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高空长航时无人飞行器(HALE UAV)由于飞行环境空气稀薄、雷诺数低导致其气动性能恶化,如何通过流动控制改善机翼低雷诺数气动性能受到越来越多的关注。在低速风洞中通过测力、测压和边界层测试等试验技术开展了NACA 633-421直机翼模型气动特性试验和流动控制研究。天平测力结果表明:随雷诺数降低(Re<1.4×10~5)机翼气动特性迅速恶化;最大升力系数损失严重,失速迎角急剧降低;分析翼面压力分布结果显示,机翼表面产生层流分离泡(LSB),其长度变化、位置前移和最终发生破裂的发展过程是导致机翼低雷诺数气动性能恶化的主要原因。采用合成微射流(Micro-SJ)对翼面层流分离泡进行流动控制,失速迎角推迟了11°,机翼最大升力系数由0.59提升至1.10,最大升阻比增加了13.6%。合成微射流控制具有选频特性,驱动频率f=200~400Hz的合成微射流控制效果最佳,更易促进分离剪切层提前转捩,形成湍流再附,使得层流分离泡长度缩短。
HALE UAV Due to the air thinning in the flight environment and the low Reynolds number, the aerodynamic performance of the HALE UAV is getting worse. How to improve the aerodynamic performance of the wing at low Reynolds number through flow control is receiving more and more attention. In the low speed wind tunnel, the aerodynamic characteristics and flow control of the NACA 633-421 straight wing model were studied by using the testing technologies such as force measurement, pressure measurement and boundary layer test. The results of balance force measurement showed that the aerodynamic characteristics of the wing deteriorated rapidly with Reynolds number (Re <1.4 × 10 ~ 5), the maximum lift coefficient loss was severe, and the angle of attack (AOA) sharply decreased. The analysis of the airfoil pressure distribution showed that the wing surface The main reason of the low Reynolds number aerodynamic performance deterioration is the laminar flow separation bubble (LSB), its length change, the position advance and the final rupture development. Micro-SJ was used to control the laminar airfoil flow in the airfoil. The stall angle of attack was delayed by 11 °. The maximum lift coefficient of wing was increased from 0.59 to 1.10 and the maximum lift-drag ratio increased by 13.6%. The synthetic micro-jet control has the characteristic of frequency selection. The synthetic micro-jet with the driving frequency f = 200-400Hz has the best control effect, which facilitates the pre-rotation of the separation-shear layer and forms turbulent re-attachment, thus shortening the length of the laminar separation bubble.