【作者】 白亚磊；

【导师】 明晓；

【作者基本信息】 南京航空航天大学 ， 流体力学， 2011， 博士

【摘要】 分离流控制是流动控制的一个重要方向,大攻角机翼分离流控制研究具有非常重要的理论意义和工程应用前景。本文系统全面地研究了一种新的分离流控制方法——流动偏转器。首先,从流动控制应用现状入手,研究目前应用较多的控制方法,吸取这些方法的流动控制理念,提出一种新的流动控制方法。通过研究某型多段翼在低速情况下的流动控制特性,认识其流动控制原理,即引用下翼面的压力对上翼面的边界层进行吹气,进而增加上翼面边界底层的能量,抑制分离。该方法的缺点是减小了下翼面的压力。基于这种考虑,本文提出在机翼上翼面前缘附近进行流动控制,采用偏转导引来流动量的方法,对上翼面边界层进行吹气,这样既保证了下翼面的压力,又能对上翼面的流动分离进行控制。本文在机翼的前缘加装流动偏转器,使来流向机翼上表面偏转,从来流中提取能量,增加流动底层的速度,使之抗分离的能力增加,进而抑制分离,推迟失速。其次,采用风洞实验方法,研究了流动偏转器对分离流的实际控制效果。文中采用了三种不同类型的流动偏转器,由最初流动偏转器的流场显示看出,流动偏转器可以有效地控制分离。由第二种流动偏转器的风洞测力测压实验看出,流动偏转器可以使失速攻角推迟3度,由于流动偏转器对来流的偏转作用,可以使机翼上翼面的压力峰值保持到攻角24度。与干净机翼相比较,最终改进型流动偏转器可以使失速攻角推迟6度。由PIV流场测量结果看出,在流动偏转器的控制下,翼型上表面大的分离涡结构被抑制,失速攻角推迟;翼型上表面涡量变化较大的区域下移,壁面边界层与来流之间的能量交换加剧,底层能量增加,抗分离能力增强。第三,采用数值计算方法,研究流动偏转器的流动控制机理,并结合基因算法,对偏转器进行多参数优化。通过对流动方向变化规律和翼面边界层的深入研究,探寻了偏转器的控制原理:使来流向机翼吸力面偏转;削弱机翼前缘附近流动的三维效应使流动趋近二元化;使边界层内速度型变得饱满,减小速度型形状因子H₁₂,增大速度型的稳定性,抑制流动分离。基因算法的优化结果提升了流动偏转器的应用潜力。在流动控制中,经过基因算法优化后的流动偏转器,可以更加有效的提高翼型的气动性能。计算流体力学（CFD）和基因算法（GA）的结合是一种有效的强大的优化方法,它在当前的流动控制设计中具有前瞻性。通过iSIGHT设计平台,结合Fluent ,形成一个高效的优化平台,可以推广到更广泛的流体应用领域。另外,本文把遗传算法应用到空气动力学的实验当中,可以为飞行器工程设计和空气动力学理论分析提供更加优化的实验方案;流动偏转器是实现遗传算法在空气动力学试验中应用的合适载体;为了满足遗传算法对参数变化的高精度要求,本文提出把超声电机精密驱动技术应用于流动控制。既推进了遗传算法在实验当中的应用,也推进了流动偏转器控制技术的实际应用。最后,研究了偏转器的实际工程应用。对风力机专用S809翼型的数值模拟结果表明,流动偏转器可以有效的控制分离,改善翼型的失速特性,增加翼型气动性能的稳定性。通过对流动偏转器参数的基因算法优化,得到了在一定范围内失速控制的最优参数,较大的提升了流动偏转器流动控制性能,使最大升力系数提升24%,18°攻角下升阻比提高50%以上,失速攻角推迟2度。且使失速过程变缓。由于风力机多数时候会运行在失速状态,失速的变缓,可以减少叶片抖动,提升运行品质。更多还原

