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Control of flow separation around an airfoil at low Reynolds numbers using periodic surface morphing

机译:使用周期性表面变形,在低雷诺数的翼型周围控制流动分离

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AbstractThe paper investigates experimentally the low Reynolds number flow (Rec=50,000) around a model that approximates a NACA 4415 airfoil and the control of separation using periodic surface motion. Actuation is implemented by bonding two Macro Fiber Composite patches to the underside of the suction surface. Time-resolved measurements reveal that the peak-to-peak displacement of the surface motion is a function of both the amplitude and frequency of the input voltage signal but the addition of aerodynamic forces does not cause significant changes in the surface behavior. The vibration mode is uniform in the spanwise direction for frequencies below 80?Hz; above this frequency, a secondary vibration mode is observed. The flow around the unactuated airfoil exhibits a large recirculation region as a result of laminar separation without reattachment and consequently produces relatively high drag and low lift forces. Various actuation frequencies were examined. When actuated atVf+=2.0, the spectra in the vicinity of the trailing edge and near-wake were found to be dominated by the actuation frequency. Sharp peaks appear in the spectra suggesting the production of Large Coherent Structures at this frequency. The increased momentum entrainment associated with these enabled a significant suppression of the separated region. The result was a simultaneous increase inCLand decrease inCDand therefore a large increase in theLDratio. In addition, a delay in the onset of stall results in a significant increase in the maximum achievable lift.]]>
机译:<![cdata [ Abstract 本文通过实验调查低雷诺数流( r E C = 50 000 )围绕一种近似NACA 4415翼型的模型以及使用周期性的表面运动控制分离。通过将两个宏观纤维复合贴片粘合到吸入表面的下侧来实现致动。时间分辨测量表明,表面运动的峰值位移是输入电压信号的幅度和频率的函数,但是添加空气动力的增加不会导致表面行为的显着变化。振动模式在30℃以下的频率方向上是均匀的。在该频率之上,观察到二次振动模式。由于层间分离而没有重新连接,因此un伸出的翼型围绕的流动表现出大的再循环区域,因此产生相对高的阻力和低升力力。检查了各种致动频率。当在 v f + = 2 0 ,发现后缘和近似尾巴附近的光谱被发现由致动频率主导。锐峰出现在光谱中,表明在此频率下产生大的相干结构。与这些相关的增加的动量夹带使得能够显着抑制分离区域。结果是 C L 和减少 c D ,因此 l < MML:MO> / D 比率。此外,延迟失调的延迟导致最大可实现的升力的显着增加。 ]]>

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