Super-lift coefficient of active flow control airfoil: What is the limit?
Super-lift coefficient of active flow control airfoil: What is the limit?
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主动控流翼型的超升力系数：极限是多少？
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发表时间：
2017
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通讯作者：
Gecheng Zha
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作者：
Yunchao Yang;Gecheng Zha
本文研究了利用共流射流（CFJ）主动流控翼型提高最大升力系数和巡航效率的方法。对于潜在的流动，最大升力系数的限制是导出为CLmax = 2π(1+t/c)对于任何翼型厚度为t/c。研究表明，CFJ主动流控翼型能够实现远超理论极限的最大升力系数。它被称为超升力系数。采用Spalart-Allmaras（S-A）湍流模型的二维RANS求解器，非粘流采用5阶WENO格式，粘流项采用4阶中心差分格式。研究的动量系数Cμ为0.02 ~ 0.60，攻角（AoA）为0 ~ 74◦。两个CFJ翼型配置创建从基线NACA 6421翼型翻译向下吸力面和调整喷射和吸槽尺寸。一个CFJ翼型与较小的喷射尺寸是实现高CLmax起飞和降落。另一个CFJ翼型与较大的喷射尺寸是为了实现高巡航效率。在AoA=70◦，M=0.063, Cμ = 0.60时，最大升力系数为12.6。它比理论极限7.6高66%，厚度为21%的翼型附带流动。在CFJ翼型周围实现的循环是如此之大，以至于滞止点与翼型固体体分离，库塔条件不再适用。CLmax似乎没有限制。它取决于有多少能量可以添加到流动中，这随着主动流动控制方法的不同而变化。研究表明，当CLmax处于较低水平时，CLmax的增加对能量的增加非常敏感。在低CLmax水平下，CLmax的增加与CFJ功率的消耗几乎呈线性关系。即使不断增加CFJ功率的消耗，CLmax最终也会趋于平稳。CLmax与CFJ功率系数有很好的相关性。在AoA为70◦的超升力条件下，CFJ喷射区涡结构呈现出从翼型壁面到远场自由流依次相邻的4层涡结构：1)翼型吸力面顺时针方向的边界层涡片；2)逆时针CFJ涡层由于高动量射流和上游前缘边界层脱落的剪切层；3)高动量共流射流经混合剪切层诱导的顺时针诱导涡层；4)最后一层为逆时针涡层，二次诱导射流通过该涡层过渡到较慢的自由流速度。引入了一种新的参数——生产力效率，定义为C L/CD，用于衡量飞机载重最大航程的巡航运输能力。对于第二个设计用于巡航条件的CFJ翼型，假设CFJ泵浦效率为80%，包括CFJ功率消耗的峰值气动效率（L/D）c比基线翼型高约53%。CFJ翼型的生产效率C L/CD提高了109%。CFJ翼型被证明能够在非常大的迎角起飞/降落时实现超级升力系数，在低迎角巡航时实现超高效率。*博士候选人，AIAA学生会员†教授，ASME Fellow， AIAA associate Fellow批准公开发布；分发是无限的。[1] [D] [j], [j], [j], [j], [j], [j]。0 0 0 0 0 0 025 / 14 /6。2017年1月13日，美国德克萨斯州Grapevine， AIAA 2017-1693版权所有©2017由本文所有作者所有。由美国航空航天学会出版，已获许可。AIAA科技论坛
This paper studies the enhancement of maximum lift coefficient and cruise efficiency using Co-Flow Jet (CFJ) active flow control airfoils. For potential flows, the maximum lift coefficient limit is derived as CLmax = 2π(1+t/c) for any airfoil with thickness of t/c. The present study indicates that the CFJ active flow control airfoil is able to achieve the maximum lift coefficient that far exceeds the theoretical limit. It is named super-lift coefficient. The research is based on validated CFD simulation, which employs 2D RANS solver with Spalart-Allmaras(S-A) turbulence model, 5th order WENO scheme for the inviscid fluxes, and 4th order central differencing for the viscous terms. The momentum coefficient Cμ studied is from 0.02 to 0.60 and the angle of attack (AoA) is from 0◦ to 74◦. Two CFJ airfoil configurations are created from the baseline NACA 6421 airfoil by translating the suction surface downward and adjusting the injection and suction slot sizes. One CFJ airfoil with smaller injection size is to achieve high CLmax for takeoff and landing. The other CFJ airfoil with larger injection size is to achieve high cruise efficiency. The maximum lift coefficient of 12.6 is achieved at AoA=70◦, M=0.063 and Cμ = 0.60. It is 66% higher than the theoretical limit of 7.6 for a 21% thickness airfoil with attached flow. The circulation achieved around the CFJ airfoil is so large that the stagnation point is detached from the airfoil solid body and the Kutta condition does not apply anymore. The CLmax appears to have no limit. It depends on how much energy can be added to the flow, which varies with the active flow control method. This study indicates that the CLmax increase is very sensitive to energy addition when the CLmax is at low level. There is almost a linear relationship between the CLmax increase and the CFJ power consumed at low CLmax level. The CLmax eventually becomes plateaued even with continuously increased consumption of CFJ power. The CLmax correlates very well with the CFJ power coefficient. For the super-lift condition at AoA of 70◦, the vortex structures in the CFJ injection region appear to include 4 vortex layers one next to each other from the airfoil wall surface to the far field freestream : 1) clockwise boundary layer vortex sheet on the airfoil suction surface; 2) counter clockwise CFJ vortex layer due to the high momentum jet and the shear layer shed from the upstream leading edge boundary layer; 3) clockwise induced vortex layer induced by the high momentum co-flow jet via the mixing shear layer; and 4) the last vortex layer is a counter clockwise vortex layer, through which the secondary induced jet transits to the slower freestream velocity. A new parameter named productivity efficiency defined as C L/CD is introduced to measure the cruise transportation capability of aircraft to carry a gross weight for maximum distance. For the second CFJ airfoil designed for cruise conditions with an assumed CFJ pumping efficiency of 80%, the peak aerodynamic efficiency (L/D)c that includes the CFJ power consumption is about 53% higher than that of the baseline airfoil. The productivity efficiency C L/CD of the CFJ airfoil is 109% higher. The CFJ airfoil is demonstrated to be able to achieve super-lift coefficient for takeoff/landing at very high angle of attack and ultra-high efficiency for cruise at low angel of attack. ∗ Ph.D. Candidate, AIAA student member † Professor, ASME Fellow, AIAA associate Fellow Approved for public release; distribution is unlimited. 1 D ow nl oa de d by G ec he ng Z ha o n M ar ch 3 , 2 01 7 | h ttp :// ar c. ai aa .o rg | D O I: 1 0. 25 14 /6 .2 01 716 93 55th AIAA Aerospace Sciences Meeting 9 13 January 2017, Grapevine, Texas AIAA 2017-1693 Copyright © 2017 by all the authors of this paper. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. AIAA SciTech Forum