【Abstract】 As an important tendency of fluid mechanics, research of wing separation flow control at high angle of attack is of profound theoretical and practical significance. In this paper, a new flow control method was comprehensively researched.Firstly, starting with look through the present state of flow control, these commonly used methods were deeply studied. By absorbing the essence of these methods, a new flow control technology was introduced, called flow deflector. By researching the flow control characteristics of the multi-element airfoil, the principle of the flow control was found. The flow from the low surface of the airfoil through the gap at the leading edge and blows the boundary layer of the up surface. The energy of the boundary layer was enhanced and the separation was suppressed. The shortcoming of the method was that the pressure of the low surface of the airfoil was also reduced. Based on such consideration, some devices, fixed at the leading edge, could deflect the coming flow to control the flow separation. Then the idea of the flow deflector was born. Fixed at the leading edge, the parallel flats could make the coming flow deflect to the up surface of the airfoil. The velocity of the boundary layer was enhanced, the separation was retrained and the stall was delayed.Secondly, some experiments indicated that the flow deflector can restrain the flow separation. By increasing recognition of the flow deflector, three flow deflector models were produced to meet requirement of the research. The first model was used in the flow visualization experiment. The results validated the basic idea of controlling separation. The second model was used in the force measurement experiment. The results indicated that the flow deflector could delay the stall angle by 3 degree. As a function of the flow deflector, the peak of the pressure on the up surface was keep to angle of attack 24 degree. At last, the third model could delay the stall angle by 6 degree.The results of the PIV measurements indicated that there are many differences between the airfoil with and without flow deflector. By the control of the flow deflector, the separation vortices were retrained and the stall angle was delayed. The region where the vorticity changed extremely moved down to the up surface. The energy exchange between the coming flow and the boundary layer was sharp. The energy of the boundary layer was enhanced. And the ability of restrain the separation was improved.Thirdly, analysis of mechanism and optimization were done on the new flow control method. Deep research of flow direction changing trend and boundary layer are carried out to investigate the mechanism of flow deflector. The results indicate that the flow deflector increase the angle of flow around the leading edge of the wing and decrease the angle of the coming flow to make it deflect to the upside of the wing. The flow deflector can suppress the three dimensional effects and maintain the two-dimensional flow characteristics to some extent. Furthermore, the flow deflector can easily change the velocity profile in the boundary layer and make it more“fuller”. It decreases the shape factor and increases the stability of the boundary layer to restrain the flow separation.The results of the genetic algorithm optimization demonstrated the basic idea and application prospect. In the flow control experiment, the optimal flow deflector could enhance the aerodynamic characteristics effectively. Computational fluid dynamics in con-junction with a searching algorithm like a genetic algorithm potentially offers an efficient and robust optimization method and is a promising solution for current flow control designs. With the iSIGHT a highly efficient optimization platform combining with the FLUENT software can be extended to a wider field of fluid application.In this paper, the genetic algorithm in aerodynamics experiment was put forward for the first time. The platform could provide better plan for the experiments of aircraft design and aerodynamics theory analysis. The flow deflector, restraining the separation and delaying the stall angle effectively, is a proper carrier for the genetic algorithm in aerodynamics experiment. To meet the high precision demand of the parameters’varation in genetic algorithm, the using of the precision actuate technology in flow control was put forward for the first time. This technology spread the application of the genetic algorithm in experiment and the flow deflector in actual enginerring.Lastly, an application case in engineering was give. The results of numerical simulation for the airfoil S809 show that the flow deflector can control the separation effectively and improve the aerodynamic characteristics of the airfoil. An optimum flow deflector is obtained by genetic algorithm, which enhances the ability of separation control. It is indicated that the lift coefficient of the airfoil with flow deflector is increased by 24% and the lift-drag ratio by more than 50%. The stall of the airfoil is delayed by two degrees and the stall process is slow. Most of the time, the wind turbine run in the airfoil stall state, the slow stall process could reduce the blade dithering and enhance the running quality.更多还原