has been used to enhance the aerodynamics performance of subsonic and supercritical airfoils, high-lift devices and delta wings. In order to take stock of recent research and development of Gurney flap, we have carried out a review of the characteristics and mechanisms of lift enhancement by the Gurney flap and its applications. Optimum design of the Gurney flap is also summarized in this paper. For the Gurney flap to be effective, it should be mounted at the trailing edge perpendicular to the chord line of airfoil or wing. The flap height must be of the order of local boundary layer thickness. For subsonic airfoils, an additional Gurney flap increases the pressure on the upstream surface of the Gurney flap, which increases the total pressure of the lower surface. At the same time, a long wake downstream of the flap containing a pair of counter-rotating vortices can delay or eliminate the flow separation near the trailing edge on the upper surface. Correspondingly, the total suction on the airfoil is increased. For supercritical airfoils, the lift enhancement of the Gurney flap mainly comes from its ability to shift the shock on the upper surface in the downstream. Applications of the Gurney flap to modern aircraft design are also discussed in this review.     

脉冲吹气对无缝襟翼翼型气动性能的影响

只有采用足够小的能量输入,获取更大的空气动力收益后,主动流动控制才有可能在真实飞机上获得更广泛的应用。脉冲吹气比定常吹气所需能量更少,控制效果更好,在改善翼型气动性能上得到广泛的研究。数值模拟了脉冲频率、占空比、动量系数等参数对无缝襟翼翼型升阻特性的影响规律,研究表明,脉冲频率接近于涡脱落频率时增升效果最好,当脉冲频率小于涡脱落频率时,阻力增加,当脉冲频率为涡脱落频率2倍时,阻力减小最多;动量系数较小时,占空比越小,冲击效应越强,增升效果越好;动量系数小于临界动量系数时,脉冲吹气增升效果优于定常吹气,当动量系数大于临界动量系数时,脉冲吹气控制效果低于定常吹气。研究脉冲吹气参数对翼型性能的影响规律,对采用周期性激励增升减阻、舵面增效的飞行器设计具有一定参考意义。     

Gurney襟翼对双三角翼气动特性影响的低速风洞实验研究

通过低速风洞实验研究了Gurney襟翼对双三角翼气动特性的影响,结果表明Gurney襟翼可以提高双三角翼的升力系数、最大升力系数以及中高升力系数情况下的升阻比。此外,进一步证实了Gurney襟翼的有效迎风面积是影响增升效果的主要因素。     

Experimental study on transfer functions of an active rotor under different flight conditions

Vibrations impose negative impacts on the effectiveness and public acceptance of helicopters. Active rotors with trailing-edge flaps have been proved to be an effective way to actively eliminate helicopter vibrations. For the existing control algorithm based on offline system identification, the transfer functions of an active rotor under different flight conditions are pre-requisites to implement closed-loop vibration control. In this study, a three-bladed active rotor with improved trailing-edge flaps is designed, and wind-tunnel tests are conducted to identify the transfer functions of this active rotor using frequency sweep and phase sweep methods. The experimental results demonstrate that these transfer functions are insensitive to the variation of flight speeds: the amplitude of the transfer function varies slightly, while the phase delay almost remains unchanged. In addition, this finding is validated through closed-loop vibration control tests with the active rotor. The transfer function obtained from the hover test results is also applicable to closed-loop vibration control tests under the forward flight conditions. This will dramatically simplify the implementation and operation of an active rotor.