Symmetric NACA airfoils tend to undergo abrupt stall characteristics at higher angle of attacks. The abrupt stall has deteriorating effect on lift as well as the efficiency of the airfoils. Abruptness in stall restricts the airfoil to operate only at lower angle of attacks. So, in order to improve the efficiency of airfoils at higher angle of attacks and make it suitable for operation over higher range of angle of attacks, there are many flow control techniques. One such technique is addition of leading-edge protuberance. Leading-edge protuberances are the leading-edge modification of the wing. Leading-edge of the wing is modified with sinusoidal structural modification. This modification has two parameters i.e., Pitch and Amplitude. Many configurations of the protuberances can be obtained by changing the Pitch to Amplitude ratio of the protuberance. In the present work, the Reynolds number is 50k for NACA 0009. The Pitch to Amplitude ratio is varied from PAR1 to PAR27. PAR6 is found to be the better case which has higher lift and efficiency in the post-stall angle of attacks. At the deep stalling AOA of the baseline, i.e., at 13.6o, PAR6 is found to have the highest increase in lift and efficiency compared to the other post stalling AOAs with it having around 39.6% more lift and 27.3% more efficiency compared to the baseline.

翻译：对称NACA翼型在较高攻角下易发生突失速现象。突失速对升力及翼型效率均有恶化影响。失速的突发性限制了翼型只能在较低攻角下运行。因此，为提升翼型在较高攻角下的效率并使其适用于更广的攻角范围，存在多种流动控制技术。其中一种技术是添加前缘隆起结构。前缘隆起是对机翼前缘的改型设计。通过正弦形结构改型对机翼前缘进行修正。此改型包含两个参数：节距与振幅。通过改变隆起的节距-振幅比可获得多种构型。本研究针对NACA 0009翼型，雷诺数为5万。节距-振幅比从PAR1变化至PAR27。研究发现PAR6为较优方案，其在失速后攻角区间具有更高的升力与效率。在基准翼型的深度失速攻角（13.6°）条件下，PAR6构型相较于其他失速后攻角表现出最大的升力与效率提升，与基准翼型相比升力提高约39.6%，效率提升约27.3%。