Flow control over an airfoil using virtual Gurney flaps
Flow control over an airfoil using virtual Gurney flaps
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DOI：
10.1017/jfm.2015.22
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发表时间：
2015-02
影响因子：
3.7
通讯作者：
Lihao Feng;K. Choi;Jinjun Wang
中科院分区：
文献类型：
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作者：
Lihao Feng;K. Choi;Jinjun Wang
摘要 NACA 0012 翼型的流量控制是使用雷诺数为 20 000 的介质阻挡放电 (DBD) 等离子体致动器进行的。这里，等离子体致动器放置在翼型靠近后缘的压力（较低）侧上，从而产生逆着自由流的壁射流。这种反向流动形成了准稳态再循环区域，降低了翼型压力侧的速度。另一方面，翼型吸力（上）侧上的空气被再循环吸入，从而增加了其速度。测量的相位平均涡度和速度场还表明，等离子体致动器在压力表面上产生的再循环区域改变了近尾流动力学。机翼周围的这些流动变化导致升力系数增加，这类似于机械格尼襟翼的效果。这种 DBD 等离子体致动器的配置是本研究中首次研究的，因此被称为虚拟格尼皮瓣。本研究的目的是通过仔细研究机翼上的整体流动行为来了解虚拟格尼襟翼增强升力的机制。首先，再循环区域从后缘周围的吸力表面吸入空气。然后，上剪切层与来自压力表面的相反符号的剪切层相互作用，从翼型产生更强的涡旋脱落。其次，由 DBD 等离子体致动器在压力表面上创建的再循环区域使正剪切层远离翼型，从而使近尾流区域向下移动。虚拟格尼瓣还通过开尔文-亥姆霍兹不稳定机制加速层流到湍流的转变，从而改变层流分离气泡和相关涡流结构的动力学。特别是，分离点和转变开始被提前。重新附着点也会通过等离子控制向上游移动，尽管在大迎角时会稍微延迟。
Abstract Flow control over a NACA 0012 airfoil is carried out using a dielectric barrier discharge (DBD) plasma actuator at the Reynolds number of 20 000. Here, the plasma actuator is placed over the pressure (lower) side of the airfoil near the trailing edge, which produces a wall jet against the free stream. This reverse flow creates a quasi-steady recirculation region, reducing the velocity over the pressure side of the airfoil. On the other hand, the air over the suction (upper) side of the airfoil is drawn by the recirculation, increasing its velocity. Measured phase-averaged vorticity and velocity fields also indicate that the recirculation region created by the plasma actuator over the pressure surface modifies the near-wake dynamics. These flow modifications around the airfoil lead to an increase in the lift coefficient, which is similar to the effect of a mechanical Gurney flap. This configuration of DBD plasma actuators, which is investigated for the first time in this study, is therefore called a virtual Gurney flap. The purpose of this investigation is to understand the mechanism of lift enhancement by virtual Gurney flaps by carefully studying the global flow behaviour over the airfoil. First, the recirculation region draws the air from the suction surface around the trailing edge. The upper shear layer then interacts with the opposite-signed shear layer from the pressure surface, creating a stronger vortex shedding from the airfoil. Secondly, the recirculation region created by a DBD plasma actuator over the pressure surface displaces the positive shear layer away from the airfoil, thereby shifting the near-wake region downwards. The virtual Gurney flap also changes the dynamics of laminar separation bubbles and associated vortical structures by accelerating laminar-to-turbulent transition through the Kelvin–Helmholtz instability mechanism. In particular, the separation point and the start of transition are advanced. The reattachment point also moves upstream with plasma control, although it is slightly delayed at a large angle of attack.